Effect of temperature and particle size on the thermal desorption of PCBs from contaminated soil

Thermal desorption is widely used for remediation of soil contaminated with volatiles, such as solvents and distillates. In this study, a soil contaminated with semivolatile polychlorinated biphenyls (PCBs) was sampled at an interim storage point for waste PCB transformers and heated to temperatures from 300 to 600 °C in a flow of nitrogen to investigate the effect of temperature and particle size on thermal desorption. Two size fractions were tested: coarse soil of 420–841 μm and fine soil with particles <250 μm. A PCB removal efficiency of 98.0 % was attained after 1 h of thermal treatment at 600 °C. The residual amount of PCBs in this soil decreased with rising thermal treatment temperature while the amount transferred to the gas phase increased up to 550 °C; at 600 °C, destruction of PCBs became more obvious. At low temperature, the thermally treated soil still had a similar PCB homologue distribution as raw soil, indicating thermal desorption as a main mechanism in removal. Dechlorination and decomposition increasingly occurred at high temperature, since shifts in average chlorination level were observed, from 3.34 in the raw soil to 2.75 in soil treated at 600 °C. Fine soil particles showed higher removal efficiency and destruction efficiency than coarse particles, suggesting that desorption from coarse particles is influenced by mass transfer.     

Some technical issues in managing PCBs

Polychlorinated biphenyls (PCBs) were important industrial chemicals featuring high thermal and chemical stability and low flammability. They were widely used as dielectric and thermal fluid in closed electro-technical applications (transformers, capacitors…) and also in numerous dispersive uses, ranking from auto-copying paper to sealant or coatings. During the 1960s, severe environmental consequences started becoming apparent. The stability of PCBs contributed to their persistence in the environment, their lipophilic character to bio-magnification. Fish-eating species seemed threatened in their existence. In Japan and in Taiwan, thousands of people consumed PCB-contaminated oil. The production of PCBs stopped completely during the 1980s. Usage could continue in closed applications only. In this paper, particular attention is given to two issues: the cleaning of PCB electric transformers and the potential impact of PCB-containing building materials. Other contributions will cover the management and treatment of PCB-contaminated soil, sludge or fly ash. The complete survey is being prepared by request of the Knowledge Center for Engineers and Professionals.     

Planning of methane emission control from hoggery using an inexact two-stage optimization model

This study aims to develop an inexact two-stage optimization model to gather manure distributed over the southwest Taiwan and convert it into bioenergy. In the method, local optimization of each hauling zone is performed first using a gray mixed-integer programming model. Then, the hauling zones are prioritized by its performance on four gray scenarios. Although the biogas yield and the manure generation rate are ambiguous, one can easily evaluate his opportunity and risk by gray interval, which is a group of values within the lower and upper bounds. The analyses reveal that the biogas yield dominates the profit in this project, and it leads to the failure of the project when the biogas yield is below the level of 0.2 m³ kg^?1. With the goal of reducing 45% of methane emissions from pig farms, seven hauling zones are required to be developed. The farmers living in these zones from the project get carbon credits ranging from 478 to 3269 ton CO_2eq per year, and the investors own the carbon credits in the range of 3264–11820 ton CO_2eq per year. Through the carbon trading, both the investors and pig farmers are able to make profits by trading their carbon credits.

Implications:Biogas recovered from hoggery can be used as a bioenergy source and mitigate the atmospheric greenhouse effect and global warming. This research develops an inexact two-stage optimization model to evaluate the potential of gathering manure for biogas and converting it into bioenergy. The analyses reveal that the biogas yield dominates the profit in this project, and it leads to the failure of the project when the biogas yield is below the level of 0.2 m³ kg^?1. This study has provided a useful reference for the management of biogas production and carbon trading from hoggery for bioenergy.     

Effects of water-emulsified fuel on a diesel engine generator’s thermal efficiency and exhaust

Water-emulsified diesel has proven itself as a technically sufficient improvement fuel to improve diesel engine fuel combustion emissions and engine performance. However, it has seldom been used in light-duty diesel engines. Therefore, this paper focuses on an investigation into the thermal efficiency and pollution emission analysis of a light-duty diesel engine generator fueled with different water content emulsified diesel fuels (WD, including WD-0, WD-5, WD-10, and WD-15). In this study, nitric oxide, carbon monoxide, hydrocarbons, and carbon dioxide were analyzed by a vehicle emission gas analyzer, and the particle size and number concentration were measured by an electrical low-pressure impactor. In addition, engine loading and fuel consumption were also measured to calculate the thermal efficiency. Measurement results suggested that water-emulsified diesel was useful to improve the thermal efficiency and the exhaust emission of a diesel engine. Obviously, the thermal efficiency was increased about 1.2 to 19.9%. In addition, water-emulsified diesel leads to a significant reduction of nitric oxide emission (less by about 18.3 to 45.4%). However, the particle number concentration emission might be increased if the loading of the generator becomes lower than or equal to 1800 W. In addition, exhaust particle size distributions were shifted toward larger particles at high loading. The consequence of this research proposed that the water-emulsified diesel was useful to improve the engine performance and some of exhaust emissions, especially the NO emission reduction.

Implications:The accumulated test results provide a good basis to resolve the corresponding pollutants emitted from a light-duty diesel engine generator. By measuring and analyzing transforms of exhaust pollutant from this engine generator, the effects of water-emulsified diesel fuel and loading on emission characteristics might be more clear. Understanding reduction of pollutant emissions during the use of water-emulsified diesel helps improve the effectiveness of the testing program. The analyzed consequences provide useful information to the government for setting policies to curb pollutant emissions from a light-duty diesel engine generator more effectively.     

纳米TiO2-石墨烯光催化剂的水热合成及其光催化性能

以钛酸四正丁酯和石墨为原料,通过水热法制备了锐钛矿型为主的纳米TiO2复合光催化剂（纳米TiO2-石墨烯）,并采用XRD,FTIR,FESEM,TEM技术对其进行了表征。通过紫外光照射降解溶液中的罗丹明B（RhB）研究了TiO2-石墨烯的光催化活性,分析了初始罗丹明B质量浓度、催化剂加入量、溶液pH和催化剂使用次数等影响降解效果的因素。实验结果表明：在初始RhB质量浓度为20 mg/L、溶液pH为7.10、催化剂加入量为1.000 g/L的条件下,紫外光照射30 min时,纳米TiO2-石墨烯对RhB的降解率高达98.69%,明显高于纳米TiO2的44.69%;纳米TiO2-石墨烯稳定性较强,可多次重复使用。     

翅碱蓬-沙蚕对Cu污染沉积质理化性质的影响研究

以中国北方滩涂湿地的优势种植物翅碱蓬(Suaeda heteroptera Kitag.)和优势多毛类动物双齿围沙蚕(Nereis succinea)为实验对象,以向沉积质中添加Cu2+来模拟重金属污染,通过盆栽实验,分别测定翅碱蓬、沙蚕及两者混合培养对Cu污染沉积质的pH、氧化-还原电位(Eh)、总氮含量、总磷含量及脱氢酶活性的影响,研究它们对Cu污染沉积质理化性质的改善作用。结果表明,翅碱蓬、沙蚕对Cu污染沉积质理化性质的影响与Cu处理浓度有关。翅碱蓬-沙蚕体系对Cu污染沉积质理化性质的影响与两者单独作用时均不同,且对不同Cu处理浓度沉积质的影响效果也不尽相同;总体来看,对于Cu污染沉积质,翅碱蓬-沙蚕体系可促使pH升高,Eh下降,总氮含量升高,脱氢酶活性升高,而对总磷含量的影响不明显。     

A2O-MBR工艺处理城市污Z作农业灌溉用水中试研究

为开发一种污水再生利用于农田灌溉领域的新型技术,本实验以城市污水为研究对象,采用A2O—MBR工艺进行中试研究,并将系统出水水质与《农田灌溉水质标准（GB5084—2005）》的主要水质指标进行对比分析。结果表明,系统COD和BOD,出水浓度范围分别为3．2～59．6mg／L、1．0～7．6mg／L,系统出水pH为7．16～7．54,悬浮物浓度几乎为0,上述指标均符合标准;TP、TN和氨氮的出水范围分别为0．03～0．79mg／L、1．6～17．7mg／L和0．8～10．3mg／L。《农田灌溉水质标准》没有对上述3个指标提出具体要求,且少量的氮磷是植物生长的营养元素。该系统出水的主要水质指标符合标准兽求．     

高效脱硫菌的筛选及其性能研究

从高硫污染的活性污泥中富集培养,分离纯化得到一株可以降解噻吩的菌株s_4,并对该菌株的形态特征进行观察。应用Design—Expert8．0．5b软件进行响应面优化实验,研究了反应时间、噻吩浓度、微生物浓度3个因素的组合对菌株s_4脱硫效果的影响,并拟合得到多元二次回归方程,得出最佳实验条件。拟合结果表明,当反应时间27．46h,噻吩浓度为1．04％,微生物浓度4．04％时,预测噻吩降解率为14．8％,通过验证得最佳条件下的降解率为14．3％,与预测值相符。     

表面活性剂改性4A分子筛对Cr(VI)的吸附行为

采用浸渍法对4A分子筛进行表面改性,通过引入阳离子表面活性剂,使4A分子筛表面附着季铵型阳离子,并与反离子Br-形成"阴离子交换膜",从而促使更多的Cr(VI)阴离子通过离子交换吸附到改性4A分子筛上,通过X-射线衍射(XRD)和傅里叶变换红外光谱(FTIR)对样品的物相结构和组成进行表征分析。研究表明,表面活性剂的类型和疏水碳氢链结构会影响4A分子筛的吸附能力,十八烷基三甲基溴化铵(OTAB)碳氢链长,在分子筛表面形成的双分子层密,对Cr(VI)的吸附量最大。采用准一级、准二级、Elovich和Bangham动力学模型对六价铬的吸附数据进行拟合,其中准一级动力学方程最符合十八烷基三甲基溴化铵改性分子筛的吸附行为。同时,分别从Langmuir和Redlich-Peterson等温吸附模型获得六价铬的最大吸附量为13.98 mg/g,且改性分子筛以均一表面吸附为主。     

柴油机微粒中可溶性有机成分的真空干燥条件

柴油机碳烟颗粒(PM)中可溶性有机组分(SOF)含量是其重要的特性参数,而真空干燥法可方便、高效、可靠地分析颗粒SOF含量,对其干燥条件的探索具有重要的研究意义和应用价值。首先采用模拟的柴油机颗粒,分析不同的干燥条件对模拟SOF(柴油、润滑油)挥发率的影响规律,得出模拟的SOF分析的最佳干燥条件;在此基础上,探索了真实柴油机颗粒SOF分析的最佳干燥条件为:干燥温度220℃、干燥时间3 h、真空度98 kPa,得知SOF组分干燥的难易程度介于柴油和润滑油之间;同时,根据此干燥条件,分析了排气管末端采集的真实碳烟颗粒的SOF含量特性。