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.
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