Physical and biological performance of self-inoculated UASB reactor treating raw domestic sewage

The dynamics of a self-inoculated upflow anaerobic sludge blanket (UASB) re actor treating raw sewage has been studied. The results suggest two types o f start-up periods. During the first 6 weeks of operation, the reactor achi eved a removal efficiency of up to 65% of total chemical oxygen demand (COD ) and 73% of suspended solids. During this primary start-up period, the rem oval of organic matter was mainly due to interception in the reactor. The s econd start-up period expressed by biogas release was reached after 14 week s. An intermediary period between these two start-up periods was characteri zed by a slight drop of pH and increase of volatile fatty acid in the efflu ent. The long time to reach the second start-up period seemed to be respons ible for the large discrepancy between removed COD and recovered biogas (10 7 mL/g COD removed). it is thus suggested that process optimization should focus on shortening the time needed to reach the second start-up period. A model that represents a possible description of the process dynamics of sel f-inoculated UASB reactors is proposed.