Effect of dosing sequence and raw water pH on coagulation performance and flocs properties using dual-coagulation of polyaluminum chloride and compound bioflocculant in low temperature surface water treatment

A series jar test was conducted to study the impact of dosing sequence and solution pH on coagulation and flocs properties by dual-coagulants of polyaluminum chloride (PAC) and compound bioflocculant (CBF) in low temperature surface water treatment. The results showed that DOC removal could be improved when CBF was used, especially by CBF-PAC (CBF dosed first). And both of the maximum DOC and UV254 removal were achieved at pH6. Moreover, the flocs size and growth rate were enhanced significantly when dual-coagulants were used, while flocs strength and flocs dimension decreased. The recovery ability of flocs was improved when PAC-CBF was used, but decreased in condition of CBF-PAC. And recovery ability decreased as pH increased, while flocs were more compact as pH increased. (C) 2013 Elsevier B.V. All rights reserved.