| Granular Activated Carbon (GAC) as tertiary treatment to secondary biological effluent (trickling filters) was studied at Duck Creek Wastewater Treatment Plant, Garland, Texas. Two sets of pilot plants were operated for a period of eighteen months to determine optimum treatment conditions to obtain best effluent water quality.;Performance of the pilot plants far exceeded expectations of pollutant removal capacity which could be achieved by adsorption alone. The sustained high level of treatment efficiency was attributed to biological activity within the GAC beds, generally referred to as "Biological Activated Carbon".;Increasing EBCT improved performance, but pretreatments which increased dissolved oxygen concentration prior to GAC contact were more beneficial to effluent water quality than EBCT alone. No significant differences in water quality between pretreatment with oxygen or oxygen-ozone (10 mg/L applied ozone dose) were observed, demonstrating that the main benefit of oxygen-ozone was the oxygen component.;Pretreatment with oxygen or oxygen-ozone resulted in nitrification, achieving 85% ammonia reduction, from 10 mg/L to 1 mg/L or less. Oxygen pretreatment prior to GAC contact at 20 minutes EBCT achieved consistent effluent water quality of 2 mg/L TSS and 6 mg/L BOD5. Economic analysis indicated that Biological Activated Carbon (BAC) is an economically viable tertiary treatment process, competitive in capital and operating costs with other tertiary processes such as conventional GAC treatment, Granular Media Filtration, and Second Stage Nitrification for control of organics (BOD5), suspended solids, and ammonia.;Empty Bed Contact Time (EBCT), from 8 to 32 minutes, was studied on one set of pilot plants. Pretreatments of wastewater before GAC treatment were studied on the second set of pilot plants. These pretreatments were aeration to 6 mg/L dissolved oxygen (D.O.), oxygenation to 20 mg/L D.O., and ozonation at 10 mg/L applied ozone dose using oxygen as the ozone feed gas. |
