Fouling and Cleaning of Fine Bubble Ceramic Dome Diffusers
This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.
Report no. UWRAA 14
Fine bubble ceramic dome diffusers used for aeration in the activated sludge process are subject to fouling and performance deterioration with time. In this study test data from three Engineering and Water Supply (EWS) Department treatment works, collected over a period of six years, were analysed to determine the effect of fouling and refiring on performance and to determine optimum cleaning methods and schedules. The study included physical and chemical characterisation of the microstructure of clean and fouled diffusers, and review of the experiences of other authorities in Australia and the USA.
It was found that diffuser fouling at the three EWS treatment works was caused by a surface biofilm, plus internal fouling with both organics and chemical precipitates. Relationships between the degree of fouling and performance characteristics were developed. A logarithmic model of fouling rate was also developed, which differs from the linear model proposed by the US Environmental Protection Agency.
Alternative diffuser cleaning techniques, including refiring, ultrasonic cleaning and leaching with a range of chemicals were explored in the laboratory. It was concluded that refiring was the most effective technique. A guideline refiring interval of 10 years was recommended on economic grounds.
Guidelines for condition monitoring and design were also drawn up.