Role of H2O2 dosage on methane production from tannery wastewater: experimental and kinetic study

A pretreatment with H2O2 was conducted to improve the performance of the anaerobic digestion (AD) process for a partial treatment of tannery wastewater (TWW). Four different H2O2 dosages (0.5, 1, 2, and 4 g/L) were tested by adding to TWW different volumes of a 30% (m/v) H2O2 solution in order to improve the biodegradability of TWW organic load and decrease the total Cr concentration. Indeed, a less total Cr concentration was detected in pretreated samples that showed a minimum removal efficiency of 11% and a maximum removal efficiency of 41%. Moreover, several Biomethane Potential tests (BMP) were conducted to assess the enhanced biodegradability of pretreated TWW. Methane yields resulted in 594, 1151, 1090, 767, and 525 mL CH4/g TVS for the unpretrated TWW and for those pretreated with 0.5, 1, 2, and 4 g/L of H2O2, respectively. BMP tests proved that the best pretreatment condition for TWW, in terms of methane production and consequently total COD reduction, was achieved with a low dosage of H2O2 (0.5 g H2O2/L), corresponding to 1.0·10−4 g H2O2/g TVS and 3.2·10−5 g H2O2/g COD, whereas the highest dosage (4 g H2O2/L) was not related to the highest methane yield. Such contradictory results highlights the relevance of an appropriate dosage of H2O2, Finally, a kinetic study was also conducted.