Zero sludge discharge strategy for Fenton oxidation wastewater treatment technology: Biological regeneration and in-situ cyclic utilization - A feasibility study

Classical homogeneous Fenton oxidation wastewater treatment technology (abbreviated as Fenton process) shows advantages of simply process, high efficiency and low equipment requirements. However, the generated Fenton iron sludge (FIS) is a kind of hazardous solid waste and the treatment cost is high. The resource utilization of the FIS is of great significance for the cost reduction and further application of the Fenton process. In this study, we propose a zero sludge discharge strategy of FIS, biological regeneration and in-situ cyclic utilization. In this strategy, the FIS is firstly experienced an anaerobic biological digestion process to convert the Fe(Ⅲ) to Fe(Ⅱ) by iron reducing bacteria (IRB) using the residual organics as an electron donor; then the digested sludge is acidified to extract the Fe(Ⅱ) resource in the form of Fe2+ ion; finally, the Fe2+ ion is in-situly cyclic utilized for Fenton oxidation and the residual sludge containing abundance of IRB flows back to the anaerobic digestion tank. This strategy is verified by using both artificial and practical FIS. Besides temperature, it is found that the Fe/organics ratio, P (in the form of orthophosphate) level and solid content show a great effect on the conversion efficiency of the Fe(II) during anaerobic digestion of the iron sludge. The optimal pH for extraction of Fe(II) resource from the digested sludge is around 3.5, under which not only over 90% of the regenerated Fe(Ⅱ) could be extracted, but also the activity of the IRB in the residual sludge could be preserved. The extracted Fe2+ ions are cyclic utilized used for Fenton oxidation and show comparable performance to that of the commercial ferrous sulfate. The Fenton process coupling of the biological regeneration and in-situ cyclic utilization strategy could lead to an over 60% cost reduction and zero waste discharge. This study provides a sustainable strategy for the disposal of iron sludge and can promote the further popularization of the Fenton process.