Revealing the correlation of biomethane generation, DOM fluorescence, and microbial community in the mesophilic co-digestion of chicken manure and sheep manure at different mixture ratio.

Batch co-digestion tests of chicken manure (CM) and sheep manure (SM) at different ratio (Rs/c) were conducted under mesophilic condition (35 °C). Batch kinetic analysis of bioCH4 production, excitation-emission matrix (EEM) fluorescence of dissolved organic matter (DOM), and microbial community were investigated. The well-fitted modified Gompertz model (R2, 0.98-0.99) resulted that the co-digestion markedly improved the methane production rate and shortened the lag phase time. The highest bioCH4 yield of 219.67 mL/gVSadd and maximum production rate of 0.378 mL/gVSadd/h were obtained at an optimum Rs/c of 0.4. Additionally, a significant variation of DOM was detected at the Rs/c of 0.4 with a consistent degradation of soluble microbial byproduct-like and protein-like organics. The positive synergy effects of co-digestion conspicuously enhanced the bioCH4 production efficiency. FI370 and NADH were significantly correlated to Rs/c (p < 0.05). Moreover, the correlations among process indicator, EEM-peaks and different environmental parameters were evaluated by Pearson correlation analysis. The high diversity of acetoclastic methanogens and hydrogenotrophic methanogens in the co-digestion improved the stability of process. Graphical Abstract.