Bio-oxidation of thiocyanates typical of coal conversion effluents. Final report

Abstract

Thiocyanates have been found in most coal conversion and coke plant effluents. The objectives of this study were to develop data for the biological degradation fate kinetics of thiocyanate removal, and to develop material balance information for the fate of sulfur and nitrogen resulting from such bio-decomposition of aqueous thiocyanates. A literature review of thiocyanate bio-degradation indicates that while much biochemistry information is available, little information in the biological processing arena is known. Based on both batch and continuous culture experiments utilizing an activated sludge type of system with strictly thiocyanate degradating organisms, the specific utilization rate for SCN degradation was found to follow a substrate inhibition biokinetic relationship as: d(SCN)/dt-X = 2.24/(1 + (5/SCN) + (SCN/1340)/sup 6/) where; d(SCN)/dt-X = lb SCN used/lb biomass-day, SCN = mg/L SCN in effluent. The observed biomass sludge production rate was quantified as a function of sludge age in the bio-reactor. The major metabolic by-products of SCN aerobic biodegradation are ammonia and sulfate, with such formation being stochiometric with SCN. High levels of SCN in coal conversion and Stretford system effluents may lead to biological nitrification process requirements to be added to the wastetreatment scheme for compliance with BAT effluent ammonia discharge restrictions.