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Spectroscopic Analysis And Theoretical Simulation Of Aquatic Dissolved Organic Matter And Its Environmental Behaviors

Posted on:2024-05-03Degree:DoctorType:Dissertation
Country:ChinaCandidate:B GongFull Text:PDF
GTID:1521306929492244Subject:Environmental Engineering
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Dissolved organic matter(DOM)is a ubiquitous mixture with high heterogeneity.DOM plays a critical role in the biogeochemical process and interacts with other substances in waters,affecting the physicochemical properties of pollutants and altering their reactivity,transportation,transformation,and final fates.DOM can also influence wastewater treatment technologies,altering the efficiency or mechanisms of pollutant removal and the quality of effluents.However,due to the complexity of DOM,the current analysis methods are not sufficient for multiple-component determination,and elucidation of the influence of DOM fractions is still lacking.In this thesis,based on spectroscopic,mathematical,and other methods,I developed a convenient and reliable method to determine the main components of DOM,and compared the environmental behaviors of model DOM and actual environmental DOM fractions.I also fractionated the groups of DOM and elucidated their influence mechanisms on wastewater treatment processes.The highlights and results of the study are as follows:1.Constructing a fluorescent approach for simultaneous determination of multiple components in DOM.In this work,I developed a fluorescence approach based on the excitation-emission matrix(EEM)combined with a new algorithm,denoted as matrix reconstruction coupled with prior linear decomposition(MR-PLD),to simultaneously quantify multiple DOM fractions,including saccharide,protein,and humic substances.The accuracy and robustness of this approach compared with conventional parallel factor analysis and prior linear decomposition were validated through a series of simulated and actual water sample tests.I conducted simulations and actual experiments to test the anti-interference performance of MR-PLD,with results indicating that the quantification of DOM would not be significantly affected by other fluorophores.This method was successfully applied in analyzing both natural water and wastewater treatment plants.This study provides a new approach to characterizing DOM with EEM,contributing to convenient concentration monitoring for further exploration of its environmental impacts and other studies.2.Confirming the use of tryptones rather than bovine serum albumin to explore protein-pollutant interactions in the environment.As one of the most important components,protein is readily degraded in the environment.Thus,it is unknown whether "protein-like substances" in environments are a group of intact proteins or a mixture of peptides and even amino acids.Therefore,the widely adopted model protein bovine serum albumin(BSA)was compared with tryptones,an assortment of peptides,to evaluate their similarity to the proteins extracted from environmental samples(EP).First,based on their physicochemical properties characterization,the environmental protein-like substances and tryptones were found to have more aromatic groups than BSA,and they were more unstable than BSA.The interaction between proteins and metal ions or humic acids(HA)was then examined.Unlike other proteins,only the mixtures with BSA exhibit more significant fluorescence quenching and more positive specific ultraviolet-visible absorbance after interactions.After binding to metal ions or HA,BSA tends to aggregate,whereas tryptones and environmental protein-like substances do not.These results reveal that the EP samples are more similar to tryptones than the model protein,BSA.Our work implies that tryptones,rather than BSA,should be a more appropriate alternative model in the investigation of protein-pollutant interactions.3.Comparing the microfiltration membrane fouling caused by model proteins and environmental protein-like substances.In addition to the previous protein-pollutant interaction,proteins were reported to be important in membrane filtration and membrane fouling.However,due to the different properties,whether the model proteins can represent the actual proteins’membrane fouling performance still needs to be explored.Therefore,in this work,the intrinsic properties and membrane filtration impacts of EP obtained from different sludge sources were evaluated.The theoretical simulations and experimental analysis results indicate that,with more unsaturated groups,such as aromatic amino acid residues,all the EP samples have a higher tendency to aggregate to larger molecules than two model proteins—BSA and tryptones.However,during the ceramic membrane filtration processes,an unexpected result indicates that the model proteins and all the EP samples display similar light membrane fouling,only leading to a weak flux decrease.On the one hand,these results suggest that in studies related to ceramic membrane fouling,using both BSA or tryptones is suitable for obtaining reliable results.On the other hand,with external forces,intermolecular interactions or protein-membrane interactions may not be the dominant factor causing severe membrane fouling,cautioning us to carefully evaluate the rationale of model substances in different research cases.4.Investigating the effects of DOM on the H2O2 activation over a-Fe2O3(001)surfaces.Besides membrane filtration,the heterogeneous Fenton process is one of the most efficient methods for wastewater treatment.The heterogeneous Fenton process is one of the most efficient methods for wastewater treatment.However,the inevitable impact of DOM on H2O2 activation is not yet clearly understood.Therefore,the αFe2O3(001)surfaces were chosen as the model materials,and the effects of the major functional groups in DOM on H2O2 activation were systematically investigated using density functional theory simulations.The adsorption and activation of H2O2 on the surfaces were simulated,confirming the superior catalytic properties of the Fe sites on the α-Fe2O3(001)surface with an oxygen vacancy.I then found that the phenol,carboxyl,amide,and quinone groups adsorb more strongly on the surfaces than H2O2,whereas the hydroxyl and aldehyde groups show weaker adsorption.I also simulated the co-adsorption of the DOM molecules and H2O2 and the consequent influence on the Fenton reaction.On pristine surfaces,the intermolecular interactions promoted or inhibit the H2O2 cleavage with some DOM molecules.However,for surfaces with oxygen vacancies,due to the competition for adsorption sites,some DOM functional groups were found to substitute the H2O2 at the most reactive Fe site,thus inhibiting its activation.The direct interactions between the DOM molecules and H2O2 do not significantly affect H2O2 activation.This study reveals the various effects of DOM on H2O2 activation and contributes to the application of heterogeneous Fenton technology.
Keywords/Search Tags:dissolved organic matter, excitation-emission matrix, multiple components determination, protein-pollutant interaction, microfiltration membrane fouling, H2O2 activation, intermolecular interactions, adsorption competition
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