ACCUMULATION OF METABOLIC INTERMEDIATES DURING SHOCK LOADS IN BIOLOGICAL FLUIDIZED-BED REACTORS

Groundwater containing benzene, toluene, and p-xylene (BTX) was treate d in fluidized bed reactors using nonactivated carbon (FBR) and activa ted carbon (BAC-FBR) as the biofilm carriers. BTX removal and accumula tion of metabolic intermediates were studied at steady state and durin g single-substrate step-loading increases. At steady state (organic lo ading rate of 2.2 kg-COD/m(3)-d), no intermediates were detected in th e effluents. However, intermediates were found in the effluents of bot h systems during a sevenfold p-xylene step increase under different su pply levels of dissolved oxygen (DO) and nutrients. Intermediate conce ntrations increased with increasing dissolved oxygen in the influent b ut were not affected by the level of nutrients. The accumulation of in termediates was also evaluated quantitatively by subjecting both react or systems to 20-, 12-, and 7-fold step increases in the organic loadi ng rates of benzene, toluene, and p-xylene, respectively. In all of th e step increase experiments, the effluent intermediate concentrations were less for the BAC-FBR than for the FBR system. We conclude that th e combination of biological and adsorptive removal mechanisms in the B AC-FBR resulted in enhanced removal of both BTX and metabolic intermed iates under shock-load conditions.