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氧微纳气泡改性覆盖材料及其对富营养化缺氧水体增氧研究
Alternative TitleOxygen micro/nano-bubbles modified capping materials and their oxygenation effect on eutrophication induced hypoxia
苗肖君
Subtype博士
Thesis Advisor潘纲
2019-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name理学博士
Degree Discipline环境工程
Keyword微纳气泡,富营养化,覆盖, 缺氧, 多孔材料 micro/nano-bubbles, Eutrophication, Capping, Hypoxia, Porous Materials
Abstract

        富营养化引起的水体缺氧现象是一个受科研群体和社会公众普遍关注的全球性环境问题。 在大量藻华暴发的富营养化水体中,藻类分解消耗掉了水中大量的溶解氧( DO),诱发水体缺氧现象发生,这不仅严重恶化了水体水质、水中生物群落以及水体底泥质量,还破坏了生态系统的平衡和自我调节能力,造成水体功能的 全面退化,并最终导致了水体“黑臭”(或黑水团)现象的发生。而具有高稳定性、高活性和高传质效率的氧微纳气泡 MNBs 为解决水体缺氧现象提供了新思路。本文在系统地研究了 5种微纳气泡制备方法,并探索出一种既能释放出大量体相 MNBs,又能通过沉积物覆盖的方式将界面 MNBs输送到沉积物表面的多孔材料法 MNBs制备方法,之后对常用的 15种孔性覆盖材料进行了筛选,并对 MNBs进行了表征,接着考察了改性过程的影响因素,并提出了改性机理,最后考察了改性材料对太湖模拟柱的增氧效果,主要结果如下
       (1)系统地研究了 5种 MNBs制备方法 气泡发生装置法、醇水交换法、传统变温法、微波法和孔材料法。其中,首次提出了孔材料法微纳气泡的制备方法,可同时制备氧体相 MNBs和氧界面 MNBs,有望通过沉积物 原位 覆盖的方式实现对上覆水体和沉积物界面的同步增氧;也首次提出了微波法微纳气泡的制备方法,微波法易在疏水的 高序热解石墨( HOPG 表面生成界面纳米气泡,但体相纳米气泡的生成效率较低;在现有醇水交换法基础上提出了醇注入水可控交换的纳米气泡制备方法,制备出高浓度、小粒径、具有单一粒径分布峰的体相纳米气泡;在变温法中,通过控制溶液温度的变化,可 实现 颗粒活性炭( GAC 表面纳米气泡的溶解和析出,且增加变温次数,可增加活性炭表面氧纳米气泡的吸附量;利用微纳气泡发生装置可在短时间内制备出大量含氧 MNBs的悬浊溶液,实现对水体的迅速增氧 但 MNBs浓度会因气泡合并而迅速降低。
       (2)用孔材料法氧 MNBs制备方法筛选了 15种常用的孔性覆盖材料,其中活性炭和沸石的增氧效果最好,氧 MNBs释放容量最大,但活性炭的气泡释放速度较快,而沸石的气泡释放速率相对缓慢;改性材料释放的微米气泡呈规则的球形;气泡在材料的 表面孔处 生成和长大,最后脱离进入水体;活性炭对气泡有很 强的亲和力,而沸石对气泡的亲和力相对较弱;改性活性炭和改性沸石释放气
泡的平均粒径接近,但活性炭释放的气泡发生了明显的合并并造成气泡上升速率的增加;改性沸石比改性活性炭有更高的氧MNBs生成效率。
       (3)天然沸石极易吸收水分,且残存水会极大的影响其氧 MNBs改性效果,但 高温活化 可有效去除残余水,并使 沸石 活性恢复;颗粒尺寸会影响改性沸石的气体释放性能,包括微纳气泡释放速率、释放持续时间和有效释放容量,也会影响 氧 MNBs在覆盖层中的滞留;改性沸石的 MNBs释放容量和沸石对氧的吸附量有关,可以通过改变吸附压力来调控 氧 MNBs的释放容量;此外,改性沸石在空气暴露过程中有严重的改性衰减效应,在应用时应对改性沸石的保存条件格外注意。
        (4) 无论是 疏水性的 活性炭还是亲水性的沸石,经氧改性后的覆盖均优于传统未经改性的覆盖,但两种材料又有很大区别,改性沸石在上覆水增氧上占绝对优势,而改性活性炭却能维持更高更稳定的沉积物 -水 界面氧化还原电位。 增加改性活性炭覆盖厚度对模拟柱影响不大,而改性沸石在覆盖厚度不足 2 cm时,增大厚度可 较大 提升上覆水的增氧效果, 2 cm以上无进一步提升;从成本角度出发, 无论改性活性炭还是改性沸石, 1 cm覆 盖均为建议覆盖厚度,若根据实际需要增加覆盖厚度,应多次少量添加以充分利用氧微纳气泡。 将氧 MNBs改性材料与改性当地土壤( MLS)技术结合可有效改善富营养化实际水体的水质和底质情况,并使沉水植被恢复。

Other Abstract

       Eutrophication-driven hypoxia is one of the major environmental issue of global concern to both the scientific community and general public. Eutrophication-driven hypoxia is one of the major environmental issue of global concern to both the scientific community and general public. In eutrophic water suffering harmful algal blooms, degradation of organic matter (algae cells) consume the dissolved oxygen (DO) and induce hypoxia/anoxia which not only deteriorated water/sediment quality and aquatic community but also devastate the equilibrium of water ecosystem and also the self-adjusting ability, resulting in comprehensive degradation of functions of water, and eventually also leading to the outbreak of black-odor water (black bloom). The oxygen (O2) micro/nano-bubbles (MNBs), which are characterized of high stability, high activity and high mass transfer efficiency, provide a new perspective to combat water hypoxia. In this study, 5 different preparation methods of MNBs were systematically investigated to develop an effective porous material-based MNBs preparation. The porous material-based preparation method not only can release massive O2 bulk MNBs to the overlying water, but also can deliver O2 surface MNBs to the bottom sediment by sediment capping. Then 15 commonly used porous capping materials were screened, and characteristics of O2 MNBs were investigated. Factors controlling O2 MNBs loading on natural zeolite (NZ) were also studied along with the development of O2 MNBs modification mechanism Finally, the oxygenation effect of the O2 MNBs modified capping materials on simulated columns of Lake Taihu were investigate. The main results were list as follows:
       (1) Five MNBs preparation methods i.e., MNBs generator method, ethanol-water exchanging method, traditional temperature variation method, microwave-induced method and porous material-based method, were systematically investigated. The first proposed porous material-based MNBs preparation method could prepare O2 bulk MNBs and O2 surface MNBs simultaneously, and was promising to realize the synchronized oxygenation of the overlying water and the bottom sediment by in situ capping. Microwave-induced MNBs generation method was also first proposed, and it could induce generation of surface MNBs effectively on hydrophobic HOPG (High order pyrolytic graphite), yet a low generation efficiency in bulk NBs. A new controllable ethanol-water NBs generation method was developed based on the traditional ethanol-water exchanging, which could produce bulk NBs with high concentration, small bubble diameter and single bubble diameter. In temperature variation NBs generation method, the dissolution and nucleation of O2 NBs could be controlled by changing temperature of solutions, and surface O2 NBs increased with increasing temperature variation times. The MNBs generator could produce amount of O2 MNBs containing water in a short time realizing quick oxygenation of water, however, O2 MNBs concentration reduced rapidly due to their coalescence.
       (2) 15 commonly used porous capping materials were screened by porous material-based O2 MNBs preparation method. From them GAC (granular active carbon) and NZ (natural zeolite) showed the best oxygenation effect and the largest O2 MNBs releasing capacity, with modified GAC released O2 MNBs fast and modified NZ released relatively slow. The O2 MBs were in regular spherical shape, and generated and grew up at the surface pores of the materials, and finally detached into water. GAC had a strong affinity with O2 MBs, while NZ had a slightly weak one. The mean diameters of MBs released by modified GAC and modified NZ were similar, yet bubbles were coalesced for GAC and resulting in an increased bubble rising velocity. Modified NZ had a higher O2 NBs generation efficiency than modified GAC.
       (3) Natural zeolite tended to adsorb water vapor easily, and the residual water suppressed oxygen loading and affected the O2 MNBs releasing capacity, and even disabled O2 MNBs releasing when residual water was 10.3%. However, activation with high temperature could remove the residual water and the O2 MNBs releasing capacity can recover accordingly. Particle sizes affected the O2 MNBs releasing performance, including releasing velocity, releasing duration time and valid releasing capacity, and also affected the O2 MNBs entrapment in the capping layer. The O2 MNBs releasing capacity was associated with the O2 adsorption quantity on NZ, and could be controlled by modification/adsorption pressure. In addition, air exposure had significant attenuation effect on modified NZ, and great care should be taken to preserve the modified NZ.
        (4) For both of the hydrophobic GAC and the hydrophilic NZ, modification capping was superior to traditional capping, however, there were also significant differences between the two porous materials. While modified NZ dominated in oxygenation of overlying water, modified GAC had advantages on maintaining a higher and more stable oxidation reduction potential (ORP) values of sediment-water interface. Increasing capping thickness of modified GAC did not affect the simulated columns significantly, while for modified NZ, increasing capping thickness could promote the oxygenation effect significantly on overlying water when thickness was no more than 2 cm, but with no further promotion when thickness exceeded 2 cm. In consideration of the cost, 1 cm modified capping was the suggested capping thickness for both GAC and NZ. However, if thicker capping was needed according to practical requirement, repeatedly small doses adding would be more feasible than single adding in order to make the best of O2 MNBs. Combination of the oxygen MNBs modified materials with modified local soil (MLS) technology could improve water and sediment quality in natural eutrophic water, and restore the submerged macrophytes.

Pages152
Language中文
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/42269
Collection环境纳米技术与健康效应重点实验室
Recommended Citation
GB/T 7714
苗肖君. 氧微纳气泡改性覆盖材料及其对富营养化缺氧水体增氧研究[D]. 北京. 中国科学院生态环境研究中心,2019.
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