The Solomon Islands Environment Ministry is promoting a septic system based on traditional Japanese manure pools called koedame in the Solomon Islands, where the contamination of underground water and rivers is a serious problem.

In koedame manure pools, human waste is naturally fermented and converted into fertilizer. The ministry plans to promote the system in developing countries after studying its results on the islands.

Since 2011, the ministry has been encouraging companies with such technology to expand their businesses overseas, with the aim of utilizing advanced Japanese technology in water purification in developing countries. The contract with the Solomon Islands is a result of this support system. It was launched in December by Tokyo-based Original Engineering Consultants Co., which is engaged in water supply and sewerage works.

According to the company, polluted water on the islands is often discharged into the ground and rivers without being treated. Public lavatories are not common there, and the hygienic environment there has been deteriorating due to population growth. About 24,000 people among the population of about 500,000 suffer from diarrhea every year.

The septic system adapts the traditional Japanese system to convert human waste into fertilizer. Polluted water from flush toilets is poured into an underground tank, where disease-causing bacteria are killed by the natural heat of fermentation at about 40 C.

The water then goes through crushed stones in the tank, which filters out floating substances, and is poured into an adjacent field, where soil-dwelling bacteria further purify it.