Influence of flow regime on the concentration of cyanide producing anaerobic process inhibition

A study was conducted to analyze the effects of cyanide on methanogenic bac terial populations in both continuous and batch reactors. The appropriate t oxicity assays were divided into two parts, i.e. 1) batch assays, and 2) co ntinuous flow assays, using a 6.5-1itre up-stream anaerobic sludge blanket reactor (UASB). A synthetic substrate was used as feed for both assays usin g 99% sucrose as a carbon source, and potassium cyanide (KCN) as a free cya nide source. In the first part, the treatments with the lowest and highest percentages of Specific Methanogenic Activity (SMA %) were 3 and 10 mg CN/1 . A 0.96 mg/l concentration of cyanide caused methanogenic activity inhibit ion by 50% during the, exposure stage. During the recovery stage, Methanoge nic Activity of treatments bad a considerable increase compared to the resu lts from direct cyanide exposure, except for treatments of 7 and 10 mg CN/l . The concentration of cyanide that inhibits Specific Methanogenic Activity by 50% was 6.1 mg CN/l during this stage. In the second part, the reactor was continuously fed with a synthetic substrate(COD approximate to 1500 mg/ l). After the anaerobic sludge became acclimated, cyanide concentrations fr om 0.5 and 130 mg CN/l were progressively added. The hydraulic retention ti me remained constant at 12 hours throughout the entire experiment. Results indicated that while partial inhibition occurred for concentrations of 3, 2 0 and 100 mg CN/l,severe inhibition occurred for 130 mg CN/l. (C) 1999 Publ ished by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved.