Integrated coupled systems as biodegradability enhancement of textile wastewater by photo-fenton process

Photo-Fenton process was explored as photochemical pre-treatment to enhance and improve the biodegradability and complete mineralization of a wastewater coming from a textile industry located in the east of Germany containing reactive dyes which was characterized as biorecalcitrant, non-biodegradable and refractory organic compounds. Wastewater treatment was carried out including a series of bench scale experiments, to identify optimum operating conditions for the treatment of textile wastewater at the end of the pipe effluent. The effect of operating parameters as: pH, irradiation time and initial concentrations of both H2O2 and Fe2+ on the photomineralization processes as a pretreatment step have been studied and the optimal conditions were found. Chemical oxygen demand (COD), total organic carbon (TOC) and colour removal are the parameters used to trace the experiments course. The color removal of the textile wastewater reached to above 100% within 30 min of photocatalytic treatment. The wastewater was completely degraded by a photo-Fenton treatment after 60 min irradiation time by using a 50 mg/L of Fe2+ catalyst concentration and the H2O2 concentration was 1000 mg/L and pH=3 at 25°C. At these optimum operating conditions % removal of TOC, COD and colour removal were 89, 95 and 100 respectively of photo-mineralization. The experimental results show that the ratio of BOD5/COD of the wastewater increased from original 0.09 up to 0.7 after 60 min. The result implies that photocatalytic oxidation enhanced the biodegradability of the dye-containing wastewater and therefore relationship between decolorization and biodegradability exists. When the color disappeared completely, the wastewater biodegraded normally and could be discharged for further treatment. The biodegradability tests also demonstrated that photo-treated effluents within a short time of starting the photo-Fenton process were biodegradable with a BOD5/COD ratio of 0.4 after 30 min of irradiation time. The experimental results demonstrate that it is possible to combine photocatalysis with conventional biological treatment for the remedy of wastewater containing generally non-biodegradable azo dyes. The results of the present study revealed that the treated effluent by photo-Fenton process is complying with the environmental regulations for discharge of textile wastewater in Germany.