| Landfill is the primary treatment of municipal solid waste, and aerobic degradation is aindispensible process in a landfill system. However, large amount of odors could be producedduring aerobic landfill, and significantly affect urban air quality, residential health as well as cityimage. With this regard, it is important to explore odors production mechanism and developrelated control/removal techniques. But due to the limitation in analytical strategies, most studieshave concerned the occurrence of odors in landfill sites, and few work has been done on the timeseries of odors, especially at high time resolution, e.g., hours, and studies on odor formationmechanism has also been rarely reported.Thus, in this study odors produced during aerobic degradation in a simulated landfill systemhave been studied by using a novel ambient mass spectrometry, online membrane injectionsingle photon ionization mass spectrometry (MI-UVSPI-ToFMS) together with the facile E-nosetechnique. By taking advantages of MI-UVSPI-ToFMS in no sample pretreatment, directanalysis and universal ionization, various odors (i.e., sulfur-containing odors, benzenes,oxygenated odors) have been successfully detected in tens of gas samples, and the productionmechanism has been investigated when the production of other volatile organic compounds andphysicochemical indices (e.g., concentration of oxygen, pH) of aerobic degradation have alsobeen considered. Conclusions have been achieved as follows:(1) MI-UVSPI-ToFMS and E-nose methods for online detection of odors have beendeveloped. The accumulation time in total ion chromatogram has been optimized to60s for dataanalysis of MI-UVSPI-ToFMS; accumulation time is a key parameter affecting limit of detection(LOD), linearity and reproducibility for quantitative analysis. Seven odor standards have beenquantified by MI-UVSPI-ToFMS with linearity ranging from1–100ppb (R20.991–0.998);LODs have been obtained as0.4–2.4ppb, lower than the thresholds or emission standards ofindividual odor standard. E-nose has been tested by odor standards as well, and specific patternhave been observed for each specie.(2)By using MI-UVSPI-ToFMS E-nose almost100of gassamples have been collected during aerobic degradation (26days) of banana peels in a simulatedlandfill system, and directly analyzed without pretreatment. The results showed that odors produced during aerobic degradation included sulfur-containing odors (e.g., dimethyl sulfide,diethyl sulfide), oxygenated species (ethyl acetate, valeric acid, acetaldehyde) and benzenes(toluene, styrene). Diethyl sulfide（sulfur containing compounds）and methylbenzene（benzenes）peaked on the4th day, styren（ebenzenes）and valeric aci（doxygenated odors）reached the highestconcentration on the8th day, and the peak level of acetaldehyde (oxygenated odors) was foundaround10th day. Ethyl acetate remained stable over the whole period. The above results suggestthat odors have been produced at different periods throughout the whole aerobic degradationprocess, and compounds of the same species could undergo different degradation procedure,resulting in different emission time.(3) Combined with the emission of other volatile organic compounds (VOCs) andphysicochemical parameters (e.g., concentration of oxygen, pH), most of odors observed at theearly stage of aerobic degradation (1–4days) have been attributed to the composition in banana;with the progress of the degradation from4–13days, odors have been produced due to thedegradation of banana peels, which can also be evidenced by the decreases in pH and oxygenconcentration while increases in carbon dioxide concentration and compost temperature; at thelast stage of degradation, odors as well as other VOCs have been hardly produced in the system.Therefore, control/removal strategies should be customized with the consideration of emissionsources and formation mechanism of odors released at different aerobic degradation stages inorder to improve removal/control performance. |
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