__MAIN_TEXT__

Page 1


ISSN 0310-0367

AUSTRALIAN WATER & WASTEWATER ASSOCIATION

Australian Water & Wastewater Association Incorporated ARBN 054 253066 FEDERAL SECRETARIAT Executive Director - Chris Davis Business Manager - Margaret Bates PO Box 388, Artarmon 2064 Telephone (02) 413 1288 Facsimile (02) 413 1047

FEDERAL PRESIDENT Barry Sanders, Phone (09) 420 2453

FEDERAL SECRETARY Greg Cawston, Phone (042) 29 0236

FEDERAL TREASURER John Molloy, Phone (03) 615 5991

BRANCH SECRETARIES Canberra, ACT Alan Wade, PO Box 306, Woden 2606 Phone (062) 513 368 New South Wales Nick Apostolidis, GCEC, 39 Regent Street Railway Square 2000 Phone (02) 699 9922 Victoria

John Park, Cl- Water Training Centre, PO Box 409, Werrtbee 3030 Phone (03) 741 5844 Queensland Don Mackay, PO Box 412, West End 4101 Phone (07) 840 4844 South Australia Neil Palmer, CJ- State Water Laboratories, E&WS Private Mai I Bag, Salisbury 5108 Phone (08) 381 0268 Western Australia Steve Gibson, CMPS, 200 Adelaide Terrace Perth 6000 Phone (09) 325 9366

Tasmania Annette Ferguson , GPO Box 503E, Hobart 7001 Phone (002) 28 2757 Northern Territory Lindsay Monteith, PO Box 351 , Darwin 0801 Phone (089) 81 5922

EDITORIAL CORRESPONDENCE E.A. (Bob) Swinton, 4 Pleasant View Crescent, Glen Waverley 3150 Office Phone-Fax (03) 560 4752 Home (03) 560 9306

ADVERTISING Ann Sykes-Smith, Appita, 191 R0yal Parade, Parkville 3052 (03) 34 7 2377 Fax (03) 348 1206

PRODUCTION EDITOR John Grainger, Appita, 191 R0yal Parade, Parkville 3052 (03) 347 2377 Fax (03) 348 1206

Volume 19, No. 2, April 1992

CONTENTS 3

My Point of View Association News News from the Executive It Seems To Me

4 5

News from the Branches 12 IAWPRC News 13 Industry News Convention Report

16

Hazardous and Solid Waste Convention and 1st Ozwaste Trade Exhibition

Features 21 Emerging Technologies for the Treatment of Industrial Wastewaters R. J. Eldridge 24 Removal of Heavy Metals from Effluent Streams by the Guardsman ACF Process B. Copper 26 Membrane-based Solutions to the Plating waste Problem - A Review 29 Seminar - Blue-Green Algae 32 Candowie Reservoir - Blue-Green Algal Bloom I. M. Bartlett and I. McNish 34 Measured Infiltration Rates Indicate Significant Savrngs in Design A. M. Norish and C.R. Weeks 38 Erosion Control by Macrophyte Planting D. Hutchinson and J. Locke 42 Product Information 44 Conference Calendar

OUR COVER

Our picture shows the receival laboratory at the aq ueous waste plant, of the waste recyc lin g and processing service of New South Wales, Lidcombe. Two tankers await the results of a ten-minute screen in g test before discharging in the unloading bay in the background. The plant design was featured in an issue of Water, October .1988. It has functioned successfully with only minor modifications to the original design, and is now operat in g seven days a week, to cope with the increased load of industrial wastes. Physico-chemical treatments reduce the mixed wastes to an effluent which after strict monitoring is discharged to sewer, and sludges which are buried at the Cast lereagh secure landfill . A recent development is to be the addition, after pilot plant trials, of a fina.l biological treatment (Water December, 1991) Both Lidcombe and Castlereagh sites were visited during the First National Hazardous and So lid Waste Convention.

PUBLICATION Waler is bi-monthly. Nominal distribution times are the third weeks of February, April , June, August , October, December.

IMPORTANT NOTICE The views expressed by the contributors are not necessarily erdorsed by 1he Australian Water and Wastewater Association. No reader should act or fail to act on the basis of any material contained herein. No responsibility is accepted by the Association, 1he Editor or !he contributors for the accuracy of information conlained in lhe 1ext and advertisemenls. The Australian Waler and Wastewater reserves the righl to al1er or to omit any artic le or advertisemenl submitted and requires indemnity from advertisers and conlribUlors against damages v.-hich arise from material published . All material in Water is copyright and should rot be reproduced wholly or in part without the wri1ten permission of the editor.

WATER April 1992

1


CONVENTION REPORT

Emerging Technologies for the Treatment of Industrial Wastewaters by R. J. ELDRIDGE SUMMARY Some recent advances in physico-chemical treatment of wastewater are reviewed, with an emphasis on proces.ses which achieve complete destruction of hazardous wastewater constituents or recovery of valuable ones. Examples include ion exchange in combination with either chemical or electrolytic reduction of metal ions; sorption, photolysis or chemical oxidation of organics, and recovery of metals as crystalline carbonates. Improved precipitants for unrecoverable metal ions are also described.

Rob Eldridge is a Principal Research Scientist in the Division of Chemicals and Polymers, CS/RO, Clayton. His main area of interest is the synthesis and application of novel reactive polymers to industrial problems, water and wastewater treatment.

PRINCIPLFS Discharge of industrial wastewater to sewer is preferred by Australian regulatory authorities over direct ·discharge to the environment. Sewage treatment plants deal effectively with readily biodegraded wastewater constituents, but many wastewaters contain toxic substances at levels too high for discharge to sewer to be acceptable. Where waste avoidance is not possible, sewer authorities now require pretreatment to remove such toxic substances. The range of treatment processes available is almost unlimited, and some rational basis is needed to guide the choice of an appropriate process. Logically, the first consideration should be the preferred fate of the pollutants to be removed. This in turn depends on their economic value, their chemical nature (i.e., are they degradable?) and the level of environmental hazard they represent. Any wastewater treatment process is based on one or more of four principles: • dilute and disperse - innocuous constituents • recover - mercury, nickel, chromate ... • destroy - cyanide, hazardous organics • concentrate and contain - mixtures of metal salts. The last three of these are relevant to pretreatment, with recovery or destruction being environmentally preferable. This paper will outline some innovative approaches, both proven and experimental, to recovery, destruction or disposal of wastewater constituents.

RECOVERY OF WASTEWATER CONSTITUENTS Recovery usually requires a multi-step process which concentrates the valuable constituents and converts them to a desired chemical form. Concentration can be achieved by evaporation, various membrane processes, adsorption on an ion exchanger or other sorbent, solvent extraction or crystallization. A novel crystallization process is described below. This section will outline some recent innovations in sorption processes. Recovery of heavy metals by selective ion exchange As well as concentration, recovery commonly requires separation of valuable from unwanted constituents. Ion exchange (IX) can be used to separate metals or other ionic solutes from wastewaters. The selectivity of most ion exchanges is low, but with good control of process conditions selective removal of targeted metal ions is possible. A process developed by CSIRO (Becker, 1992) uses a commercial chelating IX resin to remove mercury (II) cations from a complex, acidic smelter wastewater also containing iron, zinc, cadmium and lead. Mercury concentrations are reduced from about 10 mg/L to < 50 /kg/L. The resin is regenerated with brine. Mercury is desorbed as HgCl/- ions which are readily reduced to calomel (Hg 2Cl 2), or the metal, for recovery and sale (Figure 1). The depleted brine is then reused as regenerant. There is no waste regeneration effluent to be disposed of. Wastewaters containing anionic mercury complexes

This paper is based on the presentation given at the session on "Emerging Technology" at the National Convention on Hazardous and Solid Uilste.

eluted Hg(II)

Hg(II) 10 mg/I

CHELATING

in NaCl

ION EXCHANGE

Hg(0) or calomel

RESIN Hg< 50 p.g/1

Fig. 1 -

recycled regenerant (20% NaCl)

Flowsheet for recovery of mercury by ion exchange

such as HgCI/- can be treated similarly, except that an anion exchanger is used. In this case regeneration with a recycled solution of a complexing agent yields a concentrated solution from which the mercury is isolated as a crystalline complex. This is again reduced to the chosen end product. Short-cycle IX Processes The high resin costs associated with conventional IX installations are avoided in two processes employing small amounts of resin which are regenerated on short cycle times. The Canadian Recoflo process (Brown, 1988) uses short fixed beds which are regenerated at intervals of a few minutes, which in CSIRO's moving-bed process (Chin, 1988), magnetic resin beads are continuously cycled between an adsorption column and a smaller regeneration column. Both processes employ small beads to ensure rapid reaction in both the adsorption and regeneration steps. Several hundred Recoflo installations in North America recover plating chemicals from metal finishing wastewaters and acid from spent pickling solutions. The CSIRO magnetic resin process has not been installed commercially, but has been piloted on a 2.5 m 3/hr scale. It has the advantages of simple operation and of not requiring preclarification since the moving resin bed is not affected by the suspended solids usually present in wastewater. Combined IX-electrodeposition The regeneration effluent from an IX unit can be recycled in-house if it contains only a single ionic species at a high enough concentration. In other cases it is possible to recover metal values by electrodeposition and sell or reuse the metal cathode. However, electrodeposition requires relatively concentrated solutions, and is very inefficient at removing the last traces of metal. Also, since it is fairly slow and best operated as a batch process, it is not easily used to treat a continuous flow of wastewater. Combining IX with electrodeposition solves both these problems. The IX step yields treated water suitable for discharge or reuse and a small flow of concentrated solution suitable for electrolysis. Most of the metal is removed from this concentrate in the electrolytic step while at the same time hydrogen ions are formed at the anode. The resulting acidic solution is not discharged but reused as regenerant (Figure 2). The Canadian company Tallon Metal Technologies markets a

WATER April 1992

21


Dilute wastewater

+

I

ION EXCHANGER

Purified water

Fig. 2 -

+

t

Concentrate

l

L~!o~.!.! Jl

Acid containing residua l metal ions

I

Metal recovery by combined ion exchange-electrodeposition

combined IX-electrolysis process based on Retec high surface area cathodes and Vitrokele selective ion exchangers (Holbein, 1990). The process seems particularly suited to the treatment of spent etchant solutions from printed circuit board manufacture, where there may be no in-house use for copper salts, but recovered copper metal can readily be sold. Wastewaters from electroless plating, which contain complexed metal ions, are another likely application. Recovery of Chlorinated Hydrocarbons Recovery of toxic organic compounds from wastewater is rare, but Wacker Chemie in Germany provides one example (Huber, 1988). Wastewater from vinyl chloride production, containing 300-3500 mg/L chlorinated hydrocarbons, is treated with Amberlite sorbents to reduce these levels to < 1 mg/L. The resins are regenerated with steam and the condensed organics recycled to the manufacturing process. Steam consumption is only 15% of the requirement for direct stripping of the wastewater and removal of less-volatile compounds is better. On the other hand, capital costs are high. The overall cost is estimated to be 6-7 times that of biological treatment, but physicochemical processes are better able to cope with occasional high concentrations and the presence of inhibitory compounds. Wacker are offering to license the process. Rohm and Haas use a similar process to remove propylene dichloride from wastewater at their Philadelphia plant, but in this case steam is not an effective regenerant. Instead, the sorbent is stripped with methanol and the contaminated methanol burnt as fuel.

DESTRUCTION PROCESSES Photocatalytic Destruction of Organics Treatment processes for toxic organic compounds usually aim at destruction. In recent years there has been a great deal of research into photochemical destruction of aromatic compounds, chlorinated hydrocarbons, chlorophenols, PCBs, pesticides and other organics. Light sources include mercury lamps, 'black light' fluorescent tubes and the sun. Degradation is enormously accelerated by semiconducting catalysts such as zinc oxide or titanium dioxide (Matthews, 1991). The catalyst may simply be suspended in the wastewater, but several reactors have been designed in which wastewater flows over TiO2 coated on a transparent support in the light path. Ultraviolet photons create electron-hole pairs in the semiconductor. These may react directly with adsorbed organics, or create hydroxyl, peroxy or superoxide radicals which attack organics in solution. Dissolved oxygen is the usual oxidant, but destruction rates are higher if another oxidant such as hydrogen peroxide is added. Published results need to be interpreted with care because some authors simply measured the rate of disappearance of the starting compound, which might in fact be converted to another compound of equal or greater toxicity. Other authors monitored the appearance of ultimate decomposition products such as carbon dioxide and inorganic chloride. Early reports suggested that chlorobenzenes either do not react or are converted only to chlorophenols, but more recent work at CSIRO's Division of Coal and Energy Technology and elsewhere has now confirmed complete mineralization. In fact all but the most recalcitrant compounds, such as highly chlorinated biphenyls and dioxins, can be completely mineralized. Even these have been photolytically dechlorinated in the presence of sensitizing dyes such as methylene blue. Partial dechlorination reduces their toxicity and facilitates degradation by other processes. Although prototype photocatalytic reactors have been reported, the process is not yet fully commercial. Catalyzed Oxidation by Hydrogen Peroxide Chemical oxidation is routinely used to destroy toxic pollutants such as cyanides, sulfides, phenols and organic sulfur compounds. Chlorine is the most commonly used oxidant, but hydrogen peroxide is gaining in favour because it eliminates the risk of forming toxic

22

WATER April 1992

organochlorine compounds. Oxidation with Hp 2 can be catalyzed by transition metal ions or ultraviolet li~ht. These cleave hydrogen peroxide, yielding hydroxyl radicals which are capable of attacking organic molecules resistant to uncatalyzed HiO 2 â&#x20AC;˘ Thus Fenton's reagent (Hp/Fe2+) is used to destroy phenols, and recent work has demonstrated its effectiveness in destroying nitrophenols found in wastewater from explosives manufacturing (Lipczynska-Kochany, 1991). Half-lives for the disappearance of two nitrophenol isomers initially present at 14 ppm fell from > 15 hours with Hz0 2 alone to < 25 minutes with Fen ton's reagent. After about 7 hours no aromatic compounds remained. Transition metals other than iron are also used to catalyze peroxide oxidations, but if added in soluble form they are themselves pollutants. Another problem with chemical oxidation is that reaction rates are often sensitive to pH, and the cost of acid or base for pH adjustment can be considerable for large flows of dilute wastewater. Work at FMC Corporation in New Jersey has demonstrated that transition metal ions supported on zeolites or other oxide minerals can greatly accelerate the oxidation by peroxide of thiosulfate, sulfide, mercaptans and cyanide (Bull, 1990). No metal ions are released into solution, and the need for pH control is reduced. Table 1 summarizes some batch and continuous experiments in which metalloaded Zeolite X or Y was compared with soluble metal or metalfree zeolite. There is a clear increase in removal of each substrate. In the sulfide case, reduced consumption of peroxide is an additional benefit, since oxidation of elemental sulfur is catalyzed at the expense of a competing reaction in which four moles of H 2 O 2 oxidize sulfide all the way to sulfate. Table 1 - Destruction of Pollutants by H 20 2 with and without supported catalysts C

0

ppm

ppm

thiosulfate

250 250 180 125 207 207 200 200

35 35 190 133 350 350 245 245

sulfide ethyl mercaptan cyanide

Temp

H202

Pollutant

Catalyst

Cu / zeolite X 10 ppm Cu 2 + Ni/ zeolite Y (zeolite Y) Ni/zeolite Y (zeolite Y) Ag/ zeolite Y , (zeolite Y)

â&#x20AC;˘c

22 22 20 20 50 50 22 22

Time

min

15 15 2 2 60 120 60 60

Removal 0/o

97 85 JOO 80 88 30

95 7

Ultraviolet light is another promising catalyst for peroxide oxidations. The process works w)l:h aliphatic compounds, phenols and explosive nitro compounds. Work at the University of Connecticut has demonstrated its effectiveness with aromatic hydrocarbons, chlorinated aromatics and phthalate esters (Sundstrom, 1989). Water contaminated with organics was recirculated through an annular quartz reactor surrounding a uv tube emitting 5.3 watts at 254 nm. Removal rates in the absence of peroxide varied from 98% in one hour for 2,4,6-trichlorophenol (TCP) to < 10% in three hours for diethylphthalate. Addition of HPi at a 7:1 molar ratio increas_ed these rat~s to 98% in ~o. ~nutes and Y80Jo m two hours, respectively. TCP 1s converted m1tially to less-chlorinated phenols; other pollutants are also converted to intermediates which are still hazardous, but after 4-5 hours no aromatic compounds remained. Batch experiments showed that chlorinated aliphatics are quickly mineralized when present in pure solution, but benzene greatly retards the destruction of trichloroethylene (Sundstrom, 1990). This finding underlines the necessity for the work on synthetic solutions to be extended to real wastewaters. Similar work at FMC has demonstrated that peroxideuv destroys phenols much more effectively than uv alone and, unlike Fenton's reagent, is effective in alkaline solution (Castrantas, 1990).

PRECIPITATION OF HEAVY METALS Precipitation remains the most common treatment process for those wastewater constituents which can be neither destroyed nor easily recovered (for example, mixtures of heavy metal compounds). However, there are now many alternatives to the traditional process of precipitating metal hydroxides with lime or caustic, followed by settling, dewatering and disposal to landfill. Precipitation with Sulfides Since the sulfides of most metals are less soluble than the hydroxides, precipitation of sulfides is one way to meet strict limits on dissolved metal ion concentrations. Sulfide precipitates also tend to be less hydrated and therefore less voluminous than hydroxides. Sodium sulfide is an effective precipitant even in the presence of chelating agents, reducing the concentration of most heavy metals


from 100 mg/ L to much less than 1 mg/L in solutions containing 100 mg/L of citrate or tartrate (Peters, 1984). Even in the presence of 100 mg/ L EDTA, copper can be removed to below 1 mg/ L, but zinc and nickel concentrations remain about 10-20 mg/ L. Two disadvantages of sulfide precipitation are the danger of hydrogen sulfide release at low pH and the fact that sulfide ion is itself a pollutant if dosed in excess. The problem of overdosing can be avoided by using a sparingly sulfide such as FeS. The wastewater must first be neutralized to prevent the generation of H 2S. It is then dosed either with solid ferrous sulfide or with solutions of ferrou s sulfate and sodium sulfide. These chemicals achieve at least three objectives: hexavalent chromium is reduced to the trivalent form, toxic metal ions are precipitated as sulfides and a precipitate of iron hydroxide help coagulate the precipitated sulfides. The insolubility of ferrous sulfide controls the sulfide concentration of the treated water. The precipitated iron hydroxide adds to the volume of sludge, but even so, the total sludge volume can be much lower than with lime. Ferrous sulfate - sodium sulfide treatment enabled wastewater from a US Air Force metal finishing faci lity in Oklahoma to meet strict limits on chromium (VI) (0.05 mg/L), cadmium (0.015 mg/ L), copper (0.05 mg/L), lead (0.05 mg/L) and other metals. Sludge was thickened in a solids contact clarifier dosed with polyelectrolyte. Sludge production was reported to be less than 10% of that from lime treatment of the same wastewater (Carpenter, 1991). Precipitation with Magnesium Oxide or Hydroxide Another attractive precipitant is calcined magnesia, MgO, which has a greater neutralizing capacity per kg than either caustic soda or lime. Addition of MgO to water yields a magnesium hydroxide slurry which will remove dissolved heavy metals both by precipitation and by adsorption. Sludge volumes may be reduced by more than hal f compared to caustic or lime, settling rates are much higher and sludges are more readily dewatered. Moreover, because the insolubility of Mg(OH) 2 limits the pH of the slurry to about 9.5, overdosing does not cause the pH of the treated water to rise excessively and there is no danger of precipitated metal hydroxides redissolving. A Detroit plating shop which switched from NaOH to Mg(OH) 2 reported a 60% decrease in sludge volume, a reduction in settling time from 90 to 10 minutes, an increase in the solids content (after filter pressing) from 25% to 39% and reduced polymer consumption (Louchart, 1987). Use in wastewater treatment of MgO produced from Kunwarara magnesite is being investigated by Queensland Metals Corporation and CSIRO's Division of Mineral Products, in collaboration with ICI Australia. Precipitation of Crystalline Carbonates Precipitation of heavy metals is not limited to the formation of amorphous hydroxides or sulfides. Where recovery is an option, precipitation of crystalline carbonates is an attractive alternative. The Dutch company DHV has developed a process in which metals such as nickel are precipitated as crystalline carbonate pellets (Scholler, 1988). Wastewater is mixed with a recycle stream, dosed with a concentrated sodium carbonate solution and passed upwards at high velocity (about 100 m/ h) through a fluidized bed of solid nuclei such as grains of filter sand (Figure 3). The high carbonate concentration and high surface area promote rapid crystallization of NiC0 3 or basic carbonates. However, some of the metal forms an amorphous precipitate which is not captured. This is removed in a subsequent filtration step and filter backwash returned to the pellet reactor. When the carbonate pellets grow too big to remain fluidized they are removed and stripped with acid, yielding a pure metal salt solution and clean sand, which can both be reused . The principle has long been used in the softening of potable water, producing crystalline calcium carbonate. Heavy metal recovery is a more recent application. In laboratory work on NiS0 4 solutions, the Ni concentration could be reduced from 1350 < 0.1 mg/L after

WATER FACTS Copies are available at $5 each from Allan Mooy, Water Resources Council Secretariat, (02) 895 7049. A new, comprehensive statistical handbook covering water use in NSW. Compiled by Lee Hill and Mark Harris of the Water Policy Division D.W.R.

+

MEMBRANE

PELLET

Backwash dissolve in acid & recycle

or DUAL-MED IA

REACTOR

FILTER Recycle

Metal- contai ning

f

I

I

Product

Concentrated sodium carbonate

wastewater

Fig. 3 -

Recovery of metals as crystalline carbonates

filtration. The first full-scale plant, treating wastewaters containing 3-8 g Ni/L, produced an effluent still containing 15-20 mg/ L of Ni, but more dilute initial waste streams could be expected to give final concentrations closer to those found in the laboratory.

CONCLUSION Wastewater treatment is no longer limited to the traditional disposal processes. Destruction and recovery processes similar to those outlined here are now well established in Europe and North America. With tightening environmental regulations .and rising landfill charges they can be expected to supplant offsite disposal of toxic wastes in Australia as well.

REFERENCES Becker, N.S .C. and Eldridge, R.J. (1992). Selective Recovery of Mercury (II) from Industrial Wastewaters. I. Use ofa Chelating Ion Exchanger Regenerated with Brine. Reactive Polymers, submitted. Brown, C.J. a nd Fletcher, C. J. (1988). The Recoflo Short Bed Ion Exchange Process in Streat, M. (ed). Ion Exchange for Industry. Chichester, UK, Ellis Horwood, pp. 392-403. Bull, R.A. and McManamon, J.T. (1990) . Supported Catalysts in Hazardous Waste Treatment in Tedder, D.W. and Pohland, F.G. (eds) . Emerging Techno logies in Hazardous Waste Management. ACS Symp. Series 422. 52-66. Carpenter, C.J. (1991). Overview of the Air Force Engineering and Service Center's Hazardous Waste Minimization Program. Proc. 45th Industrial Waste Conference. Chelsea, MI , Lewis, pp. 211- 220. â&#x20AC;˘ Castrantas, H.M. and Gibilisco, R.D. (1990). UV Destruction of Phenolic Compounds under Alkaline Conditions in Tedder and Pohland, op cit, pp. 77-99. Chin, W.J. and Eldridge, R.J. (1988). Treatment of Metal Finishing Wastewaters by Continuous Moving-bed Ion Exchange with Magnetic Resins. Proc. Chemeca '88, Sydney, I. E. Aust, pp. 89-96. , Holbein, B.E. (1990). Vitrokele, High-efficiency, Selective, Metal-chelating Adsorbents: Integrated Use with Electrolytic Metal Recovery for Closed-cycle Elimination of Metal Wastes in Freeman, H .M. (ed). Inn ovative Ha zardous Waste Treatment Tech nology 2. Lancaster, PA, Technomic, pp. 111-116. Huber, L.J. (1988) . Waste Water Treatment at the Wacker Chemie Chemicalpetrochemical Plant, Burghausen, F. R.G. Water Sci. and Tech. 20(10). 13-19. Lipczynska-Kocha ny, E. (1991). Degradation of Aqueous Nitrophenols and Nitrobenzene by Means of the Fenton Reaction. Chemosphere 22. 529-536. Louchart, G.W. (1987) . Howard Plating Cleans Up their Act with Magnesium Hydroxide. Proc. Am. Electroplaters, Surface Finishers/ EPA Con/, 8th , EPA/ 600/ 9-87/ 012, Cincinnat i, pp. 122-30. Matthews, R.W. (1991). Environment: Photochemical and Photocatalytic Processes. Degradation of Organic Compounds in Pelizzetti, E . and Schiavello, M . (eds) . Photochemical Conversion and Storage of Solar Energy. Dordrecht , Kluwer, pp. 427-449. Peters, R.W. and Bhattacnaryya, D. (1984). T he Effect of Chelating Agents on the Removal of Heavy Metals by Sulfide Precipitation. Proc. 16th Mid-Atlantic Industrial Waste Conference. Lancaster, PA, technomic, pp. 289-317. Scholler, M. , van Dijk, J.C., van H aute, A., Wilms, D. , Pawlowski, L. and Wasag, H. (1988). Recovery of Heavy Metals by Crystallization in the Pellet Reactor, a Promising Development in Pawlowski, L., Mentasti, E., Lacy W.J. and Sarzanini , C. (eds). Chemistry for Protection of the Environment 1987. Amsterdam, Elsevier, pp, 77-90. Sundstrom, D.W., Weir, B.A. and Klei, H.E. (1989). Destruction of Aromatic Pollutants by UV Light Catalyzed Oxidation with Hydrogen Peroxide. Environmental Progress 8(1). 6-11. Sundstrom, D.W., Weir, B. A. and Redig, K.A . (1990). Destruction of Mixtures of Pollutants by UV-Catalyzed Oxidation with Hydrogen Peroxide in Tedder and Pohland, op. cit., pp. 67-76.

MEMBERS! IF YOU ARE CHANGING YOUR ADDRESS PLEASE ADVISE YOUR BRANCH SECRETARY

NZ Water Supply and Oisposal Association 1992 Annual Conference

INTEGRATED ENVIRONMENTAL MANAGEMENT Christchurch, NZ, 26-28 August

WATER April 1992

23


CONVENTION REPORT

Removal of Heavy Metals from Effluent Streams by the Guardsman ACF Process by B. COPPER (ICI Watercare) SUMMARY Swinburne Institute of .Technology, Victoria, and ICI Watercare have developed a process utilising adsorbing colloid flotation to remove contaminants from industrial effluents. Removal efficiencies in excess of 98% have been achieved both at laboratory scale and in a pilot plant operating at an electroplating works. The benefits of the "Guardian ACF" process over conventional precipitation/sedimentation systems include smaller sludge volumes and a high tolerance of organics/oils which interfere with settling processes.

INTRODUCTION The removal of heavy metals from effluent has become of great importance in recent years. A number of processes are available, mostly involving chemical conversion of the metals to an insoluble form, followed by sedimentation of the insoluble product. Polyelectrolytes or other settling aids are frequently employed to assist in the process. Given adequate residence time, no large flow variations and an absence of oils, gas bubbles, etc, it is possible to achieve very good results with such systems. In many cases, however, the disturbing factors of oils or other organics are present and space available may cause the volume of the settling tank to be borderline for good performance. An obvious possibility is then the flotation of the solid material and separation from the liquid stream, but it still remains difficult to achieve the high percentage separation required to satisfy discharge licence requirements (typically below lOppm). For some time, it has been known that many of the heavy metals can be adsorbed on colloidal hydroxide particles, either formed in situ, or added to the effluent. In many cases, the efficiency of removal can be high at pH levels lower than those that would no'rmally be required for precipitation of the metals. The work carried out at Swinburne has been aimed at utilising the advantages of colloid adsorption and of flotation, in a novel process to overcome the deficiencies of the latter.

DISCUSSION

SMBS

Collold formers ewaterlng

Effluent

Air Fig. 1 -

Dry foam

Diagram of the ACF flowsheet

cope with variations in the effluent composition has been found to be extremely good. The effluent is now passed to the flotation column, where air is introduced to convert the solution to a stable foam. From the top of the column, the foam flows on to de-watering trays, where the wet foam becomes progressively drier as it passes over them. The liquid draining from the foam is the final effluent, ready for discharge to sewer. The final dry foam contains the contaminants and may either be air dried, or collapsed to yield a small volume of sludge. Pilot Plant In order to move from laboratory scale to full production, a pilot plant was constructed to treat 5kL per day, as a batch process. This plant was installed at an electroplating works and has been consistently able to produce effluent well below the discharge licence requirements. It has also been used to test the limits of the process and develop the mechanical systems such as the air injection, to give best possible performance. ' Further Development At the time of writing, the pilot plant is in the process of being up-rated and automated to give a 40kL per day performance rate. To achieve this, it will be converted from batch processing to continuous operation. It is also proposed to produce a "containerised" version of the plant, as a transportable module that can be leased for specific effluent problems. The Future Research work is in progress at Swinburne to link organics removal using ACF with a biodegradation stage, to handle a wide range of difficult effluents.

Screening The process has a number of variables that can be used to tune for optimum performance on any effluent. The usual first step is, therefore, to carry out laboratory trials, which are really a miniature replica of the full scale process. Experience has shown that the -parameters developed can scale up successfully to the operational plant. Process The first stage involves ensuring that the metals are in the correct valency state for precipitation. This usually involves the use of sodium metabisulfite, or another reducing agent and possibly adjustment of pH. The colloid forming materials are then introduced and the pH adjusted to start the process of colloid formation. The materials used may be iron salts, or mixtures of iron and aluminium salts, as determined by the laboratory screening process. The hydroxides formed are then made hydrophobic by the use of a blend of surfactants. Here again, the surfactant blend may be tailored to the effluent by the laboratory screening trials. It should be stressed at this point, however, that even though the process is optimised for the particular effluent, the ability of the system to

Application The "Guardsman ACF" process offers a robust system suitable for treatment of effluents containing a wide range of heavy metals. It is particularly appropriate for low to medium range concentrations (10-lOOppm) and the removal rate is frequently in excess of 98%. The process may also be used as a polishing step, where higher strength effluents are treated by conventional processes. Where it is essential to achieve even low levels in the final effluent, two stage processing can be employed, but will obviously increase the overall cost. Economics It is a little early to give precise cost comparisons, but indications are that it is competitive with existing processes when sludge disposal costs are included. Most importantly, it will achieve required standards when other processes may be struggling.

This paper is based on the presentation given at the session on "Emerging Technology" at the National Convention on Hazardous and Solid Waste.

Editor's Note: This program commenced in 1989 at the Swinburne Institute of Technology, and gained financial support from the Industrial Waste Grant Scheme of the (then) Melbourne Board of Works. It incorporates the PhD studies of Peter Sanciolo, and also forms the basis for international patents secured by the Swinburne Applied Colloid Science Group. Bruce Copper is Technical Manager !CI Watercare. The company has licensed the process and is assisting with its development.

24

WATER April 1992

CONCLUSIONS


CONVENTION REPORT

Membrane-Based Solutions to the Plating Waste Problem - A Review by R. G. MACOUN and A. G. FANE SUMMARY This paper introduces the range of membrane-based solutions to the problem of heavy metal contamination of waste waters and uses the plating industry to illustrate the possibilities. A review of plating waste problems, heavy metal contamination of waste waters and excessive use of water for rinsing is given and also a consideration of the recycling and treatment strategies for these problems. An explanation of the operation of the membrane processes . nanofiltration (NF), ultrafiltration (UF) and supported liquid membranes (SLM) is presented along with experimental results showing the highly selective separations possible with them. In light of these experimental results some combinations of membrane treatment for various plating waste situations are suggested.

INTRODUCTION The plating industry generates various wastes including aqueous wastes that contain heavy metals, cyanides and numerous organic additives. This noxious mixture can have a severe detrimental effect if released into the environment. However, the environmental damage is not the only cost of this waste because these heavy metals, additives and other pollutants are costly inputs in the plating process. Therefore the object of the membrane-based solutions presented here is twofold, to reduce the impact of plating wastes on the environment and to recycle the wastes back into the plating process. The bulk of waste waters in the plating industry are the rinse waters, although accidental spills, leaks and the dumping of spent plating bath solutions also contribute to the waste waters. The problem of dealing with plating waste waters is not simple since they come from a variety of sources and can contain a range of metal ions such as chromium, tin, lead, copper, zinc, cadmium and nickel. A representative sample of our recent wastewater analyses is shown in Table 1. In addition to the metal contaminants shown in Table 1 significant quantities of anions such as chlorides, sulphates, nitrates, cyanides and chromates, as well as proprietary "additives" are present. These additives serve as brighteners, levellers and fume suppressants. They may include compounds such as sodium lauryl sulphate, hydrogen peroxide, aromatics (nickel baths), citric acid, tartaric acid, oxalic acid, saccharides (chromium baths), gelatin, phenol, thiourea and molasses (copper baths), in varying combinations and proportions. Table 1 - Typical heavy metal concentrations in plating wastes Sample

Pb

Ni

Cu

Cr

Zn

Cd

Cr bath Cr rinse Zn rinse Ni rinse Cd rinse Cu rinse

53.5 II.I <0.1 <0 .1 0.1 0.2

1940 530.6 < 0.1 782.4 34.2 < 0.1

1368 326.1 < 0. 1 0.1 250.0 8.9

293900 44590 < 0.1 < 0.1 4. 1 < 0. 1

450.4 160.4 3.2 < 0.1 991.5 < 0.1

1550 0.3 < 0.1 < 0.1 2557 N.D.

Concentration in mg/ L. Samples from plating shops in the Sydney region

The solutions to the plating waste problem can be divided into two complementary strategies, treatment and minimisation. The treatment strategy requires the removal or neutralisation of the toxic components of the waste before discharge. The minimisation strategy involves the recycling of the plating wastes so that the volume of waste that needs to be treated is minimised, leading to lower consumption of resources and a lessened impact on the environment. The decision as to which strategy to follow for any

This paper is based on the presentation given at the session on "Emerging Technology" at the National Convention on Hazardous and Solid Uilste.

26

WATER April 1992

Richard Macoun is a PhD candidate in the Centre for Membrane and Separation Technology at UNSW. He gained a BSc (Hons) in Physical Chemistry from Sydney University and has worked with Dow (Aust) and the CS/RO.

Tony Fane is Professor of chemical Engineering and Director of the Special Research Centre for Membrane and Separation Technology. The Centre activities range from fundamental studies to practical applications, with a growing interest in Water and Wastewater Treatment.

particular plating shop will depend on the politics and economics of each situation, taking into account environmental and water authority standards and charge~, and the cost , effectiveness, flexibility and ease of operation of the options available. The current practice is essentially the treatment option with minimisation limited to the use of counter-current rinsing. There are standard treatment technologies in practice for reducing the discharge of most commonly occurring pollutants, these being the oxidation of cyanides, the reduction of toxic hexavalent chromium to the trivalent state and the neutralisation and co-precipitation of metals. These generally lead to compliance with the Sydney Water Board Trade Waste discharge to sewer limits, if discharged to the sewer or comply with the Clean Waters Act 1970 (NSW) if discharged to a water course. However these treatments generate a metal sludge which is becoming increasingly difficult to dispose of at landfill sites. The current cost of treating rinse waters in the above manner ranges typically between $0.40 and $6.00 per kL. The cost appears to be primarily dependent on the sophistication of the treatment process, man-hours required for its operation and maintenance, and how flexible the system is to changes in flow and quality loadings. Should the discharge from treatment fall outside the discharge limits heavy penalties are incurred. While the current technology follows the treatment strategy it is in the more desirable recycling and minimisation strategy that membrane-based solutions have most scope. The highly selective separatiobs that are possible with membranes allow key ingredients to be separated for recycling or for contaminants to be removed from the recycle stream. The ability of membranes to separate the key components without changing their physical or chemical nature and without using large amounts of hazardous or costly chemicals also makes them ideal for recycling plating wastes. The membrane solutions considered here are nanofiltration (NF), ultrafiltration (UF) and supported liquid membranes (SLM). Nanofiltration can be used to selectively recycle the rinse waters and to recover the plating salts for reuse in the plating bath, as well as removing heavy metals from the waste streams. A combination of reversible chelation of metal ions and ultrafiltration can be used to remove metals from waste streams with high flow rates .


Supported liquid membranes offer the possibility of highly selective removal of metals from waste streams or from process waters. Each of these membrane processes is covered in more detail in the following sections.

NANOFILTRATION Nanofiltration (NF) is a pressure-driven aqueous phase membrane process that has a proven ability to separate metal ions. It is this ability to separate between metal ions that characterises nanofiltration . Membranes that are classified as nanofilters lie between the more common Reverse Osmosis (RO) and Ultrafiltration (UF) and are sometimes called loose RO membranes or tight UF membranes. Table 2 shows the different rejection patterns displayed by some commercially available nanofiltration membranes (rejection is defined as R(OJo) = (1 - [concentration of permeate/ concentration of feed]) x 100). Table 2 -

example illustrates a potentially beneficial selectivity using NF. Practical application of this membrane pro~ably requires a slightly higher level of rejection of divalent anions. Heavy metals are the major pollutant in plating wastes, and because they are usually in a multivalent form and are usually well hydrated they are amenable to treatment by NF membranes. NF ~embranes can be applied to the plating waste problem in two ways, either to treat the waste produced or to reduce the amount of waste produced. In the treatment mode nanofilters can be used to separate and concentrate the dangerous heavy metals without the need of additional chemicals to precipitate the metals. In the waste reduction mode the nanofilter is used to separate the plating metal from any contaminants in the system and to recycle the plating metals back to the plating bath while at the same time providing clean water for rinsing water.

ULTRAFILTRATION

Salt rejections of NF membranes

Membrane

NaCl

NF70 1 XP45 1 XP20 1 UTC-20HF 2 UTC-60 2 SC-LIOO 2 NTR-7410 3 NTR-7450 3 CXM4 PSA 5

75 50 20 66 85 75 15 51

NaSO 4

MgCl

2

70 83 99 .7 99.9 97 55 92 86.6 95

17

MgSO 4

97.5 97. 5 85 99 .7 99.8 98 9 32 91.1 92

99.4 85 90 4 13 95.6 39

I. Cadotte et al 1988, 2. Nakagawa et al 1988, 3. Ikeda et al 1988, 4. Breslau et al 1979, 5. Battacharyya and Grieves 1977.

Our research has shown that the rejections displayed by NF membranes usually fall into one of two categories: the hydration pattern or the charge pattern, named after the rejection mechanisms that dominate in each case (Macoun et al 1991). In the hydration pattern the large, well-hydrated ions are more strongly rejected by the membrane that the small, poorly hydrated ions, the rejection increases as the size of the hydrated ion increases. In the charge pattern it is the ions that have the same charge sign as the membrane that are strongly rejected and the larger the ion charge the more strongly it is rejected, conversely the ions of the opposite charge to the membrane are attracted to the membrane and the larger the ion charge the more they are attracted. These two rejection patterns can lead to some interesting effects when operating with feeds of mixed salts. For example a mixed feed of sodium sulphate and magnesium chloride can lead to a permeate that is mostly sodium chloride if the hydration pattern is followed or a permeate that is predominantly magnesium chloride or sodium sulphate, depending on the membrane charge, if the charge pattern is followed. In some special circumstances negative rejections, where the permeate has a higher concentration than the feed, are possible leading to a concentration of some solutes in the permeate. An application of the XP-20 membrane to a diluted chrome plating bath solution (ca. 103 mg/ L CrO/-) is shown in Figure 1. This membra_ne gave reason8:ble r~jec!ion of the divalent Cro/and SO/-, with low to negative reJect1on of the monovalent Cl-, as well as low rejection of monovalent Na+ . Under some conditions, the contaminant divalent cations also leaked to the permeate. The fluxes achieved were high (ca. 45 L/m2·hr at 500kPa and 160 L/m 2 at 2000kPa). The rejection behaviour showed characteristics of charge pattern (multivalent counter ions pass) at low fluxes, but become more typical of the hydration pattern at higher flux. This

The use of ultrafiltration (UF) is gaining considerable attention in many industries. This is due to the simplicty of plant operation and moderate energy consumption. UF has been applied to the treatment of wastewater, water recycling and reuse and the recovery of valuable materials such as proteins and paints. UF membranes have larger pores and porosities than NF membranes and allow molecules with molecular weights in the tens of thousands of daltons to pass through. UF can be effectively applied to plating wastes if metal ions can be made to form large aggregates using macromolecules through complexation processes. This process can also provide selective metal separation if metal specific complexing agents are used . UF can also be coupled with ion exchange resins where the use of UF membn•nes allows the resin beads to be ground into extremely small particles. The use of finely divided resin improves the mass transfer and kinetics of the process. Our study of complexation in tandem with UF used the macromolecule alginic acid (molecular weight of 240 000 daltons) and the UF membrane PfGC (nominal molecular weight cut off of 10 000 daltons) to remove copper from an aqueous stream. Figure 2 shows our rejection results for the UF of 0.25 mMolar copper solutions with and without the alginic acid present. The copper with no alginic acid shows some rejection at low pHs because of the residual charge of the membrane, the rejection mechanism is the same as for nanofiltration. As the pH is increased the copper is hydrolysed and forms colloidal particfes that subsequently cogulate to form relatively insoluble hydrous copper oxide precipitate (Eilbeek and Mattock 1987), which is rejected by the membrane. In the presence of a macromolecule like alginic acid remarkably high rejections, close to lOOOJo, have been observed for pH ranges greater than 4. This is due to copper ions being bound to the alginic acid which is not able to pass through the membrane. At low pH rejection falls although it is still quite high. This is probably due to alginic acid precipitating to form a gel at low pHs which hinders the passag~ of the copper ion through the membrane even though it is not bound to the alginic acid. The copper can be released from the alginic acid by lowering the pH and filtering with a microfiltration membrane. This leads to about 800Jo recovery of the copper and an alginic acid solution that could be reused. The use of ion exchange resins in conjunction with UF membranes was studied using the cationic exchange resin Amberlite IRC 718 and the PTGC UF membrane described above. The rejection of copper and the flux of water through the membrane for both the extraction and washing phases are shown in Figure 3. The 100

100

----

80

t C 0

. tiQI

60 40 20

a:

---0--

0

80 CrO4= SO4• Cu+2 Zn+2 Na+ Cl-

l

60

z

0

i= 0 w -, w a:

40 20

NO ALGINIC ACID • WITH ALGINIC ACID

0 0

2

4

6

8

10

12

-20 0

500

1000

Pressure

Fig. 1 -

1500

2000

2500

(kPa)

Rejection of various plating ions using a Filmtec XP-20 membrane (pH 3.2)

pH

Fig. 2 - Rejection of copper with and without alginic acid

WATER Apr il 1992

27


100

200 180

l z ;::: 0

WASHING PHASE

-:x:

FLUX

><

140 :ii

0 120

(.)

..,LIJ

100

CHELATING PHASE

LIJ

a:

80

-100 0

100 TIME

Fig. 3 -

160

REJECTION

200

60 300

d 1/)

2><

:::, ..J

LL

(MIN UTES)

Rejection and flux versus time for processing copper (305 ppm) using ion exchange resin

effectiveness of the system in removing the copper is indicated by the 100% rejection during the extraction phase, and the ease of removal by acid washing is indicated by the negative rejections in the washing phase. The final recovery during the washing phase was greater than 95% and Figure 3 shows that the volume of acid needed to achieve this was half the volume of copper solution originally . processed. The advantages of UF in tandem with complexation or ion exchange are its selectivity and its low energy costs. This makes it useful for treating high flow rate streams. Its selectivity makes it most applicable for the selective removal of pollutants from discharge streams or the removal of contaminants from recycle streams. It is not suited to batch processing.

SUPPORTED LIQUID MEMBRANES Supported liquid membranes (SLM), which are analogous to solvent extraction, offer an attractive alternative approach to traditional techniques for separation, recovery and purification of metal species in solutions. In a SLM a thin liquid layer is immobilised within a microporous substrate. The selectivity and flux can be enhanced by using a carrier in the membrane liquid . The carrier has the ability to selectively react with the metal ion to be separated. If multi-metal ions are to be removed at the same time, as in the treatment of plating wastewater, mixed carriers can be chosen. The availability of hollow fibres permits the use of very compact separation modules characterised by high membrane area densities. This enables us to achieve significant separation in a single stage while using high feed / strip ratios and hence obtain low energy consumption and capital cost. The intrinsic advantages of SLM are: (i) low capital and operating costs; (ii) low energy consumption; (iii) low inventory of extractants (which could be very expensive materials); (iv) possibility of separating and concentrating metals in one step; (v) solutions containing suspended solids can be treated . For SLM processes, in addition to the chemical reaction and transport properties of the system, the stability of the membrane is the determining factor for successful operation. The instability of a SLM can lead to degradation of the membrane and eventually to total loss of separation ability. The mechanisms of SLM instability could include: (a) transmembrane pressure; (b) loss of membrane liquid by solubility in the adjacent aqueous solutions; (c) osmotic pressure gradients (this is disputed); (d) progressive wetting of the support induced by the lowering of organic-water interfacial tension; (e) spontaneous and / or shear-induced formation of emulsion. The stability of a SLM can be much improved by selecting the proper conditions. For example the characteristics of the membrane support are directly related to the stability of a SLM. It is the capillary force that holds the membrane liquid within the micropores. We have shown that the capillary pressure within the irregular membrane pores is related to the membrane pore size (dh), pore structure (reflected in the 'structure angle' a), the interfacial tension g and the contact angle qR,i by the equation DP=4 g Cos(qR,i+a)/dh (1) Where DP is the displacement pressure difference. Although smaller pore size is favourable for holding the membrane liquid, too small a pore size could hinder solute diffusion through the pores. The recommended pore sizes are in the range of 0.02-1 mm. Our experimental results indicate that once a SLM becomes leaky the membrane liquid may be continuously depleted, dragged out by the organic solution if the support membrane .pores are highly

28

WATER Apri l 1992

interconnected and round-edged. A membrane with a morphology of less connected network and sharp por? edge is more suitable as a support. We have used SLM to recover gallium from Bayer spent liquor. In the Bayer spent liquor, gallium exists together with much higher concentrations of Al and Na. The mass ratio of Al/Ga is approximately 150 to 400. We can use SLM to recover and concentrate gallium from such solutions with a separation factor of approximately 400. Because the chemical compositions of the liquor are not changed in the SLM process the solution can be directly recycled to the production after separating gallium. An alternative approach, which is potentially more stable than the SLM, is the use of the hollow fibre membrane contactor (HFMC). In this system the contaminated aqueous stream flows on one side of the membrane (for example the shell side) and the organic phase on the other side (the lumen) . The organic phase can be circulated between two hollow fibre modules, one the 'extract' module, the other the 'strip' module. We have applied this concept to the removal of phenol from water and were able to continuously reduce 2000 ppm to less than 10 ppm with a flux in the range of 5-50 g/ m 2 .hr. Studies are in hand to remove copper from aqueous solutions using this approach .

CONCLUSIONS From this brief review of membrane separation systems it is clear that they have excellent separation capabilities that can be applied to the treatment of plating wastes. They can be used to recover the valuable and harmful components from plating wastes so that the bulk of the wastewater can be disposed of safely. Membranes have the advantage of being highly selective and of not changing the physical form of the waste which leads to potential savings in energy and cost. However the real niche for membrane separation systems is in the recycling of the plating wastes. In these systems the advantages of several membrane systems can be combined. For example NF can be used to remove the monovalent ions from spent rinse water and provide concentrate for recycling to the plating bath and clean water for rinsing. A SLM system can be coupled with this to remove the multivalent contaminants from the concentrate line prior to recycling to the plating bath and combination of chelating and UF can be used to remove harmful heavy metals from the discharge stream before releasing it into the enviro~ment.

ACKNOWLEDGEMENTS This paper is based , in part, on the work of the following, who are gratefully acknowledged: Rahman Awang, Marjetica Bolko, Yanrong Shen and Fufang Zha. The authors acknowledge the support of the Australian Research Council, the Waste Management Authority (NSW) and the Urban Water Research Association.

REFERENCES Bhattacharyya, D. and Grieves, R.B. , (1977). Recent Developments in Separation Science. Vol3 CRC Press Inc. Breslau , B.R., Testa, A .J., Milnes, B.A. and Medjanis, G. , (1979). Ultrafiltration Membranes and Applications. Plenum Press. Cadotte, J., Forester, R., Kim, M., Petersen , R. and Stocker, T. , (1988). Nanofiltration membranes broaden the use of membrane separation technology. Desai., 70. 77 Eilbeek , W.J. and Mattock, G., (1987). Chemical Processes in Waste Water Treatment . Ellis Harwood Ltd., 39-91. Ikeda, K ., Nakano, T. , Ito, H ., Kubota, T. and Yamamoto, S., (1988). New composite charged reverse osmosis membrane. Desai., 68. 109- 119. Macoun, R.G., Shen, Y.R., Fane, A.G. and Fell, C.J.D., (1991) . Nanofiltration: Theory and applications to Ionic Separations. Proc. CHEMECA 91, Newcastle, 398- 405. Nakagawa, Y., Kurihara, M., Kanamura, N. and Ishikawa, M., (1988) . Solute separation and transport characteristics through charged RO membranes. MRS International Meeting on Advanced Materials, Tokyo, Japan.

WHY LOOK ELSEWHERE? If it's to do with our industry

LOOK ... AND ADVERTISE IN OUR MAGAZINE


SEMINAR BLUE-GREEN ALGAE A report by Jonathan Crockett The drought conditions in southern Queensland and northern NSW in the summer of 1991-2 stimulated a dramatic and very visible rise in the algal blooms on the River Darling, which necessitated some emergency actions, even involving the Army, to ensure safe water supply to communities along its banks. As has been reported in a recent issue of Crosscurrent the resultant public (and media) furore has stimulated the formation of a number of Task Forces to study the problem. Blooms of toxic cyanobacteria (blue-green algae) are by no means new ... and probably pre-date European settlement in Australia. They are equally common in the similar climate of South Africa. The problems they cause for domestic water supplies are compounded by the erratic appearance of the blooms. They occur more frequently in the arid climate of South Australia, and a Seminar was organised by the ACWTWQR in April, 1989 to discuss matters relating to the UWRAA research project being conducted there (Water August, 1989). In Victoria, in late 1991, blooms occurred in a number of reservoirs, but the main subject attracting media attention was the pro-active emergency action taken at the Candowie treatment plant immediately prior to the tourist season for Phillip Island. To update Victorians in current state of knowledge on the problems, a full-day seminar was organised in February by the Melbourne office of Gutteridge Haskins & Davey. One hundred persons attended, and were rewarded by a full review ranging from evolutionary biology to the costs of activated carbon treatment and methods of dealing with the public and the media.

Copies of the papers are available from GHD for $25 KEY POINTS A brief summary of the points made by each speaker follows: Prof. Bill Williams (University of Adelaide): Introduction to Algae • stressed that toxins from cyanobacteria are only released on cell death • blue greens dominate in eutrophic waters perhaps because they require less CO 2 and some can fix nitr~gen from air. . • stressed that Australia has an opportumty to be a leader m the subject for sub-tropical and tropical areas. Prof. Peter Tyler (Deakin University): Characteristics of Algae • pointed out the fundamental difference between cyanobacteria and algae - the fact that they are Prokaryotes - lacking a defined nucleus. • illustrated just some of the complexity which makes a full understanding of reservoir behaviour impossible. • made the point very clear that algae, more particularly cyanobacteria will always be there - Beijerinck's Dictum. • the fact that cyanobacteria form akinetes, a spore form which can survive for years and be easily spread is particularly significant. • also explained another competitive advantage that some cyanobacteria have: the ability to accumulate phosphorus. Dr Rod Oliver (MDFWRC): Physical Factors Influencing AJgal Growth • moved on.to the physics of algal blooms after stressing that blue green blooms have occurred throughout the Murray Darling basin over a long time. • explained euphotic depth and mixing, and the fact that some algae (blue-greens) can float and others tend to be sinkers. All combine to make prediction of blooms, sampling and interpretation of results difficult. • pointed out how turbidity and colour in water are important controlling factors on algal growth. • illustrated the importance of soluble phosphate and particulate phosphorus and how the latter dominates in the lower Murray Darling. • illustrated that the desorbability of phosphorus from particles varies

widely and that phosphorus in more turbid waters is likely to be more readily desorbed; about 50% of particulate phosphorus is desorbable in the Lower Darling compar , to 30% in the Ovens. Dr Dennis Steffenson (EWS): Algae Problems in South Australia • stressed that for water supply authorities taste and odour is the more common problem. • pointed out that toxicity is real - at least for direct contact recreation but· that recording has been poor. • the problem of cyanobacteria and other T & 0 algae in South Australia is very real. He explained the three level alert and action plan in SA. • illustrated the difficulty or impossibility of being responsible in informing the community without being accused of being overconservative. Michael Burch (EWS): Toxicity of Cyanobacteria • pointed out the uncertainty about the health significance of blooms. • relatively few species are known to produce toxins, so far only four in Australia, but nevertheless there can be a number of toxins produced by each species. • some blooms are always toxic - eg. some anabaena are only occasionally toxic. You cannot prove potential toxicity by identifying one of the four Australian toxic species. • explained what the toxins were and what their structure and action are: Hepatotoxins - which can affect the liver; Neurotaxins (alkaloids) - block muscle movement and possibly of less significance but little known about them. Michael Muntisov (GHD): Problems Caused by AJgae in W..ter Supplies • outlined all the problems algae can occur with emphasis on T & 0. • these include filter clogging and interference with coagulation in a WTP (if you are lucky enough to have one), increased DOC, increased raw water pH, increased C1 2 demand. • 530Jo of all water supplies in Australia had experienced T & 0. • growth in large open basins - including attached growth - covering is the only full solution. Phil Jeffrey & Martyn Kirk (HD,Vic): Health Aspects • to date have used mouse bioassay in Victoria. • State Lab is setting up HPLC for toxin detection. • stressed the unknowns about algal toxins and the need for more biological and medical study. • reviewed the many human illnesses that can be caused by fresh and marine algal blooms. • presented an outline of the procedures that the department requires to be followed in the event of cyanobacteria exceed.mg 2000 cells/ mL. • the uncertainty about whether mutagenic effects are real is not uncommon and has the greatest implication in public relations. • there may be other undiscovered toxins. Ian Bartlett (Barden Consultants): Case study of the Candowie Reservoir • illustrated the difficulty some face with catchment management. • a poll of consumers indicated that T & 0 was a greater problem than dirty water. • PAC trials inconclusive and now testing GAC. • we need a test for toxins in treated water. • the need for informing the community of what is being done. • the need for improved co-ordination between government departments and responsible water boards. • the usefulness of sunlight in degrading toxins in open storages perhaps needs to be considered contrasted with the problems open storages cause. • illustrated the cost of reacting with CuS04 - $40 000 not including the cost to tourism. * Prof. Peter Cullen (University of Canberra): Catchment Management • catchment management does help but blooms were here before we were. • non-point nutrient inputs are intermittent with runoff - it is complex but most input is from relatively few storm events. • The paper is published in this issue.

WATER April 1992

29


• what does catchment management involve? buffer strips prevent stock access basic soil conservation drought management - a replacement to the current scorched earth approach feedlot waste management say by wetlands. • point sources can also be very important. • stressed the importance of available phosphorus. • the need for better predictive methods where we have most input P as particulate. • no significant connection between chlorophyll and P. • both good catchment management and a good WTP's are needed to solve algal problems.

----OKI SUBMERSIBbE AERATORS

Dr Dennis Steffensen (EWS): Reservoir Management

• • • • • • • • • • • • •

we do need some quick fixes. Cu toxic to phytoplankton at levels befow toxicity to humans. there is increased use of chelated forms of Cu to give longer effects. difficult issue of acceptability of copper - his view, is that it is only acceptable for drinking water reservoirs. other chemicals not approved except C1 2 or C1NH 2 • difficult to decide on how long to leave a reservoir closed after dosing. try to dose before T & 0 threshold is reached. EWS monitors algae twice per week. thinks T & 0 control is equivalent to toxics control. should focus on covering of reservoirs and on manipulation. presented SA's well-developed approach to CuS04 • shallow flat reservoirs are hard to destratify. not enough energy into mechanical mixing at Myponga.

Alan Strom (GHD): Conventional Water Treatment

• described 'conventional' water treatment processes and their ability to deal with algae. • pointed out that coagulation/ flocculation and solids removal remains the main workhorse of water treatment. • conventional treatment is generally upset by algae. • particular problems with clarifier-only plants. • if you have an algal problem it is another reason for needing a water treatment plant. Jonathan Crockett (GDD): Oxidation Processes and Biologica] lreatment • indicated that oxidants have a role, but are not a full solution nor are they without problems. • the most effective are also the most costly. • introduced the concept of biological treatment combined with carbon ahead of the filters to lower AOC in finished water and possibly before coagulation.

Aerators

Michael Muntisov (GHD): Activated Carbon

OKI aerators are used extensively in activated sludge plants for treatment of Municipal and Paper and Pulp Wastewater. The OKI aerator feeds pressurised air into the sludge under controlled cavitation conditions. The air is sheared into fine bubbles at the rotor blades and dispersed, resulting in a number of significant advantages; • Low energy consumption -up to 50% less than surface aerators -up to 30% less than diffusers • No noise • No spray • Easy maintenance -2 year service interval -no tank drainage • Easily relocated to optimise oxygen profile

• outlined the ease, effectiveness and cost of PAC & GAC - this is the process that- appears to be the most effective process overall for T & 0 and toxicity removal. • option of retrofit with GAC is worthy of consideration. Wendy van Dok (Monash University): Monitoring Algae

• parlous state of monitoring in Victoria. • we need to monitor more than just algae to understand algal problems. • we need to be selective about the technique and report with care. Michael Burch (EWS): Toxicity Testing

• good practical advice on how testing for toxicity can be carried out. • mouse bioassay for neurotoxin takes minutes, for hepatotoxins takes hours. • we need to improve our knowledge of likely toxins so we can use HPLC instead of mouse testing. Warren Wealands (DWR, Vic): Contingency Planning

• • • •

Supaflo - Aerating with OKI

Jonathan Crockett (GHD): Strategy Planning for \\uter Quality Improvements

'1!l!l!!:JJ},

• action must be planned for. • strategy will include many components of catchment management to advance treatment. • optimum strategy and timing will differ from place to place. • sufficient information is available for an assessment of costs.

SUPAFLO TECHNOLOGIES PlY. LTD. 1/ 14 Roseberry Street, Balgowlah, N.S.W. 2093 Ph. (02) 949 3011 Fax (02) 905 5856 PERTH: Ph . (09) 316 1966 Fax (09) 316 1952 MELBOURNE: Ph . (03) 526 3628 Fax (03) 526 3652

'

• THICKENERS • VACUU M AN O PRESSURE FilTEAS • FLOAT CELLS • EFFLUENT TREATMENT

past actions have been too late so a working party was formed. contingency planning must be for all sorts of events. the aim is to be prepared. gave good basic advice on resources needed to deal with a bloom.

continued on page 3 7

'£'."5


MANAGEMENT Candowie Reservoir - Blue-Green Algal Bloom December 1991 by I. M. BARTLETT and I. McNISH INTRODUCTION Candowie reservoir is a medium sized shallow storage located approximately 100km south-east of Melbourne, Victoria, on a tributary of the Bass River known as Tennants Creek. The reservoir supplies the popular resort area of Phillip Island and neighbouring mainland towns. The reservoir has a nominal full supply volume of 2430 ML covering an area of 61 ha, With a maximum depth of 14.5m, and _mean depth of 4.0m. The maximum depth is highly misleading as it is measured in the original creek bed which had a depth of around 5.0m. The reservoir was constructed in 1962 with a nominal capacity of 1100 ML, raised in 1977 to 1900 ML and again in 1983 to its present level. Candowie's catchment covers 19 km 2. of rich agricultural land which has been extensively cleared and sown to improved pasture. The catchment is relatively steep, having slopes of 5 to 3007o, thereby allowing rapid run-off response and transport of nutrients. Land use in the catchment involves dairying, fat cattle and lamb production. There has been .a noticeable trend away from dairy farming since 1980 with a reduction in numbers from 13 farms to the current three. Application of superphosphate to the catchment is regularly carried out.

WATER QUALITY Typical raw water quality in Candowie is summarised as follows; Turbidity (NTU) 3- 10 Colour (Hazen) 30--50 Iron (mg/ L) 0.2-0.6 0.2-0.4 Manganese (mg/ L) pH 7.5-8.0 60-80 Alkalinity (mg/L) Temperature °C 12-21 As shown above, the water has moderately high colour and alkalinity and high iron and manganese levels which resulted in severe dirty water problems throughout the distribution system. Water leaving Candowie and other open service reservoirs is disinfected by flow-paced gas chlorinators. A poll of all consumers in 1985 clearly indicated that taste and odour problems were considered of greater concern than dirty water. Between 1980 and 1986 at least six blue-green algal blooms occurred with surface counts of up to 75 000 cell/mL. Heavy chlorination of supplies led most consumers into retaining a rainwater tank for drinking water. Records prior to 1980 are poor but a review of Board minutes indicates that blooms occurred as early as 1968.

WATER TREATMENT In 1985 a program for implementation of water treatment was commenced. Mixing: The initial strategy was installation of a mixer to prevent reservoir stratification. The primary aim of the mixer was to prevent formation of anoxic conditions in the reservoir which allows uptake of iron, manganese and phosphorus in the bottom muds to re-enter into solution. The unit has operated effectively resulting in complete mixing of the water column near the offtake tower. However substantial doubt as to mixing effectiveness in more remote areas of the reservoir does exist.

This paper was presented at the Seminar on Blue-Green Algae, in Melbourne, February 21, 1992.

32

WATER April 1992

Jan M. Bartlett B.E., Sixteen years experience in the Victorian Water Industry including four years with Melbourne consulting firm and eleven years with the Westernport Water .Board as Engineer and Engineer/ Manager. In 1991 formed own consulting firm known as Barden Consulting Engineers who are currently managing implementation of major sewerage project and water supply works at Westernport. Jan McNish is the Secretary-Manager of th Westernport Water Board.

An additional benefit of the mixer has been to allow the operator to select the best quality water from a wider range of drawoff levels. Dissolved Air Flotation/ Filtration: In 1988 a 30 ML/day DAF treatment plant was commissioned. The plant incorporates a number of processes to overcome problems with the raw water quality, as follows; (a) Pre-dosing with Potassium Permanganate to oxidise iron and manganese (b) Flocculation of impurities with Alum (c) Dissolved Air Flotation removal of floe and algal cells (d) Filtration (e) pH correction with Caustic Soda The plant has been extremely successful with typical treated water quality as follows ; 0.5 Turbidity (NTU) Colour (Hazen) 5 <0.05 â&#x20AC;˘ Iron (mg/ L) Manganese (mg/ L) <0.05 pH 7.8 Algal Cells/ mL NIL In 1989 during a severe blue-green bloom of Anabaena, taste and odour complaints were received from some consumers . Consequently, the Board commenced trials using addition of powdered activated carbon . Unfortunately the trials were inconclusive, although a reduction in taste and odour was claimed by some of the testing staff.

ALGAL BWOM -

DECEMBER 1991

In late November 1991 an increase in numbers of the blue-green algae Anabaena was noticed in the reservoir. (Approximately 9007o of blue-green blooms at Candowie involve Anabaena with the remainder either Microcystis or Anacystis). The following chronicle of events outlines steps taken during the bloom. Algae were noticed on the reservoir by the Water Treatment Plant Operator, and reported at the Board meeting held on Wednesday November 27, 1991. Tests were taken on Thursday November 28, 1991 which confirmed the presence of blue-green algae Anabaena. A surface count of 54 000 cells/ mL was identified with a count of 2800 cells/ mL at a depth of 9.5m. A trawl of the surface algae was taken and this trawl proved positive for toxins through a mouse toxicity test. This was not considered of major concern as supplies were being drawn from 9.5 metres and algae counts were zero in the treated water. No taste or odour was detectable in the treated water. Results were made available to the Victorian Department of Health and, in view of the treatment process utilised, it was agreed to continue operations as normal with an increase in testing. Tests were then taken on the Monday and Tuesday both by the Board, the Health Department and State Water Laboratories which confirmed levels were still acceptable.


The Secretary and Consulting Engineer met with senior staff of the Health Department on Thursday December 5 and it was agreed that dosing with copper sulfate was not justified at that stage due to the concern about releasing large quantities of hepato-toxins. (No analysis of the type of toxin present was available at this time, although general opinion by several experts was that Anabaena commonly releases a vast predominance of neuro toxins) . As an additional precaution a powdered activated carbon dosing system involving a 2 kL tank, air compressor (for mixing) and dosing lines using gatevalves to control flow was installed. A dosage rate of 25 mg/ L was selected on the basis of overseas research which indicated that over 90% hepato-toxin removal should be achieved. The PAC was introduced into the first flocculation chamber allowing approximately 15 minutes contact prior to removal by the DAF process. Still no taste or odour was detectable in the treated water. The Health Department offered to formulate a press release advising people of the situation in view of the current media coverage of the Darling River bloom. It was agreed that with the introduction of powder activated carbon (PAC) the system was working very effectively and safely. After the meeting the results of samples taken that morning showed a marked increase in the algae count at the offtake to 8000 cells/ mL and this information was passed onto the Health Department. Concern was expressed by all parties that the trend to increased numbers would continue. Utilisation of the PAC gave both Authorities confidence that the situation was still acceptable from the public health point of view. Further tests were taken early on December 6, which confirmed that the situation was deteriorating. Cell counts at 9.5 m. depth were in the vicinity of 30 000 cells/ mL and the reservoir had turned a very intense pastel green colour. With the bloom intensifying and concern about maintaining supplies over the busy holiday season, it was decided at 11 a.m. to close down supply and treat the reservoir with copper sulfate despite confidence that the treatment plant was removing toxins. It was clear that there was a great deal of uncertainty amongst the experts regarding effects of algal blooms and until a conclusive test for toxin residuals in treated water is available the possibility of being closed down is always present. The decision to treat with an algicide on the December 6 was necessary to allow sufficient time for biodegradation of any toxins released before demands increased with the tourist season. A dosage rate of 2.0 mg/ L was recommended to the Board and 5000 kg. was spread that afternoon. When the system ceased operating approximately 39 ML was held in the reserve storage, which was at approximately 82% of full capacity.

COMMUNITY NOTIF1CATION Immediately the decision was taken all staff were briefed and a plan implemented to commence the process of consumer notification. This was achieved in three major ways: (1) All areas supplied in townships were broken up on maps and cas'ual staff were sent out for a letter drop to approximately 8000 properties. (2) All rural properties (400) were contacted by phone where possible. (3) Special interest groups were notified by phone (approximately 200 properties). Phone numbers were made available at the Board, the Shire and the Health Department for the weekend. Special mention should be made of the Shire of Phillip Island who recalled 15 staff to assist immediately. The neighbouring Wonthaggi Inverloch Water Board also provided staff to assist in planning the public notification as well as a work boat, and copper sulfate to carry out the dosing, Everything went very well on December 6 except that substantial delays in finalising the proposed Consumer Notice and Press Release were encountered mainly as a result of poor communication between the relevant Government Departments and the Board. Response by the public was generally outstanding, with water consumption levels down by &pproximately 50%. Public awareness was very high due to the success of the letter drop carried out by casual staff.

TOXICITY TESTING On Monday December 9, discussions were held with Dr G. Jones of CSIRO, Griffith, NSW - a prominent expert in the field of algal toxicity testing , Dr Jones advised that his tests confirmed that the toxins found in surface scums on the reservoir were predominately neuro-toxins and not the more stable and long lasting hepato-toxins. In fact the hepato-toxins were measured at 0.05µg / mg at the peak of the bloom, a level considered insignificant by Dr Jones. Dr Jones advised that neuro-toxins are very unstable in ultra-violet light and have a life of only 3-4 hours in sunlight. Consequently, the Secretary/ Manager met with the Health Department on Monday December 9, and it was agreed to commence recharging the system during daylight hours on Wednesday December 11, via the uncovered 2.3 ML Almurta Basin. PAC dosing was to be kept in place until after the weekend. Water restrictions could be removed on the Friday one week after the algicide treatment.

RECOMMENDAl'IONS The events during the bloom raise a number of points worthy of note and, hopefully, further research and action; (a) Clearly the most important point involves the development of a comprehensive test for type and level of toxins present. This is essential to enable authorities to maintain potable water supplies. Until an analytical method is available which can identify the presence of toxins in both raw and treated water then a huge amount of capital will be wasted on water treatment plants which may be shut down based on the conservative conscience of a Health Department. The conservative attitude of the Health Department is understandable until more quantitative evidence is available on the actual danger a bloom may have to community health. (b) There is need for improved level of liaison between Authorities and the media. The apparent heightened degree of awareness of algal problems this year appears proportionate to the media's involvement and ability to make a story. We'note with some irony the media's reluctance to report on the situation once the allclear was given. Perhaps the Water Industry should consider the advantages of providing a media unit offering a centralised voice ' during times of emergency. (c) Improved communication between the Department of Health and Department of Water Resources in relation to preparation of public notices would have been of great assistance. (d) For many years authorities have been aiming to cover all service reservoirs to prevent bacteriological contamination. Authorities may have to consider leaving service reservoirs prior to any consumers uncovered to allow U.V. penetration if the risk of neuro-toxin formation is high in their syscem. (e) Increased research on the concept of integrated management is desirable involving; • catchment controls and land use practices • reservoir management by biological, chemical or physical means such as low energy mixing, etc. • improved treatment methods e.g. PAC, GAC (This will require development of the analytical improvements outlined above) (f) In the absence of analytical testing, a review of design standards for in-system storage is necessary. The common practice of providing a few days balancing and emergency storage is not appropriate if an authority is confronted by a severe bloom involving hepato-toxins with a biodegradation period of up to 2 to 3 weeks. (g) All Authorities should be encouraged to formulate a plan to implement the notification process used during such emergencies. (h) Authorities should be encouraged to investigate the need for storage of sufficient quantities of urgently needed chemicals such as copper sulfate or PAC.

COSTS It is of note that the total cost to the Board of the bloom and shutdown was approximately $40 000. The cost to the community in terms of lost tourism and confidence will never be known .

WATER April 1992

33


TECHNOLOGY

Measured Infiltration Rates Indicate Significant Savings in Design A Case Study on the Mornington Peninsula by A. M. NORRISH and C R. WEEKS ABSTRACT The sewerage systems of the Mornington Peninsula have been designed by consulting engineers Gutteridge, Haskins & Davey Pty Ltd (GHD) using empirical methods. These methods have been based on historical data and supplemented with catchment gaugings during the 1960/ ?0s. This paper describes recent work undertaken to validate the design technique and assess the performance of four · sewered catchments in Seaford and Mt Eliza, Victoria.

Tony Norrish is a senior civil engineer with Consulting Engineers, Gutteridge Haskins & Davey. He has 11 years water and wastewater experience in the fields of design, construction, operation, system management, and infiltration and inflow reduction programs including a Masters' Study at Monash University.

INTRODUCTION Reviews of sewerage system performance are essential to enable empirical methods to be progressively updated to reflect improvements in materials and design and construction practices for new schemes. The continuance of existing design and construction practices can also be assessed. This paper describes recent work to check an empirical method for the design of contemporary sewerage systems and compares the performance of the system to the original design basis. The flow characteristics that were assessed by the investigation include: • permanent infiltration allowances; • domestic flow; • dry weather flow peaking factors; • unit dry weather flow characteristics; and • wet weather flow characteristics. The use of unduly conservative design methods will result in greater capital cost to the constructing authority. This will be passed on to the consumers in the form of higher rates. Four sewerage catchments on the Mornington Peninsula were selected for investigation. The catchments were considered to be representative of new systems with regard to materials technology and design and construction practices. The terms used in this paper are defined in Appendix A.

Clive Weeks is a Principal of Gutteridge Haskins & Davey. He has over 20 years experience in the water industry and is currently responsible/or the services GHD provides to Melbourne Water.

of sewers by the clerk of works and house connection drain construction by the plumbing inspector. Design Criteria Flow Estimation. The catchments investigated were designed using the following empirical relationship:

PWWF

=

D.(P, + PJr + A.(PJ + SJ) 86,400 + Qi + l:Qp

[ ] 3

where,

SEWER DESIGN CRITERIA Flow Components A wide variety of terms defining the components of wastewater

flow are found in literature. The components of flow defined for the purposes of the investigation are: • sanitary flow (SF) • baseflow (BF) • industrial flow (IF) • stormwater infiltration (PI). The major components can be further subdivided as follows : • Sanitary Flow is the sum of domestic sewage and commercial sewage: [l] SF = DF + CF • Baseflow comprises permanent or groundwater infiltration and leakage from plumbing fixtures: [2] BF = PI + leakage Wastewater flow components are shown graphically in Figure 1. Design Strategy

The sewers in the study area are based on the concept of a flexible sewer system modified to suit local conditions by GHD. The flexible sewer system is capable of deflection to accommodate differential ground settlement and/ or superimposed loads without structural failure or loss of watertightness. The design strategy to achieve a flexible sewer system, and hence control of infiltration, includes tight standards on pipe materials, pipe joints, flexible pipe bedding, manhole construction, sewer laying details, air testing, inspection

34

WATER April 1992

o.

Average ultimate domestic sewage flow (L/c/d) Equivalent residential population Equivalent commercial population pc r Ratio of maximum to average DWF from residential and commercial areas A Catchment area (Ha) PI Permanent Infiltration (L/Ha/ d) SI Stormwater Infiltration (L/Ha/d) Q. Industrial flow (Lis) l:QP Sum of pumped discharges (Lis) Domestic Flow. The design domestic flow was 230 L/c/d. Commercial Flow. The contributions from commercial and nonresidential establishments were assessed as equivalent population (EP). Industrial Flow. There were no industrial flows in the catchments. Peaking Factor. The peaking factor, r, is used to derive peak DWF from the average DWF. The peaking factors applicable to the catchments investigated were determined using the following relationship:

P,

r

= ( 2.25 +

15p~41!Q6

)116

(4)

where: = Peaking factor r P = Equivalent Residential Population Permanent and Permanent Infiltration . The design values adopted for permanent and stormwater infiltration are shown in Tobie 1.


Table 1 Design Infiltration Values Permanent Infillration (L/ Ha/ d)

Stormwater Infiltration

(L/Ha/ d)

Catchment

Seaford (sands) Mt Eli za (clays)

Above

Below

Above

Below

GWT

GWT

GWT

GWT

I 100

5 600

17 000

II 000

900

NIA

23 000

NIA

TIME

Fig. 1 -

FIELD INVESTIGATION The Study Area Four catchments on the Mornington Peninsula were investigated. Three catchments were located in Seaford whilst the fourth was located in Mt Eliza. Each catchment discharges to a wet well pump station. The Seaford area is relatively flat with predominantly sandy soils and high groundwater table. The Mt Eliza area has steep slopes with clayey soils. Each catchment is predominantly residential. Sewers are constructed of rubber-ring jointed vitrified clay pipe, and house connection drains are typically constructed of solvent w'e!ded UPVC pipe. The age of the oldest sewers is about 14 years. Catchment characteristics are given in Table 2. Design flows have been calculated using current populations. Table 2 Catchment Characteristics Area

Location

Catchment

321 2 321 7 32 18 3223

Seaford Sea ford Seaford Mt Eliza

(Ha)

Equivalent Population

93. 2 49 .2 38.2 158.9

2630 1443 1415 1792

Monitoring Flow and rainfall monitoring was undertaken over a nine week period from October to December 1988. Flows at pump stations were derived using pump event loggers which were installed at the main pump station in each catchment. Rainfall data were obtained using tipping bucket rain gauges and electronic data loggers . Analysis The flow analysis was undertaken by: • dry weather flow analysis - to determine domestic flows and peaking factors for each catchment; • baseflow analysis - to determine permanent infiltration and leakage: • wet weather flow analysis - to determine wet weather infiltration.

RESULTS Baseflow The baseflows in all catchments are on average less than 200Jo of the design rates. A comparison of measured and design baseflows is presented in Table 3. Table 3 Comparison of Measured and Design Baseflow Baseflow (L/ Ha/ d) Pump Station

PS PS PS PS

3212 3217 3218 3223

Measured

Design

765

4760 5400 5400 1100

905 Negligible

* Data riot reliable due to leakage from plumbing fixtures from a school in the catchment

Particular features which are considered to have enabled these low rates to be achieved are: • the use of high quality rubber-ring jointed vitrified clay pipes; • quality control of materials; • detailed supervision and inspections during construction and prior to acceptance of the sewer; • air testing of all sewers during construction and at the completion of construction; and

\¼stewater hydrograph components

• specific design strategy for flexible sewer systems. It is evident that baseflow rates vary with the differing soil types in the catchment. The measured baseflows for PS 3212, 3218 and 3223 are less than one sixth of the design rates. These results indicate the original basis for estimating permanent infiltration to be unduly conservative. It is possible that the design rates for permanent infiltration could be reduced by more than 500Jo. However, significant reduction in design values should only be implemented after the effects of aging on watertightness have been determined through further monitoring of similar but older systems. Domestic Flow The measured average domestic flow was 160 L/ c/ d, that is about 700Jo of the current design rate of 230 L/ c/ d used for this system. This is considerably less than allowances reported in literature and those in use by other Australian authorities. Typical weekday and weekend dry weather flow hydrographs for PS 3223 are shown in Figure 2.

10,-------------------------,

,./........._____ WEBXBNDHYDllOORAPH

TIME

Fig. 2 -

PS 3223 -

,

Dry weather flow hydrograph

Wet Weather Flow The original design basis for estimating peak stormwater infiltration for the study area is based on a storm with a five year recurrence interval. A four year storm (Seaford area) resulted in negligible stormwater infiltration at PS 3217 and low rates at PS 3212 and PS 3218. The latter flows were about one sixth of the deiign rates. The estimated peak rate of stormwater infiltration of 24 500 L/Ha/ d occurred at PS 3223 (Mt Eliza). This storm had an estimated average recurrence interval greater than 20 years. As the measured rate of SI is only marginally greater than the design rate it is considered that actual SI for a design storm (5 year ARI) would be significantly lower. (The average rainfall intensities for a 5 and 20 year storm of one hour duration are 23 and 31 mm/ hr respectively). The return ratio for the catchments ranged from O.1 to l. 3 OJo, and this is indicative of good performance. Older systems with good performance have been found to have return ratios of about 40Jo. Based on the results given in Table 4, the Seaford data indicates that actual stormwater infiltration is less than 200Jo of that adopted for design. The Mt Eliza data indicates that for a 5 year storm event the actual stormwater infiltration is less than the design rate. Thus reduction in the design rates is justified, however, there is insufficient data to allow the recommendation of particular values. In addition, the effects of aging and subsequent deterioration of the system on watertightness and therefore storm water infiltration require further investigation. Comparison With Other Design Data The measured and design flows for each catchment in the study area are presented in Table 5 and compared to those calculated using Melbourne Water design data for the metropolis . Measured flows are typically less than 500Jo of design flows for Seaford catchments. WATER Apri l 1992

35


Resultant Savings Reduced sewage flows result in savings in annual operating costs, and savings in capital cost of future infrastructure are available if lower flows are adopted as design criteria. Existing sewerage systems may also have a reserve capacity available for redevelopment of existing areas to higher densities, thus deferring the need to provide expensive relief sewers in established areas. The reduced wastewater flow rates that have been achieved in these catchments translate into immediate savings in operational costs by reductions in wastewater volumes that must be pumped, treated and disposed of. For the Frankston sewerage system (population 41 000) these savings are estimated to approximate $100 000 per annum. Extrapolated over the whole of the sewered population on the Mornington Peninsula (approx . 220 000) savings of the order of $500 000 pa are indicated. If design wet weather flows were reduced to half and the entire system were reconstructed, capital cost savings in sewer construction of the order of $10 million are indicated. Further savings in pumping stations, pumping equipment, pressure mains and treatment plant hydraulic structures would result. Overall, capital cost savings of the order of 20% are believed -achievable. Table 4 Comparison of Measured and Design Stormwater Infiltration Stormwater Infiltration Pump

Station

PS PS PS PS

32 12 321 7 3218 3223

Storm ARI (YR)

4

4 4 >20t

(L/Ha/ d)

Measured

Design*

2, 186 Negligible 2,010 24,500t

12, 100 11,300 11,300 23,000

PWWF (LIS) Pump

PS PS PS PS

3212 3217 3218 3223

• •

ACKNOWLEDGMENTS The author wishes to thank Melbourne Water for permission to publish this paper.

REFERENCES

• Based on a 5 year design storm . t Estimated data. Table 5 Comparison with Design Flows

Station

The measured domestic flows ranged between 130 and 183 L/c/d and averaged 160 L/c/d compared to a'tlesign rate of 230 L/c/d; measured stormwater infiltration is less than the design rates. However there was only a single storm, with an average recurrence interval of 4 years, that could be used to evaluate the performance of the systems for comparison with design; a reduction in the current design rates in similar catchments for permanent infiltration, domestic flow and stormwater infiltration is justified. Reductions of 50% in the design rates for permanent infiltration are feasible whilst lesser reductions could be implemented for domestic flow and stormwater infiltration. However, the effects of system deterioration with age, and the relationship between the 5 year design storm and peak stormwater infiltration require further investigation; the design and construction strategy adopted for the purpose of minimising the entry of permanent infiltration and stormwater infiltration into the sewer system have been effective as demonstrated by the measured flows; the performance of the catchments examined is comparable with or better than the published results of other sewerage systems with good performance; further investigations are required to evaluate the performance of other contemporary systems with catchments of similar and differing characteristics so that lower design rates can be adopted with confidence and applied to a wider range of catchments; and a reduction in the design parameters will enable a decrease in the required capacity of new sewerage systems, and this will enable the systems to be constructed at a lower capital cost which would benefit the · community in the form of lower rates. Significant savings in pumping, conveying and treating of sewage also results.

Measured*

Designt

MW§

33 9 9 53*

74 20 18 57

92 54 45 71

Fella, C. & Claringbould, R.J. (1983) 'Estimation of Sewage Flows' Post Graduate Course in Public Health Engineering, University of Melbourne. OHO (1974) 'Hydraulic Design of Sewerage Reticulation' . Internal Technical Bulletin . Unpublished. Longstaff, A.G. (1984) 'A Flexib le Approach to "Design and Upgrading of Sewer Systems' . Unpublished. , Murray, J.B. (1981) 'Comparison of Design Infiltration Rates with Rates Determined from Measured Sewage Flows'. AWWA 9th Federal Convention, 18/ 16-17. Murray, J.B. (1986) 'Infiltration Rates for Separate Sewage Collection Systems'. Int. Assoc. on Water Poll. Res. and Control, Proc. of the 13th Biennial Conj of, Rio de Janeiro, Brazil., V19, N2-3, pp 589-ji0l. MWSDB (1979) 'Design of Separate Sewerage Systems'. Norrish A.M. (1991) 'An Investigat ion of Flow Components in Separate Sewerage Systems'. Minor Thesis - Department of Civil Engineering, Monash University.

Flows based on 4 year storms for all sites except PS 3223. Measured flows derived by summing peak flow components. t Design flows based on a 5 year storm. t PWWF from a 20 year storm . § Design flows based on parameters adopted by Melbourne Water for a 5 year ARI storm in the metropolis.

MURRAY-DARLING BASIN GROUNDWATER WORKSHOP 3

SUMMARY AND CONCLUSION

This is the third in a series of biennial workshops to present and discuss recent hydrogeology work carried out in the MurrayDarling Basin. The aim is for greater co-ordination of research effort and the distillation of priorities for future work.

The use of empirical methods for the design of separate sewerage systems is widespread, with the various design parameters developed from past performance. Significant improvements to achieve a greater level of watertightness in contemporary sewer systems have been implemented by such measures as improved materials and design and construction practices. These improvements result in sewerage systems of different performance from those which provided the basis of established empirical design methods. Accordingly, the validity of design parameters and their application to new sewerage systems must be reassessed. The results of this investigation of four catchments on the Mornington Peninsula identify the conservative basis of the previous design techniques and confirm the need to undertake further monitoring over a larger range of catchments to update the basic design parameters relating to permanent infiltration, domestic and commercial flow, stormwater infiltration and the peaking factors. The main conclusions from the investigation are • measured rates.of permanent infiltration for catchments with and without sewers located below the groundwater table are much less than design rates. Two catchments with high groundwater water tables recorded baseflows of 765 and 905 L/Ha/d compared to design rates of 4760 and 5400 L/Ha/d respectively; • measured domestic flows are considerably less than design rates.

36

WATER April 1992

Chaffey Theatre, Renmark October 27-29, 1991

CALL FOR PAPERS • salt disposal • recharge control • salinity mitigation (drainage and interception) • modelling • contamination

• environmental consequences of groundwater salinity • recent hydrogeological investigations • future policy directions

For further information, contact: Steve Barnett SA Dept of Mines and Energy PO Box 151 EASTWOOD SA 5063 Phone: (08) 274 7583 Bob Newman EWS Dept GPO Box 1751 ADELAIDE SA 5001 Phone: (08) 226 2510

Glen Walker CSIRO Div of Water Resources Private Bag 2 GLEN OSMOND SA 5064 Phone: (08) 274 9385


BLUE-GREEN ALGAE Seminar Report continued from page 30 Mary Balfour (PR Consultant): Community Relations • emphasised the need for careful planning of communication with the community. • illustrated many pitfalls. • explained the difference between issues management and crises management. lnportant things to emerge from the seminar: • algae have always and always will bloom. • there is justification for and benefit in catchment management but it will not solve algal problems. • emphasis on reservoir management should be on manipulation rather than CuSO 4 dosing. • CuSO 4 is still a useful quick-fix, but needs very frequent algal monitoring. • when algal bloom has been killed by CuSO4 , the toxins are released into the water, and must be degraded either by UV or oxidation. • a water treatment plant is necessary to remove algae - they can do this very well but will not remove any toxins and taste and odour compounds that have been released. • it appears likely that if you remove taste and odour you will also remove toxins. Nevertheless, test methods for toxins in treated water are needed. • it is difficult to convey information on toxicity to the community but it can be done with careful planning. • monitoring and recording of algae is currently very· poor. • Prof. Tyler recommended the following book on Blue-Greens Peter Fay - The Blue Greens - Arnold Series in Basic Biology

CONCLUSIONS Firstly catchment management and land care practices can provide quite rapid benefits in terms of control of nutrient runoff. Although in large reservoirs, catchment management will take some time to

have an effect on the extent of algal growth it is necessary to institute programs as part of an overall algal control strategy. There are a number of effective reservoir management techniques including destratification, use of multiple draw-offs and the dosing of copper sulfate. The latter is only appropriate where immediate drinking water quality concerns outweigh environmental concerns for the particular storage. However, these source control techniques cannot fully solve serious algal problems. It is necessary to have an effective water treatment plant as part of a full solution. Conventional water treatment plants vary in their ability to cope with algal blooms and in all cases bluegreen algal toxins and taste and odour compounds are only poorly removed by conventional processes. The removal of algal cells is virtually 100% if the plant includes properly run filters but clarifier-only plants will suffer severely during algal blooms. Filter clogging by algae can be serious as it greatly downgrades water treatment plant capacity. The best current technology for dealing with algal tastes and odours is the use of activated carbon either in granular or powdered form. Some oxidants can be reasonably effective in reducing taste, odour and toxins. The most effective oxidant is ozone followed by chlorine dioxide. Potassium permanganate can deal with some taste and odours but not with taste and odour due to blue-green algae. Powdered activated carbon added to a clarifier or even a direct filtration plant is a convenient method bearing in mind that algal blooms are intermittent and the high capital cost of granular carbon contactors may not be justified. In whichever way it is used, the cost increase of activated carbon treatment is high. In future we are likely to see additional front-end processes in water treatment including biological activated carbon and ozonation. These processes offer the ability to reduce dissolved organic carbon in the treated water as well as dealing with man-made organics and algal metabolites. Post-filter GAC contractors, while still popular, do suffer from the problem of increased bacterial counts entering the disinfection stage and reticulation .

15m flDfRAl (ONUlNllON GOLD COAST APRIL 18-23, 1993. 0

CONVENTION UPDATE Keynote Speakers

Poster Papers

• Professor George Tchobanoglous from the University of California and Dr Rufus Chaney from the United States' Department of Agriculture are two of the keynote speakers confirmed for the Convention. • Professor Tchobanoglous is perhaps best known for his book "Wastewater Engineering - Treatment, Disposal and Reuse". He will be addressing the conundrum of sewage treatment standards and effluent disposal options. • Dr Chaney is one of the world leaders in sludge management and has been keynote speaker at a number of international conferences. His address will provide the latest information on many aspects of sludge management.

One of the major emphases of the 1993 convention will be quality poster presentations with additional interaction between presenters and audience for selected topics. The organising committee recognise that posters encourage interaction and discussion in a manner often not possible in a platform presentation. Presenters are encouraged to prepare papers specifically for the poster sessions. The committee is currently deciding on a suitable format for publication.

DEADLINES

Receipt of Abstracts Notification of Acceptances Receipt of Full Text

30 April 1992 30 June 1992 30 November 1992

INQUIRIES

All correspondence, including abstracts, should be addressed to: Sonja van den Ende, Conference Secretariat GPO Box 2600 BRISBANE QLD, AUSTRALIA 4001 Phone: (07) 234 1993, Fax: (07) 224 7999

WATER Apri l 1992

37


TECHNOLOGY

Erosion Control by Macrophyte Planting by D. HUTCHISON and J. WCKE SUMMARY The Werribee Treatment Complex of Melbourne Water processes the majority of its wastewater inflow in huge lagoons bordering Port Phillip Bay. Each lagoon consists of a series of about ten ponds, ranging from anaerobic to aerobic, separated by levee banks. The length of bank for a typical lagoon complex can total some 30 km, and conventional beaching costs of the order of one to one and a half million dollars. Trials were conducted aimed at reducing the cost of conventional rock and filter beaching by planting semi-aquatic macrophyte species into the beaching material. After some failures, success was achieved using an endemic species, River Clubrush (Schoenoplectus validus), at an initial spacing of 0.5 m up to 1 m. Application of this technique could allow a lower grade of rock beaching to be used, which could approximately halve the cost, with extra benefits in the area of aesthetics and biological environment.

INTRODUCTION The Werribee Treatment Complex treats some 500 ML per day of mixed domestic and industrial wastewater from the city of Melbourne (Bremner & Chiffings, 1991). It comprises an area of 10 850 ha of mainly flat land, embodying three systems of treatment: land filtration, grass filtration and lagoons (which were first introduced in 1937). The lagoons now handle over 60% of the inflow, and have been steadily expanded in area over the years, with further expansion and technical improvements (such as forced aeration) being instituted to cope with the ever increasing flows. Whereas the early lagoons were small, the more recent large lagoons have been subdivided into ponds with very high aspect ratios. The current largest pond is 2.2 km long and 0.12 km wide, and is accompanied by similar ponds, as can be seen in Figure 1. They lie in a southwesterly direction along the coast line.

Fig. 1 -

Werribee Treatment Lagoons

The majority of these ponds are aerobic and in order to maximise oxygen transfer from tl}e air by wind and wave action they are relatively shallow, being on average 2 m deep. The winds in the locality are prevalently westerly, but significant winds arise in all quarters. With such long fetches over shallow water, strong winds can generate sizeable waves, which are compounded

This paper has been prepared by the Editor, based on technical reports and discussions with the authors.

38

WATER Apr il 1992

David Hutchison is Engineer; Research & Development at Melbourne Water's Werribee Treatment Complex The Section carries out a variety of wastewater treatment investigations, provides logistics for other researchers and is responsible for wildlife matters particularly works associated with the Farm's Conservation Management Plan. A Civil Engineer by training, David previously worked with the Rural Water Commission. Judith Locke, Technical Officer, Research in the Research & Development Section, is one of two project officers dealing with conservation issues. Before joining Melbourne Water, Judy worked at Melbourne University's field station at Mount Derrimut as an animal technologist. She is currently studying horticulture at VCAH (Burnley).

.

by the refraction from the linear banks. For design purposes a wave height of 0.5 m was specified. Optimisation of the design of the levees, taking into account land layout and beaching costs, resulted in the specification of a batter slope of 2.5 to 1. The conventional method of erosion protection involves an upper layer of graded beaching rocks, of median size 200 mm, and depth of 300 mm, laid down over a filter medium to protect the subsoil from washaway by the return flows of the broken waves beneath the rock layer. The options for the filter layer are either a geo-textile membrane, or a sufficient layer of sand/ gravel mix with low permeability and high cohesion. Such protection of a levee bank is estimated to cost of the order of $70 per metre, expressed in 1991 dollars. Since the total length of beaching for a typical lagoon complex is currently 30 000 metres, and further lagoons are planned for the future, there was a significant window of opportunity for a cheaper system to be devised. When the lagoon expansion program commenced in the early '80s a literature search revealed the use of macrophyte plantings in the Netherlands, to protect the polder banks. Those banks, however, were constructed with a much shallower batter, with more variable water depths. The experience of the (then) State Rivers and Water Supply Commission using Phragmites in the lakes of north Victoria was also drawn upon. The considered decision was made to construct the beaches with graded rock beaching but without the filter layer, based on the estimate that the underlying clay of the Werribee area should be sufficiently stable to resist wash-away to any gross amount, and to rely on corrective maintenance to remedy any erosion if and when it occurred. At the same time trials of macrophyte planting were commenced, on older ponds, from which the rock beaching had been removed . These first trials were aborted by the damage caused by a violent storm, and the project fell into limbo. However, within a couple of years of operation of the first new lagoon the underlying clay proved to be not as stable as estimated, and the cost of replacement of rock beaching began to escalate. The planting project was therefore revitalised in 1987, with a Technical Officer with horticultural training working with the Development Engineer.


TRIAL 2, 1988

AIMS OF THE PROJECT Apart from the stated aim of stabilising the banks by a biological system which should be cheaper than the engineering solution, .there was a further aim to improve the aesthetic appearance of the huge lagoons, and to provide a better habitat for the thousands of water birds which live in the Werribee treatment complex. (Bremner & Chiffings, 1991). For this purpose a mix of species was preferred.

CHOICE OF SPECIES Two species of semi-aquatic plants were indigenous to the area: Phragmites australis (Common Reed) and Schoenoplectus validus (River Clubrush), and it was decided to concentrate on these in the first instance ... Phragmites australis The mature plant resembles a small bamboo and propagates in nature by horizontal extension of the rhizome. Seeds, however, are difficult to collect and establish. Schoenoplectus validus River Clubrush has spiked foliage, can propagate vegetatively by rhizomes, but is also fairly easy to grow from seed. An alternative plant, Typha (Cumbungi), was eliminated as being too rampant, and likely to spread throughout drains and shallow ponds.

Clubrush:

In autumn (April 1988) Clubrush seed was collected from plants growing around the perimeter of Lake Borrie, and propagated in veneer tubes in Melbourne Water's then Southern Region Nursery. Planting commenced in the following Spring, (October) by placing each tube under a rock at 1 m spacing. However, this was less than successful, because the seedlings were too small. Allowing the tube stock to acclimatise by submerging them in their carry-boxes in a small aerobic pond for four weeks proved more successful. Some damage was caused by swans grazing the tops of the new plants, but the majority of the plants were established within six months. Common Reed: In mid-winter, 1988, a dense stand of reeds on the banks of the Werribee River was dug out by front-end loader, and a stock of rhizome cuttings prepared. They were planted along the short ends of the lagoons, where erosion was more evident. However, only 30% of the plants survived. The decision was made to concentrate on River Clubrush, but to persevere with some interplanting and replanting of Common Reed in order to achieve some visual variety and biological diversity.

THE RESULTS EARLY TRIALS, 1983 The first trial was conducted by removing lengths of rock beaching from the bank of an old small lagoon and planting various macrophytes including Clubrush seedlings directly into the underlying clay. It was planned that the roots would bind the soil, and once established, the plants would act as a buffer against wave turbulence. Some weeks after planting out, winds of over 50 km/ h generated such waves that the plants were washed right out. The rock beaching was rapidly replaced, and as mentioned above, the project allowed to lapse.

TRIAL 1, 1987 The project was restarted two years after the commissioning of the new 115E lagoon, the banks of which were showing signs of severe erosion. The aim of the new trial was to determine better conditions for establishment. Immature plants were planted through the existing rock beaching into th·e clay, or alternatively, purely hydroponically by lifting a suitable rock, placing the plant beneath it, and replacing the rock to hold it in place (Figure 2). Time of the year and initial spacing were also variables to be considered.

Two growing seasons after the 1988 plantings, almost the whole perimeter of the huge lagoon was protected by the macrophytes, as evidenced by Figures 1, 3 and 4. Clubrush

This species proved very successful. It formed a dense stand along the water's edge, without intruding over the levee banks . At 0.5 m spacing it formed a dense wall within one season. At 1.0 m, it gave reasonable protection in one season, and a dense wall in two seasons. However, at 2.0 m spacing it would require two seasons to provide adequate protection, which would not be a tolerable risk. Common Reed: In 1989/90, further trials of techniques for rhizome transplant were investigated, but to date, no fully successful method for massive

Fig. 3 - Clubrush at 1.0 m spacing after 18 months growth

Fig. 2 -

Hydroponic planting of clubrush

During October 1987, a number of rhizomes of Phragmites were dug out of the banks of a drainage channel and from the final aerobic lake, Lake Borrie. One hundred rhizomes were planted at intervals of 0.5 m, 50 at I m, and 25 at 2 m. While 750'/o were planted into soil, 250'/o were embedded under a rock. After one season, those at 0.5 m spacing had become a continuous stand, those at I m had almost joined. Hydroponic planting was significantly more successful than planting in soil, and much easier. No seeding was noted.

40

WATER Apri l 1992

transplanting has been developed, despite the success of the initial trial of 100 plants. In 1989, replanting was performed from stock collected from a drain where the plants were growing in water rather than on a dry river bank. Cuttings were transferred to a shallow pond for six weeks, where they grew new shoots, but these proved to be too fragile to withstand transplant. Direct transplant of selected cuttings from the drain to a bank showed a minor increase in survival rate. Even the established plants are sparse and less vigorous than the Clubrush, but they do provide a pleasing visual variety. River Clubrush is preferable to Common Reed because: • Good seed supply is available, and it can be propagated in normal nursery conditions. • It has an excellent survival rate and is a vigorous grower, and requires no further management. • It prefers the water's edge to the top of the bank • It does not die down in winter. However, it may require a stable water level. This is provided in the case of the lagoons which do not vary more than ± 0.2 m. Also, it has not been proven that it can self-regenerate in-situ if the lagoon has to be drained for a lengthy period.


Fig. 4 -

Clubrush, fully established

EROSION CONTROL Since the establishment of the macrophytes, the amount of maintenance required on the rock beaching has been minimal. The rushes reduce wave ride-up during storms, and damp down the normal lapping of waves along the water edge. COST COMPARISON An estimate has been made of the alternatives, extended to 1991 costs. Rock beaching only: Graded beaching of sufficient size $63 per metre run Filter membrane, e.g geotextile $7 per metre run. Rock beaching plus macrophytes Graded beaching of lower quality $40 per metre run Macrophytes at 0.5m spacing $3 per metre. The cost of macrophytes is a total comprising gathering seed (or rhizomes), propagation in nursery conditions, acclimatisation, then planting out by manual emplacement under convenient rocks. CONCLUSIONS The macrophyte-screened beaches have withstood severe windstorms so successfully that for future lagoons it is an option to reduce the specification of the rock beaching material even further, and thus to save significant costs. The visual aspect of the lagoons is improved, along with the environment fot bird life. It is now feasible to consider planting of other species to enhance the appearance of the levees. Trials have demonstrated that as well as River Clubrush and Swamp Clubrush, some larger species such as She-oak and particularly Swamp Paperbark can be planted on the intermediate banks. Larger trees, however, should not be planted on the overall perimeter banks, since if their roots die, they could lead to undermining of the bank. ACKNOWLEDGEMENTS The authors acknowledge the co-operation and support of G. Addison (Farm Manager) and T. Scott (Engineer Process & Operations) during the various trials. Also we thank the field staff in the R & D Group for their labours in establishing the plantings. REFERENCE Bremner & Chiffings, 1991. The Werribee Treatment Complex - An Environmental Perspective. ff11ter 19, 3. June 1991.

AUSTIIALIAN HADE

ACCURACY with RELIABILITY

DRY: Acromet 1000 Dry Bulk Materials Feeders LIQUID: Acromet 3000 Metering Pumps GAS: Advance Chlorination Systems CHEMICAL FEEDERS FOR ALL INDUSTRIAL & MUNICIPAL APPLICATIONS

BUY AUSTRALIAN • BE NATIONALISTIC BUY ACROMET • FOR TOTAL QUALITY

ACRCIM-a, 1 1

"'---,sa2~

ACROMET [AUST.) PTY LTD MELBOURNE Ph: (03) 544 7333 Fax: (03) 543 6706 SYDNEY Ph: (02) 6821488 Fax: (02) 682 4580 A.C.N. 005 550 514 Service available in all states

WATER April 1992

i 41

Profile for australianwater

Water Journal April 1992  

Water Journal April 1992