EFFECT OF PROCESS VARIABLES ON THE TREATMENT OF TOXIC WASTEWATERS WITH ANAEROBIC GAC REACTORS

The expanded-bed anaerobic GAC reactor, operating with GAC replacement , was demonstrated to effectively treat hazardous wastes. This study i nvestigated the effects of GAC replacement rates, organic loading, and hydraulic retention time (HRT) on the treatment efficiency of an inhi bitory wastewater. A synthetic toxic wastewater containing 5 g/l aceti c acid, 3 g/l phenol and 0.9-1.8 g/l ortho-cresol was fed at a constan t flow rate to three anaerobic GAC reactors, two of which were operate d at an unexpanded empty-bed HRT of 1.0 d and the third at a HRT of 0. 5 d. The reactors affected more that 97% COD removal throughout the st udy. Excellent treatment of the toxic waste was accomplished at GAC me an residence times as low as 8 d, and at COD loading rates of 35 kg/m3 -d. The reactors converted over 90% of the biodegradable influent COD to methane gas at high GAC residence time. The methane conversion effi ciency dropped to about 64% in the reactors operated at a HRT of 1.0 d and 80% in the reactor operated at a HRT of 0.5 d at GAC residence ti mes of 8 d. The GAC replacement rates were sufficient to overcome the toxicity of ortho-cresol. Organic loading rates and HRT appeared to ad versely influence process performance, particularly when phenol was pr edominantly removed by biodegradation.