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Effects of hydraulic retention time and sulfide toxicity on ethanol and acetate oxidation in sulfate‐reducing metal‐precipitating fluidized‐bed reactor
Author(s) -
Kaksonen Anna H.,
Franzmann Peter D.,
Puhakka Jaakko A.
Publication year - 2004
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.20061
Subject(s) - chemistry , sulfide , alkalinity , hydraulic retention time , sulfate , effluent , nuclear chemistry , ethanol , wastewater , inorganic chemistry , environmental engineering , biochemistry , organic chemistry , engineering
The effects of hydraulic retention time (HRT) and sulfide toxicity on ethanol and acetate utilization were studied in a sulfate‐reducing fluidized‐bed reactor (FBR) treating acidic metal‐containing wastewater. The effects of HRT were determined with continuous flow FBR experiments. The percentage of ethanol oxidation was 99.9% even at a HRT of 6.5 h (loading of 2.6 g ethanol L −1 d −1 ), while acetate accumulated in the FBR with HRTs below 12 h (loading of 1.4 g ethanol L −1 d −1 ). Partial acetate utilization was accompanied by decreased concentrations of dissolved sulfide (DS) and alkalinity in the effluent, and eventually resulted in process failure when HRT was decreased to 6.1 h (loading of 2.7 g ethanol L −1 d −1 ). Zinc and iron precipitation rates increased to over 600 mg L −1 d −1 and 300 mg L −1 d −1 , respectively, with decreasing HRT. At HRT of 6.5 h, percent metal precipitation was over 99.9%, and effluent metal concentrations remained below 0.08 mg L −1 . Under these conditions, the alkalinity produced by substrate utilization increased the wastewater pH from 3 to 7.9–8.0. The percentage of electron flow from ethanol to sulfate reduction averaged 76 ± 10% and was not affected by the HRT. The lowest HRT did not result in significant biomass washout from the FBR. The effect of sulfide toxicity on the sulfate‐reducing culture was studied with batch kinetic experiments in the FBR. Noncompetitive inhibition model described well the sulfide inhibition of the sulfate‐reducing culture. (DS) inhibition constants (K i ) for ethanol and acetate oxidation were 248 mg S L −1 and 356 mg S L −1 , respectively, and the corresponding K i values for H 2 S were 84 mg S L −1 and 124 mg S L −1 . In conclusion, ethanol oxidation was more inhibited by sulfide toxicity than the acetate oxidation. © 2004 Wiley Periodicals, Inc.