JUNE 1986
JOURNAL OF THE AUSTRALIAN WATER AND WASTEWATER ASSOCIATION
SCIENCE & TECHNOLOGY IN THE INDUSTRY OXIDATION OF SULPHIDES IN WASTEWATER HYDRAULIC INFRASTRUCTURE - RENEWAL WATER FOR OLYMPIC DAM PROJECT
Registered by Australia Post-publication no. VBP 1394
water
ISSN 0310-0367
Official Journal AUSTRALIAN WATER AND WASTEWATER ASSOCIATION
Vol. 13, No. 2, June 1986 FEDERAL PRESIDENT R. Lloyd , G. H. & D., GPO Box 668, Brisbane 4001.
FEDERAL SECRETARY F. J . Carte r, Box A232 P.O. Sydney Sth ., 2001.
FEDERAL TREASURER J . D. Molloy , Cl- M.M.B.W.
625 Lt . Colli ns St. , Melbourne , 3000.
BRANCH SECRETARIES Canberra, A.C.T. Dr. L. A. Nagy, 8 Belconn en Way, Page, A.C.T. 2614. (062 54 1222)
CONTENTS Viewpoint-D. J. Dole Aust. Water Resources Council
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Association News, Views and Comments . ... . .. . ............. ... .
6
IA WPRC News ...... .. .... .... .... .. ................ . ....... .
7
People ...... . ...... ... .... .. ..... .. .. .. . ................ .. . .
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Science and Technology in the Victorian Water Industry -W. M. Drew ..................................... . .... . .
12
The Olympic Dam Mining Project-Water Management -P. Nadebaum and T. Amiconi . ....... .. ......... . ........ .
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Australia's Hydraulic Infrastructure1 Planning for Renewal -A. G. Longstaff and F. B. Barnes .............. ... .. ... .... .
20
Book Reviews ............... ... ... .. ... .. ........ . .......... .
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Conferences-Courses- Technical Interests
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Staged Oxidation of Sulphides in Wastewater using Mechanical Aerators -G. Williams and R. G. Shaw .. .. .. ........ ........... ..... .
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Calendar
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New South Wales C. Davis , G. H. & D. P/L, P.O. Box 39, Railway Square 2000 (02 690 7070)
Victoria J . Park , Water Training Cent re, P.O. Box 409, Werri bee, 3030. (74 1 5844)
Qu ee nsland D. Mackay, P.O. Bo x 412, West End 4101. (07 44 3766)
South Australia A. Glatz, State Wa ter Laborato ri es , E. & W.S. Pri vate Mai l Bag , Sa lisbury, 5108. (259 03 19)
Wes tern Au stra li a Dr B. Kavanagh , Water Auth. of W.A. , PO Bo x 100, Leedervill e 6007 (09) 420 2452
Tas mani a G. No lan, G. P.O. Box 78A Hobart , 700 1. (002 28 0234)
Northern Territ ory M . Lukin , P.O. Box 37283 Wi nn ellie, N.T. 5789.
EDITORIAL & SUBSCRIPTION CORRESPONDENCE G. R. Goff in , 7 Mossman Dr., Eaglemont 3084 03 459 4346
COVER PICTURE The equipment shown is typical of the many segmented flow automatic analysers employed for nutrient analyses by the State Water Laboratory, Victoria. It is by the extensive use of sophisticated instrumentation such as this, coupled with extensive quality control procedures, that modern Water Laboratories are able to achieve a sustained high volume throughput. Automated instrumentation also lends itself to computer based data acquisition and result calculation, to both reduce manpower needs and further improve the quality of the end result. Cover photo donated by the Rural Water -Supply Commis s ion , Victoria ..
The statements made or opinions expressed in ' Water ' do no t necessarily reflec t the views of the Australian Water and Wastewater Association , its Council or committees.
WATER Jun e, 1986
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SCIENCE AND TECHNOLOGY IN THE VICTORIAN WATER INDUSTRY W. M. Drew INTRODUCTION Paterson in a recent paper pointed out that over the last 15 or so years, throughout Australia, the water industry has been undergoing, in some form or another, restructuring. In South Australia the industry was consolidated into one department in the mid-1970s . The Western Australian Government has followed with the· Western Australian Water Authority coming into full operation in July this year. The A.C.T . and N.T. have similar arrangements for the management of all aspects of water resources. In N .S. W. fragmented management has prevailed although this arrangeme nt is currently the subject of a review. In Victoria, the management of water resources issues traditionally rested with two major authorities, the Melbourne and Metropolitan Board of Works and the State Rivers and Water Supply Commission, a Ministry and a plethora of smaller agencies. This situation was seen as unsatisfactory and in 1980 the task of reducing the size of the problem became the first matter to be referred to the newly established public bodies review committee. By the time this committee had published its eighth report it had essentially decided upon a central model with the S.R. & W.S.C. becoming the central management agency for water resources in Victoria. As it is now well known, the Government chose not to proceed with this recommendation, instead the water (Central Management Restructuring) Act of 1984 reduced the role of the S. R. & W .S.C., creating a new body titled the Rural Water Commission (R.W .C.) and established out of the Ministry for Water Resources a Department of Water Resources with significantly greater powers and responsibilities than its predecessor in relation to statewide planning. The Department sees itself in the position of dealing with matters of information, policy, advice and the allocation of resources to the operating agencies (i.e. M.M.B.W ., R.W .C. etc). The Department is therefore currently concentrating on establishing a multi-disciplinary team composed principally of people skilled in planning, policy development, financial, physical and manpower resource allocation and in education and training. Because of the size of the operating agencies they also have personnel with similar skills but their focus is necessarily narrower than those to be engaged by the Department. The agencies, because of their operating role, have the majority of the technical skills and resources, and it is in this area particularly that their assistance will be required in the development by the Department of new policies and strategies. It is suggested that we are now entering the early adult phase of the new era of water resources management in Victoria with the institutional frameworks in place and their organisational structures shaped, although not fully settled in terms of senior appointments . A new level of co-operation and understanding must be reached between agencies whereupon the resolution of water resources management issues can be achieved from inputs involving financial, technical , legal , educational and environmental factors. It is the area of technical inputs that will be addressed in the remainder of this paper. 1
THE NEED FOR TECHNICAL EXPERTISE IN THE WATER INDUSTRY Lewis 2 in his introductory panel discussion remarks at the National Water Management Seminar in Adelaide in November 1984 expressed a concern which I am sure has bothered many technical people in the water industry for some time. Lewis stated ... 'The greater pressure for better management skills and accountability has absorbed a great deal of managers' efforts at a// levels of the Department. There is now some evidence emerging to suggest that This paper is a precis of an address by Dr Drew to the Victorian Branch upon his retirement as President of the Branch in August 1985. 12
WATER June, 1986
Dr. Wayne M. Drew, Ph.D.(Mon.), M.En g .Sci .(Melb.), F.R.M.I. T ., F.l.E.Aust., A.R.A.C.l. , is the Manager of the Water, Materials and E n vironmental Science Branch (including the State Water Laboratory) of th e Rural Water Commission of Victoria. He has been in volved in research and laborat ory management for over 25 years. He commenced his career with th e State Electricity Commission of Victoria where Wayne M. Drew he spent six years in the Central Research Laboratories. In 1969 he moved to th e Rural Water Commission (th en the State Rivers and Water Supply Commission) and he has been responsible for the management of Scientific Services in the Commission since 1971. His Branch is currently undertaking a number of research projects and con tributions to many State and Federal comm ittees on water related policy and standards. this has been at the expense of technical, scientific and operational expertise. The position has, of course, been exacerbated by mandatory staffing reductions. 'It is quite possible that the pendulum has swung too far and that one of our many other management needs is to redress the balance.' This concern, of course, is not unique to the water industry and there are now many people, organisations and to some extent Governments , expressing concern over the imbalance and the 'devaluation' of technology . ' Over the last few month s a few articles from journa ls, seminar proceedings and the press have been collected, and the headings, the authors' names and key comments are of interest. • 'Anti-Science' - Editorial comment by A. J . Birch, President of the Australian Academy of Science, Chemistry in Australia, April 1985 3 ). 'Australian Governments, whatever th e political complexion, are almost anti-science. 'Scientists should strive to press valid viewpoints so that Governments might become convinced that there are votes in Science.' • 'Engineers downgraded as Managers' - Report on retiring President' s address, Engineers Australia, April 1985 4 • In th is article the retiring president, Mr. Tognolini, was quoted as saying that: 'New position titles in organisations such as Director, Manager, Superintenden t have the effect of creating the impression that lack of a professional qualification is no impediment to discharging the duties and responsibilities of a position even though it may have a strong technical content. ' • 'Criticism of C.S.I.R.O. simplistic and naive says chairman' reported comments by Dr . Paul Wild, Chairman, C.S.l.R.O., Laboratory News, April I 985 5 • 'If the Boards of companies want their company to be innovative, the first thing to do is to appoint an engineer rather than an accountant or lawyer to the top position. 'Accountants and lawyers have an important place in senior management, but at the very top they are often so preoccupied with next year's bottom line and takeover manoeuvers that they forget that future success ... depends on inno vation capacity.' • ' Australia should train more engineers' - Reported comment by Dr. Ian Mair, Vice President, Institution of Engineers Australia, Engineers Australia, May 1985°. 'Australia should follow the lead of Britain which is allocating about $83 million during the next three years to train more students in engineering and technology ... 'Britain is striving to increase its number of engineering graduates from 250 per million population to more than 310. By comparison, the Japanese figu re is about 630, while Australia is a low 150. 'To be competitive we need to develop our skills lo use new technology. 'We are devoting roo high a proportion of our limited tertiary education funding to the "Arts".'
• 'Preparing for the advanced society ' - perspective comment by Professor John Ward, Vice-Chancellor and Principal of Sydney University'. '.. . Australians are likely to look to impro ved technology to produce more leisure rather than more wealth ... 'Unless persuaded to think otherwise, their response ro changes of technology may be to a/tempi to select for use those advances thar produce an easier life than than those that strengthen production ... 'This year, rhroughout Australia, most universities have reported some decline of interest in computer science, electrical engineering, elec1ronics, science generally, medicine and veterinary science.'
Ward also says that students have guessed wrongly that we have enough technical graduates. They are however, expressing the view of the society that produced them which is resisting technological change. 'OECD examiner's report on Australia's Science and Technology 2nd April 1985 8 • 'Modern technology, such as computerized process and produc1ion control or computer aided engineering will reduce costs, improve products and quality, and give greater flexibility. The installation and operation of such technology will require highly skilled and welleducated personnel. More university graduates will be needed - and Government will have to see to it that enough of them become available. '
The examiners also remarked that between economists and technologists: ', . . profound differences of attitude make ii a major challenge io bring grearer mutual understanding of rhe two groups. 'Both sides need the other, and each manageable programmes of cooperation . 'One possibility would be ro involve technical experls more closely in rhe work of the economic ministries' long term analysis.' It should be evident from the above samples that a number of
'Technologists' at the highest levels of their professions, particularly those in a position to evaluate Australia's performance, are expressing a common concern regarding the need for a National perspective on technology. Government are said to have a bewildering array of policies on science and technology and also for the education and training of such. However , with a 'U niversal' community desire to increase productivity (wealth) and not leisure time , the chances of successfully introducing these policies to the advantage of the community appears to be remote . It is impossible to live in today's world as a technologist without feeling some form of concern for where the world is heading and in the particular case of the water industry without trying to provide a technical perspective to balance the overwhelming concern for financial, administrative and legal matters. Under these circumstances I believe, that as never before, there is a need for the strongest , most professional , technical advice to be delivered to decision and policy makers. The advice must not only be so und , but the way in which it is delivered must match the style of those providing what can be said to be 'softer' information. Technologists must, in my opinion, seek out those in their professions who can communicate effectively and present strong arguments to politicians and chief executives on the technical iss ues confronting th eir industries, including of course the water industry , before those very industries start to fail. In so me quarters the word 'fail' may be considered to be too emotive, even provocative, however I would suggest that now is the time to be concerned, not in a few years when the infrastructure on which industry is based starts to break down because of lack of und erstanding by those responsible for its management. Many technical graduates from Australian universities and institutions are perfectly well equipped in terms of economic and manage rial training to participate in all facets of top management and should be so ught out to take part. However , if we are only going to produce 150 per million engineering graduates each year our choice will be limited. Almost invariable man y of the top graduates are eagerly so ught by multi-national companies and many end up overseas. Others und ertake post-graduate courses overseas and land jobs in co untries which export technology in the form of finished products to A ustralia. If we continue in this fashion, we will not only lack technologists in top manage ment, we will no t have enough engineers and scientists in our indust ries to properly introduce , operate and maintain the available new technology. I cannot imag ine how our non-technical colleagues propose to overcome this situation other than by buying in from overseas the necessary technical expertise. Ho weve r , the OECD examiners report 8 sees
the result as a polarisation of the labour market, with shortages of certain technically skilled workers and high unemployment among the unskilled. They see technical training within enterprises as providing one way of avoiding such divisions and recommended its encouragement with financial incentives if necessary. They also see: 'Australia's "technical people" are its greatest technological resource, for industry and for the economy as a whole. A system of training programmes which stimula1e rechnical training and retraining within industrial enterprises would be among the mos! important contributions of !he education and training sysiem to narional economic recovery.'
The means of ensuring that the water industry is properly equipped for the future in terms of human and technical resources is in the hands of the industry itself. How is the industry respon.. din g to the challenge? There is some good news regarding current initiatives at the state and national levels. These initiatives are in the form of committees and working groups established to prepare recommendations on future action regarding: • Education and training • Research and development • Water qualit y improvement The following discussion examines each of the initiatives and indicates their current status.
EDUCATION AND TRAINING Standing Committee of the Australian Water Resources Council established an Education and Training Working Group in April 1981 with the objective: 'Review the adequacy of currenl education and training and make recommendations for any action considered necessary lo meet the changing needs of !he waler indusrry.'
In order to collect data from the water industry nationally, the working group distributed a questionnaire to a large range of authorities in November 1982. However, whilst the level of response was good, the data proved difficult to analyse, mainly due to the imperfect nature of the questionnaire structure. As a result it was decided that it was still very important to gain information for the industry to determine future action. Consequently Standing Committee approved the letting of consultancy contract with the following object-ives: (a) Identify current tasks of water industry management and operational/service organisations . (b) To identify manpower levels and skills needed to carry out current tasks. (c) To identify gaps in supply of skilled manpower. (d) In the context of 'Water 2000' to identify new and emerging tasks. (e) Identify changes in manpower skills necessary to copy with these new talks/issues. (f) Recommend action to better match future supply and demand for appropriate skilled manpower. The consultant chosen to undertake this task was P.A. Australia in conjunction with British Water International as a sub-consultant and it is expected that their report will be available early in 1986.
RESEARCH AND DEVELOPMENT In January 1984, following a statement in Parliament by the Victorian Minister of Water Supply in December 1983 , a Central Management Restructuring Project commenced with the objective of examining the management requirements of the entire water portfolio in Victoria. In particular th e project had the primary aim of developing objectives, structures, roles and functions for the Department of Water Reso urces and the Rural Water Commission. During the course of th e project, a need was identified by the project team, to be advised more fully on coordination and fundin g of research and development , new technology and technology transfer. A working party was therefore established in June 1984 to report within six weeks against the following terms of reference•:
Terms of Reference of the Research and Development Working Party (a)
Prepare an audit of current research initiatives in the Victorian Water Industry, identifying gaps, opportunities for development and priorities. WATER June, 1986
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(b) Recommend strategies to develop permanent arrangements both government and non-government to enable ongoing programmes of research to be developed and effectively managed . (c) Document present sources of research funding and develop options for new sources of funding for research and development withing the water industry . (d) Recommend processes for future co-ordination, priority setting and publication of findings of research projects and programmes in the water portfolio. The Working Party found, in ter alia, that a near-completed aud it of current research in Victorian water industry already exists under the 'Streamline' data base which is operated by the Federal Department of Resources and Energy . It was also determined that the highest priority areas for research from a Victorian perspective are: • Investigation of aquatic ecosystems in terms of sediments and nufrients and their interaction with stream biota. • Investigations into low-cost processes for water and wastewater purification. With regard to co-ordination of research it was recommended that this should be arranged through a Research and Develop. ment Unit within the Department of Water Resources . The unit would be responsible for identifying emerging research and technology needs, and managing information transfer. Assessment of funding levels indicated that the formal fund s committed to water research in Australia were amazingly low, i.e. for the two year period 1982/ 83 to 1983/ 84 the total funding provided through the Australian Water Reso urces Council was only $83 6 000 . Aggregate agency spending was somewhat greater but occurred almost exclusively in the experimental, development or tactical research areas. Strategic research has to date suffered significantly, however, it is hoped that this situation will be substantially redressed through the workings of the newly formed Australian Water Research Advisory Council (A.W .R.A .C .)1 °. The formation of this council was in response to the report of the Interim Council for an Institute of Freshwater Studies 11 • The report, in addition to recommending the formation of A.W .R.C. , recommended that spending on water research should grow progressively over the next five yea rs from its current level to approximately $8 million per year. The research funding to be set against priorities established by the council. As a result of the work of these state and national committees, commitments already made in Victoria regarding research have been supported . Typical projects are: • Application of the slow sand filtration process to the treatment of small town water supplies. • Pollution ecology of freshwater macro-invertebrates - a labo ratory streams projects. • A pilot scheme for increasing the use of recycled water from the South Eastern purification plant. It should also be noted that other research and development opportunities in priority areas are being established by the newly formed water Technology Committee of the Australian Water Resources Council.
WATER QUALITY IMPROVEMENT In 1983, the then Minister of water suppl y directed that a state water plan be prepared to provide a basis for the long term development and management of Victoria 's water resources. As a result of the work on the plan , it identified drinking water quality as an issue . Consequently a task force was established to prepare a 'strategy plan to upgrade drinking water quality in Victoria."' The Task Force's discussion paper was widely distributed earlier this year for review and comment. As a companion to the discussion paper, a questions and answers document was prepared on 'microbiological drinking water quality .' 13 Amongst the recommendations contained in the discussion paper are those relating to: • The adoption of the lastest W.H.O . 'Guidelines for Drinking Water Quality' . • The introduction of an expanded microbiological and trace organics testing program to provide a basis for assessing town water supply quality and which monitor the effectiveness of new policies. • A capital works programme designed to upgrade existing water
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WATE R June, 1986
suppl y systems to a standard to provide a measure o f protection against water-borne disease. The State Water Laboratory which is a part of the Rural Water Commission 's Water, Materials and Environmental Science Branch has provided significant input into the preparation of the strategy plan and the question and a nswers booklet and has a part to play in providing the in for mation in future upon which the effectiveness of the various po licies will be judged.
CONCLUDING REMARKS It is hoped from the foregoing comments that it is realised that
the concern expressed by ' technologis ts' in water industry over the last few years regarding the downgrading of their positions and advice is not unique and in fact exists wit hin many other indu stries . It is also hoped that the message comes through loud and clear that it is believed that the conditions experienced are not likely to be temporary and a re the result of 'over correction ' by those responsible for steering the reshaped industry. The industry was, and still is to some extent , in bad shape admin stratively and financiall y. However, in correcting this condition chief executives must be careful not tc let the pendulum swing too fast or too far lest it creates the problem seen by Keith Lewis'. It is ma intained that the best defence mechanisms 'technologists' have in their armoury are their technical ski lls. These skills are patently essential to the success of the industry and they must be blended with those of the economists and others as observed by the OECD examiners• . New ed ucation and training packages will be necessary in the future to assist all professionals to cope with the technologies of the future. Technologists will need to retrain in their own specialist areas as well as to receive training in new acco un ta ncy and administrative procedures. The opposite will apply for nontechnical personnel who will need to become more familiar with technology. P eople will have to learn to fit into multi-disciplinary teams spanning across the scien ces, arts and financial professions . To some extent this occurred in the past and this co-operative cultu re needs to be firml y re-established in t he various orga nisations if they are to be successful. The thesis advanced is that, notwi thstanding the immediate past, technologists should in fact see themselves poised to agai n take a lead role in the water industry, in conjunction as before , with other professions. The leaders an d key managers will , as always, come to the top because of their overall skills. It is up to the technologists to ensure that amongst their ranks there are a sufficient number of broadly trained entrepreneurial people available to take on the business of running the 'show '. Hopefull y in the futur e it will not matter from which side of the professions the chief executive gained his/ her basic training, as the tra ining process should have equipped a ll sides with sufficient skills to understand the needs and as pirations of the others.
REFERENCES (!) PATE RSO N, J. Water Planning: A New Start in Victo ria , CRES Work shop
o n State Water Planning, A.N .U. Canberra, 22 Ma y, 1985. (2) LE WI S, K. W. Panel Di scussio n Remark s, National Water Management Semina r AWWA, Adela ide, 22 a nd 23 May, 1984. (3) BIRC H , A. J. Ant i-Science. Chemistry in Australia, April 1985, p . 11 6. (4) Engi neers Downgraded as Ma nagers. Retiring President' s a dd ress, Engineers Austra li a Apri l 5, 1985 , pp . 15- 16. (5) C riti cism of CS IRO Simpli stic a nd Naive. Laboratory News, April 1985, p. I a nd 4. (6) Austra lia Should Tra in More Engin eers . Engineers A ustralia, May 3, 1985, p. 12. (7) WARD, J . Preparing for the A dva nced Society. Engineers Australia, May 3, 1985, p. 43-45. (8) OECD examiners report on Austra li a' s Science a nd Technology (DR AFT) 1985. (9) Report of the Working Part y o n Research a nd Development in the Water Secto r, Centra l Management Restructuring Project T eam , 31 Jul y 1984. ( 10) EVANS, G. ew Austra lian Water Research Body Formed. Press stateme nt, Minister for Resources a nd Energy , 26 June 1985. ( 11 ) Report o f Int erim Co uncil. Proposa l for a n Institute o f Freshwa ter Studi es . . A ustra lia n Gove rnment Publishing Serv ice, Canberra 1984. (12) Strategy Plan to Upgrade Drinking Water Quality in Victori a . Report p repared by th e task force o n urban drink ing water quality, Department o f Water Reso urces, Victoria, J anuary 1984. ( 13) Microbiological Drinking Water Qualit y, Q uesti o ns a nd Answe rs . Suppo rtin g doc ume nt to th e strategy pla n to up grade drinking water. •
THE OLYMPIC DAM MINING PROJECT -WATER MANAGEMENTP. Nadebaum and T. Amiconi ABSTRACT The Olympic Dam Mining Project invo lves one of the world's largest undeveloped base metal deposits. The project area is located in an arid area of South Australia. Water resources include highly saline local aquifers and mine drainage, and brackish water from the Great Artesian Basin, some 100 km north. The net requirement of water for the initial project is 12.5 ML/day, and includes 4.7 ML/day of desalinated water for potable and process use. Strategies for ¡ maximising water reuse and the use of local high ly saline water where possible are described.
INTRODUCTION The Olympic Dam Mining Project, located on the Roxby Downs pastoral lease area north of Woomera, is the most significant mining development in Australia today. The project area is arid, having an annual evaporation of 3000 mm, and an average rainfall of 160 mm. There is effectively no surface water available at the project site. The costs associated with supply and treatment of water for the project are significant, as the possible water resources are either of poor quality, or are only available from a considerable distance. Water resources include highly saline local aquifers, mine drainage water, and brackish water from the Great Artesian Basin, some 100 km north. This paper discusses the water demands of the project, the water a nd treatment requirements, and the measures taken to minimise water usage.
THE DEVELOPMENT OF THE PROJECT The Olympic Dam project involves the development of a major copper-uraniumgold deposit at Olympic Dam, in South Australia, some 520 km north of Adelaide, and some 30 km west of Andamooka. 'Olympic Dam' was previously a livestock watering point on the Roxby Downs Station, which co ntinu es to operate independently. In 1975 Western Mining Corporation (WMC) were granted exploration licences covering some 15 000 square kilometres. Their first exp loration hole showed low grade copper ore. Subsequent holes showed this to be a major copper, uranium and gold deposit. The recognition of the very large size of the deposit led WMC to seek a co-venturer, BP Australia Ltd. A joint Venture was formed, and the project is managed by Rox by Management Services Pty. Ltd., a wholly owned su bsidiary to WMC. The deposit is one of the world's largest undeveloped base metal resources. The orebody is an unusual strata-bound sed iment-hosted orebody extending over
20 square kilometres, and with vertical orebody thickness of up to 1000 m. The orebody contains two distinct ore types for purposes of metallurgical processing: a copper-uranium ore, containing minor amounts of gold and silver; and a gold ore, containing some copper and uranium. The average grades and probable reserve, based on 450 Mt ore are as follows: Copper @ 2.5% 11 Mt Uranium oxide@ 0.8 0.36 Mt kg/ tonne Gold @ 0.6 gi t 270 t Silver @ 6 g/ t 2700 t These reserves make the orebody the largest reserve of copper ore in Australia and one of the largest uranium reserves in the world. Mining will be carried out by underground development, with the use of mobile equipment. The mine workings will be backfilled with cemented backfill. An Environmental Impact Statement prepared under the direction of the Joint Venturers was released in Draft in October 1982, and was open to public comment. The Draft and its supplement, which incorporated responses to public and government comments, were approved in mid 1983. An exploratory shaft, the Whenan Shaft was completed to a depth of 500 m in 1982, and underground development was carried out to obtain bulk ore samples and to enable further geological exploration to proceed. To test the samples a small scale pilot plant was constructed in 1983 / 84. Its main purpose was to test the metallurgical process, finalize design parameters, and to confirm some environmental aspects of the operations, such as tailings disposal and gas emission. Testing was carried out in 1984. In 1984, Fluor Australia Pty. Limited,
P. Nadebaum
T. Amiconi
Dr. Peter R. Nadebaum is an Associate of Camp Scott Furphy, and Manager of their Environmental Technology Division. He is a chemical engineer, with a Ph.D. and M.A.Sc. from the Un iversity of Waterloo in Canada, and B.Eng. from Monash University. He has wide experience in municipal and industrial water and wastewater treatment, and environmental control, including air pollution control. He has been responsible for the design of a number of desalination plants in remote areas of Australia, and also has particular experience in industrial water treatment and corrosion control. Tony Amiconi is currently a Principal Engineer with Fluor A ustrafia. As a Civil Engineer, with a diploma from the Royal Melbourne Institute of Technology, Tony has worked for Fluor and Consultants in Australia and overseas in the field of water supply and waste disposal. As Project Engineer t1n the Olympic Dam Study, Tony was responsible for a{{ Water Management aspects of the study which included Water Supply, Waste Disposal (including Tailings) and the co-ordination and review of work by Specialist Co nsultants. were engaged to carry out a Technical Study, which led to a Feasibility Study for the Project. The Technical study involved
Olympic Dam Mining Project -
locality plan WATER June, 1986
I5
The Basin is confined by overlaying low permeability beds . The potentiometric surface is above ground level in most locations, and artesian flow s occur from uncapped bores and naturally occurring springs ('mound springs').
WATER QUALITY AND TREATMENT REQUIREMENTS Typical analysis of water from the main water sources, the Great Artesian Basin and the local aquifers, are listed in Table 1. TABLE 1. WATER SOURCE QUALITY (Typical, mg/ L as ion)
TDS pH Na Ca Mg K Cl
Olympic Dam Village
some 70 000 manhours. It concluded tha, the proposed tonnages cou ld be sustained, and it enabled capital and operating cost estimates to be prepared to a required Âą 15 0Jo to permit investment decisions to be made. Camp Scott Furphy was engaged as a sub-consultant to advise on water management, minimisation of use, and treatment. The material for this paper was developed during the Technical Study. At present the Olympic Dam village has a population of some 300 people housed in single accommodation, a caravan park, and a small housing area. The project will eventually require a significant township, in the order of 3000 persons initially, with provision to expand to 9000 in the future. At present, electricity is generated onsite, and later will be supplied for the project via a 132kV powerline from Woomera. Water is presently being trucked to the site from a bore on the Great Artesian Basin (GAB), and ultimately will be supplied via a pipeline from the same source.
WATER SOURCES The various sources of water considered for the Project are as follows: Surface Water
Th ere is effectively no surface water resource. Rainfall in the area is in the order of 160 mm/ year, and varies between 30-500 mm /year. Evaporation is in the order of 3000 mm/year, and the monthly evaporation is in excess of the average monthly rainfall for all months of the year. If required, the Government will supply water from Port Augusta via pipelines constructed at the expense of the Joint Venturers. The amount available is limited to 9 ML/day without upgrading headworks at the intake on the Murray River. This option was not considered economic as additional water was required, and as the local groundwater is not suitable, it would still be necessary to provide a long pipeline and develop a 16
WATER Jun e, 1986
borefield in the Great Artesian Basin . Local Saline Groundwater
The local groundwater is found below the 50-60 m level, and has a salt concentration of some 20 000-40 000 mg/ L, rather similar to seawater. Local recharge rates are estimated to be small, e.g. 30- 100 m 3 / km 2 year (e.g. 0.02-0.060Jo of rainfa ll). The local groundwater will be intersected in the mine area at the decline and shaft , and will be low in suspended solids. The drainage water originating from the mine workings will have a high suspended solids content. The availability of local saline aq uifer water is estimated to be up to 6 ML/ day. Great Artesian Basin Water
The Great Artesian Basin (GAB) water will be drawn initially from Wellfield A, located some 110 km north of the project site. Extensive investigations have been carried out by Australian Groundwater Consultants as consultants to Roxby Management Services Pty . Ltd. Subsequently a special Water Licence was granted by the State under the Indenture Ratification Act to develop Wellfied A. Wellfield A will comprise approximately eight bores, and these will pump into a local storage. The bore water will be pumped via a 375 mm pipeline to the project site, and sufficent storages will be provided to enable pumping to be carried out continuously. The availability of water from Wellfield A is estimated to be up to 15 ML/ day. The water quality ranges between 2000-3000 mg/ L Total Dissolved Solids, and is predominantly sodium chloride and sodium bicarbonate in composition . The usage of Great Artesian Basin water represents a very small portion of the Basin's resources. The total estimated recharge is some 3100 ML/ day, and the current discharge from 11ll bores is 1500 ML/day, of which less than 150 ML/day is used effectively with the remainder going to waste .
so, HCO, Fe Mn F SiO, Zn
u Pb
Local Groundwater
Great Artesian Basin (Wei/field A)
34 000 7 10 000 900 600 70 17 000 4500 200
2450 7.5 850 20 25 25 670 90 1250 0.1
50 2 1.2 15 2-50 0.002-0.01 0.2-2
3 15
Potable Water Requirements
Potable water comp lying with World Health Organization , standards (and in particular with a TDS of less than 500 mg/ L), is required for general drinking and domestic uses, and for some process requirements. The quantity required is 4. 7 ML/day. Suppl y to the township comprises the major portion of this (2.5 ML/day), and is based on a population of 3300 persons. Water usage rates allowed are 650 litres/ day/ person as specified in the Indenture Agreement with the State Government. Potable water could be obtained by desalination of either local saline water, or the brackish Great Artesian Basin water. However, given an overall water usage which requires large quantities of Great Artesian Basin water to be supplied to the site, it is more economic to desalinate the better quality Great Artesian Basin water, and use the local saline water for other purposes requiring a lower grade of water. Desalination will be carried out by either electrod ialys is (ED) or reverse osmosis (RO). Both processes are well proven and are technicall y feasible for the Great Artesian Basin water . The great Artesian Basin water is a soft, sodium chloride/ bicarbonate water. The hardness level is sufficiently lo w that calcium sulphate scaling does not represent a problem, and the silica level is also low and does not limit the water recovery achieved. Other difficult species such as iron and manganese are also absent. It is of interest to note that a significant hydrocarbon content is present (e.g. 100 mg/ L methane and ethane). This has been observed in other Great Artesian Basin sources (e.g. at Moomba), but in the present case higher molecular weight organic species causing taste and odour problems
GAEA::SRl~ESIAN .._.._1;,;;2 . s.,__ _ _ _ _ _ _ _ __
EVAPORATION
plant to operate on a continuous flowrate basis. Brine from the desalination plant will be approximately 10 000-14 000 mg/ L TDS, and will be blended back into the raw Great Artesian Basin feed water to the copper-uranium plant.
•
BRACKISH WELLFIELD
A
5.5
7.0
Copper-Uranium Plant Water Requirements
COPPER - URANIUM PLANT
The copper-uranium plant comprises the fo llowing operations:
i
Concentrator
t
TAILING S STORAGE
t
• Primary crushing., fine grinding and classification . • Flotation, to produce a copper concentrate . The copper concentrate will also contain approximately 15% of the uranium .
Hydrometallurgical Plant Figure 1. Water demands and water balance (initial phase of project)
are absent. The hydrocarbon content is non-toxic and does not affect the operation of the desalination plant.
WATER DEMANDS T he overall water demands and a water balance for the initial project are shown in Figure 1. Overall Water Requirements
Overall , the initial water requirements for the total project are 7 ML/ day , and this will increase to 12 .5 ML/ day. The brackish water from the Great Artesian Basin can be used to supply this water, although significant quantities of the brackish water will require to be desalinated. In addition, 1.8 ML/day of saline aq uifer water, supplied from mine dewatering, could be used . Major Water Users
The major water user is the copperuranium plant, which requ ires 8.6 ML/day of water. Of this, 7.0 ML/day can be of brackish Great Artesian Basin water, and 0.8 ML/ day must be potable (desalinated) water. The copper-uranium plant also can use 0.8 ML/day of reject brine from the desalination plant. Effectively all of the copper-uranium plant requirements are supp lied from the Great Artesian Basin. Use of potable water for domestic uses is the other major Project requirement, with about 3.2 ML/day being required to suppl y the towns hip and construction services area. Water supply for potable use also originates from the Great Artesian Basin, and is desalinated for this purpose. The mine requires a small supply of potab le water (0.4 ML/day) and saline aquifer water (0.6 ML/day), but is a net producer of saline water from mine dewatering. The gold plant is a significant user of water, requiring 1.6 ML/day. The gold extraction processes are not affected by high dissolved salt levels, and saline mine water su itable for this purpose. The percentage recovery of desalinated water has been set at 85 OJo, a level which
can be reliably achieved by either desalination process. Higher recoveries are possible, but are not required as the reject brine can be used in the metallurgical plant and does not represent a loss of water from the system . A pilot 200 m 3 / day Ionics electrodialysis (EDR) desalination plant has been in operation at Olympic Dam for 18 months, supplying potable water for the existing village and pilot plant operation. Brackish Great Artesian Basin feed water has been trucked to the site in 80 tonne road tankers, and is stored in a lined and covered pond. Pretreatment of the Great Artesian Basin feed water has been limited to a precautionary sand filtration; softening or the dosing of chemicals has not been necessary. Roxby Management Services engineers report electrodialysis to be a reliable and successful treatment process. The storages of Great Artesian Basin feed water and desalinated product water will be sized for the initial project to provide for both dail y and seasonal peak demands. This will permit the desalination
• Acid leaching of the copper concentrate to recover the uranium , followed by repulping and refloating in a cleaner circuit to concentrate the copper concentrate to bet wen 52-60% copper. • Separate acid leaching of the tailings from the primary concentration flotation circuit to recover uranium. • Clarification and a two stage solvent extraction of the pregnant solutions from both leach circuits will be carried out to recover copper and uranium .
Smelter • An electric smelting furnace may be installed to upgrade the copper concentrate to either a granulated copper matt or blister. • Sulphuric,. acid plant to provide sulphuric acid for the leach circuits . Water for Hydrometallurgical Processing
A major water use in the copperuranium plant is to provide the water medium for the hydrometallurgical processing operations. Uranium extraction involves anionexchange operations, and high concentra~
Pilot desalination plant WATER J11ne, 1986
17
GA B WA TER
..
t
670 2500
~
~
~
SMELTER ( COOLING TOWERS ) TA ILI NGS y
5300
I 4500 I 1200
DES ALINATED SR I NE
1400
...
Qi
y
14 , 000
,
3750
'
...
'
,
URANIUM
CONCENTRATOR
SOLVENT
y
6300
~
LEACHING
1700
'
EXTRACT IO N
~
~
DES ALINATED WA TER
~
5 00
I TDS
130 ( E XCLUDES ACID AND LEACHED SOL I DS )
Figure 2. Salinity balance on copper -
tions of competing anions (es pecially the chlo ride ion) reduce the selectivity of the process, and the recove ry of uranium . Typical levels fo r the chloride ion at which interferences start to occur are in the order of 2.5 g/ L, and this does not permit the saline local aqu ifer wate r (1 7 g/ L C l) to be used . Pilot work to date had shown that the Great Artesian Basi n brackish water (0 .7 g/ L C l) is suitable; and moderate increases in salinity (e.g. by adding desalination plant brine) have also not been found to be significant. The dissolved salt content of the leach liquor increases to high levels during the leaching process , a nd it is not possible to reuse the liquor a fter the leachi ng process is complete. T his is shown in Figure 2. The barren spent liquor passes out with the tailings to the tailing storage . T he tailings storage is designed to prevent infiltration , and free water is ultimately disposed of by evaporation . Higher purity water is requi red for the a mmonium d iuranat e (ADU or yellowca ke) processing steps, in order to achieve a high purity fi nal product. A small quantity of desalinated water is needed for this pur pose . In addition , desalinated water is required as feed to demineralisers fo r th e production of steam to heat the leaching operations. Saline aquifer water is used for washing the coarse sands fra ction of the tailings, prior to mixing with cement and pumping to the mine as back fill . The primary requirement of the water used fo r this pu rpose is that it does not contain high levels of suspended solids. W ater for Smeltin g
The cooling tower water requirements are significant and the volume requi red 18 WATER June, 1986
I
mg/L
Cl mg/L
I
uranium plant
depends on the concentration factor selected for operation of the cooling circui ts. It is possible to use either saline aqu ifer wate r, brack ish Great Artesian Basin wate r, or desali nated water, fo r cooling purposes . Saline aquifer water could be used in a cooling system similar to those used fo r seawater cooling. Seawater systems usually operate on a low concentration fac tor (e.g. 1.3- 1. 5), a nd incur significant expenses through the extensive use of corrosion resistant alloys (e.g. bronze, Albronze, copper-nickel alloys etc. ) . Saline aqui fer water was not recommended fo r cooling purposes because of the limited availability of saline aq ui fer water , and the high capital cost of cooling system . P articular consideration was given to the use of either brac kish Great Artesian Basin water or desalinated water fo r cooling purposes . Both waters have a similar ionic make- up , although the dissolved salt conte nt of the brac kish water is approximately fi ve times that of the desalinated water. The blowdown res ulting from both the use of brackish or desalinated water can be used as make-up to the copperurani um plant , as the small amo unt of added salinity and the presence of conditioning chemicals such as chromate are able to be tolerated by the uranium leaching process . Further, operation at a low concentratio n factor (i .e. wit h a high blowdo wn) does no t incur a penalty through loss of water from the total system, although it will increase the cost of conditioning chemicals. Acid used to control the pH of th e circulating cooling water is also of no direct cost, as acid is required to be added la ter in the leach circuits. Both brack ish a nd desalinated wate rs prese nt similar condi tioning requirements.
Neither water has problems wi th scaling of calcium sulphate or magnesium silicate, and the major problem is to overcome corros ion by the high chlo ride level (and sulphate if sulphuric acid is to be used to cont ro l pH) , and to avoid calcium carbonate seal~ if the pH is allowed to rise to high levels. Two approac hes to condi tioning are possible. One approach is to allow the pH to stabilise at a moderately high level (e.g. 7 .5-8), and use a dispersive corrosion inhibitor system , involving polyphosphate or ph osphonate, possibly contai ning zinc. Such a program is being used elsewhere in South Austra lia fo r a circulating cooling water system with a rat her similar water analysis (e.g. 4000 mg/ L T DS) to that which would be the case if brac kish water were used for ma ke-up . T he other approach is to maintain the pH at a lowe r level (e.g. 7) and add a c h ro mate-z in c co r ros io n inhi bit o r. Chro mate-zinc inhibitors are ge nerally recognised as the most effective in a corrosive environment. A fin al decisio n on the chemical conditioning treatment will be made fo llowing test wo rk during the detailed design phase of the project. ¡T he costs of using brackish Great Artesian Basin water we re compared with those of using desalinated water . The use of Great Artesian Basin water at a low conce ntration factor (1. 5-2) was adopted , as it was fo und to have a lower cost than using desalinated water. In partic ular, the use of brac kish wa ter avoids the substantial cost of additional desalination plant.
CONTINUED ON PAGE 29
Australia's Hydraulic Infrastructure Planning for Renewal A. G. Longstaff and F. B. Barnes Some infrastructure rebuilding activities result in more political mileage than do others. Opening a newly widened and repaved freeway is popular and positive, but no one will show up to commemorate the relining of a trunk sewer. To solve the f ull range of our infrastructure p roblems, we need to "sell" refurbishing as much as we do new or re-constructed facilities. J. L. Mart in Professional Issues Journal, ASCE
1. BACKGROUND Over the last few years there has been a growing concern in Australia, accentuated by the work of the CSIRO Division of Building Research and the paper by Blakey and Finighan 1 , that our hydraulic infrastructure may be reaching the condition reported to exist in many cities of Europe and the United States where much of the infrastructure has decayed to the point where a crisis situatio n appears imminent. This paper presents an overview of the perceived condition of the Australian hydraulic infrastructure and of the requirements of the water industry, to continue providing the service to the community necessary for public health , safety and continued economic viability . Information has been gathered from most of the major Australian water authorities in order to assist in the review. H ydraulic infrastructure is taken to include , for water supply the means of harvesting, storing, conveying, purifying and distributing water; for sewerage systems it includes collecting, conveying, treating, and disposing of sewage; for stormwater it includes similar collection systems and, with more emphasis being placed on environmental effects of urban stormwater discharges, treatment needs are also becoming a factor. The infrastruct ure of water supply systems therefore comprise water supply catchments, aquifers, major dams, diversion weirs, offtakes, aq uad ucts, bores , treatment plants, pumping stations, service reservoirs, tanks, disinfection facilities, d istribution mains, meters, pressure and flow regulating devices and control installations, and for sewerage includes reticulation sewers, pumping stations, rising mains, main and trunk sewers, treatment plants, outfa lls and disposal works. Drainage and irrigation works include channels, undergro und conduits, dams, retarding basins, pumping stations, offtakes and reg ulating works. T hese hydraulic works normally last man y decades and signs of deterioration even for above-grou nd structures are slow to emerge; indeed for in-ground structures deterioration is often not recognised until structural or functional failure occurs. Once a project has been completed, and the need for it satisfied, there is a tendency for the community to forget it. However, like other - man-made assets, the hydraulic infratructure has a finite physical and economic life. In many areas, advanced decay is now apparent and remedial work required urgent ly. For water, sewerage, drainage and irrigation works this economic life may vary from less than 25 years to in excess of 200 years wit h an overall average of about 75 years. Phys ical life may in fact be longer, but unless an asset is replaced at the end of its economic life overall costs increase, although capital expend iture may be (and often is) deferred at the price of uneconomicall y high maintenance or lack of adequate service.
2. OVERVIEW METHODOLOGY In order to obtain information on the present state of hydraulic infrastructure in Australia, information has been sought from most of the major responsib le authorities on the placement cost of the existing infrastructure, its age, anticipated life, known condition, the adeq uacy of funds a nd other reso urces, and authority programs and proposals for renewal or remedial works. Information was also sought on the backlog of capital works and any inadequacies in the existing hydrau lic systems. Consistent with the purpose of this paper to present a national overview, and bearing in mind the sensitivity of many of the 20
WATER June, /986
A lan Longstaff is the Director of Gutteridge Haskins & Davey responsible nationally for wastewater infrastruct ure. He is a Civil Engineer and has for over 30 years been involved in the design, construction and operation of water and wastewater systems in most Australian states and overseas. A lan is a Past-President of the Victorian Branch of this Association. A. G. Longstaff
Frank Barnes graduated in Civil Engineering from th e University of Melbourne in 1947 and worked with the Melbourne and Metropo litan Board of Works for 34 years. H e has been involved in nearly all of Melbourne's major sewerage and water supply projects in that time, and in the overall integration and p lanning of the total hydraulic infrastructure. Frank retired in 1985 as a Deputy Director of Engineering, having been in charge of investigation, planning and design for th e last 12 years.
F. B. Barnes
issues, the authors aggregated the information given rather than identifying speci fic problems of individual authorities except where the information had been published previously. Information from a uthori ties responsib le for hydraulic services serving 82% of the Australian population was obtained. On the basis that this 82% sample is representative of the whole of Australia, the data has been extended to give a total national picture . Even though most authorities are a long way from completing detailed assessments, they are still the only ones with any rea l know ledge of the state of the in frastructure under their control. T hey have been most helpful in providing the best estimates available to enable this national overview to be prepared. Nat ura lly, the separate estimates, such as the expected life of structures still in good condition , will have a subjective element and will not be uniform for authorities. As a consequence, some interpretation and approximation has been necessary to enable the data to be aggregated. The authors are of the view that the information given in this paper is the best available at this time and properly represents the size of the problem facing the natio n. A great deal more time and effort must be invested over th e next few years so that the optim um solutions can be defined, accurate estimates of cost prepared and explicit programmes for renewal or rehabilitation works finalised . In this rega rd the Engineering a nd Water Supply, South Australia is well advanced and is developing tech niques which may be of value to other authorities.
3. VALUE OF ASSETS Most authorities have prepared estimates of the value of their assets in terms of their replacement cost in today's do llars and using today's methods. Some have worked on the basis of original costs and adjusted these for changes in the value of money a nd for im provements in productivity and construction tec hniques. Alternatively estimates have been prepared based on present-day construction costs. The former method does not take into account the existence of other adjacent services and co nstraints not originall y present, which will increase the costs of replacement when the works were carried out. The indications are that th is increase would average out at about 60%. Neither method evaluates costs to other section of the communit y due to interruptions, lack of service and disruption of access and interference to other normal activities, factors wh ich can add significantly to cost
estimates . Thus the aggregate values qu oted must be regarded as lower bounds of the full cost of replacement. On th e basis set out above th e estimated value of Australia's hydraulic systems assets are as follows: Water Supply $ 25 000 million Sewerage assets $225 000 million Irrigation $ 7 000 million The value of drainage assets proved to be much more difficult to obtain as responsibility for drainage works is distributed differently in different States with individual municipalities often having the major responsibility. Where in formation was available, the value of the main drainage system was between 100'/o and 15 0'/o of the value of th e sewerage system. On this basis the value of the urban main drains wo uld be as follows: Urban drainage assets $2500 million To this must be added th e value of th e local collecting drainage networks usuall y the responsibility of the municipalities. Thus the agg regate value of the existing hydraulic infrastru cture of water supply, sewerage and urban mai n drainage is some $49 000 million , and irrigation $7000 million .
4. AGE OF ASSETS .1 General: The oldest major hydraulic assets in Australia date from about 1850. From the late 1800s to 1930 was a period of major constru ction activity, and by 1930 some 250'/o to 300'/o of th e tota l infrastru cture was constructed . From 1930 to 1960 construction acti vity was at a low level a nd a large back log of wo rk developed. From the early 1960s onwards construction activit y resumed with the resu lt that 60-70 0'/o of the existing infrastru cture is less than 25 years old . During this latter period the extensive back log of services has been largely overcome. In all fi elds of construction, water suppl y works preceded sewerage works. Typically some 150'/o of water supply works are more than 80 years old. Whilst main collectors for several major sewerage systems are now over 100 years old th ey and th eir newer portions of the system are still proportionately newer than their water co unterpart. Broadly speaking the major city infrastructure is probab ly in better condition than the coun try services and the water supply infrastructure in better condition than the sewerage infrastructure. . 2 Water Mains: water mains cannot be taken out of operation for inspection. Assess ment of the ir condition is based on the incidence of bursts, press ure testing and examination of the portions of the main removed durin g repai rs. Deterioration resu lts in a great increase in the incidence of bursts as the main nears the end of its economic li fe so some of the data is not necessarily representative . Water mains from 100 mm up may be rehab ilitated by in-situ cement mortar lining to overcome internal corrosion as well as bridging over small defects. T he small loss of diameter du e to the mortar lining is usually more than compensated by th e improved flo w characteristics and the hydra ulic capacit y normally increases. External corrosion is the usual source of ultimate fa ilu re requiring repl acement or abandonment of a main. In many areas asbestos cement pipe has been used for the smaller ret iculation water mains and those laid some 50 years ago have now reached th e end of their economic life and are in th e process of being replaced. Authorities put the economic life of water mains (other than PVC) at between 60 and 80 years. .3 Sewers: large sewers, particularly those of walkable dimension, are more readil y inspected than water mains, and th eir condition is generally well known . Main sewers may be inspected by closed circuit TV or stereo camera, although interpretation of th e TV or stereo image is difficult and this aspect requires much more in vestigation. Reticulation sewers (up to 225 mm) are usuall y assessed by the incidence of blockages or collapses. Overall only a relatively small portion of main and reticulation sewers have yet been adequately inspected. Much more inspection and detailed assessment needs to be don e before the extent of the deterioration of the sewerage system can be full y describ ed and remedi al work programmed. T runk sewers can usually be walked and minor repairs carried out from the inside. If this is don e regu larly, the economic li fe of the sewer can be greatly extended . However, where attack by hydro gen sulphide or other aggressive material takes place, deterioration is li kely to extend over most of the length of sewer and replacement or relining may be the only feas ible option. Wit h
main and reticulation sewers in-situ lining or " pull throu gh" sleeving may be used, which usually res ults in satisfactory hydraulic capacity despite th e reduced size, due to the smoother bore . Methods are also now in use which enable a lining of equal or larger size to be inserted in the deteriorated pipe. There are also other 'trenchless' methods of replaci ng old pipes with new. Cost of these various lining or repair methods usually varies between 500'/o and 800'/o of the cost of total replacement of the pipe, but for shallow sewers in read il y accessible areas, replacement may prove to be the most economical solu tion. T he useful economic life of sewers is put by vario us authorities at between 50 and 100 yea rs. T his range refle cts the experience of the authority, particularly with regard to hydrogen sulphide attack, and th e quality of the original pipework and construction . Concrete sewers have been known to fail in less than 20 yea rs where hydrogen sulphide attack is severe. .4 Piped Drains: underground drains are generally readily inspected and remedial wo rks carried out as part of normal maintenance (whether this is actually done by other th an major authorities is however open to qu estion) . Life of this asset should therefore be greater than for sewers - say not less than 100 years . .5 Surface works: water and sewage treatment plants, pumping stations and water service reservoirs are generally readily assessed. Mechanical and electrical components are usually assigned a 15-30 year life and the economic life of civil works is assessed at 50-7 5 years. Irrigation and drainage channels, offtakes, pumping stations and other works are readily assessed and remedial works carried out as part of normal maintenance . However, many channels constructed prior to 1940 may need upgrading or replacement due to the cheaper form of constru ction used at that time. Large dams require sophisti cated surveillance procedures and highly specialised professional assessment. The consequences of fai lure of large dams, with the possibility of loss of li fe, is well known. Human li fe apart, costs of damage arising from failure may exceed the value of the dam by several orders of magnit ud e. The implications of fa ilure and the relatively low cost of surveillance and remedi al measures must th erefore give this wo rk ' a very high priority. T he economic life of dams is placed va riously at between 100 an d 200 years plus, with concrete dams usually ass umed to have a lesser life th an earth and rockfill dams . Recent review of the potential for very heavy rainfall in Australia has resulted in a signifi cant increase in the magnitude of design floods for dams. As a consequence man y of the earl y dams have less spillway capacity than now considered necessary and works to assess, des ign and construct additional capacity is being put in ha nd . This work will take man y years to full y complete and each dam must be treated individually. It is therefore not possible to give any indication of total cost of this across Australia at this time.
5. COST IMPLICATIONS Water Supply, Sewerage and Urban Main Drainage As previously indicated the replacement cost of the urban hydraulic infrastructure is at least of the order of $49 000 million, and the average economic asset li fe is taken to be 75 years. This implies th at average replacement cost wi ll eventually become $650 million per year, ass uming the assets can be rehabilitated or replaced for no greater cost th an their presently assessed value. Ac tu al condition at major repair or rep lacement is a critical factor. W here major rehabilitation is undertaken in time th e above average cost may be reduced by 20-35%; in other cases where replacement must be done from the sur face the overall costs will probably be much greater. If th e average economic li fe can be extended to JOO years the 'steady state' rep lacement cost wou ld reduce to about $500 million per year; conversely, lack of maintenance and poor operating procedures, such as those ado pted to save energy costs at sewage pumping stations, res ult in conditions which lead to more rap id deterioration of th e system and hence increase the overall replacement cost. Extending the asset li fe by timely and good quality rehabilitatio n is therefore a critical factor which can greatly reduce th e magnitude of future ¡ costs. Because most of the hydra ulic infrastructure has been constru cted within the last 25 years and very little shows signs of deterioration at this time, this 'steady state ' situation is still some way off. Ho wever , in the major cities the oldest assets a.re now WATER June, 1986
21
well past the 100 year mark and 25 to .300Jo are more than 55 years o ld. T he average age of this gro up wo uld now be about 70 yea rs and it must be expected that at least 800Jo will req ui re rep lacement or major rehabilitation within the next 30 years. With the availability of new techniques and the utilisation of re habilitation rather than replacement, costs of some works cou ld be reduced by 35 0Jo. As against this, where replacement is necessary in now builtup and central business areas, costs could double , and it is therefore prudent to assume that the overall cost of rehab ilitation or replacement would average out at about present assessed replacement cost. On this basis it is expected that the cost of re habilitating or replacing that part of our urban hydraulic infrastructure built before 1930 which has passed its economic life will total some $12 000 million over the next 30 years, an average of $400 million per year. By way of comparison expenditure on renewal or rehabilitation of decaying assets is identified at $86 million for the current financia l year. Due to the distribution of age and conditions of these older assets and the need to do considerable investigation work before ¡ realistic programmes can be prepared , smaller expenditures are appropriate in the earlier years. However, it is a nticipated that by the early 1990s expenditures will need to increase to a bout th is $400 million mark each year. To put these costs in perspective it is noted that capital expenditure on new hyd raulic infrastructure was identified at $2000 million for the current financia l year, $ 1500 million of this coming from public sources (the balance being provided by subdivision developers). If action on a national basis is not taken over the next decade we will be faced wit h a critical situation early in the next century. In some cities this situation is rapidly approaching now. Replacement or rehabi litation of major decayed assets has already commenced in some areas but not in a ll the critical ones.
6. SUGGESTED MANAGEMENT ACTIONS In general the age of our hydraulic infrastructure is less than that of Europe o r the United States (although our earliest sewers are of similar vintage), so we have their experience as a guide to what is in store for us. UK and US experience is that lack of maintenance and refusal, until recently, to face up to the situation has in many areas produced a crisis situation which is necessitating a massive expenditure over a relatively short period. To avoid a lik e situation here, we must act now to: 1. Assemble the necessary data and performance history of our hydraulic infrastructure. 2. Develop better methods of inspection and assessment of infrastructure condition and assess the future life of every significant part of the infras tructure. 3. Monitor and continue to monitor the condi tion of our hydraulic infrastructure. 4. Reassess and agree reasonable and affo rdable standards of service to carry us well into the next century. 5. Reassess our hyd raulic systems in the light of estimated costs of maintenance , rehabilitation or renewal, and of all existing demands and physical feat ures to ensure that future costs are optimised for the whole system and not just for individual works. 6. Ensure that the best technology with respect to first cost and life-cycle cost is developed and available for Australian conditions, and used. Make sure that new assets are built fo r dura bility so that their li fe-cycle cost and the eventual im pact of their replacement cost on society is minimised. 7. Because of the cost of in frastructure renewal, make every effort to prolong the economic li fe of existing assets with properly engineered rehabili tation and not just 'band-aid ' measures. 8. Ensure that realistic programmes are developed for asse t replacement which are both timel y and achieva ble. This may mean replacing some assets slightl y ahead of time and others later than optimum so that the reso urce input is practicable on an ongoing basis. 9. Encourage the adoption of more rea listic and ap propriate financ ial policies, par ticularly in the non-metropolitan areas. 10. Commit resources and sta rt the initial steps of plann ing, inspection , assess ment and monitoring the in frastructure now , even for those assets whose performance still ap pears to be satisfactory. 22
WATER Jun e, 1986
It is pleasing to note that all operating authorities interviewed recogn ised the problem of decaying in frastructure, the need for better and much mo re intensive inspection and assessment, and the requirements for funding and programming to meet this problem. Some authorities have already started majo r remedial works, but even in these cases it is clear that expenditure will need to increase substantially over the next 15 years. Most authorities however do not have the resources at the present time and fea r that governmental restrictions, now fa irly general in Australia, limiting rate increases to the CPI or less, will resu lt in further redu cing their ability to carry out the essential work of keeping the hydraulic infrastructure in working condition . Either the revenue available to the water and sewerage aut horities from customers must increase or a new source of funds be provided. T he problem of managing ageing infrastructure revolves around fin ances.
7. GOVERNMENT ATTITUDES TO INFRASTRUCTURE American experience has been that gove rnments have been much more willing to provide money for new works than to provide for renewal or rehabilitation of existing wo rks. The problem in Australia is no t ye t as ac ute as in the United States but the solution is a long term and continuing one. The only really via ble means of providing the necessary funds on a continuing basis is from the user. This implies recognition by gove rnments that: (i) charges must increase to meet the total real costs, and (ii) water authorities (and their users) cannot afford to be made the ' milch cows' for other governm ent programs if a legacy of neglect is not to be perpetuated. Reha bilitation cannot be deferred for Jong and fai lu re to face the issue will lead to progressive break-down of the system. An expenditure of $400 million over the whole of Australia each year represents a cost of some $42 for every property provided with wa ter and $39 for every property for which sewerage is provided, to which must be added $5 for urban main drainage a to tal of $86 per year for each property provided with water and sewerage, This must be compared with the average capita l in ves tment of $11 000 for each fu ll y serviced property.
8. CAPITAL EXPEND,,ITURE AND THE BACKLOG .1 Capital Expenditure
Over the past 25 years there has been a rate of capital expenditure which has enabled the completion of most works necessary to meet the requirements of the increasing Australian populatio n as well as overcoming most of the backlog of services which had accumulated from the previous 30 years. As the rate of population increase has now declined substantiall y and the backlog has been substantiall y eliminated, the need for capital expenditure on new wo rks has correspondingly decreased . In the current financial year the hydraulic authorities have budgeted fo r capital expenditure of some $1500 million. To this must be added an estimated amount of so me $500 mi llion for the contribu tion of developers to the system infrastructure . Thus the total expenditure on the hyd ra ulic infrast ru ctu re is in the order of $2000 million this year. Total expenditu re for fu ture years, in rea l terms, is programmed to decrease, altho ugh expansion of major units will still be needed as population and demand increase. Any decrease in need for new capita l works will provide the opportunity to phase in the add itiona l resources required for renewal or rehabilitation of the decaying infrastru cture. .2 Remainin g Backlog of Works
T he major back log of capital works is in sewerage. Whereas most capital cities have virtuall y overcome the sewerage backlog, or will do so within the next four to five years, there is sign ificant need for more and improved services in rural areas of the eastern states . The cost of these servi ces is in the order of at least $430 million . The largest back log problem is in metropo litan Perth where there are approximately 168 000 properties still served by septic tank s. The current back log of sewerage services is estimated at 110 000 properties . The Corporate P lan of the Water Authority of Western A ustralia 2 (Water Authority of W .A.) points out that abo ut 350Jo of the developed metropoli tan area is not sewered and estimates the cost of providing for these unsewered areas at $800 million. This back log is leadin g to other disproportionately
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YEAR high community costs, inhibiting more desirable higher density development in reasonab le proximity to the city centre, and dispersing new development. Septic tank effluent must be expected to pollute the groundwater and in time cause eutrophication of rivers and waterways. This lack of sewerage faci lities is thus leadi ng to higher community costs for transport, service distribution and other area-related services as well as potential long-term disbenefits of water pollution and eutrophication. Desirably, most of this backlog should be cleared in 8-10 years and be out of the way before the burden of major renewal and rehabilitation work hits ratepayers. The total of all backlog works additional to that in current programmes identified by the various authorities as being justified on either cost benefit or socio-economic gro unds is some $1400 million. It is recognised that many other schemes have been put forward which are claimed to be backlog works, but without further supporting data these cannot responsibly be included in this present review, particularly in the present economic climate.
9. SUMMARY TABLE -
tury. The likely capital expenditure for entirely new services for an increasing population based on the present trends is also indicated. The graph shows that the impact of restoring the decaying infrastructure can be met largely by the decrease in spending on new works now evident and resulting from having overcome the backlog in most parts of Australia. The identified backlog additional to that included in current programmes requires an increase of 7% of the total present capital expenditure on the hydraulic sector. Overall the trends suggest a need for total capital expenditure in the range $2000-$25<10 million (1984-85 value). The long-term continuing increase in infrastructure restoration costs is due to the ageing of assets constructed in the last 25 years, the increasing difficu lty and cost of their replacement due to interference with other services, and the increasing total infrastructure needed to service the increasing population, which must be restored in due course. It must be emphasised that Figure I is indicative of the overall national position only. The requirements of individual authorities va ry in timing due to the age and condition of their individual assets, and the extent of their back log where it exists.
FINANCIAL ASPECTS
The financial aspects of this overview may be summarised as: Replacement cost of urban hydraulic $49 000 million infrastructure 75 years Anticipated average life of assets $ 650 million Long-term average annual cost of decay Anticipated average cost per year for $ 400 million next 30 years Value of hydra ulic infrastructure assets per property serviced with water and $11 000 sewerage Average cost of infrastructure replacement $ 86 per year per property for next 30 yea rs Present annual expenditure on remedial $ 86 million work Present annual capital expenditure on hydraulic infrastructure - pub lic and $ 2 000 million private $ I 400 million Backlog of justifed capital works Cost per year of overcoming backlog, $ 140 million not already budgetted for, in IO years (Monetary amounts are in 1984-5 dollar values.)
10. INDICATIVE CAPITAL EXPENDITURE Figure I illustrates the general trends in capital expenditure needed to restore decaying infrastructure over the next half cen-
11. CONCLUSION Decay of the urban hydraulic infrastructure in Australia is continuing and the need for rehabilitation or replacement works is inevitable. If we programme now for the restoration of this infrastructure, and the completion of the hydraulic backlog works, on a regular and orderly basis we can avoid massive increases in total annual expenditure (although these will not reduced below the present $2000 million level of capital expenditure on hydraulic infrastructure by both public and private sector) . In this way we will be able to avoid the crisis situation occurring in European and United States cities. If we do not face these issues squarely there will be progressive break-down of our hydra ulic infrastructure with consequent reduction in the level of service able to be provided. Shou ld this be permitted to happen then, to quote Duane L. Georgeson 3 of the City of Los Angeles 'our economy will suffer, our quality of life will be eroded, standard of living will decline'. ¡
12. ACKNOWLEDGEMENTS The authors gratefull y acknowledge and thank the many offi cers of the major water authorities who provided the backgro und data and information without which the preparation of this national overview would not have been possible.
REFERENCES: Continued on.page 29 WATER June, 1986
23
Staged Oxidation of Sulphides in Waste Water using Mechanical Aerators G. Williams and R. G. Shaw ABSTRACT A septic tanker effluent preaeration plant has been installed at
the Toukley Sewage Treatment Plant of the Wyong Shire Council (NSW) to oxidise sulphides in three stages, prior to treatment of
the septage. The paper discusses sulphide oxidation in sewage and describes an experimental technique for measuring oxidation rates. Since sulphide oxidation rates are strongly sulphide concentration dependent, the paper explains the adoption of three staged oxidation and compares it with the more common single stage oxidation . In staged oxidation, concurrent air flow is recommended to reduce the sulphide load on air scrubbing equipment. The paper suggests that similar staged oxidation could be used to solve sulphide problems in pumped sewers.
INTRODUCTION Septic tanker effluent is considerably more septic than most sewages, with sulphide concentrations to 20 mg/ L, and will cause odour problems in most treatment plants if the effl uent is a significant proportion of the sewage flow. This is the case at Wyong Shire Council 's Toukley Sewage Treatment Plant. Pretreatment techniques available for septic tanker effl uent are diverse. Chemical precipitation (lime, ferric chloride), chemical oxidation (chlorine, hydrogen peroxide), oxygen treatment, or preaeration with foul air odour adsorption, can all control odours effectively. The Wyong Shire Council invited tenders for a preaeration plant. The successful tenderer was Aeration and Allied Technology and this paper describes the design concept adopted in the preaerationplant installed . As was anticipated, experiments proved sulphide oxidation rates to be markedly concentration dependent and this led to the development of a three stages sulphide oxidation process as a practical alternative to the theoretically ideal plug flow reactor .
SULPHIDE OXIDATION IN SEW AGE Sulphide Concentration
Sulphide formation in septic sewage by Desulphovibrio desulphuricans is carried to its completion in septic tanks. Virtually all the sulphate and organic sulphur present in the sewage is converted to sulphide . However this sulphide is readil y oxidisable if.dissolved oxygen is present, and the operation of emptying septic tanks, transportation and discharging tankers , causes considerable aeration of the septage. T he sulphide content on arrival at the treatment works is very variable because of this partial oxidation - probably in the range of 20 mg/ L to O mg/ L at Toukley.
Grant Williams is Assistant Water and Sewerage Engineer with th e Wyong Shire Council. He graduated in Civil Engineering at the University of New South Wales in 1969. He also holds a Masters Degree in Engineering Science, majoring in Public Health Engineering. He has worked in contracting in Australia and New Guine and in various government departments and has considerable experience in water and sewerage reticulation and treatment design . He joined Wyong Shire Council in G. Williams 1981 as Design Engineer for water sewerage and special projects. Robert Shaw is Technical Director of Aeration & Allied Technology Pty. Ltd., a company specialising in biological waste water treatment . He graduated in Chem ical Engineering at Birmingham University in the U.K. in 1962. H e worked in the petroleum and cryogenic engineering field in Europe before migrating to Australia in 1971. He began his involvement in wastewater treatment in 1972 heading up C.J. G's development of oxygen applications in wastewater treatment. R. Shaw Prior to fo rming Aeration & Allied Technology in 1982 (in partnership with Ray Anderson) he ran his own consulting business for Jive years. He has been granted a number of patents for his work in wastewater treatment. mains. If the oxidation is allowed to proceed to the point when no dissolved sulphide is left , some sulphate is present mixed with the other partially oxidised species. Wj1en no sulphide is present, no H 2S gas can be liberated, so this degree of oxidation suffices for odour control purposes. In sewage , biochemical oxidation is carried out by a variety of different bacteria, so me of wh ich are obligate sulphide oxidisers but most can survive in the absence of sulphide. The biochemical oxidation product depends on the bacteria. Most bacteria oxidise sulphide to thiosulphate(J) but some oxidise to sulphur e.g. ge nus thiothrix and Thiobacillus concretivorus oxidise to sulphate (or sulphu ric acid) . The biochemical oxidation rate of sulphide in sewage is generally independent of sulphide concentration but is very dependent on bacteria population. The combined rate of chemical and biochemical oxidation of sulphide in sewage is dependent on too many variab les to permit theoretical prediction and an experimen-
¡ Oxidation Mechanism and Rates
The oxidation process in septage is complex being part straight chemical oxidation and part biochemical oxidation. The reaction rate cannot be described in simple terms e.g. zero order, first order etc. because of this complexity. Obviously the rate of oxidation must be known for design purposes. The straight chemical oxidation of su lphide as in sewage, also occurs in clean water and has been separately studied by researchers. The rate of oxidation is heavily dependent on sulphide concentration , less dependent on oxygen concentration, is catalysed or inhibited by a number of chemicals, some of which are present in sewage. Transitional metals (Ni, Co, Mn, Cu, Fe) and calcium and magnesium in so lution accelerate the chemical oxidation of sulphide. The chemical oxidation pathway is: s -- s.-S - S2O3-- - So3-- - so.-! Sulphide
(Polysulphidc)
Sulp hu r
Thiosulphate
Su lphi te
Sulphat e
During chemical oxidation, all the above species can be present together , but, as the oxidation proceeds, the concentration of the species on the right increases and the concentration of those on the left decreases. After prolonged oxidation ¡only sulphate re26
WATER Jun e, 1986
Septage preaeration plant at Toukley showing a tanker unloading. The three oxidation tanks are to the back of the picture with balance tanks in the foreground .
tal determination of oxidation rates is necessary at each location investigated. An experimental determination was carried out on Toukley septage and is described below . Oxygen Requirements
For design purposes, it is necessary to have some quantification of oxygen requirements for sulphide oxidation. Oxygen requirements will depend upon the degree of oxidation required to reach zero sulphide level and upon the time required to reach zero sulphide, since the sewages normal respiratory oxygen requirements must also be supplied during the sulphide oxidation process . In the writers' experience (mainly based on oxygen injection in pumped sewers) dissolved oxygen requirements for sulphide oxygenation with concurrent respiration approximate 1.5 mg oxygen per mg of sulphide. This figure should be used with caution when applied to sewage pumping mains since oxygen or air injected is by no means certain to dissolve. Bearing in mind the concurrent respiration of sewage, the writers generally concur with the USEP A Process Design Manual for Sulphide Control Statement that biochemical oxidation is mainly to thiosulphate viz: 2HS- + 202 - S2Ol -- + H2O The oxygen requirement for this action is one mg 0 2 per mg of sulphide and the remaining 0.5 mg oxygen per mg of sulphide found in practice is the sewage's respiratory oxygen. For Australian sewages, respiration rates vary over the range of 5-15 mg/ L/hr, dependent on the temperature, age (cell count), and strength. Settled sewages and very septic sewages often use less oxygen than this, due to a reduced aerobic bacteria population. SULPHIDE LEVELS AND RATES OF SULPHIDE OXIDATION AT TOUKLEY
Tender documents for the Toukley preaeration plant specified sulphide levels as exceeding 6 mg/ L. No information was given on oxidation rates. Tenderers were invited to take samples and test them as required. Upon testing it was found that sulphide levels ranged from 0-10 mg/ L in the tankers discharging septage but, after prolonged storage and in the absence of oxygen, sulphide levels could reach 20 mg/ L. Sulphide oxidation rates were determined experimentally using dissolved oxygen levels which could sensibly be attained by mechanical aeration. The experiment technique was as follows: Samples of septage were allowed to build up septicity over a period of two days .
Figure 1 shows the resulting curve of nine runs on septage samples from different tankers. The tangent to these curves represents the rate of sulphide oxidation. The oxidation rate is plotted against sulphide concentration in Figure 2, from which it can be seen that the rate of oxidation is 30 mg/ L/ hr at sulphide levels of 10 mg/ L falling to 2 mg/ L/ hr at zero sulphide concentration .
SPECIFICATIONS FOR TOUKLEY The specifications for Toukley described the septic tanker effluent as follows: Flow: Septic tanker effluent disposal volume 1200 ml/day Peak hourly effluent flow 37 litres/ sec. Minimum effluent flow 18.5 litres/ sec. Instantaneous peak flow (four tankers at once) 242 litres/ sec. Septic Quality: BODs 350 mg/ L Suspended solids 175 mg/ L pH 7.5 Ammonia (free saline) 87 mg/ L Ammonia (organic) 22 mg/ L T.D.S. 586 mg/ L Total sulphide > 6 mg/ L O mg/ L Dissolved oxygen The required Ouput Quality was: not > 200 mg/ L BODs > 2 mg/ L · Dissolved oxygen Dissolved sulphide O mg/ L A further requirement limited the discharge of treated effluem to the main treatment plant to a maximum 25 Li see requiring a balancing capability of approximately 270 ml . 20
CONDIT IONS:TEMPERAT URE: 20°C ! 2° DISSOLVED OXYGEN: 4-8 mg/L H2 5 STR IPP ING MIN IMISED W ITH A CLOSED AIR SYSTEM
,o
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CONDITIONS: HMPERATURI : 20°c ! 2° DISSOLVED OXYGEN: 4 - 8 mg/L USING AIR . H2 S STRIPPING MINIMISED W ITH A CLOSED AIR SYSTEM
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0
~
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10
15
20
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MEAN SULPH IDE REMOVAL RATE
10
8
30
35
40
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Figure 2. Total sulphide removal rate versus sulphide concentration
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DESIGN FOR TOUKLEY
TIME IN M INUTES
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Figure 1. Total sulphides versus time
300 mL sealed bottles were half filled with septage, stoppered and shaken for one minute every 10 minutes. During shaking a close approach to oxygen saturation relative to air was achieved (8-9 mg/ L). During the 10 minutes of respiration the dissolved oxygen levels did not fall below 4 mg/ L. Since the bottles were half full of air, sufficient oxygen was available (equivalent to 280 mg/ L of oxygen) for total run lengths of up to 90 minutes without significant depletion of oxygen content. Every 15 minutes sufficient septage was removed to test for sulphide using the Colorometric Methylene Blue method (428B in Standard Methods).
If a circular tank is well aerated the contents are completely mixed . If this aerated tank is used for sulphide oxidation to a sulphide level of O mg/ L, the oxidation must be carried out at the slowest rate, 2 mg/ L/hr for Toukley septage (see Figure 2). At least 10 hours of aeration are required to handle the peak sulphide concentration (design maximum 20 mg/ L). Ideally a reactor which inhibits perfect plug flow is required to achieve the shortest oxidation time but it is difficult and costly to build perfect plug flow aeration tanks because of the length required. A practical compromise is to arrange a number of complete mix stages in series. Three stages of oxidation were adopted in three 90 ml covered tanks arranged in series. At peak flow (133 ml/hr) and strength, with the experimentally determined oxidation rates, the series should produce zero sulphide in all conditions. Figure 3 shows the three tanks diagramatically together with the main process parameters and sulphide and oxygen balance data . W T ER Jun e, 1986
27
'Sinkair' entrainment aerator entraining headspace air in septage.
Since a balancing facilit y and rising main followed the prearation, it was decided to all ow the third stage of oxidation to occur in the balance facility with dissolved oxyge n carried over from the aeration of the second stage. Aeration of the first and second stages was achieved by contacting the septage with the air in the head space of the covered ta nks using 'Sinkair' entrainment aerators (transfer capacity at standard conditions, 7. 5 kg/ hr) . A controlled concurrent air flow of 120 m 3 / hr was drawn through the head space of first and second stages by a centrifugal fan extracting the foul air and discharging to a caustic scrubber for deodorising. The benefit of staged oxidation can be seen more clea rl y by comparing the upper and lower diagrams of figure 3. H ydraulic detention time is reduced from 10 hours for the single stage to two hours for the three stage and the oxygen transfer required is approximately halved.
H 2 S CONTROL When septage is aerated, a small proportion of the sulphide is stripped from solution as H ,S gas. KLA for H ,S transfer is 72% of
Caustic scrubber and vent stack for foul air disposal. KLA for oxygen transfer(!). On this basis less than IO OJo of H 2 S in
the septage is stripped in th e first stage of ~era ti on at Toukley. By arranging air flow concurrently as shown in Figure 3 most of the stripped H ,S redissolves in the second stage and after two stages only 3.3% of th e sulphide is left in the spent aeration air. A caustic scrubber designed al~ng conventional lines was in-
3 STAGES AS INSTALLED AT TOUKLEY 120M3/hr AIR IN""L-;E""T,---133M3/hr ------i911 5' =20mg/L
APPROX 5OOVPM H2S (0•09 kg/hr) 3RD STAGE
5 ' =omg/1S' =Omg/L H.R.T.= 40min. TO BALANCE - - - - - - - T A N K S & S.T.P.
SULPHIDE LOAD= 2·7 kg/hr S' OXIDATION RATE= 21 mg/L/hr 0 2 REQUIRED FOR S = 2 ·7 kg/hr FOR RESPN.= 0•5 kg/hr TOTAL 3·2 kg/hr VOLUME 90M 3
5'= 1•5mg/1.
S' =6m /L
S' LOAD= 0•8 kg/hr S' O.R.= 7mg/L/hr 02REQD FOR 5 =0•8kg/hr FOR RESPN.= O·S kg/hr TOTAL 1 •3 kg/hr VOLUME 90M 3
S' LOAD= S' O.R;:: 0 2REQD FORS = FOR RESPN.= TOTAL
0 ·2 kg/hr 2mg/L/hr 0 ·2 kg/hr 0·5kg/hr 0·7 kg/hr
VOLUME 90M 3
SINGLE PHASE FOUL AIR
133M 3/hr S'
= 2Omg/L 5' =Omg/L H.R.T.= 1Ohrs VOLUME 1350M 3
S' =Omg/L OXYGEN REQUIRED FOR SULPHIDE 2·7kg/hr FOR RESPIRATION 6•8 kg/hr TOTAL 9·5 kg/hr
Figure 3. Comparison of 3 stage a nd single sta ge sulphide oxidation Sulphide in - 20 mg/ L. Sulphide out - 0 mg/ L. (Worst possible instance - Toukley) 28
WAT E R June, 1986
stalled to remove this residual sulphide. Caustic consumption in this scrubber is very small, confirm ing a very lo w sulphide load. The undersides of th e roofs of the oxidation tanks were sandblasted and painted with chlorinated rubber paint to protect them from corrosion due to acid attack .
0-0 . 1 mg/ L. Sulph ide can reform in the rising main to the treatment works and pump well when held overnight and at weekends . The Touk ley works appear to be coping satisfactorily with the extra flow of oxidised se ptage added to the input since the installat ion of the preaeration plant.
CONSTRUCTION AND COSTS
FUTURE DEVELOPMENTS
The work covered by the preaeration plant contract included four tanker unloading points, fencing, three covered oxidation tanks, aerators, two open balance tanks , a pump we ll and two Flygt transfer pumps, caustic scrubber and associated pipe work, excavation etc. The installation was completed in two and a half month s at a total cost of $ 120,000. Approximately half this sum was directly related to th e preaeration treatment. The remainder was for tanker unload ing points , flow balancing and pumping, which would have been required irrespective of the treatment process employed. Runnin g costs of the preaeration plant are mainly power charges and labo ur. The aerators are operated contin uously during the day period .when septage is received, but intermittently during the night and weekends using time clock control. Week day power consumption for the oxidation plant (excluding Flyg t transfer pumps) averages 122 kWh / day. At 12c/ kWh this amounts to an annual cost of $3,750 p.a. Attendance by plant operators and maintenance fitters costs an estimated $2,700 p .a. These treatment costs are low in comparison with other treatment alternatives.
Sulphide formation in sewage pumping mains in Australia still presents man y a uthorities with severe problems. These rising mains have almost perfect plug flow characteristics and co uld therefore attain the maximum sulphide oxidation rate if utilised for this purpose. It wou ld seem an obvious development to apply the staged aeration approach to these sewers to remove sulphides. In long deten tion sewage pumping mains, sulphide levels of some 5 mg/ Lare not un common and for oxidation at this level, dissolved oxygen of 7 .5 mg/ L only is required. This can be provided at the normal operating press ure in such mains by the inj ection of relat ively small amounts of compressed air through a suitable entrainment aerator. The time required to oxidise 5 mg/ L of sulphide in a plug flow situation approximates 30 minutes. It is common practice to size intermittently pumped rising mains with a capacity of 5-7 times average dry weather flow to allow for wet weat her flow conditions. In dry weat her, when sulphide problems are encountered, the average sewage velocity in the main often approximates only 0.2 m/ 5 and an aeration installation only 3-400 metres from the outlet wou ld provide time for complete oxidation. Spent aeration air wou ld have to be scrubbed to remove residual odour.
PERFORMANCE
REFERENCES
The plant performs satisfactorily and maintains di ssolved sulphide levels at the head of the treatment works in th e range of
UN ITED STATES ENV IR ONMENTAL PROTECTIO N AGENCY ( 1974). Process Design Ma nua l fo r Sul ph ide Control in Sanitary Sewerage Systems. •
*
P . NADEBAUM AND T. AMICONI Continued from Page 18 In addition to water for cooling purposes, the smelter has other minor water requirements: desalinated water for feed to the demineralisers for steam production and for make-up in acid making; saline aquifer water for blister casting and slag cooling; and brackish water for hose down. Gold Plant
T he gold plant comprises a combination of flotation, gravity concentration and cyanidation processes, and produces gold bullion and a copper/ gold concentrate. The hydrometallurgical processing steps are not sensitive to dissolved salt content, and highl y saline aquifer water is used for supply to the go ld plant. Mine
Water is required for the followin g mining operations: • Use in rock drilling equ ipment • Hosing down and dust laying • Changerooms • Vehicle wash ing down Particular consideration was given to using th e poorer quality water wherever possible, and experience in the existing min e workings indicates that saline aquifer water can be used successfull y in the work drilling equipm ent, and can also be used for hosing down and dust laying. Desalinated water is required for changerooms and vehicle washing down, to ens ure that dusts containing uranium and other heavy metals are removed from vehicles and persons leaving the mine workings. The major usage is for ve hicle was hing.
*
*
*
EFFLUENT AND STORMWATER DISPOSAL Tailings Retention System and Waste Disposal
Tailings slurr y wi ll be disposed of in a tailings retention area, some 2 km west of the plant area. Tailings disposal will be by sub-aerial deposition, which res ults in a dense dry cake with very low permeability. A pilot test ing program has confirmed this method of disposal as being the most suitable with regard to the local climate and topograph y. Evaporation ponds are located close to th e mine workings to provide for disposal of contaminated water and effluent from th e mine workings, and wash water used to wash the backfill sands. Sewage from the industrial area and central services area is pumped to local sewage treatm ent p lants. Towns hip sewage effl uent will be chlorinated and full y utilised for watering of ovals, playing fi elds and parks. Stormwater collected from areas away from the main mine and metallurgical processing areas will be directed into depressions, and wi ll be disposed of by irrigation, infiltration a nd evaporation. Rainfall fa lling within th e mine and metallurgical processing areas, wh ich is subj ect to contamination, will be collected and either pumped into the process stream or pumped to a local evaporation pond. The contrib ution of rainfall to the average process requi rements is negligible.
CONCLUSIONS T he Olympic Dam Project req uires significant quantities of water , a nd bec·a use of the costs of supplying and
*
treating the water, careful management is req uired. The net requirement of water for the initial project is 12.5 ML/day . There are opportunities for reuse of some of the process water, including desalination brine (0.8 ML/d~y) and coo lin g tower blowdown (2 .6 ML/ day) . However , major increases in dissolved salts which occur in the hydrometallurgical processing operations preclude further reuse, and require a net water input to the project. Saline local aquifer water can be used for salt tolerant process requirements (e.g. the gold plant) and for the other uses such as washing the tailings sands required for backfilling the mine workings . The balance of the water requirements must come from the Great Artesian Basin . This water is brackish , and while it can be used directly for major process requirements, it requires desalination for potable and the more critical process uses .
•
•
A. G. LONGSTAFF AND F. B. BARNES Continued from Page 23
REFERENCES ( I) BLAKEY, F . A. and FINIGHA N , W. R. (1984). Bui ldi ng Our Third Ce ntur y : Rebu ilding Our First and Second. CS IRO - Division of Building Researc h , Highett, Vic., 1985 . (2) W ATE R AUT H OR ITY OF WESTERN AUSTRA LI A (1985). Corporate P la n 1985- 1990. Water Aut horit y of Western Australia , Leederville , W.A.: John Tonk in Water Centre , 1985. (3) GEORGESON, D. L. ( 1984). Management of Aging Assets in the Un ited States. Na ti onal Wat er Management Seminar P a pers . Austra lia n Water and Wastewater Associa ti on a nd The Institutio n of E ngineers, Austra lia , H otel Obero i, Adelaide, S.A., 22 & 23 November 1984 - Adelaide: [T he Association , 1984]. • WAT ER June, 1986
29