Foulingand Cleaning of Fine Bubble Ceramic Dome Diffusers

ReportNo WSAA 14

July 1990

SYNOPSIS

Finebubble ceramic dome diffusers used for aeration in the activated sludge processare subject to fouling and performance deterioration with time. In this studytest data from three Engineering and Water Supply (EWS) Department treatmentworks, collected over a period of six years, were analysed to determine theeffect of fouling and refiring on performance and to determine optimum cleaningmethods and schedules. The study included physical and chemicalcharacterisation of the microstructure of clean and fouled diffusers, andreview of the experiences of other authorities in Australia and the USA.

Itwas found that diffuser fouling at the three EWS treatment works was caused bya surface biofilm, plus internal fouling with both organics and chemicalprecipitates. Relationships between the degree of fouling and performancecharacteristics were developed. A logarithmic model of fouling rate was alsodeveloped, which differs from the linear model proposed by the US EnvironmentalProtection Agency.

Alternativediffuser cleaning techniques, including refiring, ultrasonic cleaning andleaching with a range of chemicals were explored in the laboratory. It wasconcluded that refiring was the most effective technique. A guideline refiringinterval of 10 years was recommended on economic grounds.

Guidelinesfor condition monitoring and design were also drawn up.

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