Simultaneous high-concentration pyridine removal and denitrification in an electricity assisted bio-photodegradation system

Abstract In this study, enhanced degradation of high-concentration pyridine and simultaneous denitrification were achieved in an Electricity assisted bio-photodegradation system (EBPS) with a photoanode zone, a biocathode zone and an aerobic zone. The recombination of photoelectron-hole pairs was significantly suppressed in EBPS, which could not only improve the pyridine oxidation in photoanode zone, but also accelerate the biodegradation process in biocathode zone. NH4+ produced from pyridine degradation could be effectively nitrified into NO2- and NO3- in aerobic zone, which was recirculated into biocathode zone to serve as electron acceptor for accelerating pyridine biodegradation. When influent pyridine concentration was as high as 1250 mg L-1, pyridine was completely degraded without adding any extra electron donors, and complete denitrification was achieved in biocathode zone. Microbial community analysis confirmed the enrichment of the pyridine biodegradation species (Rhodococcus, Hydrogenophaga, Truepera and Thermovirga), denitrification species (Thiobacillus, Thioalkalispira and Rhodococcus) and electroactive species (Thiobacillus, Thermovirga, Hydrogenophaga, Thioalkalispira and Rhodococcus). Furthermore, the mechanism of pyridine metabolism, denitrification and extracellular electron transfer processes in EBPS was investigated, utilizing Phylogenetic Investigation of Communities by Reconstruction of Unobserved States 2 (PICRUSt2). The results showed that the genes involved in pyridine degradation, denitrification and extracellular electron transfer were remarkably enriched in EBPS, indicating the crucial role of photoelectrical stimulation. This study provided a sustainable technical approach for simultaneous removal of pyridine and nitrogen in wastewater.