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Official Journal of the AUSTRALIAN WATER AND WASTEWATER ASSOCIATION

IVol. Registered for posting as a periodica l -

Category 'C '.

4 No. 1, March 1977 Price $1.00I


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44 Koornang Road, Scoresby, Victoria, Australia 3179 Telephone: 763 -8988 Te lex: AA31868 50 Liechhardt Street, Spr ing Hi ll , Queens land. Austra li a 4000 Telephone: 229-5800 Telex: AA41049

'Precipitator' clarifier tanks 'Graver Reactivator'* clarifier tanks Vertical flow settling tanks Coagulant Chemical Dosing plant Pressure Sand Filters Activated Carbon filters 'Graver Monovalve'* Sand filters 'lmmedium'* up-flow sand filters Gravity sand filters 'Stelmet' replaceable cartridge filters 'Stellar' candle-element pre-coat filter 'Meta" ring-pack element pre-coat filter 'Industrial'* leaf and tube pre-coat filters Reverse Osmosis¡ ultra filtration • Made by PERMUTIT. AUSTRAL I A under li cen c e.

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· te .... I

EDITORIAL COMMITTEE Chairman: C. D. Parker Committee: G. R. Goffin G. R. Scott F. R. Bishop L. C. Smith R. L. Clisby Joan Powling A.G. Longstaff B. S. Sanders E. A. Swinton W. Nicholson A. Macoun J. H. Greer Publisher: A.W.W.A

BRANCH CORRESPONDENTS CANBERRA A.C.T.: A. Macoun, P.O. Box 306, Woden, 2606. NEW SOUTH WALES: G. R. Scott, James Hardie & Coy. Pty. Ltd., P.O. Box 70, Parramatta, 2150. VICTORIA: M. Smith, Ministry of Water Resources and Water Supply, 9th Floor, 100 Exhibition St., Melbourne, 3000. QUEENSLAND: L. C. Smith, 24 Byambee Street, Kenmore, 4069. SOUTH AUSTRALIA: R. L. Clisby,

C/- E. & W. S. G.P.O. Box 1751, Adelaide, 5001. WESTERN AUSTRALIA: B. S. Sanders, 39 Kalinda Drive, City Beach, 6015. TASMANIA:

W. Nicholson, 7 Swansea Court, Lindisfarne, 7015. NORTHERN TERRITORY: C/- N. R. Allen, 634 Johns Place, Nightcliff, Darwin, 5792. · Editorial Correspondence: C. D. Parker, 15 Earl St., Carlton, 3053. Or to State Correspondents. Advertising Enquiries: Mrs L. Geal, C/- Appita, 191 Royal Par., Parkville, 3052. Phone: (03) 347 -2377.

j ,ssN 0310

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Official Journal of the !AUSTRALIAN WATER AND !

'ASTEWAtER A"SSOCIATION I

• •

Vol. 4, No. 1, March 1977

CONTENTS Editorial

....

5

.

Association News

6

8th I.A.W.P.R. Conference Keynote Address - C. D. Parker .. ..

8

Industrial Wastewater and Environmenti Protection in Tasmania - B. 0. Healey

9

Ti-Tree Bend - J. W. Bowen Bacterial Denitrification - Nancy F. Millis

12 A Review 15

The Use of Natural Tritium for Evaluating Aquifer Recharge - G. B. Allison ....

19

Conference Calendar

23

Recent Developments in Hydraulics Within the Hydroelectrics Commission of Tasmania - Part 1 - P. T. A. Griffiths

24

• INSTRUCTIONS TO AUTHORS Articles should be of original thought or reports on original work of interest to the members of the A.W.W.A. and preferably not more than 5,000 to 7,000 words. Full instructions are available from Branch correspondents or the Editor.

FRONT COVER Spring flood water flows over the Hydro-Electric Commission's Repulse Dam, one of three in Tasmania's Lower Derwent Power Development. Completed in 1968, the 42.3 metres high arch dam has a crest length of 206.9 metres and overspi ll capacity of 3228 cub ic metres per second. The gross capacity of the reservoir is 7.28 x 101::i cubic metres. The installed capacity of the Repulse Power Station is 28 megawatts at 25.15 metres head and a flow of 125 cubic metres per second.


Handles Water ¡ Beautifully Applications

Typical Specifications:

"Len" Anthracite can be used:

Specific Gravity: 1.40-1.45 Acid Solubi lity : 1.0% (max) Effective Size: Type 2 0.85-0.95mm Type 3 Q.50-0.60mm Uniformity Coefficient: 1.4 Voidage: 55%

D To increase the capacity and efficiency of existing filtration equipment D To reduce the capital cost of new equipment D For filtration of Alkaline Water: Caustic Acid Solution, Boiler Water and Oxidised Chemicals.

Distributed in Australasia by Kembla Coal & Coke Pty. Limited Box 1770, P.O. Wollongong, N.S.W. 2500. Telephone (042) 28 7455 Telex: 29172

2


Research work is vital. Research work is essential in A.P.M.'s activities to ensure that the company continues to produce economically and efficiently year by year products which are an integral part of the production and distribution of goods within the community. We are finding out how to grow more and better trees per hectare of land and how to harvest and process pulpwood with a minimum of waste. At our own research centre in Melbourne and with our associates overseas we are investigating completely new paper and paperboard manufacturing processes.

•

A large proportion of our research is devoted to environment improvement work, forest development, improved treatment of mill process water, increased recycling, both in the manufacturing process and of reclaimed paper and paperboard. The community and the company share the value of our research through the contribution it is making to. conserving and renewing resources and containing costs.

~ AUSTRALIAN PAPER ~

MANUFACTURERS LIMITED

AP27

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this iS : drin~ng wateF

it is still Water and mou tains are the natural ingr~.dients of our electricity. We wou ldn't want to spoil either of

~ 4

Tasmania's 1..,.~""'


FEDERAL SECRETARY: P. Hughes, Box A232 P.O. Sydney South,

EDITORIAL

2000. FEDERAL TREASURER:

J. H. Greer, C / - Melbourne & M.B.W., 625 Lt. Collins St., Melbourne, 3000. BRANCH SECRETARIES: Canberra, A.C.T. D. Butters, C / - Dept. of Housing & Construction Phillip, A.C.T., 2606 New South Wales: P.J. Mitchell, C / - Envirotech Australia Pty. Ltd., P.O. Box 220,

Artarmon, 2064. Victoria: R. Povey, C / - S.R. & W.S. Commission, 590 Orrong Rd., Armadale, 3143. Queensland: ~: P@Higrew, P.O. Box 129, Brisbane Markets, 4106. South Australia: A. Glatz, C / - Engineering & Water Suppl)'. Dept: Ylotorla Square, Adelaide, 5000. Western Australia: R.J. Flmmel,

Box 388, West Perth, 6005. P.O .

iasmania: f::E. §pratt, C/- Fowler, England & Newton, 132 Davey St., Hobart, 7090. Northern Territory: N.R. Allen, · 634 Johns Place, Nightcliff, Darwin, 5792.

THIS ISSUE Thank you to the Tasmanian Branch for your contribution to this Issue.

Tasmania, with less than 1 % of Australia's land area, 4% of the population and 13% of water run-off, is well endowed with supplies of fresh water. The State's resources have attracted major industries which are dependent either directly or Indirectly on water and this has given rise to a per capita consumption of water which is high by Australian and overseas standards. Historically, ,exploltatlon of abundant water supplies has led to abuses, particularly in the dl1posal of wastes. Tasmania Is no exception in this regard and many of the State's rivers, estuaries and coastal waters bear witness to lack of adequate care In the past. The result is despoilation of bathing and recreational s1reas, damage to fisheries and the siltation and eutrophlcation of river systems. Protection of the environment Is now aocepted In Tasmania, as elsewhere In Austral la, as an Integral part of decision-making In the development of natural rHources. The Implementation of the Environment Protection Act Is, furthermore, leading to progressive upgrading of existing effluent treatment faollltles by industry al!fdi local authorities. As industrial aotlv[ty Increases to meet aspirations for economic: growth it Is Inevitable that oonflicts will occur as a result of competing demands for resources. In thle situation It Is essential that the environmental Implications of expanding water utilisation should be carefully assessed along with technical and economic svaluatlon. The costs IIW€JIVe6 in.. ffi§ijttng envlranmental standards must ultimately be borne oy tHe eommunity. In a World bedevilled by economic problems It is easy f~ ~etattade people that euch costs are unacceptable. It Is to be hoped that tht1 t,feeent aberration In the world economy will not deflect priorities away from thi Urgent need to protect and Improve the quality of our environment. As Jimmy Carter a§serted during the U.S. Presidential election campalgn:"We shouid not be dlvarted from out cause by false claims that the protection of our ecology and wildlife means an end to growth and a decline in jobs."

tt,e

J. F. POTTINGER, Qlreetot of Environ mental Control, Beparlment of tfitJ Eh~lronrnent Tasmania, President of Tasmanian Branch.

A.W.W.A. MEMBERSHIP Requests for Appllcatlon Formt for Membership of the A11oclatlon should be addressed to the Hon. Federal Secretary, P. Hughes, Box A 232 P.O. Sydney South 2000. Membership is In four categories: 1. Member-qualifications sultable for membership In the Inst. of Eng ineers, or other suitable profeaslonal bodies. 2. Associate-experience In the W. & W.W. Industry , without formal quallflcatlons. 3. Student. 4. Sustaining MeffiB@r-an organisation Involved In the W. & W. W. Industry wishing to §U§taln the Association.

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ASSOCIATION NEWS EDITORIAL COMMITTEE Tony Truman has asked to be excused from the task of Editor of this journal. He was our inaugural editor, and held the fort for our first twelve issues . He bore the brunt of establishing the format, of getting in contribu tions and working out the various arrangements for printing, and overseeing the subscription and mailing . Further than that, he took on the onerous task of setting out each issue. The present status of the journal is an excellent monument to his hard work and attention to detail, and we owe him hearty thanks. , The members of the Committee based in Victoria have reorganised his ¡ workload among themselves, and Mr Barrie Murphy of the MMBW has consented to take on the coordinating role as Editor.

AWWA SUMMER SCHOOL 1978 This is projected on the theme of Low Cost Treatment Methods, and will be held in Tasmania in January .

SENATE STANDING COMMITTEE OF ENQUIRY ON NATIONAL RESOURCES On the eighth of December, 1976, Senate referred the following question to a Committee of Enquiry . " The Commonwealth role In assessment, planning and management of Australia's water resources, having particular regard to: 1, The diverse responsibilities of the Commonwealth and the States. 2. The National Water Polley Statement, recently endorsed by the Australian Water Resources Council. This is an important enquiry, which affects us all, not only as citizens of Australia, but also as the people primarily concerned with the actual practice of this responsibility . State Authorities have prepared submissions, but also A.W .W.A. Branch Committees have drafted views, which will be collated by Federal Council. It is hoped that the wider views held by our very diverse membership will thus be represented at a suitably high level. 6

VICTORIA 1976 ended with the annual Ladies night , a dinner-dance at the City and Overseas Club . This function was as successful as ever , and the venue has been booked again for next year. The first meeting for 1977 was a bus-trip to the Farago Reservoir, one warm afternoon in February. Over 70 members attended, and the S.R.W.S.C. put on a varied programme . We had, in in fact, a mixed foursome, since Joan Powling and Barbara Bowles spoke on the biological problems caused by stratification, notably the solubllisation of ferrous iron in the anoxic hypollmnion, and its subsequent deposition in the pipeline. Frank Burns then demonstrated the deceptively simple technique of destratlfication , using a single bank of aeration nozzles, which effectively mixed the reservoir throughout its whole length of 7 km . Changing subject, Gordon Hirth showed us the new fluoridation plant, discussing the practical parameters affecting its design, and also the developments on polythene coating of the main pipeline. The roundrobin concluded with a barbecue on the lawns looking down at the reservoir nestling peacefully in the Gippsland hills. The ride back to the city was notable for the volubility of the conversation. The second meeting was held on March 2nd jointly with the Civil Branch of the Institution of Engineers . About 150 members heard Ian Sandford, of G. H. and D., talk on the subject "Sewage Reuse - it's harder than you think" . He covered the subject on a broad spectrum, basing his talk on the report prepared for the Commonwealth on "Sewage as a Resource" . This covers not only the potential for recovery of water but also the nutrients and sludge . The branch will hold their 1977 weekend conference at the Thornton Motel, near Lake Eildon , sometime In October. The meeting for April will be addressed by Mr S. Y. Ip , officer- in - charge of the CSIRO Advanced Waste Treatment Research Station at Lower Plenty. He will talk on developments in Ammonia Stripping and Activated Carbon treatment of wastewater. Mr J. D. Lang, well-known as the Chief Engineer for Town Water Supplies of the Victorian State Rivers and Water Supply Commission is retiring from his post at the end of April. Jack has been prominent in the affairs of the Association for over ten years, and in particular, he has concerned himself with the field of Education and Operator Training, and schools which are operating at the moment being a tribute to his conviction and hard work. So much so, that the Commission has requested him to continue with this work after his official retirement . We

wish him well , not only in this task , but also for a more relaxed w~y of life.

TASMANIA The first meeting of the year for the Tasmanian Branch will be held on Tuesday , March 29th at the H. E,C. Theatrette . The subject of the meeting will be environmental issues arising from a recent Gold Coast sewage study . The meeting should be of great interest to local government representatives , both councillors and staff . The speakers, of Camp , Scott & Furphy, are currently in Hobart conducting a similar study to that carried out for the Gold Coast . The local study covers the Greater Hobart Area and it Is hoped to have the findings of the Investigation discussed at a future meeting . Meetings for the remainder of the year are currently being arranged by the Programmes sub-committee headed by Don Walters. Early planning Is to have a meeting towards mid-year in Launceston or Burnie for Northern members . One of our members Peter Wilson has recently transferred to New South Wales . Peter was Branch Manager In Tasmania for Mono Pumps. We would like to wish him well in his new position . Branch Secretary Peter Spratt has been kept busier than usual over the last twelve months working towards a Masters Degree in Environmental Studies at the University of Tasmania. With one year to go Peter is now engaged on a joint project with Dr Selgenau of Adelaide studying the environment of the River Jordon which flows into th e Derwent estuary above Hobart . The result of their project could make an interesting talk at some fu t ure date .

• NEW SOUTH WALES On February 23rd, Mr E. D. Hespe spoke to the Branch on " The Management of Radioactive Wastes". In his paper, Mr Hespe outlined the basic philosophies and general design tech nology and its application . He emphasised that disposal is only one element in the efficient management of radioactive wastes . He outlined several philosophies and explained that their adoption is dependent on the dose limitations recom mended by the International Commission of Radiological Protection . Mike Dureau, who has worked so hard for this Association In New South Wales , has accepted a new position In Victoria and has had to resign from the Committee . We wish Mike and his wife and family every success in their new Iife down South . On Friday, 7th January , the N .S.W. Committee farewelled Mike Dureau at the Imperial Services Club . The farewell was enjoyed by all those who attended.


Mr Jack Knight, our President, has f ill ed the pos ition of Federal Councillor vacated by Mike Dureau . Again, because of M Ike Dureau's res ignat ion from the N.S .W. Committee, it has been necessary to find a new Branc h Correspondent who is now Geoffrey F. Scott of James Hardie & Coy . Pty . Ltd . Mr Ken Waterho use has accepted the appointment as the Association representative to t he Standards Association of Austral ia Committee CE / 14- Management of Civi l Engineering Quantities .

QUEENSLAND High lights of Queens land . program for 1977 inc lude: -

branch

Symposium 1977-This will invo lve a program of four papers plus a group di sc uss ion to be he ld on 22nd Apri I, 1977 . Fu ll deta il s wi ll be circulated to membera induecourae .

Joint Meeting with Institution of Engineers

On 21st September, 1977, the branch wil l jo in with the Institution of Engineers for a meeting at which Mr C. S. Cook will present a paper "Recreationa l use of Urban Water Supply Reservoirs " . It is hoped that this meeting can be held in our own " territory" which provides a convivial atmosphere conducive to good attendances .

8th Biennial Convention 1979

Whi le members are looking forward to attending the Seventh Biennial Convention at Canberra In September, 1977 , initial planning has already commenced by the Queensland Branch Comm ittee for the 1979 Convention. At th is stage the committee favours a convention held at Surfers Paradise during the first week in October, 1979 . Members wi ll recall the tremendously successfu l convention held on the Go ld Coast in 1968 and the committee will be cal ling for assistance from local members to ensure the success of the 8th Convention .

CANBERRA The Canberra Branch held a symposium for its 31st General Meeting in November on Water Research in the Australian Capital Territory. The meeting was an outstand ing success with record attendance and clearly der.,onstrated the need for co -ordination of research act ivities within the A.C .T. It is intended to follow-up the symposium with a number of workshops so that the various inst itut ions and organisations invo lved can present details of their research in more detail. It is hoped to hold the f irst workshop in Apri l or May. Dr J. W. C. Lund of the U.K. Freshwater Bio logical Association addressed the 32nd meeting of the branch on 6 December, 1976 and despite prob lems with the venue gave an informal but highly informative address . Preparations are in hand for the Seventh Bienn ial Convent ion, which wil l be held in Canberra from September 21st-24th, 1977. The venue wil l be the Lakes ide Hotel, and it is hoped that delegates from all over Aust rali a wil l be ab le to enjoy Cherryblossom Time , as we ll as the technical sess ions and social occasions .

TH E SCIEN CES CLUB A Licensed Club which aims to promote and foster the better communication and interchange of ideas between scientists, technologists and Industry

The Sciences Club is seeking new members. You may not rea lise that membership of the Institute entitles you to apply for membership of the Club .

TH E SCIENCES CLUB APPLICATION FOR MEMB ERSHIP Date . . . . .. ... . . .

I wish to make application for membership of the Sciences Club. I am a financial member of th e . .... .. . .. .. ... . .......... . .. . . . . .. . .. . .. . . . . .. .. .. . . . . .... .. . .. . ... . . ... . .. .... ... . . .. Qualifications .. ..... .. .. . NAM E ..... .. ..... . . . .. . ......... . . .. .... . . .. . . .. .. ........ .. . .. .... . (Surname) (Christian Names) ADDRESS ..... . ........ .. .. . . ... ... .................... . . . ... ..... .. .

The joining fee is $30 and the annual subscription is $50. For those seeking a person as nominator contact A.W.W.A. Secretary . Complete the tear off app lication and return It to The Secretary , Sciences Club, 191 Royal Parade , Parkville, Victoria 3052 .

TELEPHONE: Business .. . . .. ... .. .. ... .. . . . . . . ..... .. Home .. . ... ..... . OCCUPATION . . ... .. . . . .. . . .. . . .... ... . .. . . . . . ..... . .. . . ....... . .. . . . SIGNATURE ... .. . . ..... . . ... . .. . ....... . .. . ..... . ... . .. . . . ... . .. . . . . . NOMINATED BY . . . . ....... . ... . . .. ..... . . . . . .. . . .. .. ... . .. . . .. .. . .. . . SECONDED BY . . .. .. ... . ... . .. ..... ..... ............ . .. . ..... . .. . .... . Joining Fee $30

Subscription $50

Cheque enclosed $ ..... . . . .

7


8th I.A.W.P.R. CONFERENCE K·EYNOTE-ADDRESS by C. D. Parker C. D. Parker, one of the original members of the I.A.W.P.R . and one time President and Federal Councillor of the AWWA, gave the keynote address at the highly successful 8th Conference of the International Association of Water Pollution Research held in Sydney from 17th-22nd October, 1976. Excerpts from Mr Parker's address are given below. • To day we open the 8th Conference of 1.A.W.P.R., fourteen years, and some , 3,000 miles away from the Inaugural meeting, held in London, in 1962. • From that distance In time and space, it is appropriate to make comment on developments which have taken place over the period. In 1962 there was a general recognition of the need for our activities; through the period there has developed an Intense appreciation of the consequences of pollution, and pressures for improvement; at the present, there is recognition of newer threats, with constraints largely controlled by economic realities and Influenced by deficiencies In quantitative aspects of our body of knowledge . • Each of us comes to this Conference with somewhat different objectives, Administrators, Engineers, Scientists, from Universities, Research Laboratories, Government Departments, Engineering offices, and Industry . The topics we seek for discussion relate each to his own particular background and the situation he is associated with . • Many addresses have been given, and much media time and space has been devoted to emphasize the risks of pol lution to the survival of our envir~ onment. Dr Stander has already covered this today and I will not add to that aspect, except to quote a remark of Sir Julian Huxley, who after listening to a tirade of advice on steps which needed to be taken to protect the hippopotamus, the lions and elephants of Africa, was con·strained to remark, "Gentlemen remember human beings are also part of the ecology" . • The history of civi lization has shown that when man recognizes an objective and defines the components of its attainment, he is usually able to assemble the information and devise means to find the solution . Achievement is dependent on the recognition of realities and the will to resolve and apply the answer . 8

• It is our task to provide the detailed body of information on which sound policies can be developed, to reconcile the desirable objectives of ensuring an acceptable condition for the physical environment of our human society, consistent with a desirable leve l for our material, cultural, and intellectual standard of living. • The key to implementation is man agement to reconcile the varying demands for water as a resource for domestic supply , Industry, agriculture , recreation, and the quality requirements appropriate to each ; the pollution loads related to the discharge of agricultural runoff , sewage effluents, industrial wastes , solid wastes and urban drainage; the procedures and costs related to appropriate stabilization or removal of pollutants . These are the components of management from which policies need to be developed . It is factual information on these variou s topics we look for in our research contri butions to this meeting . One of the workshops on the programme Is Water quality control management. • In the address given to the first I.A.W.P.R. Conference, the late Prof . Gordon Fair, with his wide grasp of the subject of water pollution, detailed , area by area, the fields that needed attention and the needs of each area. the B.O.D . test, benthal demand , the new organics , toxins and carcinogens, nutrients and eutrophication, effluent disposal and irrigation, treatment processes. In 1962 these were the topics and the priorities. Over the Intervening years, the emphasis has changed . Detergents, reuse, viruses, phosphorus, nitrogen, trade wastes, land use , leachate were the words . Today we have urban runoff, stream and estuary modelling, biological monitoring , as our new emphases . • Our first function I believe remains the same , to define the problem and produce the facts . As Prof . Fair stated in his first address "the abi lity to measure what is going on in the world about us, or in the experimental model we develop to simulate existing or potential happenings Is an essential element of research". We also need more critical appraisal of the capabilities and deficiencies of operating treatment plants. Too often

we restrict research to the test tube and the laboratory bench . The final test of the value of academic research findings is in the ability to translate them to the performance of the full scale plant. • Recognition of en~rgy demands re lated to the operation of conven tional treatment processes and the use of chemicals for treatment, emphasizes the current interest in developing and understanding the capabilities and limitations of the simpler and less costly processes of irrigation and pond treatment. Where land areas are available and labour costs are low, these processes have many advantages. • The abundance of saline and brackish waters and the increasing demand for fresh water indicate the importance of reducing the cost of demineralization processes . Interesting Australian work in the field of thermal regeneration of demineralizing resins is reported at this meeting . Increasingly stringent regulatory requirements demand more efficient processes for treating an increasing variety of industrial wastes . Here the technology of operating physical and chemical processes at high levels of performance is particularly Important. • Demineralizati on , nutrient-eutrophic relationships and the significance of estuarine and coastal pollution are of particular continuing concern. Many processes developed achieve a concentration of pollutants. The ultimate disposal of these concentrates whether they be resin regenerant brines, hydroxide and organic sludges , or absorbed solids , is an area demanding further endeavour. Urbanization tends to create increasing prob lems from unsewered areas and surface storm water runoff , other unresolved areas . • Overall there is a need for a greater proportion of our financial and manpower resources to be devoted to research and investigation, compared with that currently directed to administration , regulation, licencing and monitoring . Unless we resolve the realities we cannot achieve the objectives . The realities are the production of facts , the development of treatment processes , the technology to apply and the finance to build and operate. On these, achievemen't is dependent.


INDUSTRIAL WASTEWATER AND ENVIRONMENT .PROTECTION IN TASMANIA by 8. 0. Healey, B.E., M.Eng.Sc., F.I.E.Aust., F.R.S.H., Member A.W.W.A. SYNOPSIS: This paper describes the legis lative approach to environment protection in Tasmania , with special reference to discharges from industrial sources to natural streams. The admin istrative po licies and procedures adopted in that State are also summarised . INTRODUCTORY REMARKS In attempting in this paper something of a broad overview of the environmental situat ion, it is nevertheless desired in the interest of complying with the allotted space to confine discussion to discharges to the environment which enter into natural streams and which originate from an industrial source . The information was originally prepared to assist those required to treat wastewat er discharges to comply with Tasman ian standards of quality . It is thought to be of interest to those who enforce standards anywhere . The title of this paper embraces an area where the aspirations of the community are expressed in a legal , social, economic and technological context, and all these aspects have their pol itical implications. No discussion of the subject can be complete which neglects any of these aspects , so be assured from the outset that there is no claim herein to be comprehensive . If it be assumed that all these aspects are synthesised politically within a democracy into its leg islation , then a review of the legislation and its administration can assist waste treatment engineers to define the constraints external to their own factory within which they work . Therefore , much of this paper will be concerned with legislative enactments in Tasmania, namely the Environment Protection Act 1973, hereinafter referred to as the Act, and one of several regulations under that Act, namely the Environment Protect ion (Water Pollution) Regulations 197 4, being Statutory Rule No . 56 of 197 4. The lega l def inition of the environ ment is "the land , water, and atmosphere of the earth". For practical purposes it can usual ly be considered as anything outside private property . The relationship of living things to their environment is the subject of the sc ience of ecology . With few exceptions , it is generally considered that there is an inbuilt system of checks and balances whereby living species adapt to their environment or are replaced by those which do . Man alone ~as such The author is the Water Pollution Officer, Department of the Environment, 161 Davey Street , Hobart , Tasmania . 7000.

ability to damage the environment that it is now general ly cons idered that he must either voluntarily or under the compulsion of his fellows restrict that damage . In other words, it is necessary to protect the environment from him and his pollution . EN~RONMENTPROTECTION In this context then , pollution has been defined : - "pollution " means any direct or indirect contamination or alteration of any part of the environment so as (a) to affect any beneficial use adversely; or (b) to cause a condition that is detrimental or hazardous or likely to be detrimental or hazardous to(i) human health , safety, or welfare ; (ii) animals, plants , or microbes; or (iii) property; caused by emitting anything . To emit is defined to include deposit and discharge. A beneficial use has been defined to mean a use of the environment or any part thereof that is conducive to human benefit, welfare, safety , or health . This would seem to include not only the use of water for well recognised purposes commonly possib le on ly with engineering assistance , such as urban water supply, irrigation , navigation and hydro-electricity , but also the conservation of ecological associations between plants and animals on the one hand and habitat on the other , in open water, swamp , fen , or repetitively changing flood plain. It would also include use of water for human benefit in passive pastimes of viewing, photography and painting, and more act ive pastimes of nature study , swimming , water skiing, snow skiing, sailing, canoeing, other forms of boating , fishing, picnicking, or even duck shooting . A pollutant is also defined: " pollutant " means any substance, whether liquid , solid, or gaseous and whether living or not , which directly or indirectly(a) causes pollution of the environment ; or (b) causes odours or noises that are offensive or prejud icial to man; POLLUTANTS For convenience in identifying whether a given substance is legally a po l I utant , the author prefers to categorise water pollutants under six classes of effects on the environment. Toxic materials kill or are injurious to life in one or more species . They are

generally chemical in nature. Many have been used, because of their tox ic qualities, as pesticides , weedicides, fungicides, etc . It includes the "heavy metals", some of which are directly toxic to man, yet others , which are relatively harmless to man in moderate doses , are diastrous to microbiological life or fish larvae in low concentrations approaching the limit of detection. Alternatively, concentration seems to occur in the food chain , from the smallest living species to man , to become toxic at the human level , despite the existence of only minute traces in the environment. Infectious matter transfers disease mainly in the form of bacterial or viral infection, but can also include protozoa , fungi and the ova of other forms of life . Infectious matter is presumed to be absent when treatment has reduced faeca l co liforms to a low level. The oxygen demanding po llutants are usually identified either as Chemical Oxygen Demand (COD) or as Biochemical Oxygen Demand (BCD) . The former gives a measure of those substances which can be oxidised chem icall y in a few hours by a strong oxidising agent . The latter measures those which can be uti li sed as food by bacteria or protozoa over a period of several days, thereby taking up oxygen from the water and combin ing it biochemically . There is some possibi lity that in future the change in totait organic carbon (TOC) over a period can be used to obtain a measure of oxygen demand. The eutrophic pollutants are usually phosphoric, and sometimes nitrogenous . As fertilisers they stimulate abnormal growth, sometimes to the detriment of another species, sometimes to the eventual death of the stimulated species, leading for examp le to malodorous masses of decaying vegetation. Ant i-aesthetic po llutants produce unacceptable degrees of odour or colour. This class is probably more like ly than any other to bring forth complaints from the public, who have no difficulty in recognising its existence as definite fact. Unfortunately, engineering and scientific skill has not yet prod u.ced a meter for its measurement, its assessment is subjective in an intransigent way, and its legal definition and proof is difficu lt . Inert materials either mineral or organic, may be classed as pollutants simply by reason of their concen-

a

9


tration , if the concentration exceeds the limit acceptable to the senses ot man or to the life processes of fish or smaller organisms . It should be noted this classification is in terms of polluting effects , and is not mutually exclusive. The one pollutant could belong to two or more classes , yet is unlikely that a pollutant exists wh ich cannot be ident ified in one of these six c lasses of effects . POLLUTION CONTROL From the considerations and def initions dealt with so far, it is apparent that environment protection becomes almost synonymous with pollution control. Although the Act confers upon the Director of Environmental Control the duty to co-ordinate all activities , whether governmental or otherwise, as are necessary to protect, restore , or improve the environment of the State of Tasmania , it is almost who ll y concerned with pol lution contro l by means of cor:,trol of em iss ions. The Act lays upon the Crown , servants of the Crown, pub lic and loca l authorities, and municipalities , the duty to avoid causing or permitting po llution of the environment , " so far as is reasonable and practicable". The words " reasonable and practicable" assume tremen dous significance in relation to other sections which, on the one hand , create an offence to emit any pollutant whatsoever into the env ironment, and on the other hand state there is no offence if a standard has been prescribed and the em ission compl ies with that standard. Such standards have been prescribed in the water po ll ution regulations referred to above . The standards are prescribed separately for four classes of receiving water , and certain specific provisions are made for effluents from si x classes of industry . The four classes of receiving waters are : 1. Special ly protected waters , into which no pu llutants at all can know ingly be d isc harged . 2. Inland waters . Em iss ions sha ll not exceed 20 mg/1 of BOD, 30 mg/1 of non-filtrable residue, 200 faecal coliforms per 100 ml., and a I ist of 30 restricted substances must be below specified concentrations . The concentration of BOD and non filtrable residue may be doubled where there is a specified dilution , and there is an over-riding requirement that oxygen content of the receiving waters shal l not be reduc ed be low 50% of saturat ion .

3. Bays and estuarine waters are subject to essent ially the same requirements as in land waters , except that the l imit for faeca l coliforms is increased to 1,000 per 100 ml. and the limits for certain of the restricted substances are re laxed. 4. Coastal waters . Emissions shall not exceed 200 mg/1 of BOD or of non10

filtrable residue , and oxygen content of the receiving waters must be maintained as for other classes of water. For discharges to inland waters and bays and estuaries there are also specified limits of 10 mg/1 for grease and oil in stable dispersions , of 3 picocuries per litre of gross alpha radioactivity , and 30 pico-curies per litre of gross beta radioactivity . In addit ion to requirements set numerically as above , there are requirements to avoid undesirable effects in the environment , of the type described earlier. The si x classes of industry are : 1. Pulp and paper mills in production before 1st January , 1975. 2. Woodchip mills in production before 1st January , 1975. 3. Industrial gas scrubbers . 4. Scheduled premises upon which mining , concentrating , sme lting or ref ining of metalliferous ores is in product ion before 1st January, 1975. 5. Fruit and vegetab le process ing factories , canneries, and abattoirs . 6. Factories processing milk or milk products . PRINCIPLES UNDERLYING THE EMISSION STANDARDS Readers will no doubt have some acquaintance with the complexities of emission standards of other countries as described in the literature or as disclosed in their own practice. Some understanding of the principles adopted in drawing up these standards will be of use in relat ion to licenses and exemptions . These are matters for wh ich provision is rrade in the Act, but of which mention has not so far been made in this paper . The regulations were made , as the Act provides , upon the recommendation of the Environment Protection Advisory Council, which has 19 mem bers . The Council appointed an expert committee of 8 members to draft the water pollution regulations . The standards represent the consensus of opinion of these persons as to what the standards shou ld be in terms of their individual understanding of the Act and how it would be administered. This paper makes no attempt to set forth the reasons why any person other than the author arrived at these standards , for two very good reasons . In the first place , in case of agreement , reasons were normally not expressed ; and secondly in cases of disagreement, it would be inappropriate to discuss ex parte the views of the protagonists of differing opinions . Basically there are two ways of setting lim its for emission standards . An upper lim it can be set at that which wil l start to cause ascertainable harm in the environment ; another upper limit can be set at the lowest limit which available technology will enable industry to attain. The difficulties with the first approach are that the limit of harm is rarely ascertainable, and that contin-

uing research discloses progressively lower limits are needed; also , the apportioning of the permissible pollution load among industries ex isting and putative is impracticable , and prediction of effects under variables of temperature , stream flow , synergistic effects , etc . may not be much better than simply guessing . It was put to the committee , and for the most part endorsed , that the " availab le techno logy" approach be adopted. At the very least this maintains ex isting standards , and at best considerable improvement is possible . If it is found that in a particular case the environment needs even lower pollution than current technology can provide , then the situation is identical wit b. that under the first approach . Because the standards of the regulations provide a defence against prosecution, they are tantamount to permission for all potential polluters to d ischarge up to that l imit. Therefore, it is reas onab le that the limit shou ld be set at t hat at which most industries can comply , even if it be known that availab le technology will not permit some few industries (which could be very large industries and large polluters) to comply. Fortunately , the Act' provides that exemption may be granted in such cases by the Minister. In a number of cases , provision for the scale of operations has been made by specifying the allowable amount of po l lutant in re lation to the volume of production. This has been done for BOD in emissions from ex ist ing pu lp and paper mi l ls and ex isting woodchip m ill s ; also for non -filtrable residue from existing woodchip mills. Although the emission' standards are generally expressed in concentrations in mg/1 it is nevertheless the total load of pollutant which it is desired to limit. This is assisted tly a regulation which prohibits dilution of restricted substances except in so far as it is reasonab ly necessary for the purposes of the industry , as d ist inct from the purpose of meeting a test result . This prohib ition does not app ly to d ischarg es to coastal waters, nor to BOD or non-filtrable residue , which are not " restricted substances" . In the case of applications for exemption , the total pollution could be given closer attention than the concentration. LICENSING The Act provides that 25 categories of industry in the First Schedule and therefore described as " scheduled premises " shal I not operate after a certain date without having applied for a l icence. For new ind ustries , the date is the 26th Ju ly, 1973, and for ex isting industries the 31st December, 1974. A license has no effect on the emission standards , which are universally applicable .

A license may have conditions attached . These are five in nature, involving action by the licensee :-

I...

l


(i) To do specified things to prevent , minimize , or control pol lut ion or noise . As far as possib le it is des irable for industry to achieve the standards in whatever way it sees fit , without use of these condit ions . However, where an exempt ion is sought , it is reasonable to anticipate these conditions could be used to ensure that pollution leve l is neverthe less reduced as far as practicable, and they cou ld wel l be used to maintain standards of operating practice as distinct f rom requiring new capital instal lat ions ; (ii) To comp ly with specif ied stan dards for the emission of pol lutants or noise . In general , standards are prescribed in the regu lat ions . However , t hese co nditions could be used in respect of pol lutants not covered by the regulations , such as pH or thermal effects . On rare occasio ns , in an environmenta ll y sens it ive locat ion , it wou ld seem possib le for a level lower than the regu lations to be spec ified ; none are forseen at prese nt; (iii) To carry out , at his own expense, a specified routine of monitoring emissions and supplying specified informat ion abo ut the resu lts th ereof. These co nd it ions will be attached to al l licenses other than perhaps for the smallest of scheduled premises ; (iv) To do spec ified thin gs to remove , cover up, or avo id anything unsight ly on the premises . Perhaps it could be considered something of a ref lection on the management of the ind us try if it is necessary to invoke this clause . It is outside the scope of this paper ; (v) To do specified things for the restorat ion of t he surface of the land and the vegetation of the premises . This has an obvious application to mining and quarrying , and is aga in normally outside t he sco pe of t hi s paper . In add it ion , the li cence may spec ify points of emission and of mon itoring . EXEMPTIONS Any ind ust ry kno wi ng ly em itting a discharge which does not comp ly with the regulations has been liab le to prosec utio n since 12th _ March , 1974. Such an in d ust ry wo uld be well ad vi sed to - app ly to t he Min ister for an exemption under sections 15(7), 16(5), or 17(2) of the Act , as may be applicab le. The Act specifies neit her the gro un ds nor the l imi ts applicab le to exempt ion , but some comments are offered on certain gro unds upon wh ich exemption may be sought. The technology Is not available to achieve the prescribed standard. From the foregoing , it may be assumed this is contrary to the opinion of those who drew up t he regu lat ions. Yet it is by no

means impossible that it was one of the few indust ries referred to earlier from whom an exemption app lication could be anticipated , or that it was one (hopefully few in ¡ number) which was overlooked . It can be anticipated the Minister would seek a report from the Department or the Advisory Counc il and a decision would be based on the facts of the case . Although technology is available, it will take time to design, obtain and instal equipment . Subject to a check of the facts , it would be departmental policy to recommend an exemption , but with the exempt ion approval and/or the l icence imposing condit ions for stages of the design , procurement and instal lation to be complete by certain dates. Although technology is available, it is not economically possible to comply . The determination of this app l ication involves every aspect of value judgements by the community ; in the long run , the decision must be po litica l, t ho ugh techniq ues of defin ing and presenting the issues to the decision maker are improving . Industry must

take cogn isance of the change in values reflected in com munity att it udes in recent years , and th'e onl y comment offered here is that it is not getting any easier for industry to maintain this argument . CONCLUSION In attempting in this paper to summarise the effects of legis lation and its administration , it is most important that ment ion should be made of the fact that environment protection demands the conti nued co -o perat ion of all parties in t he work in g out of com mo n prob lems . Any po larization of attitudes for or against any aspect is to be deplored . ACKNOWLEDGEMENTS This paper is presented with the permission of the Director of Environ mental Co ntrol , Mr J. F. Pottinger . Any op in ions expressed are neverthe less those of the autho r and not necessari ly those of the Department of the Environment'.

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Tl-TREE BEND J. W. Bowen, M.I.E.Aust., M.ASCE., M.A.W.W.A.*

In common with other cities , Launceston in Tasmania has been engaged over several years in eliminating discharges of untreated sewage . This paper describes the approach to the provision of sewage treatment facilities for the greater part of the City, and the progress made to date on the construction of a sewage treatment plant at Ti-Tree Bend, Launceston . The investigations and designs were prepared using imperial units which have been directly converted to metric units and in some cases rounded off in this paper. History Launceston was proclaimed a Municipality in 1852 and was one of the first communities In Australia to have a water carriage sewerage system, with work commencing In 1860. The sewerage system used was the 'combined system' in which domestic wastes and stormwater use the one system as distinct from the 'separate system' in which separate systems of sewers are provided for stormwater drainage and for sewerage . In later years the separate system has been used for areas newly sewered. These early sewers and subsequent extensions are now intercepted at a number of pumping stations which lift the sewage through a common rising main to an outfall at Ti-Tree Bend on the Tamar River. After considerable investigation a report on Ti-Tree Bend Sewage Treatment Plant was submitted to the Launceston City Council In 1969 and subsequently some works have been constructed and further designs prepared . CATCHMENT AREA SERVED The catchment area of the treatment works comprises almost the whole of the City Area, plus a small number of properties in neighbouring Municipali ties. Approximately 2000 people In North Mowbray Heights are served by a treatment plant in the Newnham Area of the Lilydale Municipality . The catchment area has six main drainage areas served by three major pumping stations. Trevallyn , Summerhill and West Launceston go to Margaret Street Pump ing Station . East Launceston (including Newstead, Punchbowl and Hobart Road area) go to St. John Street Pumping Station. • Associate , Scott & Furphy Engineers, Launceston, Tasmania

12

lnveresk , lnvermay and Mowbray South go to Forster Street Pumping Station . These three major pumping stations have a common rising main and it is the magnitude of the pumping station outputs that determine the instantaneous flow at the treatment works. POPULATION The population within the City Boundary has not shown much increase since the late 1940's due to most of the readily serviceable areas being by then occupied and the urban area extending into the neighbouring Municipalities . There are approximately 370 hectares ava il ab le for development in the Summerhi ll area and there will possibly be some amendment to the catchment area from time to time either by agreement to serve adjacent areas or by alterat ion s in the City Boundary. The future population could also be increased by more intensive land use with higher population densities . From a consideration of these and other factors it has been assumed that the population contributing to the treatment works by the end of this century will be 63 ,000 persons and the initial stage of the treatment works shou ld be capable of serving 45,000 persons . SEWAGE STRENGTH AND VOLUME Being, in the older areas, a combined sewerage system, there are four sources of waste water: a) Domestic discharges from bathroom, laundries , kitchens and water closets . b) Trade effluent from manufacturing processes. c) Stormwater from roads, roofs and paved areas . d) Infiltration of subsoil water through broken pipes and pipe joints .

There was no direct method of measuring sewage flows and they have been inferred from the outputs of the sewage pumping stations and from water consumption records. a. Domestic From these sources it has been assessed that the present domestic discharge is approximately 290 litres per head per day . For design purposes a contribution of 295 litres per head has been taken as appropriate and due to the observed increase in sewage f low..s with increase in prosperity a flow of 327 litres per head has been assumed for the later stages . Metering of the flows to the treatment works wi ll establish the validity of the initial figure and enable a later re-assessment of the second figure . From the assumed figures for populat ion and contribution the sewage dry weather flow to the treatment works is expected to be 13275 M3 per day in 1983 and 20640 M3 per day in the year 2000. The usual measure of sewage strength is in terms of the biochemical oxygen demand (BOD) at 5 days after incubation at 20°C, and the suspended so lids content, both expressed miligrams per litre (mg/1 ). Limited sampling led to the adoption of 215 mg/1 of BOD and 245 mg/1 suspended solids for design of the first stage and assumption for planning purposes of 220 mg/1 BOD and 250 mg /1 suspended solids fo r stage 2. The above results are summarised in the table below . b. Trade Waste • The major contributor to trade wastes are the wool len Industries which contribute approximate ly half of the flow, the 1969 estimate being 3230 M3 per day of a total of 7 455 M3 per day.

Ory Weather Flow

Strength

Stage

Populat ion

1 / h/d

M3

B.O.D.

S.S.

1

45000

295

13275

2

63000

327

20640

215mg/1 2858 kg/day 220 mg/1 4535 kg/day

245 mg/1 3265 kg/day 250 mg/1 5170 kg/day

Trade

Estimated Discharge

Woollen Brewing Railway Hospital Dairy Gas Miscellaneous

Biochemical Oxygen Demand

Suspended Sol ids

M3 per day

mg/1

kg/day

mg/1

kg/day

3978 659 409 455 545 159 3250

1300 1950 350 550

5160 1279 143 249 435 16 973

1500 2200 375 575 325 100 300

5953 1447 154 261 177 16 973

-9455

BOO

100 300

-8255

8980


The strength of trade wastes varied wide ly and the results of spot samples for the report ind icated f igures as high as 9,120 mg/1 for BOD and 35,100 mg/1 for suspended solids . The trade eff luent flows for Stage 1 and loads were estimated as shown in the table. For stage II the assumption is that f low wil l increase to 10274 M3 per day with 10,700 kg / day BOD and 11 ,600 kg/ day suspended solids . This represents a growth rate of 1 ½% per annum up to the year 2000. c. Stormwater Flows

It has become general practice to pass on ly six times dry weather flow to sewage treatment works , al lowing the remain ing flow to by-pass . d. Subsoll Water lnflltratlon

Subsoil water infiltration into the sewers forms part of the dry weather f low and has been estimated at approx imately 1820 M3 per day.

the treatment plant . This site was part of the al luvial plain and had been used for some years up til l the early 1960's for the disposal of river silt dredged from the upper r-eaches of the Tamar, and in the 1800's for the growing of wheat . It was obvious from previous experience with levee banks and other structures that the area is subject to considerable ground movement when add itional loads are superimposed and as settlements of the order experienced were unacceptable for hydrau lic structures and pipe lines the foundations were investigated in some detail , and t he desirability of moving to an alternative site was assessed . The investigation concluded that it wou ld be more expensive to move to another site and that the timber piles traditionally used promised the best support . However, the eastern part of the acqu ired site had significantly better bearing capacity and the major structures are located in this area .

e. Total Flows and Loads

Treatment Plant Stage 2 Approx . year capacity is provided 1,983 2,000 Dry weather f low m3/day 24 ,550 32,730 Wet weather flow m3 / day, 147,300 196,390 B.O . D. Kgs per day Domestic 2,858 4,535 Trade 8,255 10,700 Total 11 ,155 15,235 Suspended Solids

kgs per day Domestic Trade

3,265 5,170 8,980 11,600 Total 12,245 16,770

For stage I the above loads are equivalent to average strengths of 455 mg/1 B.O. D. and 500 mg/1 suspended solids. EFFLUENT STANDARDS

The Environmental Protection (Water Pol lution) Regu lations 1974 under the Env ironment Protection Act 1973 now prescribe the standards for the effluent to be discharged from the treatment plant , however, the designs for the primary treatment units were completed before these regu lation·s were promul gated . In the case of the Tamar River the eff luent standard must also be approved by the Port of Launceston Authority as we ll as the other interested parties. The proposed standard of effluent from the Ti-Tree Bend Plant is 20 mg/1 B.O.D. and 30 mg/1 suspended so li ds wh ich will satisfy those requirements of the legis lat ion . SITE AND SITE CONDITIONS

A site at Ti-Tree Bend on the River Tamar , only 2.4 ki lometres from the City centre, had been acqu ired by the City with a view to the establishment of

PROPOSED TREATMENT PLANT

The principal units and processes for treatment of sewage in a conventional treatment plant as proposed at Ti-Tree Bend are : · 1. Screens - to remove sticks and stones, bottles and bones , rags and other similar large size debris . 2. Grit Channels - to remove nonorganic particles larger than approximately .2 mm . 3. Primary Sedimentation Tanks - to settle out as a sludge material in suspens ion. Treatment- to break 4. Blologlcal down and oxidise the putresc ible organic matter in the sewage . 5. Secondary Sedimentation Tanks to settle out as a sludge the fine ly divided material passing over from the biological treatment stage . 6. Sludge Treatment - to render the sludges settled out in the primary and secondary sedimentation tanks innoxious and inoffensive. 7. Disinfection - to ki ll or reduce to acceptab le limits living pathogenic organisms . PROPOSED STAGES OF WORKS

In order to spread the financial load over as long a period as possible while progressively improving the standard of eff luent discharged to the river, the works were proposed in three main phases . Stage I provides for treatment of flows up to 24,550 M3 with a pollution load of 11 ,155 kg . per day of BOD and 12,245 kg per day of suspended solids and th is stage has been divided into Stage 1 A in wh ich primary treatment will be provided and Stage 1 B in which partial secondary treatment will be provided; with an effluent standard of 50 mg/1 BOD and 40 mg/1 suspended so lids .

Stage 2 works will provide for flows up to 32,730 M3 with pollution load of 15,235 kg . per day BOD and 16,770 kg. per day suspended solids . The effluent is then expected to -have 20 mg / 1 BOD and 30 mg/1 suspended solids . STAGE 1A WORKS

Comprise the construction of the fol lowing: 1. Access Road from Murphy Street to the site off Clyde Street with a sea led surface above flood level. This road has now been constructed. 2. Inlet Structure A connect ion from the existing outfal l main to the grit removal building has been constructed In reinforced concrete pipe as a ris ing main. The inlet works comprise screens , grit removal and flow measuring fac ilities and these are designed to accommodate flows of up to 6 times dry weather f low of 32,730 M3. The flow is discharged through two automatically raked bar screens thence through two aerated grit collecting channels of nominal dimensions 13 metres long 2.7 metres wide and 2.7 metres deep , and then flow measuring flumes . The screenings from the automati cally raked bar screenings go through disintegrator pumps which cut the screenings to nominal 20 mm size and return them to the flow upstream of the screens . These screens operate automatically on a t imed sequence with over-riding level control which actuates the raking mechanism whenever the sensors show that the bank up of sewage upstream of the screens has reached the predetermined level. Emergency overfloy., channels are provided with hand raked screens to handle flows in the event of power failure or other plant breakdown. The aerated grit channels allow grit and similar site non organic matter to sett le from the sewage whilst allowing the lighter and usually more putresclble material to pass through to later treatment units . The grit channels are scraped automatically by buckets attached to chains and the grit Is discharged to a washer which is also an elevator. The washed grit is held In dump trucks for removal by truck to be • later buried . At present after leaving the grit channels the sewage flows through a comminutor wh ich chops the solids into approximately 10 mm size particles . The f lumes downstream of the grit removal bui lding operate flow measuring equipment which indicates, records and integrates the f lows entering the works . A new outfal l main has been constructed in reinforced concrete and concrete lined mild stee l pipes to discharge to the river. Primary Sedimentation

A battery of rectangular sedimentation tanks, nominally 41 metres long 13


6 metres wide and 3 metres water depth with sludge rakes and scum skimmers ha91ng about 3 hours detention at dry weather flow of 24,550 M3 are under construction and the effluent from these tanks is expected to have 265 mg/1 BOD and 190 mg/1 suspended solids . Sludge Treatment The sludge deposited in the sedimen tat ion tanks will be pumped to two heated digesters of diameter 16.75 metres and volume of 2265 cubic metres with gas collecting covers . Due to the large quantities of trade wastes and their composition considerable thought has been given to alternative methods of sludge treatment and disposal including: no treatment and disposal to sea by barge, digestion and disposal to land by tanker, drying or filtering , chemical or polymer conditioning and disposal to landfill or lnclner. ation , Porteous heat treatment , Zimpro wet oxidation and disposal to landfill. The Porteous heat treatment process was favoured initially due to its ability to handle all types of sludges. However, the Indicated annual costs In the early stages were higher than for digestion . Sludge Lagoons After digestion the sludge will go to slud ge lagoons for conso lidat ion to an expected water content of 70 per cent . Administration Building and Laboratory This building will have offices, store , control room, switchboard, staff amenities and laboratory . The laboratory wll I be used for in-plant process control and also for trade waste and other monitoring work associated with the sewerage system . Stage IB Works This stage will consist of the addition of secondary treatment for the effluent from the primary sedimentation tanks constructed as part of Stage IA works, and also the provision of stormwater tanks. Stormwater Tanks

In this stage it is proposed to separate flows in excess of 3 times DWF with the lower flows going to the Stage IA sedimentation tanks with the excess going to the stormwater tanks for approximate ly 40 minutes deten tion . Biological Treatment

The act ivated slud ge process is proposed in which a floe rich In bacterial life is mixed with the settled sewage and the mixture provided with oxygen necessary to support the large bacterial population while it attacks and breaks down the polluting matter in the sewage . The oxygen will be supplied by mechanical surface aerators operating in pockets in the aeration tanks . 14

Final Settlement

Excavation

After aeration the sewage will go to flat bottom circular tanks fitted with sludge scrapers fo r t~e collection of the settled activated sludge for return to the aeration channels , with surplus sludge going to the sludge digesters . The final effluent at this stage is expected to be approximately 50 mg I 1 BOD and 40 mg/1 suspended solids . Stage 2 The treatment capacity proposed for stage 2 is : 32 ,730 M3 dry weather flow 15, 235 kg/day B.O. D. 16,770 kg/day suspended solids . and the units comprise : additional stormwater tanks duplication of the activated sludge plant supplementation of the f inal settlement tanks and additiona l digester capacity . The final effluent is expected to be then 20 mg/ 1 BOD and 30 mg/ 1 suspended solids and the amount of slud ge removed from the sewage to be 16 tonnes dry weight per day .

A system of well point s was installed for the excavation and construction of the below ground sections of the grit removal building , digesters and galleries and this enabled stable batters to be maintained at reasonably steep slopes . PIiing Most of the piling to date has been done with a Delmag D22 deisel hammer although some initial piling was done with a drop hammer. Test loads were applied to selected piles . All piles are of timber , those with heads below ground water level being untreated and those with head levels above ground water having Tanalith treatment . Approxi mately 680 piles have been driven on site . Outfall to River The outfall sewer to the river was constructed of reinforced concrete pipe to the river bank and thereafter in concrete lined steel pipe supported on pile bents with timber cross heads . The construction contractors offered a design variation from a straight graded pipe to a large radius curve to allow the steel pipe sections to be welded at the one shore station with the pipeline then being moved out towards the river one pipe length as the pipes were attached to the upstream end .

Construction

Some work on access road foun dation , test piling etc . had been done previously but serious construction started in May 1972 with contracts being let for access road completion and the screening and grit removal complex with associated pipelines . As mentioned previously the site had been used for the hydraulic desposition of river silt and it was expected that site access and mobility of equipment would be most adversely affected during the wetter months of the year . In the event the weather during the construction to date has been quite kind and has not greatly interfered with the construction program . Part of the work done to date includes the road foundations in the vicinity of the next units to be constructed so site access shou ld not constitute a major problem for future works .

STATUS QUO

At the present time the access road to the site has be-;in constructed; the connection to and extension of the rising main and the new outfall main have been comp leted ; the grit removal building and the measuring flumes including all necessary equipment have been completed and ars in operation, and the laboratory building is completed and occupied . ACKNOWLEDGEMENT

The subject matter contained in this paper is a project for the Launceston City Counci l and their kind permission to present the information is acknowledged with thanks .

-.._

l


ORGANIC NITROGEN

BACTERIAL DENITRIFICATION -A REVIEW-

Proteolysis

or aerob i c)

By Nancy F. MIiiis, Ph.D., Department of Mlcroblology, University of Melbourne, Parkville, Australia. i tr .i.j ica tion WHY REMOVE NITRATE? In treating wastewater, the oxidation of organic nitrogen to nitrate is a desirable objective, but when the treated water is to be reclaimed directly for drinking purposes or enters a lake or stream which is the source of drinking water for another community, a high content of nitrate may be deleterious . The pH of the stomach of children under 6 months Is about 4 and this pH permits nitrate-reducing bacteria to grow in the stomach . The nitrate so formed can be absorbed Into the bloodstream and cause methaemoglobinaemla (Comly, 1945; Ewing and Wh lte, 1951). For adults, the nitrate content of drinking water Is of little significance because the low pH of the adult stomach inhibits the nitratereducing bacteria . The WHO standard (1970) suggests that drinking water shou ld ideally contain less than 11 mg N-NO 3 /1 and never more than 22 mg N-NO3/1 . A high content of nitrate In treated water can also be undesirable when the treated eff luent contributes sign ificantly to the water in a river or inland lake because the nitrate may stimulate an unwanted bloom of algae, especial ly when the water has a lon g residence time . The results of the current practice in Victoria of discharging treated eff luent into the open sea, does not appear to warrant the cost of removing nitrate from the water before discharge . METHODS OF REMOVING NITRATE Given the need to remove nitrate, there are two possible approaches, physico-chemical and biological. The high solubi lity of nitrate makes It extreme ly difficult to remove by precipitation techniques . Ion-exchange is of course possible but expensive and technically troublesome, If the wastewater has significant suspended solids. There are three common biological methods of removing nitrates-land irrigation , harvesting algal growth and den itrification. Recently, there have been interesting advances in the management of denitrlflcatlon and according ly, this review will concen-

(Aerobic) I

(Aerob i c)

Denit r if i cation (Anaerobic)

NI TROGEN +---- Figure 1. The llnk between denltrlflcatlon and the other transformations of nitrogen occurring during waste-water treatment. T_ he broad arrows are major reactions, the narrow arrows are minor reactions. Nitrification Is strictly aerobic, denltrlflcatlon Is strictly anaerobic and proteolysis and deamlnatlon are lndep~ndent of oxygen.

trate on denitrificatlon, but this In no way implies that the other methods are unsatisfactory. Denitrification (ON) is defined for this review as the reduction of nitrate to nitrogen or gaseous oxides of nitrogen . Denitrlf ication Is seen in Figure 1 in relation to other transformations of nitrogen occurring In the conventional treatment of wastewater. The heavy arrows In Figure 1 Indicate the major reactions . The light arrows are reactions of littl e significance during wastewater treatment, since both the fixation of gaseous nitrogen and the reduction of nitrate to ammonium by microbes occur only when combined nitrogen is unavailable which is not usual in wastewaters. The important transformations of comp lex organic nitrogen to peptides and amino acids and their subsequent deamlnation to release ammonium, occurs at all stages of the treatment plant In both aerobic and anaerobic situations. Con version ot the ammonium to nitrate Is a strictly aerobic process, and It may be achieved in either an activated sludge unit or a trickling f ilter. Nitrification must be complete before denitrification can be in stituted, since denltrificatlon requires anaerobic conditions.

THE BIOLOGY OF DENITRIFICATION From an inspection of the nitrogen cycle , it is cl!ÂĽlr that the flux of nitrogen gas to the atmosphere is significant, and must equal nitrogen fixation. This implies that the ab ili ty to denitrify is widespread and indeed it has been demonstrated in many species of facultatively aerobic bacteria (Payne, 1973). However, whether such bacteria actual ly denitrify is determined by the env ironm ent. It is important to apprec- . iate that bacteria exert considerable control over protein synthesis; although they may have the genetic capabi lity of synthesizing a particular enzyme, synthesis may be repressed when they are grow in g in certair. environments . The enzymes responsibl e for denitrification (nitrate and nitrite reductases) are a case in point. Bacteria repress the synthesis of these enzymes totally if oxygen is present in the environment . The cell gains more energy from the oxidation of a substrate if oxygen is the electron acceptor than if nitrate is the acceptor. However, when oxygen is not availab le, repression of synthesis is relieved and bacteria with the genet ic potential to make the reductases, do so . Then 15


electrons pass from the substrate via a modified electron transport pathway to nitrate in stead of to oxygen . The alternat ive routes the electrons may take when passing from an oxidizable substrate (AH 2 ) to either oxygen or nitrate are shown in Figure 2. It is clear that nitrate is then acting as an alternat ive to oxygen and has a respiratory (or dissimilatory) function . The respiratory reductases are quite different enzymes from the assim il atory nitrate reductases . The assimi latory red uctases reduce nitrate to ammonium and the ammonium is used in synthesis and growth; the ir synthesis is repressed by the presence of combined nitrogen and is in different to the presence of oxygen. The differences In these two reductase systems are summarized in Table 1.

I

I

AH -

Aaalmllatory reduct111

RHplratory reductaae

Form of the enzyme In t he cell Condit ions for prod uct ion Effect of ammonium In the growth medium Final end product

Solu ble

Particle bound

Aerobic or anaerobic No enzyme produced

Anaerobic only

Ammonium

Nitrogen

Enzyme produced

From this discussion, it will be apparent that for denitrif ication to occur, (i) species with the genetic capability - - lodenitrify must be present, (ii) nitrate must be present, (ii i) anaerobic conditions must prevail, (iv) a source of reducing power must be provided. In an efficient treatment plant, the eff luent wil l contain nitrate, and before ch lorination it will also have an adequate microbial flora for denitrification . The effluent must then pass through a stage where the dissolved oxygen content is reduced to zero and a source of electrons is provided . Duri ng routine monitoring of the treatment of wastewater, negative balances for nitrogen are sometimes found in activated sludge plants that have an overall high rate of nitrification . Th is may occur when a particu larly high load of BOD enters the unit, or if the un it has areas where the disso lved oxygen fa ll s to zero . During secondary sed im entation, sludge may lift due to the release of nitrogen from nitrate. Workers in Germany, USA, South Africa and U.K. have attempted to exp loit these reactions to remove nitrate from treated eff luents . The research has made rapid progress over the past five years, though the purposeful encouragement of denitrificat ion was reported as much as 20 years ago. 16

FP

-

Qui none -

Cy t ochrome

)~fom ete ~ /

A

.

N03

Ni t r a t e ( ~ re du ct'a s e--+ \ NO

I

I

2

Cytoch r ome c

/ Cytoch r ome a , a

/

Oxygen

3 ANAEROBI C

AE ROBI C I

Figure 2. The pathway for the passage of electrons from an oxldlzable substrate [AH2J to oxygen or altematlvely, to nitrate when conditions are anaerobic. NAO = nlcotlnamlde adenlnedlnucleotlde FP = flavoproteln

G- y

TABLE 1 COMPARISON OF THE DIFFERENT NITRATEREDUCTASES Property

NAD -

b

Figure 3. Flow diagram for denltrlflcatlon by a proceaa designed by Wuhrmann [1964). Settled sewage enters the activated sludge [AS] unit and Is then held In an anaerobic unit for denltrlflcatlon [ON]; sludge from the final settling tank Is returned to the sewage Input. DENITRIFICATION IN TREATMENT PLANTS There are two approaches to encouraging denitrification: (i) to separate the oxidative , nitrific cation stage from the denitrlfication (ON) stage , usuall y with the addition of an electron donor to the ON reactor , (ii) nitrification and ON are carried out in the existing reactors using sludge or settled sewage to accom plish nitrate reduction . Separated Stages The early processes such as that of Wurhmann (1968) simp ly added an anaerobic holding tank after an activated sludge unit and returned the

sludge that settled after den itrification to the activated sludge unit (Figure 3) . This system had the disadvantage that the returned sludge was often inactive after the anaerobic holding period . Several groups tested systems where organic carbon (electron donor) was added to the ON reactor. The ideal carbon source is one wh ich is cheap , contains no nitrogen, is readily metabo lized, is co lourless, odourless, harm less, taste less and does no,t stimulate the production of much biomass . Sugar , molasses, methane, organic acids, acetone and alcohols have been tried . Perhaps the best studied electron donor is methanol. ~cCarty, Beck and Am ant (1971) carried out the pioneering work with methanol added to a separate

,.,T~-YrC:J~y

'"ra~ v ~ ~ r 8 -> y~ Me thano l

t

(c)

rB-Yr~--YT 8 ~y ~

Figure 4. Flow diagrams of processes to achieve denltrlflcatlon during waste-water treatment . AS = Activated sludge DN = Denltrlflcatlon reactor [a] Johnson & Schroepfer [bl Balakrlshnan & Eckenfelder [c) Barth, Brenner & Lewis


DN reactor. From their work, the two rule-of-thumb equations shown below were deve lo ped which predict the amount of methanol needed and the amount of biomass that develops during the oxidat ion of methanol. The equations take into account the methanol that will be oxidized by both nitrate and nitrite as well as that oxidized by any res idual dissolved oxygen . Methanol needed = 2.47 Nitrate + 1.53 Nitrite + 0.87 Dissolved Oxygen Biomass formed = 0.53 Nitrate + 0.32 Nitrite + 0.19 Dissolved Oxygen This approach incurs the extra cost of the methanol and the construction of the holding and sedimentation tanks. Fu ll scale plants using methanol have been operated in a number of countries, though the increased price of petrochemicals must make methanol less attractive now than when the original work was carried out. Raw, settled sewage and I or return sludge have been considered as reductants for a separate denitrlfying unit . Some examples of such systems wi ll now be out li ned . Johnson and Schroepfer (1964) tested a two-stage system; the first stage was an activated sludge (AS) system with Its own sludge return . The second stage was an anaerobic DN unit which received 1 / 5 of the flow of the original sett led sewage and the sludge from the settling tank which followed denitrification (Figure 4a). Balakrishnan and Eckenfelder (1970) used a three-stage system, with the first stage for the removal of organic carbon in a contact reactor, the second for nitrification and the third for denltriftcatton . Sludge from the final sedimentation tank was returned to the first contact reactor; the so lids from this reactor were used to provide the reducing power for the DN reactor (Figure 4b) . Both of these systems suffer from the disadvantage that either raw sewage, or sludge from a non-aerated contact reactor are added to the DN reactor and so the final effluent Is likely to have an undesirably high content of ammonium . Such a situation would add great ly to the cost of chlorinating reclaimed water. Other three-stage systems were investigated by Barth, Brenner and Lewis (1968) and by Dart and Spurr (1 968). Barth et al used separate units, each with their own sludge return . .Carbon was removed in the first, nitrificiation occurred In the second and methanol was added to the third (FigurEI 4c). Dart and Spurr used a similar system but replaced the DN reactor and clarifier with a submerged filter column into wh ich methanol was injected. This approach gave very high rates of nitrificat ion in the second reactor, but involved the addit ional costs of buildin g and operating the third stage. Barnard (1 973) also tested a threestage system with methanol added for

TABLE2 RESULTS FROM A DENTRIFYING SYSTEM USING A CONTACT¡ STABILIZATION UNIT FOLLOWED BY NITRIFICATION AND DENITRIFICATION WITH ADDED METHANOLt STEPS Sludge cone. g/1

Unit Feed Contact tank Clarifier Stablization tank Nitrification tank Denltrlflcation tower

Temp . ("C)

COD (mg/1)

COD removal (per cent)

TKN" (mg/1)

Nitrate N (mg /1)

70

1.0 0.5

565 8.62

19.0 20.0

18.82

22.0

1.12

22.0

117

79.0

44

61

89 .2

3

54

90.5

1

SVI' (mg/1)

56

tFlow rate = 1 .5 I/ h with a sludge return rate of 0.6I/h Slud ge co ncentration in the stabl l lzatlon tank was 10.4g/ l

~

50.5 4.5

"TK N = Total Kjeldahl nitrogen SV I = Sludge volume Index

..__ _ _ Sta bil ize r Figure 5. Three-stage system of Barnard for denltrlflcatlon. Stage 1 removes carbon with a sludge stablllzer and contact reactor. Oenltrlflcatlon [ON] takes place In a tower to which methanol Is added.

-1 1 Return slud e

C.O.D.

340

46

40

Kje l dahl -N

81

13

0

0. 8

N0 -N

3

35

35

1. 6

3. 4

1. 6

15

0.8

3. 4

I

Figure 6. Four-stage system of Barnard for denltrlflcatlon. The residence time In each stage Is Indicated above the respective units. The MLSS from the AS unit was mixed 4/1 with settled sewage. The return sludge waa mixed 1/1 with the settled sewage plus M LSS. The date beside the broken fines Indicate the concentrations of COD, Kjeldahl-nltrogen and nitrate-nitrogen In mg/1 at thoae points In the system.

17


1/5 set tl e d sewag e

.>-

)

1/ 1 Return s ludge Figure 7. Flow diagram of the Rye Meads activated sludge plant operated to achieve a high rate of denltrlflcatlon, using sewage as the reductant. The shaded areas Indicate anoxlc zones, while the unshaded areas receive normal aeration. The 1/5 of the raw sewage Is fed to the third pass and 4/5 enters the first pass.

denitrification in a fixed medium tower. Figure 5 shows the system and Table 2 the results of laboratory studies run at 19° to 22°C with a sludge volume index of 56 in the stabilization tank . Although the system gave good performance , the cost of the methanol was a disadvantage; Barnard then tried using sludge itself as the reductant in a four-stage system. This process is outlined in Figure 6, which includes information on the performance of the . unit. The first anaerobic stage was fed with a mixture of sett led sewage, M.L.S.S. and returned sludge from the final clarifier . In the first stage, the nitrate formed in the second stage Is reduced-about 70% of the total nitrate removed is lost in the first stage . In addition , COD is reduced by 86% . Nitrification is virtually complete in the second stage , as shown by the low Kjeldahl-nitrogen in the effluent from the second stage . The third anaerobic stage also reduces nitrate but this accounts for only 30% of the total nitrate removed. A final short aeration is necessary to achieve good settling and final clarification . At the Water Research Centre in Britain, Bailey and Thomas (1975) were also studying denitrification using both methanol and sewage itself as reductants. They were first interested in the removal of nitrate from natural water to be used for drinking. They tested the efficiency of methanol added to towers of sand , gravel or plastic saddles (25 mm) which could be operated with either upward or downward flow . They found up to 90% removal of nitrate with very short retention times (1 hr to 5 min, depending on the size of the void space). Towers with 1 mm particles gave short retention times but needed backwashing twice daily . The media in the towers developed a microbial flora dominated by a stalked bacterium Hyphomlcroblum. This organism has a holdfast and forms long fine branching filaments which end in an oval cell; sand grains 1 mm in diameter grew a film of these organisms about 3 mm 18

thick . Denitrification was found to be sensitive to temperature ; at 8°, 12°, 17 • and 22 • , the reduct ion of the nitrate was 77, 81, 89 and 96%, respectively . Low temperatures in winter cou ld present difficulties in operating this process . Integrated Unit At Rye Meads sewage treatment works , Bailey and Thomas tested a method of denitrification which is accomplished within the existing activated sludge unit, with sett led sewage as the reductant. Th is process developed from the observation that as activated sludge plants become overloaded, they tend to become anaerobic in the first pass which rece ives the returned sludge containing nitrate; then a negative nitrogen balance is often found . They first carried out laboratory tests with 4 x 12 1 aerated and stirred reactors with an overall retention time of 11 .4 h, and in which the flows of raw sewage and sludge could be manipulated . From these experiments, regimes were proposed and tested at Rye Meads . This plant handles 9,100 m3 (2 million gl) per day in an act ivated sludge unit with plug-flow in four passes, each fitted with aerators. The nominal retention time in the unit is 1O h. To provide an anoxic zone in the first pass , the aerators were turned off and stirrers installed (operated at 88 rev/min) . The first pass was fed with 1 /1 mixture of settled sewage and return sludge, aeration was normal after the first pass. This gave a final effluent having half the nitrate of a comparable effluent from a conventionally operated plant, that is , the first pass totally removed the nitrate returned with the sludge . The efficiency of BOD removal and of nitrification was unimpaired . Significantly, equally effic ient removal of nitrate was achieved simply by turning off two out of every three aerators in the first pass, ttius saving on both the cost of the stirrers and of aeration, compared to a conventional activated sludge unit .

Another mode of operation was tested where only half of the first pass was anaerobic, fo llowed by a second anaerobic zone in the third pass (Figure 7) . The inflowing sett led sewage was sp li t so that 4/5 entered the first pass and 1 /5 the third pass . The returned sludge was mixed with settled sewage entering the first pass in the ratio of 1 /1 . This mode of operation allowed up to 80% removal of the nitrate which would have been formed in the conventional operation of the unit . The success of these experiments in a full sca le plant is encourag in g and suggests that at least one of the problems in the rec lamation of treated water and the contro l of eutrop hi cat ion may in future be so lved in a less expensive fashion than was previously the case. I

REFERENCES Bailey , D. A. and Thomas, E. V. (1975) . The removal of inorganic nitrogen from sewage effluents by biological denitrification . Water Pollut. Control , 74, 497 ..Barnard , J . L. (1973) . Biological dentrification. Water Pollut . Control , 72, 705. B.alakrishnan , S. and Eckenfelder, W. W. (1969). Nitrogen relationships in biological treatment processes . Ill. Dentriflcatlon in the modified activated-sludge process. Wat. Res. , 3, 177. Barth , E. F., Brenner, R. C. and Lewis, R. F. (1968). Chemical-biological control of nitrogen and phosphorus in wastewater eff lu ent. J . Wat. Pollut . Contro l Fed ., 4, 2040 . Comly , H. H. (1945). Cyanosis in infants caused by nitrates in well waters . J. Am . Med. Ass ., 129,112. Ewing , M. C. and White, A. M. M. (1951 ). Cyanosis in infancy from nitrates in drinking water. Lancet, 260, 931 . Dart , M. C. and Spurr, T. (1968) . Treatment of domestic sewage by the contact-stablizatlon process . Wat . Waste Treat ., 12, 12. Johnson , W. K. and Schroepfer, G. J. (1964) . Nitrogen removal by nitrification and denitriflcation. J. Wat. Pollut. Control Fed ., 36, 1015. McCarty, P. L., Beck, L. and Amant , P. St. (1969) . Biological dentrification of waste waters by add it ion of organ ic materials. Proc. 24th Ind . Wastes Cont. Perdue Uni v., p. 1271. Payne, W. J. (1973) . Reduction of nitrogenous oxides by micro-organisms . Bacterlol . Rev., 37, 410 . World Health Organisation (1970) . European standards for drinking water, 2nd ed., Geneva, p.

36. Wuhrmann , K. (1968) . Objectives , technology and results of nitrogen-phosphorus removal process . In Advances in water quality improvement , ed. Gloyna and Eckenfelder. Univ. of Texas Press, Austin and London, p. 21.


THE USE OF NATURAL TRITIUM FOR EVALUATING AQUIFER RECHARGE G. B. Allison*

Introduction Inhomogeneities in aqu ifer materials often make reg iona l estimates of aqu ifer parameters d ifficu lt or impossible to determine. For examp le estimates of hydraulic conductivity made from pump tests or of loca l recharge made us ing lysimeters are often of litt le value in describing the behaviour of an aqu ifer on a regiona l sca le. One of the motivations for study ing natural tritium in the hydro logic cycle is the possib il ity of obtaining regional aquifer parameters from a study of the variat ion of tritium concentration within an aquifer. Tech niques described in th is paper are concerned with ¡ making both point and regiona l estimates of aquifer parameters. A range of other techniques , inc luding water leve l and outflow mon itoring and the use of other natura l tracers (such as chloride, deuterium , oxygen-18 and carbon-14), are also availab le for studying aqu ifer behaviour on a regional scale . 0

Tritium is an ideal tracer for investigating water movement as it is incorporated in the water molecu le (as 1 Hi H 0) and apart from smal I effects due to the presence of the heavier isotope it moves as water does. It has the additional advantage since it is radioactive that it is possible to obtain information about the time scale of water movement in aqu ifers (the half life of tritium is 12.3 years). Recharge to groundwater usua lly takes place from rivers or rainfa ll . To use the tritium concentration of water in aquifers to obtain quant itative hydro logic information, an historica l record of the tritium concentration of water at input over the preceed ing years is requi red. Trit ium has always been present in rainfall but its concentration has changed marked ly over the past two decades du e to thermonuc lear testing. Mean annual concentrations in rainfall in southern Australia have varied from approximately 5 to 60 Tritium Units (TU) (1 TU represents a concentration of 1 tritium atom in 101s atoms of hydrogen) . Us ing vintage wines together with rainfa ll data since 1964 it has been possible to obtain a comp lete record of the tritium concentration of rainfall in southern Australia since the prethermonuc lear era (IAEA 1969; Al lison and Hughes 1976) . This record is essential for the interpretat ion of natura l tritium data. Natural tritium In aquifers Determ ination of the tritium concentration of water samp les taken from boreho les or springs can readily give qua li tat ive information about the aqu ifer . For examp le a non-zero tritium concentration infers that at least some of the groundwater reaching the samp li ng po int fel l as ra in less than 60 years ago . To obta in quantitative information from tritium concentrations , some hydrogeo logica l information is requ ired so that an approximate mathematical model descr ibing water movement can be developed .

*CS IRO , Divis ion of So il s, Adela ide

A paper de li vered to Sect ion 3, 47th A.NZAAS conference, Hobart, 1976.

Many of the mode ls described in the literature in the past decade have been developed to meet specific fie ld situations . However some genera l features of some of the mode ls which have been deve loped, together w ith the hydro logic parameters which may be est imated, are_ discussed below. Only an out li ne is given here; for further dttails the reader is referred to the orig ina l papers . [a] Confined Aquifers A simple conf i ned aquifer is usual ly env isaged as having d iscrete recharge and d ischarge areas. Samp ling may be from either bore- holes or springs . Two extreme models for describ ing water f low in such aquifers have been developed . The first of these assumes that water in the aquifer moves via piston f low i.e. recharge occurring in yearn lies immed iately upgrad ient of that occurring in year n-1 . In th is case the trit ium concent ration of water C at the samp ling point is g iven by C = Coexp(-â&#x20AC;˘t) (1) where Co (TU) is the initia l concentration, t (yr) the time s ince the water fe ll as rain and .{ (yr-1) the radioactive decay constant. The second model assumes that flow is ful ly mixed i.e. recharge water is quick ly mixed throughout the whole aquifer. In th is case the tritium concentration of water at the samp ling point (TU) is given by (Nir 1964) (2) C = Co/(1 + .{ t) Using either of these fairly crude models estimates of the t ime that water has taken to travel between the recharge area and the samp ling point can be made, provided the input tritium concentration is known . However, in fie ld s ituations, the flow mechanism fa ll s somewhere between these two extremes due to the processes of diffusion and dispersion . A detailed mathematical model which takes these processes into account has been deve loped by Nir (1964) . A more empirical approach adopted by Di~cer and Davis (1967) who used a binominal distribut ion to describe the contribution of each year's recharge to water collected at the sampling point , appears more promising for appl ication to field s ituations . The basis of their approach is that, due to diffusion and dispersion , the water taken at a sampl ing point is a mixture of waters having a range of ages. They used the distribution funct ion to predict the contribution of each year's recharge to the sample of water collected. Different degrees of dispersion can be stimulated by varying the standard . deviation (<JJ of the distribut ion. In practice, a range of these are tested in order to obtain the best fit between calculated tritium concentrations and field data collected over a range of t imes and location s. This procedure provides information about d ispers ive behaviour as well as trave l time in the aqu ifer . An example of the use of this mode l is shown in F ig. 1, wh ich shows the simu lation of dispersive behaviour for an Austra!ian aquifer. [b] Unconfined Aquifers Most of the model ling work on both confined and unconfined aquifers has assumed that the areal extent of the aqu ifer is large compared with its depth . This allov,;-s the simp l ifying assumption that flow is always parall el to the base of the aqu ifer. It has been shown for an isotropic unconfined aquifer of un iform thickness and having uniform recharge at the surface, that there is a constant relat ionsh ip between the time t (yr) that water has been beneath the earth's surface and 19

I ¡

1


1000 Q: UJ

PISTON FLOW

~

500

DISPERSIVE { MOOELS

~in _,J _,J

co

C7I

UJ ....

~o ....

- -------

cr2

= 0 YEARS 2 =0路5 YEARS 2 = 1路0 YEARS 2

cr2

= 2路0 YEARS 2

cr2 cr2

u.

0~

-u ::::, UJ !::: Cl z Q:

100

00

- u.

~ Q: . Cl

.... UJ

ZI-

UJ

u

,,I

u UJ z Q: 0 Q: uo ~ u ::::,

I

~

Q:

....

*

--

/.

50

/

'/ I,

';

I'

10

3

2

4

5

6

7

8

9

10

11

12

13

.

14

TIME OF SAMPLING ( yr l AFTER A DATUM DETERMINED BY THE RELATIVE LOCATIONS OF THE RECHARGE AND SAMPLING SITES

depth h (m) beneath the water table (Vogel 1967) viz, where a is the porosity of the aquifer matrix, q t

aH

=-

q

H

1n -

h

the recharge and sampling locations are some distance apart. (3)

(m yr路 1 ) the local recharge rate and H (m) the total thickness of the aquifer. Equation 3 enables tritium concentrations taken at different depths in an aquifer to be used to calculate local recharge to the aquifer. Ideally only one depth of sampling is necessary but, in practice, several aquifer samples should be used. A similar model to this was developed and used by Atakan et al. (1974) to estimate recharge to a shallow aquifer In Germany. Another type of model has been developed (Allison and Holmes 1973) which allows the mean local recharge over the surface of an unconfined aquifer to be obtained from the trit ium concentration at the outflow. This model predicts the tritium concentration of water as It moves along streamlines in the aquifer, and given the geometry of the aquifer, an est imate of hydraulic conductivity can be made. The values of the parameters so obtained are ''whole aquifer averages". In both of these models dispersion is assumed to be neg ligible. Digital models can be also used to simulate the way In which tritium and water move in both confined and

20

Fig. 1. Relatlonshlp between cal~lated tritium and concentration of well water and time of sampling (based on Davis et al 1967). *This data applies when recharge and sampling sites are adjacent. An earlier datum Is required If

unconfined aquifers. A simple approach is to divide the aqu ifer into a series of compartments or cells (Przewlockl and Yurtsever 1974; Allison and Hughes 1975). Conservation of mass equations for both water and tritium can then be set up and these allow recursive equations describing movement of water and tritium to be formulated. It Is assumed that mixing is instantaneous and complete within each cell. By varying the number of cells into which the aquifer is partitioned, a range of dispersive behaviour can be simulated. Th~s. If t~e aquifer is considered as a single cell comp lete m,x,ng 1s simulated. Piston flow is simulated by using an infinitely large number of cells. We have used this type of approach to estimate lateral flow into an unconfined aquifer, together with local recharge to two separate parts of the aquifer. Natural tritium In the unsaturated zone It has been found that beneath the surface rooting zone where cracking may occur, infiltrating rainfall usually perco lates through the soil by piston flow (Zimmerman et al., 1967). Provided that estimates of the tritium concentration of water moving through the bottom of the root zone each year


are obtainable, it is possible to estimate the amount of deep percolation (or local recharge) to an aquifer. All that Is required, in addition to the tritium concentration of Input water, is the way in which both tritium concentration and water content of the soil change with depth. This technique requires that there is a reasonable thickness (<5 m) of soil material overlying the aquifer. Estimates of local recharge may be obtained in either of two ways (Smith et al. 1970; Allison and Hughes 1974): (i) from the total quantity of tritium stored in the soil profile. The quantity of tritium T (TU.mm), which would be stored in the soil profile assuming unit recharge (in this case 1mm), can be calculated as 00

T=

(4)

LC• exp (-n• ) n = O

TRITIUM CONCENTRATION (TU) -+-

0 .-----4-r-_ _ _s___"'"',r-2_ _--'1;:..6~-,....::.20_ _--'2::;,4

I

I

\ \

\

\

' ::t I--

Cl.

~ /.

/ 3

/

/

I

I I I 4

--OBSERVED -

-

CALCULATED

I I

I I Fig. 2. Observed and calculated tritium concentration vs. depth profiles for a mean annual local recharge of 40mm (based on Allison and Hughes 1974).

where Ch is the tritium concentration (TU) of water moving into the soil profile in yearn, and n is the number of years before the present. Mean annual recharge can then be determined by dividing the t9tal tritium in the soil profile by T. Corrections , which are dependent on the time of the year at which sampling occurs, have to be made to account for the water lost from the root zone by evapotranspiration (Allison and Hughes 1974). (ii) from the shape of tritium profile. Based on the assumption of piston flow, tritium profiles can be calculated for different amounts of local recharge. After allowing for diffusional redistribution of tritium, calculated profiles can be compared with the observed profiles to determine local recharge. For example, Fig. 2 shows observed and calculated values of tritium concentration as a function of depth for a sampling station near Mt. Gambier, South Australia. The mean annual local recharge at. this station is estimated to be 40 mm. Deviations of calculated tritium concentrations from the observed values at depths greater than 3 m Indicate that the simple piston flow model does not fully describe water movement in the unsaturated zone at this site. In our experience the agreement between estimates of local recharge based on the two methods is good. Conclusions and summary Natural tritium is now an accepted tool in hydrologlc studies. As the models described here show, the main application is in the determination of recharge rate - a parameter which has been difficult to obtain In the past . Because much of the basic data needed to obtain maximum information from tritium concentrations is obtained from routine investigations, the method Is most useful In hydrogeological studies when used In conjunction with standard techniques . References Allison G.B . and Holmes J.W. (1973). J. Hydro!. 19, 131-43. Allison G.B. and Hughes M.W. (1974) . Proc. Symp. "Isotope Tech. In Groundwater Hydrology", IAEA, Vienna 57-72. Allison G.B . and Hughes M.W. (1975). J. Hydro!. 28, 245-54. Allison G.B. and Hughes M.W. (1976). History of tritium fallout in southern Australia as Inferred from wine samples in preparation . ' Atakan Y., Roether, W., Munnich, K.-O., Matthes, G. (1974). Proc. Symp. "Isotope Tech. In Groundwater Hydrol.", IAEA , Vienna 21-43 . Davis G.H. (1966) et al. Proc. Syl'llp . "Isotopes In Hydrol." IAEA, Vienna 451-73. Dincer T. and Davis G.H . (1967) . Int. A11oc. Hydrogeol. Memoirs. 8 276-86. IAEA Environmental Isotope Data No. 1. (1969) Tech Rep. Ser. No. 96, Vienna 421 pp . Nir A. (1964) . J. Geophy. Res. 89 2589-95. Przewlocki K. and Yurtsever Y. (1974). Proc . Symp. "Isotope Tech. In Groundwater Hydro!." IAEA, Vienna 425-50. Smith D.B., Wearn, P.L., Richards, H.J., Rowe, P.C. (1970) . • Proc. Symp. "Isotope Hydro!.", IAEA, Vienna, 73-87. Vogel J.C. (1966). Proc. Symp. "Isotopes In Hydro!." IAEA, Vienna, 355-69. Zimmerman U., Munich, K.-O., Roether, W. (1976). Geophys. Monograph No. 11 (ed . Stout G.E.) Amer. Geophys. Union 28.

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AUSTRALIAN WATER & WASTEWATER ASSOCIATION JOURNAL I enclose herewith the sum of $ ............ (Australian) as prepayment for supply of the following issues of 'WATER'. June D Sept. D Dec. D 197March D Note: All subscriptions conclude with the December issue, renewals are due by the end of February for a full year's subscription. Price, including surface mail to all countries, is $1.00 (Aust .) each issue, made payable to the A.W.W.A. 'WATER' . Name ..... ... .... ......................... ....................................... . Address ...... ... ...................................................... .......... . Mail this form to: Subscriptions Manager, F. R. Bishop, c/- Camp, Scott & Furphy

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Department of Construction Canberra, A.C.T.

LOWER MOLONGLO WATER QUALITY CONTROL CENTRE

Conference Calendar A.W. W.A. Seventh Biennlal Convention, Canberra, September 21-24, 1977

Expressions of interest are invited for the following positions.

Senior Technical Officer (Engineering) Grade 3 SALARY - within the range S14622-15004 DUTIES - No. 1270 - As Shift Superintendant, the occupant will be responsible for th e direct operation of the plant including organisation , control and discipline of all shift personnel. Under the most complex investigations and analysis of plant operations and performance . Prepare reports and within delegation formulate and implement alterations to operating procedures or alternatively make recommendations to management major variations to operational procedures . Train and test staff in the operation of equipment and issue Certificates to Operate. Liaise with the Maintenance Engineer to ensure co-ordination of the operational and maintenance functions . Act as relief Shift Supervisor and control relief shift crew . Note: This position may involve occasional shift work .

Senior Technical Officer (Engineering) Grade 2 SALARY - within the range $13516-14237 DUTIES - No. 1271 - Control and direct the work of a shift crew operating the Lower Molonglo Water Quality Control Centre. Undertake the more major pliant adjustments and instrument changes in plant mode of operation. Co-ordinate and control technical work associated with the setting up, calibration and operation of complex equipment. Oversee development work relating to equipment , systems and facilities to meet operational requirements . Perform more difficult tests , measurements, investigations and trials of equipment and facilities . Review and recommend amendments to the Operations and Maintenance Manual. Note: The occupant of this position will be a member of a shift crew .

Quallflcatlons (above two positions) - An approved certificate from a technical college or institute of technology (Science , Engineering or Marine Engineering) or its equivalent , or such other qualifications as the Public Service Board considers appropriate together with requisite experience. Applicat ions wi ll be considered from persons who do not possess the above qualifi cations, provided they have applicable experience over a minimum period of six years . Such an applicant , if selected , will be required to pass a test to establish eligibility for the position .

Conditions of Service - Four weeks recreation leave per year with additional recreation leave for shift workers up to a maximum of one week per year. Sick leave provisions of 2 weeks per year on fu ll pay plus 2 weeks on half pay . Payment of shift penalties for shift workers . Successfull applicants will be obliged to contribute to the Superannuation Scheme subject to a medical examination. Long Service leave of 3 months after 10 years service. Assistance with fares and transfer expenses may be borne by the Department.

REGISTRATION 'Public Aspirations and Realltles In Water Resources ManageQ1ent Venue: Noahs Lakeside International Hotel, Canberra Features of the 7th Biennial Convention Include parallel technical sessions and keynote addresses by an emminent list of lecturers, a social programme highlighted by the conference banquet and several technical inspections including the Lower Molonglo Water Quality Control Centre during commissioning trials. A Trade Display will also be held to operate continuously during the period of the Convention. Ladies are particularly welcome and are encouraged to participate in the non-technical sessions of the convention as well as the special attractions and tours arranged for them during presentation of technical papers. The conference fee Is all Inclusive with the exception of the banquet and accommodation. Conference Fees: Delegate $60 Ladles $20 Banquet $20/person Registration forms are available from Branch Secretaries or by returning the form below . Conference Convenor, AWWA Seventh Blennlal Convention, P.O . Box 359, CANBERRA CITY, ACT 2601. NAME . . .. . .. . . . . .. ..... . . . . . ..... . -,. . . .. . ... .. ....... . .. ... . . ADDRESS

The Water Research Foundation of Australia, New South Wales State Committee, is holding a workshop on "REUSE OF EFFLUENT" The one day workshop is to be held at University of N.S.W. on FRIDAY, 1st JULY, 1977 Further information is available from The Foundation, Cl- School of Civil Engineering, The University of N.S.W., P.O. Box 47, Kingsford, N.S.W. 2032. Telephone: Sydney 663.4257 23


RECENT DEVELOPMENTS IN HYDRAULICS-WITHIN THE HYDROELECTRIC COMMISSION OF TASMANIA PARTI P. T. A. Griffiths• INTRODUCTION The paper describes some novel developments in hydraulics which were adopted for economy and to overcome the associated civil, mechanical and electrical components of various problems. Few hydraulic problems are solved without the use of models and for a number of years the Hydrau lic Laboratory of the Hydro-E lectric Commiss ion (H .E.C. ) has been located within the Civil Eng ineering School of the University of Tasmania. The H .E.C. staff operates the laboratory but benefits have been derived from the presence of the University staff and their equ ipm ent. • Although each development is complex enough to require a more detailed treatment, the paper deals mainly with their general aspects.

THE ELIMINATION OF SURGE TANKS The design of the Poatina penstock started in 1958. It resulted in the elimin at ion of the surge tank from the Poatina penstock. When a surge tank is required it is located as near as possible to the turbine and it reduces the pressure changes within the conduit system when the discharge changes as the turbine load changes. That part of the conduit between surge tank and turbine is called the penstock . If there is no surge tank the entire pressure conduit becomes the penstock . Prior to specifying the design pressures for the Poatina penstock it had been assumed that a surge tank would be required as shown on Figure 1. However it is not practical to so lve this problem without considering the penstock as a component of a comp lex system. Pressures within th is penstock are governed by the rates at which the spear valves of the pelton wheel turbines open and close . These rates are normally controlled by the turbine governor but the maximum rates are control led by other devices. The maximum rates should be chosen • The late P. T. A. Griffith s was Group Engineer I in charge of the Hydraulics, Penstock and Valve des ign sections of the Civil Eng ineering Branch of the H.E.C. His untimely deat h occurred on 4th May 1974 , and Mrs Griffiths' perm iss ion to publish this paper is gratefu ll y acknowledged. This paper has been ed ited by H. H. McF ie from an address given by the author.

24

'

I POATINA P£NST00( FICI I

having regard for the ability of the turbine to control system frequency and to cope with emergency situations. This ab ili ty to contro l system frequency and emergency situations is influenced by the characteristics of the penstock and the electrical network. Thus to determine reasonable maximum rates of spear movement which govern penstock pressures, it was necessary to consider the operation of the system of which the penstock was only part . Factors are related as shown in Figure 2.

CHA.NOE IN PENSTOCK PRESSURE

PENSTOCK CHARACTERIST ICS

ANO ELECTR ICAL NE TWORK

1------

CHAR ACTE RtS T ICS

_

_____

A BI LITY OF STATION TO GOVERN SYSTEM FREQUEN CY AN O TO COPE WITH

EMERGEN CY CONDITIONS CHOSEN M,._ XIMUM

RATES OF MO\IEMEMENT 1 - - - - - ~ OF TURBINE SPEARS MAXIMUM RATE S - -- - - - - 1 OF CH ANGE OF PENSTOCK DISCHARG E

FIGURE 2

The problem was expressed in mathematical form and some aspects were so lved using graphical and other manual procedures. As an understanding of the problem grew, the difficulties increased because normally accepted procedures gave incorrect results in some cases, whilst, in others normally accepted approx im ations were

not adopted because there appeared to be no easy way of proving whether they would give acceptab le results for Poatlna with its extreme ly long pen stock. In the end some aspects became far too complex to solve by manual methods and the digital computer, Silliac, at Sydney Univers ity was used , This was an interesting operation at a time when digital computers were somewhat new to Australia. In the end it was demonstrated that, • opening and closing times t)t the turbine spears could be much longer than was normally accepted in such an installation ; ' • the presence of a surge tank had much less affect than expected on penstock pressures and on the abi lity of that station to govern system frequency; and • that any benefit due to the aurge tank was insufficient to Justify Its cost and, according ly, it was eliminated , The Poatlna design made it a relatively easy matter to indicate that surge tanks should not be installed at the Rowallan, Lemonthyme, Wilmot or Fisher power schemes and this was of major economic significance. It also indicated that some older schemes were not operating as safely as thO)' could and the turbine guide vane or spear operating times at a number of stations were altered as a result . One of these was the Lake Echo station . This was particularly Interesting because the maloperation of a device to indicate the temperature of the main turbine bearing had caused machine shut down . The gu id e vanes closed in a second or so but the turbine relief valve failed to open and the resu lting pressure burst the penstock , It was shown that the guide vane closing time could be so Increased that , if the relief valve failed to operate ,


the, genstock would not be overstressed and ·the surge tank would come near to, but would not overflow. Lake Echo was an Interesting situat ion. The turbine bearing was not hot but a protective device failed and initiated shut down. The turbine relief valve, a protective device, failed to operate and burst the penstock . The hi II top valve - also a protective device - then failed to operate but contrary to what one m ight have expected, the water from the burst pipeline did little damage being diverted by the topography away from the power station. SPRING LOADING RELIEF VALVES The eli mination of the Poatina surge tank lead to the introduction of spring loaded relief va lves on the present sca le within the H .E.C . although there was one spring loaded valve on the Derwent pumping scheme in recent times and much earlier spring loaded · relief valves had been used , but were abandoFted . The elimination of the surge tank made the Poatina penstock perhaps the longest penstock in the world without any measures for re li eving pressure within it along its length . It is nearly 27 000 feet long . Normal ly a pressure wave travels from turbine to surge tank , which is a point of relief, within ½ second ; however at Poatina a pressure wave takes 6 seconds to traverse the penstock . It was decided that there were four possible causes of very high pressure, the first three of which wou ld make the penstock water column resonate : (1) Mal-operation of turbine valve seals with the station closed down. (2) Cyclic opening and closing of the turbine spears in response to cyclic load changes . (3) Cycli c opening and closing of the turbine spears due to governor instabitily. , (4) Mal-operation of a main turbine valve causing it to close very quick ly when the only machine operating is the one it serves. The water in a penstock has a natural period of oscillation which is the time a pressure wave takes to traverse the length of the penstock four times. If a small discharge occurs repeatedly at penstock frequency, the pressure f luctuations rapidly approach plus and minus 100% . Two sets of spring loaded relief valves to li mit the pressure rise were used on the penstock as shown on Figure 1, one set as near the station as possible without placing it underground (where no one wanted valves for fear of the consequences of a broken spring and water discharging out of control under a head of nearly 3 000 feet) and the other set where pressure waves, which escaped the first set of valves, would be most likely to be caught by the second set.

The effect of these valves on penstock pressures can be great . In the absence of a relief valve, a cyclic variation of discharge of a few cusecs at penstock natural frequenc'y could cause pressure rises of almost 100%; however with a relief va lve , this resonance cou ld cause a pressure rise of about 10% since there have been several cases of resonance in H.E .C. conduits, present practice is to insta ll spring loaded valves upstream of most important penstock valves. Before deciding to use the spring loaded va lves a great deal of thought was given to checking whether they cou ld themse lves be a cause of trouble as, on occasions, other protective devices have been, particu larly since no penstocks protected by valves of the type proposed were known of . (Fig. 2and 3).

remain open until the penstock pressure fell very considerab_iy below the threshold pressure. When the valve did close it appeared that it would shut very quickly . Figure 4 shows the expected variation of spring and water forces with penstock pressure, when the valve opening is limited by stops well before adjacent coils of the spring come in contact. The valve opens when the water force just exceeds the spring force. As the penstock pressure increases, the spring force increases much less than the water force . The valve opening is limited by stops when the water force is near ly double the spring force. The 1 ~~~ti~ro~r~~:u:eattr10:~! ~af1~n~~~~: the spring when the valve closes quickly. lPA

ROOS TO HOL D SPRING AMO HOOD

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_W~E~~~

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FIG l

Figure 3 is a diagram of the valve. It involves an offtake from the penstock which receives an isolating valve and nozzle. Above the nozzle is a ground and lapped disc which is loaded by a spring . The spring is held by an assemb ly which also holds a deflecting hood. When the penstock pressure rises above the threshold pressure, the disc leaves the nozzle and the valve discharges. The discharge is supposed to be linear with respect to head until the valve is wide open when the discharge is proportional to the square root of the head . (Fig . 4, 5 and 6) . Figure 4 indicates why misgivings were felt about these valves.. When the valve is on the point of opening, the force on the valve disc exerted by the water is equal to the penstock pressure multip li ed by the nozzle area, (PxA) but when the disc has moved far enough from the nozzle so that the disc does not influence the discharge, momentum considerations show that the force exerted by the water on the disc is given by twice the pressure mult iplied by the area i.e. by 2 PxA if losses are ignored. Since the spring has a linear characteristic whi le the water force has not it was hard to see why there should be a linear relation between head and discharge . It appeared possible that, if a valve opened far enough, it would

Pl1£S5"'E

NOZZLE AREA

p

A

PENSTOCI<

RELl~F VALVE FORCES FIG 4

A model was made which indicated that all was well while th e valve opening did not exceed 1/eth the nozzle diameter. If the opening were greater, the valve appeared to open in the non-linear way expected. As a result of thi s stops were installed on all valves to prevent their opening beyond 1/eth of the · nozz le diameter. During the commissioning of the Wi lmot power scheme a series of tests were conducted to obtain the basic data necessary to explain the behaviour of the valves and a rig was built to enable the steady state discharge to be obtained for various valve openings ~and constant head. Strain gauge equipment was used to measure the force exerted by the water on the disc for constant head in the penstock and chosen valve openings and dynamic recording equipment was used when the valves were made to open by closing the turbine quickly . Figure 5 shows the forces exerted by water and spring on the valve disc for constant penstock pressure . When

25


the valve is about to open , water force and spring force are equal. When the valve first discharges the water force exceeds the spring force and the valve opens to point B and vibrates gently at 80 hertz. If the valve opens for some reason to point C, the water force again exceeds the spring force and the valve will open to point D where its operation is much more violent . If the valve opens beyond point E, the disc wi ll open wide and rapid ly .

~

A o

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LfilAfl.E

!uNSTAEl,E VALVE OPENS TO LIMIT OF

VALVE OPENS TO POINT 'O'

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lfilfil ~ VAlVE OPENS TO POINT 'B'

VALVE OPEN ING

RELIEF VALVE CHARACTERISTICS FOR CONSTAN T HEAD f' 1G S

The precise details of this characteristic have not been obtained with sufficient accuracy for small openings but this is the shape requ ired to explain our experiences. There are two modes of operation for a given head. When the · valve is closing, it adopts mode D . The expected cure for this undesirable situation involves increasing the spring rate as shown . Figure 6 is indicative of graphs obtained from experimental data. The top figure shows the water force, for various penstock pressures , plotted against valve opening. Shown also is spring force plotted against valve opening . The intersections of spring force and water force lines define operating conditions and these are numbered . ,1

FORCE ON DISC

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26

Provided the valve does not open beyond the point A , the operating points for the opening and closing cycles are much the same and are numbered 1, 2 and 3. The corresponding graph of penstock pressure against valve discharge is shown by the solid line of the lower figure where the numbers 1, 2 and 3 also appear . The discharge is proportional to the square root of the pressure when the pressure exceeds that pressure requ ired to open the valve to point A. The operating points of the upper figure are not the same for opening and closing cycles , when opening is permitted to point B. When the valve opens beyond point A , the water force exceeds the spring force and the valve opens to B even if there is no further increase in penstock pressure . This operating point is numbered 4. The penstock pressure must fall to Just below the pressure indicated by point 5, before the water force becomes less than the sprin g force when the valve will begin to close. The further it closes, the more the spring force will exceed the water force and the valve will close very quickly to the operating point 6. The graph of pressure against discharge is shown by the line defined by points 1 to 6 on the lower figure . The closing pressure is below the opening pressure. The discharge is proportional to the square root of the pressure , when the pressure exceeds that to open the valve to po int B. It is to be noted that the relation between penstock pressure and valve discharge depends on the spring stiffness and the permitted opening as well as the shape of the water force curve. What is desirable will depend on the particular installation . At present it is considered undesirable to permit openings beyond point A on H .E .C. penstocks. The pressure versus discharge characteristic at Wilmot is not linear when valve opening is restricted to Veth of the nozzle diameter and the valve sea ls 8% below the opening pressure; however the characteristic could be made more nearly linear if the spring stiffness were increased . In summary , from these tests it was concluded that for these valves: (1) the head -discharge characteristic is not linear; (2) for penstocks it is necessary to limit the valve opening to Veth the nozzle diameter, where the steady discharge is given by:Q = 0.3 A(2gH)½ where A = nozzle area H = penstock pressure (3) the penstock pressure at which the valves shut is 8% below the pressure at which they open; (4) there are two modes of operation of the valve at constant penstock pressure; (5) the valves vibrate at about 80 hertz but their natural frequency

is only 3 or 4 hertz and the character of the offtake from the penstock determines largely now the valves vibrate; (6) the penstock pressure near the valve does not fluctuate at high frequency ; (7) the spring rate should preferably be increased to eliminate the second mode of operation ; (8) the losses in the offtake influences the operation of the valve and future offtakes will be designed for lower losses; (9) the valves in a group of valves should not have the same seating pressure but should differ by about 1 % from each other; (10) prov ided the valves · are well set , prolonged vibration at small openings does not damage the valve seat , presumably because a cushion of water remains between the metal components; (11) during penstock resonance, the valves are expected to perform as assumed when generally choosing the valves and the fact that the discharge characteristic is non linear does not appear to be important; (12) when choosing valve capacity, allowance should be made for the fact that the valves may vibrate; (13) it is desirable to find a way of damping the valves in some situations . In some ways the Wilmot relief valves have not behaved as expected, but it is Important to know that the performance defects are not dangerous things are ones, however two important . The valves must not be allowed to open more than Ve th the nozzle diameter and the threshold pressure should be raised a few % above the recomqiended pressure to ensure that the valves will close quickly when the pressure falls to normal pressure . The H.E.C. is confident that these valves should be used to protect the conduits from severe pressure rises small discharges associated with because no other devices of comparable simplicity and economy are known.

A second part of this paper has been held over to our next Issue. -[Editor)

ACKNOWLEDGEMENTS: Appreciation is expressed to the Knight, Commissioner , Sir Allan C.M .G., M .E., B .Sc ., B.Com. , F .I.E . Aust ., for permission to pub li sh this paper and to thank those who have ass isted with Its preparation particularly, Mr R. F. Edmondson Section Engineer , Gates and Valves , and his staff together with the many people throughout the Commission who have worked on these projects and whose combined efforts have resulted in some interesting developments in the general field of hydraulics .


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MAX . LOAD ING IN Kg. B.O.D./24 HOURS 14 19 26

~

38 The unit is ideally suited for installation in industrial plants, hospita ls, construction and mining camps, country hote ls, mote ls and caravan parks and in residential communities from 25 to 650 persons . Simply installed, it is highly eff icient and may be moved from one site to another. A descript ive leaf let is available .

PAR BURY HENTV &CO. PTY. LTD. MINING DIVISION 1 Lincoln Street, Lane Cove, N.S. W. 2066 Telephone428 3533

28


The U~)]l[{g Aquasieve

• • • • • • •

Reduces sewered waste and water pollution Recovers reusable solids to increase total product utilisation Requires minimal ma intenance Rapidly pays for itself Installs easily in confined spaces Reduces capital outlay and operating costs

We are more than willing to demonstrate this unit to you. Ring, write or call personally - let's talk.

ANZIEL PTY. LTD. 6 Bowen Crescent MELBOURNE. 3004. Australia. Telephone 267-1333 Telex 31-308

32 Hastie Avenue MANGERE, AUCKLAND, NEW ZEALAND. Telephone 633-969 Telex NZ-2473


. fRIFUGES

Sharples centrifuges for wastewater treatment

Sharples Super-0 -Canter ® solid-bowl. continuousdischarge cent rifuge .

Sharples SludgePak® solid-bowl centrifuge with skimmer and knife . Sharples Nozljector ® disc-type. continuous centrifuge with i nterna I recycle concentrator.

No single type of wastewater centrifuge can handle all sludges - that's why Sharples makes all types.

SHARPLES-STOKES PTY. LTD. MAIL: BOX 367, ARTARMON. N.S. W. 2064 PHONE: SYDNEY 439-3378/4458 CABLES: PENNWALT SYDNEY

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Water Journal March 1977  

Water Journal March 1977