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。

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.

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.

PRB处理酸性矿山废水的地球化学反应模拟研究

随着工业的迅速发展,矿产资源的需求也随之增加,采矿过程中产生的酸性矿山废水(Acid Mine Drainage,AMD)对周围环境具有严重危害性,可渗透反应墙(Permeable Reactive Barrier,PRB)通过下放置反应材料,利用自然水力梯度拦截污染羽流,该技术已成为有效处理AMD的手段之一。为研究PRB内化学反应堵塞对其处理效果的影响,搭建了规模为60 cm×15 cm×20 cm的箱体装置,模拟石灰石PRB处理AMD的过程;基于箱体实验得到的数据,并利用化学反应输运模型理论开发了一种新的地球化学算法,来描述PRB处理AMD过程中可能会发生的化学反应,最后通过MODFLOW和RT3D的耦合模拟并预测PRB有效处理污染物质的最大寿命。结果表明:①有效地模拟出了PRB中石灰石的酸性中和能力及其对酸性废水中总铁、Al^(3+)的去除效果,并且很好地反映出PRB系统的化学堵塞过程;②模拟结果与实测值吻合程度较好。进口区域、中间区域以及出口区域3个不同位置处出水的pH实测值与预测值的最大误差分别为0.38、0.30和0.29,总铁质量浓度实测值与预测值的最大误差分别为1.570、0.102和0.124 mg/L,Al^(3+)质量浓度实测值与预测值的最大误差分别为1.010、0.374和0.160 mg/L;③预测结果表明,该实验室规模的PRB装置在前30 d出水中的总铁和Al^(3+)质量浓度最低,去除效果最好,且去除能力随着时间逐渐减弱。参照地下水质量标准限制,判断出该石灰石PRB能够有效处理总铁的最大寿命为132 d,有效处理Al^(3+)的最大寿命为63 d。

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.

基于EK−PRB修复镉污染土壤的微生物优化技术

采用电动-可渗透反应墙(EK-PRB)联合微生物优化技术,研究其对Cd污染土壤修复效果的影响。利用固定化微生物技术,制备粉煤灰-酵母菌小球、壳聚糖-酵母菌小球和生物炭-酵母菌小球,并对比制备的PRB小球和单一的PRB材料(粉煤灰、生物炭、壳聚糖)对Cd去除效果的影响。结果表明,相对于单一的PRB材料,PRB小球可增加土壤中的电流和电导率,对Cd的去除率更高,但是对pH影响较小。通过对PRB材料进行表征分析,证实了其对Cd去除效果有一定影响。考虑到经济成本与修复效果,选择电压梯度为2.5 V·cm^(-1),PRB材料为粉煤灰-酵母菌小球去除Cd,去除率可达53.70%。研究结果证实了固定化微生物结合EK-PRB技术的可行性以及修复优势。

非正规生活垃圾填埋场污染地下水修复的PRB反应介质试验研究

我国存在大量的非正规生活垃圾填埋场,由于它们在运行之前没有采取严格的防渗防污措施,垃圾渗滤液下渗导致当地地下水严重污染。地下水污染原位修复技术中的渗透性反应墙(PRB)技术由于其运行成本低、能长期有效运行、不影响生态环境等优点已得到广泛应用。以湖北省石首市某非正规生活垃圾填埋场渗滤液污染的地下水为研究对象,通过静态批次试验,探索了PRB单一反应介质类型、反应温度、单一反应介质投加量、复合反应介质配比对污染地下水的修复效果,并通过SEM、XRD、FT-IR对不同反应介质的污染物去除机理进行了讨论。结果表明:3种单一反应介质即海藻酸钠(SA)-聚乙烯醇(PVA)包裹微球、生物炭和聚合氯化铝(PAC)-阳离子聚丙烯酰胺(C-PAM)改性膨润土对污染地下水中六价铬、氨氮、COD、总磷的最大去除率分别为99.96%、98.97%、88.58%、99.20%;在研究区地下水温度变化范围内,温度对单一反应介质去除污染物性能的影响不大;单一反应介质投加量对六价铬、氨氮和总磷最终去除率的影响不大,仅对COD的去除效果有影响,反应时间为120 h时1 g/100 mL的单一反应介质投加量下污染地下水中COD的去除率为88.58%,3 g/100 mL和5 g/100 mL的单一反应介质投加量下对COD的去除率均可达98.42%;按照3种单一反应介质2∶1∶1的质量比制备的复合反应介质,反应时间为120 h时其对污染地下水中六价铬、氨氮、COD、总磷的去除率分别为99.61%、96.03%、81.25%、99.20%。该研究结果可为研究区利用PRB技术修复非正规生活垃圾填埋场渗滤液污染的地下水提供理论依据。

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.

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.

炭铁材料修复三氯乙烯污染地下水的性能

采用生物炭(BC)为载体的纳米零价铁复合材料作为可渗透反应墙系统(PRB)中的反应介质,通过柱实验和渗透实验,研究了生物炭负载纳米零价铁(BC-nZVI)对三氯乙烯(TCE)的去除效果和炭铁复合材料在长期水流作用下的渗透性能.结果表明:炭铁复合材料对TCE的去除率在2h内可达到90%以上,10h时接近100%,随着炭铁复合材料的消耗,去除率逐渐降低,但在24h内仍能保持显著的修复效果,去除率保持在90%以上,72h后降为73.96%.PRB系统中反应介质材料在长期水流作用下出现明显的迁移,炭铁复合材料的稳定性随着炭铁比的减小而降低.5BC-1nZVI材料在持续3d的渗流作用下,其迁移流失率最低,相比纯BC材料的迁移流失情况具有明显的改善效果.微观结果表明球磨法可成功合成炭铁复合材料,合成后的nZVI颗粒存在一定程度的氧化,与TCE接触反应后的炭铁复合材料由于降解产物的附着,炭铁复合材料的表面会形成一层白色薄膜,孔径变小,进而炭铁复合材料对TCE的去除性能降低.

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.

改性载体厌氧氨氧化生物膜在浅层地下水修复中脱氮效能的模拟研究

为探究厌氧氨氧化菌(AnAOB)在模拟地下水环境条件下脱氮性能的研究,以人工配水为进水,采用可渗透反应墙(PRB)作为模拟装置,使用纳米零价铁(nZVI)改性生物炭(BC)(nZVI@BC)厌氧氨氧化菌(AnAOB)生物膜作为填料,设置装置模拟温度从高温(33℃)降至实验室室温(21℃)的过程,探究降温过程中AnAOB生物膜填料对PRB装置脱氮性能的影响。结果表明:①PRB装置经过71 d的模拟运行,nZVI@BC载体AnAOB生物膜的PRB装置总氮(TIN)去除率达到82%,明显优于空白组(59.27%),且AnAOB生物膜脱氮贡献率占22.73%。②随着温度的变化,AnAOB生物膜的红色逐渐变淡,且生物膜污泥逐渐流失。③微生物群落结构表明,微生物多样性下降,优势物种在富集。从门水平上看,绿弯菌门(Chloroflexi)的相对丰度提升,逐步成为优势菌门,而浮霉菌门(Planctomycetota)和变形菌门(Proteobacteria)的相对丰度则降低。从属水平上来看,AnAOB优势属Candidatus Brocadia的相对丰度逐步提升,Candidatus Kuenenia的相对丰度则降低。研究显示,nZVI@BC载体AnAOB生物膜填料组成的生物膜微生物系统在PRB装置降温过程中维持稳定,同时AnAOB生物膜群落结构随降温过程的变化而变化,以应对降温过程中带来的不利影响。

复合矿物介质动态去除重金属多污染物实验研究

本文针对广西某多金属矿山尾矿库渗滤液造成的地下水污染问题,以蛭石、十六烷基三甲基溴化铵(CTAB)改性蛭石及赤铁矿作为PRB复合介质材料,进行了动态去除水中多污染物Cu^(2+)、Zn^(2+)、Mn^(2+)、CrO_(4)^(2–)的实验,研究了三种介质材料的组装方式对多种污染物的去除行为。动态吸附实验表明,介质的不同组装方式会影响体系的p H值,及吸附柱对多污染物的去除效果。通过对反应前后矿物介质的物相、形貌等测试表征,讨论了矿物介质材料对污染物的去除机理。赤铁矿以表面吸附为主,蛭石、CTAB改性蛭石以离子交换为主,也存在表面吸附等过程。以上成果为复合矿物介质实际用于重金属污染地下水的原位修复奠定了重要基础。

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。