Aerobic Granular Sludge Treatment of Piggery Wastewater: Solution to the Problem of Non-Filamentous Bulking and Analysis of Microbial Community Structure in Practical Application

Aerobic granular sludge (AGS) shows promise in treating piggery wastewater compared to conventional activated sludge methods. However, current AGS research primarily remains confined to the laboratory, with limited practical applications in actual piggery wastewater treatment. Besides, AGS faces challenges such as unstable structure and susceptibility to sludge bulking in practical settings. This study aimed to assess AGS's efficacy in treating actual piggery wastewater and successfully resolved the non-filamentous bulking issue through various measures. AGS formation occurred by the 13th day of operation, demonstrating high pollutant removal rates, with ammonia nitrogen (NH₄⁺-N), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorous (TP) removal rates reaching 99%, 99%, 90%, and 96%, respectively. However, Zoogloea overgrowth led to increased polysaccharide secretion and subsequent non-filamentous bulking on the 32nd day, which adversely impacted TN, COD, and TP removal efficiency. To address the bulking issue, the influent COD concentration was initially adjusted from 500 ± 50 mg/L to 2000 ± 50 mg/L and then decreased to 700 ± 50 mg/L. Additional measures included lowering water temperature, enhancing hydraulic shear force and selective pressure, and conducting manual screening, resulting in a notable decrease in sludge bulking by the 60th day. Throughout the granulation process, there was a reduction in species diversity and microbial biomass in the sludge, especially noticeable before and after addressing the sludge bulking issue. Initially, Zoogloea dominated the AGS, but following the resolution of the non-filamentous bulking issue, there was a shift to Thauera as the dominant bacterium.