Toxic effects of cadmium (Cd2+) on anaerobic biomass: Kinetic and metabolic implications

Abstract

Cadmium ion (Cd2+) toxicity on anaerobic systems, used for organic matter removal, was assessed by studying its effect on kinetic parameters and metabolic changes. This fundamental study was performed in a continuous fixed bed anaerobic bioreactor that treated synthetic wastewater simulating domestic sewage. The biomass was immobilized on a fixed bed made of polyurethane foam. Under influent cadmium concentrations of 0.0, 0.4, 4.4 and 6.2 mg Cd2+ L-1 the organic matter removal efficiencies were 84%, 82%, 72% and 52%, respectively. At influent concentration of 6.2 mg Cd2+ L-1 the reactor had reached its limit for cadmium toxicity. In the removal of dissolved organic matter, the first-order apparent kinetic coefficients (k1app) were 0.84, 0.67 and 0.10 h-1 for the operations with 0.0, 0.4 and 4.4 mg Cd2+ L-1, respectively. The apparent inhibition coefficient for cadmium (kiapp) was 1.69 mg L-1. Despite the toxic effects of cadmium on anaerobic organic matter removal at large Cd2+ concentrations, the results demonstrated that the anaerobic process was suitable for cadmium concentrations below 29.8 mg Cd2+ L-1, considering the bioavailable fraction of adsorbed cadmium in the support when the cadmium influent concentration was 6.2 mg Cd2+ L-1. © 2012 Elsevier Ltd.