Physical and Biological Performance of Self-Inoculated UASB Reactor Treating Raw Domestic Sewage

The dynamics of a self-inoculated upflow anaerobic sludge blanket (UASB) reactor treating raw sewage has been studied. The results suggest two types of start-up periods. During the first 6 weeks of operation, the reactor achieved 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 removal of organic matter was mainly due to interception in the reactor. The second start-up period expressed by biogas release was reached after 14 weeks. An intermediary period between these two start-up periods was characterized by a slight drop of pH and increase of volatile fatty acid in the effluent. The long time to reach the second start-up period seemed to be responsible for the large discrepancy between removed COD and recovered biogas (107 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 self-inoculated UASB reactors is proposed.