Moisture effects on gas-phase biofilter ammonia removal efficiency, nitrous oxide generation, and microbial communities

We established a four-biofilter setup to examine the effects of moisture content (MC) on biofilter performance, including NH₃ removal and N₂O generation. We hypothesized that MC increase can improve NH₃ removal, stimulate N₂O generation and alter the composition and function of microbial communities. We found that NH₃ removal efficiency was greatly improved when MC increased from 35 to 55%, but further increasing MC to 63% did not help much; while N₂O concentration was low at 35-55% MC, but dramatically increased at 63% MC. Decreasing MC from 63 to 55% restored N₂O concentration. Examination of amoA communities using T-RFLP and real-time qPCR showed that the composition and abundance of ammonia oxidizers were not significantly changed in a "moisture disturbance-disturbance relief" process in which MC was increased from 55 to 63% and then reduced to 55%. This observation supported the changes of NH₃ removal efficiency. The composition of nosZ community was altered at 63% MC and then was recovered at 55% MC, which indicates resilience to moisture disturbance. The abundance of nosZ community was negatively correlated with moisture content in this process, and the decreased nosZ abundance at 63% MC explained the observation of increased N₂O concentration at that condition.