Gas permeability of biochar-amended clay: potential alternative landfill final cover material

Compacted biochar-amended clay (BAC) has been proposed as an alternative landfill final cover material in this study. Biochar has long been proposed to promote crop growth, mitigate odor emission, and promote methane oxidation in field soils. However, previous studies showed that soil-gas permeability was increased upon biochar application, which will promote landfill gas emission. The objective of the present study is to investigate the possibility of using compacted BAC as an alternative material in landfill final cover by evaluating its gas permeability. BAC samples were prepared by mixing 425-μm-sieved peanut shell biochar with kaolin clay in different ratios (0, 5, 10, and 15 %, w/w) and compacting at different degrees of compactions (DOC) (80, 85, and 90 %) with an optimum water content of 35 %. The gas permeability of the BACs was measured by flexible wall gas permeameter and the microstructure of the BACs was analyzed by SEM with energy-dispersive x-ray spectroscopy (EDX). The results show that the effects of biochar content on BAC gas permeability is highly dependent on the DOC. At high DOC (90 %), the gas permeability of BAC decreases with increasing biochar content due to the combined effect of the clay aggregation and the inhibition of biochar in the gas flow. However, at low DOC (80 %), biochar incorporation has no effects on gas permeability because it no longer acts as a filling material to the retard gas flow. The results from the present study imply that compacted BAC can be used as an alternative final cover material with decreased gas permeability when compared with clay.     

Effects of 4-methylbenzylidene camphor (4-MBC) on neuronal and muscular development in zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>) embryos

The negative effects of overexposure to ultraviolet (UV) radiation in humans, including sunburn and light-induced cellular injury, are of increasing public concern. 4-Methylbenzylidene camphor (4-MBC), an organic chemical UV filter, is an active ingredient in sunscreen products. To date, little information is available about its neurotoxicity during early vertebrate development. Zebrafish embryos were exposed to various concentrations of 4-MBC in embryo medium for 3 days. In this study, a high concentration of 4-MBC, which is not being expected at the current environmental concentrations in the environment, was used for the purpose of phenotypic screening. Embryos exposed to 15 μM of 4-MBC displayed abnormal axial curvature and exhibited impaired motility. Exposure effects were found to be greatest during the segmentation period, when somite formation and innervation occur. Immunostaining of the muscle and axon markers F59, znp1, and zn5 revealed that 4-MBC exposure leads to a disorganized pattern of slow muscle fibers and axon pathfinding errors during the innervation of both primary and secondary motor neurons. Our results also showed reduction in AChE activity upon 4-MBC exposure both in vivo in the embryos (15 μM) and in vitro in mammalian Neuro-2A cells (0.1 μM), providing a possible mechanism for 4-MBC-induced muscular and neuronal defects. Taken together, our results have shown that 4-MBC is a teratogen and influences muscular and neuronal development, which may result in developmental defects.     

Remediation of a nonachloro biphenyl congener with zero-valent iron in subcritical water

Dechlorination of a nonachloro biphenyl congener with zero-valent iron in water under high temperature and pressure was investigated over time. Temperature has the main influence on the speed of dechlorination. Determination of polychlorinated biphenyls (PCBs) according to the grade of chlorination was performed by gas chromatography with mass selective detection in single ion monitoring mode. Dechlorination results in a variety of lower chlorinated biphenyls. The level of chlorination decreases with time. The amount of PCB molecules decreases to one-third within 90 min at 250 degrees C and 100 atm. However, no increase of biphenyl could be detected over time. A first-order kinetic model fitted the data obtained.     

Supercritical fluid extraction of polycyclic aromatic hydrocarbons from white pine (Pinus strobus) needles and its implications

A supercritical fluid extraction (SFE) method was developed for the extraction of polycyclic aromatic hydrocarbons (PAHs) from fresh and fallen pine needles. Toluene-modified CO2 was used as the extracting fluid, and the extracted PAHs were analyzed by GC-MS. Using a two-stage extraction procedure, a static extraction at 180 degrees C and a dynamic extraction at 60 degrees C, and an in-cell silica gel plug plus a post-oven silica gel column, the extraction and fractionation of PAHs can be accomplished in one step. Over a seven month period, a significant variation was observed for PAHs in urban samples, while PAHs in mountain samples were at much lower levels (by a factor of approximately 8) and showed little seasonal change. Although dry fallen needles and fresh needles contained similar amounts of PAHs, in the fallen needles the lower molecular weight PAHs were partially lost while the higher molecular weight PAHs were slightly enriched. Pollution in urban areas was found to be highly localized, and buildings and trees are believed to be important factors in the restriction of atmospheric PAHs.     

Paper fibers as a carbon source for the de novo formation of polychlorinated dioxins and furans

The formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) from carbon that was produced by the pyrolysis of paper fibers and from wood charcoal was investigated experimentally. Fibers obtained from filter paper were pyrolyzed at 300° and 800°C to produce low- and high-temperature carbon samples. The two types of carbon and wood charcoal were mixed with silica (SiO₂) and trace copper oxide to produce three synthetic fly ash samples. Experiments to measure the formation of PCCDs/Fs from the three ash samples were conducted using a bench-scale reactor. The two carbon samples derived from paper fibers generated more PCDDs/Fs than was generated by the wood charcoal. The PCDDs/Fs generated by the low-temperature carbon and by the wood charcoal were dominated by the lower-chlorinated PCDFs. Such unique homologue distribution patterns are very similar to those generated by the open burning of household waste. The high-temperature carbon generated more highly chlorinated PCDDs/Fs. The effect of pyrolysis temperature on the de novo formation of PCDDs/Fs from residual carbon is discussed. Paper and paper products contained in household waste are likely to be the source of unburned carbon that contributes to high PCDD/F emissions in the open burning of household waste.     

Sorption equilibria of metal ions on bone char

The ability of bone char to adsorb three metal ions, namely, copper(II), zinc(II) and cadmium(II) ions from wastewater has been studied. Three single-component equilibrium systems and three binary equilibrium systems have been measured experimentally. The three single-component equilibrium data were analyzed using the Langmuir and the Sips equilibrium isotherm equations. The Sips isotherm gave a better fit of the experimental data than the Langmuir isotherm based on the sum of squares errors (SSE) analysis. The Cu-Zn, Cu-Cd and Cd-Zn binary equilibrium experimental data were examined by incorporating the Langmuir and the Sips isotherm equations into the ideal adsorbed solution theory (IAST). The solution methods and the predicted results for the three binary systems at different metal ion compositions have been evaluated. In addition, the application of the IAST to the model prediction for the fixed bed system is presented.     

城市降雨径流模型的参数局部灵敏度分析

运用Morris筛选法对城市降雨径流模型SWMM的水文水力模块的相关参数进行局部灵敏度分析,以便对模型灵敏参数识别和不确定性分析.结果表明,影响3场降雨径流深的最灵敏度参数均为不透水率,灵敏度分别是0.88,0.98和0.43.影响峰值流量的灵敏参数因不同雨强的降雨场次存在波动,雨强最大的降雨最灵敏参数为管道曼宁糙率,雨强最小的降雨最灵敏参数为无低洼地不透水区所占百分比.不同降雨强度SWMM模型水文水力模块的灵敏参数有所差异,尤其是下渗率相关的参数.