Abstract
Recently, up-flow anaerobic fluidized bed reactor has been developed as an effective device for wastewater treatment. Up to now, studies in the up-flow fluidization are mostly focused on the biofilm growing on different supports, such as sand, activated carbon and glass beads. However, littile information is available in literatures regarding immobilized growing cells. Since our laboratory has developed a novel PVA-immobilization technology for entrapping cells, the hydrodynamic characteristics including particle densities, terminal velocities, drag coefficient, bed expansion characteristics, and minimum fluidzation velocities for various particle size of PVA beads were studied. From experimental measurements of the single particle terminal settling velocity, the corresponding drag coefficient was found to be large than that of a smooth, rigid sphere at the same Reynolds number. A new simple correlation describing this finding is suggested. According the buoyancy force based on the bulk density of the bed, a correlation for the bed expansion of particulately fluidized spheres based on dynamic equilibrium of individual particles was presented. Other focus of the study was to determine the feasibility of biodegradation of azo dye (Red RBN) using PVA immobilized-cell beads in the up-flow anaerobic fluidized bed reactor. The effect of typical process variables such as hydraulic retention time (HRT), influent dye concentration level, particle number density, particle size, and degree of bed fluidization on removal efficiencies were also studied. Using PVA particle diameter of 2.965 mm and particle number density of 19200 particle l-1, results indicate that nearly complete color removal (94 %) was easily accomplished for Red RBN under hydraulic retention time of 12 hr, bed expansion of 60 %, and influent dye concentration of 200 mg/l. Besides, the overall effectiveness factor ηDf was used to illustrate the mass transfer (pore and film diffusion resistances) in fluidized bed reactor. Taking into account mass fransfer of PVA immobilized-cell beads, biodegradation of azo dye and liquid mixing in the reactor, a general model for the design of fluidized bed reactors operating with immobilized-cell in spherical porous PVA particles is presented.