Effect of Photocatalytic Treatments on Physical and Biological Properties of Textile Dyeing Wastewater

Abstract

The main objective of this research was to observe and evaluate the photocatalytic treatability of textile industrial wastewater to reuse it again for different purposes such as agricultural irrigation, recreational uses, groundwater recharge, industrial reuse, environmental uses, non-potable urban uses, indirect potable reuse and direct potable reuse. The heterogeneous photocatalytic degradation of real and another four prepared simulated textile industrial wastewater (Vat yellow, Reactive black, Reactive blue and Cowboy dyes were carried out on a laboratory scale using three commercial photocatalysts namely, anatase, rutile and zinc oxide. Comparison between the efficiency of the three photocatalysts indicated that their efficiency followed the decreasing order of ZnO > TiO₂ (anatase) > TiO₂ (rutile). However, the amount of zinc oxide required to reach the optimum activity is two times more than that for titanium dioxide (anatase or rutile) and the sequence was changed in the favor of anatase when the same concentration of mass was used (175 mg L^-1). Photocatalytic treatments carried out over a suspension of titanium dioxide (anatase or rutile) or zinc oxide under artificial irradiation. The progress of treatment stages was followed by using different techniques of analysis. Water quality, physical and microbiological parameters for untreated and treated industrial wastewater were determined using different techniques. The physical parameters include colour, temperature (ºC), turbidity/NTU, electrical conductivity (μ mohs cm^-1), total suspended solids (ppm) and total dissolved solids (ppm). Under optimal conditions, the extent of decolorization was 100 % after 42, 35, 10, 12 and 17 min of irradiation for real industrial wastewater and prepared simulated textile industrial wastewater (Vat yellow, Reactive black, Reactive blue and Cowboy dyes), respectively, when titanium dioxide (anatase) was used. The time for complete decolorization for real and simulated Vat yellow, Reactive black and Reactive blue dyes was found longer when rutile was used (370, 300, 120 and 90 min). However, simulated Cowboy dye did not decolorized completely even when the time of irradiation was increased to 400 min when rutile was used as photocatalyst. When zinc oxide was used the extent of decolorization was 100 % after shorter time compared with that needed when anatase and rutile were used (30, 20, 7, 5 and 12 min for the real and simulated textile wastewater dyes, respectively). The temperature of real industrial wastewater was 40 ºC at the collection point while for simulated samples was about 25 ºC. The temperature of all treated textile wastewater dyes was about 30 ºC at the end of irradiation time of each textile wastewater dyes. It was observed that turbidity was reduced from 820 to 4.68 NTU for the real textile wastewater dyes (more than 99 %) when ZnO used for treatment and for simulated textile wastewater dyes turbidity was removed by 92-98 %. After treatment with anatase, rutile and zinc oxide, the electrical conductivity of real and simulated textile wastewater dyes was found to decrease up to 14-92, 20-68 and 29-80 %, respectively. Total suspended solids and total dissolved solids values for real and simulated textile industrial wastewater fell within the range 4-6350 and 10-7820 ppm, respectively before treatment. Total suspended solids and total dissolved solids values were removed after photocatalytic treatments by 92.86-100 and 75-98.90 %, respectively.