Chemical and biological removal of arsenic from sewage sludge

Abstract

Chemical and biological leachings of As and metals from sewage sludge were carried out using a batch reactor under an aerobic condition. Addition of phosphate to the sludge was ineffective for the elution of As from the sludge at neutral pH. Akalization of the sludge to pH 11 eluted sufficient As, whereas it was ineffective for Al, Cd, Mn and Zn. Furthermore, the effectiveness of ferric sulfate and iron oxidizing bacteria was investigated under acidic conditions. The application of ferric iron and/or iron oxidizing bacteria eluted As from the sludge more effectively than that of sulfuric acid only at pH 2. However, at pH 3, addition of ferric acid decreased significantly the amount of As eluted. It was found that the optimum pH was 2 for removing simultaneously As and metals from the sludge utilizing ferric iron or iron oxidizing bacteria.