Effect of PAC on the operation characteristics of A-BAF

To overcome the shortcoming of biological aerated filter (BAF) on phosphorus removal, poly aluminum chloride (PAC) was dosed into the anoxic tank of anoxic-biological aerated filter (A-BAF). The effects of PAC on the phosphorus, organic matter and nitrogen removal by A-BAF and the head-loss development of BAF were investigated through a lab-scale experiment. The results showed that the addition of PAC had a positive effect on phosphorus removal by A-BAF, but had no effect on the removal of organic matter and nitrogen. With the PAC dosage of 100 mg/L, the TP concentration in effluent was reduced from 2.57 mg/L to 0.34 mg/L, when the influent TP concentration was 3.5 mg/L. The COD, NH ₄ ⁺-N and TN concentration in effluent were 30, 1 and 11 mg/L separately, which were similar to those in the effluent without PAC. Meanwhile, the backwashing cycle of BAF was increased from 4 d to 10 d and the specific resistance to filtration of the excess sludge was decreased from 210 × 10 ¹²m/kg to 125 × 10 ¹²m/kg after PAC dosing.