Biodegradation and adsorption in refractory leachate treatment by the biological activated carbon fluidized bed process

A real leachate from a landfill site of old landfill-age was treated by the biological activated carbon fluidized bed (BACFB) process. Steady-state removal of dissolved organic carbon (DOC) and changes in molecular size distribution, adsorption characteristics and amount of humic substances of the leachate were evaluated as a function of the hydraulic retention time (HRT). The steady-state removal of the leachate DOC was enhanced from 42 to 58% when the HRT was increased from 24 to 96 h, indicating that biological oxidation was indeed responsible for the removal of the leachate organics. This increase was found to be due primarily to the biodegration of the leachate organics of low molecular weight (LMW); the high-molecular-weight organics may be highly refractory. Activated carbon preferentially adsorbed the LMW organics of both the leachate and the BACFB-treated effluents. This preferential adsorption was consistent with the removal of the LMW organics by the BACFB process. Adsorption may act as a prerequisite step toward biodegradation. Humic substances accounted for about 30% of the leachate DOC. The BACFB process removed about 70% of the humics with a HRT of 24 h; however, the concentration of the humics remained constant (about 10 mg l−1) with increasing HRT.