Enhanced microbial reduction of aqueous hexavalent chromium by Shewanella oneidensis MR-1 with biochar as electron shuttle

Biochar, carbonaceous material produced from biomass pyrolysis, has been demonstrated to have electron transfer property(associated with redox active groups and multi condensed aromatic moiety), and to be also involved in biogeochemical redox reactions. In this study, the enhanced removal of Cr(VI) by Shewanella oneidensis MR-1(MR-1) in the presence of biochars with different pyrolysis temperatures(300 to 800 °C) was investigated to understand how biochar interacts with Cr(VI) reducing bacteria ...     

Performance and mechanism of Cr(VI) removal by zero-valent iron loaded onto expanded graphite

Zero-valent iron (ZVI) was loaded on expanded graphite (EG) to produce a composite material (EG-ZVI) for efficient removal of hexavalent chromium (Cr(VI)). EG and EG-ZVI were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and Brunauer–Emmett–Teller (BET) analysis. EG-ZVI had a high specific surface area and contained sub-micron sized particles of zero-valent iron. Batch experiments were employed to evaluate the Cr(VI) removal performance. The results showed that the Cr(VI) removal rate was 98.80% for EG-ZVI, which was higher than that for both EG (10.00%) and ZVI (29.80%). Furthermore, the removal rate of Cr(VI) by EG-ZVI showed little dependence on solution pH within a pH range of 1–9. Even at pH 11, a Cr(VI) removal rate of 62.44% was obtained after reaction for 1 hr. EG-ZVI could enhance the removal of Cr(VI) via chemical reduction and physical adsorption, respectively. X-ray photoelectron spectroscopy (XPS) was used to analyze the mechanisms of Cr(VI) removal, which indicated that the ZVI loaded on the surface was oxidized, and the removed Cr(VI) was immobilized via the formation of Cr(III) hydroxide and Cr(III)–Fe(III) hydroxide/oxyhydroxide on the surface of EG-ZVI.     

氨基改性生物炭负载纳米零价铁去除水中Cr(VI)

以聚乙烯亚胺（PEI）为功能单体,玉米秸秆生物炭为载体,制备了氨基改性生物炭负载型纳米零价铁（nZVI@PEI-HBC）,并利用扫描电镜（SEM）、红外光谱（FTIR）和X射线光电子能谱（XPS）等手段对材料进行了表征,分析了溶液pH、温度、材料投加量等因素对其去除Cr（VI）的影响及其去除机理.结果表明：在投加量为0.5 g·L^-1,温度为20℃,pH值为5,Cr（VI）初始浓度为20 mg·L^-1条件下,各材料对Cr（VI）的去除率大小为nZVI@PEI-HBC > nZVI > PEI-HBC > HBC.SEM显示nZVI颗粒较均匀地分散在生物炭表面,FTIR分析表明PEI改性后材料表面增加了氨基等重金属配位基团,这可能是nZVI@PEI-HBC去除Cr（VI）效果更好的原因.影响因素研究表明,材料具有较好稳定性,老化28 d后其Cr（VI）去除性能变化不大;酸性环境、升温、增大材料投加量均有利于nZVI@PEI-HBC对Cr（VI）的去除.机理研究发现,水中溶解氧加速了nZVI的腐蚀和Fe（II）的释放,促进Cr（VI）还原为Cr（III）,然后通过共沉淀作用和氨基等基团的吸附作用被去除.     

Al(III)对糖浆溶液中有机还原物质还原六价铬的影响

通过批实验研究了Al(III)对糖浆溶液化学还原六价铬反应的影响,揭示了不同条件下Al(III)对六价铬还原反应动力学的影响.结果表明:Al(III)能够促进糖浆溶液还原六价铬反应进行;其作用机制是Al(III)与糖浆溶液中有机还原物质及Cr(VI)反应形成三者的络合物,降低糖浆中多酚等有机还原物质还原Cr(VI)的反应活化能,提高六价铬还原反应速率.Al(III)存在时,该六价铬还原反应符合准一级动力学反应; pH 2.0,2.5,3.0,3.5时,添加Al(III)的实验组中六价铬反应速率常数比对应的空白对照组中反应速率常数分别增加了0.0251,0.0139,0.0058, 0.0048h-1.添加Al(III)前后反应体系中六价铬还原的反应活化能(Eа)分别为66.38,62.80kJ/mol.当糖浆浓度不足时,Al(III)能够提高糖浆溶液还原六价铬的反应去除率.     

铜绿假单胞菌负载Fe(III)对水中六价铬的生物吸附性能研究

采用原位沉积技术将Fe（Ⅲ）负载于铜绿假单胞菌（Pseudomonas aeruginosa,简称Pa）表面制备了Fe（Ⅲ）与细菌的复合体（Fe-Pa）,研究了Fe-Pa对水溶液中Cr（VI）的吸附特性,探讨了最佳合成条件、Fe-Pa投加量、溶液pH值、时间和Cr（VI）初始浓度等因素对Cr（VI）吸附效果的影响,同时利用SEM、FT-IR、XPS和Zeta电位对Fe-Pa进行表征分析.吸附实验结果显示,Fe（Ⅲ）浓度为600 mg·L^-1、细菌投加量为0.5 g·L^-1制备的Fe-Pa效果最佳;Fe-Pa去除Cr（VI）适宜于酸性条件进行;Fe-Pa对Cr（VI）的吸附速率较快,60 min内可达到吸附平衡,为自发的吸热吸附,且符合准二级动力学和Langmuir等温模型.表征结果表明,Fe（Ⅲ）成功地负载到铜绿假单胞菌上,为吸附Cr（VI）提供更多的活性位点,主要机制为静电吸附作用、络合作用和还原作用.经过4次吸附/再生后,Fe-Pa对Cr（VI）的吸附能力仍在72%以上,表明Fe-Pa具有较好的重复使用性.     

两性与两性复配修饰膨润土增强塿土吸附Cr(VI)的研究

为了证实添加修饰黏土对塿土吸附Cr(VI)的增强作用,分别将2%、5%、8%和10%(质量分数)的200%CEC BS-12(十二烷基二甲基甜菜碱)修饰膨润土(B200B)和100%CEC BS-12+100%CEC DTAB(十二烷基三甲基溴化铵)复配修饰膨润土(B100B/100D)加入到天然塿土,以批处理法研究供试土样对Cr(VI)的等温吸附特征,并对比了p H值、温度和离子强度(I)对Cr(VI)吸附的影响.结果表明:不同B100B/100D塿土(B100B/100D混合塿土)和B200B塿土对Cr(VI)的吸附量分别是CK(塿土)的1.52~4.28和1.99~5.12倍,且等添加比例下B200B塿土对Cr(VI)的吸附量高于B100B/100D塿土.10~30℃范围内,CK、2%B100B/100D和2%B200B塿土对Cr(VI)的吸附呈增温正效应;当修饰土添加比例大于2%时,温度效应由增温正效应向负效应转变.CK对Cr(VI)的吸附量在不同p H值(4~7)处理下差异不显著,而B100B/100D和B200B塿土对Cr(VI)的吸附量均随p H值升高而降低.CK和B100B/100D塿土对Cr(VI)的吸附量均随离子强度(I)的增大而降低,B200B塿土对Cr(VI)的吸附量以I=0.1 mol·L~(-1)时最高,以I=0.5 mol·L~(-1)时最低.B100B/100D和B200B塿土吸附Cr(VI)是自发的物理过程,随修饰土添加比例的增大,吸附表现为焓增、熵减特征.     

生物催化合成的施氏矿物对废水中Cr(VI)的吸附

在模拟多种金属离子[Cr(VI),Cu²⁺,Zn²⁺和Cd²⁺共存的电镀废水中,采用新型生物催化合成矿物无定型羟基硫酸高铁(Schwertmannite,施氏矿物)去除废水中的Cr(VI).实验结果表明,施氏矿物对Cr(VI)络阴离子具有很强的选择性吸附,整个吸附过程符合Langmiur方程.吸附的最佳pH值为6.0～7.0,最大吸附量为55mg/g,且当Cr(VI)初始浓度≤100mg/L时,去除率达90%以上.在温度20～50℃范围内,温度变化对吸附的影响较小.一价阴离子(如Cl^-和NO₃^-)对Cr(VI)的去除干扰极小,而仅当介质中SO₄^2-和PO₄^3-与Cr(VI)的摩尔比分别超过5:1和1:5时,2种无机阴离子才影响施氏矿物对Cr(VI)的吸附.     

啤酒酵母吸附去除水中Cr(Ⅵ)的研究

研究了吸附剂用量、重金属初始浓度、pH对非活性啤酒酵母菌体吸附Cr(Ⅵ)的影响.结果表明,吸附剂的用量越高,对Cr(Ⅵ)的去除率也越高,但单位菌体吸附量却越低;相反,Cr(Ⅵ)初始浓度越高,对Cr(Ⅵ)的去除率就越低,但单位菌体吸附量却越高;溶液的pH也是影响吸附去除效果的重要因素之一,当pH为1时,吸附去除效果最好,非活性啤酒酵母菌体对Cr(Ⅵ)的吸附过程可用Langmuir和Freundlich等温吸附模型来拟合,但Langmuir等温吸附模型的拟合效果更好,由Langmuir等温吸附方程得到最大吸附量为9.17mg/g干菌体.     

Reduced graphene oxide-nano zero value iron (rGO-nZVI) micro-electrolysis accelerating Cr(VI) removal in aquifer

Nanoscale zero-valent iron (nZVI) assembled on graphene oxide (GO) (rGO-nZVI) composites were synthesized by reduction of GO and ferrous ions with potassium borohydride, for use in Cr(VI) removal from aqueous solution. The results showed that the two-dimensional structure of GO could provide a skeleton support for Fe⁰, thus overcoming the bottleneck of aggregation for nZVI. Also, rGO-nZVI would form a ferric-carbon micro-electrolysis system in Cr(VI)-contaminated aquifers, enhancing and accelerating electron transfer, exhibiting high rate and capacity for Cr(VI) removal. The optimum dosage of the applied rGO-nZVI was linearly correlated with the initial Cr(VI) concentration. Characterization of rGO-nZVI before and after reaction with Cr(VI) revealed the process of Cr(VI) removal: rGO-nZVI firstly transferred electrons from Fe⁰ cores via their Fe(II)/Fe(III) shells to the GO sheet; there, negatively charged Cr(VI) received electrons and changed into positively charged Cr(III), which was adsorbed by the negatively charged GO sheet, avoiding the capping and passivating of nZVI. rGO-nZVI formed a good electrically conductive network, and thus had long-term electron releasing properties, which was important for groundwater remediation.     

Novel functional fiber loaded with carbon dots for the deep removal of Cr(VI) by adsorption and photocatalytic reduction

A novel functional fiber (PAN-CDs) loaded with carbon dots (CDs) with excellent photoreduction and adsorption properties for Cr(VI) was prepared via an amidization reaction between the CDs' carboxyl groups and amine groups on polyacrylonitrile (PAN)-based ion exchange fibers, which could completely preserve the fluorescence properties of the CDs. The photoluminescence (PL), photocatalysis and adsorption properties of PAN-CDs were characterized and analyzed. The PAN-CDs possess high adsorption capacity (297.6?mg/g) and excellent kinetic behavior (attaining adsorption equilibrium in 30?min) for Cr(VI) adsorption. Furthermore, the residual Cr(VI) (approximately 3?mg/L) after adsorption could be removed completely by subsequent photoreduction by the PAN-CDs. The Cr-saturated PAN-CDs could be easily separated by filtering and regenerated, with no observable decay of removal efficiency after five regeneration cycles. In addition, due to the PL quenching action of Cr(VI), the PAN-CDs can also be used as sensor for quantitative detection of trace Cr(VI) in aqueous solution.     

Preparation of cross-linked magnetic chitosan with quaternary ammonium and its application for Cr(VI) and P(V) removal

Pollutants that exist in anionic species are issues of concern in water treatment. Compared to cationic pollutants, the removal of anionic pollutants by adsorption is more difficult because most adsorbents carry predominantly negative charges in neutral and alkaline environments. In this study, a cross-linked chitosan derivative with quaternary ammonium and magnetic properties（QM-chitosan） was prepared and employed to remove chromium（VI） and phosphorus（V）（Cr（VI） and P（V）） from aqueous environments. The QM-chitosan was characterized by Fourier transform infrared spectrometry（FT-IR）,thermogravimetric analysis（TGA）, energy dispersive X-ray（SEM-EDX） and zeta potential.Batch experiments show that QM-chitosan can effectively remove Cr（VI） and P（V）, and the main mechanism was believed to be electrostatic interaction. A pseudosecond-order model was fitted to describe the kinetic processes of Cr（VI） and P（V） removal. The adsorption isotherms of both Cr（VI） and P（V） on the QM-chitosan were well fitted by the Langmuir isotherm equation. The saturated adsorption capacity of P（V）（2.783 mmol/g） was found to be higher than that of Cr（VI）（2.323 mmol/g）, resulting from the size of the H2PO-4ions being smaller than that of the HCr O-4ions. However, the theoretical calculation and experimental results showed that QM-chitosan had a stronger affinity for Cr（VI） than P（V）. The adsorption–desorption of the QM-chitosan was evaluated, and high regeneration rates were demonstrated.     

Synthesis of a novel illite@carbon nanocomposite adsorbent for removal of Cr(VI) from wastewater

A novel illite@carbon (I@C) nanocomposite adsorbent has been synthesized via a facile hydrothermal carbonization process (HTC) using glucose as carbonaceous source and illite as the carrier. The morphology, microstructure and surface properties of the prepared nanocomposite adsorbent were analyzed by FESEM, TGA, XRD, FT-IR and Zeta potential measurements. Batch experiments were carried out on the adsorption of Cr(VI) to determine the adsorption properties of the composite. The adsorption of Cr(VI) onto the I@C nanocomposite was well described by the pseudo-second-order kinetic model and Langmuir isotherm. Compared with the illite and carbon material (SC) separately, the prepared I@C nanocomposite adsorbent exhibited enhanced adsorption performance for Cr(VI) with a maximum adsorption capacity of 149.25 mg/g, which was higher than that of most reported adsorbents. In addition, the adsorption process was spontaneous and endothermic based on the adsorption thermodynamics study. The adsorption of Cr(VI) by I@C was highly pH-dependent and the optimum adsorption occurred at pH 2.0. The Zeta potential analysis results indicated that the electrostatic interactions between anionic Cr(VI) and the positively charged surface of the adsorbent might be critical to the adsorption mechanism. This study demonstrated that the I@C nanocomposite should be a promising candidate for a low-cost, environmental friendly and highly efficient adsorbent for the removal of toxic Cr(VI) from wastewater.     

剩余污泥燃料电池处理含铬废水的效能及机理

采用剩余污泥为阳极底物,六价铬为阴极电子受体,构建双室微生物燃料电池(MFC).MFC启动成功后,考察阳极室污泥初始浓度和阴极室六价铬初始浓度对MFC产电性能及六价铬还原速率的影响.较高的污泥浓度(8~12g/L)对六价铬的还原速率影响均较小,且去除率均可达99%以上.污泥浓度为10g/L的MFC具有较高的产电性能,内阻为108Ω,最大功率密度输出为3621mW/m3.阴极室较高的Cr(VI)初始浓度可维持较长时间的高输出电压,但对阳极污泥降解并无明显影响.XPS测试结果表明,阴极Cr(VI)的还原产物为Cr(III),因电场作用被吸附在电极片上,使得阴极溶液中的总铬浓度降低.研究表明,剩余污泥为底物的微生物燃料电池可以在产电的同时实现剩余污泥的资源化及电镀废水的无害化.     

Cr(VI)对活性污泥硝化活性的抑制及在污泥中的分布特点

重金属铬(Cr(VI))是废水中常见的、困扰很多污水生物处理系统运行效果的污染物.本文通过静态试验和静态冲击试验,研究了Cr(VI)在活性污泥系统中的分布特点和对硝化效率、活性等的影响,并进行了模型分析.结果表明,活性污泥对Cr的吸附很快,但吸附量有限,Cr(VI)投加浓度为1、5、10和30 mg · L^-1的溶液中,Cr的12 h-吸附量分别为0.79、1.98、3.19和5.78 mg · g^-1.Cr(VI)投加到活性污泥混合液中后形态分为溶解态、可洗脱和不可洗脱态,可洗脱的Cr能够向不可洗脱态转变.Cr(VI)对活性污泥硝化活性的抑制程度随着Cr(VI)浓度的增大而提高.静态试验中,1、3、5、10和30 mg · L^-1 Cr(VI)对氨氮平均降解速率的抑制率分别为5.25%、9.80%、10.41%、17.54%和21.38%.Cr(VI)对微生物的抑制作用大小是:氨氧化菌 >亚硝酸盐氧化菌 >异养菌.模型分析发现,Cr(VI)对氨氧化菌和异养菌比耗氧速率的抑制符合Haldane动力学模型,属于非竞争性抑制.冲击试验表明Cr对硝化等的抑制主要是不可洗脱的Cr造成的,抑制效果的出现具有滞后性.     

双表面活性剂修饰下纳米零价铁对水中Cr(Ⅵ)污染去除研究

为解决纳米级零价铁（nZVI）在环境中易团聚、易氧化的问题,强化其去除水中Cr（VI）的能力,选择非离子型表面活性剂聚乙烯吡咯烷酮（PVP）和阴离子表面活性剂油酸钠（NaOA）同时对nZVI进行修饰.同时,通过对比不同pH值、材料干湿状态、初始浓度及共存离子条件下的反应效果,结合材料的XRD和XPS表征、动力学实验和25℃等温线的拟合进行机理分析.结果表明：酸性条件有利于Cr（VI）的去除;材料的干湿状态对去除效率影响较大;材料去除水中Cr（VI）可在3 h内达到反应平衡,去除效率在90%以上,实验条件下最大去除量为183.1 mg·g^-1,反应过程符合准二级动力学模型及Langmuir模型;反应过程中Cr（VI）大部分转化为Cr（Ⅲ）.     

粉煤灰对含铬废水的吸附研究

通过静态吸附实验,研究原状粉煤灰与粉煤灰滤料对Cr(Ⅵ)的吸附效果的影响,并通过正交实验进行实验结果对比。实验确定粉煤灰滤料的吸附平衡时间为90 min,在pH为3的条件下适于进行吸附实验;同时,粉煤灰滤料的吸附性能优于原状粉煤灰,六价铬溶液的初始浓度、滤料的投加量以及温度的改变对吸附性能具有显著影响,且粉煤灰滤料吸附时所受影响更为明显。     

壳聚糖/改性平菇复合吸附剂对Cr(VI)的吸附特性

以壳聚糖和经酒石酸改性的平菇粉末为材料,通过戊二醛进行交联反应,制得壳聚糖-改性平菇凝胶小球（CMPOD）复合生物吸附剂,用于水溶液中Cr（VI）的吸附去除.结果表明,在实验所测pH值（2~10）范围内,复合吸附剂对Cr（VI）的吸附量随着pH值上升而降低;随着Cr（VI）初始浓度或温度的提高,吸附剂对Cr（VI）的吸附量均相应增加,当Cr（VI）初始浓度为600mg/L,温度为50℃,Cr（VI）吸附量可达190mg/g以上;Cr（VI）的吸附符合准二级动力学方程及Freundlich等温吸附模型;热力学分析表明,吸附剂对Cr（VI）的吸附过程为自发的吸热反应.扫描电镜（SEM）分析显示,吸附剂具有发达的网状结构,吸附Cr（VI）后网状孔隙被填充,且能谱分析（EDS）出现明显的Cr（VI）吸收峰;傅立叶红外光谱分析（FTIR）表明,壳聚糖中的氨基成功引入复合吸附剂中,在Cr（VI）吸附中为主要作用官能团.     

吡啶环改性石墨相氮化碳光催化还原Cr(VI)的研究

以三聚氰胺和吡啶二羧酸为原料,通过水热合成有机大分子前驱体,设计了吡啶环改性的石墨相氮化碳(x% Py-CN).利用TEM、XRD、XPS、FT-IR、EIS等手段对所得x% Py-CN催化剂进行表征分析.以水中Cr (VI)为目标污染物,考察了x% Py-CN催化剂的光催化还原性能.结果表明,在模拟太阳光照射下,10% Py-CN具有最佳的光催化性能,光照3h对15mg/L Cr (VI)光催化还原率达85%.x% Py-CN催化剂光催化活性提升的原因在于,吡啶环的修饰有效提高了光生电子空穴对的分离效率.此外,重复循环实验表明该催化剂具有良好的稳定性和循环利用能力,具有良好的应用前景.     

Enhanced remediation of Cr（Ⅵ）-contaminated groundwater by coupling electrokinetics with ZVI/Fe3O4/AC-based permeable reactive barrier

Although widely used in permeation reaction barrier（PRB） for strengthening the removal of various heavy metals, zero-valent iron（ZVI） is limited by various inherent drawbacks, such as easy passivation and poor electron transfer. As a solution, a synergistic system with PRB and electrokinetics（PRB-EK） was established and applied for the efficient removal of Cr（Ⅵ）-contaminated groundwater. As the filling material of PRB, ZVI/Fe₃O₄/activated carbon（ZVI/Fe₃O₄     

桉树遗态Fe/C复合材料对水中Cr(Ⅵ)的动态吸附探讨

为研究桉树遗态Fe/C复合材料（PBGC-Fe/C）对水中Cr（Ⅵ）的净化能力及其动态吸附过程,以PBGC-Fe/C吸附剂为固定床,选择溶液初始pH、进水流速、溶液初始浓度、吸附剂投加量和环境温度为影响因素开展动态吸附试验分析.结果表明:在溶液初始pH为2,进水流速为5.14 mL/min,吸附剂投加量为2 g和环境温度为35℃的条件下,PBGC-Fe/C对水中Cr（Ⅵ）的最佳平衡吸附容量达到10.72 mg/g;提高溶液初始pH、进水流速和溶液初始质量浓度或降低吸附剂投加量均可缩短反应穿透时间和衰竭时间;Thomas和Yoon-Nelson模型均能较好地描述PBGC-Fe/C对水中Cr（Ⅵ）的动态吸附过程,说明该吸附过程中内部扩散和外部扩散均为非限速步骤,吸附速率常数（k_Th）随着进水流速的增大从1.3×10-3 mL/（min·mg）升至2.6×10-3 mL/（min·mg）,随着溶液初始质量浓度的增大从2.7×10-3 mL/（min·mg）降至1.4×10-3 mL/（min·mg）.研究显示,PBGC-Fe/C对水中Cr（Ⅵ）具有较好的动态吸附能力,具有较好的市场应用前景.