Coupled electrocoagulation-integrated fixed-film activated sludge process for treatment of low C/N ratio aquaculture wastewater

Aquaculture wastewater is typically characterized by low organic matter content and high nitrogen concentrations, with the accumulation of suspended solids impairing the health of aquatic species and the stability of aquaculture systems. Traditional biological treatment processes are challenged under low C/N conditions, while single-process treatment technologies are often insufficient to simultaneously achieve suspended solid removal and efficient nitrogen conversion. This study established and evaluated the performance of a coupled electrocoagulation-integrated fixed-film activated sludge (EC-IFAS) process for aquaculture wastewater treatment. Single-factor experiments and response surface methodology were applied to optimize EC operating parameters, with turbidity removal efficiency as the response variable. The effects of reaction time, current density, salinity, and stirring speed were investigated. The results demonstrated that the EC process achieved 93.6% turbidity removal efficiency under the conditions of 60.2 A/m² current density, 35.7 min reaction time, 0.65‰ salinity, and 258 rpm stirring speed. Subsequent optimization of operating modes for the IFAS reactor indicated that a 6-hour operational cycle with 2-hour intermittent aeration effectively enhanced the simultaneous nitrification-denitrification process. The coupled EC-IFAS system achieved 97.2% total turbidity removal efficiency, 93.8% average COD removal efficiency, stable TN removal efficiency ranging from 75.1% to 81.2%, and consistent PO 4 3- -P concentration below the detection limit. Microbial community analysis indicated that Thauera and Terrimonas were the primary dominant genera, which closely associated with organic matter degradation and denitrification processes, respectively. Additionally, the IFAS biofilm showed higher species diversity compared to suspended sludge.