A continuous system for Fe0 reduction of nitrobenzene in synthetic wastewater

Nitrobenzene is a major environmental pollutant, and its degradation is difficultto achieve. Hence, a chemical reduction pretreatment is sought in this research, before the resulting aniline can be treated by enzyme-mediated oxidative polymerization. Zerovalent iron (Fe0) has been successfully employed to reduce nitrobenzene to aniline in synthetic wastewater in both batch and continuous flow reactors. The concentration of nitrobenzene studied was thatwhich would be present in industrial wastewater streams (millimolar, 123 ppm), a concentration range considerably higher than those studied previously with groundwater by other researchers. Anaerobic conditions were maintained in the reactors by including Na2SO3 as an oxygen scavenger in the presence of CoCl2.6H2O, which acted as a catalyst. Batch reactors exhibited adsorption of aniline on the Fe0, which could be described by a langmuir isotherm. A 200 g Fe0 (particle size: 1-2 mm) bed completely converted 1 mM of nitrobenzene flowing upward for about 600 pore-volumes before experiencing flow reduction due to clogging due to corrosion products. Green-black precipitates (Fe0 corrosion products) were formed at the influent end of the column which were identified as maghemite.