Integrated constructed wetland and bioelectrochemistry system approach for simultaneous enhancment of p-chloronitrobenzene and nitrogen transformations performance

Constructed wetlands (CWs) integrated with the bioelectrochemical system (BES-CW) to stimulate bio-refractory compounds removal holds particular promise, owing to its inherent greater scale and well-recognized environmentally benign wastewater advanced purification technology. However, the knowledge regarding the feasibility and removal mechanisms, particularly the potential negative effects of biorefractory compounds on nitrogen removal performance for the CWs is far insufficient. This study performed a critical assessment by using BES-CW (ECW) and conventional CW (CW) to investigate the effects of p-Chloronitrobenzene (pCNB) on nitrogen transformations in CWs. The results showed that low concentration (1 mg·L-1) of pCNB would inhibit the ammonia oxidation in CWs, while ECW could improve its tolerance to pCNB to a certain level (8 mg·L-1) due to the high pCNB degradation efficiencies (2.5 times higher than CWs), accordingly, much higher TN and nitrate removal efficiencies were observed in ECWs, 81.71% - 96.82% (TN) higher than CWs, further leading to a lower N2O emission from ECWs than CWs. The main intermediate of pCNB degradation was p-Chloroaniline (pCAN) and the genera Geobacter and Propionimicrobium were consider to be the responsible pCNB degradation bacteria in the present study. However, too high concentration (20 mg·L-1) of pCNB would have a huge impact on ECW and CW, especially microbial biomass. Nevertheless, ECW could improve the 1.87 times higher microbial biomass than CW on the substrate. Accordingly, considerably higher functional gene abundance was observed in ECW. Therefore, the introduction of BES has great potential to ensure CW stability when treating industrial wastewater containing bio-refractory compounds.