Sorption and phase distribution of ethanol and butanol blended gasoline vapours in the vadose zone after release

Sorption and attenuation of petroleum VOCs in five unsaturated soils: Microcosms and column experiments

The fate of volatile organic compounds (VOC) vapors in the unsaturated zone is the basis for evaluating the natural attenuation potential and vapor intrusion risk. Microcosm and column experiments were conducted to study the effects chemical speciation and soil types/properties on the fate of petroleum VOCs in unsaturated zone. The biodegradation and total attenuation rates of the seven VOCs obtained by microcosm experiments in black soil and yellow earth were also generally higher than those in floodplain soil, lateritic red earth, and quartz sand. The VOC vapors in floodplain soil, lateritic red earth, and quartz sand showed slow total attenuation rates (<0.3 d-1). N-pentane, methylcyclopentane, and methylcyclohexane showed lower biodegradation rates than octane and three monoaromatic hydrocarbons. Volatilization into the atmosphere and biodegradation are two important natural attenuation paths for VOCs in unsaturated soil columns. The volatilization loss fractions of different volatile hydrocarbons in all five unsaturated soils were generally in the order: n-pentane (93.5%-97.8%) > methylcyclopentane (77.2%-85.5%) > methylcyclohexane (53.5%-69.2%) > benzene (17.1%-73.3%) > toluene (0-45.7%) > octane (1.9%-34.2%) > m-xylene (0-5.7%). The fractions by volatilization into the atmosphere of all seven hydrocarbons in quartz sand, lateritic red earth, and floodplain soil were close and higher compared to the yellow earth and black soil. Overall, this study illustrated the important roles chemical speciation and soil properties in determining the vapor-phase transport and natural attenuation of VOCs in the unsaturated zone.

Vapor-phase biodegradation and natural attenuation of petroleum VOCs in the unsaturated zone: A microcosm study

Traditional natural attenuation studies focus on aqueous process in the saturated zone while vapor-phase biodegradation and natural attenuation in the unsaturated zone received much less attention. This study used microcosm experiments to explore the vapor-phase biodegradation and natural attenuation of 23 petroleum VOCs in the unsaturated zone including 7 monoaromatic hydrocarbons, 6 n-alkanes, 4 cycloalkanes, 3 alkylcycloalkanes and 3 fuel ethers. We found that monoaromatic hydrocarbon vapors were easily attenuated with significantly high first-order biodegradation rates (9.48 d^-1-43.20 d^-1) in live yellow earth, of which toluene and benzene had the highest biodegradation rates (43.20 d^-1 and 28.32 d^-1, respectively). The 13 aliphatic hydrocarbons and 3 fuel ethers all have relatively low attenuation rates (<0.54 d^-1) in live soil and negligible biodegradation contribution. We explored the effects of soil types (black soil, yellow earth, lateritic red earth and quartz sand), soil moisture (2, 5, 10, and 17 wt%) contents and temperatures (4, 15, 25, 35 and 45 °C) on the vapor attenuation. Results showed that increasing soil organic matter (SOM) content, silt content, porosity and soil microorganism numbers enhanced contaminant attenuation and remediation efficiency. Increasing moisture content reduced the apparent first-order biodegradation rates of monoaromatic hydrocarbon vapors. The vapor-phase biodegradation had optimal temperature (∼25 °C in yellow earth) and increasing or decreasing temperature slowed down biodegradation rate. Overall, this study enhanced our understanding of vapor-phase biodegradation and natural attenuation of petroleum VOCs in the unsaturated zone, which is critical for the long-term management and remediation of petroleum contaminated site.

Transport and natural attenuation of benzene vapor from a point source in the vadose zone

The vadose zone is a very dynamic and active environment that directly affects natural attenuation and vapor intrusion of volatile organic compounds (VOCs). Therefore, it is important to understand the fate and transport of VOCs in the vadose zone. A column experiment combined with model study was conducted to investigate the influence of soil type, vadose zone thickness, and soil moisture content on benzene vapor transport and natural attenuation in the vadose zone. Vapor-phase biodegradation and volatilization to atmosphere for benzene are two main natural attenuation mechanism in the vadose zone. Our data showed that biodegradation in black soil is the main natural attenuation mechanism (82.8%) while volatilization is the main natural attenuation mechanism in quartz sand, floodplain soil, lateritic red earth and yellow earth (>71.9%). The R-UNSAT model-predicted soil gas concentration profile and flux were close with four soil column data except for yellow earth. Increasing the vadose zone thickness and soil moisture content significantly reduced the volatilization contribution while increased biodegradation contribution. The volatilization loss decreased from 89.3% to 45.8% when the vadose zone thickness increased from 30 cm to 150 cm. The volatilization loss decreased from 71.9% to 10.1% when the soil moisture content increased from 6.4% to 25.4%. Overall, this study provided valuable insights into clarifying the roles of soil type, moisture, and other environmental conditions in vadose zone natural attenuation mechanism and vapor concentration.

Estimation of Carbon Dioxide Emissions from a Diesel Engine Powered by Lignocellulose Derived Fuel for Better Management of Fuel Production

Managing of wastes rich in lignocellulose creates the opportunity to produce biofuels that are in full compliance with the principles of sustainable development. Biomass, as a suitable base for the production of biofuels, does not have to be standardized, and its only important feature is the appropriate content of lignocellulose, which assures great freedom in the selection of input. Biobutanol, obtained from this type of biomass, can be used as fuel for internal combustion engines, including diesel engines. In the era of strict environmental protection regulations, especially concerning atmospheric air, any new fuel, apart from good energetic properties, should also show beneficial ecological effects. This study investigates the carbon dioxide emissions from biobutanol powered diesel engine by means of use of the simulation model. The parameters of a real passenger car powered by a diesel engine were used for simulation carried out accordingly to the WLTP (Worldwide Harmonized Light Vehicle Test Procedure) approval procedure as the current test for newly manufactured cars. The results obtained for biobutanol were compared with simulated exhaust emissions obtained for conventional diesel and with FAME (fatty acid methyl esters)—the most popular biofuel. Biobutanol, in spite of its higher consumption, showed lower direct carbon dioxide emissions than both: the conventional diesel and FAME. In addition, a LCA (life cycle assessment) was carried out for the fuels and vehicles in question using the SimaPro package. Therefore, the implementation of butyl alcohol as a fuel provides favorable environmental effects. This result gives arguments towards biofuel production management indicating that implementation of biobutanol production technology mitigates carbon dioxide emission, as well as promotes lignocellulosic resources rather than edible parts of the plants.

Treatability of volatile chlorinated hydrocarbon-contaminated soils of different textures along a vertical profile by mechanical soil aeration: A laboratory test

Mechanical soil aeration is a simple, effective, and low-cost soil remediation technology that is suitable for sites contaminated with volatile chlorinated hydrocarbons (VCHs). Conventionally, this technique is used to treat the mixed soil of a site without considering the diversity and treatability of different soils within the site. A laboratory test was conducted to evaluate the effectiveness of mechanical soil aeration for remediating soils of different textures (silty, clayey, and sandy soils) along a vertical profile at an abandoned chloro-alkali chemical site in China. The collected soils were artificially contaminated with chloroform (TCM) and trichloroethylene (TCE). Mechanical soil aeration was effective for remediating VCHs (removal efficiency >98%). The volatilization process was described by an exponential kinetic function. In the early stage of treatment (0-7hr), rapid contaminant volatilization followed a pseudo-first order kinetic model. VCH concentrations decreased to low levels and showed a tailing phenomenon with very slow contaminant release after 8hr. Compared with silty and sandy soils, clayey soil has high organic-matter content, a large specific surface area, a high clay fraction, and a complex pore structure. These characteristics substantially influenced the removal process, making it less efficient, more time consuming, and consequently more expensive. Our findings provide a potential basis for optimizing soil remediation strategy in a cost-effective manner.

Dynamics of dissolved organic carbon (DOC) through stormwater basins designed for groundwater recharge in urban area: Assessment of retention efficiency

Managed aquifer recharge (MAR) has been developed in many countries to limit the risk of urban flooding and compensate for reduced groundwater recharge in urban areas. The environmental performances of MAR systems like infiltration basins depend on the efficiency of soil and vadose zone to retain stormwater-derived contaminants. However, these performances need to be finely evaluated for stormwater-derived dissolved organic matter (DOM) that can affect groundwater quality. Therefore, this study examined the performance of MAR systems to process DOM during its transfer from infiltration basins to an urban aquifer. DOM characteristics (fluorescent spectroscopic properties, biodegradable and refractory fractions of dissolved organic carbon -DOC-, consumption by micro-organisms during incubation in slow filtration sediment columns) were measured in stormwater during its transfer through three infiltration basins during a stormwater event. DOC concentrations sharply decreased from surface to the aquifer for the three MAR sites. This pattern was largely due to the retention of biodegradable DOC which was more than 75% for the three MAR sites, whereas the retention of refractory DOC was more variable and globally less important (from 18% to 61% depending on MAR site). Slow filtration column experiments also showed that DOC retention during stormwater infiltration through soil and vadose zone was mainly due to aerobic microbial consumption of the biodegradable fraction of DOC. In parallel, measurements of DOM characteristics from groundwaters influenced or not by MAR demonstrated that stormwater infiltration increased DOC quantity without affecting its quality (% of biodegradable DOC and relative aromatic carbon content -estimated by SUVA254-). The present study demonstrated that processes occurring in soil and vadose zone of MAR sites were enough efficient to limit DOC fluxes to the aquifer. Nevertheless, the enrichments of DOC concentrations measured in groundwater below infiltration basins need to be considered in future studies to especially assess their impact on groundwater quality.