Integrated Fixed-Film Activated Sludge System for Upgrading Overloaded Municipal Wastewater Treatment Plants

Abstract

Overloaded municipal wastewater treatment plants often experience reduced treatment efficiency, insufficient nutrient removal, and operational instability due to increasing wastewater flow and organic loading beyond original design capacity. Upgrading existing treatment infrastructure using advanced hybrid biological systems has therefore become essential for sustainable urban wastewater management. The present study investigates the application of an integrated fixed-film activated sludge system for upgrading overloaded municipal wastewater treatment plants under varying operational conditions. The research focuses on evaluating organic pollutant removal, nutrient reduction efficiency, biomass retention, and process stability associated with hybrid attached-growth and suspended-growth treatment processes. Experimental analysis was conducted to examine the influence of hydraulic retention time, aeration intensity, carrier media filling ratio, sludge retention time, and organic loading rate on treatment performance and microbial activity. Results demonstrate that the integrated fixed-film activated sludge system effectively enhances biomass concentration and microbial diversity through the simultaneous operation of suspended activated sludge and attached biofilm growth mechanisms. The study further reveals that optimized carrier media configuration and aeration conditions significantly improve nitrification, denitrification, and organic matter degradation while maintaining stable operation under overloaded conditions. Increased biofilm development contributed to improved resistance against hydraulic shock loads and enhanced pollutant removal efficiency.