LABORATORY-SCALE EVALUATION OF AEROBIC FLUIDIZED-BED REACTORS FOR THE BIOTREATMENT OF A SYNTHETIC, HIGH-STRENGTH CHEMICAL-INDUSTRY WASTE STREAM

Laboratory-scale fluidized bed reactors (FBRs) containing either sand or granular activated carbon (GAC) as biocarriers for immobilized bacteria were evaluated for biotreatment of chemical industry wastes. The FBRs were fed high levels of a synthetic waste stream containing aniline (ANL), methyl ethyl ketone (MEK), p-nitrophenol (PNP) and sodium formate (FRM) at concentrations increasing from approximately 3 600 mg/L total chemical oxygen demand (COD) up to 17 000 mg/L COD. Microbial biomass attached to the GAC increased from 15 000 mg/L at a COD loading of 3.2 Kg COD m-3 d-1 to over 40 000 mg/ L at a maximum COD loading of 16.0 Kg COD m-3 d-1. The sand was colonized slower during start-up but supported biomass levels of 2600 to 20 000 mg/L at COD loadings up to 9.6 COD m-3 d-1. Scanning electron microscopy confirmed biomass measurements and showed that high levels of bacteria were retained on GAC after a toxic surge in COD loading, but were significantly reduced in the sand reactor resulting in diminished performance. Specific chemical analyses showed over 99% removal of organic feed components by both reactors throughout the study. The sand reactor study was terminated early due to its inability to handle an accidental surge in COD loading. Biological solids production from the GAC reactor ranged from 0.056 to 0.184 g solids/g COD removed. The GAC reactor demonstrated a greater ability to handle rapid increases in COD loading (for adsorbable chemicals) than the sand reactor. This study has increased fundamental understanding of the operation and performance of FBRs treating a representative chemical industry waste stream and has demonstrated some advantages of GAC over sand as a biocarrier.