THE ELECTRO-DEWATERING OF SLUDGE: INFLUENCE OF THE POLY- ELECTROLYTE DOSAGE AND THE OP- ERATING CONDITIONS

Abstract

In this research the process of electro- dewatering (EDW) of sewage sludge has been stud- ied. The sludge samples, aerobically or anaerobically stabilized, have been taken from four wastewater treatment plants (WWTPs) around the metropolitan area of Milan. For the EDW tests two types of samples have been used: (i) thickened sludge (LI), taken before conditioning and (ii) mechanically dewatered sludge (DM). The EDW tests on LI sludge  allowed the dewatering of the samples up to a dry solid con- tent (SS) of 18.4-31.1%, equal to an increase of 2.0- 12.7% compared to the conventional mechanical dewatering treatments used in the four WWTPs. Together with the final DS increase, the EDW process allowed to reduce the polyelectrolyte dosage with respect to that used in the WWTPs. The tests on DM sludge achieved DS values between 30.1-41.0%.  It has been shown that the operating conditions, such as electrical potential and cake thickness, have consider- able influence on the efficiency of the EDW process, both on LI and DM sludge. The cost of the polyelec- trolyte, the consumption of electric energy and  the cost of sludge disposal associated to the EDW process have been compared to conventional dewatering used in the four WWTPs. It was found that the use of the EDW process would reduce sludge management costs by up to 37% per year for LI samples and up to 50% for DM samples.