Microwave-Enhanced Fe⁰-H₂O₂ Treatment Of Refractory Organic Minerals In SAARB Leachate

In recent years,with the acceleration of urbanization and the continuous improvement of people's living standards,the production of municipal solid waste has also rapidly increased.However,in the waste treatment process,large amounts of landfill leachate are inevitably generated.It is a kind of organic wastewater with complex composition.In addition,organic wastewater is complex in composition,although membrane technology has a good treatment effect at the present stage,it will produce a large number of concentrated leachate which is difficult to treat.Therefore,the combined process‘Semi-aerobic aged refuse biofilter?SAARB?+Microwave coupled Fe⁰/H₂O₂?Fenton-like?'not only achieved a great treatment efficiency on refractory organic matter but also avoided generating secondary pollution.SAARB is used as a pretreatment method in this study.The best COD removal effect of young and old landfill leachate is 88.09%and 70.21%,respectively,which are qualified to Discharge Standard GB16889-2008.UV-Vis and 3D-EEM demonstrate that the organic content is greatly reduced and tryptophan with smaller molecular weight is completely removed.In addition,the biodegradability?BOD/COD?of SAARB effluent?namely SAARB leachate?decreased below 0.04,herein,proportion of micro-molecular organic increased.In consideration of improving the biodegradability,advanced oxidation processes?AOPs?are used in sequential treatment.Traditional Fenton method,as one of AOPs,is used to the treatment of SAARB leachate from old landfill leachate?namely old SAARB leachate?.Results showed that SAARB leachate mainly compromise fulvic-like substance[C1,Ex/Em?nm?,?245?280/405]and humic-like substance[C2,Ex/Em?nm?,?260?360/435].The more Fe²⁺dosage,longer reaction time?with a proper range?and slight acid condition improved the degradation efficiency of organic matter.While an excess dosage of H₂O₂ depressed the removal rate by inhibiting Fenton reaction process.The maximum C1 and C2 removal efficiencies were 77.81%and 52.97%under conditions Fe²⁺dosage 5 mmol/L,n?H₂O₂/FeSO₄?ratio 4,initial pH 4 and reaction time 60 min.Herein,humic-like substance was better removed than fulvic-like substance using traditional Fenton method.UV-Vis spectroscopy indicated that unsaturated bond of humic-like substance was destroyed and therefore the aromatic degree,hydrophobic degree,molecular weight and humification degree were declined in traditional Fenton method.The degradation of macro-molecular organic matter resulted in the significant improvement of biodegradability from 0.05?influent?to 0.36?effluent?.However,the dose of oxidant reagents is high and sludge production is huge.In order to overcome these shortcomings,Fe⁰/H₂O₂ coupled with Microwave?MW?process is used to treat old SAARB leachate.The MW-Fe⁰/H₂O₂ process was setup to the treatment of old SAARB leachate.The maximum COD,UV₂₅₄ and color number?CN?removal efficiencies achieved to28.11%,48.60%and 81.21%,respectively,under optimum conditions of reaction time14 min,initial pH 3.0,Fe⁰ dosage 0.2 g/L,H₂O₂ dosage 7.5 mL/L and MW power 450W.MW-Fe⁰/H₂O₂ process showed the best performance in degradation of organic matter in SAARB leachate comparing to single processes?MW,Fe⁰ and H₂O₂?and/or other combined processes?MW-Fe⁰,Fe⁰/H₂O₂,Fenton and MW-H₂O₂?.In addition,Fe⁰ particles used in MW-Fe⁰/H₂O₂ process before and after were tested by atomic absorption spectroscopy?AAS?,scanning electron microscope-energy dispersive spectrometer?SEM-EDS?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.Results showed that ferrous ion would be leaching into the wastewater in MW-Fe⁰/H₂O₂ process.Thus,the surface of Fe⁰ particles became tough,and of ion-based oxides?FeO,Fe₂O₃ and FeOOH,etc.?were generated,which can further catalyze Fenton-like process.The reaction mechanisms of MW-Fe⁰/H₂O₂process include homogenous and heterogeneous Fenton reaction,precipitations and coagulation effects of ion-based oxides and the acceleration of MW irradiation.