aDepartment of Chemistry, Faculty of Science, University of Guilan, P.O. Box: 1914, Rasht, Iran.
b Kimya Problemleri Ìnstitutu, Azerbayjan Milli EA-mn, Azerbaijan.
* Corresponding author.
In this research, effects of natural polymers (Carboxymethylcellulose (CMC), chitosan and sodium alginate) and chemical coagulants (Al2(SO4)3, Fe2(SO4)3, FeCl3 and CaO) on sewage sludge dewatering were studied. To do so, determining the time to filtration and measuring the moisture content of the resulted sludge cake were used to assess the sludge dewatering ability. Therefore, first, optimum pH for sludge dewatering and then, optimum coagulant concentration for the minimum time to filtration were determined. According to test results, among chemical coagulants, Fe2(SO4)3 was the most suitable substance for dewatering the returned activated sludge and FeCl3 was found to be the best coagulant for the aerobic digested sludge. Studying the results showed that sludge dewatering speed compared with control samples increased by about 77.5% and 80%, respectively. Also, among natural polymers being used, chitosan having the lowest consumption level in comparison with other coagulants increased the dewatering speed for the digested sludge by about 61%. In this case, the sludge moisture content compared with that of the control decreased by 13%. In all cases, sodium alginate had a negative effect on the dewatering speed and reducing the sludge moisture content. The effect of CMC (carboxymethylcellulose) on decreasing the sludge TTF was also negligible. In fact, it reduced the TTF for activated and aerobic digested sludges by about 5% and 10%, respectively.
Sludge treatment, Sludge conditioning, Sludge dewatering, Chemical coagulant, Natural polymer
