Solubilization of Heavy Metals during Anaerobic Digestion of Sewage Sludge Using Acidogenesis

Abstract

Sewage sludge produced by many municipal wastewater treatment plants contains various heavy metals that limit its use on agricultural land. The existing treatment processes for removing heavy metals are not cost-effective or eco-friendly due to the requirement of aeration or the use of various harmful leaching agents. This paper explores the solubilization of heavy metals present in the sewage sludge using the acidogenesis phase of the anaerobic digestion process without using any harmful compounds. To achieve this objective, an anaerobic batch reactor was used, in which sewage sludge was added with different solid concentrations and carbon source (glucose) concentrations. During this process, volatile fatty acids were produced, which decreased the pH of the system. The maximum decrease in the pH was observed in the reactor that had the maximum glucose concentration and the minimum total solid concentration. In this reactor, the pH dropped below 4.5. The solubilization of heavy metals was observed as Zn: 41% (333 mg/kg), Ni: 31% (8.5 mg/kg), Cr: 30% (13 mg/kg), Pb: 29% (11 mg/kg), Co: 28% (1.4 mg/kg), and Cd: 27% (0.5 mg/kg).