Simultaneous nitrification and denitrification in an aerobic biofilm biosystem with loofah sponges as carriers for biodegrading hydrolyzed polyacrylamide-containing wastewater

Simultaneous nitrification and denitrification (SND) during treating hydrolyzed polyacrylamide (HPAM) containing wastewater were explored in an aerobic biofilm reactor biosystem. Here, loofah sponges as the environment-friendly and low-cost material were applied as the carriers in this biosystem. The removal efficiencies of HPAM and total nitrogen (TN) reached 43.6% and 54.3%, respectively, after 120 days stabilized running periods. Moreover, the structure of loofah sponges affected anaerobic microenvironment significantly which was indispensable for realizing a high-performance of SND. Key microorganisms in this biosystem included nitrobacteria, denitrobacteria and HPAM-biodegrading bacteria. The abundance of nitrobacteria and denitrobacteria on the biofilm was increased by 17.2% and 15.3%, respectively, through cultivation. Meanwhile, the biotransformation mechanisms of HPAM and diverse valence of nitrogen under different chemical oxygen demand (COD)/N and dissolved oxygen (DO) conditions were investigated. When COD/N and DO were 8:1 and 2 mg/L, HPAM biodegradation, SND efficiency and TN removal achieved their maximum, and the values were 54.3%, 92.3% and 60.1%, respectively. Key enzyme activities also reached their maximum in this condition. The optimal COD/N and DO was pivotal to achieve the high-performance of SND, and it was closely correlated with HPAM biodegradation. Meanwhile, SND could facilitate the biotransformation of HPAM.