Effluent Reuse: Land and Wet Weather Storage Requirements
This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.
Report no. UWRAA 80
This project, jointly funded by the Urban Water Research Association of Australia and NSW Public Works, determines the extent that effluent reuse for irrigation of land is a feasible proposition and provides basic design data.
The work was undertaken by computer model studies of the operating behaviour of systems using climatic data and recorded effluent flows for a sample of town in various locations in NSW.
A daily simulation model of effluent reuse was developed to monitor storage, runoff and overflow volumes for a given system with general applicability to any locality. The model was used to size works and produce basic regional design charts relating effluent flow rate, land area and storage volume.
The regional design charts vary according to differences in evaporation and precipitation and the rainfall distribution and intensity for the region. The charts show that in general for a given land area higher effluent application rates are attainable for inland regions where evaporation greatly exceeds precipitation as opposed to coastal regions. Consequently the wet weather storage volume requirements for zero discharge will be less for inland areas.
The achievement of 100% reuse and the condition of zero discharge for wet weather storage are generally costly due to the large land area and storage requirements. A more practical approach would involve partial reuse and the allowance of overflows from the wet weather storage volume at some reasonable frequency such as a 1 in 10 year event.
The increase in sewage flow due to infiltration and inflow to the sewer system during high rainfall events significantly increases the storage requirements for reuse schemes. Effluent reuse schemes should be accompanied by a sewerage system improvement program to reduce wet weather flows thereby improving the performance and reducing the cost of the reuse scheme.
The regional charts provide a more rigorous solution in comparison to other techniques in the sizing of works in a reuse scheme. Compared to other methods the regional charts provide a simple, quick but rigorous initial method for sizing an effluent reuse scheme taking account of daily data, site runoff and wet weather inflows.
For final design of effluent reuse systems, a daily simulation model should be used to assess system performance taking account of local climatic data, wet weather inflows and the irrigation and drainage characteristics of the irrigation site.