Removal of humic substances from aqueous solutions by the coagulation process

Laboratory studies were carried out on model solutions prepared on a tap-water base. The content of humic substances was 20 mg l(-1). Hardness and pH parameters of these solutions were altered using appropriate reagents. The coagulation process was run in a conventional manner using the two most popular coagulants, i.e. aluminium sulphate and iron chloride III. Optimum doses of coagulants, as well as the effect of hardness and pH of the purified solutions on coagulation process effectiveness, were determined. The efficacy of coagulation using the optimum doses of coagulants was the greatest for solutions having the highest hardness. The coagulation process progressed most efficiently in the pH range from 5 to 6. In order to describe a coagulation process with a mathematical model, the concentration of humic substances was changed from 5 to 30 mg l(-1). The results of these experiments served as a basis for the determination of the dependence of coagulant dose on the initial concentration of solutions.