Removal of refractory organics in wastewater by coagulation/flocculation with green chlorine-free coagulants

Coagulation/flocculation is considered an economical and practical technology to remove refractory organic matter from wastewater. Coagulants containing chlorine may release chloride ions into water, thereby resulting in corrosion. A green chlorine-free coagulant of polyaluminum ferric silicate (PSAF) was synthesized to treat non oily (e.g., humus wastewater) and oily refractory wastewaters (e.g., lubricating oil wastewater). Results showed that the highest removal efficiency of humus substances in non-oily wastewater achieved 96.0% at pH 7.0 using PSAF alone. When treating oily wastewater, the dosage and addition sequence of PAMALAM significantly affected the coagulation performance. The removal efficiencies of turbidity, chemical oxygen demand, and total nitrogen were increased by 0.3, 1.8, and 5.9 folds, respectively, with the optimal adding sequence of PSAF +0.08% PAMALAM. More fulvic acid-like substances can be removed during this process. The analysis of zeta potential and floc properties revealed that charge neutralization, sweep, and adsorption/entrapment mechanisms existed during the single PSAF coagulation process, and PAMALAM mainly improved the adsorption, bridging, and sweep function. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

Coagulation/flocculation with the green chlorine-free coagulant PSAF showed high removal efficiencies for organic substances in non-oily wastewater and oily wastewater, with the addition sequence of PAMALAM significantly impacting the coagulation performance. The mechanisms of charge neutralization, sweep, and adsorption/entrapment were identified during the coagulation process, with PAMALAM mainly enhancing adsorption, bridging, and sweep functions.