報告書番号

V08051

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３) -共存イオン存在下における排水中の水溶性セレンの除去-

タイトル（英文）

Utilization of Complex Microbial Community in Environmental Countermeasure Technology (Part 3) -Removal of Selenium Oxyanions from Wastewater Containing Nitrogen and Sulfur Oxyanions-

概要 （図表や脚注は「報告書全文」に掲載しております）

脱硫排水からの生物学的セレン除去において、共存イオン存在下で阻害を受けずに水溶性セレンの不溶化を行い、その除去プロセスを簡易化することを目指している。共存する水溶性窒素を除去してセレン除去に対する阻害を低減するために脱窒菌を加えることを考案し、セレン酸還元菌と硫酸還元菌と脱窒菌を混合して、模擬排水中の水溶性セレンの除去を検討した。その結果、除去速度は6.8倍増加し、硝酸を含まない場合と同等の速度で水溶性セレンを不溶化でき、セレン除去に対する阻害を防ぐことが可能となった。また、３種類の微生物を固定化した場合、不溶性セレンは不織布上に集積したため、不溶性セレンの除去プロセスを簡易化できる可能性が示された。その除去機構に関して、新たに加えた脱窒菌によって亜硝酸の蓄積無しに硝酸還元反応が速やかに進んだため、硫酸還元菌は亜硝酸による阻害を受けず、その結果として亜セレン酸の除去速度が増加したと考えた。

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. Chemical treatment of selenium oxyanions requires a sufficient amount of chemicals. Further, it results in the formation of a large amount of sludge. On the other hand, reduction of selenium oxyanions by biological treatment is inhibited by coexistent nitrogen oxyanions. In the previous report, a novel method for the removal of selenium oxyanions was demonstrated by using selenate-reducing and sulfate-reducing bacteria, with ethanol as an electron donor. In the method, it is necessary to insolubilize selenium oxyanions and simplify the process of removing insoluble selenium from wastewater in the presence of coexistent nitrogen oxyanions. The objectives of this research are as follows: (1) insolubilization of selenium oxyanions without inhibition by coexistent nitrogen oxyanions, (2) simplification of the process used for the removal of insoluble selenium, and (3) clarification of the mechanism used for the removal of soluble selenium oxyanions using bacterial combination.
Artificial wastewater containing nitrate in addition to selenate and sulfate was treated with a combination of selenate-reducing and sulfate-reducing bacteria. The rate of removal of selenium oxyanions decreased to 0.15 times that observed in wastewater without nitrate. To ensure effective removal of selenium oxyanions, a denitrifier was added to the combination of selenate-reducing and sulfate-reducing bacteria. The improved combination of denitrifier and selenate-reducing and sulfate-reducing bacteria was examined in suspension for the treatment of artificial wastewater containing selenate, nitrate, and sulfate. The rate of removal of selenium oxyanions increased to 6.8 times; this rate was equivalent to the rate observed using a combination of selenate-reducing and sulfate-reducing bacteria in wastewater without nitrate. The improved bacterial combination ensured effective removal of selenium oxyanions.
To simplify the process of removing insoluble selenium, cells of three bacterial strains were immobilized together in a polymeric gel. The artificial wastewater containing nitrate in addition to selenate and sulfate was treated using the immobilized cells. The immobilized bacterial community could also remove selenate by converting it to insoluble selenium. The immobilized cells in polymeric gel were pigmented pink, and a small amount of pink insoluble selenium was present in wastewater. This indicated that the insoluble selenium was completely captured in the polymeric gel.
Moreover, the effects of various coexistent oxyanions (selenate, selenite, nitrate, nitrite and sulfate) present in wastewater on bacterial reductions caused by a denitrifier and selenate-reducing and sulfate-reducing bacteria were investigated. Nitrite present in the wastewater strongly inhibited the reduction of sulfate reacted by sulfate-reducing bacteria. From this result, we concluded that in the case of a bacterial combination of selenate-reducing and sulfate-reducing bacteria, sulfate-reducing bacteria was inhibited by nitrite and the rate of removal of selenite by using hydrogen sulfide produced by sulfate-reducing bacteria decreased. On the other hand, in the case of adding a denitrifier to the combination of selenate-reducing and sulfate-reducing bacteria, it was found that the denitrifier reduced nitrate to nitrogen gas without nitrite accumulation. Therefore, the sulfate-reducing bacteria were not inhibited by nitrite and the rate of removal of selenite increased to the same level as that in the artificial wastewater without nitrate. We concluded that selenite reduced from selenate by selenate-reducing bacteria, and it was insolubilized quickly by sulfate-re

報告者

キーワード