Wastewater treatment: a case study of electronics manufacturing industry

Abstract

Industrial wastewater from electronics industries contains a high load of cyanide, toxic metals and chemical oxygen demand (COD). In the present study, a chemical treatment of electronics industry effluent was carried out for one of the largest electronics factories in Egypt. Alkaline chlorination and chemical reduction were performed sequentially as pretreatment steps with the aim of removing cyanide and Cr +6 from the effluent of the nickel–chrome production line. Thereafter, pretreated water was mixed with the end pipe effluent containing wastewater of all production lines and evaluated for final treatment using coagulation process. Different coagulants (CaO, FeSO 4 , polyelectrolyte) were applied with different compositions and concentrations. The water quality parameters such as COD, biological oxygen demand (BOD), cyanide, heavy metals and pH were estimated in an attempt to achieve a higher treatment efficiency. The results showed that the alkaline chlorination removed 100% of cyanide at pH 11 during 2 h of reaction time. Sequentially, a complete reduction of hexavalent chromium (Cr +6 ) to non-toxic trivalent chromium (Cr +3 ) was achieved at pH 2 during pretreatment of nickel–chrome wastewater. Among various coagulants, the combination of CaO (80 mg/L) with FeSO 4 (60 mg/L) represented highest treatment efficiency of wastewater within the permissible limits. BOD and COD were decreased to as low as 43 and 67 mg/L, whereas heavy metals (Cr, Cu, Ni and Zn) were found below 0.02 mg/L. Overall, the results revealed that this method could be adopted to establish an economical and efficient wastewater treatment system for effluents of electronics industries.