Laboratory-Scale Iron EDTA-Based NO X Scrubbing Process with Biological Treatment and Regeneration of Spent Scrubber Water

Abstract

A laboratory-scale apparatus was configured and operated to evaluate the efficacy of a unit process that integrates the absorption of nitric oxide in an aqueous solution of ferrous ethylenediaminetetraacetic acid (EDTA), with biological treatment and regeneration by reduction of oxidized species in that solution. The reactor was initially inoculated with anoxic denitrifying and strictly anaerobic biomass from two municipal wastewater treatment plants. After successful development of biomass using nitrate and ferric EDTA as the primary electron acceptors and ethanol as the primary electron donor, the system was modified to continuously load nitric oxide in the form of the nitrosyl adduct of ferrous EDTA. The process was operated in this manner for 107 days, including a steady-state period that was maintained for more than 70 days. During the period of steady-state operation, 0.194 mol of NO and 0.166 mol of ethanol were loaded per day. This corresponded with biogas formation at a consistent rate (0.669 liters per day) and composition (0.91 atm of N₂), high NO scrubbing efficiency (97.9% removal), and consistent consumption of neutralizing acid (0.330 acid equivalents per day). Results of process operation and discussion of implications for future process development are presented.