The Excellent Brazilian Experience with UASB Reactors

The use of anaerobic treatment for domestic sewage is under current expansion in Brazil. Anaerobic treatment is already a well known technology in Brazil, the main units designed and constructed being Upflow Anaerobic Sludge Blanket – UASB – reactors.It presents many advantages, such as being a compact system, with practically no equipment in the anaerobic vessel, low construction and operational costs, very low energy consumption, low excess sludge produced. However it also has important disadvantages, such as limited efficiency for BOD, COD and TSS removal, and the possibility of bad odors, due to H2S generation.In order to avoid poor effluent quality, and meet legal water quality standards, post treatment has been studied and practiced, with excellent results, and great reduction in investment costs. The same is true if the scheme is seen as a secondary plant with an UASB reactor as primary treatment.Design criteria for the anaerobic reactor, and for different secondary treatment processes are discussed in the paper, according to a two year research sponsored by FINEP – Financiadora de Estudos e Projetos, of the Ministry of Science and Technology of Brazil.