Design and feasibility analysis of a self-sustaining biofiltration system for removal of low concentration $N_2O$ emitted from wastewater treatment plants

Abstract

$N_2O$ is a potent greenhouse gas and ozone-depletion agent. In this study, a biofiltration system was designed for removal of $N_2O$ emitted at low concentrations (<200 ppmv) from wastewater treatment plants. A biofiltration system was designed to utilize untreated wastewater from the primary sedimentation basin as the source of electron donor and nutrients and minimize the energy requirement by utilizing gravitational force and pressure differential to direct liquid medium and gas through the biofilter. The experiments performed with laboratory-scale biofilter in two different configurations confirmed the feasibility of the biofiltration system. The biofilter operated with cycling of raw wastewater exhibited up to 94% and 53% removal efficiency with 100 ppmv $N_2O$ in $N_2$ and air, respectively, as the feed gas, corroborating that untreated wastewater can serve as a robust source of electron donor and nutrients. The laboratory-scale biofilter operated with a continuous flow-through of synthetic wastewater attained >99.9% removal of $N_2O$ from $N_2$ background at the gas flowrate up to $2,000 mL \cdot min^{-1}$ and >50% $N_2O$ removal from air background at the gas flowrate of $200 mL \cdot min^{-1}$. nosZ-containing bacterial genera including Flavobacterium (5.92%), Pseudomonas (4.26%) and Bosea (2.39%) were identified from the biofilm samples collected from the oxic biofilter, indicating these organisms were responsible for $N_2O$ removal.