Long-term evaluation of adsorption capacity in a biological activated carbon fluidized bed reactor system

The adsorption capacity of biofilm coated activated carbon from a biological fluidized bed reactor which treated toluene contaminated water was determined systematically over an extended period of operation. The adsorption capacity of biocoated carbon remained at greater than 70% of initial levels during the first two months. After six months of operation, the remaining capacity was still approximately 40, 52 and 57% of the initial value for equilibrium toluene concentrations of 0.1, 3 and 10 mg/L, respectively. If the adsorption removal mechanism is used to provide a buffer during the transient conditions, this remaining capacity may be sufficient without carbon replacement. There was no direct relation between the amount of biomass or the thickness of the biofilm on the carbon and the remaining adsorptive capacity. The loss of adsorption capacity over an extended period of operation appears to result directly from bioactivity, rather than from toluene loading. Bioregeneration of this long-term capacity loss was not observed with continued operation for 100 days after the toluene feed was stopped and the nutrient and oxygen supplies continued.