Mitsubishi Develops High-Efficiency Recovery Technology to Derive Methane, Phosphorous from Sewage

Dec 6, 2006
Takuya Otani, Nikkei Electronics

Mitsubishi Electric Corp. has developed a treatment technology, which enables highly efficient recovery of methane and phosphorous at the same time out of sewage sludge generated at sewage plants. Through proving tests at its test plant, the company confirmed a twice higher methane recovery efficiency compared to its previous technology, and phosphorous recovery of 90% compared to a total amount contained in sewage. "This technology has more impact than almost any other technologies in our research and development conducted this year. We would like to apply this technology to a broad extent," said Junji Hirotsuji, Director, Environmental Technology & Systems, Advanced Technology R&D Center, Mitsubishi Electric. From FY2007 forward, the company will promote the technology's introduction to sewage plants and other facilities in collaboration with plant manufacturers.

There were two key factors behind this development. One was the increasing burden on sewage plants reflecting the increased amount of sewage sludge emission accompanied with the larger amount of water consumption. The amount of sludge emission in Japan reportedly reaches approximately 400 million m3 per year. However, about 80% of a weight of dried sludge is organic, and therefore its efficient utilization as energy has been highly expected. The other factor was the large amount of phosphorous, a resource concerned for exhaustion, contained in sludge. Due to this, sludge has been focused on as a resource to recover phosphorous.

The technology is based on Mitsubishi Electric's proprietary "ozone alkaline treatment technology." The company explained that implementing this treatment before the existing anaerobic digestion treatment results in two major effects as follows: (1) prompted sludge dissolution and reformulation, higher methane gas generation, and a lower amount of sludge remain; (2) recovery of phosphorous, which is dissolved from sludge. In the ozone alkaline treatment, alkaline treatment is added to sludge after ozone treatment. The treatment reportedly exerts synergies including microbial cell wall dissolution in sludge, which cannot be expected through sole treatment of either ozone or alkaline.

Meanwhile, the increased amount of methane gas generation and reduced amount of sludge remain can trim cost for sludge disposal. According to calculations by Mitsubishi, compared to that required when the ozone alkaline treatment is not added, cost can be lowered by about 30%. This calculation is on an assumption of 100,000 m3 sewage treatment per day.

This technology development was a contract Mitsubishi Electric received as one of the development projects proposed by Japan's New Energy and Industrial Technology Development Organization (NEDO). The achievement is slated for display at the "Eco-Products 2006" event to be held at Tokyo Big Sight from December 14 to 16, 2006.