Anaerobic digestion of elephant camp–derived wastes: methane potential, kinetic study, and biorefinery platform

Anaerobic digestion (AD) of elephant camp–derived wastes was studied using series of batch experiments. Three different materials derived from elephant dung namely fresh elephant dung (FD), washing water (WW), and washed fiber (WF) served as the substrates. The theoretical methane potentials of the solid substrates were 786.0 and 580.6 LCH₄/gVS_added at standard temperature and pressure, for FD and WF, respectively. In addition, the cumulative methane yields were 275.7±1.6, 266.7±14.3, and 202.6±1.6 NmL/gVS_added for FD, WW, and WF, respectively. Also, there were no signs of an acid accumulation throughout the studies. For the kinetic study, the modified Gompertz equation fitted well with the experimental data with an R² more than 0.98. Moreover, FD showed the highest predicted methane production potential of 293.2 NmL/gVS_added. Since the methane yields of FD and WW were not significantly different, in practical terms, FD should be washed and subsequently, the generated WW could be served to anaerobic digestion. However, direct combustion seems to be a more promising biorefinery-based option for WF since its methane potential was relatively low, but the fibers had a high heating value. The integrated AD and thermochemical process could potentially generate more than 14,500 kJ/kg of FD.