Activated sludge process control via particle monitoring

The interrelationships between activated sludge plant operation and flee characteristics were examined in order to determine process control mechanisms for the effective treatment of domestic wastewaters and surplus activated sludge. A quantitative indicator of the physiological flee characteristics was developed and termed the morphological index, This maybe evaluated by plant operators using a simple assessment form and matching photographic guide of various flee structures, The morphological index and flee size distribution were found to be useful tools for activated sludge process control and monitoring the dewaterability of surplus activated sludge. It was found that flee size, morphology and in turn the dewaterability of surplus activated sludge varied with different operating conditions. Hydraulic retention times (HRTs) of < 10 hours and sludge ages of less than or equal to 8 days, resulted in the presence of small diffuse flee structures in the mixed liquor. The effluent quality was poor and the activated sludge had unfavourable filtering and dewatering properties, Switching plant operation to sludge ages in the region of greater than or equal to 8 days and HRTs of greater than or equal to 10 hours, was found to improve effluent quality and the dewaterability of surplus activated sludge, Here the flocs were large compact structures with short filaments protruding from the flee body. (C) 1997 IAWQ. Published by Elsevier Science Ltd.