Effects of microwave, H2O2/MW and H2O2/heat pre-treatments on the methane production from wastewater sludges: experimental and modeling approach

The wastewater sludge stabilization by anaerobic digestion is sufficient to reduce the organic content of the sludge, so that it can be safely disposed of without causing odor problems and pathogen contamination, while producing energy in form of biogas. Efficiency of anaerobic digestion in terms of biogas/methane production and organic removal can be enhanced by pretreating the sludge prior to anaerobic digestion. This study compares the effects of microwave (MW), combined hydrogen peroxide/microwave (H2O2/MW), and combined hydrogen peroxide/heat (H2O2/heat) pre-treatments on the digestion efficiency and methane production potential of wastewater sludges. The methane productions were also estimated by using modified Gompertz equation through the calculation of the kinetic parameters. The pre-treatments applied to sludge samples speeded up the hydrolysis step and improved the biodegradability of the organics by increasing their solubility. Application of MW, combined H2O2/MW, and combined H2O2/heat pre-treatments increased the methane yields by 64%, 38%, and 19%. The modified Gompertz model fitted well to the experimental results (R-2 of 0.999, 0.983, 0.997, and 0.998 for control, MW, H2O2/MW, and H2O2/heat, respectively).