Treatment of highly polluted paper mill wastewater by solar photocatalytic oxidation with synthesized nano TiO₂

Photocatalytic processes in the presence of titanium dioxide provide an interesting route to destroy hazardous organic contaminants, being operational in the UV-A domain with a potential use of solar radiation. The solar photocatalytic degradation of paper mill wastewater has been studied over synthesized nano TiO₂. The catalyst was characterized by techniques like X-ray diffraction (XRD), gravimetric-differential thermal analysis (TG-DTA) and IR. The enhanced photocatalytic activity of the synthesized catalyst is attributed to the crystallinity, nano-size, large amount of surface hydroxyl species and reduced band-gap. The results show that prepared TiO₂ in the presence of solar light can be employed as an effective photocatalyst for the removal of chemical oxygen demand (COD) from the wastewater but in optimized conditions. The effects of catalyst loading and pH have been investigated. The degradation was strongly enhanced in the presence of electron acceptor such as H₂O₂. It was found that the photocatalytic degradation of the paper mill wastewater obeys the pseudo-first order kinetic reaction in the presence of the photocatalyst. At optimum dose of 0.75g/L TiO₂ and pH value of 6.5, 75% COD removal of the wastewater was achieved within 180min solar irradiation time. A reduction of 80% of total suspended solids (TSS) from the wastewater was also obtained at the same operating conditions. The experimental results have also shown that the non-biodegradable substances can be very effectively degraded by the solar photocatalytic treatment. The biodegradability of the wastewater treated photocatalytically was measured in terms of BOD₅/COD. A substantial improvement in BOD₅/COD (0.35) could be achieved, but it required the removal of at least 70.5% of the total organic carbon originally in the water.