Evaluating fugacity models for trace components in landfill gas

Emission of volatile organic compounds during aerobic decomposition of banana peel

Emissions of volatile organic compounds (VOCs) were continuously measured during the aerobic decomposition of banana peel in a laboratory-scale landfill simulator over 25 d. Using direct membrane inlet single-photon ionisation time-of-flight mass spectrometry (MI-SPI-ToF-MS), 18 VOCs belonging to 10 functional groups were detected in the air samples, and their VOC emission profiles were established using cluster analysis on time-resolved data. Three emission stages were clearly identified, with the major release for most VOC compounds occurring during the first 14 d. The emission patterns of the individual compounds were quite similar despite the different release mechanisms. In addition, no apparent increase in temperature was observed inside the simulator during the entire experimental period. We suggest that the volatilisation of the constituents in the waste pile contributed equally to VOC emissions as did the degradation of banana peel via microbial activity. The average emission rate of total VOCs reached 44.3 × 10^-3 mg VOC kg^-1 of dry banana peel, with more than half belonging to malodourous substances. The malodourous emissions of the decaying banana peel in an aerobic environment mainly originated from styrene, dimethyl sulphide, and diethyl sulphide, the most common contributors to offensive odourants during food waste biodegradation.

Removal of labile arsenic from flooded paddy soils with a novel extractive column loaded with quartz-supported nanoscale zero-valent iron

Efficient removal of labile arsenic (As) from paddy soil is a fundamental pathway mitigating As accumulation in rice from a long-term perspective. In this study, a porous and pencil-shaped column prepacked with quartz-supported nanoscale zero-valent iron (NZVI) was designed to extract elevated porewater As from paddy soil under flooded condition. With fine quartz as supporting medium in the core layer, only 0.07% out-migration of the loaded NZVI occurred in arsenite As(III) solution. At pH 5-9, removal of aqueous As(III) with NZVI-column was 73-78%, while silicic acid and phosphate at their environmentally realistic concentrations exhibited 27-30% and 14-17% inhibition on As(III) extraction, respectively. For two paddy soils with slight (S-As) and moderate (M-As) As contamination, four cycles of intermittent extraction with NZVI-column induced steady and marked decrease in porewater As. By the end of four successive extractions, profiles of DGT-labile As in S-As and M-As soils decreased by 22% and 29% on average with simultaneous decline of the most available fraction of soil As (including soluble and exchangeable fraction) by 26% and 17%, respectively. For the post-extracted two soils, As accumulation of rice seedlings declined by 29-57% than those in control. These results identify the effectiveness of NZVI-column in extracting elevated labile As from paddy soils with the aid of flooding. Targeting fast removal of high porewater As, column-extraction could serve as the first step in "remediation train" of paddy soils with relatively high As to shorten cleanup time by rendering much lowered soil As burden for the following phytoextraction and other measures.

Field investigation of temporal variation of volatile organic compounds at a landfill in Hangzhou, China

Variation of volatile organic compound (VOC) concentration and composition in an active landfill were monitored by a developed static chamber for 2 years. The landfill gas from 82 sampling points including 70 points on working face, 8 points on geomembrane (GMB), and 4 points on final cover were analyzed for VOCs by GC-MS. Twenty-eight types of VOCs were detected, including terpenes, sulfur compounds, aromatics, hydrocarbon, oxygenated compounds, aldehyde compounds, and halogenated compounds. Terpenes were the dominant VOCs recorded in the spring, autumn, and winter seasons, whereas sulfur compounds dominated in the summer season. Limonene, ethyl alcohol, and acetone were identified as the main VOCs emitted from the waste working face of the landfill. Limonene dominated the terpenes with a maximum concentration of 43.29 μg m^-3 in the autumn season. Limonene was also the dominant VOC escaping from the defects of geomembrane temporary cover reaching an average concentration 38 μg m^-3. The defects of geomembranes can be a great emission source of VOCs. Emission rate of limonene was 2.24 times higher than that on the working face. VOC concentrations on the final cover can be 166 times less than those obtained on the working face. VOC emitted from the landfill did not represent a health threat for human health. However, concentrations of methyl mercaptan and ethanethiol on the working face were 3.4-22.8 times greater than their odor threshold, which were the main compounds responsible for odor nuisance. Results obtained from CALPUFF model indicated that methyl mercaptan and ethanethiol would not be a nuisance for the residents around the landfill. However, these compounds are harmful to the workers on the landfill.

Characterization of trichloroethylene adsorption onto waste biocover soil in the presence of landfill gas

Waste biocover soils (WBS) have been demonstrated to have great potential in mitigating trichloroethylene (TCE) emission from landfills, due to the relatively high TCE-degrading capacity. In this study, the characteristics of TCE adsorption on WBS in the presence of the major landfill gas components (i.e., CH4 and CO2) were investigated in soil microcosms. The adsorption isotherm of TCE onto WBS was fitted well with linear model within the TCE concentrations of 7000 ppmv. The adsorption capacity of TCE onto WBS was affected by temperature, soil moisture content and particle size, of which, temperature was the dominant factor. The adsorption capacity of TCE onto the experimental materials increased with the increasing organic matter content. A significantly positive correlation was observed between the adsorption capacity of TCE and the organic matter content of experimental materials that had relatively higher organic content (r = 0.988, P = 0.044). To better understand WBS application in practice, response surface methodology was developed to predict TCE adsorption capacity and emissions through WBS in different landfills in China. These results indicated that WBS had high adsorption capacity of TCE in LFG and temperature should be paid more attention to manipulate WBS to reduce TCE emissions from landfills.

Emission assessment at the Burj Hammoud inactive municipal landfill: viability of landfill gas recovery under the clean development mechanism

This paper examines landfill gas (LFG) emissions at a large inactive waste disposal site to evaluate the viability of investment in LFG recovery through the clean development mechanism (CDM) initiative. For this purpose, field measurements of LFG emissions were conducted and the data were processed by geospatial interpolation to estimate an equivalent site emission rate which was used to calibrate and apply two LFG prediction models to forecast LFG emissions at the site. The mean CH(4) flux values calculated through tessellation, inverse distance weighing and kriging were 0.188±0.014, 0.224±0.012 and 0.237±0.008 l CH(4)/m(2) hr, respectively, compared to an arithmetic mean of 0.24 l/m(2) hr. The flux values are within the reported range for closed landfills (0.06-0.89 l/m(2) hr), and lower than the reported range for active landfills (0.42-2.46 l/m(2) hr). Simulation results matched field measurements for low methane generation potential (L(0)) values in the range of 19.8-102.6 m(3)/ton of waste. LFG generation dropped rapidly to half its peak level only 4 yrs after landfill closure limiting the sustainability of LFG recovery systems in similar contexts and raising into doubt promoted CDM initiatives for similar waste.

Emission inventory for PFOS in China: review of past methodologies and suggestions

Perfluorooctane sulfonate (PFOS) is a persistent, bioaccumulative, and toxic chemical that has the potential for long-range transport in the environment. Its use in a wide variety of consumer products and industrial processes makes a detailed characterization of its emissions sources very challenging. These varied emissions sources all contribute to PFOS' existence within nearly all environmental media. Currently, China is the only country documented to still be producing PFOS, though there is no China PFOS emission inventory available. This study reviews the inventory methodologies for PFOS in other countries to suggest a China-specific methodology framework for a PFOS emission inventory. The suggested framework combines unknowns for PFOS-containing product penetration into the Chinese market with product lifecycle assumptions, centralizing these diverse sources into municipal sewage treatment plants. Releases from industrial sources can be quantified separately using another set of emission factors. Industrial sources likely to be relevant to the Chinese environment are identified.

Overview on LFG projects in China

Since the first landfill gas (LFG) power plant in China was built in 1998, by now more than 10years have passed. In this period the LFG utilization process has progressed greatly in China. An overall review of the process is presented in this paper, which includes the background of policies, the information about the approval procedure of LFG projects, and the theoretical methods used to estimate the amount of LFG's generation. Detailed analysis on the project practice, such as LFG collection techniques, LFG utilization condition in China, is made. According to statistic data, before the end of 2008, 26 LFG power projects have been built and put into operation with total power capacity around 56.8MW, and 2.234 million tons of carbon dioxide equivalent abatement has been achieved annually by all of these LFG projects. The future of LFG industry in China is expected that there is still considerable developing space for LFG utilization in the near coming years, however after 2012, the progress speed may slow down because of some adverse aspects, such as available landfill resource becomes scarce, new laws implemented in China might exclude Chinese landfills from future CDM activities, etc.

Fugacity modelling to predict the distribution of organic contaminants in the soil:oil matrix of constructed biopiles

Level I and II fugacity approaches were used to model the environmental distribution of benzene, anthracene, phenanthrene, 1-methylphenanthrene and benzo[a]pyrene in a four phase biopile system, accounting for air, water, mineral soil and non-aqueous phase liquid (oil) phase. The non-aqueous phase liquid (NAPL) and soil phases were the dominant partition media for the contaminants in each biopile and the contaminants differed markedly in their individual fugacities. Comparison of three soils with different percentage of organic carbon (% org C) showed that the % org C influenced contaminant partitioning behaviour. While benzene showed an aqueous concentration worthy of note for leachate control during biopiling, other organic chemicals showed that insignificant amount of chemicals leached into the water, greatly reducing the potential extent of groundwater contamination. Level II fugacity model showed that degradation was the dominant removal process except for benzene. In all three biopile systems, the rate of degradation of benzo(a)pyrene was low, requiring more than 12 years for soil concentrations from a spill of about 25 kg (100 mol) to be reduced to a concentration of 0.001 microgg(-1). The removal time of 1-methylphenanthrene and either anthracene or phenanthrene was about 1 and 3 years, respectively. In contrast, benzene showed the highest degradation rate and was removed after 136 days in all biopile systems. Overall, this study confirms the association of risk critical contaminants with the residual saturation in treated soils and reinforces the importance of accounting for the partitioning behaviour of both NAPL and soil phases during the risk assessment of oil-contaminated sites.