The relative volume of inoculum to be used in the assays can vary a lot, depending on the activity and biomass concentration of the inoculum and on substrate concentration and biodegradability. The relative volume of inoculum, can be lower in case that concentrated/dense inocula are used such as granules containing a concentrated amount of active microorganisms, while much higher relative volumes of inocula are need in case of less dense inocula such as digested manure or sewage sludge. In any case the amount of inoculum should be enough to prevent the accumulation of volatile fatty acids and acidic conditions.