Spent coagulant in water supply plant sludge was extracted with H 2 SO 4 and the effi ciency of the reused coagulant was studied. The optimum pH values for coagulant extraction and clarifi cation with the reused coagulant were 3.0-4.0 and about 6, respectively. In treating raw infl uent obtained from a sewage treatment plant and wastewater from a coastal landfi ll site, the removal of chemical oxygen demand (COD), total nitrogen, and total phosphorous with the recovered coagulant was higher than that with commercial aluminum sulfate or polyaluminum chloride. In addition, the sludge settling properties, the extra sludge mass formation, the supernatant quality, and the cost of reagents were also studied. The coagulant recovered from water supply plant sludge by H 2 SO 4 extraction could be successfully reused for the clarifi cation of domestic and food industry wastewaters.
Key words Water supply plant sludge · Recovery and reuse of coagulant · Clarifi cation · COD · Nutrients
Materials and methods
SamplesClarifi er sludge (water content, 69.3%; ignition loss, 10 27.7%) from a municipal water supply plant was used for the recovery of coagulant. The plant uses Al 2 (SO 4 ) 3 and PACl coagulants. 11 Raw infl uent (pH, 7.5; COD, 44.0-79.6 mg/l; T-N, 31.4-33.0 mg/l; T-P, 2.70-3.29 mg/l) from a J Mater Cycles Waste Manag (2007) 9: [167][168][169][170][171][172]
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