Diffusion of tritiated water and Na through non-degraded hardened cement pastes

Diffusion experiments through hardened cement pastes (HCP) using tritiated water (HTO) and ²²Na⁺, considered to be conservative tracers, have been carried out in triplicates in a glove box under a controlled nitrogen atmosphere. Each experiment consisted of a through-diffusion test followed by an out-diffusion test.The experimental data were inversely modelled applying an automated Marquardt–Levenberg procedure. The analysis of the through-diffusion data allowed the extraction of values for the effective diffusion coefficients, D_e, and the rock capacity factor, α. Good agreement between measured and calculated tracer breakthrough curves was achieved using both a simple diffusion model without sorption and a diffusion/linear sorption model. The best-fit K_d-values were found to be consistent with R_d-values measured in previous batch-sorption experiments.The best-fit values from the through-diffusion tests were then used to predict the results of subsequent out-diffusion experiments. Good agreement between experimental data and predictions was achieved only for the case of linear sorption.Isotopic exchange can only partially account for both the amount of tracer taken up in the batch-sorption tests and the measured retardation in the diffusion experiments and, hence, additional mechanisms have to be invoked to explain the data.     

Perchlorate as an environmental contaminant

Perchlorate anion (ClO4-) has been found in drinking water supplies throughout the southwestern United States. It is primarily associated with releases of ammonium perchlorate by defense contractors, military operations, and aerospace programs. Ammonium perchlorate is used as a solid oxidant in missile and rocket propulsion systems. Traces of perchlorate are found in Chile saltpeter, but the use of such fertilizer has not been associated with large scale contamination. Although it is a strong oxidant, perchlorate anion is very persistent in the environment due to the high activation energy associated with its reduction. At high enough concentrations, perchlorate can affect thyroid gland functions, where it is mistakenly taken up in place of iodide. A safe daily exposure has not yet been set, but is expected to be released in 2002. Perchlorate is measured in environmental samples primarily by ion chromatography. It can be removed by anion exchange or membrane filtration. It is destroyed by some biological and chemical processes. The environmental occurrence, toxicity, analytical chemistry, and remediative approaches are discussed.     

Leaf age affects the responses of foliar injury and gas exchange to tropospheric ozone in Prunus serotina seedlings

We investigated the effect of leaf age on the response of net photosynthesis (A), stomatal conductance (g_wv), foliar injury, and leaf nitrogen concentration (N_L) to tropospheric ozone (O₃) on Prunus serotina seedlings grown in open-plots (AA) and open-top chambers, supplied with either carbon-filtered or non-filtered air. We found significant variation in A, g_wv, foliar injury, and N_L (P < 0.05) among O₃ treatments. Seedlings in AA showed the highest A and g_wv due to relatively low vapor pressure deficit (VPD). Older leaves showed significantly lower A, g_wv, N_L, and higher foliar injury (P < 0.001) than younger leaves. Leaf age affected the response of A, g_wv, and foliar injury to O₃. Both VPD and N_L had a strong influence on leaf gas exchange. Foliar O₃-induced injury appeared when cumulative O₃ uptake reached 8-12 mmol m⁻², depending on soil water availability. The mechanistic assessment of O₃-induced injury is a valuable approach for a biologically relevant O₃ risk assessment for forest trees.     

水力停留时间对阴离子交换膜生物反应器去除硝酸盐的影响

考察了水力停留时间(HRT)对阴离子交换膜生物反应器去除硝酸盐的影响。实验结果表明,当进水NO3-浓度在113.96~116.01 mg/L范围内,HRT从11.12 h降低到4.82 h,硝酸盐去除率降低,但出水中NO3--N浓度符合我国饮用水水质标准中10 mg/L的要求(NO3-浓度≤44.29 mg/L)。厌氧生物反应器具有良好的反硝化性能,出水NO3-浓度低于20 mg/L。硝酸盐膜通量随着HRT的增加而增加,出水pH值稳定在7左右。     

垂直厌氧折流板反应器处理树脂废水的中试研究

介绍了采用垂直厌氧折流板反应器(VABR)处理离子交换树脂生产废水的中试实验装置以及实验研究过程,并着重分析了COD容积负荷和盐分对COD的去除率及出水VFA的影响,并确定了该废水的厌氧产沼气率。研究结果表明,在中温(37±1℃)环境下,容积负荷在9 kg COD/(m3.d)左右时,HRT为24 h的条件下,VABR对COD的平均去除率保持在70%左右,平均每去除1 kg COD约产生沼气0.44 m3,且运行稳定。     

Environmental Services Provided from Riparian Forests in the Nordic Countries

Riparian forests (RF) growing along streams, rivers and lakes comprise more than 2% of the forest area in the Nordic countries (considering a 10 m wide zone from the water body). They have special ecological functions in the landscape. They receive water and nutrients from the upslope areas, are important habitats for biodiversity, have large soil carbon stores, but may emit more greenhouse gases (GHG) than the uplands. In this article, we present a review of the environmental services related to water protection, terrestrial biodiversity, carbon storage and greenhouse gas dynamics provided by RF in the Nordic countries. We discuss the benefits and trade-offs when leaving the RF as a buffer against the impacts from upland forest management, in particular the impacts of clear cutting. Forest buffers are effective in protecting water quality and aquatic life, and have positive effects on terrestrial biodiversity, particularly when broader than 40 m, whereas the effect on the greenhouse gas exchange is unclear.     

Carbon exchange between ecosystems and atmosphere in the Czech Republic is affected by climate factors

By comparing five ecosystem types in the Czech Republic over several years, we recorded the highest carbon sequestration potential in an evergreen Norway spruce forest (100%) and an agroecosystem (65%), followed by European beech forest (25%) and a wetland ecosystem (20%). Because of a massive ecosystem respiration, the final carbon gain of the grassland was negative. Climate was shown to be an important factor of carbon uptake by ecosystems: by varying the growing season length (a 22-d longer season in 2005 than in 2007 increased carbon sink by 13%) or by the effect of short- term synoptic situations (e.g. summer hot and dry days reduced net carbon storage by 58% relative to hot and wet days). Carbon uptake is strongly affected by the ontogeny and a production strategy which is demonstrated by the comparison of seasonal course of carbon uptake between coniferous (Norway spruce) and deciduous (European beech) stands.     

天然沸石颗粒对NH4^＋动态吸附过程中的离子交换特性研究

采用天然斜发沸石颗粒,进行了沸石吸附水溶液中NH4^＋的动态吸附实验研究。实验结果表明,沸石颗粒粒径、沸石床高度、上升流速、进水氨氮浓度、进水水质等因素对沸石颗粒吸附NH4^＋有着明显的影响,在工程实践应用时,要根据动态吸附实验结果选择合适的设计及运行参数。离子交换机理研究表明,Na^＋首先被交换出来,随着反应进行,Ca^2＋浓度逐渐增加,两者成为离子交换的主要对象。对于人工氨氮配水,整个运行期间金属阳离子液相增加量明显大于NH4^＋去除量,这与金属阳离子在固液两相间的再分配作用有关;对于厌氧工艺出水,在吸附初期,NH4^＋去除量大于金属阳离子液相增加量,随着反应进行,两者逐渐持平。     

Effects of black carbon on bioturbation-induced benthic fluxes of polychlorinated biphenyls

It is unknown whether carbonaceous geosorbents, such as black carbon (BC) affect bioturbation by benthic invertebrates, thereby possibly affecting sediment-water exchange of sediment-bound contaminants. Here, we assess the effects of oil soot on polychlorinated biphenyl (PCB) mass transfer from sediment to overlying water, for sediments with and without tubificid oligochaeta as bioturbators. PCB levels were so low that toxicity to the oligochaeta played no role, whereas soot levels and binding affinity of PCBs to soot were so low that pore water PCB concentrations were not significantly affected by binding of PCBs to soot. This setup left direct effects of BC on bioturbation activity as the only explanation for any observed effects on mass transfer. Mass transfer coefficients (K_L) for benthic boundary layer transport were measured by a novel flux method using Empore™ disks as a sink for PCBs in the overlying water. For the PCBs studied (logK_ow 5.2-8.2), K_L values ranged from 0.2 to 2 cm × d⁻¹ in systems without tubificids. Systems with tubificids showed K_L values that were a factor of 10-25 higher. However, in the presence of oil soot, tubificids did not cause an increase in mass transfer coefficients. This suggests that at BC levels as encountered under field conditions, the mechanism for reduction of sediment-water transfer of contaminants may be twofold: (a) reduced mass transfer due to strong binding of the contaminants to BC, and (b) reduced mass transfer of contaminants due to a decrease in bioturbation activity.     

大气汞的来源及其浓度分布特征研究进展

大气汞是全球性的污染物,其来源有自然源和人为源,亚洲地区是最大的人为大气汞排放源,占全球人为排汞量的67％(质量分数),其中又以中国为最.燃煤和有色金属冶炼对中国大气汞排放的贡献最大.环境界面的释汞通量是全球大气汞预算的重要组成部分,也是目前的研究热点之一.综述了不同环境界面的释汞通量及其影响因素,并比较了不同地区大气...