Every biological treatment system requires a certain mass of active microorganisms to inoculate the facility at the beginning of its operation or to restore the biological population after a system upset.
Some types of technologies, such as anaerobic technologies utilizing granular sludge, require specialized forms of biomass to function properly. This material is often difficult to find due to high demand and can delay a process startup or restart.
When not available locally, it can be costly to transport in from afar. In some cases, large amounts of biomass are needed, and sufficient quantities are simply not available in specific locales.