みずみち棒による重力濃縮効果の導入後現場データを用いた検証

摘要

重力濃縮法は下水処理場における汚泥処理工程で一般的手法であり，重力濃縮効率向上技術である「みずみち棒」が全国11箇所の下水処理場に導入されている.本研究では，みずみち棒導入前後の現場での維持管理データを元に，導入効果の検証を試みた.標準活性汚泥法からの混合汚泥については，水温が濃縮汚泥濃度に大きな影響を及ぼすと考えられ，28℃程度以下でみずみち棒により濃縮汚泥濃度の増加する傾向が見られた.みずみち棒導入後の濃縮汚泥性状が後段の嫌気性消化反応へ及ぼす影響は少なく，汚泥量削減による効率化が考えられた.オキシデーションデイッチ法からの余剰汚泥については，汚泥容量指標(SVI)が濃縮汚泥濃度に大きな影響を及ぼし，SVI 350mL/g以下でみずみち棒による濃縮効率安定化の可能性が考えられた.アンケート調査により，濃縮汚泥濃度向上効果は，みずみち棒の運転条件の設定など現場での工夫によるところも大きいと考えられた.%Gravity thickening is one of the most common traditional methods of sewage sludge thickening, and is advantageous because of its simple mechanism and structure, and low energy consumption. Water Path Forming Poles (WPFPs) were developed by upgrading Picket Fence Thickener to improve gravity thickening performances. As of June 2014， WPFPs are in operation at 11 sewage treatment plants in Japan. On-site data analysis was carried out to evaluate the effect of WPFPs on gravity thickening performances. In conventional activated sludge processes, the effect of water temperature was significant, and the performance improvement was observed at less than approximately 28℃. In oxidation ditch processes, the effect of sludge volume index (SVI) was significant and the performance improvement was possible at SVI of less than 350 mL/g. A questionnaire result revealed that not only installation of WPFPs but also efforts of on-site technicians contributed to the performance improvement.