Efficient treatment of the starch wastewater by enhanced flocculation–coagulation of environmentally benign materials

The high concentration, complexity and refractory of organic pollutants in actual starch wastewater are becoming major obstacles to realizing efficient water purification. Herein, bentonite was selected from four kinds of clay minerals (i.e. kaolin, zeolite, attapulgite and bentonite) as coagulant aids, and chitosan-modified bentonite combined with polyglutamic acid was used for enhanced coagulation treatment for starch wastewater. Among them, bentonite can adsorb soluble pollutants in starch wastewater, chitosan modification can enhance the coagulation effect, and the flocculant of polyglutamic acid is conducive to the removal of particulate matter through bridging effects. The combination of the three can effectively and deeply remove pollutants in starch wastewater. Under the optimal conditions, the removal rates of chemical oxygen demand, total nitrogen, total phosphorus and turbidity can reach 86.2 %, 80.3 %, 52.3 % and 98.2 %, respectively, which are far higher than that of the vast majority of coagulants currently reported. Density functional theory calculation was carried out to reveal the mechanisms for the enhanced coagulation-flocculation system and explained the adsorption and coagulation mechanism, respectively. The electrostatic potential around aluminum in bentonite of 14.248 kcal.mol−1 is more conducive to the adsorption of negatively charged organic pollutants, and that bentonite has lower adsorption energy (-1.43 eV) than chitosan and polyglutamic acid.