Application of Fenton's Reagent to Remove Simultaneously Pathogens and Organic Polluants from Raw Wastewater to Produce Reclaimed Water

The removal of pathogenic bacteria and helminth eggs present raw wastewater was assessed in laboratory by applying Fenton's reagent (FE) as a pretreatment in a treatment chain to produced reclaimed water. This advanced oxidation process was compared to the advanced treatment process “ATP” (coagulation-flocculation with alum). Trials in batch and continuous reactor were performed in laboratory. The jar-test experiments were conducted to determine the process (FE or ATP) to be evaluated in a continuous pilot system for obtaining the maximal removal of COD, color and turbidity. Initial values of these parameters of raw wastewater were 370 mg O2/L, 566 Pt-Co units and 118 NTU, respectively. At these conditions, the removal of physicochemical parameters was similar between FE and ATP. Nevertheless, the former showed to be more efficient than APT (at the best experimental conditions) for removing pathogens, since none of the selected pathogens were detected in the effluent or the sludge produced from the Fenton's reagent treatment. The best results obtained by applying Fenton's reagent were 25 mg Fe2+/L, 25 mg H2O2/L and pH = 4. At these experimental conditions, complementary experiments were performed in a laboratory scale pilot reproducing in continuous mode each stage of Fenton's reagent (pH conditioning, rapid and slow mixing, advanced oxidation) and sedimentation and sand filtration processes. These experiments allowed determining the stage(s) of the Fenton method which the microorganisms are removed more efficiently. Removal efficiencies of COD, color and turbidity were 90.2, 72.9 and 98.4%, respectively. Counts of fecal coliforms (8.1 × 107 MPN/100 mL), Escherichia coli (2.1 × 106 MPN/100 mL), Shigella (5.5 × 107 MPN/100 mL), Salmonella sp (2.6 × 105 MPN/100 mL) and helminth eggs (4.6 ova/L) were high in raw wastewater. After rapid and slow mixing, none of these pathogenic bacteria were detected in the effluent. Helminth eggs were only partially removed by Fenton's reaction (21.7%). The removal of these microorganisms can be attributed to the combined effect of the acid pH and to the attack of hydroxyl radicals produced during the Fenton's reaction.