Performance evaluation of the anaerobic fluidised bed system: I. Substrate utilisation and gas production

COD removal efficiencies in the range 75 to 98% were achieved in an anaerobic fluidised bed system designed for the recovery of methane from liquid wastes, when evaluated at COD loadings of between 5.8 to 108 kg m−3 day−1, hydraulic retention times of between 4.45 to 8 h, and feed COD concentrations of beween 480 to 9 000 mg dm−3. More than 90% of feed COD could be removed up to COD loadings of about 40 kg m−3 day−1. Up to around 300 dm2 of methane were produced per kg COD removed and this methane production rate was independent of the COD loadings applied in this investigation. Volatile acid concentration in the reactor increased sharply at a COD loading of about 40 kg m−3 day−1 and therefore, sufficient alkalinity should be provided to prevent pH from dropping to the undesirable level. The anaerobic fluidised bed system can be operated at a significantly higher liquid throughputs while maintaining its excellent efficiency.