Re-use of effluent

In Western Australia, country towns must re-use their effluent before being allowed to take new water from State supplies. As a result, some thirty-four towns spray chlorinated effluent on school and public sports grounds. Effluent is used similarly in Adelaide and the Queensland Gold Coast, and on some hundred golf courses around the nation. Wine grapes are drip-irrigated in South Australia and Victoria, there are several tree-growing projects and many pasture enterprises, and effluent is used in Western Australia for dust suppression and similar purposes in the mining industry.

Innovative proposals on a large scale have been put forward for the re-use of effluent from the Melbourne South-Eastern Purification Plant (SEPP) which was commissioned in 1975. This plant is a fine-bubble activated sludge plant of American design serving about 800,000 people, and producing a high-grade secondary effluent currently at the rate of 240 ML/d. At present, this effluent is discharged to the ocean via a 56 km pipeline. With increasing load on the system, this pipeline will have to be duplicated by the year 2000, or the effluent re-used elsewhere.

Proposals for re-use include landscape watering in Melbourne suburbs; industrial use as cooling water in the Latrobe Valley brown coal power stations and associated industries about 130 km to the east; aquifer recharge; and direct potable use, after further treatment, in the Melbourne water supply system, as is being investigated in the USA and South Africa.

All these proposals involve technological challenges whilst posing social and institutional problems. The last of them is potentially the most valuable and certainly the most challenging for the future. To quote from a recent paper -

The reasons advanced in the past for the non-consideration of potable water development from Melbourne's SEPP have been the technological complexity, availability of other sources, and that it would be unacceptable to Melbourne's population, encouraged as it has been to consider its supply of pristine purity. Although complex, it is increasingly feasible; other sources are likely to be costly economically or politically; and we believe people's acceptance of the efficiency of technology today, combined with the hip-pocket nerve effect, would, with an adequate long-term education program, lead to widespread acceptance of potable water production.

Collection systems

The concrete pipes generally used in sewerage systems are subject to severe corosion from the by-products of hydrogen sulphide generated in raw sewage.

In 1951, the major sewerage authorities in Australia initiated significant changes in the design, construction and operational concepts for sewers and pumping stations. One technique, developed principally in Perth, was to inject oxygen into pressure mains to prevent the development of anaerobic conditions.

Australian Academy of Technological Sciences and Engineering