| Dissolved organic matter?DOM?is ubiquitous in aquatic environmental systems.Molecular characterization of dissolved organic matter?DOM?is important for understanding its environmental behavior and fates.Although the concentration of DOM can be measured as dissolved organic carbon?DOC?analysis in general,the chemical compositions of DOM are still little to known.The property and composition of DOM has been proved significantly affect the water treatment efficiency.In addition,DOM in wastewater in the chemical industry,such as coal and petroleum industry,contains not only natural organic matter?NOM?,but also some coal or petroleum-derived organics.The objectives of this work were therefore to characterize the molecular composition of DOM in typical chemical industrial wastewater.Novel sample pre-treatment,molecular composition analysis method and water treatment process were made to explore the molecular composition of DOM in raw wastewater and its transformations during wastewater treatment.The property of DOM in raw and a series of treated coal gasification wastewater?CGW?was characterized using DOC,fluorescence?EEM?and Fourier transform ion cyclotron resonance mass spectrometry?FT-ICR MS?analysis?Chapter 2?.The DOC in CGW is relatively high and decreased along the treatment processes.The EEM results show that protein-like compounds are easy to be removed,while fulvic acid-like organics are refractory to CGW water treatment processes and left in the effluent.The liquid-liquid extraction?LLE?and solid phase extraction?SPE?was combined to divide the DOM into hydrophobic and hydrophilic portions.The percentage of hydrophobic portion decreases along the CGW treatment processes.The molecular diversity increased during aerobic biological processes.In addition,Cl-containing compounds with potential toxicity were formed in the last NaClO treatment and should be concerned.A novel SPE based DOM fractionation method was proposed and applied to separate DOM from raw CGW and refinery wastewater?Chapter 3?.Four sub-fractions can be obtained including hydrophobic acid?HOA?,hydrophobic neutral?HON?,hydrophobic base?HOB?and hydrophilic substance?HIS?.More DOM can be extracted using this new combined method?72.6%vs.59.1%?compared with conventional resin fractionation.The obtained extracts are salt-free,and its molecular compositions can be characterized by negative-ion?-ESI?and positive-ion?+ESI?ion FT-ICR MS.The-ESI FT-ICR MS results show that compounds with higher oxygen numbers were enriched in HOA sub-fraction,while N-containing compounds are the dominant by+ESI FT-ICR MS.Compared with single SPE procedure,compounds with lower oxygen number,especially for nitrogen-containing compounds with lower oxygen number,can be recovered from the combined SPE method.UV activated persulfate?UV/Persulfate?process was used to degrade naphthenic acid model compounds in aqueous solution,and the behind mechanisms were also investigated in Chapter 4.Compared to commonly used UV/H2O2 process,UV/Persulfate process showed high removal efficiency towards cyclohexanoic acid?CHA?at the same conditions and exhibited a pseudo-first-order kinetics pattern.The results showed CHA could directly react with SO4·-with a rate constant of 5.3×107M-1 s-1.·OH radicals generated from the reaction between SO4·-and hydroxide ion react with CHA and are the dominant pathway for CHA removal in this process.In addition,the existence of long carbon chain,cyclic ring,and aromatic ring accelerated the reactivity of NAs in the UV/persulfate process.The UV/Persulfate process was further used to treat real oil sand process-affected water?OSPW??Chapter 6?.Several analytical methods including synchronous fluorescence spectra?SFS?and ultra performance liquid chromatography time-of-flight mass spectrometry?UPLC-TOF-MS?were used to monitor the changes of fluorescent organics and NAs species in OSPW.Fluorescent compounds were removed preferentially during UV/Persulfate process.The removal efficiency towards O2-,O3-,O4-,O5-NAs species was 83.8%,49.3%,46.8%and-29.8%,respectively.The UV/Persulfate also showed a pseudo-first-order kinetics pattern towards O2-NAs with the rate constant from 0.0156 min-1 to 0.1511 min-1.The acute toxicity of OSPW towards Vibrio fischeri decreased from 32%to 11%,indicating the efficient detoxicity of this method.The effect of different radicals on the molecular transformation of DOM in OSPW was investigated using three different radical-based advanced oxidation processes?AOPs?,including UV/H2O2,UV/Chlorine,and UV/Persulfate processes.The DOC results showed the DOM transformation rather than mineralization happened during these AOPs.The property of DOM became more and more hydrophilic due to the decreasing DOC percentage from LLE extractable portions.The UV/Persulfate process showed the highest removal efficiency towards classic NAs?O2-NAs?and detoxic ability among three processes.The behind mechanisms were explored based on the variations of H/C ratio,O/C ratio,DBE and carbon oxidation state?COS?.For CHO species,the different distribution trend of H/C ratio was found at a low and high dose of oxidants means different mechanisms involved.One and two Cl-containing CHOCl class species were identified in UV/Chlorine process due to the formation of chlorine radicals,and the formula number increased with the increasing sodium hypochlorite?NaClO?.One Cl-containing CHOCl was also found in UV/Persulfate process with 4 mM persulfate,meaning chlorine radical might generate from competitive reactions.The results from the principal component analysis?PCA?on the molecular profile of DOM showed that UV/H2O2 process and UV/Persulfate process have the same trend of molecular transformation due to the effect of OH radical,which is different from the UV/Chlorine process with the effect of chlorine radical. |
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