In-storage psychrophilic anaerobic digestion of swine manure: Acclimation of the microbial community

Covering a concrete manure storage tank with an air-tight floating membrane should induce anaerobic digestion of the stored manure. If the microbial community in the manure can acclimate to the ambient conditions, then In-Storage Psychrophilic Anaerobic Digestion (ISPAD) could be used by Canadian livestock producers to produce methane and stabilize manure. The objective of this study was to determine whether the microbial community in swine manure can successfully acclimate to the psychrophilic operating conditions in ISPAD and develop robust anaerobic digestion. This was done in the laboratory by analyzing manure from a three-year old full-scale pilot ISPAD facility located in St. Francois Xavier, Quebec, Canada, along with fresh manure and manure from an uncovered storage tank. Biochemical methane production assays performed at the three temperatures were used to quantify the performance of the microbial community and its temperature dependence. The ISPAD microbial community produced methane, in terms of VS added, at rates of 44.6, 9.8 and 8.5 dm3 kg−1 d−1, at 35, 18 and 8 °C, respectively. The ISPAD process reduced the organic matter content of the manure by 24% while releasing 63% of the potential methane in the manure, as opposed to the open storage tank where no measurable reduction in solids occurred, and only 15% of the potential methane was released. These results indicate that a robust, acclimated microbial community actively digests manure in the pilot ISPAD installation.

► In-Storage Psychrophilic Anaerobic Digestion in a covered swine manure storage tank develops a robust acclimated microbial community within 1–2 years.
► Comparable to mesophilic installation, 24% of the manure organic matter (VS) was transformed into methane, representing 63% of the ultimate methane potential, B0.
► Standard laboratory analyses, VS and B0, can be used to monitor acclimation in new ISPAD installations.
► ISPAD could be used for digestion of waste activated sludge from small and medium-sized waste water treatment operations, producing methane and stabilizing biosolids for land application, possibly combined with struvite precipitation for nutrient removal and revenue generation.