(399b) COD Reduction From Leachate with An Advanced Oxidation Process (AOP)

A landfill in the eastern part of United States was in operation between early to mid 1990s. The existing leachate treatment facility consists of pH adjustment, chemical coagulation, solid/liquid separation, sand filtration, carbon adsorption, and sludge dewatering. After the treatment, the water is discharged to the river, and is regulated by a National Pollution Discharge Elimination System (NPDES) permit. Occasionally, the discharge from the treatment facility exceeded the permit limitations for Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD), and Total Organic Carbon (TOC). The objectives of this study were to determine treatment methods which would enable compliance with the applicable discharge limitations; to establish the desired operating conditions of the process; and to investigate the effect of various parameters such as pH, catalyst dosages, reaction time, etc. on the COD destruction efficiency.

A series of influent and effluent samples were collected from the existing leachate treatment facility to characterize the wastewater, to determine the efficiency of the existing treatment system, and to perform treatability studies. All samples were preserved and handled in accordance with the U.S. EPA approved procedures. All analyses were performed in accordance with the procedures described in Standard Methods for the Examination of Water and Wastewater. Treatability studies were conducted using the following oxidation technologies: chlorine, potassium permanganate at different pH conditions, Fenton Reagent (hydrogen peroxide in presence of Ferrous ion), and Hydrogen peroxide/UV light.

 The initial wastewater characterization results reveal that the COD, BOD, and TOC concentrations of the sample were approximately 150, 33, and 50 mg/L respectively. The sample had a pH of about 10.8, contained phenol ranging between 3 and 5 mg/L. 

 Chlorine, and potassium permanganate under acidic as well as under alkaline conditions were not effective in reducing COD to less than the discharge limitation of 35 mg/L. Treatability study results revealed Fenton Reagent or a combination of H2O2/UV which generated hydroxyl radicals (OH*) were capable to reduce the COD to below 35 mg/L within 30-minutes of reaction.  The Fenton reaction was conducted at a pH of about 3.5 in presence of a hydrogen peroxide dosage of 1700 mg/L and about 200 mg/L of ferrous iron. After the reaction was completed, the residual hydrogen peroxide was removed from the reactor using a reducing agent, and the pH of the resultant mixture was raised to about 8.0 by the addition of sodium hydroxide. COD reduction with H2O2/UV is similar to that described above, except that in this process, the organic molecules will be oxidized using a combination of UV/H2O2/catalyst.