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Five biofilm airlift suspension (BAS) reactors filled with ceramic materials as biocarriers were used to investigate the hydrodynamics, liquid mixing, and biofilm detachment kinetics in the BAS reactor. A mathematical model was developed to describe the internal liquid circulation within the BAS reactor. The Froude number was introduced to correlate the relationship between the Froude number and superficial gas velocity at different biocarrier concentrations. The validity of the empirical model was verified over a wide range of experimental conditions and the result shows that the internal liquid circulation velocity was proportional to the square root of the reactor height and the superficial gas velocity. Because the internal liquid circulation flow rate was much larger than influent flow rate, the BAS reactor had a strong capacity to resist shock loading caused by the change in influent organic matter concentration. Shock loading resistance increased with the height of a BAS reactor. Although biofilm detachment was a very complicated process which involved many mechanisms, dimensional analysis was employed to successfully analyze the biofilm detachment kinetics. It was found that the biofilm detachment rate was proportional to the first power of the superficial gas velocity and biofilm thickness, and to the 2/3 power of the number of biocarriers in the reactor, respectively. Use of the Froude number and dimensional analysis provide an effective and accurate method to study the characteristics of the BAS reactor. DOI: 10.1061/(ASCE)0733-9372(2005)131:6(874) CE Database subject headings: Hydrodynamics; Biofilm; Reactors; Mathematical models; Circulation; Water treatment; Wastewater treatment.

This work investigates the use of membrane air-stripping (MAS) contactors containing microporous polypropylene hollow-fiber membranes to remove volatile organic compounds from water into the gas phase. Experiments using countercurrent and cross-flow flow configurations to remove trichloroethylene (TCE) from water into air were performed. The effects of influent TCE concentration, liquid and gas flow rates, and air-to-water ratio were investigated. In each case studied, it was found that mass transfer in MAS contactors is controlled by liquid-phase resistance. Maximum removal of TCE was obtained at air-to-water ratios that were significantly lower than those required for conventional packed-tower stripping. Mathematical models based on empirical correlations for the liquid-phase convective mass transfer coefficients were developed and validated with experimental data, and subsequently used to perform simulations of full-scale MAS contactors. At the operating conditions explored, full-scale cross-flow contactors were shown to be superior to countercurrent-flow contactors: for the same gas and liquid flow rates and number of fibers, cross-flow contactors removed more than 95% of the original TCE in the feed liquid whereas countercurrent-flow contactors removed less than 50%. In comparison with packed-tower stripping, MAS contactors are shown to be an alternative feasible technology. DOI 10.1061/(ASCE)0733-9372(2004) 130:11(1232) CE Database subject headings: Air stripping; Membranes; Volatile organic chemicals; Water treatment; Mass transfer; TCE; Contactors; Abatement and removal.