かび臭原因物質を産生する河床付着性藍藻の挙動と対策: 多摩川上流域での事例

摘要

近年，東京都の水源である多摩川では，かび臭原因物質2-MIBを産生する河床付着性藍藻Phormidium autumnaleに起因する問題が続いており，平成25年8月には浄水場の原水で220ng/Lという極めて高い濃 度を記録している.夏季の高水温期には少ない藍藻数でも河川中の2-MIB濃度は高くなる一方で.冬季の 低水温期に藍藻が多数繁殖しても，2-MIB濃度はさほど高くならないことから.この藍藻の2-MIBの産生 および放出は水温の影響を受けているものと推定された.浄水場における高濃度2-MIB除去対策として. 水理模型実験を踏まえて，中次亜注入方式を導入したところ，粉末活性炭の除去効率が約2倍に改善された.%Recently Tama river, the water source of Tokyo, has a problem with 2-MIB caused by Phormidium autumnale. In August 2013, 220 ng/L of 2-MIB was detected from raw water of the purification plant. In high water temperature period in summer, 2-MIB concentration was very high although there were a small amount of cyanobacteria. In contrast in low temperature period in winter, 2-MIB concentration wasn't so high although there were a large amount of cyanobacteria. From these results, it is suggested that production and release of 2-MIB of cyanobacteria was affected by water temperature. Based on the result of a hydraulic experiment model, we introduced intermediate chlorination to take measures against high concentration 2-MIB. As a result the removal capacity of 2-MIB was doubled.