Methane production and microbial community acclimation of five manure inocula during psychrophilic anaerobic digestion of swine manure

For small-scale farms, the development of rustic and cheap psychrophilic anaerobic digestion systems appears as an opportunity to treat manure, mitigate gaseous emissions and promote decentralized renewable energy production. However, the development of such processes is limited by our understanding of their start-up. In this research, we tested the ability of one mesophilic digestate and four different manure to be used as inoculum for the start-up of psychrophilic anaerobic digestion of swine slurry at 13 ?. The most efficient inoculum appeared to be a swine manure that had been stored for 2 months in a pit. After 9 months of acclimation, the corresponding reactor produced a maximum methane yield of 42L of CH4/kg Volatile Solide(substrate)/day and a CH4 volume of 125L of CH4/kg-Chemical Oxygen Demand(added). The maximum methane production expressed at 13 ? was between 55% and 68% of that obtained at 37 ?. Monitoring of the microbial community dynamics by high throughput 16S rDNA sequencing showed the smooth adaptation of manure microbial species, underlining the transient dominance of the acetogen syntroph candidatus Cloacimonas during acclimation and the enrichment in the Methanosaeta and Methanosarcina methanogens for an efficient methane production.

Automated summary

For small-scale farms, the development of rustic and cheap psychrophilic anaerobic digestion systems is an opportunity to treat manure, mitigate emissions, and promote renewable energy production. In this study, the most efficient inoculum for the start-up of psychrophilic anaerobic digestion of swine slurry at 13 ℃ was found to be swine manure stored for 2 months. After acclimation, the reactor produced a high methane yield, with a production efficiency of 55-68% at 13 ℃ compared to 37 ℃.