【作者】 刘雪梅；

【导师】 王小铭；

【作者基本信息】 重庆大学 ， 环境科学与工程， 2024， 硕士

【摘要】 垃圾填埋系统是陆地生态系统中塑料和含氟消费品等废弃物的“汇”集场所。过度的塑料生产和不完善的废物管理导致大量塑料垃圾进入填埋环境并不断裂解为微塑料。大量研究证实各类含氟消费品(如纺织品、纸类、食品接触材料和化妆品等)赋存不同水平与组成的全(多)氟化合物(PFAS),在其使用寿命终结时,多以废弃物形式被弃置于填埋场。国内外学者报道了世界多国填埋场渗滤液微塑料和PFAS的污染水平,但鲜有研究报道渗滤液微塑料负载PFAS的污染特征。现有少量关于海洋、河流环境和生物固体中微塑料对PFAS载带研究表明:环境中微塑料可作为PFAS吸附载体,且可能是PFAS的持久释放源。然而,目前对垃圾渗滤液微塑料吸附PFAS的行为特性与作用机制认识明显不足,亟需开展渗滤液特征环境微塑料对PFAS的吸附行为研究。本研究选择填埋渗滤液赋存水平最高的传统塑料(聚乙烯(PE))和与其机械性能相似的常见生物降解塑料(聚乳酸(PLA))为研究对象,开展实验室加速老化实验,制取不同老化程度微塑料样品。采用扫描电镜-X射线能量色谱仪(SEM-EDS)、X射线光电子能谱(XPS)和X射线衍射(XRD)等形貌、成分、物相和光谱表征方法,解析老化对微塑料结构形貌的影响。选取5种典型PFAS,包括传统C8长链(全氟辛酸(PFOA)和全氟辛烷磺酸(PFOS))、替代C4短链(全氟丁酸(PFBA)和全氟丁烷磺酸(PFBS))和醚类C6替代(六氟环氧丙烷二聚酸(Gen X)),在纯水避光环境下,开展不同老化程度微塑料对PFAS的序批式吸附实验。结合吸附动力学和等温吸附模型,分析PFAS在老化改性微塑料上的吸附特性。选取渗滤液典型有机质(腐殖酸(HA))和无机盐组分(钠、钙、氯)作为合成渗滤液成分,开展不同老化程度微塑料对合成渗滤液环境PFAS的序批式吸附实验。结合紫外可见光谱、三维荧光光谱等特征,分析吸附前后荧光变化,对比纯水吸附实验结果,阐明合成渗滤液组分对微塑料吸附PFAS行为的影响。研究结果将有助于提升对填埋环境PFAS迁变规律的科学认知,也可为微塑料和PFAS等复合污染的协同治理提供基础理论依据。主要研究结论如下:(1)老化对微塑料结构性能的影响。(1)老化对微塑料物理特性的影响:初始时刻,PE和PLA微塑料表面光滑,老化后其表面出现凹坑、孔洞和裂纹。老化导致PE和PLA微塑料持续裂解,在老化120 h液相样品中检测到纳米级颗粒(442.5～744.1 nm)的存在。比表面积结果显示,PE和PLA微塑料成分结构不同,导致其老化后比表面积变化趋势不同:老化PE微塑料比表面积提高0.4～2.6倍,而老化PLA微塑料比表面积则降低0.6～0.8倍。(2)老化对微塑料化学特性的影响:老化导致PE微塑料表面产生含氧官能团,且以羰基为主;而PLA微塑料因赋存含氧官能团(羧基),经老化后其含氧官能团组分与含量发生变化,从而产生引发π-π*跃迁的发色基团。(N+O)/C原子比分析表明,老化导致PE和PLA微塑料极性分别提高3.1～6.3倍和-0.05～0.27倍,且不同老化程度PLA微塑料极性指标(0.517～0.658)显著高于PE微塑料(0.011～0.080)。水接触角结果显示,老化改变了PE微塑料的亲疏水性,但未改变PLA微塑料亲疏水性。(2)不同老化程度微塑料对纯水环境典型PFAS吸附行为与机制。(1)老化PE和PLA微塑料对5种PFAS吸附符合不同吸附动力学模型,其中多为准一级吸附动力学和颗粒内扩散模型,表明不同老化程度PE和PLA微塑料对PFAS的吸附存在物理吸附和化学吸附。(2)吸附动力学平衡分配系数(K_d)结果显示,老化提高PE微塑料对C6 PFAS吸附亲和力(K_d值均增加1.4倍),使得长链PFAS在PE微塑料上的吸附亲和相对优势(C8>C4和C6)随老化改性而降低;而PFAS在PLA微塑料上的吸附亲和力趋势并未随老化程度增加而改变,均遵循C6>C8>C4的顺序,老化提高PLA微塑料对醚类Gen X和羧酸PFOA吸附亲和力(K_d值分别增加1.5～3.3倍和0.1～0.6倍)。(3)等温吸附结果表明:老化PE和PLA微塑料对PFAS的吸附主要表现为多分子层吸附,其吸附机制因微塑料结构性能的变化(如多孔结构、比表面积、含氧官能团、极性和疏水性等)而呈现复杂性,涉及到范德华力、取向相互作用和疏水作用等。(3)合成渗滤液环境对老化微塑料吸附典型PFAS的影响。在合成渗滤液环境背景下,(1)PE和PLA微塑料对PFAS吸附前后,溶液特征光谱参数变化不一。(2)K_d值结果显示,PE微塑料对PFAS吸附亲和力呈现长链高于短链趋势(C8>C4和C6),而PLA微塑料对PFAS吸附亲和力与链长无关,可能与官能团有关(醚类>羧酸和磺酸)。(3)相比纯水环境,PE和PLA微塑料对不同PFAS吸附亲和力不同:PFBA和PFOA的K_d值分别增加1.2～3.4倍和0.1～1.2倍,表明合成渗滤液组分有助于增强羧酸类PFAS在PE微塑料上的吸附。同样,合成渗滤液组分也促进PFOS和Gen X在PLA微塑料上的吸附(K_d值分别增加0.6～1.2和0.2～1.9倍)。更多还原

【Abstract】 The landfills serve as a storage for waste,including plastics and fluorinated consumer products in terrestrial ecosystems.Due to excessive plastic production and imperfect waste management,plastic waste eventually ends up in landfills and continuously cracked into microplastics.Many studies have confirmed that various fluorinated consumer products(such as paper,textiles,food contact materials,cosmetics,etc.)contain varying concentrations and compositions of per-and polyfluoroalkyl substances(PFAS),which are mostly discarded in landfills as waste at the end of their service life.Domestic and international scholars have reported on the pollution levels of microplastics and PFAS in landfill leachates around the world,but there are few studies reporting the pollution characteristics of microplastics loaded on PFAS in leachates.Limited research on PFAS-loaded microplastics in marine,river environments,and biosolids suggests that microplastics in the environment can serve as PFAS adsorption carriers and may be a persistent release source of PFAS.However,there exists currently a glaring lack of knowledge regarding the behavior characteristics and mechanism of microplastics adsorbing PFAS in leachates,to urgently conduct research on the adsorption behavior of PFAS on microplastics in leachates characteristic environments.Polyethylene(PE),a conventional plastic,which causes the most pollution in landfill leachates,and polylactic acid(PLA),a common biodegradable plastic,which has mechanical qualities similar to PE,were used in this study.A laboratory-accelerated aging experiments were conducted to obtain microplastic samples with different alteration degrees.Using scanning electron microscopy,X-ray energy dispersive spectroscopy(SEM-EDS),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),and other techniques to characterize the morphology,composition,phase,and spectrum of microplastics,the impact of aging on the structural morphology of microplastics was examined.Five typical PFAS were selected,including legacy C8 long chains(perfluorooctanoate(PFOA)and perfluorooctane sulfonate(PFOS)),substituted C4 short chains(perfluorobutanoate(PFBA)and Perfluorobutane sulfonate(PFBS)),and ether C6 substitution(hexafluoropropylene oxide dimer acid(Gen X)).The sequential batch adsorption experiments were conducted on PFAS by microplastics with different alteration degrees in the ultrapure water and dark environment.Combining adsorption kinetics and isothermal adsorption models,the adsorption characteristics of PFAS on aged modified microplastics were analyzed.Using typical organic matter(humic acid(HA))and inorganic salt components(sodium,calcium,and chlorine)from landfill leachates as components of synthetic leachates,the sequential batch adsorption experiments were conducted on PFAS by microplastics with different alteration degrees in synthetic leachates environment.Based on the characteristics of UV visible spectrum and 3D fluorescence spectrum,the fluorescence changes before and after adsorption were analyzed,and comparing the results of ultrapure water adsorption experiments to elucidate the composition effect of synthetic leachates on the adsorption behavior of microplastics for PFAS.The findings will contribute to enhancing the scientific understanding of the migration law of PFAS in landfills,and also provide a basic theoretical basis for the collaborative treatment of composite pollution such as microplastics and PFAS.The main research conclusions are as follows:(1)The impact of aging on the structural properties of microplastics.(1)The effect of aging on the physical properties of microplastics:At the initial stage,the surface of PE and PLA microplastics was smooth,but after aging,pits,holes,and cracks appeared on the surface.Aging caused continuous cracking of PE and PLA microplastics,and the nanoscale particles(442.5～744.1 nm)was detected in the liquid phase samples aged for120 hours.The specific surface area results showed that the different composition and structure of PE and PLA microplastics resulted in different trends in their specific surface area changes after aging.The specific surface area of aged PE microplastics increased by 0.4～2.6 times,while that of aged PLA microplastics decreased by 0.6～0.8times.(2)The effect of aging on the chemical properties of microplastics:Aging led to the formation of oxygen-containing functional groups on the surface of PE microplastics,mainly carbonyl groups.Due to the presence of oxygen-containing functional groups(carboxyl groups)in PLA microplastics,the composition and content of oxygen-containing functional groups change after aging,resulting in the formation of chromophores that triggerπ-π*transitions.(N+O)/C atomic ratio analysis showed that aging led to an increase in the polarity of PE and PLA microplastics by 3.1～6.3 times and-0.05～0.27 times,respectively.However,the polarity index of PLA microplastics with different alteration degrees(0.517～0.658)was significantly higher than that of PE microplastics(0.011～0.080).The water contact angle results showed that aging altered the hydrophilicity and hydrophobicity of PE microplastics but not that of PLA microplastics.(2)The adsorption behavior and mechanism of typical PFAS on microplastics with different alteration degrees in the ultrapure water environment.(1)The adsorption of five typical PFAS by aged PE and PLA microplastics followed various adsorption kinetics models,most of which were quasi first order adsorption kinetics and intraparticle diffusion models,indicating that both physical and chemical adsorption were involved in the adsorption of PFAS by PE and PLA microplastics with different alteration degrees.(2)The results of adsorption kinetic equilibrium distribution coefficient(K_d)showed that aging enhanced the adsorption affinity of PE microplastics for C6 PFAS(K_d values increased by 1.4 times),resulting in a relative advantage of long-chain PFAS adsorption affinity on PE microplastics(C8>C4 and C6)decreasing with aging modification.Following the sequence C6>C8>C4,the adsorption affinity trend of PFAS on PLA microplastics with different alteration degrees remained constant with chain length.Aging increased the adsorption affinity of PLA microplastics for ether Gen X and carboxylic acid PFOA(K_d values increased by 1.5～3.3 times and0.1～0.6 times,respectively).(3)The isothermal adsorption results indicated that the adsorption of PFAS on aged PE and PLA microplastics mainly manifests as multi-layered adsorption.The adsorption mechanism is complex due to the various structural changes in microplastics,such as porous structure,specific surface area,oxygen-containing functional groups,polarity,and hydrophobicity,involving van der Waals forces,orientation interactions,and hydrophobic interactions.(3)The effect of synthetic leachates environment on the adsorption of typical PFAS by aged microplastics.Under the background of synthetic filtrate environment,(1)The characteristic spectral parameters of the solution varied before and after the adsorption of PFAS by PE and PLA microplastics.(2)The K_d value results showed that the adsorption affinity of PE microplastics for PFAS showed a trend of long chain higher than short chain(C8>C4 and C6),while the adsorption affinity of PLA microplastics for PFAS was independent of chain length and may be related to functional groups(ethers>carboxylic acids and sulfonic acids).(3)Compared to ultrapure water environment,the adsorption affinity of PE and PLA microplastics for different PFAS was different:the K_d values of PFBA and PFOA increase by 1.2～3.4times and 0.1～1.2 times,respectively,indicating that the components of synthetic leachates enhanced the adsorption of carboxylic acid PFAS on PE microplastics.Similarly,the components of synthetic leachates promoted the adsorption of PFOS and Gen X on PLA microplastics(K_d values increased by 0.6～1.2 and 0.2～1.9 times,respectively).更多还原