A new insight on improved biomethanation using graphene oxide from fermented Assam lemon waste

Abstract

The present study comprises valorization of Assam lemon waste through anaerobic digestion. The uniqueness of the study lies in its process of substituting cow dung with a mixed anaerobic culture (MAC) and in evaluating the effect of graphene oxide (GO) on the fermentation process. A sequential improvement of biomethane yield was observed to be 93.86 ± 0.31, 216.54 ± 1.63, 219.64 ± 0.14 and 231.55 ± 0.27 ml/g VSfed in presence of single variable such as substrate concentration, time, GO and inoculum volume, respectively. Further optimization was carried out adopting central composite design (CCD) based response surface methodology (RSM). The maximum biomethane yield of 243.23 ± 1.99 ml/g VSfed was achieved when the solid loading was kept at 25 g TS/L, 0.06% (w/v) concentration of GO, incubated for 30 days at 37 °C which has resulted into 19.04% enhanced methane yield. Kinetic analysis exhibited lowest deviation with experimental cumulative methane yield, lowest value of λ (4.37 days) and RMSE (5.85) in modified Gompertz model. Digested biomass characterization revealed 18.46% reduction in crystallinity along with a major change in FTIR peaks. Materials and energy flow of the underlying process show 70.88% efficiency of the process with 4.96 kJ/g net energy gain. The report on AD of generated Assam lemon waste to biomethane with the intervention of GO is rare. Thus the result obtained from the current study will encourage the scientific community to improve the biomethane yield by the addition of conductive materials.