Variations of morphology of activated sludge flocs studied at full-scale wastewater treatment plants

Abstract

Digital image analysis has been intensively developed over the last two decades including its application to describe morphology of activated sludge flocs. However, only few studies concerned the variation of flocs morphology with respect to the operational conditions, particularly oxido-reductive conditions, in a full-scale wastewater treatment plant (WWTP). In this work, morphology of activated sludge flocs was monitored over one year in two different full-scale WWTPs. The main aim of this study was to find the relationship between the operational parameters and morphology of sludge flocs. Simultaneously, the variations in floc size along activated sludge chamber were studied with respect to the oxido-reductive conditions. It was found that the sludge loading rate was one of the most important operational parameters influencing floc size. It was estimated that its values higher than 0.1 kg BOD5 kg TS−1 d−1 contributed to the decrease in floc size. Also, the oxido-reductive conditions influenced the floc size. It was statistically proved that flocs from the anaerobic zone were usually smaller than flocs from the anoxic or aerobic zones. Distribution of floc size in a full-scale WWTP usually could be described by a log-normal model.