Simulation of phytoremediation of a TNT-contaminated soil using the CTSPAC model

Knowledge of water movement in the plant-xylem system and contaminant bioavailability in the soil environment is crucial to evaluate the success of phytoremediation practices. This study investigated the removal of 2,4,6-trinitrotoluene (TNT) from a contaminated sandy soil by a single poplar (Populus fastigiata) tree through the examinations of temporal variations of xylem water potential, root water uptake, and soil TNT bioavailability. A mathematical model, CTSPAC (Coupled Transport of water, heat, and solutes in the Soil-Plant-Atmosphere Continuum), was modified for the purpose of this study. The model was calibrated using laboratory measurements before its application. Our simulations show that the xylem water potential was high in the roots and low in the leaves with a potential head difference of 3.55 cm H2O, which created a driving force for water flow and chemical transport upward from the roots through the stem to the leaves. The daily average root water uptake rate was 25 cm3 h(-1) when an equilibrium condition was reached after 24 h. Our simulations further reveal that no TNT was found in the stem and leaves and only about 1% of total TNT mass was observed in the roots due to the rapid biodegradation and transformation of TNT into its daughter products. About 13% of the soil TNT was removed by the poplar tree, resulting mainly from root uptake since TNT is a recalcitrant compound. In general, the soil TNT bioavailability decreased with time due to the depletion of soil solution TNT by the poplar tree. A constant bioavailability (i.e., 3.1 x 10(-6)) was obtained in 14 d in which the soil TNT concentration was about 10 mg L(-1). Our study suggests that CTSPAC is a useful model to simulate phytoremediation of TNT-contaminated sites.     

THREE‐DIMENSIONAL KRIGING ANALYSIS OF SEDIMENT MERCURY DISTRIBUTION: A CASE STUDY1

ABSTRACT: This study presents an application of a three‐dimensional kriging technique to estimate spatial distribution of total mercury (Hg) in the Cedar‐Ortega Rivers watershed located in the lower St. Johns River basin, Florida. The kriging procedures, including preliminary data analysis, structural data analysis and the log kriging estimation, are presented. Results show watershed wide Hg contamination of river sediment to a depth of 1.0 m. A three‐dimensional plot of Hg against the Florida Sediment Assessment Guidelines (i.e., the probable effect level or PEL) demonstrates that the Cedar River is more contaminated with Hg than the rest of the watershed. The maximum sediment depth with Hg concentrations above PEL value (0.696 mg/kg) is 1.5 m. Hg concentrations at or above this level could pose a significant hazard to aquatic organisms. Analysis of the spatial distribution of Hg in the watershed finds multiple input sources. This study suggests that there is a need to identify the major sources of Hg in the watershed, and to determine the pathways that allow Hg to enter the river.     

Study of chest injuries to 3-year-old child occupants seated in impact shield and 5-point harness CRSs

Objective: The objective of this study was to investigate whether the 5-point harness or the impact shield child restraint system (CRS) or both have the potential to cause chest injuries to children. This is determined by examining whether the loading to the chest reaches the internal organ injury threshold for children.

Method: The chest injury risk to a child occupant in a CRS was investigated using Q3 dummy tests, finite element (FE) simulations (Q3 dummy and human models), and animal tests. The investigation was done for 2 types of CRSs (i.e., the impact shield CRS and 5-point harness CRS) based on the UN R44 dynamic test specifications.

Results: The tests using a Q3 dummy indicated that although the chest deflection of the dummy in the impact shield CRS was large, it was less than the injury threshold (40 mm). Computational biomechanics simulations (using finite element FE analysis) showed that the Q3 dummy's chest is loaded by the shield and deforms substantially under this load. To clarify whether chest injuries due to chest compression can occur with an impact shield or with the 5-point harness CRS, 7 experiments were performed using Tibetan miniature pigs with weights ranging from 9.7 to 13 kg. Severe chest and abdominal injuries (lung contusion, coronary artery laceration, liver laceration) were found in the tests using the impact shield CRS. No chest injuries were present when using the 5-point harness CRS.

Conclusion: When using the impact shield CRS, the chest deformed substantially in dummy tests and FE simulations, and chest and abdominal injuries were observed in pig tests. It is possible that these chest injuries could also occur to child occupants sitting in the impact shield CRS.     

Effects of Land Use Changes on the Ecosystem Service Values of a Reclamation Farm in Northeast China

Intensive agricultural development can change land use, which can further affect regional ecosystem services and functions. With the rapid growth of the population and the national demand for food, the northeast of China, which is located in the high latitudes, has experienced four agricultural developments since the 1950s. The original wetlands of this area were developed for farmland. The evaluation of ecosystem services is conducted to reveal the ecosystem status and variable trends caused by land reclamation. The aim of this study is to provide scientific basis for environmental management and for the sustainable development of agriculture in Northeast China. With GIS-RS technology, a typical farm was chosen to analyze variations in the ecosystem service value in response to land use changes during the study period. The total ecosystem service value of the farm decreased from 7523.10 million Yuan in 1979 to 4023.59 million Yuan in 2009 with an annual rate of ?1.6?% due to the decreasing areas of woodland and wetland. The increased areas of cropland, water area and grassland partly offset the loss of the total value, but the loss was still greater than the compensation. Waste treatment and climate regulation were the top two service functions with high service values, contributing to approximately 50?% of the total service value. The spatial difference of the ecosystem service value also was analyzed. The wetlands located in the central and northeastern sections of the farm changed significantly. From the aspect of ecosystem service value, the wetland and water area should be conserved, as they have the highest value coefficients. The accuracy of the value coefficient, however, needs to be studied further in future research.     

改良型A2／O-MBR工艺的反硝化除磷性能研究

重点考察了-种改良型膜生物反应器（A2／O—MBR）的脱氮除磷性能。该工艺主要特点在于对膜池硝化回流液进行了固液分离,并将上清液和浓缩污泥分别回流至缺氧池和厌氧池,这种改进提高了系统对氮、磷的同步去除效率。实验结果表明,在水力停留时间（HRT）为12h,污泥龄（SRT）为30d,混合液回流比为200％的运行条件下,进水COD、NH4＋-N、TN和TP平均浓度分别为（225±38）、（24．8±3．9）、（26．7±2．9）和（2．90±0．53）mg／L时,增加膜池硝化回流液固液分离装置前后,系统对COD和NH4＋-N的去除都维持在较高水平,而系统对TN和TP的去除效果显著提高,出水TN和TP平均浓度分别由（14．9±3．3）mg／L和（1．95±0．72）mg／L下降到（9．4±1．9）mg／L和（0．91±0．38）mg／L,表明增加膜池硝化回流液固液分离装置显著改善了A2／O-MBR系统的脱氮除磷效果。反硝化除磷活性实验结果进一步表明,改进后系统中反硝化除磷活性占总除磷活性的比例由51．5％上升至61．7％,说明增加膜池硝化回流液固液分离装置强化了系统的反硝化除磷性能。     

Organochlorine pesticides in the dust fall around Lake Chaohu, the fifth largest lake in China

The residual levels of organochlorine pesticides (OCPs) in the dust fall around Lake Chaohu were measured using gas chromatography mass spectrometry from April 2010 to March 2011. The fluxes, components, temporal–spatial variations, and sources of OCPs were also analyzed. Twenty-one types of OCPs were detected in the dust fall samples around Lake Chaohu, with a total concentration of 51.54?±?36.31 ng/g and a total flux of 10.01?±?13.69 ng/(m² day). Aldrin (35.3 %), endosulfan (39.1 %), dichlorodiphenyltrichloroethanes (DDTs) (49.8 %), and isodrin (37.1 %) were the major OCPs in the spring, summer, autumn, and winter, respectively. Both the residual level and the flux were higher in the spring than in other seasons and higher at the outer lake sampling sites than inner lake sampling site. The potential source of the hexachlorcyclohexanes in the dust fall may be recent lindane usage. The DDTs mainly came from historical dicofol usage, and a significant input of DDT was found during April and June. The presence of endosulfan may be due to the present use of technical endosulfan. The aldrin in the dust might be due to its occasional usage, and isodrin may be a result of long-distance transport from other countries.     

生物表面活性剂在城市污泥静态强制通风好氧堆肥中的作用

采用静态强制通风好氧堆肥模式对城市剩余污泥进行堆肥降解,并研究了生物表面活性剂鼠李糖脂对堆肥过程的作用。结果表明,堆肥过程中,添加了质量分数为0.015%鼠李糖脂溶液堆制处理和空白对照堆制处理的堆温变化都明显呈现出中温期0～5 d、高温期6～12 d和降温期13～28 d 3个阶段。实验组比空白组的堆体升温快、高温期持续时间长、堆体的含水率高。鼠李糖脂的添加,使实验组的微生物数量高于空白组。添加鼠李糖脂的堆体和空白堆体的种子发芽指数(GI)在堆肥结束时分别为53.70%和50.80%,说明鼠李糖脂促进了堆肥的腐熟,但由于相对浓缩效应,堆肥产品的重金属含量略高于空白堆体。生物表面活性剂的介入促进了堆肥中木质纤维素的初步降解。研究表明,添加鼠李糖脂能够改善堆肥处理的微环境,促进有机质降解和堆肥的腐熟。     

Cr(VI) uptake mechanism of Bacillus cereus

In this study, we investigated the Cr(VI) uptake mechanism in an indigenous Cr(VI)-tolerant bacterial strain -Bacillus cereus through batch and microscopic experiments. We found that both the cells and the supernatant collected from B. cereus cultivation could reduce Cr(VI). The valence state analysis revealed the complete transformation from Cr(VI) into Cr(III) by living B. cereus. Further X-ray absorption fine structure and Fourier transform infrared analyses showed that the reduced Cr(III) was coordinated with carboxyl and amido functional groups from either the cells or supernatant. Scanning electron microscopy and atomic force microscopy observation showed that noticeable Cr(III) precipitates were accumulated on bacterial surfaces. However, Cr(III) could also be detected in bacterial inner portions by using transmission electron microscopy thin section analysis coupled with energy dispersive X-ray spectroscopy. Through quantitative analysis of chromium distribution, we determined the binding ratio of Cr(III) in supernatant, cell debris and cytoplasm as 22%, 54% and 24%, respectively. Finally, we further discussed the role of bacterium-origin soluble organic molecules to the remediation of Cr(VI) pollutants.     

Water, heat, and airborne pollutants effects on transpiration of urban trees

Transpiration rates of six urban tree species in Beijing evaluated by thermal dissipation method for one year were correlated to environmental variables in heat, water, and pollutant groups. To sort out colinearity of the explanatory variables, their individual and joint contributions to variance of tree transpiration were determined by the variation and hierarchical partitioning methods. Majority of the variance in transpiration rates was associated with joint effects of variables in heat and water groups and variance due to individual effects of explanatory group were in comparison small. Atmospheric pollutants exerted only minor effects on tree transpiration. Daily transpiration rate was most affected by air temperature, soil temperature, total radiation, vapor pressure deficit, and ozone. Relative humidity would replace soil temperature when factors influencing hourly transpiration rate was considered.     

Stormwater runoff quality from different surfaces in an urban catchment in Beijing, China

Urban stormwater runoff quality, widely investigated around the world, has been monitored less in Beijing, China, which impedes the municipal government to use best management practices to protect surface water. In this study, rainwater and stormwater runoff samples from roofs, roads, and a lawn on the campus of the Research Center for Eco-Environmental Sciences (RCEES) (Beijing, China) and from a ring road, with heavy traffic, have been sampled and analyzed for 31 storm events from June 2004 to August 2005. Total suspended solids (TSS), chemical oxygen demand (COD), 5-day biochemical oxygen demand (BOD5), total nitrogen, and total phosphorus concentrations in rainwater and runoff ranged over 2 or more orders of magnitude, meaning that the highest concentration of a certain pollutant did not always occur in a certain kind of runoff. Runoff contained significantly higher concentrations of pollutants than rainwater. On the campus of RCEES, TSS and total phosphorus in runoff samples from the lawn and roads were significantly higher than those from roofs, while the COD, BOD5, and total nitrogen concentrations were not significantly different in runoff among surfaces. Compared with runoff from the roads on campus, runoff from the ring road contained more COD and total nitrogen, but less TSS, BOD5, and total phosphorus. All pollutants measured in runoff from roofs on campus and from the ring road showed a peak concentration in starting runoff, which then decreased sharply. The peak concentrations of COD, BOD5, total nitrogen, and total phosphorus in the roof runoff increased with the increase in time of the antecedent dry period. Thus, urban stormwater pollution control, especially for first-flush control, is of great importance for the full use of rainwater and prevention of water pollution.