報告書番号

V10005

タイトル（和文）

環境対策技術への適用を目指した複合微生物系の利用（その４）－セレン酸還元細菌を利用した排水処理装置の開発－

タイトル（英文）

Utilization of Complex Microbial Community in Environmental Countermeasure Technology (Part 4) Development of wastewater treatment system by using selenate-reducing bacteria

概要 （図表や脚注は「報告書全文」に掲載しております）

石炭火力発電所の脱硫排水には、石炭由来のセレン（セレン酸と亜セレン酸）が含まれる。そこで、脱硫排水処理への適用を想定して、当所の保有するセレン酸還元細菌を用いたセレン酸から亜セレン酸までの還元処理装置、ならびに本装置と組み合わせる亜セレン酸処理装置の開発を試みた。まず、セレン酸還元細菌の付着担体を充填した上向流カラム型の装置で、セレン酸含有排水の連続処理を行った。細菌の担体への付着方法と有機物（エタノール）の種類や供給量を適切に選択することにより、150日以上にわたって安定したセレン酸から亜セレン酸までの還元処理が可能であった。次に、亜セレン酸の処理を行う方法として、付着担体に混合できる吸着剤による吸着処理と、硫酸還元細菌や亜セレン酸還元細菌を用いた還元・不溶化処理を適用した。5mg/Lのセレン酸を加えた試験水の処理実験において、活性水酸化鉄系吸着剤を混合した担体を、セレン酸還元細菌の付着担体として用いることで、セレン酸・亜セレン酸とも安定かつ高速（装置容積あたりの処理速度：32mgSe/(L・日)）に処理できた。一方、細菌による還元・不溶化処理では、吸着処理に比べて2倍の滞留時間が必要であるものの、同等の処理水質が得られた。

概要 （英文）

Wastewater that is desulfurized in coal-fired thermal power stations contains selenium oxyanions in the form of soluble selenate and selenite. To remove soluble selenium, physicochemical process has been developed so far. Although selenite can be treated easily by using the process, the treatment of selenate requires a large amount of operating costs. On the other hand, it has been reported that biological process is effective for the reduction of selenate to selenite. However, no biological process has been put into practical use because of the unstable treatment ability of selenite. The purpose of this study is, therefore, to develop (1) biological reduction system for selenate by using a selenate-reducing bacterium (Pseudomonas sp. 4C-C), and (2) biological or physicochemical treatment system for selenite removal.

As the first step of the development, an upflow packed column-type reactor filled with attaching carriers for Pseudomonas sp. 4C-C was operated. After the optimization of the operational conditions (ethanol supply, coagulant addition before the attachment of the bacteria), the reactor could stably reduce selenate to selenite. To remove selenite, we carried out the adsorption treatment by using adsorbent attached to the carrier and the biological reduction treatment by using selenite-reducing bacterium (Paracoccus pantotrophus JCM-6892) and sulfate-reducing bacterium (Desulfovibrio sp. HT-1). In the case of the treatment for synthetic wastewater containing 5mg-Se/L of selenate, the combination of the biological reduction by Pseudomonas sp. 4C-C and adsorption by active iron hydroxide could remove both selenate and selenite to below the detection limit. The removal rate of selenium (sum of selenate and selenite) per volume achieved 32mg-Se/L/day. On the other hand, although the combination of the selenate-, selenite-, and sulfate-reducing bacteria was also effective to remove selenium to below the detection limit, the removal rate is about a half of the former system. A further direction of this study will be to evaluate of the effect of actual wastewater (selenium load, coexisting substances, and so on) on the treatment abillity. In addition to the treatment system, it is also necessary to develop the disposal method of used adsorbent and insolbulized selenium.

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