[Comparison of the treatment performance in fresh and mature landfill leachates by Fenton process].

The experiments focused on comparing the removal efficiencies of organic matters in fresh and mature landfill leachate by Fenton treatment. The changes in dissolved organic matter before and after Fenton treatment were assessed using gross organic parameters such as organic compound relative molecular mass (Mr) distribution, chemical oxygen demand (COD), total organic carbon (TOC) and the ratio of COD to TOC. The results from this study demonstrate that high Mr fractions of mature landffill leachate are more easily converted into dissolved small Mr fractions (Mr < 10(3)) by Fenton reaction than those of fresh landfill leachate, since the average Mr of mature landfill leachate is higher than that of fresh landfill leachate and the Mr > 10(5) fraction of the mature leachate account for 64% of the total mass. Operating parameters such as pH, [Fe2+] and [H2O2]/[Fe2+] demonstrate that the COD removal efficiency of the fresh landfill leachate (from 61% to 84%) is higher than that of the mature landfill leachate (from 31% to 60%), while it is converse for TOC (from 85% and 52% to 91% and 80% for the mature and fresh landfill leachate, respectively). Oxidation seems to play a more active role in COD reduction than coagulation whatever for the mature or fresh landfill leachate. Oxidation efficiency apparently controls coagulation efficiency, so that high oxidation efficiency may cause relatively low coagulation. The mass balances indicate that TOC removal by oxidation (TOCoxid) is more than COD removal by oxidation (CODoxid) for the mature landfill leachate while TOCoxid is less significantly than CODoxid for the fresh landfill leachate. The COD/TOC ratios are 1.17 and 1.58 for the initial mature landfill leachate and fresh landfill leachate, respectively, but they are 1.96 and 0.68 after Fenton treatment by oxidation, respectively. This phenomenon suggests that complete oxidations occur in the mature landfill leachate while both partial and complete oxidations occur in the fresh landfill leachate. The changes of CODcoag and TOCcoag illustrate that the oxidation state of the organic matters removed by coagulation in the mature landfill leachate is significantly lower than in the fresh landfill leachate.