In-storage psychrophilic anaerobic digestion: acclimated microbial kinetics

Abstract

In-storage psychrophilic anaerobic digestion develops by microbial acclimation in covered swine-manure storage tanks, producing CH₄ and stabilizing organic matter. To optimize the system's performance, the process kinetics must be understood. The objective of this study was to evaluate kinetic parameters describing the major stages in the digestion process, and to investigate the effect of temperature acclimation on these parameters. Specific activity tests were performed using manure inocula and five substrates at three incubation temperatures. Extant substrate activities were determined analytically for each case, and intrinsic kinetic parameters for glucose uptake were estimated by grid search fitting to the Monod model. The results demonstrate that this acclimated microbial community exhibits different kinetic parameters to those of the mesophilic communities currently modelled in the literature, with increased activity at low temperatures, varying with substrate and temperature. For glucose, the higher uptake is accompanied by lower microbial yield and half-saturation constant. Decomposing these values suggests that active psychrophilic and mesophilic microbial populations co-exist within the community. This work also confirms that a new method of assessing microbial substrate kinetics must be developed for manure microbial communities, separating microbial mass from other suspended organics.

Keywords:

• psychrophilic anaerobic digestion
• specific substrate uptake
• manure treatment
• microbial kinetics
• swine manure

Acknowledgements

The authors wish to acknowledge the financial contributions of the Natural Science and Engineering Research Council of Canada, GTI of Fredericton, New Brunswick, Canada, and the Biotechnology Research Institute of the National Research Council of Canada, as well as the personal contributions of Luis Ortega, Helene Leblanc, Grant Clark and Dominic Frigon.