Simultaneous biological nitrous oxide abatement and wastewater treatment in a denitrifying off-gas bioscrubber

Abstract

The simultaneous treatment of N2O-laden air emissions and domestic wastewater was assessed in a novel denitrifying bioscrubber composed of a packed bed absorption column interconnected to a fixed bed reactor (FBR). The influence of liquid recycling velocities (UL) and gas empty bed residence times (EBRTs) in the absorption column on bioscrubber’s performance was evaluated using synthetic wastewater (SW) and a 100 ± 8 ppmv N2O air emission. Steady state N2O removal efficiencies of 36 ± 3% concomitant with SW total organic carbon removals of 91 ± 1% were achieved at an EBRT of 3 min and at the highest UL tested (8 m h−1). The removal of dissolved N2O by heterotrophic denitrification in the FBR constituted the main N2O biodegradation mechanism and limited the abatement of N2O. While the supplementation of SW with Cu2+ (a cofactor of the N2O reductase) did not result in an enhancement in N2O reduction, the increase in FBR volume supported a higher N2O removal. The increase in EBRT up to 40 min supported an enhancement in the gas N2O removal of up to 92%. The DGGE-sequencing analysis of FBR microbial population revealed a high microbial diversity and the abundance of denitrifying bacteria capable of reducing N2O to N2.