Comparison of photo-Fenton, O3/H2O2/UV and photocatalytic processes for the treatment of gray water.

This research was carried out to compare and optimize the gray water treatment performance by the photo-Fenton, photocatalysis and ozone/H2O2/UV processes. Experimental design and optimization were carried out using Central Composite Design of Response Surface Methodology. The results of experiments showed that the most effective and influencing factors in photo-Fenton process were H2O2/Fe2+ ratio, in ozone/H2O2/UV experiment were O3 concentration, H2O2 concentration, reaction time and pH and in photocatalytic process were TiO2 concentration, pH and reaction time. The highest COD removal in photo-Fenton, ozone/H2O2/UV and photocatalytic process were 90%, 92% and 55%, respectively. The results were analyzed by design expert software and for all three processes second-order models were proposed to simulate the COD removal efficiency. In conclusion the ozone/H2O2/UV process is recommended for the treatment of gray water, since it was able to remove both COD and turbidity by 92% and 93%, respectively.