Denitrification efficiency and biofilm community succession in a bidirectional alternating influent biofilter

Biofilters are widely used for nitrogen removal in wastewater treatment. This study developed a bidirectional alternating-influent biofilter to reduce clogging and enhance nitrogen removal. Alternating influent utilized biofilm on the media as a denitrification carbon source. With initial ammonium, nitrate, and total nitrogen concentrations of 8.49±0.30, 12.52±0.20, and 19.89±0.79 mg/L, the forward influent achieved ammonium, nitrate, and total nitrogen removal efficiencies of 81.6%, 66.8%, and 71.2%, increasing by 13.3%, 3.0%, and 4.8% at the effluent. Reverse influent further boosted nitrate and total nitrogen removal by 14.0% and 5.5%. The natural DO gradient under conventional influent conditions was simulated, and the nitrogen removal mechanism and treatment effect, mainly nitrification and denitrification, were discussed. Microbial analysis showed that endogenous carbon in the biofilm, derived from decaying cells and EPS, reduced clogging risk. Significant changes in bacterial count, EPS content, and microbial abundance were observed across influent directions, with Proteobacteria, Bacteroidetes, and Pseudomonas increasing under reverse flow. These results indicate that bidirectional alternating influent can significantly improve nitrogen removal and reduce clogging, offering an effective optimization for wastewater treatment.