Combined Fenton's Oxidation and Biological Aerated Filter Process Reduces Chemical Dosage

The objective of this study was to evaluate the effects of Fenton's oxidation combined with biological aerated filer process on advanced treatment of the citric acid wastewater. The effluent of an existing citric acid production wastewater treatment facility was collected and used to study the chemical oxygen demand (COD) removal efficiency of an advanced treatment process including Fenton's oxidation combined with a biological aerated filter. The bench-scale study on a batch reactor indicated that the COD removal by Fenton's oxidation increased with increase in H2O2 dosage from 0.3 to 0.9 mL/L, but decreased with further increase in H2O2 dosage from 0.9 to 1.7 mL/L. At an H2O2/Fe2+ molar ratio of 8, the optimized H2O2 dosage at pH 3.5 was 0.9 mL H2O2 per liter wastewater. Under these conditions, about 75% COD was removed by Fenton's oxidation. COD removal using Fenton's oxidation may be described with pseudo-first-order kinetics. The COD of the wastewater after Fenton's oxidation in a pilot-scale system was similar to the theoretical values calculated according to the kinetics equations. To reduce the operating cost caused by high chemical dosages in Fenton's oxidation, lower dosages of H2O2 was used for the pilot-scale studies. Decreasing the H2O2 dosage to 0.42 mL of 30% H2O2 per liter wastewater resulted in a 33% COD removal by Fenton's oxidation. Further treatment using a biological aerated filter reduced the COD in the final effluent to about 13 mg/L. Results indicted that Fenton's oxidation combined with biological aerated filter is efficient for COD removal of the citric acid wastewater. Small amount of chemicals may be used in Fenton's oxidation process for partial COD removal. After oxidation, the biological processes may further decrease the organic pollutants to very low levels. This article reported for the first time that the dosages of chemicals used for Fenton's oxidation of wastewater may be significantly decreased when it is used in combination with biological processes. The study provides a technically feasible way to use advanced oxidation processes in combination with biological processes for advanced treatment of industrial wastewater.