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The Rural South Australian Water Filtration Project
United Utilities Australia is the major shareholder in and operator for Riverland Water, a consortium that has provided 10 advanced water filtration plants in rural South Australia.
These plants have been provided under an innovative $115m Build Own Operate Transfer (BOOT) contract with the South Australian Government. The contract awarded United Utilities and its partners, AMP Asset Management and Bechtel Enterprises, the right to operate the plants for 25 years after the completion of construction phases in late 1999.
Located mainly along the banks of the River Murray, the 10 plants serve about 150,000 people living in more than 90 rural communities. Crystal clear water to better than World Health Organisation standards, is produced using world's best practice technologies backed by a 'virtual' control room methodology that allows full remote control and operation of all plants outside normal business hours.
United Utilities and its partners are environmentally conscious companies and the design of the plants reflects this philosophy as well as incorporating the most practical, cost effective technologies to treat River Murray water.
Generally, river water is cloudy or turbid because during its 3,700km journey through the Murray-Darling river system it picks up impurities in the form of very fine suspended clay particles, along with organic material.
The presence of algae in the raw water can also cause an unpleasant taste and odour, so the treatment process has been designed to allow for dosing of raw water entering the plant with powdered activated carbon, to deal with these problems as they arise.
The water is then pumped into rapid mixing tanks where a coagulant is added to begin the complex physical and chemical processes of coagulation and flocculation. During coagulation small particles and organic water in the water form into larger particles or 'flocs'.
A flocculant aid is added to the coagulated water before it passes on to a second series of more gentle mixing tanks where the floc particles fully form.
After flocculation the water passes on to the clarification stage where most of the flocs settle to the bottom of the tank in the form of a sludge which is then removed and stored in nearby sludge lagoons. After drying, the sludge can be used for a variety of beneficial purposes ranging from an additive in brick making to soil conditioning.
By this stage more than 90% of the material has been removed and the water is ready for filtration. Here, hydrated lime (or caustic soda) is added to adjust the pH of the clarified water.
Rapid gravity filters remove the remaining 10% of the flocculated particles by sifting the water through beds of sand and filter coal.
The filters are backwashed automatically, with dirty backwash water flowing to the sludge lagoons.
The filtered water is then disinfected with chlorine or chlorine/ammonia, and fluoride is added for health purposes. After a short period in a clear water storage tank, the water is pumped into local distribution systems.