Greywater treatment for reuse: Effect of combined foam fractionation and persulfate-iron based fenton process in the bacterial removal and degradation of organic matter and surfactants

Greywater (GW) represents a viable candidate in adapting to increased water scarcity due to climate change because its reuse can significantly reduce domestic water consumption. This work focused on studying the combination of physical foam fractionation (FF) as pre-treatment step and Fenton processes as polishing-step. The FF, applied for first time on real GW, allowed reaching a removal of 60 and 85% for chemical oxygen demand (COD) and total surfactants (TSU), respectively, and a bacterial removal of about 3Log units. Fenton processes using Fe2+/S2O82− and Fe2+/H2O2 were optimized through response surface methodology (RSM) with a central composite design (CCD). The concentration of Fe2+, oxidant and treatment time were chosen as variable factors, while COD and TSU removals as target responses. According to RSM results, the optimum conditions to operate Fenton processes were (mg/L) Fe2+:12.5/S2O82−:185.6 and Fe2+:50/H2O2:157.6 with a treatment time of 30 min for both processes. A COD removal of 89 and 78% and TSU removals of 99.7 and 96.6% were obtained for Fe2+/S2O82− and Fe2+/H2O2 respectively. Complete bacterial removal was detected for both Fenton processes. Fe2+/S2O82− allowed for a 4-fold lower sludge production than Fe2+/H2O2. The persulfate-based process requires low treatment time (2.5 h) and energy consumption with limited sludge production, making it a promising technology for future research and full-scale application.