Metal Recovery from Electroplating Wastewater Using Acidophilic Iron Oxidizing Bacteria: Pilot-Scale Feasibility Test

Wastewater from electroplating plants contains several valuable metallic ions such as iron, nickel, and zinc. In general, neutralization followed by sedimentation has been used for the treatment of electroplating wastewater because of low treatment cost and high stability of treated water quality. However, this method results in the production of large amounts of heavy metal sludge that may cause secondary pollution and additional cost. In addition, the recovery of valuable metallic contents from the wastewater sludge has not been technically feasible. It would be highly desirable economically as well as environmentally if a metal recovery process from the wastewater is developed. In the present work, we developed a biological process for metal recovery from electroplating wastewater. Wastewater from electroplating plants contains iron in the form of ferrous ion together with other metal ions. To add economic value to the chemical sludge, iron should be separated from other metals such as nickel and zinc in the wastewater. The iron could be separated from the mixture of metal ions in wastewater by using biological oxidation of ferrous ion into ferric ion followed by stepwise chemical precipitation with hydroxide ion since ferric ion begins to precipitate around pH 4 while ferrous ion precipitates around pH 7 similarly to the other metal ions (nickel and zinc). To improve the biological oxidation, an immobilized bioreactor using polyurethane foam as support media was developed. The bioreactor system showed a very good performance and worked stably over a long period of time.