| Dissolved organic matter(DOM)is a major pollutant in petroleum refinery wastewater,of which the molecular composition and transformation through the water treatment process are yet unclear.In this work,a method for the characterization of the molecular composition of DOM in refinery wastewaters was developed by means of the combination of distillation and solid phase extraction fractionation with Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS)and Orbitrap MS.Volatile components were characterized on molecular level,and the transformation of refinery wastewater DOM during water treatment was studied.The main contents include:The stability in TOC value and molecular composition of DOM in refinery wastewater was investigated.The TOC value and molecular composition of different refinery wastewaters both changed during storage.The molecular composition of untreated wastewater changed largely and quickly,while the stability of the sewage from the middle and later stages of water treatment is better.When the molecular composition of DOM changes,the TOC also varies in accord.Therefore,the change of TOC value can be used as an indicator of the change of molecular composition of DOM in water sample.In the process of storage,water samples with altered TOC are no longer suitable for macroscopic and molecular analysis.A pretreatment method based on distillation and solid phase extraction was established for the molecular characterization of volatile components in refinery wastewater.It was found that distillation has a decent ability of separation between volatile DOM and residue DOM.The distillate can enrich the small-molecule volatile organic compounds,and eliminate the interference of inorganic salts,which enables direct analysis by gas chromatography and/or mass spectrometry.Distillation raffinate has increased concentration of original matters,leading to a comprehensive characterization in molecular composition.The changes in molecular composition of refinery wastewater through different stages of water treatment process were studied,based on distillation and solid phase extraction combined with Orbitrap MS.It was found that the volatile component of refinery wastewater mainly contains N1 Ox,Ox and OxS1 class species.Untreated refinery wastewater contains high levels of sulfur-containing and other heteroatom compounds.After anaerobic-aerobic treatment,nitrogen-containing compounds are largely eliminated.Sulfur-containing compounds including surfactants are effectively removed after activated carbon treatment.Compared with environmental water,refinery sewage DOM are mainly small-molecule compounds with a low degree of condensation,and still contains a relatively high content of sulfur-containing compounds.A novel approach was developed for the molecular characterization of DOM in refinery wastewater.New findings in the molecular stability of wastewater DOM and its transformation during water treatment process were presented,which can be used as a theoretical guidance for the improvement of water treatment process.This method can be applied to the study of other refinery wastewaters,providing methodology and theoretical basis for the environmental risk assessment and water treatment design of refinery wastewater. |
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