Roles of oxidation and coagulation in Fenton process for the removal of organics in landfill leachate

High potential of coagulation to remove organics has not been fully recognized in Fenton process and coagulation has been used as an auxiliary process removing iron in effluent. This study evaluates the relative role of oxidation and coagulation step of Fenton process in the removing of biologically treated leachate organics of Metropolitan Landfill in Korea. This study showed that to the maximum, 30% of DOC and 40% of COD removal efficiencies were achieved by the Fenton oxidation step alone, whereas, 60% of DOC and 75% of COD removal efficiencies were achieved by the combined Fenton oxidation and subsequent Fenton coagulation step, as the same Fenton's reagent condition ([Fe2+](0) = 1250 or 2500 mg/L, and [H2O2](0) = 0 similar to 3000 mg/L) was applied in laboratory experiments. In addition, it was observed that the rapid decomposition of H2O2 with time did not lead to the corresponding removal of leachate organics. This means that OH radical generated from the H2O2 decompostion is not effectively invoved in degrading the leachate organics, pointing out the possibility of uneconomical use of H2O2 and unwarranted retention time of Fenton oxidatiom chamber in Fenton leachate treatment plant. Furthermore, the investigation of field Fenton process confirmed the observation of laboratory scale study, revealing that the DOC and COD removal effciencies in the Fenton oxidation step were less than 10similar to20% prior to the Fenton coagulation step, and major removals of DOC and COD (60similar to70%) were achieved after the finial Fenton coagulation step. These findings demonstrate the significance of the coagulation in Fenton process and raise a need for individual assessments of both oxidation and coagulation for the optimal design and evaluation of a whole Fenton processes. The individual assessments, however, should be conducted in an integrative manner because the preceding process (oxidation) may affect the performance the next process (coagulation).