The impact of inocula carryover and inoculum dilution on the methane yields in batch methane potential tests

Batch studies are used to benchmark biohydrogen potential (BHP) and biomethane potential (BMP) yields from feed substrates, digestates residues and different process configurations. This study shows that BMP yields using cellulose can be biased positively by not diluting the initial sewage sludge inoculum and the bias is independent of starting inoculum volatile solids (VS) concentration. The carryover of BHP inoculum also increased the BMP yields when using cellulose as a substrate by up to 18.8%. Furthermore it was also observed that the dilution of BMP inoculum with deionised H₂O reduced methane yields from cellulose by up to 132 ± 26 N mL-CH₄ g-VS^-1. Therefore it is proposed that inoculum and standard substrate controls (as used in this study) should be included in methane batch methodologies, particularly when using a pre-fermentation stage such as dark fermentation.