Anaerobic Fluidized-Bed Treatment of Hazardous Wastes

Abstract

The anaerobic attached film process consists of a columnar reactor containing a packing medium that serves as an attachment surface for the retention of anaerobic microorganisms that metabolize the organic constituents of a waste. The wastewater is usually applied in an upflow mode in order to submerge completely the unit and maintain an anaerobic environment (21). Anaerobic reactors have been operated in both the packed-bed and the expanded-bed modes. When operated in the expanded-bed or fluidized-bed mode, effluent recycle is often practiced to fluidize the bed and thereby establish close to completely mixed-flow conditions. Although the kinetics of substrate removal are generally lower in this type of reactor than in a “once-flow-through” reactor, dilution of the incoming waste can often enhance treatment by reducing inhibition. Dilution of the concentration of degradable inhibitory compounds in the feed, and the prevention of pH depression by suppressing the rapid buildup of volatile fatty acids at the inlet sections of the reactor, are two advantages attributed to effluent recycle (4). In addition, recycle minimizes problems with bed-plugging, leads to improved flow distribution, and allows for the entrapment of small particles within the bed, thus enhancing their degradation. Fluidization also reduces the thickness of the hydrodynamic boundary layer, thus decreasing resistance to mass transport.