Optimizing the inclined plate settler for a high-rate microaerobic activated sludge process for domestic wastewater treatment: A theoretical model and experimental validation

Abstract

This study used a theoretical model and an experimental system to investigate the feasibility of using inclined plate settlers (IPSs) to upgrade the secondary clarifier for bulking sludge recovery in the high-rate microaerobic activated sludge (MAS) process that achieved enormous reduction in aeration energy consumption during domestic wastewater treatment. Compared to bulking sludge concentration (1.2–4.2 g/L) (and thus varied sludge zone settling velocities), both the experimental results and the theoretical predictions demonstrated that the plate length-to-spacing (L/D) ratio (3.75–15) of the IPSs likely plays a decisive role in determining its treatment capacity of the IPSs for bulking sludge recovery. The theoretical model was finally simplified to predict the critical surface loading rate of the IPSs as a function of the L/D ratio. The maximum biomass concentration in the micro-aeration tank of the high-rate MAS process was set at 4.5 g/L to assure effective sludge/water separation and bulking sludge recovery. Lastly, the continuous operation of the high-rate MAS-IPS process over a lengthy period achieved stable effluent turbidity of <4 NTU and COD and NH4+-N removals of 97 ± 2% and 93 ± 6%, respectively, when the treatment capacity of secondary clarifier was enhanced by >28%.