Simultaneous Biodegradation of Refractory Organic Matters and Nitrogen from Coking Wastewater in a Step-Feed Three-Stage Integrated A/O Biofilter System

In-depth understanding biodegradation process of refractory organic matters (ROMs) and nitrogen has important practical implications for coking wastewater treatment. Herein, spectral response in combination with high-throughput sequencing was used to identify removal behavior and microbial functional traits during biodegradation of ROMs and nitrogen pollutants in a novel step-feed three-stage integrated A/O biofilter process (SFTIAOB). Long-term operation demonstrated complete simultaneous removal of COD, phenol, heterocyclic aromatic hydrocarbons and nitrogen were achieved. Mass balance analysis showed that TIN removal in A3 and O2 zone was relatively higher, while most total organic nitrogen (TON) was eliminated principally in anoxic zones. Ultraviolet visible (UV–Vis) observed initial carboxylation and subsequent ring cracking and mineralization. Fourier infrared (FTIR) found that key functional group were cracked along with the production of C=O, free C-N and N-H bond and -COOH bonds. Excitation-emission matrix (EEM) spectrum indicated that the significant transformation and elimination of tryptophan and humic acid with high molecular weight. These observations suggested the ring opening, distinct degradation and even complete mineralization of complex ROMs through the alternation of aerobic and anoxic condition, which was also verified by gas chromatography-mass spectrometry (GC-MS) analysis. High-throughput sequencing showed microbial community structure and function were significantly altered in different zones: Methanothrix dominated in the primary and secondary anoxic zones, while Gemmobacter and Pseudomonas were remarkably enriched in the third A/O phase. Moreover, the aromatic ring-cleavage enzyme (kynA, gabT, pcaG/H and catE) and denitrification enzyme (nar, nirK and nor) play the essential role for simultaneous biodegradation of ROMs and nitrogen. Finally, the biodegradation mechanism of ROMs and nitrogen was effectively illustrated. This research revealed the linkage between spectral response, microbial community and biodegradation of ROMs and nitrogen for practical application.