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首页> 外文学位 >Perchlorate bioremediation: Controlling media loss in ex-situ fluidized bed reactors and in-situ biological reduction by slow-release electron donor.
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Perchlorate bioremediation: Controlling media loss in ex-situ fluidized bed reactors and in-situ biological reduction by slow-release electron donor.

机译：高氯酸盐生物修复：控制异位流化床反应器中的介质损失以及通过缓释电子供体进行的原位生物还原。

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摘要

The main concern of perchlorate exposure through drinking water is its effects on the production of thyroid hormone, which is important for human metabolism and child's brain development. The US Environmental Protection Agency (EPA) has listed perchlorate in the contaminant list as well as in the Unregulated Contaminant Monitoring rule.;The extent of perchlorate contamination can be categorized by the level of contamination into parts per million (ppm) levels, typically in locations where perchlorate was manufactured, and parts per billion (ppb) levels where perchlorate was used for various purposes. Ion-exchange is generally adopted for treating ppb levels of perchlorate while biological reduction, bioremediation, is preferred for treating ppm level contamination.;This dissertation focuses on two important but not completely researched issues related to ex-situ and in-situ perchlorate biodegradation: (a) Use of digital image as a tool to determine appropriate backwashing frequency for fluidized bed reactor (FBR) used to treat perchlorate contaminated waters, (b) Feasibility of using a slow release electron donor, emulsified oil, to support in-situ degradation of perchlorate in groundwater with slow and fast hydraulic conductivities.;To address the first issue, two FBRs were built using five feet long and half inch diameter transparent plexiglass columns. Activated carbon was used as media and synthetic solutions containing 100 ppb, 100 ppm, and 10 ppm perchlorate were used. A high resolution camera was mounted targeting the operating zone of the FBR and pictures were taken at interval of 1.5 hours. The digital pictures were analyzed using the image processing tool, ImageJ. A biofilm model was developed and its simulated results were used to determine theoretical frequencies to backwash the filters so to avoid media loss. To address the second issue, four 5-foot long and 2.5-inch diameter column bioreactors were used to simulate saturated groundwater zones with fast and slow groundwater velocities. Soil and plastic rings were used as media to simulate slow and fast velocities, respectively.;The results revealed that the biofilm model predicted backwashing times that were very close to those observed using digital imaging. For the first FBR run, backwashing time forecasted using biomass growth, in perchlorate fed batch bioreactors, was in agreement with the other two methods used. However, the biomass growth data was unable to simulate similar backwashing for the second and third runs in the FBRs. The result of FBR operation indicates that images processed with the ImageJ closely represented the height of the expanded media in the FBR, and hence it can be used to decide backwashing frequency. A good agreement was found between the backwashing needs encountered in the FBR runs and those forecasted using the biofilm model.;For the testing of slow release electron donor, emulsified oil was proven to be an effective slow release electron donor to degrade nitrate and perchlorate in saturated groundwater zones. The removal of perchlorate required acclimation time while nitrate degraded almost immediately. Perchlorate degradation was highly impacted by high hydraulic conductivities (i.e. smaller contact time). Perchlorate degradation commenced after nitrate levels decreased to less than 0.5 mg/L. On the other hand, once a significant amount of biomass has been built into the system, degradation of both perchlorate and nitrate took place. It was found that the extent of degradation is dependent upon the relative amounts of perchlorate and nitrate present, the amount of electron donor present, and the residence time.
机译：饮用水中高氯酸盐暴露的主要问题是它对甲状腺激素产生的影响，这对人体新陈代谢和儿童大脑发育至关重要。美国环境保护署（EPA）已将高氯酸盐列入污染物清单以及《污染物监管不当》规则中;高氯酸盐的污染程度可以按污染物的含量分为百万分之几（ppm），通常是生产高氯酸盐的地点以及将高氯酸盐用于各种目的的十亿分之一（ppb）含量。通常采用离子交换法处理高氯酸盐的ppb水平，而采用生物还原，生物修复方法来处理ppm级污染。本论文着重研究与异位和原位高氯酸盐生物降解有关的两个重要但尚未完全研究的问题： （a）使用数字图像确定用于处理高氯酸盐污染水的流化床反应器（FBR）的适当反冲洗频率的工具，（b）使用缓释电子给体，乳化油支持原位降解的可行性为了解决第一个问题，使用五英尺长，半英寸直径的透明有机玻璃柱构建了两个FBR，以解决第一个问题。将活性炭用作介质，并使用包含100 ppb，100 ppm和10 ppm高氯酸盐的合成溶液。针对FBR的操作区域安装了高分辨率相机，并以1.5小时的间隔拍摄照片。使用图像处理工具ImageJ分析了数字图片。建立了生物膜模型，并使用其模拟结果来确定理论频率以反冲洗过滤器，从而避免介质损失。为了解决第二个问题，使用了四个5英尺长和2.5英寸直径的柱式生物反应器来模拟地下水速度快和慢的饱和地下水带。土壤和塑料环分别用作模拟慢速和快速速度的介质。结果表明，生物膜模型预测的反冲洗时间非常接近使用数字成像观察到的时间。对于第一次FBR运行，在高氯酸盐补料的分批生物反应器中使用生物量增长预测的反洗时间与所使用的其他两种方法一致。但是，生物量增长数据无法模拟FBR中第二轮和第三轮的类似反冲洗。 FBR操作的结果表明，用ImageJ处理的图像紧密代表了FBR中展开的介质的高度，因此可以用来确定反洗频率。在FBR运行中遇到的反冲洗需求与使用生物膜模型预测的反冲洗需求之间找到了很好的协议。;对于缓释电子给体的测试，乳化油被证明是一种有效的缓释电子给体，可降解水中的硝酸盐和高氯酸盐。饱和地下水区。高氯酸盐的除去需要适应时间，而硝酸盐几乎立即降解。高水导率（即较短的接触时间）对高氯酸盐的降解影响很大。硝酸盐含量降至0.5 mg / L以下后，高氯酸盐开始降解。另一方面，一旦将大量生物质建立到系统中，高氯酸盐和硝酸盐都会发生降解。发现降解的程度取决于存在的高氯酸盐和硝酸盐的相对量，存在的电子给体的量以及停留时间。

著录项

  • 作者

    Shrestha, Sichu.;

  • 作者单位

    University of Nevada, Las Vegas.;

  • 授予单位 University of Nevada, Las Vegas.;
  • 学科 Civil engineering.;Environmental engineering.
  • 学位 Ph.D.
  • 年度 2016
  • 页码 269 p.
  • 总页数 269
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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