Removal of contaminants from wastewater by sedimentation in a circular secondary clarifier

Abstract

In wastewater treatment, a circular clarifier is used to separate wastewater into sludge and effluent in the primary treatment process, and it is one of the core instruments in the secondary treatment process for sludge sedimentation. Since biological sludge sedimentation has strong spatially and temporally non-uniform characteristics and a relative float settling velocity, a separation structure is applied to induce a uniform flow field to improve performance. This clarifier also requires an evacuation system for frequent solid removal. The source of power consumption with the clarifier is the induced flow energy. The result is that the effluent from the clarifier will have low turbidity with a high removal efficiency of contaminants. High removal efficiency is very important to meet the standard 'B' in the Department of Environment's effluent standard. This study will use numerical analysis (CFD) to simulate and validate the results from experimental work. By using CFD, it is hoped that this study can provide a better understanding of the hydraulic behavior and provide a scientific basis for the design process of a circular clarifier for sedimentation. A circular clarifier is crucial equipment in the primary treatment of wastewater. In this study, a circular clarifier with improved structural designs, for which a set of baffle plates with appropriate dimensions and locations generating reduced flow energy, was developed. CFD simulations of contaminant sedimentation were coupled with an Artificial Fish Swarm Algorithm optimization workflow to maximize removal efficiency under operational and hydraulic constraints. This clarifier demonstrated satisfactory performance in sediment separation. Trace back simulations and artificial fish swarm algorithms were applied to determine the optimal design of the clarifier. With these optimal structural dimensions, the clarifier could effectively minimize the sludge volume accumulation rate and shorten the time required for sludge sedimentation in wastewater treatment. Additionally, sediment outlets of different dimensions and various wastewater treatment levels were considered. Both numerical simulations and experimental tests were included for performance evaluation.