【作者】 袁松虎；

【导师】 陆晓华；

【作者基本信息】 华中科技大学 ， 环境工程， 2007， 博士

【摘要】 持久性有毒物质(Persistent toxic substance, PTS)如持久性有机污染物(Persistent organic pollutants, POPs)和重金属等进入环境后,随大气沉降、降雨和地表径流等迁移并最终在土壤/沉积物上沉积,造成土壤/沉积物的污染,因而对污染土壤/沉积物的修复非常必要。绝大部分土壤修复技术对土壤的渗透性有较高的要求,处理效果随粘性增加而降低。电动力学(Electrokinetic, EK)技术利用电场驱动土壤中的污染物迁移,在粘性土壤修复上具有很大的潜力。本文在综述电动力学土壤/沉积物修复现状的基础上,指出当前电动力学土壤修复中存在的问题:(1)EK技术对多氯代芳烃类POPs污染土壤的修复效果和机理目前尚不清楚,而当前土壤受六氯苯( Hexachlorobenzene, HCB )、多氯联苯(Polychlorobiphenyls, PCBs)等污染较为严重;(2)EK技术在实际运行中的电能消耗较高,使其推广和应用受到限制;(3)在有机污染土壤修复中对电能的综合利用不够,有可能实现土壤中有机物的EK迁移和电化学降解的结合,避免或减少有机废水的后续处理。因此,本文首先研究了化学助剂强化EK技术对土壤中HCB的修复效果和机理;为降低EK过程中的电能损耗,构建了一种基于原电池原理的土壤/沉积物修复的新方法,并研究了该方法对重金属和硝基酚污染土壤修复的可行性;为避免或减少后续废水处理过程,研究了废水中有机物的原位电化学降解条件和机理。本文的主要结论有:(1)阴离子、阳离子和非离子型表面活性剂单独存在时对土壤中HCB解吸效果的强化作用为:Tween 80 >十二烷基苯磺酸钠(SDBS) >十四烷基溴化吡啶(MPB)。三种表面活性剂在土壤都有较大的吸附,其吸附量大小为:MPB > Tween 80 > SDBS。水相表面活性剂促进HCB的解吸,土壤吸附态表面活性剂抑制HCB的解吸,污染土壤中HCB的解吸率同水相胶束浓度呈正线性相关。多种表面活性剂的优化组合可以减少表面活性剂在土壤上的吸附损失,但同时对HCB的解吸效果也有所降低。(2)电渗析流(EOF)随阳极冲洗液缓冲容量(0-0.05 mmol/L)的增加先增加(0-0.025 mmol/L)后降低(0.025-0.05 mmol/L),随离子强度的增加而降低。阳极冲洗液中加入Tween 80或β-环糊精(β-CD)可以明显强化土壤中HCB的EK迁移效果。β-CD对HCB的强化解吸效果比Tween 80低,但对HCB的迁移效果更明显。HCB在化学助剂作用下先解吸并溶解进入土壤空隙水,溶解态的HCB随着电渗析流迁移。三种低氯代苯都表现出较明显的EK迁移效果,其迁移效果随水溶性增加而增加。(3)利用铁屑和活性碳构建的原电池产生电场来驱动土壤中重金属的电迁移是可行的。土壤中铜的迁移效果同土壤pH具有很强的相关性,pH越低迁移效果越明显。多个原电池的串联可以扩展处理区域,每个电池中镉的电迁移效率比在单个电池中的小。沉积物中的铜可以通过原电池技术得到去除,去除效果随上覆水层电解质含量的增加而降低,随底部沉积物中电解质含量的增加而增加。(4)原电池对土壤/沉积物中硝基酚的迁移效果较弱。土壤中的硝基酚经扩散作用向极室的迁移非常明显;沉积物中的硝基酚向上覆水层中的扩散作用较强,扩散到水相的硝基酚由活性碳吸附、铁还原、挥发和自然代谢等途径去除。铁棒对硝基酚具有很好的还原效果,还原效率随pH降低而增加。串联碳可以显著促进铁对硝基酚的还原速率和铁本身的腐蚀速率。(5)在有机污染土壤的电动力学修复中,合理调控电动力学条件,实现有机物的电动力学迁移和电化学降解的有效结合是可行的。迁移到极室的有机污染物的电化学降解,可以避免后续处理或减少后续处理的难度,抑制析氢或析氧反应,减少电极反应导致的土壤性质破坏和对电渗析流的影响。更多还原

【Abstract】 Persistent toxic substances (PTS), such as persistent organic pollutants (POPs) and heavy metals, migrate with atmospherical settling, raining and surface run off, deposit in soils and sediment and lead to soil and sediment pollution. It is therefore necessary to remediate the polluted sites. However, most remediation technologies are suitable to permeable soils. Electrikinetic (EK), which utilizes electric field to drive the movement of pollutants in soils, has shown great potential in the remediation of clayed soils.This study reviewed the literatures on EK remediation and point out the problems involved in the process. The efficiency and mechanism of EK remediation of soils contaminated with POPs such as polychlorinated aromatic hydrocarbons are still unknowm. The electric energy consumption of EK remediation is relatively high, which restricted the extensive practical application. It is possible to integrate the EK movement of organic pollutants in soils and the in situ electrochemical degradation in aqueous solutions.Therefore, this paper first investigated the EK movement of hexachlorobenzene (HCB), a typical polychlorinated aromatic hydrocarbon, in soils. In order to reduce electric consumption in EK process, a novel galvanic cell EK process was developed. The electrochemical degradation of toxic organic pollutants was studied to provide useful information on the integration of EK migration and in situ electrochemical degradation. The main conclusions are drawn as follows:(1) The potential of single surfactants to enhance the desorption of HCB from soil was obtained as Tween 80 > sodium dodecyl benzene sulfonic (SDBS) > myristyl pyridinium bromide (MPB). All the surfactants were largely adsorbed on soil and the sorption followed MPB > Tween 80 > SDBS. The desorption of HCB increased significantly and linearly with the increase of the aqueous micelle concentrations of surfactants. Optimal combination of surfactants could reduce the sorption loss of surfactants.(2) With the increase of buffering capacity of anodic purging solution (0?0.05 mmol/L), electroosmotic flow (EOF) fisrt increased and then decreased. EOF decreased with the increase of ionic strength. Addition of Tween 80 orβ-CD to anodic purging solution could highly attribute to the movement of HCB. Althoughβ-CD led to less desorption of HCB from soil than Tween 80, the migration of HCB withβ-CD was more significant than that with Tween 80. The mechanism of HCB movement involved the desorption of HCB from soil to pore solution and the subsequent migration with electroosmotic flow. The EK movement of less chlorinated benzenes was significant and the efficiency increased with the increase of their aqueous solubility.(3) It is feasible to drive the electromigration of heavy metals in soil by a galvanic cell constructed with iron and carbon. The migration of copper in soil increased with the drop of soil pH. The series of multiple galvanic cells could expand the treatment area, but the migration of cadmium of each cell in the series was lower than that in separated cell. Copper in sediment could be also removed by the galvanic cell and the removal efficiency increased with the increase of electrolyte in sediment or the decrease of electrolyte in supernatant water.(4) The EK movement of nitrophenol in soil driven by the galvanic cell was insignificant. Nitrophenol in soil could diffuse into electrode compartments. Nitrophenol in sediment diffused into supernatant water and was then removed by carbon adsorption, iron reduction, volatilization and natural degradation. The reduction of nitrophenol on iron stick was clear and could be enhanced when a carbon stick was connected. The reduction of nitrophenol in both cases rose with the drop of aqueous pH.(5) In the EK remediation of organic compound polluted soils, it is possible to integrate the EK movement of organic compounds from soils to compartments and the electrochemical degradation of the compound in the compartments via conditioning the EK parameters. This integration may avoid post-treatment or reduce the post-treatment difficulty, inhibit the evolution of H2 and O2, and decrease the change of soil characteristics.更多还原