Selective concentration of sewage by forward osmosis for methane fermentation
Year: 2025
Type: article
Abstract: Anaerobic fermentation has emerged as an effective method for carbon recovery in wastewater treatment, especially for sewage sludge. However, the first supernatant from primary settling tanks, despite containing more organic matter than sludge, is rarely used due to its low total organic carbon (TOC) concentration—typically only several tens of mg/L. For efficient methane fermentation, the TOC must be concentrated to at least 600 mg/L. Conventional concentration methods involving phase transitions, such as distillation, are energy-intensive. Forward osmosis (FO), a low-energy process that avoids phase changes, offers an alternative; however, conventional FO membranes concentrate not only organic matter but also inhibitory ionic species, such as Na⁺, K⁺, and SO₄²⁻. This study proposes the use of a loose FO membrane and a high–molecular weight draw solute (Pluronic 17R-4, Mw = 2,700) to selectively concentrate organic matter while allowing ion leakage. The TOC of the first supernatant was successfully concentrated over 100-fold, reaching more than 2,000 mg/L. Methane fermentation of the concentrated solution resulted in successful biogas production, whereas a conventional FO membrane led to inhibition due to ion accumulation. This approach demonstrates the feasibility of FO with loose membranes for low-energy, high-efficiency carbon recovery from dilute wastewater streams.
Authors: Yasunao Okamoto, Haruto Morishita, Atsushi Matsuoka, Ralph Rolly Gonzales, Susumu Hasegawa, Gen Yoshida, Kazuo Kumagai, Eiji Kamio, Tooru Kitagawa, Tomohisa Yoshioka, Keizo Nakagawa, Hideto Matsuyama
Institutions: Kobe University, Scion, Bioeconomy Science Institute
Language: English
Subfield: Water Science and Technology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,350
Funder: Kobe University
OpenAlex ID: W7114807350