EFFECTS OF SULFIDE ADDITION ON COPPER INHIBITION IN METHANOGENIC SYSTEMS

Addition of sulfide can play a major role in recovery from heavy metal inhibition in anaerobic systems. Whether adding sulfide as a preventi ve means before heavy metal inhibition is more beneficial than adding sulfide after exposure to a heavy metal, is an important question. The objective of this research was to address this point by studying the effects of sulfide addition before and after copper inhibition in acet ate-fed, methanogenic systems. Anaerobic toxicity assays and batch kin etic studies were performed using serum bottles with an anaerobic acet ate enrichment culture. The results showed that recovery is possible w ith a feed copper to volatile suspended solids ratio (Cu2+/VSS) Of 0.0 11-0.022 up to 15 mg l(-1) of added copper. But the system failed with 20 mg l(-1) of copper added with a Cu2+/VSS of 0.015. Adding sulfide after copper spiking can take as long as 50 days for recovery from cop per (20 mg l(-1)) inhibition with a high Cu2+/VSS of 0.055. Interestin gly, with sulfide addition before 20 mg l(-1) of copper spiking, the m ethanogenic systems recovered rather quickly (within 4-7 days) even th ough the Cu2+/VSS was in the range of 0.054 - 0.058. Hence, the sulfid e addition before copper spiking was much more beneficial than the sam e amount of sulfide addition after copper spiking. The best-fit inhibi tion coefficient, K-1 (competitive), for copper alone was 0.038-0.068 mg l(-1). The K-1 (competitive) for sulfide addition after copper spik ing was 1.94 mg l(-1). The inhibition with sulfide addition before cop per spiking followed the uncompetitive inhibition model with the best- fit K-1 of 256 mg l(-1). (C) 1998 Elsevier Science Ltd. All rights res erved.