ACTIVATED-SLUDGE PROCESS-CONTROL VIA PARTICLE MONITORING

The interrelationships between activated sludge plant operation and fl ee characteristics were examined in order to determine process control mechanisms for the effective treatment of domestic wastewaters and su rplus 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 for m and matching photographic guide of various flee structures, The morp hological index and flee size distribution were found to be useful too ls for activated sludge process control and monitoring the dewaterabil ity of surplus activated sludge. It was found that flee size, morpholo gy and in turn the dewaterability of surplus activated sludge varied w ith different operating conditions. Hydraulic retention times (HRTs) o f < 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 unfavourab le filtering and dewatering properties, Switching plant operation to s ludge ages in the region of greater than or equal to 8 days and HRTs o f greater than or equal to 10 hours, was found to improve effluent qua lity and the dewaterability of surplus activated sludge, Here the floc s were large compact structures with short filaments protruding from t he flee body. (C) 1997 IAWQ. Published by Elsevier Science Ltd.