Removal Charactersitics Of Refractory Organics In Landfill Leachate By Fentonlike Advanced Oxidation Processes

Landfill leachate contains a large amount of refractory organic matter,which needs to be properly treated.Homogeneous Fenton and heterogeneous Fenton-like advanced oxidation technologies have attracted much attention due to their strong oxidation ability.However,both Fenton and Fenton-like processes have the problem of low utilization efficiency of oxidant.In this study,Fenton and Fenton-like processes were used to remove refractory organics from landfill leachate,the removal effects of organics in different processes were compared,and the activation mechanism of Fenton-like processes was explored;The utilization efficiency of oxidant in Fenton-like process was improved by adding oxidant in batches and producing hydrogen peroxide（H2O2）by in-situ electricity,and its mechanism for improving the utilization efficiency of oxidant in Fenton like system was clarified.The organics removal efficiency of homogeneous Fenton(Fe²⁺/H2O2)process is slightly higher than that of zero valent iron Fenton（Fe⁰/H2O2）process.Specifically,the removal efficiencies of TOC,UV254 and CN in Fe²⁺/H2O2 system can reach57.42%,71.63%and 81.03%,while the removal efficiencies of TOC,UV254 and CN in Fe⁰/H2O2 process can reach 35.74%,66.24%and 86.29%（H2O2 dosage=200 m M）.However,the sludge output of Fe²⁺/H2O2 system is much higher than that of Fe⁰/H2O2system,and the MLSS sludge index is 75.6 and 21.2 mg/L.Compared with the three heterogeneous Fenton-like processes,the organics removal of Fe⁰/H2O2 process is significantly higher than that of pyrite（Fe S2）and magnetite（Fe3O4）Fenton-like processes,and the degradation effect of humic-like and fulvic-like matter is better.In the three Fenton-like systems,the activation mechanisms of Fe⁰ and Fe S2 are the homogeneous activation of Fe²⁺and the heterogeneous activation of iron oxides.Fe3O4 is mainly based on its own heterogeneous activation mechanism of iron oxides.In order to further improve the removal effect of organics in Fe⁰/H2O2 Fenton-like process,oxidants are added in batches to improve the utilization efficiency of oxidants.The results show that the removal efficiency of organics under the condition of batch adding oxidant is higher than that of single batch adding oxidant.For example,the highest removal efficiencies of TOC,UV254 and CN of single batch adding oxidant are 29.15%,38.84%and 73.28%,while the highest removal efficiencies rates of TOC,UV254 and CN of batches adding oxidant are 56.76%,58.59%and 94.56%,and the structural damage degree effect of refractory organics are more obvious.The quantitative determination results of hydroxyl radical（HO^·）show that adding oxidant in batches can increase the HO^·yield by 53.23%,which is the key reason for the improvement of organics removal.In order to further optimize the oxidation efficiency of Fenton-like process,an in-situ electrogenerated H2O2 combined with Fe⁰ Fenton-like process was constructed.The results show that current intensity,initial p H value and oxygen flow rate have a great influence on H2O2 production.Under the conditions of current intensity of 200m A,initial p H value of 7 and oxygen flow rate of 0.3 L/min,H2O2 production can reach 2.81 m M,current efficiency is close to 80%,and the highest removal efficiency of organic matter can reach 40.70%.The results of spectral analysis also showed that the complex structure of refractory organics was obviously destroyed,and the relative content of humus decreased significantly.When using a Fenton-like process to treat landfill leachate,the activated materials and utilization form of oxidants have a great impact on the organics removal efficiency.The impact of batch dosing of oxidants on the organics removal efficiency and economic benefit should be evaluated at the pilot scale.The study can provide a useful reference for the treatment of refractory organics in landfill leachate in Fenton or Fenton-like advanced oxidation processes.