Greywater treatment by UVC/H2O2 was investigated with regard to the removal of chemical
oxygen demand (COD). A COD reduction from 225 to 30 mg l1 (overall removal of 87%) was
achieved after settling overnight and subsequent irradiation for 3 h with 10 mM H2O2. Most
of the contaminants were removed by oxidation since only 13% COD was removed by
settlement.
The removal of COD in the greywater followed a second-order kinetic equation,
r ¼ 0.0637[COD][H2O2], up to 10 mM H2O2. A slightly enhanced COD removal was observed
at the initial pH of 10 compared with pH 3 and 7. This was attributed to the dissociation of
H2O2 to O2H. The treatment was not affected by total concentration of carbonate (cT) of at
least 3 mM, above which operation between pH 3 and 5 was essential. The initial biodegradability
of the settled greywater (as BOD5:COD) was 0.22. After 2 h UVC/H2O2 treatment,
a higher proportion of the residual contaminants was biodegradable (BOD5:COD ¼ 0.41)
which indicated its potential as a pre-treatment for a biological process.