In the present research, the effect of different coagulants in conditioning of digested sludge in Qods wastewater plant, have been investigated. In order to accomplish such investigation, coagulants including cationic polyelectrolyte, feeric chloride, quicklime and alum, with different concentrations, were added to the sludge samples. Jar test, then specific resistance of sludge with respect to dewatering, TSS and VSS on sludge samples before and after dewatering were performed. In addition, TSS and VSS, COD, BOD5 and turbidity were performed on supernatant in order to determine the optimized concentration of.
The value of specific resistance of sludge to the dewatering process for raw sludge and conditioned sludge with cationic polyelectrolyte, ferric chloride, ferric chloride with lime, lime and alum are as follows: 7.68*1013, 0.347*1013, 0.839*10113, 0.89*1013, ,2.36*1013 and 2.52* 1013 m/kg. Since my decrease in specific resistance of sludge facilities the dewatering process, it could be concluded that the most suitable for fludge conditioning are, cationic polyelectrolyte, ferric chloride, ferric chloride with lime, lime and alum respectively.
By considering the results of this investigations and comparing economic factors and supplier availability, ferric chloride as pilot sludge conditioner substance was preferred. By adding ferric with concentration of 440 mg/I to the outgoing sludge from aerobic digester, the required time for drying sludge (production of sludge with DS=45%) in drying beds, is reduced from 9 days to 4 days. In other word, if input sludge to drying beds in conditioned, the required bed area, is reduced considerably (at least 50%).
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