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Fenton reaction generates reactive hydroxyl radicals by the reaction between H 2O 2 and iron
(Fe2+/Fe3+) is sometimes used in glove manufacturing industries to oxidize organic compounds in
wastewater. Chemical oxygen demand (C O D ) is an important parameter used to assess the
quality of raw and treated wastewater. The existing dichromate reflux method for organic C O D
determination assumes that dichromate is only reacting with the organic compounds in the
sample; however, the assumption is not valid for wastewater treated by the Fenton reagent
because of the presence of residual amounts of H 2O 2 and Fe2+ which also react with dichromate.
Hence the existing method was modified to improve its accuracy by eliminating these
interferences. The Fenton reagent used here has 1400 mgL'1 of H2O 2 and 150 m gL1 of Fe2+
respectively. The simulated wastewater sample was prepared using ethanol, acetic acid and
isopropyl alcohol. The Fenton reaction was initiated by mixing 100.0 mL of wastewater with 1.0
mL of the reagent. The final pH of the mixture was approximately 2.5. Sample aliquots (10.0 mL)
were withdrawn from the mixture on hourly basis for 5 hours and determined its C O D value
using the existing dichromate method. In addition, the residual concentrations of H2O 2 and Fe2+
in the sample aliquot were also determined by iodometric titration and 1,10- phenanthroline
colorimetric method respectively. The theoretical equivalents of oxygen required for oxidizing
H2O 2 and Fe2+ by dichromate were calculated from stoichiometric redox reactions between Fe2+,
H2O 2 and dichromate. The oxygen equivalents calculated from the previous step were subtracted
from the C O D values determined by the existing dichromate method to eliminate the
interference caused by them. This correction improved the accuracy of the organic C O D values.
According to the experimental data, C O D values determined by the existing method were always
20 % to 30 % greater than the corrected C O D value. It can be concluded that for the
determination of organic C O D by the existing dichromate method overestimate the C O D value if
reducible non-organic compounds are present in the sample and therefore, a correction is
required to eliminate the interferences caused by the reducible non-organic compounds.
