Enhancing biological nitrogen removal of slaughterhouse and meat processing wastewater in three-stage AO process by influent allocation: From lab-scale to full-scale investigation

Three-stage anoxic/aerobic (AO) process is promising for efficient nitrogen removal from high-strength wastewater. Herein, the effects of influent allocation modes (50/40/10 vs. 50/25/25) on nitrogen removal performance for treating slaughterhouse and meat processing wastewater (SMPW) were investigated from lab-scale to full-scale three-stage AO processes. Compared to 50/25/25 (94.1 %), the allocation mode of 50/40/10 achieved a higher nitrogen removal of 97.7 % and better adaptability to ammonia load. The second anoxic tank contributed the highest total nitrogen (TN) removal in the system with allocation mode of 50/40/10, while simultaneous nitrification–denitrification and aerobic denitrification in the thrid oxic tank effectively enhanced the TN removal efficiency. Microbial community analysis revealed that SMPW treatment systems tended to enrich lipolytic bacteria (Pseudomonas and Bacillus), cellulolytic bacteria (Christensenellaceae_R-7_group), proteolytic bacteria (Proteiniclasticum, Planococcus, and OLB8), and denitrifying glycogen accumulating bacteria (Candidatus_Competibacter). Meanwhile, the inherent nature of SMPW promoted an increase in the dissimilatory nitrate reduction to ammonium pathway, while the abundant and complex organic substances environment ensured efficient nitrogen removal. The influent allocation mode had no significant effect on nitrification process, but the 50/40/10 allocation mode obviously enriched the nitrous oxide reductase encoded by gene nosZ, which reduced carbon emission. The reliability of 50/40/10 was verified in a 35,000 m³/d full-scale SMPW treatment plant, with the effluent COD, TN, and ammonia nitrogen stabilized at 18 ± 5, 4.7 ± 1.8, and 0.9 ± 0.2 mg/L, respectively, after 48 days. This study provides a valuable reference for effective regulation of three-stage AO process in treating SMPW.