Mixture design optimisation of anaerobic co-digestion of human excreta and livestock manure for enhanced methane production
摘要
The efficient valorisation of human excreta and livestock manure via anaerobic co-digestion remains a major challenge for decentralised biogas toilet systems in low-resource settings. This study aimed to optimise substrate mixtures to enhance methane production using a statistically based mixture design. Biochemical methane potential (BMP) assays were conducted with human excreta, cow dung, pig slurry, and sheep droppings under mesophilic conditions (35 ± 2 °C). A quaternary mixture design, combined with response surface methodology and kinetic modelling, was used to evaluate interaction effects and identify optimal blending ratios under realistic constraints on the availability of household substrates. Results showed that co-digesting human excreta with livestock manure increased methane yield compared with mono-digestion. Co-digesting human excreta with pig slurry increased methane yield by up to 65% relative to human excreta alone (151.72 NmL CH4·g− 1 VS added). The most effective mixture was 10.87% human excreta and 89.13% pig slurry, yielding 265.88 NmL CH4·g− 1 VS added. Kinetic modelling using the modified Gompertz equation indicated that this synergistic effect was associated with a longer lag phase (Δλ = 0.74–1.87 days), suggesting microbial acclimation to the mixed substrate. These insights support the design of digesters that advance sustainable sanitation and energy recovery for low-resource communities.