Hybrid expanded-bed GAC reactor for treating inhibitory wastewaters

An expanded-bed anaerobic biological GAC reactor was connected to a GAC adsorber to form a hybrid reactor design for the treatment of inhibitory wastes that separates biological transformation from physical removal mechanisms. The performance of the hybrid GAC reactor was compared with a "conventional" expanded-bed GAC anaerobic reactor. Both reactors were subjected to similar operating conditions. The synthetic wastewater used in the study was comprised of acetate and 3-ethylphenol (3-ep). The COD loading ranged from 13.3 to 23.8 kg COD/m³. Partial replacement of GAC with virgin GAC was practiced in both reactors to control toxicity and facilitate the physical removal of 3-ep. The hybrid GAC reactor provided greater biological-removal efficiencies than the "conventional" GAC reactor. GAC replacement did not affect biomass retention in the hybrid GAC reactor, and sludge ages in the "conventional" GAC reactor were limited by the rate of GAC replacement. Sludge ages averaged 100 days in the hybrid GAC reactor, which allowed for significant biodegradation of 3-ep. At a sludge age of 9.3 days, 3-ep degrading organisms washed out of the conventional GAC reactor. The hybrid GAC reactor design demonstrated promise for the efficient treatment of biologically inhibitory wastewaters.