A technical prototype unit of the actual system to be used at the Expo has been finished in advance of the event. The system’s function to decompose waste and provide water for crop cultivation has already been verified. “We are going to refine the exterior design to make it more suitable for the Expo site, as the exterior consists of just two square buildings lined up in a row,” said Tajima. “The system recovers water that is nearly free of impurities by using microorganisms to decompose and purify toilet waste. Although it needs to be periodically refilled because some water evaporates during the process, it uses very little energy and can function virtually on its own.”

At the Expo site, a mobile system mounted on a chassis is to be installed at the group bus stop as a universal toilet.

According to Asakawa, “This system leaves no sludge behind and produces no odor during the decomposition process, and that is what makes it different from the portable toilets that are currently in use.” She adds that they are working on ways to maximize the system’s appeal, but it’s challenging to create a design that will make this distinction obvious to visitors. The agricultural industry has already demonstrated the use of this technology, and it has been confirmed that the recovered water facilitates the development of agricultural products. A project to grow food using water obtained from this system is currently in underway.

With that in mind, Asakawa talked about her dream, “I’m thinking about planting plants around the Expo site and having everyone enjoy watching them grow from the spring opening through the summer and fall of the Expo.” Perhaps, we will be able to see such plants, flowers, and vegetables at the Expo site, even though this is still just an idea and it remains to be seen whether it can actually be realized.

There may not be many circumstances in which this system would be required on a daily basis in Japan because the country has fully functional water and sewage systems and excellent sanitation. However, in an emergency, it could be used as a backup. “Water is a problem in many areas of the world,” Tajima said. “Clean water has the potential to save lives. We hope that this technology developed in Japan will be applied globally. We believe that this is the primary goal of bringing a Circular Bio-toilet to the World Expo through the Co-Design Challenge.”

SDG 6 of “Clean Water and Sanitation,” which seeks to ensure safe drinking water and sanitation for all, is unquestionably embodied by this system.