高度浄水処理工程における細菌現存量のフローサイトメーターを用いた迅速評価

摘要

現在、水道水中の細菌現存量は、培養法に基づく指標によって監視されているが、培養法では検出対象が限られること、分析に長時間を要することなど課題が多い。そこで、本研究では、水道水中の細菌の現存量や生死状態を正確かつ迅速に評価するために、フローサイトメーターの活用を検討した。複数の高度浄水施設を対象として、前塩素処理の有無により、全菌数、膜損傷性に基づいた生菌数が処理工程でどのように変化しているのか、時間的にどのように変動しているのかを調査した。その結果、個別の処理における全菌数、生菌数の除去特性が明らかになると共に、浄水中の生菌数が定量下限値未満に安定的に管理されていることなどが確認された。%Bacterial abundance in drinking water is currently managed by culture-dependent heterotrophic plate counts (HPC). However, HPC have several critical limitations such as low bacterial culturability and long cultivation time. In order to circumvent those limitations and rapidly evaluate the abundance and viability of bacteria in drinking water, we examined the feasibility of flow cytometer (FCM). FCM showed sensitive response and demonstrated the wide dynamic range (103-106 cells/mL) for quantification of total cells. The abundance and membrane integrity of total cells were investigated along purification process in full-scale advanced drinking water purification plants before and after implementation of pre-chlorination. Ozonation dramatically decreased total cell counts while pre-chlorination was effective to reduce intact cell counts. On average, overall process showed 2.8 log and 2.4 log removal of total cells before and after implementation of pre-chlorination, respectively. On the other hand, intact cell concentration in finished water was controlled below the quantification limit for all the plants. Frequent collection of processed water samples revealed that variation of total cell counts in ozonated water was larger than the other samples. Long term monitoring of total cell counts for 11 consecutive days was performed to investigate daily variation of total cell counts in raw water and finished water. During the monitoring period, total cell counts in raw water varied by at most 2 times while those in finished water were always maintained below the magnitude of 103 cells/mL.