Granular sludge is a preferable inoculum for the biochemical methane potential assay for two complex substrates.

The biochemical methane potential (BMP) assay is a standard method for characterizing biomethane potential and anaerobic biodegradability organic waste streams. Therefore, the BMP protocol must be standardized to reliably compare these parameters for various substrates. Here, the effect of inoculum selection on biomethane potential was investigated through BMP tests using two different substrates and inocula obtained from four different anaerobic digesters. It was found that inocula in the form of granular sludge yielded overall higher biomethane potential and generally had faster kinetics than suspended biomass. Furthermore, acclimation of inocula to substrate appeared to have little effect on degradation rates, and co-inoculation (with both suspended and granular biomass) did not perform better than single inoculation (e.g., with suspended sludge alone). These results emphasize the role of granular sludge as an preferable inoculum for BMP assay.