Performance evaluation of the anaerobic fluidised bed system: II. Biomass holdup and characteristics

The biomass holdup and characteristics of the anareobic fluidised bed system for methane recovery from liquid wastes was examined at COD loadings of between 5.8 to 108 kg m−3 day,−1 hydraulic retention times of between 0.45 to 8h, and feed COD concentrations of between 480 to 9000 mg dm−3. Under these operating conditions, the equilibrium biomass holdups increased with increasing COD loadings and varied from 15000 to 32000 mg VSS dm−3 The distribution of biomass holdup and biofilm thickness in the reactor was relatively uniform, because of the completely mixed conditions maintained and the continuous sloughing of biofilms induced by the effervescence caused by rising methane bubbles. This continuous biofilm sloughing process also eliminated the need for intentional sludge wasting and consequently, the resulting sludge retention time in the reactor decreased with increasing COD loadings. The ability of the anaerobic fluidized bed system to retain a high biomass holdup was clearly demonstrated. As a result this system is ideal for being employed as a high-rate system for methane recovery from liquid wastes, even at low feed COD concentrations.