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A prototype apparatus was configured and operated to evaluate the efficacy of a process that integrates the absorption of nitric oxide in an aqueous solution of ferrous EDTA with biological treatment and regeneration of spent scrubber water. In addition to operation of a continuous-flow, closed-loop prototype process, a series of batch reactor tests were conducted to investigate the kinetics of microbially-catalyzed reduction of the nitrosyl adduct of ferrous EDTA and microbially-catalyzed reduction of oxidized ferric EDTA.

Following a 42 day period of bioreactor start-up, the NOX scrubbing stage was added and the prototype process was operated in this configuration for 107 days. A mean scrubber efficiency of 97.9% was maintained. Eighty days of prototype steady-state operation were observed. During steady state operation, process water oxidation/reduction potential (ORP) remained between -75 and -140 mV(vs. Ag/AgCl ref.). Gas generated in the bioreactor was 91% N2 gas. Excessive loading of ethanol caused methane formation in the process bioreactor and a drop in process water ORP.

Batch reactor kinetic tests revealed that microbially-catalyzed reduction of ferric EDTA proceeds according to the Monod kinetic expression over the range of initial ethanol concentration considered. Similar tests showed strong inhibition of the microbiallycatalyzed reduction of the nitrosyl adduct of ferrous EDTA at ethanol concentrations above 0.33 g COD/l. Based on observed population parameters, including biomass yield, endogenous decay, and substrate utilization rate, the critical mean cell retention time below which bioreactor wash out occurs was found to be 11.7 days and 51.4 days for NO reducers and ferric EDTA reducers, respectively. A sludge age of 70 days or greater is desirable for stable process performance, which suggests the need for attached growth, large volume recycle, or filter retained

Document Type: Research Article


Publication date: January 1, 2004

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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