Cessnock Wastewater Treatment Plant Upgrade

Cessnock Wastewater Treatment Works was built in 1936 and consisted of coarse screening, sedimentation, biological filtration and humus clarification processes. Unheated and unmixed digestion was employed for sludge treatment, with unburnt gas emission to atmosphere.

In the 1970’s inlet works and large maturation ponds were added, and in the early 1990’s an artificial wetland was built to ‘polish’ the effluent before being discharged.

A later study showed that the plant was undersized, mechanical equipment was badly deteriorated and screening and grit removal systems were totally inadequate. The plant did not meet contemporary Workplace Health & Safety standards and was also unable to satisfy New South Wales EPA environmental requirements. The study suggested that a major upgrade of the Cessnock plant, instead of a complete rebuild would be more cost effective and achieve significant energy savings.

EPCO Australia provided consultative services during the equipment design stage of the project, before being awarded the contract to supply equipment for the upgrade, giving the company the opportunity to work once again with John Holland Water Group, (the head contractor for the project) with whom a mutually satisfying working relationship has been maintained over many years.

EPCO Australia’s work scope consisted of four distinct processes, namely:

• Primary sedimentation using two 16m diameter primary peripheral drive clarifiers featuring sludge and scum removal systems and the use of stainless steel construction throughout.

• Biological trickling filter mechanisms (rotary distributors) retrofitted to the four existing 30.8m diameter trickling filter beds. These mechanisms feature rotating centre wells fitted with 6 sprinkler arms and are specifically designed to provide ample stability and excellent accessibility for inspection, cleaning and maintenance. The units are operable at very low hydraulic losses.

• A 22m diameter secondary peripheral drive humus clarifier provides the final BOD and suspended solids reduction stage in the main stream of the humus treatment process, principally due to the removal from the liquid stream of the solids which slough of the trickling filter growth media. The solids are recycled to the digester.Clarified effluent flows to the maturation ponds.

• Primary sludge digestion equipment incorporating a 13m diameter floating gas holder roof, sequencing gas lance mixing system, sludge heating system and waste gas burning.

Hunter Water have realised their expectations of the plant upgrade with the following observations:

• Over 70% reduction of greenhouse gas emissions from the plant processes.

• Significant reduction of odour levels emanating from the plant.

• Generation of renewable energy in the form of biogas.

• The rate of gas production being achieved from the digester (over that required for sludge heating) is making the retrofitting of a congeneration plant a feasible option.

• Significant reductions to the levels of BOD, suspended solids and total nitrogen in the treated effluent going to the maturation ponds.

• Phosphorus reduction facilities have also been added.

• On site sludge dewatering is now being employed and will provide a finite reduction to plant operating expenses.

For further information or to arrange for a site assessment please contact us.

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