A Serial Biofiltration System for Effective Removal of Low-Concentration Nitrous Oxide in Oxic Gas Streams: Mathematical Modeling of Reactor Performance and Experimental Validation

Wastewater treatment plants (WWTPs) are among the major anthropogenic sources of N2O, a major greenhouse gas and ozone-depleting agent. We recently devised a zero-energy zero-carbon biofiltration system easily applicable to activated sludge-type WWTPs and performed lab-scale proof-of-concept experiments. The major drawback of the system was the diminished performance observed when fully oxic gas streams were treated. Here, a serial biofiltration system was tested as a potential improvement. A laboratory system with three serially positioned biofilters, each receiving a separate feed of artificial wastewater, was fed N2O-containing gas streams of varied flow rates (200-2000 mL·min-1) and O2 concentrations (0-21%). Use of the serial setup substantially improved the reactor performance. Fed fully oxic gas at a flow rate of 1000 mL·min-1, the system removed N2O at an elimination capacity of 0.402 ± 0.009 g N2O·m-3·h-1 (52.5% removal), which was approximately 2.4-fold higher than that achieved with a single biofilter, 0.171 ± 0.024 g N2O·m-3·h-1. These data were used to validate the mathematical model developed to estimate the performance of the N2O biofiltration system. The Nash-Sutcliffe efficiency indices ranged from 0.78 to 0.93, confirming high predictability, and the model provided mechanistic insights into aerobic N2O removal and the performance enhancement achieved with the serial configuration.