Development of methane fermentation technology for sewage using forward osmosis membrane

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K22932
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 64:Environmental conservation measure and related fields
• Research Institution: Hiroshima University
• Principal Investigator: NISHIJIMA WATARU 広島大学, 環境安全センター, 教授 (20243602)
• Project Period (FY): 2019-06-28 – 2022-03-31
• Keywords: 下水 / 正浸透膜 / メタン発酵

Outline of Final Research Achievements

The concentration of organic matter in sewage is low and energy in it cannot be recovered using methane fermentation. In this research, we aimed to develop a technique to concentrate organic matters in it by a forward osmotic (FO) membrane (FO) using the osmotic pressure difference between seawater and sewage as a driving force. Originally, the FO membrane is operated without power, but by applying constant pressure, improvement of the flow rate and improvement of the removability of inorganic salts that inhibit methane fermentation were achieved. The divalent ions tended to be more difficult to remove than the monovalent inorganic ions, but it was found that the inhibition of methane fermentation can be suppressed by increasing the removability of only the monovalent ions. It was shown that efficient cleaning can be achieved by allowing sodium hypochlorite to permeate from the seawater side and act on the adhesive surface between the foulant and the membrane.

Free Research Field

環境工学

Academic Significance and Societal Importance of the Research Achievements

下水は、現在エネルギーをかけて処理されており、我が国の電力消費量の約0.35％を消費し、処理の過程で発生する汚泥は産業廃棄物の20％に達する。しかし、下水等を濃縮することができればエネルギー回収技術であるメタン発酵によってエネルギー回収が可能となる。無動力で運転される正浸透膜を使った下水濃縮に期待がかかるが、流量が小さく、大容量の下水等の処理には向かないことに加えて、有機物とともに無機塩類が濃縮するとメタン発酵阻害が起こる。本研究では正浸透膜に多少の加圧を加えることで、処理量を増加させると同時に無機塩類の透過性を高めることに成功し、課題に克服に大きく貢献する成果が得られた。