下水処理水の臭気の強度および特徴の喚覚測定法による把握

摘要

下水処理水臭や環境水の臭気を，45℃三点比較式フラスコ法を用いて調査し，下水処理水を貯留した場合の臭気の変化についても調べた．パネル幾何平均で求めた臭気強度（TON）の半分から倍の範囲に入るパネル人数の比率は，平均44％で，個人の臭気感覚にはある程度のばらつきが見られたが，サンプルごとに最大値，最小値を与えたパネルを除外した場合としない場合とで，幾何平均値が2割以内の差に収まるサンプルは，92％であり，平均値としては，45℃三点比較式の方法によって臭気の安定した測定が可能であった．自然河川の臭気強度（TON）は46以下で，ほとんどのサンプルで13以下であった一方，下水処理水では39~713（中央値156）であった．また，環境維持再生水では通常の処理水に比較して臭気が低減されていた．下水処理水を貯留しておくと，初期には，揮散によって臭気が減少するが，空気下で撹拝を行い嫌気化を防いだ場合であっても，pHが中性の条件では，臭気の増加が見られた．訓練しない学生による選択式アンケートによると，下水処理水のにおいは，川の魚のにおい，土のにおい，カビくさいにおいに似ているとの回答が多かった．%A sensory test called three-flasks method was applied for the quantification of threshold odor numbers (TONs) of treated wastewater and of water in environments. Less than 20% differences were found between the averaged threshold odor numbers (TONs) excluding the maximum and the minimum value given by individual examiners and those without the exclusion of extreme results for 92% samples, though individual results were scattered beyond the range between the half values and double values depending on the examiners. Higher TONs of 39 to 713 were obtained for the samples of treated wastewater compared with the samples taken from natural rivers, whose TONs were less than 46 and typically less than 13. Advanced treatments followed by biological treatment were effective for the reduction of odor of the treated water. The storage of treated wastewater decreased the odor by volatilization, while the long-term storage increased the odor even when the sample was kept aerobic. According to the answers of the hearing to untrained examiners, the odor of treated wastewater was a combination of fishy, earthy, musty, and other unfavorable odors.