Removal performance of humic substances in landfill leachate by Fenton reagent.

The experiments focused on the treatment performance of humic substances(HS) in concentrated landfill leachate rejected by reverse osmosis(RO) by a Fenton reagent.The removal efficiency of COD_(Cr) in the leachate and relative content of humic acids(UV_(254)) at different initial pH,dosage of H_2O_2 and Fe~(2+) were compared using gross organic parameters such as UV_(254),chemical oxygen demand(COD_(Cr)),total organic carbon(TOC),the ratio of COD_(Cr) removal of humic substances to overall COD_(Cr)(α) and the ratio of COD_(Cr) removal by oxidation to that by coagulation.The results show that the UV_(254) removal efficiency(from 48.5% to 78.2%) is higher than that of COD_(Cr)(from 40.3% to 62.5%),and the ratio of COD_(Cr) removal of humic substances to overall COD_(Cr)(α0.77) is higher than that before the Fenton reaction(α_0=0.61).This demonstrates that the degradation of humic substances controls the overall COD_(Cr) removal.On the other hand,the results highlight the role of oxidation in controlling the efficiency of removal of COD_(Cr) by coagulation,such that high oxidation efficiency may cause relatively low coagulation.The UV_(254) and COD_(Cr) removal by coagulation(COD_(Cr coag),UV_(254 coag)) is more than those by oxidation(COD_(Cr oxid),UV_(254 oxid)) under the ratio of(c(H_2O_2)/)(c(Fe~(2+))) lower than 1.2,and is less under the condition of the ratio of (c(H_2O_2)/)(c(Fe~(2+))) higher than 2.Under the most favorable conditions(initial pH=4.0,(c(H_2O_2))=240(mmol/L,)(c(Fe~(2+)))= 40(mmol/L,) 2 h reaction time),the ratio of COD_(Cr) and UV_(254) removal oxidation to coagulation was 8.6 and 6.0,and the removal efficiencies of COD_(Cr),UV_(254),humic acid(HA) and fulvic acid(FA) were 62.5%,78.2%,95.0% and 62.7% respectively.