DESALINATION

ELSEVIER Desalination 106 (1996) 399405

Wastewater reuse studies and trials in Canberra

John Neal ACTEW Corporation, 221 London Circuit, Canberra, ACT, Australia

Far +61 (6) 248-3451

Received 15 June 1995; Accepted 10 September 1995

Abstract

Reuse of sewage effluent has the potential to both minimize the disposal of water to the environment and reduce the demand on fresh water supplies. In Canberra the Australian national capital city, trials are being undertaken to demonstrate the practicalities of reuse, The first referred to as “water mining” consists of a small treatment plant constructed within the urban environment which extracts flows from an adjacent sewer and uses the treated effluent for the irrigation of nearby playing fields. In the second project, six houses have been disconnected from the city sewerage system and each provided with its own treatment plant. Effluent is stored in tanks on-site and used for garden and lawn irrigation and toilet flushing. The third project also involves a house disconnected from the sewerage system. The blackwater and greywater strains are kept separate. A low- cost process has been devised for the treatment of the greywater stream with effluent again used for irrigation and toilet flushing.

Keywor&s: Sewage; Sewage treatment; Greywater; Effluent reuse

1. Introduction

Recently focus on the reuse of sewage efflu- ent has increased significantly. In a late 199 1 an environmental and process audit of the major sewerage treatment plant in the Australian Capi- tal Territory (ACT) [ 11, the Lower Molonglo Water Quality Control Centre (LMWQCC) was undertaken. One of the recommendations of the audit was to encourage and develop the reuse of sewage effluent.

A similar recommendation is included in the ACT Future Water Supply Strategy [2] recog- nizing the value of reuse in conserving potable water supplies. Development of the strategy evolved from 18 months of exhaustive communi- ty consultation. Reuse of effluent for irrigation enjoyed a very high level of community support, as can be seen in Table 1.

This paper examines some of the initiatives currently underway in the ACT to explore oppor- tunities for the reuse of effluent.

001 l-9164/96/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved.

PII SO01 1-9164(96)00135-X

400 1. Neal / Desalination 106 (1996) 399-405

Table 1 Community support for reuse of treated effluent for irrigation

Response Total

(%I Age group preferences

2Os, 30s 40s 50s +

Totally support 79 78 87 87 Support a little 17 19 12 10 Disinterested - - - - Against a little 1 1 Totally against - - 1 Don’t know 2 3 2

2. Wastewater recycling pilot scheme

ACTEW has recently completed construction of a wastewater recycling pilot scheme. This scheme extracts flows from an existing sewer, and after suitable treatment uses the effluent for the irrigation of playing fields previously irrigat- ed from the town water supply.

The approach adopted is the concept of “water mining”, in which flow from a major sewer is extracted and processed locally for reuse with the solids returned to sewer for processing at the LMWQCC facility. This approach allows the installation of a reuse plant within the urban area without the difficulties associated with solids hand1 ing.

The process selected for this project is shown schematically in Fig. 1. In simple terms, the scheme involves extracting flow from the sewer, passing it through a treatment facility and into a storage tank. Water is extracted from the tank for irrigation, as required.

In selecting the treatment processes, the criti- cal requirements for the technology were that it was proven and reliable, compact, capable of underground installation, minimum odour genera- tion potential, and suitable for unattended opera- tion via remote monitoring and control. Various technology options were evaluated to satisfy the criteria, and the process finally selected involves screening lime addition, sedimentation, two-stage

biological treatment, membrane filtration, and chlorination prior to irrigation. Membrane filtra- tion is via the Australian developed MEMTEC process and is included to provide the high public health protection required under the guidelines as a dual-disinfection system in combination with chlorination. The two-stage biological process is of the “Degremont” design of Biological Aerated Filter (BAF).

The standards for reuse water quality were drawn from the NSW (New South Wales, Austra- lia) Guidelines for Urban and Residential Use of Reclaimed Water released in May 1993. These guidelines were prepared by the NSW Govern- ment to cover the operation of the dual reticula- tion Rouse Hill development in Sydney by the Sydney Water Corporation and place high em- phasis on public health protection.

3. Domestic recycling trials

ACTEW is undertaking trials on domestic on- site wastewater recycling within the urban area of Canberra. The trial involves the installation of six domestic-sized wastewater treatment plants at selected properties within the urban area of Can- berra to treat all of the wastewater generated from within the household. Household waste- water is aerobically treated to a high standard and transferred to a holding tank located on the block. The treated and disinfected effluent is then pumped from the holding tank and beneficially used within the property boundary primarily for toilet flushing and lawn and garden irrigation purposes.

Two alternative treatment processes are being used for the trial. The first involves what has become the de facto standard for small-scale domestic wastewater treatment plants. This pro- cess was first introduced by Envirocycle in 1981 and consists basically of four stages of treatment: removal of solids (anaerobic), aeration, settle- ment, and chlorination. Effluent is finally pumped out of the system to a 13 kl buffer tank. Over 5000 plants of this type (Envirocycle

J. Neal / Desalination 106 (1996) 399-405 401

Potable Water

Makeup

Primaty Treatment

MICROFILTRATION

Secondary Treatment

Tertiary Treatment

SEWER PUMP

Fig. 1. Southwell Park treatment plant.

accounts for over 3000 of them) have been in- stalled throughout Australia.

The second process tested is a relatively new one for the domestic market but one which has been used extensively for municipal scale treat- ment plants. It uses an intermittent cycle, extend- ed aeration activated sludge process. As with the first system, effluent is discharged to the 13 kl buffer tank. The total plant size is approximately half that of the conventional system and has no initial anaerobic stage. This reduces the likeli- hood of odours caused by methane and hydrogen sulphide generation so sealing and venting are less crucial. Also, because of the intermittent nature of the aeration process, less energy is required and denitrification of the effluent occurs in the anoxic conditions. There is only one known manufacturer of a domestic-sized plant using this process at present, and authorization for its use in Queensland has only recently been given by the Queensland Water Resources Com- mission.

Initially, disinfection will be achieved using chlorine tablets; however, other methods includ- ing the use of ultraviolet radiation will be investi- gated. These investigations will be done in con- junction with ACT Health.

A unique feature of this trial is the inclusion of the effluent storage tank and the reuse of ef- fluent for toilet flushing. It is believed that these additions could bring about a fundamental change in attitude to waste disposal. By having the efflu- ent returned to the house, the householder is made aware of the quality of the effluent and self-interest becomes the motivating force to responsibly operate and maintain the treatment process.

The storage tank also gives the householder control over the times that irrigation will occur. Without the tank, the irrigation system would be initiated each time the chlorine contact tank reaches its upper limit, which can occur at any time. Because of this, there is a need to set aside an area of the garden for effluent disposal which

402 J. Neal ! Desalination 106 (1996) 399-405

can be used for little else. With a storage tank, the effluent can be used beneficially for irrigation of the whole garden at a time that suits the household. The tank also has the advantage of providing a buffer storage for rainy days when the garden does not require watering and disposal could be a problem. By being aware of the rise and fall of the water level in the tank, the house- holder becomes very aware of the water balance that is occurring within the household and puts them in control of their own water cycle.

Irrigation of the block will be achieved using a pressure pump to distribute the effluent to the hose taps and to the fixed irrigation system. All hose taps will incorporate fittings which are incompatible with normal hose fittings and will have appropriate signs warning that this is recy- cled water and is unsuitable for drinking. The fixed irrigation system is expected to consist of elevated drippers in shrub areas and gear-driven pop-up sprinklers for grassed areas.

In accordance with the requirements of the plumbing code, the potable water service to each residence will be fitted with an approved reduced pressure zone device back-flow prevention de- vice. In addition, each hose fitting on all external taps on the potable water supply will be fitted with an anti-siphon device. These measures are being taken to prevent contamination of the pota- ble water supply network.

The effluent pumped from the storage tank will comply with the draft ACT Waste Water Reuse Guidelines which are: biochemical oxygen demand (BOD,), 20 mg/l; suspended solids, 30 mgjl; thermotolerant faecal coliforms, 30 cfu/lOO ml (cfu, colony forming units); acidity (pH units), 6.5-8.5; and chlorine residual (at treatment plant outlet), CO.5 mg/l as Cl,.

ACTEW will carry out monthly sampling and testing during the first year to ensure that these limits are not being exceeded. In later years, it is expected that testing can be reduced to a 3- month interval. ACT Health will carry out inde- pendent monitoring on a weekly basis for the first year of the trial and at less frequent intervals after that if results are satisfactory.

4. Greywater investigation

ACTEW is currently investigating the poten- tial for reuse of greywater. In terms of house- hold discharges, greywater represents a high- volume, low-pollution level waste compared to blackwater which is a low-volume, highly pollut- ed waste. The purpose of the investigations is to pursue the potential for dual-stream on-site treat- ment with the separation of greywater and black- water streams. By separating the streams, it is expected that low-cost greywater reuse schemes can be implemented which will have low operat- ing costs, simple technology (easily maintained), insignificant sludge management problems, and quality easily improved by household activity (e.g., detergent selection).

For the purposes of these investigations, only greywater originating from the bath, shower, hand basin, laundry and under some conditions the kitchen has been considered for reuse. For the purpose of these investigations, it was attempted to identify the average expected profile of the greywater waste stream, with the recognition that some households will produce greywater of poor- er or better quality. Samples were drawn from 50 Canberra households, The samples were collected and composited. The composite was then tested within 3 h of collection for various chemical and biological qualities. The composite was then divided into five batches for simulation of vari- ous treatment options. Test processes used were:

Process 1: Storage at typical winter temperature Process 2: Storage at typical summer tempera-

ture Process 3 : Aeration at typical winter tempera-

ture Process 4: Aeration at typical summer temper-

ature Process 5: Trickle filter at typical winter tem-

perature

These processes are shown schematically in Fig. 2, with test results shown in Figs. 3-5.

The samples were collected periodically from the treatment processes over 3 weeks and

J. Neal / Desalination 106 (1996) 399-405 403

Process I -

Winter Storage Process 2 -

Summer Storage

Stone

Process 5 - Trickle Filter

(Winier)

Process 3 - Aeration (Winter)

Process 4 - Aeration (Summer)

Fig. 2. Greywater test processes.

analyzed for various chemical and biological

profiles. A composite from processes 3, 4 and 5 was then used to determine the effectiveness of peracitic acid as a disinfectant agent. The main advantage of peracitic acid is that it is totally biodegradable. The results of these tests indicate that peracitic acid can be considered an effective disinfection agent.

Its biggest advantage is that it is totally bio- degradable; however, the concentrations required do not compare favourably with conventional calcium hypochlorite dosing. The results of this testing indicate that processes 3, 4 and 5 each produced better than 20110 (BOD/SS) effluent within 1 week of treatment and better than 1000 within 2 weeks of treatment. It was found that process 5 produced more consistent results; how- ever, the energy costs of operation of this process were higher than for processes 3 and 4. It was found that peracitic acid, while effective as a disinfection agent, did not compare economically to conventional hyperchloride dosing.

Processes 1 and 2 soon became anaerobic with consequent deterioration of the biological profile of these units. The chemical tmprovement was significantly lower than the aerated units. Significant odours were evident near process units 1 and 2. Storage of the greywater in a sim- ilar fashion is not advisable.

Two basic concepts for the treatment of greywater were considered:

I. Temporary storage systems - These sys- tems generally entail a gross solids filter with a surge tank. The filtered greywater is then gravi- tated to a drip irrigation system. These systems do not permit controlled irrigation and should be seen more as a waste disposal system rather than a reuse system. In the Canberra climate it is thought that such systems could result in signifi- cant fungal infestations and run-off during winter months. Such systems would have to be bypassed back to the sewer during the winter.

2. Large storage systems - These systems generally involve some form of a digestive

J. Neal / Desalination 106 (1996) 399-405 404

180

160

140

120

sib 100

a

80

60

40

20

0

Process I *

Process 2 d

Process 3 *

Process 4 +

5 Days

10 5 Days lo 15

Fig. 3. Greywater treatment - BOD. Fig. 4. Greywater treatment - turbidity.

treatment to reduce the oxygen demand and low- er the amount of suspended solids. In practice almost all systems involved either an aerated suspended media digester or a fixed media di- gester. The effluent is of a quality to permit ex- tended storage. It is nevertheless recommended that the storage tank be aerated to maintain oxic conditions and provide some sedimentation.

More advanced membrane based treatment alternatives do exist; however, due to the cost and complexities of these units, they are not con- sidered appropriate for the use at household level at this stage.

able so that it is suitable for on-site compost- ing

l Main aeration tank baffled and sized to allow for at least 1 week* of greywater production

l Storage tank (preferably aerated) sized to at least 4 weeks of greywater production

l Disinfection unit if secondary contact is re- quired; where possible disinfection units should be based on minimum residual disin- fection levels with disinfecting methods which do not create measurable residuals; faecal coliform levels should be adopted as indica- tors of disinfection.

As a result of these investigations, the follow- ing minimum treatment components for greywater prior to reuse are recommended: gross screening, aeration (digestion/natural floccula- tion), sedimentation and disinfection (if second- ary level of physical contact is possible during reuse). A typical configuration should include: l Solids screening filter - the filter media

Trial units for full-scale testing are currently being designed for prototype implementation.

should be cheap, non-reusable and biodegrad-

*This figure has been extrapolated from Benchtop Experiments. It is expected that full-scale prototypes will be optimized to approximately 2-4 days of stor- age (i.e., a unit of 1-2 kl).

70

5il a

60

50

40

30

20

10

0

Process I w

Process 2

Process 3

Process 4 .

J. Neal / Desalination 106 (1996) 399-405 405

Process I *

10

0

Process 2 d

Process 3 -d-

Process 4 +

5 Days lo 15

Fig. 5. Greywater treatment - suspended solids.

While it has been recognized that this form of reused technology has potential, a complimentary set of conditions must be included in such a management system for broad-scale application.

Acknowledgements

The material presented in this paper is based on work undertaken by a number of officers in the Engineering Division of ACTEW Corpora- tion. The author gratefully acknowledges the initiatives and enthusiasm of these officers in bringing this work to fruition, in particular Ken Barnett, Bill Bencke and Peter Szlapinski.

References

[l] SCM consultants, LMWQCC Environmental and Process Audit, 1992.

[2] ACT Electricity and Water, ACT Future Water Supply Strategy, 1994.