某简易垃圾填埋场渗滤液在场底天然土层迁移模拟与长期预测

为了解我国早期建设的简易填埋堆场底部天然土层中污染物迁移状况,作者以安徽某填埋场为例,在前期现场勘查、取样和室内测试工作基础上建立了三维有限元分析模型,对宏量有机污染物COD在土层中的迁移状况进行了模拟分析.通过拟合求参获得COD在该场底土层中扩散系数、机械弥散系数和阻滞因子等运移参数的合理取值,在此基础上开展了污染物...     

有机污染物在HDPE膜-膨润土复合防污帷幕中的一维扩散解析解

HDPE膜-膨润土复合防污帷幕被认为是目前最为安全有效的地下污染源阻隔技术之一.针对帷幕底部嵌入不透水层和帷幕下游地下水较为活跃的工况,推导了有机污染物在HDPE膜-膨润土复合防污帷幕三层结构中的一维扩散解析解.利用本文的解析解分析了HDPE膜-膨润土复合帷幕对亲水性和疏水性两类有机污染物的阻隔效果.分析结果表明:由于亲水性有机物与HDPE膜间的分配系数低,该复合防污帷幕对其阻隔效果显著优于具有高分配系数的疏水性有机物.对于疏水性有机物,可通过增大复合帷幕中膨润土的阻滞因子和帷幕厚度来改善其阻隔效果;膨润土的阻滞因子增大10倍且帷幕厚由0.6m增大为1.0m,改进后复合帷幕对疏水性有机物的阻隔效果可达到原帷幕对低分配系数亲水性有机物的阻隔水平.工程实践中可通过对HDPE膜进行表面处理以降低其分配系数或膨润土改性以增大其阻滞因子等措施来增强该复合帷幕的阻隔效果.     

采用移动电极法提高机械脱水污泥电动脱水能效的试验研究

采用一种能移动阳极的电动脱水模型试验装置,对机械脱水污泥开展了固定间距电极和移动电极的电动脱水试验,比较分析了这2种方法的脱水效果及对应的能耗.试验结果表明:固定间距电极法脱水处理过程中,阳极附近已脱水污泥的阻抗增加,消耗的电压和电能上升;而后面未脱水污泥分得的电压下降,导致其脱水效果从阳极至阴极衰减.移动电极法通过移动阳极逐步越过已脱水污泥部分,将电压作用在未脱水的污泥,避免了电能消耗在高阻抗的脱水污泥,显著提高了能效,脱水过程中电渗流量稳定,脱水效果均匀.采用移动电极法进行脱水处理时能耗随加载电压梯度的增加而上升,随试样长度的缩短而降低.当采用8 V·cm-1电压梯度的移动电极处理5 cm长度的污泥时,污泥含水率可由初始的82.1％降至62.2％,所需要的能耗约为89.8 kW·h·m-3.     

城市污泥电渗脱水实验研究

电渗脱水是一种能有效去除污泥中水分以实现减量的处理方法.本文采用自制电渗脱水装置进行了城市污泥的电渗脱水实验.通过监测脱水过程中电渗流量、电压梯度与剩余含水率的变化,考察了电压梯度、电极间距和处理时间的影响,并进一步分析了电渗处理过程中脱水效果变化的原因.处理中随着脱水效果由阳极向阴极发展,污泥可划分为已脱水污泥与未脱水污泥,已脱水污泥内电渗停止,电渗与水分的脱除发生在未脱水污泥内,并由未脱水污泥的电压梯度决定.已脱水污泥阻值上升,使未脱水污泥电压梯度逐渐降低,造成了电渗流量与脱水效果的衰减,并使得污泥剩余含水率由阳极至阴极逐渐增加.电渗脱水的整体效果随加载电压的增加而提高,脱水能耗亦随之增加,选取较小的电极间距时电渗脱水能效较高.     

污泥-焚烧底灰混合固化配方及强度增长机理

污泥与垃圾焚烧底灰混合固化是一种以废治废的处置方式.针对水泥固化污泥早期强度高、石膏固化污泥后期效果好的特点,分别采用水泥、石膏、水泥+石膏为固化剂,和不同掺量的垃圾焚烧底灰,开展脱水污泥固化试验研究.对固化污泥的无侧限抗压强度、含水量、增容比、浸出毒性及COD、p H值进行了测试,并用扫描电镜分析了固化污泥微观结构的变化.测试与分析结果表明:脱水污泥的较优固化材料配方为100%垃圾焚烧底灰、25%水泥和25%石膏,固化污泥的强度和含水量满足填埋要求,且增容比小,浸出毒性大幅降低.固化污泥的早期强度主要来源于垃圾焚烧底灰的骨架作用和吸水作用,后期强度增长主要依靠固化剂的胶凝作用和垃圾焚烧底灰的火山灰作用;其中钙矾石的生成是固化污泥强度增长的重要因素之一.     

Passive convergence-permeable reactive barrier (PC-PRB): An effective configuration to enhance hydraulic performance

● A novel PRB configuration based on passive convergent flow effect was proposed. ● A 2D finite-difference hydrodynamic model, PRB-Flow, was developed. ● PC-PRB can significantly enhance the hydraulic capture capacity of PRB. ● The PRB geometric dimensions and materials cost are effectively reduced. ● The dominant influential factor of the PC-PRB capture width is pipe length, L_p. A novel permeable reactive barrier (PRB) configuration, the so-called passive convergence-permeable reactive barrier (PC-PRB), is proposed to overcome several shortcomings of traditional PRB configurations, such as high dependency to site hydrogeological characteristics and plume size. The PC-PRB is designed to make the plume converge towards the PRB due to the passive hydraulic decompression-convergent flow effect. The corresponding passive groundwater convergence (PC) system is deployed upstream of the PRB system, which consists of passive wells, water pipes, and a buffer layer. A two-dimensional (2D) finite-difference hydrodynamic code, entitled PRB-Flow, is developed to examine the hydraulic performance parameters (i.e., capture width (W) and residence time (t)) of PC-PRB. It is proved that the horizontal 2D capture width (W_h) and vertical 2D capture depth (W_v) of the PC-PRB remarkably increase compared to that of the continuous reactive barrier (C-PRB). The aforementioned relative growth values in order are greater than 50% and 25% in this case study. Therefore, the PRB geometric dimensions as well as the materials cost required for the same plume treatment lessens. The sensitivity analysis reveals that the dominant factors influencing the hydraulic performance of the PC-PRB are the water pipe length (L_p), PRB length (L_PRB), passive well height (H_w), and PRB height (H_PRB). The discrepancy between the W_h of PC-PRB and that of the C-PRB (i.e., ΔW_h) has a low correlation with PRB parameters and mainly depends on L_p, which could dramatically simplify the PC-PRB design procedure. Generally, the proposed PC-PRB exhibits an effective PRB configuration to enhance hydraulic performance.     

A comparative study of removal efficiency of organic contaminant in landfill leachate-contaminated groundwater under micro-nano-bubble and common bubble aeration

Environmental Science and Pollution Research - Landfill leachate-contaminated groundwater is widespread all over the world. In order to study the organic contaminant removal efficiency of landfill...     

An analytical solution to contaminant diffusion in semi-infinite clayey soils with piecewise linear adsorption

The adsorption of contaminants onto soil particles typically is nonlinear if the contaminant concentration is sufficiently high. A simplified piecewise linear adsorption isotherm consistent with experimental results is proposed as an approximation for nonlinear adsorption behavior. This approximation allows for the use of analytical solution to model solute diffusion of contaminants that exhibit nonlinear adsorption. A moving boundary is introduced to represent significant changes in the retardation factor of clay with an increase in solute concentration. The proposed analytical solutions were validated using experimental data presented in the literature. There is negligible difference between the results obtained by the proposed analytical solution and those obtained by the linear model when C_m/C₀ reached 0.5. The results also show that the model based on linear adsorption using the initial secant of the Freundlich isotherm leads to significantly lower estimated breakthrough time for the contaminant of interest than that obtained using the proposed model. The earlier breakthrough is due to an under-estimation of the amount of adsorption. The proposed method is relatively simple to apply and can be used for evaluating experimental results and verifying more complex numerical models.     

垃圾填埋场抽气竖井周边气体运移规律研究

通过建立填埋场抽气竖井周边气体轴对称稳态运移模型,分析了单层和分层垃圾体中气压力分布,并提出“降压百分比”的概念用于判定抽气影响范围,研究了垃圾产气率、气体渗透率、覆盖层厚度、覆盖层气体渗透率、抽气井深度和抽气负压对抽气影响范围和抽气量的影响,获得了竖井深度和井间距的确定方法.分析结果表明,抽气井的降压作用明显,抽气井深度和抽气负压越大,则抽气影响范围和抽气量越大.覆盖层厚度增加或其渗透率降低有助于扩大抽气影响范围和提高抽气量.抽气影响范围随气体渗透率的增加而增大,但随垃圾产气率的增加而减少;抽气量则随气体渗透率和产气率的增大而增加.抽气井深度是控制抽气影响范围的关键参数,建议竖井深度取垃圾填埋厚度的65％～75％,井间距取1.5～2.5倍竖井深度.     

垃圾填埋场渗滤液穿过垂直防渗帷幕的渗漏分析

为避免垃圾填埋场内的污染物对地下水造成污染,填埋场常采用垂直防渗帷幕.目前,我国南方的垃圾填埋场内渗滤液水位普遍较高,在高水头作用下污染物可能透过灌浆帷幕渗漏从而污染周边环境.分析了对流、扩散和吸附作用对污染物迁移的影响规律,以苏州七子山填埋场为例,分析了高水头作用下渗滤液透过防渗帷幕的渗漏,通过现场测试进行了验证,研究了灌浆帷幕渗透系数和灌浆深度对渗漏的影响.结果表明,在高渗滤液水位下,对流对污染物迁移起主导作用.实际工况下污染物穿过防渗帷幕需 19.5a,污染区域主要集中在场底含碎石粘土层中,目前污染物尚未渗漏至防渗帷幕下游,分析结果与现场实测结果一致;若防渗帷幕渗透系数能达到标准,则穿过防渗帷幕的时间将延长至填埋场稳定化之后,从而大大降低污染周边环境的可能性;但若帷幕灌浆深度不足,这一时间又将缩短至7a.防渗帷幕渗透系数和灌浆深度的控制对防止污染物向下游地区渗漏极为关键.