Cyanide degradation kinetics during anaerobic co-digestion of cassava pulp with pig manure.

Anaerobic co-digestion of cassava pulp (CP) and pig manure (PM) under cyanide inhibition conditions was investigated and modeled. Batch experiments were performed with initial cyanide concentrations ranging from 1.5 to 10 mg/L. Cyanide acclimatized sludge from an anaerobic co-digester treating cyanide-containing CP and PM was used as the seed sludge (inoculum). Cyanide degradation during anaerobic digestion consisted of an initial lag phase, followed by a cyanide degradation phase. After a short sludge acclimatization period of less than 3 days, the anaerobic sludge was able to degrade cyanide, indicating that the sludge inhibition due to cyanide was reversible. Cyanide degradation during anaerobic co-digestion of CP and PM followed the first-order kinetics with a rate constant of 0.094 d. Gas evolution during batch anaerobic degradation was modeled using the modified Monod-type kinetics to incorporate cyanide inhibition. The model predicted results yielded a satisfactory fit with the experimental data.