Metal recovery from electroplating wastewater using acidophilic iron oxidizing bacteria: Pilot-scale feasibility test

金沢大学理工研究域機械工学系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. © 2005 American Chemical Society

耐塩性鉄酸化細菌の馴養による電気メッキ排水処理の検討

金沢大学理工研究域機械工学系The iron-oxidizing bacterium, Thiobacillus ferrooxidans, is not halotolerant and cannot oxidize ferrous ions (Fe2+) to ferric ions (Fe3+) in electroplating wastewater containing high concentrations of chlorine ions. T. ferrooxidans cannot be used for the treatment of such electroplating wastewater. The acclimation of iron-oxidizing halotolerant bacteria has been studied to treat electroplating wastewater containing ferrous ions and a high concentration of chlorine ions. Iron-oxidizing bacteria that are halotolerant and able to oxidize Fe2+ to Fe3+ were obtained from the activated sludge of a steel works coke-oven wastewater treatment plant. A long-term experiment using artificial wastewater containing 20,000 mg · l-1 chlorine ions showed the stable performance of the Fe2+ oxidation ability by iron-oxidizing bacteria acclimated to seawater. It seems that the acclimated iron-oxidizing bacteria can be used for the treatment of electroplating wastewater. An analysis of genomic DNA extracted from the acclimated sludge of the reactor showed the existence of an analog of the iron-oxidizing bacterium, Thiobacillus prosperus

鉄酸化細菌を活用したスラリー型反応装置による電気メッキ排水からの金属分離回収

金沢大学理工研究域機械工学系Wastewater from electroplating plants contains several metallic ions such as iron, nickel and zinc. In general, neutralization followed by sedimentation has been used for the treatment of electroplating wastewater. However, this process results in the production of large amounts of heavy metal sludge. The objective of this research is to achieve selective metal separation, metal recovery and reduction in sludge volume. We have examined the feasibility of a biological process using iron-oxidizing bacteria in the treatment of electroplating wastewater from steel works. It was proved that iron-oxidizing bacteria acclimated from activated sludge have the ability to oxidize ferrous ion (Fe2+) to ferric ion (Fe3+) in electroplating wastewater. A bioslurry reactor, which promotes both Fe2+ oxidation and Fe(OH)3 generation in the pH range from 3.0 to 4.0, showed an almost complete Fe2+ oxidization after 2 hours of hydraulic retention time. The produced Fe(OH)3 was recovered by sedimentation in the same pH range with almost no trace of nickel or zinc. Nickel and zinc hydroxides were easily recovered by sedimentation at pH 9.0