オゾンマイクロバブル水処理装置による汚泥可溶化性能の評価

摘要

海外のインフラ未整備地域や人口密度の低い地域では，広域の下水道より居住地域単位に分散配置した小規模の下排水処理設備の導入が合理的と考えられる.水不足への対応や工業利用で再生水の需要がある場合，小規模処理方式の一つである膜分離活性汚泥法にナノフィルター（NF)や逆浸透（RO)膜処理を組み合わせた「膜分離活性汚泥法+NF/ROシステム」が有用であるが，放流水質の改善や余剰汚泥の減容が課題である.本研究では，膜処理濃縮水の残留圧力を利用して反応性の高いマイクロバブルを生成する技術をオゾン処理に適用し，オゾンマイクロバブルで濃縮水中の有機物を分解するとともに，汚泥を可溶化して浮上分離し生物反応槽に返流する水処理技術を開発した.下水処理場に設置した実証装置で性能を評価した結果，オゾン注入率50mg/Lにおいて，本装置の導入を想定している中国の放流水質を達成できる最大の可溶化率（汚泥の削減率）は75%であり，この条件で運転コストを試算すると従来比で27%削減可能である.%For aland area with inadequate infrastructure or a thinly-populated area, installation of small-scale sewage and effluent treatment facilities which are placed as a unit in alocal area is more reasonable than installation of large-scale regional sewerage systems. One of the commonly used small-scale facilities is the Membrane Bio-reactor plus NF/RO membrane filtration system (NF: nano-filtration; RO: reverse osmosis). This system has been employed to meet demands for reclamation water use as industrial water or to resolve serious water shortages. However, it has problems in getting effluent quality improvement and sludge volume reduction. In this study, countermeasures for these problems were developed. They are water treatment techniques to decompose organic materials in RO concentrated water and to get sludge solubilization and flotation using ozone micro-bubbles; the micro-bubbles are generated by residual pressure of the RO concentrated water. Solubilized sludge is returned to the membrane bio-reactor and the volume of biological excess sludge is reduced. Results from a demonstration test in an actual sewage plant showed that the maximum solubilization ratio reached 75 % at the ozone injection ratio of 50 mg/L, and there was a 27 % reduction in the operational cost under the tested conditions.