The working principle of an anaerobic UASB reactor is simple and the idea is to allow wastewater influent to pass through a sludge bed which can be either pelleted or in granular form with the biodegradation and breakdown of waste compound taking place at the same time. Usually the sludge, depending on its characteristics will become self-immobilized on its own and will aggregate together to form dense structures or granules with high settling rates that prevents it from carryover out of the reactor system even with the maximum feed rate going in. This is the most ideal condition for it to function optimally.
In order to start the process in a newly setup reactor, usually bioaugmentation approach is carried out by using sludge granules or seeds taken from an established reactor and this is the fastest and easiest method to begin with. Usually seeds are selected from a system which can withstand high flow rate and some of the most commonly used inoculum can be either taken from digested sewage sludge or cow manure. Both works fine on different occasions and proven through numerous plant trials. Choosing a suitable inoculum is one the most critical aspects towards setting up a stable and high performance working reactor that can biodegrade the waste matter efficiently and the main objective is to select the microorganisms with the desired activity and with the correct microbial process to suit the incoming wastewater.
One of the main challenges facing bioaugmented reactors is about trying to keep and ensuring that the introduced microorganisms thrive in the system. This is important because the objective is to grow and maintain the right population of bacteria that is capable of biodegrading the pollutants present in the influent. Nevertheless, the success of the bioaugmentation program largely depends on the survival of these microbial cultures after it was introduced into the system and usually failure often comes as a result of the lack of understanding and research because not all inoculated cultures can thrive in face of severe competition coming from the other microorganisms. That is why certain manufacturers even supply genetically engineered microbial strains to suit the needs based on the properties of the wastewater.
UASB reactors offer several advantages compared to the other treatment processes. First of all, biodegradation of the organic matter will generate biogas which is in high demand in the energy sector. Furthermore, since the conversion pathways are different, biomass production on sludge generation are kept within a certain limit and is far comparatively lower measured against any of the aerobic treatment systems. The UASB sludge granules are also highly stable and can be kept refrigerated for years and there are instances whereby newly setup reactors can be stabilized within days using the mixed sludge. For that matter, that is why their application is widespread and is considered an automatic choice especially in the pulp and paper mills industry.