Copper and zinc removal from sewage sludge using different organic acids

Abstract

Municipal sewage sludge often cannot be recycled as amendment material in agriculture, because concentrations of heavy metals exceed the limit values. Meta! pollution of sewage sludge is widespread across the globe. The clean up of such sludges is a difficult task. Innovative treatment meihods of sewage sludge remediation are urgently required. This study investigates the feasibility of using different low-molecular weight organic acids: nionocarboxylic- acetic, dicarboxylic- oxalic and tricarboxylic- citric acids, to remove copper and zinc from sewage sludge. Several batch tests were conducted using an extracting solution at various concentrations (0.01, 0.05, 0.1, 0.5 and 1.0 M) to enhance heavy metal removal efficiency and lo optimize the concentration of each extracting agent. All three organic acids were enough effective for the removal of zinc to meet the limit values. Organic acid ranking order of metal extraction efficiency was the following: citric acid > oxalic acid > acetic acid. Metal extraction efficiency was influenced not only by exlraetant origin and its concentration, but also by plf of the extracting solution. Specific variation of metal extraction efficiency in the case of oxalic acid was influenced by its low pH at higher concentrations.