ABSTRACT: The parameters of the power-law and log-normal floc size distribution models were correlated with the values of process operation factors for five, full-scale conventional activated sludge wastewater plants. Stepwise regression was applied to investigate the combined
effects of these factors and the interaction of selected factors. Factors affecting the frequency of occurrence of primary particles were examined by logistic regression and stepwise regression. It was found that the process operation factors affect the floc size distribution in a complex
way, but sludge loading was the most important and statistically significant factor influencing the frequency of occurrence of primary particles (<2 μm) in mixed liquor.
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