Conference Papers | 2008 Victorian Conference Papers

CLEANING OF DIFFUSERS AT EDGEWORTH WASTEWATER TREATMENT PLANT
John Stevens, Wastewater Treatment Plant Operator, Hunter Water

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ABSTRACT

The Edgeworth WWTW catchment area is 65,000 E.P. and treats an approx ADWF of 16ML/day. Edgeworth WWTW services the areas of Charlestown, Hillsborough, Cardiff, Boolaroo, Speers Point, Glendale, Edgeworth, Barnsley and Killingworth. Some of these areas, notably Cardiff and Hillsborough, contain industrial areas. There are a number of trade waste customers throughout the catchment

The original Edgeworth WWTW was constructed in 1933. The original plant consisted of primary sedimentation followed by four trickling filters and two humus tanks. Sludge was digested using covered cold anaerobic digesters.

The old plant was augmented in the following stages:

• 1968 Circular primary sedimentation tank
• 1971 Two additional trickling filters and an additional humus tank
• 1979 A heated digester control building, maturation pond and sludge lagoon
• 1980 New inlet works
• 1985 Two additional primary sedimentation tanks

In 1996 a new activated sludge plant was constructed and commissioned at the site.

Secondary treatment at Edgeworth Wastewater Treatment Works is by Modified Lutzack Ettinger (MLE) process. Flow is directed continuously between two bioreactors, which have an anoxic zone and an aerobic zone. Porous polyethylene disc diffusers supply air to the aerobic zones. There are 1306 diffuser discs in each bioreactor. These diffusers are subject to fouling and deterioration and need to be cleaned periodically. The inner surfaces may become clogged with air borne dust if the blower inlet air filtration system is defective. The outer surfaces become coated in attached biological and inorganic slimes. There has been excessive prolonged air outages due to power surges and blackouts and this will have contributed to solids settling on or entering the diffuser openings, adding to the fouling problem. Increased backpressure on the blowers and reduced oxygen transfer (seen in the inability to meet DO set points) are the best indicators of diffuser deterioration.

To keep the plant operating at its optimum level, a number of different methods were trialled to clean the diffusers. Finally a method was devised where the bioreactors were only offline for a short amount of time. This is important to maintain adequate treatment. This paper will briefly describe the methods trialled and the procedure selected which now allows the quick and safe cleaning of the diffusers and the return of the bioreactors to service with minimum disruption to the process.