Application of FeCl 3 to Adjust Urban Sewage-Dewatered Sludge (UDSS) Containing Cationic Polyacrylamide (CPAM) for Further Dewatering

Abstract

The urban sewage-dewatered sludge (UDSS) containing cationic polyacrylamide is difficult to dewater. FeCl₃ was used as conditioner to adjust the UDSS. To investigate the effect and principle, the physicochemical properties of UDSS were evaluated in terms of dewatering equipment, micro electrophoresis, Malvern laser particle size analyzer, nuclear magnetic resonance analyzer, and scanning electron microscopy. Results showed that the network structure of UDSS produced by CPAM still had high negative charge, which locked much water in the flocs and resulted in the poor dewaterability of UDSS. When Fe³⁺ was added into the UDSS, the inner structure of sludge was destroyed by the charge neutralism and releasing more water. At the same time, because the function of precipitate produced by the hydrolytic action, the inner structure of the sludge was solidified; therefore, the compressibility of UDSS decreased. Finally, the dewaterability of UDSS was improved and the moisture content of filter cakes can be decreased to 55%.

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