The UASB Reactor is a biological sewage treatment technology based on the ANAEROBIA decomposition of organic matter. Simple and economical, this type of process has been studied and improved in developing countries, such as Brazil. Initially, the use of UASB was for sewage with a high concentration of organic matter (BOD or COD), as in cases of specific industrial evictions.
Over the years, the use of UASB has gained ground in the treatment of domestic sewage (low concentration of organic matter) and is nowadays one of the main technologies used in Brazil. However, the efficiency of anaerobic domestic sewage treatment in a UASB is somewhat limited: experience has indicated BOD removal in the range of 45-75%, and COD in the range of 40-75%. The main advantages of this type of treatment are: low structural and operational costs; energy generation (biogas); and less need for space.
In order to alleviate the adverse factors to the good treatment efficiency, some recommendations should be observed in the development of a project. One can mention: Removal of coarse solids; adequate distribution of the sewer; and the upward velocity inside the reactor.