甲醇为共代谢基质时四氯乙烯的厌氧生物降解

四氯乙烯(PCE) 在厌氧条件下通过还原脱氯发生生物降解.本文研究以甲醇作为共代谢基质时PCE的降解情况.结果表明:在微生物的作用下PCE还原脱氯为TCE和DCEs,可能有VC和乙烯.因此,DCEs、VC和乙烯可能是PCE降解的终产物.PCE、TCE的降解和TCE的生成都符合准一级动力学.PCE和TCE的反应速率常数K分别为0.8991d^-和0.068 d^-;半衰期分别为0.77d和10.19d,TCE的生成速率常数为0.1333d^-.表明PCE的脱氯速度大于TCE,而TCE的生成速率大于降解速率,所以在整个实验期间都有TCE存在.     

铁还原环境四氯乙烯生物降解及其影响因素

通过实验研究了铁还原环境下四氯乙烯(PCE)的生物降解。以醋酸为共代谢基质,在20℃时,PCE可以顺序脱氯为TCE和DCEs。反应速率常数为0.2489d-1,半衰期为2.78d。在实验的第1天和第10天分别检测到了TCE和DCEs。TCE最高浓度为358.98nmol/L,是最主要的反应产物。碳平衡为88.7%～109.3%。在13d的实验周期中,微生物的数量和活性都有所增加。同时研究了不同的影响因素,如低温、不同pH和电子受体对PCE生物降解的影响。结果表明,在12℃时,PCE可以脱氯为TCE,半衰期为6.45d,降解速率为0.1075d-1,较20℃时的降解速率要低。脱氯的最佳pH值在7.0左右,较高和较低的pH值均会抑制脱氯微生物的活性。加入不同电子受体NO3-和SO42-,PCE脱氯受到不同程度的抑制,前者可能是由于NO3-是相对强的氧化剂,造成微环境中的氧化还原电位升高;后者则可能是SO42-的存在,会抑制脱氯菌的作用。     

纳米铁为脱氯菌供电降解三氯乙烯实验研究

采用一种从氯乙烯污染场址土壤中提取的脱氯菌种(Dehalococcoides spp.)进行三氯乙烯(TCE)降解实验,研究纳米铁厌氧腐蚀产氢为该脱氯菌种提供电子的可能性.结果表明,在甲醇做电子供体时,稀释25倍的菌液［（2.0±0.44）×105　cell/mL)］可以在96　h内将20 mg/L TCE完全降解,并在190　h时有2.706　μmol乙烯产生.而在无甲醇做电子供体时,96　h内只有部分TCE转化为顺二氯乙烯(cisDCE),且190　h时几乎无乙烯产生（0.159　μmol）,因此无电子供体时菌液脱氯活动不能维持.但在4　g/L纳米铁腐蚀产氢的情况下,脱氯菌可以利用纳米铁产生的阴极氢维持脱氯活动,在131　h内将20 mg/L TCE完全降解,并且其耦合的脱氯速率高于纳米铁单独降解时的速率.从乙烯的产量分析中可以看出,纳米铁供电时190　h后由脱氯菌产生的乙烯量为1.187　μmol,明显低于甲醇做电子供体时乙烯的产量2.706　μmol,表明纳米铁可能对微生物存在一定的毒性效应.同时反应190　h后乙炔的产量为0.109　μmol,相对低于与纳米铁单独降解TCE时的产量0.161　μmol,说明微生物在无电子供体的情况下,竞争利用了纳米铁与水反应产生的电子导致乙炔的生成量降低.上述结果表明,4　g/L的纳米铁与水反应生成的活性氢可以为脱氯菌提供电子,并维持其脱氯活动,这对纳米铁和脱氯菌耦合应用于地下水的有机氯修复具有重要的实际意义.     

厌氧条件下有机氯代烃污染物的氧化降解

根据土柱实验,对3种弱还原条件下氯乙烷和氯乙烯类化合物的氧化降解进行了研究.结果显示,在硝酸盐和氧化锰存在条件下,1,2-二氯乙烷(1,2-DCA)和一氯乙烯(VC)可发生氧化降解,其中,1,2-DCA转化速率在反硝化和锰还原过程中分别为1.18/h和0.54/h,VC转化速率分别为0.29/h和0.15/h.在Fe(OH)³存在条件下,VC无明显降解,1,2-DCA的降解亦受到抑制.其它有机氯代烃,如1,1,1-三氯乙烷、三氯乙烯、及二氯乙烯异构体等,在3种氧化还原条件下均未发生降     

填埋场覆盖土微生物好氧/厌氧共代谢降解氯乙烯的特性、贡献度及微生态研究

填埋场已成为氯乙烯污染的重要来源,明晰覆盖层土壤中氯乙烯的降解特性及功能微生物群落组成对氯乙烯污染控制具有重要意义.基于填埋场覆盖土系统开展了典型氯乙烯的好氧/厌氧共代谢降解研究.结果显示,好氧和厌氧条件下CH₄均可发生降解,二氯乙烯（DCE）只能在好氧条件下被降解,净降解速率为50μg·h^-1·L^-1;三氯乙烯（TCE）可同时发生好氧共代谢和厌氧共代谢转化,净降解速率分别为38和5μg·h^-1·L^-1;四氯乙烯（PCE）只能发生厌氧共代谢,降解速率为0.77μg·h^-1·L^-1,发现好氧共代谢速率远高于厌氧共代谢速率.构建了覆盖层中氯乙烯的分布模型并评估了CH₄及氯乙烯好氧/厌氧共代谢贡献度,CH₄好氧和厌氧降解贡献度分别为59%～70%和30%～41%,TCE好氧和厌氧共代谢降解贡献度分别为73%和27%.对氯乙烯厌氧/好氧共代谢降解过程的微生物群落组成及潜在功能菌属进行了分析,发现好氧...     

乳化纳米铁(EZVI)强化地下水氯代烃还原脱氯

对氯代烃污染地下水进行厌氧微生物还原脱氯时,存在微生物驯化时间长、pH值持续降低、有毒中间产物累积等限制修复效率的问题,为解决上述问题,本课题组制备了一种乳化油(EVO)包覆纳米零价铁(NZVI)的修复试剂,即乳化纳米铁(EZVI),其可以抑制NZVI钝化,增强反应速率并促进厌氧微生物脱氯反应.通过静态批实验探究了EZVI与三氯乙烯的反应动力学及EZVI对四氯乙烯(PCE)还原脱氯的中间代谢产物,并阐明了该过程机理.结果表明EZVI可以有效延缓NZVI钝化、提高反应活性,反应符合一级反应动力学,k_obs=0.182d^-1;EZVI还原PCE可以减少中间产物二氯乙烯的积累,10天内去除PCE达到97.2%,比EVO还原体系提高了68.9%;反应过程中pH值保持在6.5~7.5,ORP值在-50~10mV,提供了良好的还原环境,有效促进了厌氧微生物脱氯反应进行.     

负载型纳米Pd/Fe对氯代烃脱氯机理研究

采用实验室制备的负载型纳米Pd/Fe对几种常见的挥发性氯代烃:四氯乙烯(ICE)、三氯乙烯(TCE)、1,1-二氯乙烯(1,1-DCE)、氯乙烯(VC)和林丹(γ-HCH)进行了还原脱氯研究.负载型纳米Pd/Fe对PCE、TCE、1,1-DCE、VC和γ-HCH的还原脱氯符合准一级反应动力学方程,其反应速率常数分别为2.79 h-1、2.35 h-1、1.12 h-1、2.14 h-1和4.02 h-1.氯代烃降解过程中几乎没有中间产物生成,终产物主要为C2 H6和C2 H4,如对TCE进行降解时,生成的C2H6和C2 H4分别占总碳质量比的70%和10%.采用暴露在空气中24 h的负载型纳米Pd/Fe对PCE进行脱氯,8次循环后仍能对PCE快速完全降解,表明负载型纳米Pd/Fe的稳定性能良好.以γ-HCH为目标污染物对负载型纳米Pd/Fe的反应持久性进行了研究,200 h后负载型纳米Pd/Fe的反应性没有明显降低,表明负载型纳米Pd/Fe反应持久性能良好.温度对负载型纳米Pd/Fe的脱氯反应影响较大,测得各氯代烃脱氯反应的活化能均高于29 kJ·mol-1.对PCE、TCE进行了脱氯动力学模拟,模拟结果与试验数据基本吻合,表明负载型纳米Pd/Fe对氯代烃的脱氯,是连串、平行及多步骤反应的结合.     

羟基氧化铁对太湖底泥中多氯联苯微生物厌氧脱氯的影响

多氯联苯（PCBs）的微生物厌氧脱氯过程与底泥的理化性质密切相关.三价铁是底泥中常见的竞争性电子受体,在太湖底泥微环境中添加羟基氧化铁（FeOOH）,探究其对PCBs厌氧脱氯的影响.结果表明:①两种微环境（未添加FeOOH的对照组和添加了FeOOH的试验组）中的脱氯启动均存在滞后期,对照组的脱氯滞后期为21~42 d,而添加了40 mmol/kg（以泥浆计）FeOOH的试验组中,脱氯于42~63 d启动.脱氯启动后,对照组和FeOOH试验组的脱氯速率分别为0.035和0.014 mg/（kg·d）.第210天时,对照组内54.09%的PCBs母体被降解,而FeOOH试验组中仅去除了20.81%.因此,FeOOH对PCBs的还原脱氯具有显著的抑制作用,不仅延长了脱氯滞后期,还降低了脱氯程度和脱氯速率.②FeOOH显著抑制了间位（meta-）和对位（para-）氯的脱除（P < 0.05）.第210天时,对照组和FeOOH试验组中间位（meta-）氯原子的降解率分别为27.2%和8.9%,对位（para-）氯原子的降解率分别为17.9%和4.9%.但无论在三价铁〔Fe（Ⅲ）〕还原条件下还是无FeOOH添加的对照条件下,脱氯偏好均显示为间位（meta-）>对位（para-）>邻位（ortho-）.邻位脱氯路径仅存在于对照组中,说明FeOOH还原完全抑制了邻位脱氯进程.③脱氯过程中,对照组和FeOOH试验组的生物多样性（Shannon-Wiener指数和Simpson指数）从0天到210天逐渐降低,且Fe（Ⅲ）还原条件下的生物多样性低于对照组.随着脱氯反应的进行,厚壁菌门（Firmicutes）在两个体系中占比最高,而变形菌门（Proteobacteria）的优势地位下降,绿弯菌门（Chloroflexi）的占比有一定程度的提高.对照组和FeOOH试验组中脱氯菌Dehalococcoides均出现富集,Dehalococcoides可能对太湖底泥微环境中PCBs的厌氧脱氯具有重要作用.研究显示,FeOOH对太湖底泥中PCBs的厌氧脱氯具有抑制作用,并使微环境中的微生物群落发生了一定变化.      

不同pH条件下三氯乙烯及其脱氯产物对苯或甲苯厌氧生物降解的影响

将零价铁渗透反应格栅和生物降解格栅联用,先利用氯代烃易还原脱氯的性质通过零价铁渗透反应格栅去除氯代烃,后利用BTEX易生物降解的性质通过生物降解格栅去除BTEX,可以有效去除地下水中由氯代烃和BTEX这两种性质迥异的污染物形成的混合污染羽.但在联合格栅技术中,零价铁渗透反应格栅后的强碱性环境(pH9)、氯代烃脱氯还原中间产物(cis-1,2-DCE)的积累和可能出现的TCE穿透均可对生物降解格栅中BTEX的生物降解产生影响.针对上述问题,本文研究了不同pH条件下TCE和cis-1,2-DCE对苯或甲苯厌氧生物降解的影响.结果发现,碱性pH条件有利于苯或甲苯的生物降解,但不同pH条件下TCE或cis-1,2-DCE的加入对苯或甲苯的生物降解均产生抑制(除pH=7.9,cis-1,2-DCE=100μg·L-1时的甲苯),且TCE对苯和甲苯生物降解的抑制要明显强于cis-1,2-DCE;不同pH条件下,TCE 100和500μg·L-1对苯生物降解的抑制作用没有明显差异,但对甲苯生物降解的抑制却随着TCE浓度的增加而增加;pH=7.9时,cis-1,2-DCE的加入有利于甲苯的生物降解,之后随着pH的增加又转变为抑制.另外,在苯或甲苯厌氧生物降解过程中,可能存在cis-1,2-DCE与苯或甲苯的共代谢生物降解,且甲苯更有利于cis-1,2-DCE的共代谢降解.     

苯甲酸盐厌氧驯化体系中三氯乙烯的还原脱氯特性

采用气相色谱法实时监测了厌氧条件下,以苯甲酸盐为唯一碳源的驯化活性污泥体系对三氯乙烯(TCE)的还原脱氯情况;同时,结合454焦磷酸测序和实时荧光定量PCR技术对该体系中的微生物群落结构及脱卤拟球菌(DHC)的数量进行分析.结果表明,该驯化体系在94 d内能将TCE完全去除,最终转化产物为一氯乙烯(VC),同时伴随大量的甲烷产生;体系中微生物的多样性很高,涵盖了16个门、33个纲、52个目、88个科和129个属,而且体系中约有51.2%的微生物的分类地位尚未明确,说明体系中还存在很多未知的功能菌;体系对TCE的降解过程其实就是还原脱氯菌与其它功能菌相互作用的结果,且起主要还原脱氯作用的是携带tce A功能基因的DHC.     

A reactor system combining reductive dechlorination with cometabolic oxidation for complete degradation of tetrachloroentylene

A laboratory sequential anaerobic-aerobic bioreactor system, which consisted of an anaerobic fixed film reactor and two aerobic chemostats, was set up to degrade tetrachloroethylene (PCE) without accumulating highly toxic degradation intermediates. A soil enrichment culture, which could reductively dechlorinate 900/zM ( ca. 150 mg/L) of PCE stoichiometrically into cis-l, 2-dichloroethylene ( cis-DCE), was attached to ceramic media in the anaerobic fixed film reactor. A phenol degrading strain, Alcaligenes sp. 115, which can efficiently degrade cis-DCE by co-metabolic oxidation, was used as inocuhim for the aerobic chemostats consisted of a transformation reactor and a growth reactor.The anaerobic fixed film bioreactor showed more than 99 % of PCE transformation into cis-DCE in the range of influent PCE concentration from 5μM to 35μM at hydraulic retention time of 48h. On the other hand, efficient degradation of the resultant cis-DCE by strain R5 in the following aerobic system could not be achieved due to oxygen limitation. However, 54% of the maximum cis-DCE degradation was obtained when 10μmol of hydrogen peroxide (H2O2 ) was supplemented to the transformation reactor as an additional oxygen source. Further studies are needed to achieve more efficient co-metabolic degradation of cis-DCE in the aerobic reactor.     

A reactor system combining reductive dechloirnation with cometabolic oxidation for complete degradation of tetrachloroentylene

A laboratory sequential anaerobic aerobic bioreactor system, which consisted of an anaerobic fixed film reactor and two aerobic chemostats, was set up to degrade tetrachloroethylene (PCE) without accumulating highly toxic degradation intermediates. A soil enrichment culture, which could reductively dechlorinate 900μM (ca. 150 mg/L) of PCE stoichiometrically into cis-1,2-dichloroethylene ( cis-DCE), was attached to ceramic media in the anaerobic fixed film reactor. A phenol degrading strain, Alcaligenes sp. R5, which can efficiently degrade cis-DCE by co metabolic oxidation, was used as inoculum for the aerobic chemostats consisted of a transformation reactor and a growth reactor. The anaerobic fixed film bioreactor showed more than 99 % of PCE transformation into cis DCE in the range of influent PCE concentration from 5μM to 35μM at hydraulic retention time of 48h. On the other hand, efficient degradation of the resultant cis-DCE by strain R5 in the following aerobic system could not be achieved due to oxygen limitation. However, 54% of the maximum cis-DCE degradation was obtained when 10 μmol of hydrogen peroxide (H₂O₂) was supplemented to the transformation reactor as an additional oxygen source. Further studies are needed to achieve more efficient co metabolic degradation of cis DCE in the aerobic reactor.     

飞灰中二英热脱附行为的研究

研究了垃圾焚烧产生的飞灰中二噁英在隔绝空气受热条件下的热脱附行为及规律.通过气相和固体残留中二噁英的含量分析,推测了二噁英在不同温度条件下可能发生的几种化学反应和物理变化,同时研究了17种有毒二噁英的热脱附效率和飞灰的最佳热脱附条件.PCDD/Fs在200℃和300℃下平均脱附率分别为96.2%和95.5%,而400℃下的平均脱附率高达99.7%.结果表明,在300℃加热条件下,飞灰中的PCDD/Fs主要发生脱氯降解反应.在400℃下,飞灰中发生大量的前体合成反应,使PCDD/Fs含量显著增加.     

Coupling of zero valent iron and biobarriers for remediation of trichloroethylene in groundwater

This study attempted to construct a three series barrier system to treat high concentrations of trichloroethylene (TCE; 500 mg/L) in synthetic groundwater. The system consisted of three reactive barriers using iron fillings as an iron-based barrier in the first column, sugarcane bagasse mixed with anaerobic sludge as an anaerobic barrier in the second column, and a biofilm coated on oxygen carbon inducer releasing material as an aerobic barrier in the third column. In order to evaluate the extent of removal of TCE and its metabolites in the aquifer down gradient of the barrier system, a fourth column filled with sand was applied. Residence time of the system was investigated by a bromide tracer test. The results showed that residence time in the column system of the control set and experimental set were 23.62 and 29.99 days, respectively. The e ciency of the three series barrier system in removing TCE was approximately 84% in which the removal e ciency of TCE by the iron filling barrier, anaerobic barrier and aerobic barrier were 42%, 16% and 25%, respectively. cis-Dichloroethylene (cis-DCE), vinyl chloride (VC), ethylene and chloride ions were observed as metabolites following TCE degradation. The presence of chloride ions in the e uent from the column system indicated the degradation of TCE. However, cis-DCE and VC were not fully degraded by the proposed barrier system which suggested that another remediation technology after the barrier treatment such as air sparging and adsorption by activated carbon should be conducted.     

A review： Advances in microbial remediation of trichloroethylene （TCE）

Research works in the recent past have revealed three major biodegradation processes leading to the degradation of trichloroethylene. Reductive dechlorination is an anaerobic process in which chlorinated ethenes are used as electron acceptors. On the other hand, cometabolism requires oxygen for enzymatic degradation of chlorinated ethenes, which however yields no benefit for the bacteria involved. The third process is direct oxidation under aerobic conditions whereby chlorinated ethenes are directly used as...     

Sonocatalytic degradation of methyl orange in the presence of (nanometer and ordinary) anatase TiO2 powders

The nanometer and ordinary anatase titanium dioxide(TiO2 ) powders were adopted as the sonocatalysts for the degradation of methyl orange used as a model compound for the first time. It was found that the sonocatalytic degradation effect of methyl orange in the presence of TiO2 powder were much better than that without TiO2, but the sonocatalytic activity of the nanometer anatase TiO2 particle was obviously higher than that of ordinary anatase TiO2 particle. Although there are many factors influencing sonocatalytic degradation of methyl orange, the experimental results showed that the best degradation ratio of methyl orange could be obtained when the experimental conditions were: initial concentration 15 mg/L, nanometer anatase TiO2 adding amount 750 mg/L, ultrasonic frequency 40 kHz, output power 50 W, pH = 3.0 and temperature 40℃ within 150 min. In addition, the catalytic activity of reused nanometer anatase TiO2 catalyst was also studied and found to decline gradually comparing with initial nanometer anatase TiO2 catalyst. All experiments indicated that the method of the sonocatalytic degradation of organic pollutants in the presence of TiO2 powder was an advisable choice for non-or lowtransparent organic wastewaters.