氯化钙溶液浸泡下压实水泥改性膨胀土的膨胀特性

压实膨胀土可用于防止垃圾填埋场中的固体废弃物产生二次污染,这主要取决于压实膨胀土的抗渗特性。向膨胀土中掺加水泥进行改性后,不仅可以增强膨胀土的水稳定性,还能提高膨胀土的抗渗特性,且抗渗特性随着时间的增长而逐渐增强。因此,在制备衬砌方面,水泥改性膨胀土比膨胀土具有更大的优势。为研究水泥改性膨胀土衬砌在化学溶液下的膨胀特性,选取氯化钙溶液为渗透液体,以氯化钙溶液浓度和水泥掺量为控制变量,进行水泥改性膨胀土的自由膨胀率试验及压实膨胀试验。试验结果表明,向处在氯化钙溶液环境下的压实膨胀土中掺加一定量的水泥,可以有效地减小膨胀土的膨胀性、缩短膨胀达到稳定的时间以及增强膨胀土的稳定性。就减小膨胀土的膨胀性和增强膨胀土的稳定性来看,水泥的最佳掺量比应控制在15%左右。就缩短膨胀土达到稳定的时间来看,水泥的最佳掺量比应控制在10%左右。     

赤泥改性生物炭修复铅污染土性能研究

土壤的重金属污染是制约社会可持续发展的重要环境难题，在“双碳”背景下，本文通过共热解制备赤泥改性生物炭(RMBC),研究RMBC对铅污染土的理化性质、修复效果和工程特性的影响。结果表明，RMBC可以增加铅污染土的pH值并降低其电导率(EC)值。RMBC的掺量越大pH值越高EC值越小。通过盐酸萃取浸出毒性发现随着RMBC掺入量和修复时间的增加土中Pb(II)浸出浓度越低，7%掺量的RMBC对重金属铅污染土的修复效果最好。此外，RMBC的掺入可以增加土体的密实度在一定程度上提高土的承载能力和抗渗能力。借助微观分析揭示了RMBC的修复机理包括络合作用、离子交换和沉淀反应。赤泥改性生物炭能够有效吸附-固定土中的重金属离子，并改良土体的相关性能，在污染修复和工程应用方面具有潜力。     

生物沥浸改性后污泥基生物炭对Pb^2+和Cd^2+的吸附

为探索利用生物沥浸改性后污泥基生物炭去除废水中Pb^2+和Cd^2+的可行性,以生物沥浸改性后污泥为原料制备生物炭,并测定了该材料的性能和吸附特性。通过单因素试验研究了pH值、生物炭投加量对吸附Pb^2+、Cd^2+性能的影响,并利用吸附动力学和热力学来揭示吸附机制。试验结果表明,经生物沥浸改性后污泥基生物炭的重金属含量降低;吸附Pb^2+和Cd^2+的最佳pH值分别为5、6,最佳生物炭投加量均为2 g/L;其对Pb^2+和Cd^2+的吸附均能较好地符合准二级动力学方程和Langmuir等温线模型,在25、35、45℃三种温度下对Pb^2+、Cd^2+的饱和吸附量分别为30.68、39.95、43.93 mg/g和19.82、28.58、32.29 mg/g,吸附过程均主要以物理吸附为主,且为吸热过程。     

城市垃圾填埋场地震变形机理的振动台模型试验研究

城市垃圾填埋场是环境岩土工程研究领域面临的新问题,对其地震变形机理尚缺乏深入的了解,迄今难以建立专门的地震稳定性评价体系.针对垃圾填埋场的工程特性,精心设计8个大比尺模型进行振动台试验,采用类比方法并运用一些试验新技术,再现垃圾填埋场的震害现象,揭示沿基础衬垫层和封顶覆盖层的接触面发生较大相对滑移是地震作用下垃圾填埋场的主要破坏模式,其中封顶覆盖层的破坏模式再次印证"双滑楔体"假定;由于垃圾土低密度、高压缩性,以及垃圾填埋场具有特殊的防渗层结构等特点,垃圾堆体内部不容易出现明显的滑裂面;定性和半定量地考察、研究封顶覆盖层和基础坡比、垃圾堆体密度、接触面强度参数、地震波频谱特性等因素对垃圾填埋场地震响应及其破坏的影响.     

玉米秸秆生物炭修复重金属污染土的性能试验研究

绿色高效修复重金属污染土问题受到工程界的密切关注。文章试验探讨了玉米秸秆生物炭修复铜锌重金属污染土PH值、强度、肥力和毒性演化规律。试验结果表明,基于玉米秸秆生物炭修复铜锌重金属污染土是有效可行的,并发现修复污染土的PH值和绿豆发芽率随着生物炭掺量的增加而提高,但土的抗剪强度则有所降低,生物炭修复重金属污染土,有利于降低重金属污染土对农作物影响,但其工程特性发生劣化,为实际修复污染土的工程应用提供了参考。     

生物炭对不同土体干缩开裂特性的影响及其机理研究

自然界许多土体失水干缩后常发育裂隙，引起各类工程地质问题，在土中掺入生物炭可以有效改变土体干缩开裂特性。本研究重点针对下蜀土、红黏土两种特殊土体，探究了不同掺量木质生物炭（0,0.01,0.03,0.05,0.1 kg/kg）对土体干缩开裂特征的影响，并结合微观结构分析及液塑限试验结果，阐明了影响机理。结果表明：(1)生物炭对于不同土体的影响有显著区别。生物炭能够加快下蜀土裂隙发育初期的速度，但会降低后期裂隙发育速度并抑制开裂；抑制效果随着掺量的增加而增强，裂隙比最高可下降32.2%。生物炭显著促进红黏土的裂隙发育，且促进效果随着生物炭掺量的增加而愈加明显，裂隙比最高可上升80.4%。(2)生物炭通过两种方式影响土体干缩开裂，一方面是作为非塑性材料占据土体可收缩空间；另一方面是影响土体颗粒的水化膜厚度进而影响土体膨胀。不同生物炭改性土体的开裂特性的不同取决于两种作用方式的相对强弱。     

陈垃圾土的工程力学特性试验研究

垃圾在填埋场中填埋一定的年限后(大于5 a),其中大部分发生了物理、化学及生物变化及反应,易降解部分已经完成,此时的垃圾即为陈垃圾。陈垃圾土的成分复杂,结构松散,压缩性较大,与一般的地基土的工程力学性质存在着差异,在垃圾填埋场上新建建筑物,需对陈垃圾土的工程力学特性进行试验研究。通过在金口垃圾填埋场上进行了现场的原位静载试验,以及一系列室内试验后,得出了陈垃圾土的工程力学性能,为工程的设计提供依据,并提出相应的建议。     

污水厂污泥制备垃圾填埋场防渗衬层材料研究

以城市污水厂的污泥复合高岭土用作垃圾填埋场防渗衬层材料，研究了千污泥的掺入量及其颗粒大小、复合土密度、渗滤液性质对污泥复合土渗透性能的影响。结果表明，复合土中污泥的最佳质量分数为40％；提高复合土的干密度可显著降低其渗透系数，当干密度为1.08g／cm^3时复合土的渗透系数达10^-7cm／s数量级，符合垃圾填埋场防渗衬层的要求；渗滤液性质对渗透性能的影响较大，当其电解质浓度较大时复合土的渗透性能随之提高。此外，考察了污泥复合土对重金属的吸附效果，结果表明该复合土可有效吸附垃圾渗滤液中的Cu^2＋、Zn^2＋等重金属。     

生物炭修复高浓度铅锌污染土的试验研究

将5%、8%和10%的水稻秸秆制成的生物炭作为修复铅锌污染土的固化剂,水泥材料作为对比固化剂,对高浓度铅锌污染土场地进行修复试验。研究结果表明:土体修复完成并养护56 d龄期后,与水泥固化土相比,生物炭固化土的pH值呈中性、且土壤肥力更高;毒性浸出试验中生物炭对重金属固化效果更优;生物炭掺量为8%、10%的固化土,种子发芽率大于80%;试验用各掺量下水泥固化土的种子发芽率均低于80%,即水泥固化土无法使试验用种子发芽。这表明采用生物炭固化重金属污染土,更适合土体的种植再利用。     

改性炭对磺胺甲噁唑的吸附及解吸特性

采用商品活性炭和金属氧化物改性炭作为吸附剂,研究了几种活性炭对磺胺甲噁唑(SMZ)的吸附及解吸特性。结果表明:SMZ在几种活性炭上的吸附动力学符合拟二级动力学方程;SMZ的吸附均可采用Freundlich、Langmuir和Langmuir-Freundlich模型进行拟合,Langmuir-Freundlich吸附模型能更好地描述活性炭和改性炭对SMZ的吸附行为;铁、锰氧化物的存在对活性炭的比表面或者孔结构影响不大,并且其对活性炭吸附水中SMZ的性能影响甚微;与AC-Fe和AC-Mn相比,AC-0上吸附的SMZ更易解吸,改性炭负载的金属氧化物与SMZ的表面络合作用增强了AC-Fe和AC-Mn对SMZ的化学吸附,并且改性炭的MnOx和FeOx能氧化降解部分SMZ。     

非饱和土质覆盖层多组分气体运移机理研究

为研究土质覆盖层中各组分气体的运移规律,进行了土柱注气试验,并通过多组分气体运移理论对试验结果进一步分析。分析结果表明:在注入气体总流量不变的情况下,改变注入气体的组分,会显著影响土柱中各组分气体分布;多组分气体运移理论能较好地预测各组分气体的运移;表观气相渗透系数不是一常数,与气压大小相关;体相扩散是影响各组分气体分布规律的主要因素,通过改变有效二元扩散系数,调整各组分气体分布,可以提高土质覆盖层中甲烷氧化效果。     

An incremental model to assess the environmental impact of cap cover systems on MSW landfill emissions

Landfill cap covers are designed to contain fugitive methane emissions and to prevent uncontrolled leachate infiltration. The objective of this paper is to propose a method for assessing their impact on the mitigation of landfill greenhouse gas emissions using a new dedicated model (IMAGE-Landfill) that takes into account the different steps of landfill management history as well as the incremental methane production from the different cells. In particular, different collection and oxidation efficiencies are considered depending on the landfill operation, on its life step and on the chosen cap cover system. Two different theoretical single cell case studies and one real-scale landfill were used to calibrate the IMAGE-Landfill model. The results highlight that, depending on the selected cap cover lining system, the potential greenhouse gas emissions may be divided by a factor 2.5-7, even if no energy is recovered from the collected methane.This model is a useful tool for landfill operators to model methane production, but also to select the most appropriate cover type for each step of the landfill lifetime. Finally, this research appeals for a better consideration of environmental impacts when designing landfill barriers.     

垃圾填埋场腾发覆盖系统控制渗滤效果的研究

腾发覆盖垃圾填埋系统(ET Landfill)利用覆盖层土壤的储水能力及植被的腾发作用对进入覆盖层的降水进行调节,达到控制渗滤的目的.通过对不同覆盖层结构和植被组合的腾发覆盖系统的水均衡动态进行试验研究,探讨了不同组合条件下的土壤水分动态过程和渗滤控制效果.结果表明,相对于无植物覆盖系统,腾发覆盖系统能够有效地调节覆盖土层的储水量,减少垃圾填埋场的渗滤液.在有植物覆盖的各组试验中,种植灌木为主60 cm覆盖土层的渗滤控制效果最好,而完全种植草本植物40 cm覆盖层的控制效果最差.     

混合粉质粘土和疏浚土填埋场防渗垫层的环境土工特性研究

充分利用疏浚土有机质含量高、吸附能力强和低透水性等特点,将其作为填埋场粘土衬垫的添加材料。等温吸附试验和扩散试验的结果表明:粉质粘土掺入疏浚土后,对金属离子的吸附能力得到增强,尤其对高价Cu2+的吸附能力显著提高,同时可以显著地降低Cu2+的扩散系数。研究表明,有机质对Cu2+的强吸附能力是Cu2+扩散系数降低的主要原因。粉质粘土掺入疏浚土后极大地提高了粘土衬垫的环境土工特性,非常适合作为填埋场粘土衬垫。     

The long-term evolution of and transport processes in a self-sustained final cover on waste deposits

A new principle for confinement of waste based on a self-sustained seal is presented. The top cover is considered to consist of two main layers; an organic carbon rich surface layer that is able to support vegetation and an inorganic layer beneath it. The function of the cover is to mitigate oxidation and acidification of landfilled waste and hence the release of toxic metals. It is suggested that forest soil formation and soil development could prove to be valuable information sources for the study of the long-term behaviour of a final cover on waste deposits. Since the cover is expected to develop in northern temperate climate the focus is on Spodosol soil. A number of simulations of the long-term behaviour of the final self-sustained landfill cover are made, including the rates of influx of oxygen into the cover. A cover having a large portion of organic matter compared with a cover with no organics can considerably decrease the oxygen concentration and thus the influx of oxygen into a landfill. The calculated oxygen intrusion rate for the former case is of the order of 0.05 kg m(-2) year(-1). Degradation of the organics produces acids. Our simulations indicate that the pH-buffering capacity of the mineral layer, represented by calcite and primary rock minerals, will last for many thousands of years.     

Experimental investigation on methane advection and diffusion in geosynthetic clay liners

Geosynthetic clay liners (GCLs) are widely used in landfill and heap-leach facility cover system for mitigating rainfall infiltration and gas migration into atmosphere. Laboratory tests were conducted to investigate methane diffusion and advection through GCLs. Gas permeability coefficient of GCL for the case with moisture content = 47.5% is one and two orders of magnitude greater than the cases with moisture content = 68.5% and 80.9%, respectively, when 20 kPa vertical stress was applied. The batch adsorption tests indicated that adsorption of methane onto bentonite is negligible. The concentration variation for the adsorption of methane onto bentonite can be neglected. However, methane concentration decreased by 14.2% for the test of methane adsorption onto GCL during the first 2–3 days. This is because methane was adsorbed by the geotextiles rather than by the bentonite in GCL. The large porosity and surface area of geotextiles provide lots of micropores for methane adsorption. Analytical model was then developed to analyze the performance of GCL-based liners system with respect to methane transport. The results indicate that methane emission fluxes for the case with SL + GCL are 7.8 and 5.1 times less than the cases with SL + CCL when the moisture contents were 25.9% and 35.1%, respectively. The methane emission fluxes for both of the SL + GCL and SL + CCL can be neglected when they are fully saturated. GCL is recommended to be used in arid and semi-arid regions rather than CCL. GCL is recommended to be used in arid and semi-arid areas rather than CCL. Advection plays a more important role in methane migration through SL + GCL and SL + CCL than that of diffusion. With moisture contents = 25.9% and 32%, methane emission flux attributed to advection accounts for more than 90% of the total emission flux for both cases of SL + GCL and SL + CCL. With the increase of moisture content of SL, the effectiveness of SL in reducing methane emission increases. The saved space for using GCL + SL composite cover compared with using a single SL cover is 0.7 m when the moisture content equals 25.9%, which is 0.5 m greater than the case when moisture content equals 32%. GMB plays a dominant role in inhibiting methane migration and reducing methane emission flux. When moisture content equals 25.9%, the methane emission fluxes for SL + GMB + GCL and SL + GMB + CCL are 343 times and 2643 times less than the cases with SL + GCL and SL + CCL, respectively.     

黄土覆盖层水–气耦合运移土柱试验及数值模拟

基于水分储存与释放机理的土质覆盖层在干旱和半干旱地区垃圾填埋场具有较好的应用前景。前人研究土质覆盖层大多侧重于其雨水存储及防渗性能,忽略了填埋气在覆盖层中的运移及其影响。通过在黄土土柱底部通入甲烷和二氧化碳等比例混合气体模拟填埋气在覆盖层运移,在土柱顶部施加3 cm常水头模拟雨水入渗对黄土覆盖层中气压分布以及各气体组分分布的影响。基于试验结果,利用商业软件Geo-Studio中的Air/W模块对黄土覆盖层水–气耦合运移进行了数值模拟与分析。研究结果表明:模拟雨水入渗降低了上层黄土的导气系数,导致土柱中气压显著增加,呈现出先增加至"突破值"然后回落至"稳定值";气压"突破值"约等于上部土体进气值;数值模拟能较好地模拟水分入渗过程并捕捉到气压变化趋势,但由于其无法模拟多组分填埋气在土柱中的复杂物理过程,导致气压的模拟结果与实测值存在差距。本文为更准确模拟分析土质覆盖层中水与填埋气耦合运移过程提供了一些建议。     

垃圾填埋场衬垫土壤材料对Cr(Ⅵ)的吸附特性研究

通过静态平衡吸附试验对采用颗粒活性炭及酸活化膨润土改良的垃圾填埋场衬垫土壤材料吸附重金属的特性进行了观察。试验结果表明:研究中的所有土壤样本对Cr(Ⅵ)的吸附属于非线性的Langmuir模式。经颗粒活性炭及酸活化膨润土改良的衬垫土壤材料与天然黏土材料相比,对Cr(Ⅵ)的吸附强度有了很大的提高,说明颗粒活性炭和酸活化膨润土可以作为改良衬垫土壤的材料去吸附重金属。所有土壤样本对Cr(Ⅵ)的吸附量均随着温度的升高而增大,随着土壤固体颗粒浓度的增大而减小。Langmuir等温参数(qm,b)随着土壤固体颗粒浓度的增大而呈对数性减小,但随着土壤固体颗粒浓度进一步增大到某一临界值(例如200 g/L),其值基本稳定了,另外等温参数也随着温度的升高呈线性增大的趋势。由试验结果可以得出,采用较低的土壤固体颗粒浓度所确定的吸附参数值不适合模拟实际工程条件,其值将引起对垃圾填埋场衬垫的迟滞因子作出过高估计。因此,为了获得与实际工程条件比较接近的吸附参数值,静态平衡吸附试验必须在一个充分大的固体颗粒浓度条件下进行。     

黄土-粉土混合土对Pb(Ⅱ)的静平衡和动态吸附特性

竖向防污屏障是防止地下水土污染的主要屏障。天然土是屏障最主要的材料来源。以天然粉土为母土,黄土为添加剂,以重金属Pb(Ⅱ)作为污染物的代表,通过粉土-黄土混合土对Pb(Ⅱ)的静平衡吸附和动态吸附试验研究黄土作为添加剂对天然粉土的改良效果。试验考虑了黄土添加量、溶液pH值、反应时间以及重金属初始浓度等对吸附的影响。结果表明添加黄土可以有效改善天然粉土的吸附效果,混合土对Pb(Ⅱ)的吸附容量随黄土添加量的增加线性增长,添加20%黄土的混合土的吸附容量达天然粉土的2倍;添加黄土可减少混合土对重金属的吸附时间,在相同时间内减少迁移量。通过扫描电镜和XRD等手段揭示了黄土对Pb(Ⅱ)的吸附主要是方解石与Pb(Ⅱ)发生界面沉淀作用生成白铅矿;粉土对Pb(Ⅱ)的吸附主要是长石等矿物棱角处经风化水解形成的-OH基团对Pb(Ⅱ)的阳离子交换作用。黄土由于高方解石含量在对Pb(Ⅱ)的吸附方面表现突出,可以作为一种添加剂加入天然土层中,以增强屏障对重金属的吸附阻滞效果,减少环境污染。     

Cyclic strength of sand mixed with biochar: Some preliminary results

Biochar is a recycled material obtained through the thermal degradation of any organic biomass in the manufacture of bio-fuel inside a reactor in a process known as pyrolysis. It is an organic material that can endure in soil for thousands of years. Given its aromatic nature, biochar is highly recalcitrant, and has been considered to have great potential to sequester carbon and reduce greenhouse gas emissions. This material has been commonly used in environmental and agricultural applications, as it can store plant minerals in its pore spaces and provide a large water-holding capacity. However, little research has been done on the geomechanical properties of the resulting mixture of biochar and soil. Some studies have shown that biochar can increase the shear strength of clays and desaturate soil particles, and it may be possible that it can also increase the resistance to liquefaction in loose sand. Therefore, it would be very interesting to assess whether this material is able to present a more environmentally friendly alternative for improving the properties of soil. In this study, samples of pure sand are dry-mixed with 0%, 3%, and 5% biochar by weight and tested under cyclic undrained shearing using a simple shear test apparatus. The preliminary results indicate that biochar can increase the cyclic resistance of sand.