Characterization of Long-Term Foulants Deposited on Full-Scale Membrane Modules in Submerged MBR Processes

Two full scale membrane modules were sampled at a variety of locations, before and after maintenance and recovery cleanings, to investigate the spatial distribution of fouling on the membrane surface and through the fouling layer. Along the length of a fouled membrane fibre, the filtration resistance and biofilm thickness was consistent. Maintenance cleaning decreased foulants on membrane surfaces and within membrane pores. Recovery cleaning effectively removed the majority of organic foulants on the membrane surface. The accumulation of proteins, carbohydrates and lipids within the membrane was minimally decreased, suggesting their key role in long-term irrecoverable fouling. There was no correlation found between biofilm thickness and permeability. Furthermore, the deposition of inorganic foulants, in particularl calcium and magnesium, were identified on the membrane surface even after citric acid cleaning. Testing confirmed the formation of inorganic precipitates identifying them as as an important factor in forming long-term irrecoverable fouling.