Effect of Biochar Addition, Initial pH and Temperature on Methane Production in Two-Phase Anaerobic Digestion of Carbohydrates Food Waste

摘要

The present work examines the effect of biochar addition on methane production in the second phase of the two-phase anaerobic digestion (TPAD) under varying initial pH and temperature conditions. The seed for the culture used in the experimentation was prepared from a sewage sludge collected from local wastewater work and the feedstock was effluent from the first phase (for hydrogen production) of TPAD operating at pH 6.4 and temperature 32 °C, the optimal condition identified from a previous study. In a typical experimental run, 50 ml of the feedstock and 10 ml of the seed sludge were mixed in a 100 ml serum bottle and incubated at desired initial pH and temperature. The effect of biochar addition (5, 10, and 15 g·l~(-1)(w/v)), initial pH (5, 7 and 9) and temperature (25, 35 and 45 °C) on methane yield (Y_M) and methane production rate (R_M) was examined in turn using a Box Behnken experimental design method. A control experiment without biochar addition and incubated at an initial pH of 7 and temperature of 35 °C was also conducted. The concentration, Y_M and R_M of methane in the biogas were monitored daily using a water displacement method and a gas chromatograph. The statistical significance of the results was analysed using the response surface methodology (RSM). In an effort to reveal the biochar - methanogen interaction, the morphology of biochar before and after experimentation was examined using Scanning Electron Microscopy (SEM). The results showed that biochar addition increased Y_M by 14% relative to cultures without biochar. The effect of biochar addition on Y_M was more profound at higher pH and under mesophilic conditions, while in terms of R_M, the effect was greater under higher pH and thermophilic conditions. The maximum Y_M of 1755 ml·l~(-1) and R_M of 500.9 ml·l~(-1).day~(-1) were achieved under the optimum condition of 12.5 g·l~(-1) biochar, 36.2 °C and initial pH 7.8. The SEM imaging analysis confirmed the formation of biofilms on the biochar surface.