Effluent Reuse

A solution to the water crisis?

Scarcity of conventional sources of water in arid and semi-arid regions of the world has been behind the movement to find alternative or additional sources. Some of the possible sources are: deep groundwater, treated wastewater, and brackish water. Deep groundwater is not always available and can be very costly to access. Saline water application to agricultural land results in limited agricultural yields and salt accumulation in the soil. Wastewater, when treated, is a relatively stable water source that has uses in agriculture, industry, recreation, gardening, industrial-plant cooling, and recharge of groundwater.

Wastewater transport and collection dates back thousands of years. Sargon the Great, an Assyrian king (1705 BC), in Babylon had bathrooms and toilets that emptied into a sewer. Excavations of palace ruins in Knossos in Crete have revealed sewerage systems from the ancient Minoan Culture from around 1700 BC. The Roman palaces of Caesar, some 2000 years ago, had bathrooms, toilets and sewers.

The Roman conquest of Britain resulted in plumbing systems being established there. These early toilets were connected to cess pools (early septic tanks), or were drained into open sewers on the street. Later these systems were abandoned and sewage was taken in pipes to be dumped, untreated, into the nearest river. British colonialism took plumbing to all its colonies. The current water scarcity of water has focussed predominantly on ways to reuse water. Although there is some emphasis on reducing water use, some of the inherited practices have not been questioned enough.

The reuse of effluent for irrigation purposes has occurred for centuries, and with increasing pressure on potable water supplies, the extent of reuse is increasing. Effluent from sewage treatment plants and intensive feedlots may be a valuable source of water and nutrients for crop and pasture applications. There are a number of technical, economic, environmental and social issues associated with effluent reuse:

• Health and safety hazards and risks
• Impacts on aquatic and marine ecology
• Impacts on groundwater and surface water quality
• Environmentally sustainable effluent irrigation rates
• Socio-economic and community issues
• Air quality, odours and noise
• Cumulative impacts
• Economic risks, and
• Engineering issues.

The increasing pressure on urban water supplies is a result of population growth, climate variability resulting in less reliable yields from existing storages and the detrimental impact of discharges from urban development. Although urban and industrial water demand is less significant than that of the irrigated agricultural sector, urban water services providers are leading the search for new ways to provide water to end users.

Effluent management system options include spray irrigation, pond systems or a combination. In the spray irrigation system the effluent is sprayed directly onto pasture or crops. Optimally, provision should be made to store the effluent during periods of extended wet weather when spray irrigation of effluent should not take place.

Effluent systems based on pond techniques need to ensure that storage needs are sized according to the amount of manure, washwater and rain entering the waste system during the wetter months of the year. Effluent is treated in an anaerobic settling pond and one aerobic treatment/storage pond. Treated effluent is applied to pastures or crops by gravity or spray irrigation or recycled for farmyard washdowns.

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