Effect of initial pH on the removal of humic substances from wastewater by electrocoagulation

This investigation deals with the effect of initial pH batch removal of synthetically prepared wastewater having high concentration of humic substances by electrocoagulation method using plate electrodes. The effects of initial pH on an electrocoagulation system may be twofold. These are distribution of aluminum hydrolysis product, transformation of humic substance related to the initial pH and finally the effects of the gel layer especially in high humic substance concentrations and high initial pH formed on the anode surface. It has been observed that initial humic substance concentration and initial pH are highly effective on the removal rate and efficiency. For example, in the range of 200–500 mg L−1, decrese in the removal efficiency was observed due to gel layer formation on the surface of the anode surface. This gel formation especially starts at an initial concentration of 120 mg L−1; thickness and effect of the layer increase as concentration increases. In order to prevent this gel formation, initial pH of the wastewater was adjusted to 5.0 and high removal efficiencies were observed. Thus, the system should be operated at low pH values (i.e. 5.0) at high concentrations.