Study On The Preparation Of Fe-loaded Carbon-based Fenton Electrode And Treatment Of Salty Organic Wastewater

Most countries have increasingly stringent requirements for the discharge of pollutants in wastewater with the enhancement of people's environmental awareness.However,the concentration of salt and pollutant in wastewater generated is getting higher and higher due to the improvement of producing,water-saving and energy-saving technologies,which puts forward higher requirements for the research of wastewater treatment technology.Both the coking wastewater and the landfill leachate are typical refractory salty organic wastewater.If treated improperly,they can easily pollute the surrounding environment.Various electrochemical wastewater treatment technologies have competitive advantages in the field of environmental protection.Among them,the electro-Fenton(EF)technology has received extensive attention due to its environmental friendliness,high pollutant mineralization rate,and mild reaction conditions.The common drawbacks of various EFs are that the reaction requires an external dosage of Fe salts or H₂O₂ in acidic solution and a large amount of Fe sludge formed.To address these common problems in the EF reaction,activated carbon catalysts loaded with Fe were prepared by an impregnation and calcination method,with which a novel Fe-loaded carbon-based heterogeneous EF cathode was prepared.An electrochemical system constructed using the cathode and a dimensional stable anode(DSA)was developed to treat the landfill leachate concentrate(LLC)and coking wastewater.The modified EF technology proposed in this study was able to effectively remove organic pollutants in the wastewater and reduce the pollution indices(e.g.,COD,NH₃-N,and color)without external H₂O₂ or iron catalyst and no Fe-sludge production in the reaction process.The electrode preparation and wastewater treatment conditions were further optimized.The pollutant removal mechanism was investigated.And the reaction mechanism was explored.The study could provide theoretical basis and technical support for the modified heterogeneous EF technology.The main results are as follows:A novel heterogeneous iron-load activated carbon titanium mesh EF cathode(Fe-AC-Ti)were prepared by an Fe²⁺impregnation and calcination method with which a modified EF system was formed together with the DSA anode to treat LLC.Organic pollutants in the LLC were degraded effectively and its biodegradability was improved synergistically by cathode EF and anode electrocatalysis.The electrochemical reaction conditions were optimized based on in-depth study of the factors affecting water treatment.The highest COD removal(97.06%)was obtained at an applied voltage of 10V,initial pH of 7,and electrode distance of 1cm.The optimum conditions were applied voltage of 8V,initial pH of 3,and electrode distance of 3cm for 61.24%total organic carbon removal.BOD₅/COD ratios of all tests increased from 0.03 to 0.23-0.51.The effluent after the reaction was clear and transparent,either neutral or weakly alkaline.Neither hydrogen peroxide nor Fe ions were added to the reaction system,and no Fe precipitation was produced.In terms of kinetics,COD removal followed a pseudo-first-order reaction,while Cl^-removal and Cl O^-generation followed a zero-order reaction.Both SEM-EDS and XPS analysis results showed that the impregnation and calcination method could effectively load the Fe on the surface and in the activated carbon to form a heterogeneous Fenton catalyst.The organic pollutants were oxidized indirectly by active chlorine through electrocatalysis near anode and removed by EF reaction near cathode.A novel iron-loaded activated carbon-based foam nickel electrode(Fe-AC-Ni)was prepared by impregnation and calcination method.The heterogeneous EF technology was applied to treat coking wastewater with the electrode as cathode and DSA as anode.O₂could not only produce H₂O₂ by the two-electron transfer reaction catalyzed by carbon in the cathode,but also generate·O₂^-by a single electron transfer under the catalysis of nickel,and then converted into H₂O₂.H₂O₂generated is then catalyzed by iron supported on activated carbon to produce·OH,by which the organic pollutants were efficiently degraded.The optimized conditions based on a response surface methodology were applied voltage of 10V,electrode distance of 1cm,and initial pH of 3.42.Under these conditions,the COD removal rate could reach almost 100%after reacting for 3h.The spectroscopic analysis showed that the process could effectively remove aromatic protein analogs,microbial byproduct analogs,lactones and amide compounds in the coking wastewater.The reusable potential of the cathode was revealed by repetitive experiments in continues means.The modified electro-Fenton method was employed to treat landfill leachate evaporation concentrate(LLEC)with the self-developed Fe-AC-Ni cathode.The operating variables were optimized according to the response surface methodology basing on Box–Behnken design(BBD)design.The removal rates of COD and color were 100%and99.8%,respectively,under the optimal operating conditions of an initial pH of 6,electrode distance of 1 cm and applied voltage of 9V.Three-dimensional excitation-emission matrix(3D-EEM)fluorescence spectroscopy demonstrated that the humic and fulvic acid pollutants were almost completely removed.The results of energy efficiency analysis showed that the power consumption increased and the current efficiency decreased gradually with reaction time.The additional treatment cost per ton of landfill leachate due to LLEC treatment was RMB 9 yuan·m^-3 or so.The modified electro-Fenton method was employed to treat high-ammonia-nitrogen LLC with a self-developed Fe-AC-Ni cathode.COD,ammonia nitrogen(NH₃-N)and color in LLC could be removed simultaneously.The optimal removal rates of COD,NH₃-N and color in wastewater were 79.9%,73.2%and 99.9%respectively.During the reaction,organic pollutants were directly oxidized by the·OH generated by the cathode EF reaction to remove most of COD and part of NH₃-N.Hypochlorite generated from chloride ions through anodic oxidation reaction oxidized NH₃-N to N₂ indirectly.Air-sparking also striped little NH₃-N and N₂ from the wastewater.3D-EEM fluorescence spectroscopy revealed that the fluvic and humic acid-like substances,as well as the soluble microbial byproducts,were effectively removed.