Magnetic flocculation of algae-laden raw water and removal of extracellular organic matter by using composite flocculant of Fe3O4/cationic polyacrylamide

Algae-laden water with low turbidity is a critical problem in eutrophic lakes of arid regions. Thus, how to effectively separate algae and turbidity is an urgent problem for drinking water production. In the current study, the magnetic flocculation performance of algae-laden raw water purification was investigated by using magnetic composite flocculant Fe3O4/cationic polyacrylamide (CPAM). The Chlamydomonas sp., turbidity and UV254 removal efficiency were evaluated at different Fe3O4: CPAM mass ratios, dosages and pH values. The recovery and reusability of Fe3O4/CPAM in flocculation was tested. Moreover, the saturation magnetization of flocculants and flocs and zeta potential of supernatant in magnetic separation was examined, and the flocculation mechanism of Chlamydomonas sp. was explored accordingly. In addition, the removal efficiency of bound extracellular organic matter (BEOM) and dissolved extracellular organic matter (DEOM) was compared by using Fe3O4/CPAM. The flocculation mechanism and interactions between Fe3O4/CPAM and extracellular organic matters were analyzed according to ultraviolet (UV) spectra, fluorescence three-dimensional excitation emission matrix spectra (EEM), gel permeation chromatography (GPC), and X-ray photo electronic spectroscopy (XPS). Results show that more than 97% of chlorophyll a (Chla), 87% of turbidity, and 65% of UV254 were removed at Fe3O4/CPAM dosage of 1.2 mg/L, Fe3O4: CPAM mass ratio of 1.5:1.0, and pH of 4.0-9.0. Charge neutralization was dominant at pH < 9.0, whereas adsorption through hydrogen bond played an important role at pH > 9.0. Humic acid-like substances and tryptophan-like proteins were the main components of DEOM, whereas fulvic acid-like substances, tryptophan-like proteins and few polysaccharides existed in BEOM. Fe3O4/CPAM exhibited excellent performance in binding with the functional groups in tryptophan-like proteins, such as amino, carboxyl and hydroxyl groups. (c) 2019 Elsevier Ltd. All rights reserved.