Novel pilot-scale washing process and equipment for removing Cr(VI) from contaminated soil

In this study, a novel horizontal rotating soil washing process and equipment were developed and tested for pilot-scale remediation of soils from a site polluted by chromium ore process residue. Operating parameters, including cylinder rotational velocity, cylinder tilt angle, heating temperature and liquid/soil ratio, were investigated. The Taguchi method was used for the experiment design, and the standard L16 orthogonal array with four parameters and four levels was selected for optimising the operating parameters. Optimal removal efficiency was achieved at cylinder rotational velocity of 2.5 rpm, cylinder tilt angle of 2.6°, heating temperature of 200 °C and liquid/soil ratio of 8. The efficiency of citric acid as an extractant in the novel process was compared with that of water. The analysis of the residual Cr(VI) concentration of the soil shows that citric acid could efficiently remove 22.89 % more Cr(VI) than water in one-stage washing. The residual Cr(VI) concentration in the soil after the three-stage washing is as low as 26.16 mg/kg, which meets the screening levels for soil environmental risk assessment of sites in Beijing City (30 mg/kg). Further study is currently underway to optimise the novel process and equipment for commercial-scale use.     

Enhanced removal of arsenic from a highly laden industrial effluent using a combined coprecipitation/nano-adsorption process

Effective arsenic removal from highly laden industrial wastewater is an important but challenging task. Here, a combined coprecipitation/nano-adsorption process, with ferric chloride and calcium chloride as coprecipitation agents and polymer-based nanocomposite as selective adsorbent, has been validated for arsenic removal from tungsten-smelting wastewater. On the basis of operating optimization, a binary FeCl₃ (520 mg/L)–CaCl₂ (300 mg/L) coprecipitation agent could remove more than 93 % arsenic from the wastewater. The resulting precipitate has proved environmental safety based on leaching toxicity test. Fixed-bed column packed with zirconium or ferric-oxide-loaded nanocomposite was employed for further elimination of arsenic in coprecipitated effluent, resulting in a significant decrease of arsenic (from 0.96 to less than 0.5 mg/L). The working capacity of zirconium-loaded nanocomposite was 220 bed volumes per run, much higher than that of ferric-loaded nanocomposite (40 bed volumes per run). The exhausted zirconium-loaded nanocomposite could be efficiently in situ regenerated with a binary NaOH–NaCl solution for reuse without any significant capacity loss. The results validated the combinational coprecipitation/nano-adsorption process to be a potential alternative for effective arsenic removal from highly laden industrial effluent.     

Field controlled experiments on the physiological responses of maize (Zea mays L.) leaves to low-level air and soil mercury exposures

Thousands of tons of mercury (Hg) are released from anthropogenic and natural sources to the atmosphere in a gaseous elemental form per year, yet little is known regarding the influence of airborne Hg on the physiological activities of plant leaves. In the present study, the effects of low-level air and soil Hg exposures on the gas exchange parameters of maize (Zea mays L.) leaves and their accumulation of Hg, proline, and malondialdehyde (MDA) were examined via field open-top chamber and Hg-enriched soil experiments, respectively. Low-level air Hg exposures (<50 ng m^?3) had little effects on the gas exchange parameters of maize leaves during most of the daytime (p?>?0.05). However, both the net photosynthesis rate and carboxylation efficiency of maize leaves exposed to 50 ng m^?3 air Hg were significantly lower than those exposed to 2 ng m^?3 air Hg in late morning (p?<?0.05). Additionally, the Hg, proline, and MDA concentrations in maize leaves exposed to 20 and 50 ng m^?3 air Hg were significantly higher than those exposed to 2 ng m^?3 air Hg (p?<?0.05). These results indicated that the increase in airborne Hg potentially damaged functional photosynthetic apparatus in plant leaves, inducing free proline accumulation and membrane lipid peroxidation. Due to minor translocation of soil Hg to the leaves, low-level soil Hg exposures (<1,000 ng g^?1) had no significant influences on the gas exchange parameters, or the Hg, proline, and MDA concentrations in maize leaves (p?>?0.05). Compared to soil Hg, airborne Hg easily caused physiological stress to plant leaves. The effects of increasing atmospheric Hg concentration on plant physiology should be of concern.     

在微生物燃料电池生物阴极实现硝化过程的试验研究

微生物燃料电池(MFCs)去除废水中有机物已经进行了大量研究,然而MFCs去除营养盐的能力较弱是将来产业化的障碍之一。研究了以铁锰氧化细菌为催化剂的生物阴极稳定产电的同时实现生物硝化反应的可行性以及其影响因素,并对生物阴极中的铁锰氧化细菌以及硝化细菌进行了计数。以铁锰氧化细菌为催化剂的生物阴极MFCs的启动时间为150～200h,运行稳定时,最高电压达600 mV。研究表明,该生物阴极在稳定产电的同时实现了生物硝化反应,其NO3--N的生成速率为0.792mg/(L.h),NO2--N最高质量浓度为1.56mg/L;阴极进水中NH4+-N以及DO浓度均是重要影响因素;对生物阴极中的铁锰氧化细菌以及硝化细菌计数结果表明,铁锰氧化细菌为7.5×106 MPN/mL,硝化细菌为9.3×105 MPN/mL。     

亚甲基蓝在污泥活性炭上的吸附

以剩余污泥为原料,氯化锌为活化剂制备污泥活性炭。研究了初始pH值、吸附温度及离子强度对污泥活性炭吸附亚甲基蓝效果的影响。采用高分辨电子扫描电镜(SEM)和氮吸脱附曲线对污泥活性炭进行了表征。结果表明,随着pH值的升高,吸附量增大,碱性条件下最好。在15～55℃的范围内,亚甲基蓝的吸附量先增加后降低,温度为35℃时吸附量达到最大值。加入氯化钠后的污泥活性炭的吸附能力变弱,但随着离子强度的增大,变弱的强度减少。污泥活性炭以中孔为主和污泥活性炭具有不规则结构,预示着污泥活性炭较高的吸附能力。污泥活性炭对亚甲基蓝的吸附符合Lang-muir等温吸附方程。污泥壳活性炭对亚甲基蓝的吸附符合二级反应动力学方程反应特征。     

Effect of biochar amendment on sorption and leaching of nitrate, ammonium, and phosphate in a sandy soil

When applied to soils, it is unclear whether and how biochar can affect soil nutrients. This has implications both to the availability of nutrients to plants or microbes, as well as to the question of whether biochar soil amendment may enhance or reduce the leaching of nutrients. In this work, a range of laboratory experiments were conducted to determine the effect of biochar amendment on sorption and leaching of nitrate, ammonium, and phosphate in a sandy soil. A total of thirteen biochars were tested in laboratory sorption experiments and most of them showed little/no ability to sorb nitrate or phosphate. However, nine biochars could remove ammonium from aqueous solution. Biochars made from Brazilian pepperwood and peanut hull at 600 °C (PH600 and BP600, respectively) were used in a column leaching experiment to assess their ability to hold nutrients in a sandy soil. The BP600 biochar effectively reduced the total amount of nitrate, ammonium, and phosphate in the leachates by 34.0%, 34.7%, and 20.6%, respectively, relative to the soil alone. The PH600 biochar also reduced the leaching of nitrate and ammonium by 34% and 14%, respectively, but caused additional phosphate release from the soil columns. These results indicate that the effect of biochar on the leaching of agricultural nutrients in soils is not uniform and varies by biochar and nutrient type. Therefore, the nutrient sorption characteristics of a biochar should be studied prior to its use in a particular soil amendment project.     

Cadmium-induced DNA damage and mutations in Arabidopsis plantlet shoots identified by DNA fingerprinting

Random amplified polymorphic DNA (RAPD) test is a feasible method to evaluate the toxicity of environmental pollutants on vegetal organisms. Herein, Arabidopsis thaliana (Arabidopsis) plantlets following Cadmium (Cd) treatment for 26 d were screened for DNA genetic alterations by DNA fingerprinting. Four primers amplified 20-23 mutated RAPD fragments in 0.125-3.0 mg L⁻¹ Cd-treated Arabidopsis plantlets, respectively. Cloning and sequencing analysis of eight randomly selected mutated fragments revealed 99-100% homology with the genes of VARICOSE-Related, SLEEPY1 F-box, 40S ribosomal protein S3, phosphoglucomutase, and noncoding regions in Arabidopsis genome correspondingly. The results show the ability of RAPD analysis to detect significant genetic alterations in Cd-exposed seedlings. Although the exact functional importance of the other mutated bands is unknown, the presence of mutated loci in Cd-treated seedlings, prior to the onset of significant physiological effects, suggests that these altered loci are the early events in Cd-treated Arabidopsis seedlings and would greatly improve environmental risk assessment.     

Effects of dissolved inorganic carbon and nutrient levels on carbon fixation and properties of Thermosynechococcus sp. in a continuous system

The concept of CO₂ chemo-absorption by sodium hydroxide in a wet scrubber followed by microalgae cultivation was used as a means to reduce the major greenhouse gas. A thermophilic and alkaline tolerable cyanobacterium named Thermosynechococcus CL-1 (TCL-1) was cultivated in continuous system, with a carbonate-bicarbonate buffer as carbon source. The effects of dissolved inorganic carbon (DIC_in) and nutrient levels in influent on cell mass productivity, DIC removal efficiency, and alkaline solution regeneration by TCL-1 were investigated. The results show the highest cell mass productivity reaches 1.7 g L⁻¹ d⁻¹ under the highest DIC and nutrients level. Conversely, the best regeneration of alkaline solution proceeds from pH 9.5 to 11.3 under the lowest level. In addition, the highest ΔDIC (DIC consumption) and DIC removal efficiency are 42 mM and 43% at 113.2 and 57 mM DIC_in, respectively.     

黄淮海地区干湿状况的时空分异研究

干旱作为自然灾害的一种,对人类社会、经济的发展构成严重威胁,如何准确的监测干旱的发生发展是开展抗旱减灾工作的关键.目前学者们多选用众多的指标来指示干旱,SPI标准降水指数作为其中的一种,是以更符合实际情况的Г分布概率来描述降水量的变化.其计算过程简单,具有较强的时空适应性,因而得到广泛应用.本文选取黄淮海平原区作为研究区域,以长时间尺度(本文选取12个月与36个月)的月值SPI来表征研究区域在1961-2000年这段历史时期内干湿状况的变化,从时间和空间两个角度研究长时间尺度的SPI值在指示地表干湿状况的效用,研究分析研究区域内干湿状况的时空分异,探索其成因,得出以下初步结论:研究区内2000年偏干旱的区域面积较1963年有所增大,与此同时,极端情况相对较少;除呼和浩特与郑州外,研究区域内有相当大面积的区域呈现偏干趋向,主要位于呼和浩特与郑州之间的大范围区域,推测区域的这种总体偏干旱的趋势可能是区域对全球变暖的响应.时间序列分析结果表明:在1961-2000年这段历史时期内呼和浩特与太原站出现的极端干旱的情况相对要多一些,北京次之,郑州最少;各站点的SPI值在时间序列上变化存在巨大差异,其主导因素是它们的纬度位置.     

Decrease in catalase activity of Folsomia candida fed a Bt rice diet

Here we report the effects of three Bt-rice varieties and their non-Bt conventional isolines on biological traits including survival, reproduction, and the activities of three antioxidant enzymes superoxide dismutase, catalase and peroxidase, in the Collembolan, Folsomia candida. The reproduction was significantly lower when fed Kemingdao and Huahui1 than those feeding on their non-GM near-isogenic varieties Xiushui and Minghui63 respectively, this can be explained by the differences of plant compositions depended on variety of rice. The catalase activity of F. candida was significantly lower when fed the Bt-rice variety Kemingdao compared to the near-isogenic non-Bt-rice variety Xiushui. This suggests that some Bt-rice varieties may impose environmental stress to collembolans. We emphasize that changes in activity of antioxidant enzymes of non-target organisms are important in understanding the ecological consequences for organisms inhabiting transgenic Bt-rice plantations.