Kuruvilla Mathew

Perth, Western Australia’s largest city is under increasing pressure to implement a more sustainable means of water supply and use. The coastal city is expanding rapidly in both population and geographical size (EPA, 2005), while annual rainfall is variable and gradually decreasing (WC, 2005). On top of the supply issues Perth is continuing to implement a centralised approach to wastewater sanitation, which combines many wastewater streams before treatment and disposal to ocean outfall (EPA, 2005). This creates an open cycle system that has many sustainability issues including inefficient use of potable water supplies, loss of freshwater resources and nutrients, pollution of the receiving water bodies, as well as the need for high energy infrastructure (Ho and Anda, 2004). In response to Perth’s water supply concerns the Western Australian Government implemented a State Water Strategy in February 2003. Part of this strategy was to create a Premiers Water Foundation to support research and development projects that investigate water conservation and reuse. A project titled “Demonstration of Decentralised Wastewater Recycling in Urban Villages” was funded by the foundation and aims to achieve a number of demonstration projects and research studies. This technical report is the second of three reports within Premiers Water Foundation project and is focused on technical requirements associated with decentralised wastewater recycling. The aim of the research study is to investigate the technical requirements and technologies (technical elements) associated with the successful implementation of an urban village wastewater recycling system within the PMR, for which a model can be formulated to create reliable management systems and improved protection of public health and the environment.

Wastewater is often considered to be a source of public health problem and to be disposed of rather than considered as a resource. The choice of treatment system is usually governed by disposal strategy rather than reuse options. Domestic sewage generally consists of wastewater produced from the toilet, kitchen sink, bath, shower, washbasin and laundry. Toilet waste, which makes up 25 to 30 percent of the flow, is referred to as black water, while the rest of the wastewater is referred to as greywater. The blackwater contains the major portion of biochemical oxygen demand, suspended solids, bacteria and nutrients. So if the black water is treated separately then the treatment of greywater alone becomes easier and less complicated. Greywater reuse is widely supported by the community in Australia and promoted by researchers. However regulatory authorities have not given permission for greywater reuse. This paper illustrates a few case studies of greywater reuse trials following treatment of the greywater. The reasons for greywater reuse to be permitted by the regulatory authorities are articulated. In the future greywater reuse should be encouraged, and excess payment may be imposed if the greywater is to be treated by a municipality. This paper discusses the different treatment processes being developed to treat greywater successfully. Development of these methods and successful completion of the trials are necessary to develop public confidence to encourage greywater reuse. Present status of the methods and practices with direction for possible future developments are discussed in the paper.

Column experiments were conducted to determine the improvement in the removal of Escherichia coli, Salmonella adelaide and polivirus through sands of the Swan Coastal Plain in Perth, Western Australia, by amending the sands with bauxite refining residue. The bauxite refining residue (red mud) was neutralized using 5% gypsum and incorporated to form 30% of the amended sands. In 65 cm long soil columns the removal of the three organisms in the amended sand columns was excellent, with seven to eight orders of magnitude reduction in the concentration of the organisms between the inlet and outlet of the columns. An attempt was made to deduce the mechanism(s) of removal in the sand columns. Though obtaining reproducible breakthrough curves presented a problem, filtration, die-off and adsorption by the soil all appear to play a role in organism removal. The results also Show that E.coli can be used as an indicator for bacteria contamination, though S. adelaide was less efficiently removed than E.coli. Polivirus was on the other hand better removed than E.coli.

Laboratory column I with 30% RMG, described in last year's report, was operated for a further 11 cycles of 10 days of flooding with secondary effluent and 18 days of drying. Phosphorus removal continued to be excellent (over 96%). Nitrogen removal was poor (16%) due to minimal denitrification. TRO columns were constructed (A, 30% RMG and B, 20% RMG) and operated with primary effluent to increase organic carbon supply and reduce infiltration rate. Phosphorus removal over three cycles was excellent. Evidence of denitrification in column A Has strong (74%), though ammonium leaching was significant in both columns. Reduction in ammonium leaching by shortening the flooding period should increase nitrogen removal. It is recommended that both columns be operated for a further year to optimize nitrogen removal.

The performance of a recharge basin at the Kwinana Groundwater Recharge Site has been monitored since 1983. A primary aim of the monitoring programme is to study the improvement in the removal of faecal coliform (FC) and nutrients (nitrogen and phosphorus) by amending the sand of the recharge basin with gypsum neutralized red mud (RMG). The present report details the results of the monitoring programme from August 1985 to September 1986, consisting of 3 operating stages: Stage 1. Flooding (9d) and drying,(12d) of the basin using primary effluent (August 85 to March 86); Stage 2. Flooding (9d) and drying (12d) of the basin with a mixture of 2/3 secondary and 1/3 primary effluent (April to July 86); and Stage 3. Continuous flooding with primary effluent (August to September 86). Phosphorus removal was maintained at a high level (over 80%) in all the stages. FC removal was generally excellent (over a million fold reduction), except at the beginning of each stage when primary effluent was used and only a thousand fold reduction was achieved. Removal, however, improved with time and a million fold reduction was achieved. Nitrogen removal of about 40% was obtained with primary effluent using a cycle of flooding and drying (Stage 1). Continuous flooding with primary effluent (Stage 3) did not improve denitrification. No nitrogen removal was observed with a mixture of 2/3 secondary effluent and 1/3 primary effluent. It is recommended based on the above results that further monitoring be conducted using primary effluent to optimise nitrogen removal by adjusting the lengths of the floodin9 and drying periods.

Comprehensive review of the literature is presented and research studies of groundwater recharge with treated wastewater which offers a means for water re-use which has several advantages is described. The removal of nitrogen was studied in detail, since it is a major polutant in secondary sewage effluent and because soil adsorption is an important pre-requisite in its removal. A mathematical model was developed based on the processes contributing to nitrogen removal, in order to simulate the overall process and to optimize nitrogen removal. A simplified and yet realistic model was derived for management purposes.