The existing theories incorporated to state‐of‐the‐art, activated‐sludge‐consensus models indicate that the removal of particulate substrate from the liquid in the activated‐sludge process is a two‐step process: instantaneous enmeshment of particles and hydrolysis followed by oxidation. However, experimental observations indicate that the removal of particles is not instantaneous and needs a more accurate description. This removal process can actually be described as a three‐step process: flocculation, hydrolysis, and oxidation. The principal objective of this research was to observe and model the kinetics of the removal of suspended particles and colloidal particles. A first‐order, particulate‐removal expression, based on flocculation, accurately described the removal rates for supernatant suspended solids and colloidal chemical oxygen demand (COD). The rate of reaction for removal of colloidal COD was slow and comparable to that for soluble organic matter.
SummaryA method for calculating the mass transfer coefficient in a biological film system, under turbulent flow conditions, is presented. I t is experimentally found that fluid velocity has a positive effect on the rate of substrate utilization when the system is operated in other than the kinetic regime. A correlation is developed which indicates a dependence of the mass transfer coefficient on the fluid velocity raised to the 0.7 power.
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