DISSIPATION OF 2,4-D DMA AND BEE FROM WATER,MUD, AND FISH AT LAKE SEMINOLE,GEORGIA1

ABSTRACT: Four 10-ha plots in dense watermilfoil beds of Lake Seminole, Georgia, were each treated with either 2,4-D DMA or 2,4-D BEE at rates of 22.5 and 45 kg a.e./ha. Both formulations were shown to be rapidly converted to the 2,4-D acid form, with no detection of 2,4-D DMA or 2,4-D BEE in the water within less than 24 hours after treatment. The maximum detected 2,4-D concentrations in the high rate 2,4-D DMA and 2,4-D BEE plots were 3.6 and 0.68 mg/, respectively. However, all but seven samples at a 2,4-D BEE plot showed nondetectable herbicide levels by day 7, with all water samples showing nondetectable levels by day 13. Dimethylnitrosamine and 2,4-dichlorophenol, potentially toxic transformation products of the herbicide formulations, were at nondetectable levels in all water samples. Sediment samples showed no significant net accumulation of 2,4-D, 2,4-D BEE, or 2,4-dichlorophenol during the summer monitoring; dimethylnitrosamine remained at nondetectable levels. There was no accumulation of 2,4-D in fish collected from the two plots treated with 2,4-D DMA. Four of 24 game fish from the 2,4-D BEE treatment plots contained low levels of 2,4-D in muscle tissue, with a maximum value of 0.29 μg/g. In contrast, 18 of 20 gizzard shad collected from these plots through day 13 contained detectable 2,4-D in the muscle, with a maximum concentration of 6.9 μg/g. All fish collected after day 13 contained nondetectable levels of 2,4-D. Small decreases in dissolved oxygen and pH, associated with the complete watermilfoil control in all plots, had returned to normal summer values by day 28.     

Biodegradation of 3,5-dimethyl-2,4-dichlorophenol in saline wastewater by newly isolated Penicillium sp. yz11-22N2

In this study,the performance of 3,5-dimethyl-2,4-dichlorophenol(DCMX) degradation by a screened strain was investigated.18 S r DNA and the neighbor-joining method were used for identification of the isolated strain.The results of phylogenetic analysis and scanning electron micrographs showed that the most probable identity of the screened strain should be Penicillium sp.Growth characteristics of Penicillium sp.and degradation processes of DCMX were examined.Fourier transform infrared spectroscopy of the inoculated DCMX solution was recorded,which supported the capacity of DCMX degradation by the screened Penicillium sp.Under different salinity conditions,the highest growth rate and removal efficiency for DCMX were obtained at p H 6.0.The removal efficiency decreased from 100%to 66% when the DCMX concentration increased from 5 to 60 mg/L,respectively.Using a Box–Behnken design,the maximum DCMX removal efficiency was determined to be 98.4%.With acclimation to salinity,higher removal efficiency could be achieved.The results demonstrate that the screened Penicillium sp.has the capability for degradation of DCMX.     

碳纳米管对水中4-氯酚和2,4-二氯酚的吸附性能研究

碳纳米管是一种具有独特结构和优异性能的新型纳米材料。文章利用碳纳米管对水溶液中的4-氯酚和2,4-二氯酚进行了吸附研究,考察了吸附时间、pH值、温度等对吸附效果的影响,并采用Langmuir和Freundlich方程进行拟合,探讨了其可能的吸附机理。研究结果表明,碳纳米管对4-氯酚和2,4-二氯酚的最佳吸附酸度在pH=2～6。碳纳米管对2,4-二氯酚吸附量大于对4-氯酚的吸附量,二者动力学特征均符合准二级动力学方程。研究了4-氯酚和2,4-二氯酚在碳纳米管上的吸附等温线。研究结果表明:4-氯酚和2,4-二氯酚在碳纳米管上的吸附量随着温度的升高而下降。吸附过程是一个放热的过程,Langmuir和Freundlich等温吸附方程均能较好地拟合吸附等温线。碳纳米管能较好地用于除去水溶液中的4-氯酚和2,4-二氯酚。     

水/载O_3有机溶剂两相臭氧氧化法降解水体中2,4-二氯苯氧乙酸

以水/载O3有机溶剂(全氟萘烷)为新型两相臭氧氧化体系,研究了臭氧在全氟萘烷中的溶解度和稳定性,并以水体中2,4-二氯苯氧乙酸(2,4-D)为研究对象,考察了初始pH值、臭氧投加量、自由基抑制剂对两相臭氧氧化体系降解2,4-D效果的影响.结果表明:臭氧在全氟萘烷中有很高的溶解度和很好的稳定性;碱性pH环境有利于2,4-D的降解,随着水相初始pH的增加,2,4-D在水/载饱和O3全氟萘烷两相体系中的去除率明显增加;随着初始全氟萘烷载O3量与2,4-D物质的量比的增加,2,4-D总去除率明显增加;叔丁醇(20mg·mL-1)对两相体系中2,4-D降解影响不显著.     

钛基氧化物阳极氧化降解水中2,4-二氯酚

采用热氧化法制备了具有TiO2、RuO2和IrO2涂层的钛基氧化物电极(Ti/TiO2/RuO2/IrO2),并以其为工作电极考察了:①水中2,4-二氯酚(DCP)的循环伏安特性;②pH值、阳极电位和反应时间对阳极氧化降解DCP的影响;③阳极氧化对DCP水溶液可生化性的影响.结果表明,电极的氧化物负载量显著影响DCP的循环伏安特性.较高的介质pH值利于DCP的电化学氧化降解,而低pH值更易导致DCP挥发.低阳极电位下,DCP主要通过阳极直接氧化降解,因受电流密度过低的限制其降解效果较差;高阳极电位下,DCP主要通过阳极间接氧化降解,当阳极电位为1.8V,反应时间为360min时,DCP去除率可达100%,COD的去除超过50%,但能耗较高.COD的检测与紫外-可视光谱曲线表明,DCP的电化学氧化降解过程产生了有机中间体.Ti/TiO2/RuO2/IrO2阳极氧化可显著提高DCP水溶液的可生化性,表明其在氯酚废水预处理或脱毒领域有一定应用潜力.     

F-127改性纳米零价铁及对水中2,4-DCP的去除

为了增强纳米零价铁的分散性,本研究采用环境友好型材料Pluronic F-127对纳米零价铁(NZVI)进行表面改性,形成分散型纳米零价铁(F-NZVI),并用于水中2,4-DCP的去除.通过不同质量比的F-NZVI颗粒沉降试验和对2,4-DCP的去除试验,发现存在沉降去除和悬浮去除两个阶段,确定F-127与NZVI颗粒的最佳质量比为2∶1,2,4-DCP最大去除率为72.32%.通过SEM、FTIR、XRD、XPS对样品进行表面形貌、组成和晶体结构分析,发现F-127对提高NZVI分散性和抗氧化性有显著作用.通过控制不同因素研究F-NZVI去除水中2,4-DCP的最优条件,实验结果表明,当2,4-DCP初始浓度为20 mg·L~(-1)时,F-NZVI去除2,4-DCP的最佳pH值为5,F-NZVI最佳投加量为3 g·L~(-1).     

纳米级Pd/Fe@SiO2复合颗粒对2,4-DCP的还原脱氯研究

为有效抑制纳米级Pd/Fe颗粒的团聚和钝化及改善其表面特性,将纳米SiO_2包覆在Pd/Fe颗粒表面,超声波辐照下液相还原法制备纳米级Pd/Fe@SiO_2复合颗粒,采用TEM、SEM、XRD、EDX及BET表征其物性,以2,4-二氯苯酚(2,4-DCP)为目标污染物,探究其对2,4-DCP的还原脱氯影响因素、降解机理和动力学,结果表明:制备的纳米级颗粒粒径均匀、分散性好,比表面积大;体系中纳米级Pd/Fe投加量、钯化率、TEOS投加量、反应温度及溶液初始pH均会对2,4-DCP的降解效果产生明显影响;并推测出纳米级Pd/Fe@SiO_2复合颗粒对2,4-DCP的降解机理即快速吸附—逐步脱氯—最终脱附释放,其降解符合拟一级动力学关系.