Study Of Removal Of 16 Priority Polycyclic Aromatic Hydrocarbons From Real Textile Dyeing Sludge By Electrochemical-Fe²⁺ Activated Peroxomonosulfate

Textile dyeing industry is the pillar industry in China,there was about 2 billion tons textile dyeing waster produced in China in 2021 according to the statistics,ranking third among 41 industrial sectors,The textile dyeing sludge that originated from textile dyeing wastewater treatment contains large quantity of pollutants such as dyes,dyeing auxiliary and heavy metal.The textile dyeing sludge has been defined as hazardous waste under strict control in China.Polycyclic aromatic hydrocarbons(PAHs)are the main hazardous pollutants in textile dyeing sludge related to dyes used in the production process.sixteen PAHs have been identified as priority pollutants due to their toxic,carcinogenic and mutagenic properties by many countries.Traditional sludge disposal technologies such as such as landfill and incineration have limited treatment effect on PAHs and may transfer pollutants to the environment,causing secondary pollution.Therefore,it is necessary to find an effective method to reduce the content of PAHs in TDS before its final disposal and resourceful utilization.In recent years,advanced oxidation processes(AOPs)have attracted extensive attention due to its high efficiency to eliminate persistent organic pollutants.Compared with hydroxyl radicals produced by traditional Fenton oxidation method,sulfate radical have gained much attentions in recent years due to its higher oxidation potential(2.5V-3.1V),wider p H range and longer half-life time.This thesis proposes a method by using electrochemical-Fe²⁺activated peroxymonosulfate(PMS)oxidation to remove sixteen priority polycyclic aromatic hydrocarbons from textile dyeing sludge.Building an electrochemical system by using iron and carbon felt as anodic and cathodic electrode material.The release of Fe²⁺by electrolyzing iron activated PMS to oxidize and degrade PAHs in TDS.The main contents of this thesis are as follows:(1)16 PAHs in textile dyeing sludge were identified by GC-MS,and the contents and proportions of different PAHs in textile dyeing sludge were determined.The results showed that the total concentration of 16 PAHs in sludge was 1326ng g^-1,among which the proportion of tricyclic and tetracyclic aromatic hydrocarbons was 61.9%,and the proportion of phenanthern,benzo(a)anthracene,chrchrysene,dibenzo(a,h)-anthracene was 11%,12%,9%and 9%,respectively.(2)The effects of applied voltage,initial pH and PMS dose on the degradation efficiency of 16 PAHs in textile dyeing sludge by electrochemical-Fe²⁺activated PMS oxidation were investigated by measuring the changes of the total amount of 16 PAHs and the content of single PAHs before and after the reaction,combined with the changes of Fe²⁺and Fe³⁺concentration in the reaction process.The optimum reaction conditions were determined.The results show that:The removal efficiency of PAHs can be significantly improved by adjusting the applied voltage,initial p H and PMS dose.When the voltage is 7V,the PAHs removal rate of anode is 55.5%and 85.2%higher than that of no voltage and carbon felt as anode material.When the PMS dose increased from 100mg/g to 400mg/g,the PAHs removal rate increased gradually.Compared with the initial p H=7.0 and 8.5,the removal rates of PAHs from anode and cathode were 44.0%and 49.1%,102.0%and 79.2%higher at p H=3.0?Under the optimal conditions of 7V,3.0 and 400mg/g,the removal efficiency of 16 PAHs in anode and cathode was 64.7%and 16.1%,respectively.Electrochemical-Fe²⁺activated PMS oxidation can effectively reduce the content of 12 PAHs in 16 PAHs,and low cyclic PAHs were more easily degraded than high cyclic PAHs.The concentration of Fe²⁺determined the removal efficiency of PAHs,increasing the concentration of Fe²⁺can improve the removal efficiency.However,if Fe²⁺concentration is too high,quenching reaction will occur and the removal efficiency will be reduced.(3)The removal mechanism of 16 PAHs in textile dyeing sludge by electrochemical-Fe²⁺activated PMS oxidation was studied.The species of active substances in the oxidation system were determined by free radical capture experiment,and the contribution of each free radical to the efficiency of PAHs was determined by free radical quenching experiment.By measuring the change of TOC of textile dyeing sludge and observing the morphology of sludge before and after the reaction by scanning electron microscope,the sludge destruction effect was studied.The valence states of Fe²⁺and Fe³⁺on the cathode electrode surface were measured by X-ray photoelectron spectroscopy and the reaction mechanism of the cathode chamber was studied.The degradation pathway of PAHs in textile dyeing sludge was determined by GC-MS.The results show that:There were two kinds of free radicals SO₄^·-and^·OH in the electrochemical oxidation system.Under the optimal experimental conditions(voltage=7V,p H=3.0,PMS dose=400mg/g),the contribution efficiency of^·OH and SO₄^·-at the anode and the cathode was 29.9%,8.1%and 13.5%,4.2%to the degradation of PAHs.Sludge oxidation is a process in which sludge cells are attacked by free radicals to release intracellular organic matter and then oxidized and degraded.When the PMS dose was increased to 600mg/g,56.6%and 33.1%TOC in anode and cathode can be removed.Compared with the sludge at the bottom of the cathode chamber before and after the reaction,the Fe³⁺content on the surface of the cathode electrode was higher,indicating that the reaction occurred on the surface of the cathode electrode.The anode generates Fe²⁺through electrolysis of iron to activate PMS,and the Fe³⁺generated migrates to the cathode and gets electrons on the electrode surface to transform into Fe²⁺to activate PMS.The free radicals generated oxidize and degrade organic matter together.The degradation pathway of PAHs is that the electron-rich carbon atoms on the benzene ring are attacked by free radicals and then degraded into CO₂,H₂O,H₂S and other small molecule organic matter.The results of this study can provide basic technical parameters and theoretical basis for the application of electrochemical-Fe²⁺activated PMS oxidation in the removal of PAHs from textile dyeing sludge.