Performance and microbial communities of completely autotrophic denitrification in a bioelectrochemically-assisted constructed wetland system for nitrate removal.

A bioelectrochemically-assisted constructed wetland (BECW) system was used to treat nitrate-contaminated wastewater without organic carbon source. The denitrification performance and microbial community composition of a BECW in closed-circuit mode (BECW-C) was compared to a BECW in open-circuit mode (BECW-O). The highest denitrification efficiency (78.92±3.12%) was obtained in the BECW-C with an applied current of 15mA. No nitrite accumulation was observed during the autotrophic denitrification process in the BECW-C. The significantly higher denitrification efficiency of the BECW-C compared to the BECW-O suggested enhanced denitrification due to in situ generation of hydrogen. The bacterial communities in the anode, cathode and rhizosphere regions collected from the BECW-C (with 10 or 15mA) and the BECW-O were characterized using 16S rRNA pyrosequencing technology, which revealed different microbial community structures among the treatments. The results also indicated that Thiohalophilus and Clostridium sensu stricto might be responsible for autotrophic denitrification in the BECW-C.