Feasibility Evaluation of Using Biochar-based Permeable Reactive Barrier for the Remediation of Mercury and Arsenic Composite Polluted Water Bodies

This study employed a modified biochar material to construct a permeable reactive barrier(PRB)for the treatment of water bodies polluted with mercury and arsenic.The experimental results demonstrated that the addition of goethite-modified biochar significantly enhanced the remediation efficiency of As(III),achieving a maximum removal rate of 100%.Conversely,pure biochar exhibited high efficiency in the removal of Hg(II),with a maximum removal rate approaching 100%.Furthermore,the pH level of the water significantly influenced the adsorption efficiency of heavy metal ions,with the optimal removal performance observed at a pH of 6.0.The PRB system demonstrated excellent removal rates under low concentrations of heavy metals.However,as the concentration increased,the remediation efficiency exhibited a slight decrease.In summary,the findings of this study provide compelling evidence for the use of modified biochar in the construction of PRBs for the remediation of mercury and arsenic-polluted water bodies.Furthermore,the study reveals the mechanism by which pH and heavy metal concentration influence remediation efficiency.

Performance of Metal and Acid Ions Remediation in Contaminated Soils by Electrokinetics with Chitosan Permeable Reactive Barrier

Metal and acid ions contamination of soil in China is serious. To find an efficient solution for remediating the combined pollution,electrokinetics( EK) coupled with chitosan( CTS)permeable reactive barrier( EK/CPRB) was used to investigate the performances of metal and acid ions remediation. Adsorption characteristics of Zn^(2+),Fe^(3+),Ca^(2+),SO_4^(2-) and NO_3^- onto CTS were also conducted. The results showed the sorption of Zn^(2+),Fe^(3+),Ca^(2+),SO_4^(2-) and NO_3^- on CTS could be well described by Freundlich model. When the CTS dosage is 8 g,the total removal efficiency for Zn^(2+),Fe^(3+),Ca^(2+),SO_4^(2-) and NO_3^- is 86. 8%,90. 2%,92. 4%,90. 0% and 82. 5%,respectively. CTS enhanced ions remediation efficiencies significantly compared with the single EK system,especially for SO_4^(2-) and NO_3^-. The results indicate EK/CPRB system is suitable for the remediation of soil contaminated by both metal ions and acid ions.

Pilot Test of the Permeable Reactive Barrier for Removing Uranium from the Flooded Gunnar Pit

This work reports on applying iron oxide coated sand (IOCS) media in an experimental permeable reactive barrier to remove uranium (U) species from uranium containing water. A field study was conducted at the legacy Gunnar uranium mine & mill site that was abandoned in the 1960s with limited to no decommissioning. The flooded Gunnar mine pit presently contains about 3.2 million m3 of water contaminated by dissolved U (1.2 mg/L), Ra-226 (0.4 Bq/L), and minor concentrations of other contaminants (As, Se, etc.). The water is seeping over the pit rim into Lake Athabasca, posing potential environmental and health concerns. IOCS media can be used to immobilize uranium species through an adsorption process. Herein, the preparation of hydrous ferric oxide sorbents and their supported forms onto silica sands is described. Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (pXRD) were used for structural characterization. The adsorption properties of the IOCS sorbent media were modeled by the Langmuir adsorption isotherm, where a maximum uranium uptake capacity was estimated. Bench-scale adsorption kinetic experiments were also performed before moving to a field trial. Based on these lab results and input on field-scale parameters, a pilot permeable reactive barrier was fabricated and a field test conducted near the Gunnar pit in June 2019. This pilot test provided technical data and information needed for designing a full-scale permeable barrier that employs the IOCS media. This approach can be applied for in-situ water treatment at Gunnar and other legacy uranium sites.

固废基PRB复合颗粒填料对Cd^(2+)的吸附特性及净化机制

鉴于传统可渗透反应墙(PRB)填料价格昂贵,且易消蚀、钝化,本文以钢渣、脱硫石膏等固废材料制备了复合颗粒填料(CGF),探究CGF对Cd^(2+)的等温吸附与动力学特征,并结合浸水试验明确CGF的强度损失规律与散失特性。借助动态吸附试验探究不同条件下CGF的动态吸附规律,明确CGF对Cd^(2+)的净化机制。结果表明:CGF对Cd^(2+)的吸附过程受化学吸附与颗粒内扩散控制,符合PS-order模型与Langmuir模型。T3组CGF综合性能最好,吸附量达到8.12 mg/g,且28 d散失率最小,为4.98%,强度损失率为6.16%。Thomas模型可以很好地描述CGF的动态吸附行为,泵速对CGF的穿透曲线影响最大,且动态平衡吸附量qe随初始浓度、床层高度增加而提高。CGF通过水化反应、火山灰反应生成C-S-H凝胶、AFt等水化产物,在提供颗粒强度的同时又可通过共沉淀、离子置换等方式实现对Cd^(2+)的吸附。本文可为有色金属矿山污染场地的修复治理提供一种新思路。

PRB颗粒填料对Cd^(2+)的吸附特征及其孔隙结构动态演变规律

以PRB复合颗粒填料(CGF)开展动态吸附试验,探究其对Cd^(2+)的动态吸附规律与主要影响因素;借助可视化手段与孔隙网络模型(PNM),探究吸附前后CGF的几何特征与孔隙结构演变规律,明确填料消蚀与孔隙堵塞的动态平衡关系。研究结果表明:当泵速为10 r/min、质量浓度为50 mg/L时CGF的平衡吸附量最大,达到了1.81 mg/g;泵速对穿透曲线的影响最大,且低流量更有利于CGF对Cd^(2+)的吸附。吸附后孔隙率提高了7.79%,分形维数最多下降了7.95%,孔隙堵塞对分形维数影响较大;CGF溶蚀降低了表面积与平均等效直径,但球度在1.4~1.6范围的颗粒占比提高到75.9%。吸附后平均配位数由10.43降低至8.65,降低了17.07%;同时参与配位的“棍体”与“球体”数量分别降低了43.28%与31.63%。CGF消蚀导致动态柱中部发生堵塞,降低了孔隙与喉道的连接,但并未出现“实质性”堵塞,PNM仍保持良好的连通性能。

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

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(Wh)and vertical 2D capture depth(Wv)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(Lp),PRB length(LPRB),passive well height(Hw),and PRB height(HPRB).The discrepancy between the Wh of PC-PRB and that of the C-PRB(i.e.,∆Wh)has a low correlation with PRB parameters and mainly depends on Lp,which could dramatically simplify the PC-PRB design procedure.Generally,the proposed PC-PRB exhibits an effective PRB configuration to enhance hydraulic performance.

高级氧化-PRB修复填埋场复合污染地下水的可行性

以杭州市某生活垃圾填埋场一期地下水中复合污染的COD,NH_(4)^(+),Mn^(2+)为对象,联用了非均相Fenton氧化和渗透性反应墙(PRB),设计了活性炭(AC),生物炭(BC),BC+Fe_(3)O_(4)3种不同的氧化反应催化剂组合并将其兼做PRB氧化层活性填料,下游串联沸石吸附层.批试验和柱试验结果显示,H_(2)O_(2)可直接预氧化47%的COD.氧化层中COD在催化氧化和吸附共同作用下被削减;Mn^(2+)受多孔碳材料灰分释放影响先沉淀后溶解,然后被吸附;AC和BC表面的官能团-OH和-COOH参与了反应.吸附层中NH_(4)^(+)和Mn^(2+)与沸石离子交换引起了沸石骨架结构变化,且沸石表面的官能团-NH和-OH也参与了兜底吸附.BC+Fe_(3)O_(4)氧化层与沸石吸附层长度比为1:3的串联组合对三种污染物的去除率均较高,且PRB失效时间(即污染物出流浓度达到入流的10%且超过限值的时间)最迟,填料失效时的有效利用率最高,是最优工艺.

减压汇流式PRB渗流调控机制研究

减压汇流式PRB(Passive convergence-permeable reactive barrier,PC-PRB)是一种新型可持续的地下水原位修复技术.为评估PC-PRB水力捕集性能并揭示其渗流调控机制,本文开发了质点示踪算法精度高和数值解稳定性强的渗流模拟软件PRB-Flow.结果表明,在给定模拟条件下,与连续式PRB(Continuous permeable reactive barrier,C-PRB)相比,PC-PRB平面和剖面捕集流量分别提升约为47%和90%.敏感性分析表明,导水管长度L_(p)、减压井横向范围TD_(w)和减压井深度H_(w)是影响PC-PRB水力性能的关键参数.L_(p)与PC-PRB水力捕集性能之间存在显著的正相关关系(P<0.01).增加TD_(w)和H_(w)均可提升PC-PRB水力捕集能力,但影响程度不及L_(p).导流管的引流减压作用使得减压井内产生降深,促使井周围地下水在水头差的驱动下向井内汇聚,从而显著提升了PC-PRB的水力捕集性能.此外,PC-PRB可有效解决C-PRB因流速不均而产生的局部击穿问题.

Woodchip-sulfur packed biological permeable reactive barrier for mixotrophic vanadium(V)detoxification in groundwater

Groundwater vanadium(V)(V(V))contamination is ubiquitous in vanadium mining/smelting region and development of novel strategy for its remediation is of particular significance.Herein woodchip-sulfur packed biological permeable reactive barrier(bio-PRB)is established towards successful V(V)bio-detoxification.V(V)removal was accelerated under such mixotrophic condition,compared with heterotrophic and autotrophic V(V)reductions.The performance of bio-PRB was relatively steady with V(V)removal efficiency of 68.5%–98.2%under fluctuant geochemical and hydrodynamic conditions.Microbial community analysis indicated that heterotrophic Geobacter was the main reducer to convert V(V)to insoluble V(IV),by consumption of organic source attributed to woodchip hydrolysis and sulfur anabolism of autotrophs(e.g.,Sulfuricurvum and Thiobacillus).V(V)reduction and elemental sulfur oxidation were regulated by genes as omcA,omcB and mtrC and soxB,respectively.The elevated contents of cytochrome c and nicotinamide adenine dinucleotide implied that improved electron transfer facilitated V(V)reduction.This study provides a cost-effective,robust and sustainable route for V(V)-polluted aquifer remediation.

Long-term performance evaluation of zero-valent iron amended permeable reactive barriers for groundwater remediation-A mechanistic approach

Permeable reactive barriers(PRBs)are used for groundwater remediation at contaminated sites worldwide.This technology has been efficient at appropriate sites for treating organic and inorganic contaminants using zero-valent iron(ZVI)as a reductant and as a reactive material.Continued development of the technology over the years suggests that a robust understanding of PRB performance and the mechanisms involved is still lacking.Conflicting information in the scientific literature downplays the critical role of ZVI corrosion in the remediation of various organic and inorganic pollutants.Additionally,there is a lack of information on how different mechanisms act in tandem to affect ZVI-groundwater systems through time.In this review paper,we describe the underlying mechanisms of PRB performance and remove isolated misconceptions.We discuss the primary mechanisms of ZVI transformation and aging in PRBs and the role of iron corrosion products.We review numerous sites to reinforce our understanding of the interactions between groundwater contaminants and ZVI and the authigenic minerals that form within PRBs.Our findings show that ZVI corrosion products and mineral precipitates play critical roles in the long-term performance of PRBs by influencing the reactivity of ZVI.Pore occlusion by mineral precipitates occurs at the influent side of PRBs and is enhanced by dissolved oxygen and groundwater rich in dissolved solids and high alkalinity,which negatively impacts hydraulic conductivity,allowing contaminants to potentially bypass the treatment zone.Further development of site characterization tools and models is needed to support effective PRB designs for groundwater remediation.

Nitrate Removal by a Permeable Reactive Barrier of Fe0:A Model-Based Evaluation

Permeable reactive barrier（PRB） filled with zero valent iron（ZVI, Fe0） can be an effective option to remove nitrate from contaminated groundwater. The long-term performance of such PRBs, however, might be compromised by the problem of declining reactivity and permeability, which could cause a decrease in the nitrate removal efficiency. In this study we explored suitable model formulations that allow for a process-based quantification of the passivation effect on denitrification rates and tested the model for a 40 years long operation scenario. The conceptual model underlying our selected formulation assumes the declining reactivity of the ZVI material through the progressing passivation caused by the precipitation of secondary minerals and the successive depletion of the ZVI material. Two model scenarios, i.e., the base model scenario which neglects the explicit consideration of the passivation effect and one performed with the model in which the impact of the passivation effect on denitrification was considered, were compared. The modeling results illustrate that nitrate removal in the model of considered passivation started to be incomplete after 10 years, and the effluent nitrate concentration of PRB rose up to 86% of the injected water concentration after 40 years, in contrast to the base scenario, corresponding well with the field observations of successively declining nitrate removal efficiencies. The model results also showed that the porosity of the PRB increased in both models. In order to improve and recover the reactivity of ZVI, pyrite was added to the PRB, resulting in completely nitrate removal and lower consumption of ZVI.

零价铁PRB技术在地下水原位修复中的研究进展

PRB(可渗透反应墙)是地下水治理中新型的原位修复技术,具有成本低、处理效果好、对环境干扰小等优点,已逐渐应用到实际.原位修复技术中PRB根据结构的不同可分为单处理系统PRB和多单元处理系统PRB,单处理系统PRB适用于单一污染物、污染浓度较低、污染羽规模较小的场地,多单元系统用于污染场地较复杂、污染种类较多的场地.零价铁PRB去除地下水中无机污染物及有机组分的反应机理主要是氧化还原反应和还原性脱卤反应.实际场地PRB的运行中存在的主要问题是零价铁钝化及PRB堵塞,现阶段的解决方法主要包括超声、电化学等,但为了提高PRB技术的实用性,铁材料的解钝化技术、实际场地PRB的设计与安装、PRB体系的长期运行及服务期满后的处置均需进一步的研究探索.

用双层PRB技术处理垃圾填埋场地下水污染的可行性研究

设计了双层结构可渗透反应屏障(PRB),对渗滤液污染地下水原位处理的可行性进行实验研究.其中,第一反应器主要填充了零价铁,对复杂的不可生物降解和难生物降解的卤代烃等有机物进行分解;第二反应器主要填充了释氧剂(ORC),对有机物进行彻底的处理.实验结果表明:经过第一反应器后BOD5 COD值由0 32升高至0 75,铵离子和硝酸根离子的去除率分别达到85%和80%;ORC反应器最大释氧量为7 64mg·L-1.采用双层PRB结构治理渗滤液污染地下水是可行的.

PRB修复垃圾渗滤液污染地下水过程中pH值变化分析

随着城市化的不断发展,生活垃圾产生量越来越多,因管理不善,导致垃圾渗滤液污染地下水的问题越来越突出,污染地下水的修复研究迫在眉睫。实验模拟地下环境,以被垃圾渗滤液污染地下水为研究对象,分别用沸石、无烟煤、陶粒、活性炭、炉渣、粉煤灰、零价铁作为反应介质,设计了6种地下可渗透反应墙(PRB),分别为反应器1、2、3、4、5和6。分3个阶段对PRB技术治理污染地下水中pH值影响和变化进行模拟研究,分析反应器pH值降低的原因并探讨pH值变化机理。实验结果表明,所有反应器pH值较进口降低,第三阶段出口pH值平均值较进口平均降低0.40;因水解酸化反应存在,产生一定量NH4+和有机酸,造成反应器出水pH值降低和复合填充材料NH4+相对去除率降低,说明PRB技术治理渗滤液污染地下水具有一定可行性,但技术方法有待继续深入研究。

PRB技术处理污染地下水的试验研究

试验采用粗砂、零价铁、富含微生物的土壤和锯末按不同比例搅拌均匀形成混合物，以此为介质做成可渗透反应墙（Permeable Reactive Barrier，简称PRB）反应器；取大通垃圾场产生的垃圾渗滤液，分别稀释5倍和40倍制成水样，作为模拟污染的地下水；进行2组正交试验，对各反应器的综合处理效果进行对比分析，结果表明：地下水中污染物的含量增高时，PRB出水pH值的增幅也会随之增大；进水污染物浓度变化时同一反应器CODcr去除率、BOD5去除率差异均很大，部分反应器CODcr和BOD5去除率在50％以上，但也有反应器出水CODcr和BOD5不降反升；2组正交试验的浊度去除率都处在较高的水平，许多反应器浊度去除率达到了80％～90％；进水浓度低时反应器的色度去除率超过70％。因此，用PRB处理受垃圾渗滤液污染的地下水是可行的。同时，从正交试验结果也得出了进水污染物浓度不同时PRB的最佳介质配比、反应时间以及各影响因素的丰次排序，为PRB讲一步的研究和设计提供了依据．

堆肥-零价铁混合PRB处理铬污染地下水

分别用堆肥、零价铁、堆肥-零价铁作为反应介质,对PRB处理铬污染地下水的可行性和有效性进行了研究。结果表明:以堆肥-零价铁作为反应介质的反应柱去除Cr(Ⅵ)的效果比单独以堆肥或铁粉为介质的反应柱好;增加铁粉或堆肥的用量均有利于Cr(Ⅵ)的去除;堆肥时间对Cr(Ⅵ)的去除效果影响不大;出水总铁含量符合《生活饮用水卫生标准》要求。

PRB在地下水污染修复中的应用与研究进展

地下水污染已成为当今世界严峻的环境问题。为保护地下水资源,采取有效的地下水污染防治措施已迫在眉睫。PRB作为原位治理领域中的新型技术,具有处理时效长、可同时处理多种污染物、运行费用低等优点。综述了PRB的结构类型、反应介质、反应机理和国内外研究进展,分析了存在的问题,并对其应用前景进行了展望。

PRB连续反应单元模拟与敏感性分析

根据PRB原理,考虑对流作用、弥散作用、吸附作用、化学反应等因素对溶质运移的影响,设计了连续反应单元.结果表明,对流作用对溶质运移速度影响较大,吸附作用与化学反应对污染物的去除影响较大.分析了地下含水层水力传导系数(Kaquifer)及连续反应单元内的水力传导系数(Kcell)对溶质运移的影响.结果表明,地下含水层Kaquifer较小(Kaquifer为1和5 m/d)时,Kcell取值对溶质运移总量影响不大;当Kcell∶Kaquifer≥10时,增加Kcell值对促进溶质运移作用较小.

零价铁PRB修复硝酸盐和铬复合污染地下水

通过连续流动试验研究了Fe0(零价铁)-PRB(渗透反应格栅)修复受NO3--N、Cr(Ⅵ)以及NO3--N和Cr(Ⅵ)复合污染模拟地下水的反应特性,分析了Fe0对NO3--N和Cr(Ⅵ)的氧化还原产物,并且对NO3--N和Cr(Ⅵ)的相互影响进行了研究.采用粒径为0.15～0.42 mm的Fe0和粒径为0.15 mm的活性炭作为PRB反应介质,二者的质量比为1∶1.结果表明,Fe0单独与NO3--N反应情况下,当进水中ρ(NO3--N)为20 mg/L时,去除率达95%,NO2-为还原过渡状态,NH4+是主要产物,出水pH从原水的7.1升至9.0左右,出水中ρ(TFe)<0.60 mg/L.Fe0处理Cr(Ⅵ)情况下,对Cr(Ⅵ)有较高的去除效果,进水中ρ〔Cr(Ⅵ)〕为10 mg/L时,去除率达96%,反应产物Fe3+和Cr(Ⅲ)可以形成沉淀附着在反应介质上,不会迁移到"下游"水体中,出水pH从原水的7.0升至8.0左右,出水中ρ(TFe)<0.30 mg/L.Fe0去除NO3--N和Cr(Ⅵ)复合污染时,共存的NO3--N对Cr(Ⅵ)的去除效果没有影响,Cr(Ⅵ)的存在降低了NO3--N的去除效果.