The Study Of The Treatment Of Semi-aerobic Aged Refuse Bioreactor Leachate Tail Water By Ultraviolet Process

Semi-aerobic aged refuse bioreactor?SAARB?is a low-cost and easy-to-be-used technology to treat landfill leachate,which can effectively remove organic matter and nitrogen pollutants.However,after treated by SAARB,there will still be a high concentration of refractory organics and poor biodegradability of the effluent.The concentration of organic matter in the effluent is far to reach the relevant discharge standards,thus it is necessary to deeply treat the SAARB effluent of landfill leachate.The cost of advanced ozone oxidation technology for treating the SAARB effluent is relatively high,therefore,this study uses ultraviolet advanced oxidation technology with lower treatment cost,and the UV-Fenton,UV-H₂O₂,UV-PMS,UV-H₂O₂-PMS are constructed based on the principle of generation of radicals from oxidants?i.e.PMS and H₂O₂?to degrade organics,and these processes are accelerated by ultraviolet irritation The degradation efficiencies,transformation processes and degradation mechanisms of organics in these processes are investigated.The main work and conclusions of this study are as follows:?1?We found that the conventional Fenton process can effectively degrade fulvic-like acid and humic-like acid substances and improve the biodegradability of the SAARB effluent of landfill leachate,however,sludge production of the process is huge.The maximum removal efficiencies of COD,CN and UV₂₅₄ are 41.67%?93.38%and 64.75%,respectively,under initial pH 4.0,6 mmol/L of Fe²⁺dosage,0.056 mol/L of H₂O₂ dosage and 60min of reaction.?2?Ultraviolet coupled with Fenton process?UV-Fenton?that produces reactive oxygen species was used to decompose organics of SAARB effluent of landfill leachate due to the secondary pollution of a large amount of sludge in the conventional Fenton process.Results show that the process has a synergistic effect on the treatment of SAARB effluent of landfill leachate and the main radicals in the processes are·OH and O₂^·-,which can effectively degrade the aromatic organic substances and significantly transform the macromolecular substances into smaller molecules and remove 51.00%of fulvic-like acid in the visible area.But a small amount of sludge is still produced after treatment.Increasing the dosage of H₂O₂ and Fe²⁺can promote the ability of the process to degrade organic matter and the reaction rate.The optimized initial pH is 3.0,and neutral or alkaline conditions both obviously inhibits the degradation of organics.The removal efficiencies of COD and reaction rate constant were finally 77.22%and 0.04679,respectively,under 0.084 mol/L of H₂O₂ dosage,0.056 mol/L of Fe²⁺dosage and pH 3.0.?3?The technology of the coupling ultraviolet of H₂O₂ without Fe²⁺is used to treat SAARB effluent of landfill leachate in order to effectively eliminate the sludge caused by iron ions in UV-Fenton system.At the same time,considering that PMS is a common oxidant used in ultraviolet advanced oxidation technology.Sulfate radicals and hydroxyl radicals with strong oxidative properties are produced by activating PMS under external activation conditions and the way of using PMS to treat the SAARB effluent of landfill leachate is very rare.Therefore,the UV-H₂O₂ and UV-PMS processes were constructed to treat the SAARB effluent of landfill leachate.Results show that those two processes both can synergistically remove the pollutants and improve the biodegradability of the effluent.And no sludge is formed in both systems.The increase of the dosage of oxidant can promote the degradation ability by producing more radicals,thereby improving the removal efficiency and reaction rate of the two processes.With the initial pH increased from 3.0 to 9.0,the degradation ability and rate of the two processes are inhibited to varying degrees,and the effect of suppressing the removal of organic matter in the UV-H₂O₂ system is more obvious.The main active oxygen specie is·OH in the UV-H₂O₂ process,while the degradation of organic matter is a combination of·OH and·SO₄^-in the UV-PMS process.Both processes can effectively degrade refractory organic substances such as humus and aromatics and oxidize them into smaller molecular organic substances.The removal efficiencies of COD and fulvic-like acid of ultraviolet area in the UV-H₂O₂ and UV-PMS processes are 68.08%,26.23%,47.27%and 33.98%,respectively,under the conditions of 0.050 mol/L of oxidant and pH 3.0.Overall,The UV-PMS process has better degradation efficiency and economic benefits for humus compared with the UV-H₂O₂ process.?4?The UV-H₂O₂-PMS process is performed to treat leachate SAARB effluent of landfill leachate.The results show that the removal efficiencies of CN,UV₂₅₄ and COD in UV-H₂O₂-PMS process are 7.39%,4.28%and 8.80%lower than those in UV-PMS process,15.91%,8.25%and 16.07%,higher than those in the UV-H₂O₂process.The process has the best degradation effect in the acidic reaction condition,while inhibitory effect is shown in the both neutral and alkaline condition.Increasing the dosage of PMS can promote the organics degradation efficiency of the process,but the excessive addition of PMS will decrease the concentration of radicals in the process.The removal efficiencies of organic matter decreases with the increase of n?H₂O₂/PMS?ratio when the total oxidants dosage is fixes.And the highest removal efficiencies of CN,UV₂₅₄ and COD and k_obs are 96.52%,59.82%,35.00%and0.03097,respectively,when the ratio of n?H₂O₂/PMS?is 2:8.The degradation of organics in UV-H₂O₂-PMS process is a combination of SO₄·^-and·OH.Three-dimensional fluorescence and UV-Vis spectroscopy indicate that the complex organic matter such as humus and aromatics is effectively degraded,and the concentration,molecular weight and polymerized degree of organic matter are also greatly reduced.