In 2005, the Japanese word mottainai gained international attention. It was Nobel Peace Prize laureate Wangari Maathai, then Assistant Minister for Environment and Natural Resources of Kenya (2003-2007), who introduced mottainai to the world as a single word to describe the 3Rs (Reduce, Reuse, Recycle) of effective resource use. In Japan, the Basic Act on Establishing a Sound Material-Cycle Society was enacted in 2000, prompting many to reconsider the mass-production, mass-consumption nature of society and lifestyles, and initiating a movement toward the establishment of a sound material-cycle society through the appropriate reuse of resources and the recovery of heat.

At the same time, Japan’s population coverage rate for sewage treatment^*1 exceeded 70%, and the recovery and reuse of resources and energy from sewage became the core of resource recycling, leading to evolutions in technology intended for this purpose. One such resource is phosphorus. Phosphorus plays an important role in a wide range of fields, including fertilizer, feed, food, automobiles, pharmaceuticals, and cosmetics, but Japan is dependent on imports for most of its phosphorus. Focusing on the fact that a large amount of used phosphorus is contained in sewage, Kubota has tackled the recovery of phosphorus using the melting technology^*2 that it has cultivated for domestic waste and sewage treatment. When sewage sludge is heat-treated using melting technology, glassy particles called slag remain. This slag contains a large amount of phosphorus, and since heavy metals and pathogenic bacteria have already been removed through high temperature heat treatment, it is effective and safe as a fertilizer. The slag itself can be reused, thus reducing the amount of waste. The large amount of energy required for melting could also become a self-contained energy system by recovering and reusing the gas generated by methane fermentation of the sludge.

Kubota has improved its technology to the point where it can reproduce 50 to 100 kilograms of slag from one ton of sewage sludge and recover 90% of the phosphorus contained in the sludge, and is aiming to establish a business model to market the phosphorus as fertilizer. As the demand for resources is expected to increase with the growth of the world’s population and the rapid economic growth of emerging and developing countries, we aim to contribute to the next generation of social systems with technologies and solutions that enable the recovery of resources that lie dormant in cities, such as valuable metals and energy contained in various kinds of waste, in addition to sewage sludge.