谷壳灰对稻田土壤镉、砷生物有效性及糙米镉、砷累积的影响

为研究富硅材料谷壳灰（HA）对稻田土壤Cd、As生物有效性及糙米中Cd、As累积的影响,以稻壳为原料制备中性HA（总硅量6.26×10⁵ mg·kg^-1）,开展水稻盆栽试验.HA按质量比设置4个添加水平（0、0.5%、1%、2%）,种植3种水稻（黄华占、湘晚籼13、隆优4945）.研究结果表明：①在土壤Cd总量为2.30 mg·kg^-1、As总量为90.45 mg·kg^-1的复合污染土壤中,HA施用后,与对照相比,土壤Cd的TCLP提取态、CaCl₂提取态及酸可提取态含量呈现不同程度的降低,分别降低了7.8%~18.7%、7.4%~18.7%、0.9%~16.7%;土壤As的交换态和TCLP提取态含量也有降低,分别降低了6.1%~47.1%、4.3%~26.7%.②HA施用可促进土壤中酸可提取态Cd向难溶态Cd的转变,水稻湘晚籼13、隆优4945根际土壤残渣态Cd含量分别增大9.8%~23.5%、5.9%~28.1%;土壤中As主要以残渣态存在,HA的施用对土壤专性吸附As含量有增大效应.③HA施用能够降低糙米中Cd和无机As含量,施用0.5%~2% HA能使水稻隆优4945和湘晚籼13糙米Cd含量降低到0.2 mg·kg^-1以下,施用2% HA能使黄华占糙米无机As含量降低到0.2 mg·kg^-1以下.施用HA能够有效降低土壤Cd、As生物有效性和糙米Cd、As含量,同时增大土壤有效Si含量,有利于提高土壤质量.     

施加盐基离子调控水稻Cd的吸收与累积

盐基离子含量是土壤肥力的重要指标,也是决定土壤Cd生物有效性的重要因素.为探明盐基离子对稻田系统中Cd迁移、转运与累积的影响,本研究通过水稻盆栽试验,按照土壤中盐基离子的物质的量比施加不同浓度梯度KCl、CaCl_2、NaCl和MgCl_2到模拟制备的轻度(0.5 mg·kg~(-1))和中度(1.5 mg·kg~(-1))Cd污染土壤,分析盐基离子对土壤CaCl_2提取态Cd含量和水稻吸收累积Cd的影响.结果表明:施加盐基离子能够增加土壤阳离子交换量(CEC),在轻度和中度Cd污染土壤中,土壤CaCl_2提取态Cd含量分别下降了24.6%～56.1%和17.0%～71.1%,糙米Cd含量分别降低了9.1%～60.5%和7.2%～36.0%.在轻度和中度Cd污染土壤中,糙米Cd含量与土壤CaCl_2提取态Cd含量之间存在线性正相关关系,根、茎、叶Cd含量与Ca含量均呈线性负相关.     

黑龙江省秸秆露天焚烧污染物排放清单及时空分布

以黑龙江省为例,采用排放因子法计算了2016年秸秆露天焚烧污染物排放清单,分析了污染物的时空分布特征.结果表明,黑龙江省秸秆露天焚烧各污染物排放量为：CO₂ 1314.09万t、CO 41.92万t、CH₄ 3.77万t、NMVOCs 8.35万t、NH₃ 0.65万t、BC 0.44万t、OC 3.13万t、SO₂ 0.50万t、NO_X 3.28万t、PM₁₀ 8.81万t、PM_2.5 10.14万t.在95%的置信区间确定了排放清单的不确定性,不确定性范围为NO_X的±86%的低值到CO的±187%的高值.通过可靠性分析推断,本文的排放清单是合理的.玉米和水稻秸秆露天焚烧对同种大气污染物的贡献高于其他作物秸秆.大气污染物排放高值区位于黑龙江省西部和东部,污染物排放的时段在全年范围内具有明显的双峰特征.秸秆露天焚烧率的下降能有效促进大气污染物的减排,且农垦地区集约化和规模化的管理模式能有效控制秸秆露天焚烧.     

The mixing and segregation characteristics of rice straw in a cylindrical bubbling fluidized bed

In the present study, an experiment was performed to investigate the mixing and segregation characteristics of standard sand and rice straw particles in a cylindrical bubbling fluidized bed. The mass ratio (rice straw/standard sand = 0.5–1.25 %) of two particles and superficial gas velocity (0.13–0.18 m/s) were changed as experimental variables. The pressure drop curve and Kramer’s equation were used to determine the minimum fluidization velocity and mixing index, respectively. In all cases, the mixing index was the lowest at U/U _mf = 1.15. Based on the point of U/U _mf = 1.15, the segregation region and mixing region were observed. In the segregation region, mass ratio of 0.75 % showed the lowest mixing index. At the U/U _mf = 1.23 which was selected as the starting of fast pyrolysis considering residence time and the previous fast pyrolysis experiment, mass ratio of 1.25 % showed the highest mixing index which was 0.90.     

Prevention of surgical site infection under different ventilation systems in operating room environment

• The effectiveness of four different ventilation systems was compared in depth. • Airflow and bacteria-carrying particles concentration were quantitatively analyzed. • Vertical laminar airflow with high airflow rate could not achieve desired effect. • Temperature-controlled airflow ventilation could guarantee air cleanliness. Biological particles in the operating room (OR) air environment can cause surgical site infections (SSIs). Various ventilation systems have been employed in ORs to ensure an ultraclean environment. However, the effect of different ventilation systems on the control of bacteria-carrying particles (BCPs) released from the surgical staff during surgery is unclear. In this study, the performance of four different ventilation systems (vertical laminar airflow ventilation (VLAF), horizontal laminar airflow ventilation (HLAF), differential vertical airflow ventilation (DVAF), and temperature-controlled airflow ventilation (TAF)) used in an OR was evaluated and compared based on the spatial BCP concentration. The airflow field in the OR was solved by the Renormalization Group (RNG) k-e turbulence model, and the BCP phase was calculated by Lagrangian particle tracking (LPT) and the discrete random walk (DRW) model. It was found that the TAF system was the most effective ventilation system among the four ventilation systems for ensuring air cleanliness in the operating area. This study also indicated that air cleanliness in the operating area depended not only on the airflow rate of the ventilation system but also on the airflow distribution, which was greatly affected by obstacles such as surgical lamps and surgical staff.     

柠檬酸淋洗去除土壤中铬的实验研究

铬渣污染场地常常对其周边的土壤及地下水造成严重污染,因此,亟需探索修复铬污染土壤及地下水的技术方法.本文以某典型铬渣堆存场地内采集的污染土壤为研究对象,配置了浓度分别为0.01、0.05和0.1 mol·L-1的柠檬酸溶液,通过振荡洗脱批实验和淋洗柱实验对柠檬酸去除土壤中铬的效果和机理进行探讨.实验结果表明,柠檬酸对土壤中可还原态与可氧化态铬的淋洗效果显著优于去离子水,其对土壤中总铬的淋洗率可达80.7%,而去离子水仅为49.9%;在振荡洗脱批实验初期,土壤中50%左右的铬可以快速扩散到溶液中,且不同淋洗剂间淋洗效果无显著差异;柠檬酸的存在,使得反应体系中的六价铬逐渐被还原为三价铬,且还原速率随柠檬酸浓度的升高而增大;p H并非影响柠檬酸去除土壤中铬效果的唯一主要因素,柠檬酸对土壤中铬的去除机制还缘于其对土壤中三价铬的解吸作用.     

天然沸石中离子交换平衡的离子特异性研究

沸石在改良土壤和保护环境等方面有着广泛的应用,研究沸石离子交换中的特异性效应对更好地利用沸石有着重要意义.碱金属离子在天然斜发沸石中的交换平衡时的最大吸附量存在着明显的特异性效应;对于同价的碱金属离子,其交换吸附能力差异随着离子浓度的降低而增大.这种实验现象不能用库仑力、离子体积、水合作用、色散力、经典诱导力以及表面络合等相关理论进行完整解释.分析发现,根本原因来自离子因量子涨落而产生的极化与沸石颗粒表面电荷产生的强电场之间的相互作用,这种相互作用导致了离子间偶极矩差异随着表面电位的升高而增大,进而使离子-表面吸附能差异增大,并出现不同的交换吸附能力.由于沸石表面电荷密度较高,离子体积效应对其在双电层中的分布也起着比较重要的作用,导致碱金属离子在沸石表面的交换平衡结果在高表面电位(绝对值大于0.2 V)下才表现出较大选择性,与低电荷密度表面上的交换平衡结果存在一定差异.     

组配改良剂对土壤-蔬菜系统铅镉转运调控的场地研究

以组配改良剂LS(石灰石∶海泡石=2∶1)为试验材料,通过对湘南某矿区附近铅镉复合污染旱地土壤进行现场改良钝化,研究施加不同量的LS(0、2、4、8 g·kg-1)对茄子和苋菜植株吸收累积Pb和Cd的影响以及对Pb和Cd在2种蔬菜植株各部位间转运的调控.结果表明:1施加LS能够显著提高土壤p H,降低土壤中交换态Pb和Cd的含量.2施加LS能显著降低2种蔬菜植株各部位中Pb和Cd的含量.LS施加量为2~8 g·kg-1时,茄子果实中Pb和Cd的含量分别降低44.7%~78.6%和36.0%~78.7%;苋菜植株茎叶中Pb和Cd的含量分别降低45.8%~59.1%和40.0%~87.2%.3LS的施加降低了2种蔬菜植株各部位间Pb和Cd的转运系数.2种蔬菜植株在根-茎-果实间或根-茎叶间转运Cd的能力大于Pb,且施加LS各处理下,同种蔬菜相同部位对Pb和Cd的转运能力大小关系保持不变.