Simple and efficient treatment of high-strength industrial waste water using commercial zero-valent iron

The zero-valent iron (ZVI)/H₂O₂ Fenton system can be considered as an effective solution for the removal of many of the organic pollutants present in the waste waters generated by the drug manufacturing industry. The hydrogen peroxide concentration and dosage rate were studied in order to improve the efficiency of the oxidant in the TOC reduction and, thereby enhance the overall catalytic performance of the ZVI/H₂O₂ Fenton system. TOC reductions of up to 80 % and BOD₅/COD ratios of up to 0.6 were achieved in the waste water as received without dilution (TOC_O approximately 5 g L^?1) using hydrogen peroxide dose-staggering. This showed that the ZVI/H₂O₂ process led not only to a decrease in TOC removal but also to an increase in the biodegradability of the by-products formed. The hydrogen peroxide was consumed more efficiently and very low concentrations of iron dissolved (7 mg L^?1) were obtained in the final effluents. The final values of COD, BOD₅, the suspended solids’ content and the conductivity of the treated waste water met the limits of the Spanish legal industrial discharge, Decree 57/2005 (Ministry of Environment, Local Government and Planning, Community of Madrid, 2005). In addition, the composite thus formed, consisting of zero-valent iron and iron oxide-oxyhydroxides, can be readily removed from the treated effluent, avoiding any post-treatment step.