Pollutant removal and biodegradation assessment of tannery effluent treated by conventional Fenton oxidation process

In this research, the performance of a Fenton batch reactor (FBR) for the treatment of tannery effluent (TE) has been studied by applying response surface methodology (RSM). In the context of RSM, three important Fenton parameters (Fe and H2O2 concentrations and solution pH) were suitably changed within a full experimental design, allowing the definition of a set of 27 FBR experiments performed in batch mode. From the RSM analysis, the Fenton oxidation process showed the best removal response for chemical oxygen demand (COD) (80%), color (90%), turbidity (95%), and sludge (70%), as well as an increase in the percentage of biodegradation from 0.19 to 0.3 (BOD5/COD ratio) when conducted under conditions of 5 mg Fe2+L-1, 75 mg H2O2L-1, and pH 4 with a 60 min reaction time. Additionally, quick consumption of the initial concentration of H2O2, as observed in an acidic solution pH (similar to 3.5) containing dissolved iron, led to rapid yield of hydroxyl radicals (HO center dot), making it possible to oxidize the organic pollutants in the raw TE more efficiently. By performing kinetic experiments on the best pollutant removal, it was observed that there were high reductions in the amounts of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and total dissolved carbon (TDC). Conversely, an increase in the initial concentration of total dissolved nitrogen (TDN) was also observed, suggesting a partial mineralization of nitrogen compounds such as ammonia, nitrate, and nitrite. The Fenton reaction coupled to the Zahn-Wellens test indicated and increase in the biodegradability (Dt 79%) of the treated TE. Gas Chromatography - Mass Spectrometry (GC-MS) analysis identified contaminants present in the raw TE and persistent in the samples treated by the Fenton reaction coupled to the Zahn-Wellens test. Based on the overall results, the Fenton process has been shown to be a simple and suitable way to treat TE efficiently. The process could also be used as a pretreatment of a conventional biological system, being applied in the degradation of toxic and recalcitrant contaminants contained in TE.