纳米零价铁/过硫酸盐去除2,4-二氯酚的动力学研究

为更好地理解纳米零价铁(nZVI)激活过硫酸盐(PS)的机制和动力学,基于Langmuir-Hinshelwood机理,结合nZVI/PS体系中主要的反应步骤对2,4-二氯酚(2,4-DCP)的降解过程建立动力学模型。使用不同影响因素下(包括nZVI投加量、初始PS浓度和初始2,4-DCP浓度)PS,2,4-DCP浓度变化数据拟合动力学模型并确定速率常数,通过对速率常数的敏感性分析得到：2,4-DCP降解的整体反应动力学是由前体表面复合物内部发生电子转移反应形成硫酸根自由基SO₄^·-以及2,4-DCP被羟基自由基OH^·降解这两个过程来控制的。     

电辅助微生物还原降解五氯酚的电子传递机理

针对微生物还原降解五氯酚(PCP)缺乏电子供体及过程缓慢的问题,将电化学(电辅助)引入微生物还原降解过程。研究发现电辅助微生物体系的降解效率为97%,这比微生物体系(降解效率为62%)和电化学体系(降解效率为26%)的加和高约10%。对比研究了电辅助微生物体系和电化学体系对PCP还原降解的循环伏安曲线,结果表明:电辅助微生物体系的循环伏安曲线上存在明显的氧化还原峰,电子传递速率为0.856 m·s^-1,电子传递系数为2.024,为两电子传递过程,符合生物降解规律,证实了电辅助加速了微生物降解过程的电子传递速率。电辅助微生物体系中存在着电极、细胞色素c、cty·bc1、NAD和污染物间的逆向电子传递途径,可实现电极-微生物-污染物间多相界面的长程电子传递过程。该研究为环境污染治理提供了一种电辅助与微生物协同作用的新理念。     

微生物量对“Fe~0-厌氧微生物”联合降解2,4-DCP的影响

实验考察不同微生物量时零价铁(Fe~0)与微生物联合降解2,4-二氯酚(2,4-DCP)的效果及机理。结果表明:联合体系对目标物降解效果随微生物量增加而提高,生物量为146.25 mg VSS/L时2,4-DCP降解效果最佳。单独微生物对2,4-DCP有较强降解作用,而不同生物量时联合体系目标物降解效果均优于单独体系。联合体系与单独微生物体系反应过程pH值均有一定波动,而联合体系反应过程中的pH值高于单独微生物体系。不同微生物量时联合体系Fe~0生成的相应的铁腐蚀产物大多为Fe~(2+)离子。     

零价铁对2,4-二氯酚的还原脱氯研究

氯酚是环境中常见的难降解污染物,氯酚中氯原子的脱除可以提高其生化性。在恒温条件下,利用零价铁(Fe0)还原2,4-二氯酚(2,4-DCP)的模拟废水,研究得出在不同条件下溶液的脱氯率,表明在初始溶液pH=4.2时有利于脱氯反应的进行,Fe/C和Fe/Cu体系形成原电池,脱氯能力大大提高,Fe/Cu体系的脱氯率达到了60%,Fe/C体系的脱氯率达到了44%。溶解氧对2,4-DCP的脱氯反应有明显的抑制作用,厌氧条件下过6个小时脱氯率能够达到50%,而在好氧条件下的脱氯率为40%左右。通过XRD检测,分析了使零价铁钝化的原因。     

零价铁对2,4-二氯酚的还原脱氯研究

氯酚是环境中常见的难降解污染物,氯酚中氯原子的脱除可以提高其生化性。在恒温条件下,利用零价铁(Fe0)还原2,4-二氯酚(2,4-DCP)的模拟废水,研究得出在不同条件下溶液的脱氯率,表明在初始溶液pH=4.2时有利于脱氯反应的进行,Fe/C和Fe/Cu体系形成原电池,脱氯能力大大提高,Fe/Cu体系的脱氯率达到了60%,Fe/C体系的脱氯率达到了44%。溶解氧对2,4-DCP的脱氯反应有明显的抑制作用,厌氧条件下过6个小时脱氯率能够达到50%,而在好氧条件下的脱氯率为40%左右。通过XRD检测,分析了使零价铁钝化的原因。     

膜生物反应器对水源水中微量二氯酚的去除

通过实验室小试,研究了一体式膜生物反应器（MBR）对微污染湖水中的微量2,4-二氯酚（2,4-DCP）的去除效果。64 d的连续试验证实,当进水2,4-DCP浓度在2～200 μg·L-1时,MBR对2,4-DCP的平均去除率达936%。出水2,4-DCP浓度平均为428 μg·L-1,满足《城市供水水质标准》的要求。同时采用间歇试验对MBR去除2,4-DCP的机理进行了研究,证实生物作用在2,4-DCP的去除中起主要作用,MBR对2,4-DCP的去除符合零级动力学过程,降解速率常数为106 μg·L-1·min-1。此外,试验证实MBR对DCP的去除是基于二级基质原理,而向反应器内投加葡萄糖并不能促进MBR对2,4-DCP的去除。     

TiO2光催化降解2,4-二氯酚动力学及机理的研究

以TiO2作为催化剂,500 W汞灯作为光源,对水体中2,4-二氯酚（2,4-DCP）的光催化降解特性进行了研究。实验结果表明,TiO2光催化降解2,4-DCP效果较好,降解的最佳pH为7,催化剂的最佳投加量为200 mg·L-1。2,4-DCP的初始浓度越小,光催化的效率越高。在初始浓度为5 mg·L-1时,光催化1 h的降解率达90%。在实验的四种不同初始浓度（5 mg·L-1、10 mg·L-1、20 mg·L-1、40 mg·L-1）下,2,4-DCP的光降解速率常数近似与其初始质量浓度成一级反应动力学关系。结合高效液相色谱、气相色谱-质谱的测定结果以及Cl-、COD的变化,认为2,4-DCP的主要降解过程为：脱氯-开环-矿化、中间产物相互作用-进一步矿化。     

超声波／零价铁联合降解2，4-二氯酚的特性研究

研究了2,4-二氯酚（2,4-DCP）在超声波／零价铁联合体系中（US／Fe^0）的降解,考察了零价铁（Fe^0）投加量、初始pH、初始2,4-DCP浓度（C0）等控制参数对2,4-DCP降解效率的影响。结果表明,其降解效率分别在Fe^0投加量1．2g／L～1．6g／L,及初始pH2～3时达最大值,随目标污染物初始浓度的提高,其降解效率降低,超声波和零价铁联合体系适合降解较低浓度的2,4-DCP溶液。     

大气压介质阻挡放电降解4-氯酚废水的试验研究

采用大气压介质阻挡放电等离子体技术,对4-氯酚(4-CP)水溶液进行了降解处理,研究了放电参数对4-CP降解效率以及过氧化氢产生量的影响,并对降解动力学进行了分析。结果表明,当电源电压为160 V、电流为0.5 A、介质间距为5 mm时,4-CP的降解效果最好;随着电压、电流的提高,间距的减小,过氧化氢的生成量增加;Fe2+对4-CP的去除有明显的催化作用。动力学研究表明,4-CP的质量浓度低于200 mg·L-1时降解为1级反应,高于400mg·L-1时为0级反应。     

释氧-好氧微生物柱降解水中2,4-二氯酚的实验运行效果

以2,4-二氯酚(2,4-DCP)去除率和柱中pH、溶解氧(DO)质量浓度变化,考察释氧-好氧生物反应柱降解2,4-DCP实验的运行效果。结果表明,出水2,4-DCP质量浓度为0.9~2μg/L,去除率达98%;反应层pH范围为8.35~9.4,DO质量浓度平均为7.1 mg/L,满足微生物生长要求;释氧层稳定后DO质量浓度在8 mg/L左右,释氧良好;反应柱最终出水pH符合地表水环境质量标准。     

Ni-Fe双金属对氯代苯酚催化还原脱氯的试验

分别采用Ni-Fe双金属体系和单一零价铁对氯代有机物2,4-二氯苯酚、2-氯苯酚和4-氯苯酚进行了催化还原脱氯的研究。结果表明:单一零价铁能够对氯代苯酚还原脱氯,但效率不高,通常在10%～25%。在镍的催化作用下,零价铁对氯代苯酚的还原脱氯效率大大提高。当零价铁加入量为60 g/L,硫酸镍为0.6 g/L,初始氯代苯酚的质量浓度在25 mg/L左右,反应初始pH值控制在偏酸性的条件下,还原脱氯效率可达到70%以上。氯代苯酚降解的准一级速率常数和降解率满足以下规律:4-氯苯酚大于2-氯苯酚大于2,4-二氯苯酚。     

6种二氯酚电催化还原脱氯:表观动力学过程比较

采用自制的钯/聚吡咯(十二烷基苯磺酸钠)/钛(Pd/PPy(SDBS)/Ti)电极对二氯酚(DCP)的6种同分异构体进行了电化学还原脱氯研究。探讨了脱氯电流、溶液初始pH和污染物初始浓度对2,5-DCP脱氯过程的影响。在脱氯电流5 mA、溶液初始pH 2.5、温度25℃、污染物初始浓度100 mg·L^-1的条件下对2,3-DCP、2,4-DCP、2,5-DCP、2,6-DCP、3,4-DCP和3,5-DCP的脱氯过程进行了比较。6种DCP的脱氯产物均以苯酚为主,有少量的单氯酚产生,脱氯反应速率常数依次为4.735×10^-2、4.609×10^-2、4.845×10^-2、4.317×10^-2、3.973×10^-2、3.770×10^-2 min^-1。推测DCP的降解速率受pK_a、质子化效应和溶液pH等因素的影响,降解难度由小到大依次为2,4-DCP< 2,3-DCP< 2,5-DCP< 2,6-DCP< 3,4-DCP< 3,5-DCP。     

微弧氧化TiO2膜的电助光催化性能研究

以磷酸钠为电解液,采用微弧氧化技术制备钛基TiO2膜,以该膜为阳极,钛片为阴极与40 W紫外灯和稳压电源组成电助光催化体系,以大红染料模拟废水来评价TiO2膜光电催化能力。研究了酸度和亚铁离子质量浓度等因素对光催化的影响。结果表明:光电催化提高了TiO2膜阳极的降解率;阴极槽内亚铁离子存在会形成电-芬顿体系,有助于提高光电催化降解率。当电解液中支持电解质硫酸钠浓度为0.5 mol/L、pH=3时阳极槽的降解率达到38%,阴极槽亚铁离子质量浓度为3.0mg/L时降解率达到68%。     

Kinetic analysis for decomposition of 2,4-dichlorophenol by supercritical water oxidation

2,4-Dichlorophenol (2,4-DCP), as a halogenated model pollutant, was decomposed by using supercritical water oxidation (SCWO) in a batch reactor made of Hastelloy C-276. SCWO experiments for 2,4-DCP decomposition were performed in the range of 380–420 °C, 230–280 bar and 0.074-0.221 mol/L H₂O₂. The effect of oxidant concentration on decomposition rate and efficiency was significant near the critical temperature of 380 °C. However, the role of the oxidant concentration in the SCWO process decreased with an increase in temperature; also, excess oxidant played a key role in quite significantly decreasing the activation energy of 2,4-DCP oxidation. Variation of the reaction rate by the change of pressure was negligible even at a near critical temperature. The kinetic rate for the decomposition of 2,4-DCP in the SCWO process was well described by a simple first-order kinetic and global reaction rate model. From the SCWO experiments, the various intermediates identified with a GC/MS implied that the first reaction pathway for 2,4-DCP decomposition led to dimers such as dichlorophenoxyphenols, and the second led to single-ring and ring-opening products.     

Co3O4对2,4-二氯苯酚的吸附性能影响

以硝酸钴(Co(NO₃)₂·6H₂O)为钴源,考察了不同沉淀剂(6 mol/L氨水、1 mol/L NaOH溶液、饱和碳酸铵溶液)对Co₃O₄吸附2,4-二氯苯酚(2,4-DCP)性能的影响。考察了焙烧温度、pH值、沉淀剂种类、吸附剂用量、2,4-DCP初始质量浓度对Co₃O₄吸附性能的影响,并进行了离子干扰实验。结果表明,焙烧温度为300℃、pH=9.0、沉淀剂为1 mol/L NaOH时,Co₃O₄对20 mg/L 2,4-DCP吸附性能最佳。Co₃O₄对2, 4-DCP的动力学吸附过程符合准二级动力学方程,等温吸附方程符合Langmuir方程,吸附过程以单分子层化学吸附为主。     

2. Sensitized degradation of chlorophenols on iron oxides induced by visible light: Comparison with titanium oxide

The sensitized photocatalytic degradation of mono-, di- and trichlorophenols on iron oxides aqueous suspensions of -Fe₂O₃ and -FeOOH is reported in detail. The degradation of these compounds followed pseudo-first-order kinetics when -Fe₂O₃ was used as photocatalyst. -FeOOH was found to be inactive for chlorophenols degradation with the exception of 2,4-dichlorophenol (2,4-DCP) where a modest effect was observed. The formation of a surface complex by the chlorophenols with the iron oxide and the solubility of the particular chlorophenol in aqueous solution were observed to be the controlling parameters during the photodegradation. The results obtained with the most active catalyst -Fe₂O₃ are compared with TiO₂. Total mineralization of chlorophenols was observed on TiO₂ while on -Fe₂O₃ only partial mineralization was observed. In either case, the intermediates produced in solution during the photodegradation were found to be significantly more biodegradable than the initial compound. For mono-, di- and trichlorophenols the overall photocatalytic degradation was observed to increase in the order: 2,4,6-trichlorophenol (2,4,6-TCP)<2,3-dichlorophenol (2,3-DCP)<2-chlorophenol (2-CP)<2,4-DCP. The former sequence shows that the recalcitrant 2,4-DCP degrades more rapidly than other chlorophenols tested during this study. The photodegradation of chlorophenols on -Fe₂O₃ and TiO₂ proceeds mechanistically through para-hydroxylation of the initial compound as suggested by the intermediates found by high-pressure liquid chromatography HPLC during the course of the degradation.     

Inhibitory effect of 2,4-dichlorophenol on nitrogen removal in a sequencing batch reactor

We examined the inhibitory effect of 2,4-dichlorophenol (2,4-DCP) on nitrogen removal in the sequencing batch reactor (SBR) system. The reactor was operated with FILL, REACT (nitrification: denitrification), SETTLE, DRAW and IDLE phases in the duration ratio of 2: 12 (9: 3): 1: 1: 8 for a 24 h cycle time. The deterioration of 2,4-DCP removal efficiency from 100 to 41% was observed when the influent concentration of 2,4-DCP was increased to 30mg/L. The residual 2,4-DCP remaining in the mixed liquor was found to inhibit the nitrification process, resulting in the decrease of nitrogen removal efficiency to 25 %. For kinetic study, the result showed that the experimental data of ammoniacal nitrogen (AN) removal at every stage fitted well to the first-order kinetics equation with high R² values. The rate constant of AN removal, k _AN , decreased with increasing influent concentration of 2,4-DCP, from 0.053 to 0.0006/min when 2,4-DCP concentration increased from 0 to 30 mg/L, respectively. However, the observed gradual recovering of AN removal with respect to the removal efficiency and kinetics during the recovery stage indicated that the inhibitory effect of 2,4-DCP on the nitrification process was reversible.     

纳米Fe3O4/皂石复合材料的制备及去除2,4-二氯苯酚的性能研究

本文以水热合成法和共沉淀法制备了纳米Fe₃O₄/皂石复合材料,并用于去除水中2,4-二氯苯酚(2,4-DCP)。采用X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、扫描电镜(SEM)、透射电子显微镜(TEM)和X射线荧光光谱(XRF)等表征手段测试了纳米Fe₃O₄/皂石复合材料的物相组成、结构、形貌和元素组成,并考察了纳米Fe₃O₄/皂石复合材料在不同2,4-DCP溶液浓度、反应时间和pH等条件下对2,4-DCP的去除效果。结果表明,在皂石表面原位生长的纳米Fe₃O₄分散较为均匀,有效降低了Fe₃O₄的团聚现象。纳米Fe₃O₄/皂石复合材料在溶液pH值为6时,对2,4-DCP的最大去除量为178.46 mg/g,在反应时间为5 min时,对2,4-DCP去除量达到饱和。纳米Fe₃O₄/皂石复合材料对2,4-DCP的去除动力学符合准二级动力学模型。在此基础上,通过液相质谱联用(LC-MS)检测出2,4-DCP被降解后生成了氯酚等中间产物。本研究成果为水中有机污染物的降解提供了一种新型、环保且高效的环境功能材料。     

Treatment of Water Contaminated with Chlorinated Organic Herbicide 2,4-D by an Ozone/Gamma Process

Radiation-induced degradation of 50 ppm 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated in different ozonation times. Co-60 gamma-source was used as a gamma-source with a dose rate of 0.07 kGy/h. Ozonized samples were irradiated for the 0.2 kGy dose. It is observed that irradiation enhances the degradation of 2,4-D with ozone. The amount of passed ozone from samples is between 0.0695 g/L and 8.33 g/L with a flow rate of ozone at 0.078 L/min (10 g/h), from 10 s to 1200 s with the ozone generator. Aliphatic acids and chloride were determined with ion chromatography. Formaldehyde, dissolved oxygen, pH and total acidity were also measured. Both species and amounts of radiolytic intermediates were determined. 2,4-dichloro phenol (2,4-DCP) is one of the toxic intermediates of 2,4-D observed with GC/MS and it decomposes at further ozonation times. It is observed that combination of ozone/gamma irradiation is more effective for degradation of 2,4-D and its intermediate 2,4-DCP. Chloride ions are observed as completely released with combined processes at lower ozonation times although nearly 98% are released with 20 min' ozonation. Intermediate 2,4-DCP decomposes at earlier ozonation times than 2,4-D.