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