Wastewater Treatment

Sewage treatment plant in Japan to test biogas purification system

Sept. 16, 2022

The City of Kurashiki has agreed to evaluate and demonstrate the performance of Asahi Kasei’s biogas purification system, which uses a new adsorbent to recover both methane and carbon dioxide separately.

Picture Kojima Sewage Treatment Plant Kurashiki Okayama Prefecture Japan 63236ffe3ab92

In Japan, multinational chemical company Asahi Kasei and the City of Kurashiki have agreed to hold a trial to evaluate and demonstrate the performance of the company’s biogas purification system at a sewage treatment plant in the city.

The system refines high-purity methane gas (biomethane) by removing carbon dioxide (CO₂) from biogas utilizing Asahi Kasei’s newly developed adsorbent, K-GIS zeolite, which selectively adsorbs carbon dioxide. While conventional adsorbents adsorb methane in addition to carbon dioxide, the company says that its K-GIS zeolite adsorbs almost no methane. This enables the system to efficiently separate and recover high-purity methane while also recovering high-purity CO₂.

Crystal structure of the new adsorbent, K-GIS zeolite – the size of cavities in the crystal is slightly larger than the CO2 molecule, which allows CO2 to enter the crystal and be adsorbed while larger molecules such as methane are excluded.

Biogas from sewage sludge, garbage, etc., consists of approximately 60 percent methane and 40 percent carbon dioxide. While the use of biogas as a carbon-neutral fuel is rapidly expanding, it is also a source of biomethane as a substitute for natural gas in Europe and the U.S.

In Kurashiki City, electricity is generated using biogas derived from sewage sludge at the Kojima Sewage Treatment Plant. The system will use a portion of this biogas for the demonstration trial. If biomethane production using the system is combined with carbon capture and utilization or storage, the cycle would be carbon negative. In the demonstration trial, the separated gases are recombined to biogas as fuel for generating electricity.

The agreement plans to have equipment fabricated by November 2022, installation begun in May 2023, and operation by the end of 2023. As part of the program, Asahi Kasei will design, install, and operate the system, while also evaluating and demonstrating its performance. Kurashiki will provde the biogas generated from sewage sludge as well as the site for the demonstration trial.

The company expects to commercialize its system around 2025 or 2026, following additional trials in countries or regions where biogas purification is performed.