Removal of fluoride and turbidity from semiconductor industry wastewater by combined coagulation and electroflotation

Reduction of toxic dissolved fluoride and CaF2 nanoparticle pollution is a critical environmental problem for the semiconductor industry. In this study, suspended matter and fluoride are simultaneously eliminated by combining coagulation and electroflotation. The EF cell was equipped with DSA titanium coated with ruthenium oxide (Ti/RuO2) as anode and stainless steel as cathode. High turbidity removal efficiency is achieved by using EF as a separation technique. The effect of the following parameters: electrolysis time, coagulant concentration, initial pH, nature of neutralizing salt and current intensity was studied. Removal efficiencies of both fluoride and CaF2 nanoparticles are satisfactory. Under optimum conditions, the solid-liquid separation efficiency is about 97% in terms of turbidity removal which corresponds to a residual turbidity of 4.4NTU complying with the standard limit (5NTU), while fluoride efficiency removal may reach 73% corresponding to 10mg/L, which is below the environmental recommendations.