ABSTRACT
Reduction-oxidation processes can be used for treatment of metallic waste streams or understanding of natural/engineered processes that can change the nature of heavy metals. The chemical-induced reduction uses chemical agents to reduce/convert metal ion to its elemental form. As solution pH can change the solution chemistry of metal wastewater, it may significantly affect the treatment results of reduction. The reduction agent can be organic compounds from living or dead biomass natural organic matter, and industrial organic waste. The commonly used reducing agents are sodium borohydride, hydrazine, and formaldehyde. The biological reduction and the precipitation of the metal species can be carried out in a moving sand bed reactor. The most expensive operational cost in the biological reduction of sulfate is the electron donor. The treatment of hexavalent chromium (Cr(VI)) involves first the reduction of Cr(VI) to the trivalent form by a reducing reagent with a high dosage.
