In this study, a combined photo-Fenton and biological process for the treatment of textile wastewater was developed. Textile wastewaters are generally very complex and contain a large amount of organic compounds, many of which are non-biodegradable. In the combined system, homogeneous photo-Fenton oxidation performed in a cylindrical falling film photoreactor was first employed to degrade the biorecalcitrant components into biodegradable intermediates. These intermediates were then further mineralized into carbon dioxide and water by an activated sludge system in a membrane bioreactor (MBR). The objectives of this research were to investigate the performance of the combined system in removing the total organic carbon (TOC) in the wastewater, to determine the factors affecting it. and to...[ Read more ]

In this study, a combined photo-Fenton and biological process for the treatment of textile wastewater was developed. Textile wastewaters are generally very complex and contain a large amount of organic compounds, many of which are non-biodegradable. In the combined system, homogeneous photo-Fenton oxidation performed in a cylindrical falling film photoreactor was first employed to degrade the biorecalcitrant components into biodegradable intermediates. These intermediates were then further mineralized into carbon dioxide and water by an activated sludge system in a membrane bioreactor (MBR). The objectives of this research were to investigate the performance of the combined system in removing the total organic carbon (TOC) in the wastewater, to determine the factors affecting it. and to evaluate the feasibility of applying the combined system for treating refractory industrial effluents.

The photo-Fenton oxidation was demonstrated to significantly enhance the biodegradability of synthetic dye solutions, which were originally resistant to biodegradation. Hydrogen peroxide (H₂O₂) concentration was found to be a critical factor affecting the performance of the process. Increasing the H₂O₂ dosage beyond the optimal value not only showed little improvement in the oxidation performance, but it also increased the required irradiation time. Under the optimal conditions, complete discoloration and 77 % TOC removal were achieved by the combined process in treating 2 mM Indigo Carmine solution.

The TOC removal of a textile dyeing wastewater by the photo-Fenton oxidation was found to be greatly inhibited by high concentrations of chloride and phosphate ions. They can also form complex with Fe³⁺ ions and render them not available for the photo-Fenton reaction. Nevertheless, the photo-Fenton oxidation was still able to effectively decolorize the dyeing wastewater and enhance its biodegradability. Such discoloration could not be accomplished by biological treatment alone. Eighty-five percent of the TOC and 99 % of the total Kjeldahl nitrogen (TKN) in the dyeing wastewater were successfully removed by the combined system. The combined photo-Fenton and biological process shows a high potential in biorecalcitrant wastewater treatment.