Anaerobic processes under psychrophilic conditions have been successfully applied to municipal wastewater treatment by high
rate systems such as the up-flow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors [6,7]. However, serious problems arise when treating low strength wastewater under psychrophilic conditions using these technologies. In fact, low biomass growth rates at low temperatures and high hydraulic loading rates increase sludge wash out. In addition, applications of UASB and EGSB reactors for municipal wastewater treatment are limited by the influent high concentrations of suspended solids and inert substances [6].