Phenol degradation in a three-phase biofilm fluidized sand bed reactor

«Erworben im Rahmen der Schweizer Nationallizenzen (http://www.nationallizenzen.ch)»A previous three phase fluidized sand bed reactor design was improved by adding a draft tube to improve fluidization and submerged effluent tubes for sand separation. The changes had little influence on the oxygen transfer coefficients(KL a), but greatly reduced the aeration rate required for sand suspension. The resulting 12.5 dm3 reactor was operated with 1 h liquid residence time, 10.2dm3/min aeration rate, and 1.7-2.3 kg sand (0.25-0.35 mm diameter) for the degradation of phenol as sole carbon source. The KLa of 0.015 s−1 gave more than adequate oxygen transfer to support rates of 180g phenol/h · m3 and 216 g oxygen/h · m3. The biomass-sand ratios of 20-35 mg volatiles/g gave estimated biomass concentrations of 3-6 g volatiles/dm3. Offline kinetic measurements showed weak inhibition kinetics with constants ofKs=0.2 mg phenol/dm3, Ko2=0.5 mg oxygen/dm3 and KinI= 122.5 mg phenol/dm3. Very small biofilm diffusion effects were observed. Dynamic experiments demonstrated rapid response of dissolved oxygen to phenol changes below the inhibition level. Experimentally simulated continuous stagewise operation required three stages, each with 1 h residence time, for complete degradation of 300 mg phenol/dm3 · h