| Summary: | 碩士 === 國立雲林科技大學 === 環境與安全衛生工程系碩士班 === 99 === Conventionally applied at numerous groundwater sites, bioaugmentation of bioremediation for organic-contaminated groundwater focuses mainly on adding targeted compounds-degrading culture to a contaminated zone in order to increase the number of predominant microorganisms. However, this method appears to be limited by the direction of groundwater flow, soil heterogeneity and environment variability that can incur loss of the microorganisms, subsequently lowering the effectiveness of remediation. The ability to protect degrading cultures in a non-toxic and environmentally friendly carrier thus ensuring their presence in bioremediation wells under various stages could minimize the limitations of cell loss and make the carriers applicable to high organic-contaminated groundwater. Therefore, this study investigates the feasibility of BTEX removal efficiency based on bioaugmentation of cell-immobilized beads (CB) in a permeable reactive barrier (PRB) system by integrating CB and PRB technology for BTEX-contaminated groundwater remediation. The CB was manufactured by incorporating a biodegradable material consisting of polyvinyl alcohol (PVA) and alginate gel, as well as entrapped BTEX-degrading bacteria (Mycobacterium sp. CHXY119 and Pseudomonas sp. YATO411). The CB was installed in various locations in an artificial BTEX-contaminated groundwater system. The feasibility of BTEX removal was investigated by comparing bioaugmentation types for CB in PRB systems. The conventionally adopted oxygen-releasing compound (ORC) technology using cement as a binding material was improved by integrating CB with ORC technology to manufacture novel oxygen-releasing and cell-immobilized beads (ORCB) for both oxygen release and BTEX removal. ORCB was then installed in a lab-scale PRB to investigate how adding ORCB affects BTEX removal. This study was undertaken in three phases. In phase I, batch experiments were conducted to investigate how various amounts of CB affect BTEX degradation and the oxygen uptake. In phase II, exactly how different locations of CB in the PRB system affect BTEX removal was investigated. In phase III, BTEX removal was evaluated in the proposed ORCB system. Although the batch study revealed the presence of benzene, ethylbenzene and toluene degradation in a CB with a dual-culture system, benzene could not be removed in a single culture system. The BTEX removal efficiencies were further increased from 35–67% to 87–99% by incorporating CB into the PRB system, indicating the ability of CB technology to enhance BTEX removal. In contrast with CB, ORCB not only provided oxygen easily, but also demonstrated improved oxygen availability for microbial use. Analytical results of denaturing gradient gel electrophoresis (DGGE) suggested that the microbial community in the PRB system simplified and approached certain predominant microorganisms under long-term acclimation by BTEX. However, structural changes in the microbial community were found under transient shock organic loading conditions. Moreover, microbial community gradually recovered to their simple structure when the PRB system operated under normal-loading conditions. According to scanning electron microscopy, microorganisms could be successfully entrapped inside the pores with a homogenous distribution in the PVA/alginate beads, thus demonstrating the appropriateness of CB for the immobilization of microorganisms. Importantly, this study has successfully integrated biostimulation with bioaugmentation to remediate BTEX-contaminated groundwater. Therefore, the proposed ORCB technology and its operating conditions provide a valuable reference for future engineering design and related applications in a groundwater bioremediation system.
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