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The potential for water recycling in Australia — expanding our horizons
DESALINATION ELSEVIER
Desalination
106 (1996) 151-156
The potential for water recycling in Australia expanding our horizons J.M. Anderson Department
of Public Works and Services, 2-24 Rawson Place, Sydney, NSW 2000, Australia Fax +61 (2) 372-7522 Received
10 May 1995; Accepted
20 August
1995
Abstract This paper examines urban water use, wastewater flows, and storm water flows in the context of Australia’s water resources. The costs of water conservation and recycling are also examined together with some of the constraints. The potential for water recycling in Australia and the implications of future water conservation and recycling scenarios on Australia’s water resources and the environment are discussed. The development of new treatment systems will reduce quality constraints and open up new avenues for recycling. These may include large-scale potable reuse as well as decentralized treatment and local recycling options for both effluent and storm water. The implications of these alternatives for water recycling and the use of Australia’s water resources are discussed. Keywora!s:
Australia;
Water resources;
Water planning;
1. Introduction In proportion to its area, Australia has the lowest rainfall and runoff of all the continents. However, Australia’s population of just over 17 million is small in relation to the land mass of 8 million km2 and the available water resources. A high proportion of the population lives in urban centres located in high rainfall areas on the southern margins of the continent. This has allowed a rather liberal approach to water use. Most water is used on a “once-through” basis
001 l-9164/96/$15.00 PII
SO01
Water recycling;
before return to the natural water cycle by discharge or evaporation. There are strong perceptions in the community, born of concern for the environment, that wastewater and storm water should be recycled rather than discharged to rivers or the ocean. This paper examines the potential for water recycling in Australia in the context of Australia’s water resources and discusses the implications of alternative future recycling scenarios on Australia’s water resources and the environment.
Copyright 0 1996 Elsevier Science B.V. All rights reserved.
1-9164(96)00104-X
Water conservation
152
J.M. Anderson / Desalination IO6 (1996) 151-156
2. Water use in Australia 2.1. Available water resources The average annual run-off is approximately 50 mm or about 400 million ML. Run-off varies spatially and temporally across the continent. A quarter of the continent, Tasmania and the area north of the Tropic of Capricorn, account for more than 80% of the run-off. About 70% of it occurs as floods. Divertible surface water resources are approximately 118 million ML. More than half of the divertible surface water resources occurs in Tasmania and north of the Tropic of Capricorn, remote from the main centres of population. 2.2 Current water use Developed resources can supply approximately 22 million ML/y. Average annual water use is about 18 million ML, of which 18% is used for urban and industrial uses, 74% for irrigation and 8% for rural stock and domestic use. About 60% of this use occurs within the Murray-Darling Basin where the available surface water resources are almost fully committed to irrigation. Urban use, including commercial and industrial use, averages about 3.2 million ML/y. About half this amount, 1.6 million ML/y, is returned to the environment as wastewater flows after various forms of treatment. Urban storm water runoff varies widely both spatially and temporally according to climate. The average volume is about 3 million ML/y, about equal to the amount of water supplied for urban and industrial use. This water usually contains significant levels of pollutants. 2.3 Environmental
impact
In recent years, signs of serious environmental stress, manifested through declining water quality, have been observed in many Australian catchments. The rivers of the Murray-Darling Basin have deteriorated markedly since white settlement, principally because of agricultural land use
practices and diversion of water for irrigation, but also because of nutrients in urban wastewater and storm water discharges. Similar deterioration has occurred in the Hawkesbury-Nepean Basin which drains western Sydney, caused principally by urbanization. These two cases highlight the impact which occurs as water use approaches or exceeds the limits of sustainability in individual catchments. Compared to the Murray-Darling, the level of regulation in the Hawkesbury-Nepean is a relatively modest 30%. This highlights the constraints imposed on the use of water resources by the combined impact of water diversions and urban run-off. Better management of urban water use and of wastewater and storm water discharges will be needed if expected population growth is to be accommodated without further deterioration in the environment. 2.4. Trends in water consumption Growth is being offset to some degree by moves to better urban design and water conservation. l
l
l
l
l
There is a trend towards smaller urban allotments, dual-occupancy development and medium-density housing. The Commonwealth Better Cities Program is working towards the development of better urban design standards. Most authorities have moved to implement pay-for-use pricing for water. Water-efficient fittings and appliances are being introduced. The States are actively promoting water conservation through a “water wise” campaign.
Water conservation is the most cost effective way to provide system capacity to cater for growth. The effective unit cost to free up spare system capacity by retrofitting water-efficient appliances is A$O-12/kL to retrofit low flow shower roses and A$O-32/kL to retrofit 6L/3L dual- flush toilet cisterns [l]. It costs even less to install water efficient appliances in new develop-
ments. A number of Australian states have made dual-flush cisterns compulsory for ail new installations. 3. Wastewater and storm water recycling 3. I. Wastewater recycling
Wastewater recycling is still in its infancy in Australia. Less than 10% of water diverted for urban and industrial use is recycled. Recycling has most commonly taken the form of reuse of effluent after secondary biological treatment for irrigation of pasture or urban recreation areas and landscaping. Most wastewater recycling schemes proposed in NSW in recent years for broad acre irrigation of pasture or urban landscaping have involved effective unit costs in the range A$0.40-1 .OO/kL for recycled water. Anderson [23 and Gardiner [3] highlight some of the problems in achieving sustainable Iand i~igation systems. Annual irrigation demands can vary by plus or minus 40% from average depending on rainfall. Annual wastewater flows in a wet year can be up to 50% higher than average dry weather flow due to storm water inflows. In an irrigation system designed for average year conditions, there is a shortfall of reclaimed water for irrigation in a dry year and surplus reclaimed water in a wet year. The practice of designing systems for the wettest year in ten results in large irrigation deficiencies in dry years and still requires large expendi~es on effluent storage to minimize effluent discharges. This adds to recycling costs. In some cases, balanced irrigation design coupled with treatment to a higher standard may be preferable. 3.2. Storm water collection and recycling The most simple form of stormwater recycling is the collection of roof water in household rain tanks to use for both potable and non-potable purposes. It is widely used for rural dwellings. The cost of household rain tank systems has been estimated to be in the range A$2.00-4.00/kL de-
pending on climate and the level of reliab~li~ required. Lower costs may be achievable with community or neighbourhood storm water recycling systems if the right balance exists between storage, pipework and pumping costs. The collection and recycling of site run-off has been less common. It is now occurring more frequently on sites such as golf courses. Collection and recycling of urban run-off is relatively rare. The amount of storm water available for recycling and the amount which can be recycled varies widely depending on the climate and the variations in rainfalt from year to year. To be an effective substitute for conventional water supply, considerable storage is required to carry storm water over from wet to dry periods. Baker and Cartwright [4] have developed a proposal for storm water recycling at the Sydney Olympics site. Recycled water from this scheme would have an effective cost of A$I-60/kL. Salmon [S] has drawn attention to the adverse environmental impact on wate~ays of diverting storm water flows for recycling during periods of low flow. 3.3 Recycling for non-potable uses The first steps have been taken towards developing residential water recycling with the publication of the NSW Guidelines for Urban and Residential Use of Reclaimed Water [6]. The RWCC Guidelines allow use of reclaimed water for non-potable uses including toilet flushing, garden watering and car washing. The first major residential recycling system in Australia is currently under construction at Rouse Hill in Sydney [7]. Large residential reuse systems are under consideration at Melton and Werribee in Melbourne. A case study for residential recycling system at Werribee has been presented by Hunter et al. [8]. A drawback of non-potable recycling is the cost of establishing a second reticulation network and a second system of household pl~bing with safeguards against cross-connection. Smyth [9] and others have presented cost estimates for
154
J.M. Anderson /Desalination 106 (1996) 151-1.56
residential reuse systems. The costs translate to unit costs in the order of A$2.50-3.00/kL to supply recycled water. 3.4. Recychg
for potable uses
The technology already exists for potable recycling and has been proven in extensive trials in Denver [lo]. Planned potable recycling has taken place at Windhoek in Namibia since 1968 [ 111. Appropriate treatment processes have been described by Van Leeuwen 1121, Law [13] and Butler 1141. As time goes on, new developments in ~eatment technology will make potable recycling less costly than non-potable recycling. A debate has commenced about whether Australia should develop potable recycling. Potable recycling is not yet approved by Australian authorities, but a small amount of unplanned indirect potable reuse does occur [ 151. Law [ 13,161 has shown that indirect potable recycling would be similar in cost to non-potable recycling for the northwest development area in Sydney. A survey by Hamilton [ 151 found that a majority of the respondents were prepared to consider potable reuse if convinced of the need and the adequacy of safeguards. 3.5. Decentralized
treatment and recycling
The move 100 years ago from individual to community-wide water and sewerage systems was the most beneficial public health initiative in the history of Australia. There is now a movement for a return to individual household systems in the interests of conservation. Recycling system costs could be reduced by moving water reclamation plants closer to the point of reuse in order to reduce pipework costs. Pipework costs will be lower for individual systems. Community systems are likely to be better than individual systems in terms of performance, reliability and treatment costs. The practicalities of grey water recycling systems have been discussed by Lechte [ 171 and Jeppesen [ 181. Indicative costs given by Lechte for a grey water recy-
cling system translate to an effective unit cost of A~2.00~. lndividua~ systems are an appropriate solution for large rural residential ailotmen~ with adequate area for irrigation. Except in very dry places, there is insufficient area on a typical urban residential allotment to handle and recycle all wastewater without external run-off and environmental impact. Considerable technological improvement would be needed on current individual household systems to achieve acceptable public health and environmental outcomes in urban areas. The crystal ball is still cloudy on the subject of individual household recycling systems in urban areas. The halfway house of neighbourhood treatment and recycling systems may be the right balance in the long term. 4. Future
scenarios
4.1. Scenario 1: Do nothing Australia’s population of 18 million people is currently growing at around 1.4% per annum. Assuming a continuation of current growth factors, the population in 2016 would be over 24 million, 35% higher than in 1991; 31 million by the year 2041 and 44 million by 2091. Australia has ample water resources to accommodate such growth if development is appropriately located and designed, but we do need to consider the impact and side effects. Further development of sources would be required and some reallocation of water from irrigated agriculture to urban and industrial use might need to occur. 4.2. Scenario 2: Water conse~atj~n Over the last 10 years, many Australian communities have achieved reductions of IO-30% in per capita water usage through water conservation measures. Further reductions can be expected through better urban design and further water conservation measures. For example, further reductions of 25-30% in indoor consumption would be achievable at iow cost through univer-
J.M. Anderson /Desalination 106 (1996) 151-156 sal use of water-efficient fittings and appliances now available. It is reasonable expect that per capita demands will decrease 15% by year 2016 and 30% by year 2041. These changes in water consumption behaviour will have an impact on the potential for wastewater and storm water recycling and may affect the viability of some recycling systems. 4.3. Scenario 3: Non-potable
recycling
Recycling of wastewater and storm water for non-potable uses has the potential to reduce urban and industrial demands on surface water resources by an average of 40-50% in most Australian cities depending on climate. The actual amount will vary from year to year depending on rainfall. The impact of water conservation measures will reduce the average potential saving to approximately 30-35%. For the purpose of this scenario, it is assumed that the average saving will be 30% and that there would be 10% adoption by 2016, 25% adoption by 204 1 and 100% adoption by 2091. 4.4. Scenario 4: Potable recycling Recycling of wastewater and storm water for all uses including potable uses has the potential to reduce urban and industrial demands on surface water resources by amounts varying from 40% to 100% depending on climate. The impact of water conservation measures will reduce the average potential saving to approximately 5060%. These figures can be increased if storm water is also recycled. For the purpose of this scenario, it is assumed that the average saving will be 50% and that there would be 10% adoption by 2016, 25% adoption by 2041 and 100% adoption by 209 1. 5. Discussion
5.1 Implications for Australia ‘s water resources The impact of each scenario on projected urban water use in Australia is shown in Table 1.
155
Table 1 Projected urban water use in Australia (million ML) Scenario
1991
2016
2041
2091
Do nothing Water conservation Non-potable recycling Potable recycling -_.
3.2
4.3 3.7 3.6 3.5
5.4 3.8 3.5 3.3
7.7 5.4 3.8 2.7
5.2. Future directions
Rapid progress is being made in developing new treatment technologies. It is probable that treatment costs will come down faster than the cost of pipework and recycling systems. It follows that as time goes on: (I) decentralized treatment and recycling will become more attractive, and (2) potable recycling will become more economical than non-potable recycling. As shown in Table 1, potable recycling has greater potential to reduce demands on Australia’s water resources than non-potable recycling. Because of the high costs involved in construtting a second reticulation for non-potable recycling, the future choice between potable and non-potable recycling represents a major decision. This choice does not have to be made immediately. Table t shows that an effective program of water conservation will buy sufficient time to develop and test recycling technologies further so that an informed choice can be made. 5.3. Water quality improvement In the Murray-Darling Basin, more than onethird of effluent from sewage ~eatment works in New South Wales is applied to land. nutrient removal facilities or land application facilities are being installed in all significant plants. NSW has initiated a statewide “phosphorus action” program which aims to minimize phosphorus input to both wastewater and storm water. By the end of this decade, phosphorus inputs to the MurrayDarling system from wastewater systems in NSW will be reduced by more than 90% from 1986 levels.
156
J.M. Anderson / Desalination 106 (1996) 151-156
There are good grounds therefore to believe that gains in water quality improvement will proceed at an even faster pace than improvements in water conservation and recycling. Moves to water conservation and recycling will result in further improvements in water quality by reducing the quantity of water extracted from streams and reducing the quantity of pollutants discharged. A possible further improvement would be to filter effluent discharges. This step would cost between A$0.15-0.25kL for dry weather flows and somewhat more for wet weather flows. In some circumstances effluent filtration may be more cost effective and environmentally appropriate than recycling.
6. Conclusions The overall picture for Australia’s water resources over the next 50-100 years is one for optimism. We already have available appropriate technologies for water conservation and water recycling with which Australia will be able to meet comfortably the water needs of a growing population within the confines of available water resources. Some further development of the technologies is needed to bring down the costs of water quality improvement and recycling. We can view these technologies as a hand of cards. The hand also includes a range of supply options. The question is when to play each card. The right timing and the right choices between supply, conservation and recycling options will depend on the circumstances in each individual catchment. Water conservation and waste minimization measures are the least cost and highest priority options. In due course a decision will be needed on whether to introduce potable recycling. Whatever the right choices might be, the potential for water recycling in Australia provides greater certainty about the future of Australia’s water resources and expands our horizons.
References [II S. White, Wise water management: demand management manual for water authorities, UWRAA Research Report, 1994. PI J.M. Anderson, Development of reuse policy and guidelines, AWWA NSW Regional Seminar, Bathurst, 1992. [31 E. Gardiner et al., Sustainable land disposal of treated sewage effluent, AWWA Queensland Regional Conference, Caloundra, 1993. [41 R. Baker and A. Cartwright, Stormwater recycling proposal for Homebush Bay, 4th NSW Recycled Water Seminar, Newcastle, 1994. PI S. Salmon, Restoring the waters: An ACF proposal to move towards ecologically sustainable stormwater management, 4th NSW Recycled Water Seminar, Newcastle, 1994. Fl RWCC, NSW guidelines for urban and residential use of reclaimed water, 1st ed., NSW Recycled Water Coordination Committee, 1993. [71 D. Eisenhuth, Rouse Hill infrastructure project: A case study, 4th NSW Recycled Water Seminar, Newcastle, 1994. D. Hunter, W. Smith, L. Nagy and P. Jacob, Regional development implications of wastewater reuse: Werribee case study, UWRAA Research Report No. 70, 1993. [91 T. Smyth, Scheyville: A new approach to the disposal of treated effluent, AWWA Victoria Wastewater Reduction and Recycling Conference, Geelong, 1992. t101 W. Lauer, Denver’s demonstration of potable water reuse: Water quality and health effects testing. IAWPRC 16th Biennial Conference, Washington, 1992. H. Van Leeuwen, The South African experience, AWWA Queensland Regional Conference, Caloundra, 1993. 1121 H. Van Leeuwen, Water reclamation: The selection of unit processes, 4th NSW Recycled Water Seminar, Newcastle, 1994. u31 I. Law, Unplanned and planned indirect potable reuse: There is a difference, 4th NSW Recycled Water Seminar, Newcastle, 1994. u41 R. Butler, Cost effective strategies for urban water reuse and potable water substitution, 4th NSW Recycled Water Seminar, Newcastle, 1994. iI51 G. Hamilton, Public attitudes to potable water reuse, AWWA Queensland Regional Conference, Caloundra, 1993. 1161 I. Law, Potable reuse: Should it not be considered more fully? AWWA 15th Federal Convention, Gold coast, 1993. [I71 P. Lechte, A review of opportunities and constraints in domestic wastewater reduction and recycling, AWWA Victoria Wastewater Reduction and Recycling Conference, Geelong, 1992. [I81 B. Jeppesen and D. Solley, Domestic greywater reuse: Overseas practice and its applicability to Australia, UWRAA Research Report No. 73, 1994.
Desalination
106 (1996) 151-156
The potential for water recycling in Australia expanding our horizons J.M. Anderson Department
of Public Works and Services, 2-24 Rawson Place, Sydney, NSW 2000, Australia Fax +61 (2) 372-7522 Received
10 May 1995; Accepted
20 August
1995
Abstract This paper examines urban water use, wastewater flows, and storm water flows in the context of Australia’s water resources. The costs of water conservation and recycling are also examined together with some of the constraints. The potential for water recycling in Australia and the implications of future water conservation and recycling scenarios on Australia’s water resources and the environment are discussed. The development of new treatment systems will reduce quality constraints and open up new avenues for recycling. These may include large-scale potable reuse as well as decentralized treatment and local recycling options for both effluent and storm water. The implications of these alternatives for water recycling and the use of Australia’s water resources are discussed. Keywora!s:
Australia;
Water resources;
Water planning;
1. Introduction In proportion to its area, Australia has the lowest rainfall and runoff of all the continents. However, Australia’s population of just over 17 million is small in relation to the land mass of 8 million km2 and the available water resources. A high proportion of the population lives in urban centres located in high rainfall areas on the southern margins of the continent. This has allowed a rather liberal approach to water use. Most water is used on a “once-through” basis
001 l-9164/96/$15.00 PII
SO01
Water recycling;
before return to the natural water cycle by discharge or evaporation. There are strong perceptions in the community, born of concern for the environment, that wastewater and storm water should be recycled rather than discharged to rivers or the ocean. This paper examines the potential for water recycling in Australia in the context of Australia’s water resources and discusses the implications of alternative future recycling scenarios on Australia’s water resources and the environment.
Copyright 0 1996 Elsevier Science B.V. All rights reserved.
1-9164(96)00104-X
Water conservation
152
J.M. Anderson / Desalination IO6 (1996) 151-156
2. Water use in Australia 2.1. Available water resources The average annual run-off is approximately 50 mm or about 400 million ML. Run-off varies spatially and temporally across the continent. A quarter of the continent, Tasmania and the area north of the Tropic of Capricorn, account for more than 80% of the run-off. About 70% of it occurs as floods. Divertible surface water resources are approximately 118 million ML. More than half of the divertible surface water resources occurs in Tasmania and north of the Tropic of Capricorn, remote from the main centres of population. 2.2 Current water use Developed resources can supply approximately 22 million ML/y. Average annual water use is about 18 million ML, of which 18% is used for urban and industrial uses, 74% for irrigation and 8% for rural stock and domestic use. About 60% of this use occurs within the Murray-Darling Basin where the available surface water resources are almost fully committed to irrigation. Urban use, including commercial and industrial use, averages about 3.2 million ML/y. About half this amount, 1.6 million ML/y, is returned to the environment as wastewater flows after various forms of treatment. Urban storm water runoff varies widely both spatially and temporally according to climate. The average volume is about 3 million ML/y, about equal to the amount of water supplied for urban and industrial use. This water usually contains significant levels of pollutants. 2.3 Environmental
impact
In recent years, signs of serious environmental stress, manifested through declining water quality, have been observed in many Australian catchments. The rivers of the Murray-Darling Basin have deteriorated markedly since white settlement, principally because of agricultural land use
practices and diversion of water for irrigation, but also because of nutrients in urban wastewater and storm water discharges. Similar deterioration has occurred in the Hawkesbury-Nepean Basin which drains western Sydney, caused principally by urbanization. These two cases highlight the impact which occurs as water use approaches or exceeds the limits of sustainability in individual catchments. Compared to the Murray-Darling, the level of regulation in the Hawkesbury-Nepean is a relatively modest 30%. This highlights the constraints imposed on the use of water resources by the combined impact of water diversions and urban run-off. Better management of urban water use and of wastewater and storm water discharges will be needed if expected population growth is to be accommodated without further deterioration in the environment. 2.4. Trends in water consumption Growth is being offset to some degree by moves to better urban design and water conservation. l
l
l
l
l
There is a trend towards smaller urban allotments, dual-occupancy development and medium-density housing. The Commonwealth Better Cities Program is working towards the development of better urban design standards. Most authorities have moved to implement pay-for-use pricing for water. Water-efficient fittings and appliances are being introduced. The States are actively promoting water conservation through a “water wise” campaign.
Water conservation is the most cost effective way to provide system capacity to cater for growth. The effective unit cost to free up spare system capacity by retrofitting water-efficient appliances is A$O-12/kL to retrofit low flow shower roses and A$O-32/kL to retrofit 6L/3L dual- flush toilet cisterns [l]. It costs even less to install water efficient appliances in new develop-
ments. A number of Australian states have made dual-flush cisterns compulsory for ail new installations. 3. Wastewater and storm water recycling 3. I. Wastewater recycling
Wastewater recycling is still in its infancy in Australia. Less than 10% of water diverted for urban and industrial use is recycled. Recycling has most commonly taken the form of reuse of effluent after secondary biological treatment for irrigation of pasture or urban recreation areas and landscaping. Most wastewater recycling schemes proposed in NSW in recent years for broad acre irrigation of pasture or urban landscaping have involved effective unit costs in the range A$0.40-1 .OO/kL for recycled water. Anderson [23 and Gardiner [3] highlight some of the problems in achieving sustainable Iand i~igation systems. Annual irrigation demands can vary by plus or minus 40% from average depending on rainfall. Annual wastewater flows in a wet year can be up to 50% higher than average dry weather flow due to storm water inflows. In an irrigation system designed for average year conditions, there is a shortfall of reclaimed water for irrigation in a dry year and surplus reclaimed water in a wet year. The practice of designing systems for the wettest year in ten results in large irrigation deficiencies in dry years and still requires large expendi~es on effluent storage to minimize effluent discharges. This adds to recycling costs. In some cases, balanced irrigation design coupled with treatment to a higher standard may be preferable. 3.2. Storm water collection and recycling The most simple form of stormwater recycling is the collection of roof water in household rain tanks to use for both potable and non-potable purposes. It is widely used for rural dwellings. The cost of household rain tank systems has been estimated to be in the range A$2.00-4.00/kL de-
pending on climate and the level of reliab~li~ required. Lower costs may be achievable with community or neighbourhood storm water recycling systems if the right balance exists between storage, pipework and pumping costs. The collection and recycling of site run-off has been less common. It is now occurring more frequently on sites such as golf courses. Collection and recycling of urban run-off is relatively rare. The amount of storm water available for recycling and the amount which can be recycled varies widely depending on the climate and the variations in rainfalt from year to year. To be an effective substitute for conventional water supply, considerable storage is required to carry storm water over from wet to dry periods. Baker and Cartwright [4] have developed a proposal for storm water recycling at the Sydney Olympics site. Recycled water from this scheme would have an effective cost of A$I-60/kL. Salmon [S] has drawn attention to the adverse environmental impact on wate~ays of diverting storm water flows for recycling during periods of low flow. 3.3 Recycling for non-potable uses The first steps have been taken towards developing residential water recycling with the publication of the NSW Guidelines for Urban and Residential Use of Reclaimed Water [6]. The RWCC Guidelines allow use of reclaimed water for non-potable uses including toilet flushing, garden watering and car washing. The first major residential recycling system in Australia is currently under construction at Rouse Hill in Sydney [7]. Large residential reuse systems are under consideration at Melton and Werribee in Melbourne. A case study for residential recycling system at Werribee has been presented by Hunter et al. [8]. A drawback of non-potable recycling is the cost of establishing a second reticulation network and a second system of household pl~bing with safeguards against cross-connection. Smyth [9] and others have presented cost estimates for
154
J.M. Anderson /Desalination 106 (1996) 151-1.56
residential reuse systems. The costs translate to unit costs in the order of A$2.50-3.00/kL to supply recycled water. 3.4. Recychg
for potable uses
The technology already exists for potable recycling and has been proven in extensive trials in Denver [lo]. Planned potable recycling has taken place at Windhoek in Namibia since 1968 [ 111. Appropriate treatment processes have been described by Van Leeuwen 1121, Law [13] and Butler 1141. As time goes on, new developments in ~eatment technology will make potable recycling less costly than non-potable recycling. A debate has commenced about whether Australia should develop potable recycling. Potable recycling is not yet approved by Australian authorities, but a small amount of unplanned indirect potable reuse does occur [ 151. Law [ 13,161 has shown that indirect potable recycling would be similar in cost to non-potable recycling for the northwest development area in Sydney. A survey by Hamilton [ 151 found that a majority of the respondents were prepared to consider potable reuse if convinced of the need and the adequacy of safeguards. 3.5. Decentralized
treatment and recycling
The move 100 years ago from individual to community-wide water and sewerage systems was the most beneficial public health initiative in the history of Australia. There is now a movement for a return to individual household systems in the interests of conservation. Recycling system costs could be reduced by moving water reclamation plants closer to the point of reuse in order to reduce pipework costs. Pipework costs will be lower for individual systems. Community systems are likely to be better than individual systems in terms of performance, reliability and treatment costs. The practicalities of grey water recycling systems have been discussed by Lechte [ 171 and Jeppesen [ 181. Indicative costs given by Lechte for a grey water recy-
cling system translate to an effective unit cost of A~2.00~. lndividua~ systems are an appropriate solution for large rural residential ailotmen~ with adequate area for irrigation. Except in very dry places, there is insufficient area on a typical urban residential allotment to handle and recycle all wastewater without external run-off and environmental impact. Considerable technological improvement would be needed on current individual household systems to achieve acceptable public health and environmental outcomes in urban areas. The crystal ball is still cloudy on the subject of individual household recycling systems in urban areas. The halfway house of neighbourhood treatment and recycling systems may be the right balance in the long term. 4. Future
scenarios
4.1. Scenario 1: Do nothing Australia’s population of 18 million people is currently growing at around 1.4% per annum. Assuming a continuation of current growth factors, the population in 2016 would be over 24 million, 35% higher than in 1991; 31 million by the year 2041 and 44 million by 2091. Australia has ample water resources to accommodate such growth if development is appropriately located and designed, but we do need to consider the impact and side effects. Further development of sources would be required and some reallocation of water from irrigated agriculture to urban and industrial use might need to occur. 4.2. Scenario 2: Water conse~atj~n Over the last 10 years, many Australian communities have achieved reductions of IO-30% in per capita water usage through water conservation measures. Further reductions can be expected through better urban design and further water conservation measures. For example, further reductions of 25-30% in indoor consumption would be achievable at iow cost through univer-
J.M. Anderson /Desalination 106 (1996) 151-156 sal use of water-efficient fittings and appliances now available. It is reasonable expect that per capita demands will decrease 15% by year 2016 and 30% by year 2041. These changes in water consumption behaviour will have an impact on the potential for wastewater and storm water recycling and may affect the viability of some recycling systems. 4.3. Scenario 3: Non-potable
recycling
Recycling of wastewater and storm water for non-potable uses has the potential to reduce urban and industrial demands on surface water resources by an average of 40-50% in most Australian cities depending on climate. The actual amount will vary from year to year depending on rainfall. The impact of water conservation measures will reduce the average potential saving to approximately 30-35%. For the purpose of this scenario, it is assumed that the average saving will be 30% and that there would be 10% adoption by 2016, 25% adoption by 204 1 and 100% adoption by 2091. 4.4. Scenario 4: Potable recycling Recycling of wastewater and storm water for all uses including potable uses has the potential to reduce urban and industrial demands on surface water resources by amounts varying from 40% to 100% depending on climate. The impact of water conservation measures will reduce the average potential saving to approximately 5060%. These figures can be increased if storm water is also recycled. For the purpose of this scenario, it is assumed that the average saving will be 50% and that there would be 10% adoption by 2016, 25% adoption by 2041 and 100% adoption by 209 1. 5. Discussion
5.1 Implications for Australia ‘s water resources The impact of each scenario on projected urban water use in Australia is shown in Table 1.
155
Table 1 Projected urban water use in Australia (million ML) Scenario
1991
2016
2041
2091
Do nothing Water conservation Non-potable recycling Potable recycling -_.
3.2
4.3 3.7 3.6 3.5
5.4 3.8 3.5 3.3
7.7 5.4 3.8 2.7
5.2. Future directions
Rapid progress is being made in developing new treatment technologies. It is probable that treatment costs will come down faster than the cost of pipework and recycling systems. It follows that as time goes on: (I) decentralized treatment and recycling will become more attractive, and (2) potable recycling will become more economical than non-potable recycling. As shown in Table 1, potable recycling has greater potential to reduce demands on Australia’s water resources than non-potable recycling. Because of the high costs involved in construtting a second reticulation for non-potable recycling, the future choice between potable and non-potable recycling represents a major decision. This choice does not have to be made immediately. Table t shows that an effective program of water conservation will buy sufficient time to develop and test recycling technologies further so that an informed choice can be made. 5.3. Water quality improvement In the Murray-Darling Basin, more than onethird of effluent from sewage ~eatment works in New South Wales is applied to land. nutrient removal facilities or land application facilities are being installed in all significant plants. NSW has initiated a statewide “phosphorus action” program which aims to minimize phosphorus input to both wastewater and storm water. By the end of this decade, phosphorus inputs to the MurrayDarling system from wastewater systems in NSW will be reduced by more than 90% from 1986 levels.
156
J.M. Anderson / Desalination 106 (1996) 151-156
There are good grounds therefore to believe that gains in water quality improvement will proceed at an even faster pace than improvements in water conservation and recycling. Moves to water conservation and recycling will result in further improvements in water quality by reducing the quantity of water extracted from streams and reducing the quantity of pollutants discharged. A possible further improvement would be to filter effluent discharges. This step would cost between A$0.15-0.25kL for dry weather flows and somewhat more for wet weather flows. In some circumstances effluent filtration may be more cost effective and environmentally appropriate than recycling.
6. Conclusions The overall picture for Australia’s water resources over the next 50-100 years is one for optimism. We already have available appropriate technologies for water conservation and water recycling with which Australia will be able to meet comfortably the water needs of a growing population within the confines of available water resources. Some further development of the technologies is needed to bring down the costs of water quality improvement and recycling. We can view these technologies as a hand of cards. The hand also includes a range of supply options. The question is when to play each card. The right timing and the right choices between supply, conservation and recycling options will depend on the circumstances in each individual catchment. Water conservation and waste minimization measures are the least cost and highest priority options. In due course a decision will be needed on whether to introduce potable recycling. Whatever the right choices might be, the potential for water recycling in Australia provides greater certainty about the future of Australia’s water resources and expands our horizons.
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