Sustainable Water And Sewerage Servicing

Paper number [o7196]

Achieving Sustainable Water and Sewerage Servicing in Semi-Rural Backlog Areas Andrew Grant, CSIRO, [email protected] Ashok Sharma, CSIRO, [email protected] Grace Tjandraatmadja, CSIRO, [email protected] Francis Pamminger, YVW, [email protected] Tim Grant, RMIT, [email protected] Lisa Opray, RMIT, [email protected]

INTRODUCTION Yarra Valley Water presently has 18,500 ‘backlog’ properties that do not have appropriate sewerage services. It is estimated that to sewer these will cost in the order of $250m. With such a large capital investment Yarra Valley Water wants to ensure that they deliver the most environmentally sustainable solution. Innovative solutions such as greywater reuse and urine separation could play a role in achieving sustainable and reliable water and sewage servicing of backlog areas. Financial cost and community attitudes certainly still need to be addressed, but this study has demonstrated that from a technical perspective, sustainable water servicing is achievable. ‘Backlog’ refers to properties with ineffective septic systems. Generally, this is because the lot is too small to contain discharge, and density of local development is high, hence causing either health and/or environmental risks. To overcome this, backlog properties have been scheduled to change to a reticulated sewerage system. ‘Backlog’ usually refers to properties that do not have sewer connection to a reticulated system, however in this case there is also no connection to a reticulated water supply. To determine the best way of servicing backlog areas, Yarra Valley Water commissioned a Life Cycle Assessment of servicing options for a small peri-urban community on Melbourne’s fringe. The study included water supply, wastewater and stormwater servicing and focused on an area comprising 54 hectares with 66 dwellings and a population of 189 people. Greywater reuse, rainwater tanks, urine separation and a range of wastewater treatment measures were considered. It was not practical to connect the region to existing centralised systems due to difficult terrain and distance. This paper represents the findings of the water and contaminant balance component of the study. A complementary paper (Tjandraatmadja 2007) details the wastewater treatment options. Outcomes of the Life Cycle Assessment and Life Cycle Costing will be published soon. Analysis of the water and contaminant balance allows us to develop a better understanding of how to design water services for peri-urban, low density residential areas. It allows us to answer key questions such as: How reliable are rainwater tanks for water supply? What impact would greywater reuse have on the reliability of the water supply? What impact would outdoor greywater use have on contaminant loads to land? What impact would urine separation have on contaminant loads? What storage volume would be required for urine separation?

Water and contaminant balance modelling of urban developments has been undertaken by many researchers. Mitchell et al. (2001), Hardy et al. (2005) and Mitchell and Diaper (2005a) give overviews and McLean (2004) and Grant et al. (2006) are some examples of applications to developments in Melbourne. Studies of semi-rural, peri-urban areas are not as common. This study highlights the issues related to water and wastewater servicing where connection to existing centralised systems is not available. METHOD In consultation with the project partners, a range of servicing options were selected (Table 1). Options involved urine separation and storage, greywater diversion without treatment, greywater treatment and storage, use of existing septic tanks and centralised wastewater treatment. (Note that rainwater tanks and septic tanks are existing). Centralised treatment in Table 1 refers to locally treating the sewage from all of the properties in the study area (rather than connection to an existing sewage collection and treatment system). The methods of collection and treatment are not detailed in this paper (see Tjandraatmadja 2007 for details). On site treatment of sewage as a stand-alone measure was not analysed as the land was not capable of absorbing and containing discharges on site all year round (Whiteheads Consulting 2006). Table 1: Summary of water servicing options Options Kitchen Bathroom Water Laundry Supply Toilet Garden Urine Separation Greywater Diversion (no treatment or storage) Wastewater Greywater Treatment & Storage Septic Tanks Centralised TP On-Site TP Conventional Stormwater Swales

1.1

1.2

2.1A

2.1B

2.2A

2.2B

2.2C

2.3

Y

Y

Y

Y*

Y*

Rainwater Rainwater Greywater Y

Y

Y

Y Y

Y* Y

Y Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

* Tank volumes of 1.5 kL for Option 2.1B and 3.3 kL for Option 2.2B and 2.2C were chosen. Tanks were sized to provide a 95% volumetric reliability in Option 2.1B and 2.2B. The same size tank was used in Option 2.2C as Option 2.2B so the water and contaminant balance results could be easily compared.

Rainwater tanks were used for all options due to centralised water supply not being an option. Although no data were available, it was observed that rainwater tank sizes varied from lot to lot, with a median size of around 25 kL. Modelling individual rainwater tank sizes for each lot was beyond the resources of the project, so the median size was adopted for modelling. Urine separation was investigated because it can improve the efficiency of wastewater treatment plants (Wilsenach and Van Loosdrecht 2004) and be used as a well-balanced complete fertiliser, thus closing the nutrient loop (Jonsson 2002). Urine separation and storage requires a specially designed toilet for separate collection of urine and faeces. In this study, the urine stream was collected and stored in tanks at each individual house. It was then collected by truck every 6 months and used for nearby agriculture. Greywater was considered as a supplementary supply to rainwater. Directly diverting untreated greywater (Options 2.1A & 2.2A) was compared to using a greywater treatment and storage system (Options 2.2A, 2.2B & 2.2C). Using greywater for various end uses

was compared; Options 2.1A & 2.1B used greywater for the garden only; Option 2.2A and 2.2B used greywater for the garden and toilet; and Option 2.2C used greywater for the garden, toilet and laundry. Swales and conventional curb and channel were considered for stormwater design. Other Water Sensitive Urban Design measures such as wetlands and bio-retention trenches were not considered because of constraints of topography (i.e. the area was too hilly) and the high-quality stormwater due to the low imperviousness of the study area. Cluster scale reuse of stormwater and wastewater were not modelled because of the constraints of topography and associated cost. A suitable flat location for storage was not obvious and the costs of pumping and treatment (for such a small number of properties) meant that cluster storages were not feasible. Servicing options were assessed by using the water and contaminant balance model UVQ (Mitchell and Diaper 2005) and the stormwater treatment train model MUSIC (Wong et al. 2005). MUSIC was used for modelling stormwater because it can be operated at a six minute time-step which is important for representing constituent generation and treatment (Wong et al. 2005). UVQ’s daily time-step stormwater model was ‘calibrated’ to MUSIC’s outputs, so stormwater could be included in an integrated assessment of the water balance. UVQ was able to determine the volumetric reliability of the servicing options (i.e. the percentage of demand met over the modelling period); the loads of constituents of each stream in the water cycle; demand shortfalls; optimal sizes of greywater and rainwater tanks; and the interactions of streams (e.g. wastewater and stormwater). No runoff data for the study area or similar catchments was available so calibration was limited. The only calibration undertaken was setting the annual volumetric runoff coefficient to 35%. This value is based on the assumption that the study area would have higher runoff coefficients than most other Australian catchments given the very high annual rainfall (1130 mm per year) and steep slopes. Fleming, 1994, collated data on volumetric runoff coefficients around Australia. The upper range for the volumetric runoff coefficient was found to be 35%, so this has been assumed for this study. Daily rainfall and evaporation data spanning 1960-2005 was sourced from SILO data drill (www.nrm.qld.gov.au/silo/datadrill/) and used for UVQ modelling. Six minute rainfall data spanning one year (1968) from the closest gauging station (Mt St. Leonard, station number 86241) was used for MUSIC modelling and was sourced from the Bureau of Meteorology. Geographical and topographical data (Table 2) was obtained from Yarra Valley Water, the Australian Bureau of Statistics and aerial photography. Table 2: Geographical and topographical data. Population 189 Average Paved Area (m2) Dwellings / Units 66 Average garden and lawn area (m2) People Per Unit 2.86 Road (ha) Average Block Size* (m2) 1210 Open Space** (ha) Average Roof Area (m2) 270 Total area (ha)

30 910 1.5 44.85 54.34

*excludes area beyond building envelope **area within private property boundaries excluding building envelope

End use data was provided by Yarra Valley Water. It was derived from metered values for properties with mains connection and then downscaled to reflect the reduced demand due to reliance on rainwater tanks. End use figures for the urine separated stream (Options 2.1, 2.2 and 2.3) were adopted from the Dubbleten case study (Peterson 2001).

Table 3: End Use Figures

Kitchen Bathroom Toilet Laundry Urine Outdoor Total

Options 1.1 and 1.2 (l/c/day) 16 65 23 26 0 29 159

Options 1.1 and 1.2 (l/hh/day) 46 186 66 74 0 84 456

Options 2.1, 2.2 and 2.3 (l/c/day) 16 65 5 26 11 29 152

Options 2.1, 2.2 and 2.3 (l/hh/day) 46 186 14 74 31 84 436

Constituent data was sourced from published literature (Table 4). Whilst they are not specific for the study area they should provide a reasonable estimate of loads and are accurate enough for scenario comparison. Table 4: Constituent Characteristics Runoff and Rainwater Characteristics TN TP TSS BOD Source mg/L mg/L mg/L mg/L 1 1 1 2 Roof Runoff 2.88 0.129 37.2 4 3 3 3 4 Rainfall 1.33 0.087 17 0 1 1 1 1 Pavement Runoff 2.88 0.4 165 15 1 1 1 1 Road Runoff 2.2 0.25 68 18 1 1 1 Garden Runoff 1.66 0.08 11 Indoor characteristics Source mg/c/d mg/c/d mg/c/d mg/c/d 4 4 4 4 Kitchen 238 42 3990 7160 4 4 4 4 Bathroom 462 22 8303 10892 4 4 5 4 Toilet 11200 3000 36240 19500 4 4 4 4 Laundry 328 152 4858 5363 5 5 5 5 Urine 10000 1000 0 7500 Removal rates of treatment measures Treatment % % % % Greywater Treatment 6 6 6 6 21 7 92 94 (Pontos system) 7 8 7 7 Septic Tank 24 0 82 44 9 9 9 10 Rainwater Tank 71 68 87 25 1

COD mg/L 2

22 4 0 1 78 1 80 mg/c/d 4 14320 4 21784 4 48000 4 10726 5 15000

K mg/L mg/c/d 5

2200

5

1500

%

% 6

86 44 10 25 7

-

Duncan, 2006, 2Duncan, 1999, 3Mitchell & Diaper, 2005b , 4Gray & Becker, 2002 , 5Crockett et al., 2003, 6CSIRO, 2006, Adapted from Metcalf & Eddy Inc., 1991, 8Adapted from Metcalf & Eddy Inc., 1991 and Sarac et al., 2001, 9Calculated from Duncan, 2006 and MUSIC modelling, 10Adapted from Villereal & Dixon, 2005 and Duncan, 1999 7

RESULTS Analysis of the water and contaminant balance results (Table 5 and Table 6) suggests that Option 2.2C is the best servicing option. It has the highest volumetric reliability, lowest output flows, lowest constituent loads to the wastewater stream and slightly higher stormwater flows and constituent loads. This was achieved through the utilization of the most infrastructure and most plumbing connections. Option 2.2B and 2.1B achieved similar volumetric reliability results despite no greywater being plumbed to the laundry in Option 2.2B and no greywater being plumbed to the toilet or laundry in Option 2.1B. Option 2.1A and 2.2A had lower volumetric reliabilities and slightly higher nitrogen loads to land, but they did not have greywater treatment and storage. The use of greywater (Options 2.1A, 2.1B, 2.2A, 2.2B, 2.2C) significantly reduced the wastewater flow.

Urine separation was shown to significantly reduce nitrogen loads to wastewater. Comparison of Option 2.3 with Option 1.1 shows that 690 kg of nitrogen was collected by the urine tanks. A storage volume of between 1.2 kL and 6 kL for each house, depending on the amount of water used for flushing, is required for 6-monthly storage of urine. Comparison of Option 1.1 and 1.2 shows that septic tanks reduced the nitrogen load to the wastewater stream by 204 kg per year and suspended solids by 3000 kg per year. They had virtually no impact on phosphorous loads. Table 5: Water Balance Summary 1.1 1130 1051 8963 2005 8491 1421 0 0 0 0 214 9804 472 584

1.2 1130 1051 8963 2005 8491 1421 0 0 0 0 202 9720 472 584

2.1A 1130 1051 8480 2005 8184 1171 0 0 538 758 202 8131 296 296

Option 2.1B 2.2A 1130 1130 1051 1051 8480 8480 2005 2005 8455 7153 118 1409 0 0 0 1103 1882 298 758 758 203 203 7060 7324 26 223 5 299

90.4

90.4

96.5c

99.7c

97.0c

99.9c

103.3b,c

91.1

n/a

n/a

26.8

93.9

45.1

94.1

90.6

n/a

25

25

25

25

25

25

25

25

-

-

0.1a

2.4

0.1a

3.3

3.3

-

Total Volumetric Reliability (%)

90.4

90.4

94.4

99.7

95.0

99.9

100.0

91.1

Average days per year demand was not met

21.8

21.8

14.6

1.3

12.8

0.3

0.0

19.8

Maximum Continuous Failure Days

49

49

48

17

47

5

1

49

Rainfall Evaporation Indoor Outdoor Indoor Outdoor Laundry Greywater Toilet Use (kL/yr) Outdoor Urine Collection (kL/yr) Stormwater Flow (ML/yr) Wastewater Flow (kL/yr) Indoor Shortfall (kL/yr) Outdoor

Climate (mm/yr) Demand (kL/yr) Rainwater Use (kL/yr)

Volumetric Reliability (%) Tank Volume (kL)

a

Rainwater Tank Greywater Tank Rainwater Tank Greywater Tank

2.2B 1130 1051 8480 2005 7371 181 0 1103 1822 758 204 6042 6 2

2.2C 1130 1051 8480 2005 5766 276 1662 1051 1728 758 206 4587 1 1

2.3 1130 1051 8480 2005 8076 1476 0 0 0 758 202 8562 405 529

A temporary storage. Unused water is flushed to the sewer every 24 hours. b A volumetric reliability of greater than 100% was achieved because the rainwater tank supplied the garden, toilet and laundry when the greywater tank was unable to meet demand c It should be noted that the rainwater tank backed up the greywater tank in these scenarios

Options 1.1 and 1.2 have the least water supply infrastructure and, because of this, delivered the lowest volumetric reliability (90.4%) and highest continuous days of failure (49). As the water supply infrastructure is improved, the volumetric reliabilities increase and the continuous days of failure decrease. Adding greywater diversion to the garden increases volumetric reliability to 94.4% (Option 2.1A) and reduces continuous failure days to 48. If greywater is diverted to the toilet also (Option 2.2A), the volumetric reliability increases to 95.0% and continuous failure days reduces to 47. Greater reductions in continuous failure days are achieved by adding a greywater treatment and storage system. When these systems supply the garden (Option 2.1B), continuous failure days reduce to

17 (and at the same time increase volumetric reliability to 99.7%). This can be further improved by plumbing the greywater to the toilet (Option 2.2B) as continuous failure days reduce to 5 and volumetric reliability increases to 99.9%. Demand is almost entirely met by connecting the greywater to the laundry also (Option 2.2C). Only 1 kL of demand is not met in the entire modelling sequence out of a total of 10485 kL. Table 6: Contaminant Balance Summary

Wastewater Flow (kg/yr)

Stormwater Flow (kg/yr)

Greywater Sludge (kg/yr)

Land Application (kg/yr)

N P SS BOD COD N P SS BOD COD N P SS BOD COD N P SS BOD COD

1.1 852 222 3744 2985 6684 289 20 3956 127 595 n/a n/a n/a n/a n/a 99 7 1496 35 186

1.2 647 222 690 1671 3741 254 18 3720 113 524 n/a n/a n/a n/a n/a 99 7 1496 35 186

2.1A 156 152 3652 2348 5400 254 18 3722 114 530 n/a n/a n/a n/a n/a 105 8 1584 154 425

Option 2.1B 2.2A 130 156 149 152 2597 3663 905 2363 2648 5428 255 254 18 18 3726 3724 116 115 540 534 16 n/a 1 n/a 1120 n/a 1538 n/a 2880 n/a 114 104 10 8 1515 1572 56 138 284 393

2.2B 130 149 2592 903 2633 255 18 3731 118 553 16 1 1120 1538 2880 113 10 1514 56 282

2.2C 114 144 2587 888 2574 275 18 3738 132 630 16 1 1120 1538 2880 111 10 1513 55 261

2.3 162 153 3741 2467 5641 254 18 3721 114 528 n/a n/a n/a n/a n/a 99 7 1497 36 187

DISCUSSION Greywater treatment and storage can significantly improve volumetric reliability and decrease sewage volume discharge. It improves volumetric reliability of supply and reduces the number of continuous failure days (i.e. improves the recovery of the supply) because it is a supplementary supply source to the rainwater tank. This also means risk of failure of supply is reduced and resilience of the system to shock (e.g. a cracked rainwater tank) is improved. Using greywater for garden application also has minimal impact on contaminant loads to land; it only increases nitrogen loads by ~15% for this study. (It should be noted that higher density areas and / or areas with less rainfall will have a higher percentage increase in contaminant loads to land when greywater is used for garden). If optimization of volumetric reliability were the only objective, treating and storing greywater should be considered ahead of plumbing greywater to multiple end uses. Additional plumbing only marginally increases volumetric reliability. Connecting greywater to the toilet rather than the garden only, increases volumetric reliability from 94.4% to 95.0% for untreated greywater; and from 99.7% to 99.9% for treated and stored greywater. Far more benefit would be gained from treating and storing the greywater rather than additional connections to end uses because the reliability gains are greater (94.4% to 99.7% for garden connection) and (95.0% to 99.9% for garden and toilet connection). It is a similar story when assessing maximum continuous days of failure. Separation and storage of the urine stream, provided there is a nearby agricultural use, can also contribute to making peri-urban servicing sustainable. It can reduce nitrogen and

phosphorous in the wastewater stream by ~81% and ~31% (comparison of Options 1.1 and 2.3). Wilsenach and Van Loosdrecht (2004) have already shown that removing urine from the wastewater stream can increase the treatment efficiency of wastewater treatment. Provided a nearby agricultural use can be found for the urine, separation of the urine from the wastewater stream should be seriously considered as a servicing alternative. The water and contaminant balance results aid in decision making, however other factors such as financial cost, social impacts and life cycle assessments would further inform the decision making process. The water and contaminant balance demonstrates that from a technical design perspective, options such as greywater reuse and urine separation contribute towards sustainable solutions for backlog areas. Prior to implementing them, community approval and financial costing would be required. A life cycle assessment would also provide further context to decision making by assessing wider environmental impacts (such as energy and embodied environmental impacts of the infrastructure). A life cycle assessment has been completed and will be described in a future paper. The water and contaminant balance could also be improved by assessing variation in occupancy rates, roof areas, water demand and tank volumes. Whilst the conclusions of the study would be unlikely to change, the results would be put in context as the variation of reliabilities and contaminant loads from property to property would be known. CONCLUSION Alternative servicing configurations of low-density, peri-urban backlog areas can contribute towards sustainability. Rainwater tanks and greywater reuse in combination are capable of reliably supplying water for both indoor and outdoor use. Greywater application to land will only have a minor impact on overall contaminant loads to land given the low-density and it will significantly reduce the volume and loading to the sewage treatment plant. Urine separation and storage, provided there is a nearby use for the collected urine, could also be used to significantly reduce contaminant loads to the wastewater stream, thereby improving wastewater treatment efficiency. Greywater tanks and separation of the urine stream can contribute towards achieving a sustainable service for this study area; however they will only be implemented if they are accepted by land owners and financial costs are met by either the water authorities and / or the land owners. The social and financial aspects have to be further investigated. REFERENCES Crockett, J., Oliver, S., Millar, C., Burrows, B., Jefferson, M. and Jaques, K. 2003 Composting Toilet Study Demonstration – Feasibility Study for Smart Water, retrieved from: www.ghd.com.au/aptrixpublishing.nsf/AttachmentsByTitle/compostloo_appendices_pdf/$FI LE/compostloo_appendices.pdf CSIRO 2006, Pontos Aquacycle 900 Test 2 for Smart Water, CSIRO Document No: CMIT (C)-2006-076, CSIRO, Melbourne Duncan, H.P. 1999, Urban Stormwater Quality: A Statistical Overview, Cooperative Research Centre for Catchment Hydrology, Report 99/3, Melbourne Duncan, H. 2006, ‘Urban Stormwater Pollutant Characteristics’, in Wong, T.H.F. (ed) Australian Runoff Quality, Engineers Australia, Crows Nest, NSW

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