Wastewater upgrades gain favour

Options for legacy facilities

Until recently, Local Authorities in Queensland and Tasmania owned and operated their wastewater treatment facilities. Many of these plants were old, undersized and provided substandard levels of treatment. In most cases, the smaller plants used trickling filters or facultative ponds. By the 1970s, extended aeration package plants and oxidation ditch-type activated sludge plants became more common.

In Tasmania, regional water authorities have taken over control of the state’s water and wastewater treatment facilities and in Queensland local authority amalgamations were undertaken state-wide, followed by a further amalgamation into three regional authorities in the south-east corner.

Spending priorities resulting from these amalgamations have been severely aggravated by recent extreme weather and the subsequent budget constraints imposed. Water and wastewater quality can’t be put on hold. The serious question must now arise: “What to do with these legacy facilities to ensure water quality standards and equipment reliability?”

A variety of upgrade options can provide practical, cost-effective solutions.

• Screening water-borne weeds and debris in major reservoir water intakes is a serious consideration, particularly in times of flood.
• Screening of sewage plant intakes benefits downstream processes.
• Sludge settling can be improved by refurbishing existing clarifier mechanisms or adding additional units.
• Nutrient reduction can be achieved by the installation of a correctly sized RBC unit as the biological stage. If nutrient removal is not required, refurbishing of trickling filters is worthy of consideration.
• A purpose-designed, solar-powered mixing device can provide odour capping, aeration and prevention of blue-green algae in facultative ponds. Alternatively, they can become settling/polishing ponds if led by a biological stage such as an RBC.
• Undersized packaged plants can be improved by adding additional settling tanks and upgrading aeration systems.
• Oxidation ditches with horizontal aerators may need augmentation of their aeration capacity with a floating high-speed aerator.
• ‘A’ class effluent (less than 10 CFU) can be achieved with a sound biological treatment regime followed by a disc filter.
• ‘A+’ class waters (less than 1 CFU) can be produced from the addition of an ultra-filtration (UF) MBR or package plant followed by UF filter.