Enhancing biofilm growth in an integrated fixed-film activated sludge process through modification of polypropylene carriers

Biofilm is crucial in implementing integrated fixed-film activated sludge (IFAS) systems. However, current carriers face challenges in long-term stable operations. This study proposes using cationic polyacrylamide (PAM) as a positive-charged addictive and surface abrasion to modify polypropylene (PP) pipes to enhance biofilm growth and maintain long-time operation in IFAS applications. The modified PP carriers have significantly increased specific surface area compared to unmodified ones. The growth of biofilm on modified carriers is as much as over four times due to the improved biocompatibility of the material. The follow-up aerobic IFAS process achieves over 40% total nitrogen (TN) removal through simultaneous nitrification and denitrification with no specific anoxic stages or reactors. The sludge settling performance of the system is also improved with a stable 30-min sludge settling ratio of 18%. The maximum specific denitrification rate of the detached biofilm is 17.82 mg NO3−-N/g MLVSS/h, which is 33% higher than the pure activated sludge system. The high-throughput sequencing analysis results reveal that the abundance of biofilm-formation beneficial microbes increased from 0.02% to 16.47%.