A modified BAF system configuring synergistic denitrification and chemical phosphorus precipitation: Examination on pollutants removal and clogging development

The performance of a BAF system configuring simultaneous chemical phosphorus precipitation in the pre-denitrification stage was examined using a continuously operated setup to treat real domestic wastewater. The effects of using no chemical, dosing sole Fe²⁺, and dosing combined Fe²⁺, PAM, and NaHCO₃ in the pre-denitrification tank were assessed by monitoring COD, nitrogen, and phosphorus removal and hydraulic headloss development in the BAF column. Though dosing sole Fe²⁺ significantly enhanced phosphorus removal, it would consume alkalinity through hydrolysis and form smaller-sized sludge flocs in the pre-denitrification tank, and hence resulted in affected NH₄⁺-N, insoluble COD, and SS removal in the BAF. Dosing combined Fe²⁺, PAM, and NaHCO₃ can enhance sludge flocculation to form larger flocs and compensate alkalinity consumption. It exhibited sound performance on COD, nitrogen, and phosphorus removal, and led to less frequent BAF backwashing by slowing clogging development in the BAF filter layer.