Evaluation of the Kinetics of Biologically Catalyzed Treatment and Regeneration of NOX Scrubbing Process Waters
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 ethylenediamintetraacetic acid (Fe(II)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. Denitrifying and strictly anaerobic biomass from a municipal wastewater treatment process was cultivated using ethanol as the primary electron donor and nitrate and ferric EDTA as electron acceptors. Following 42-days of bioreactor start-up, nitric oxide (NO) scrubbed from a counter-current absorption tower replaced nitrate. After 27 days of aclimation, an 80-day period of steady state operation was observed. During steady state operation, mean NO scrubbing efficiency of 97.9% was achieved, process water oxidation/reduction potential (ORP) remained between -75 and -140 mV (vs. Ag/AgCl ref.), and generated biogas was 91% N2, by volume. Biomass in the prototype reactor was flocculent, and traveled throughout the closed-loop process. Because of the constant recirculation of washed-out biomass and low observed biomass yield (0.0393 g VSS/g COD), mass balance showed the prototype process sludge age to be 75.9 days. During steady state operation, biomass was extracted for kinetic batch analyses. Batch reactor kinetic tests revealed that both ferric EDTA and NO reduction proceed as a result of microbially-catalyzed reactions. Microbially-catalyzed reduction of ferric EDTA proceeds according to the Monod kinetic model, while strong inhibition of the microbially-catalyzed reduction of NOFe(II)EDTA was observed 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 wash out of a continuously-stirred bioreactor would occur was found to be 11.7 days and 51.4 days for NO reducers and ferric EDTA reducers, respectively. Experimental results provide insight into conditions required for the successful operation of a process for the biological treatment and regeneration of spent scrubber solution from a NOX absorption process.
Advisor:James T. Cobb; Radisav D. Vidic; Leonard W. Casson; Ronald D. Neufeld
School:University of Pittsburgh
School Location:USA - Pennsylvania
Source Type:Master's Thesis
Keywords:civil and environmental engineering
Date of Publication:01/31/2005