Enhanced coagulation of covalent composite coagulant with potassium permanganate oxidation for algae laden water treatment: Algae and extracellular organic matter removal

•Covalent composite coagulant enhanced coagulation with potassium permanganate oxidation for algae and EOM removal was evaluated.•The pre-oxidation dosing method exhibited higher EOM removal efficiency than that of simultaneous oxidation method.•Low-concentration potassium permanganate improved algae and EOM removal under low CAFM dosage.•The cell lysis caused by pre-oxidation and simultaneous oxidation was controlled in a low level.•The aluminum, iron and manganese residual after CAFM coagulation was less than that of polyaluminum coagulation. The enhanced coagulation performance for algae and extracellular organic matter (EOM) removal by using novel Al/Fe-based covalently bonded composite coagulants (CAFM) coupled with potassium permanganate oxidation was evaluated in the current study. For the CAFM coagulation and potassium permanganate oxidation combination process, two dosage sequences of oxidant and coagulant, the potassium permanganate pre-oxidation method, and the simultaneous oxidation method, was compared for algae and EOM removal. Polyaluminum chloride (PAC) and polyacrylamide (PAM) were selected as common used coagulants to compare with CAFM. The results show that 21.1% UV254, 99.6% OD686, and 98.2% turbidity were removed from EOM algae laden water at CAFM dosage of 5.4 mg/L and KMnO4 dosage of 1 mg/L. UV254 removal rate was increased by 10% in potassium permanganate oxidation treatment compared with CAFM coagulation. In addition, pre-oxidation method exhibited better extracellular organic matter removal efficiency compared with simultaneous oxidation method. Furthermore, SEM, FTIR, XRD and XPS were employed to study the physical and chemical structure of flocs, whereas ICP-MS, EEM, GCMS– and GPC were used to analyze water quality before and after treatment for coagulation and oxidation in mechanism exploration. This study proposes a new process for algal bloom control, organic pollution reduction and ensure water quality of water plant effluent to provide research basis. [Display omitted]