Application of Chemical Coagulants and Biopolymers for Sewage Sludge Dewatering

Abstract

In this work, effects of chemical coagulants [Fe₂(SO₄)₃, Al₂(SO₄)₃, FeCl₃ and CaO] and biopolymers (chitin, carboxymethylcellulose (CMC) and chitosan) on sewage sludge dewatering were studied. According to the results, Fe₂(SO₄)₃was the most suitable substance for dewatering of the returned activated sludge and FeCl₃ was found to be the best coagulant for the aerobic digested sludge. The results showed that sludge dewatering speed compared with control samples increased by about 77.6 and 80.5 %, respectively. Also, among natural polymers being used, chitin having the lowest consumption level in comparison with other coagulants increased the dewatering speed for the digested sludge by about 59.5 %. In this case, the sludge moisture content compared with that of the control decreased by 12.8 %. In all cases, chitosan had a negative effect on the dewatering speed and reducing the sludge moisture content. The effect of carboxymethylcellulose on decreasing the sludge time to filteration was also negligible.