Greywater treatment by UVC/H2O2

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 l−1 (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 = 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 = 0.41) which indicated its potential as a pre-treatment for a biological process.