Environmental problems are a worldwide concern. So recycling with a zero-emission objective is being pursued.

For this purpose, a melting process whereby sludge was converted into slag has been developed and commercialized. However, as the glass material of conventional slag is inferior compared to natural stone, the use of slag as a substitute material has been limited. Therefore, glass ceramics technology was studied to produce crystallized glass from sewage sludge. The technology was researched and developed jointly with the Tokyo Metropolitan Government in pursuing the basic study and pilot plant studied from 1991 to 1995. As a result, we have successfully commercialized this technology to convert sewage sludge into a resource as stone-like products, followed successfully by a long pilot operation. Now the commercialized plant of 150 ton-cake/day was installed and has been producing stone products from sewage sludge since 1996. In this paper, we report the results of the latest pilot plant test, and the application study of stone products for recycling use as well. For long decades, we obtain building materials from mountains and forests then built up metropolis. Then the metropolis exhaust waste and surrounding environment is polluted.

We are convinced that this technology may contribute to prevent such environmentally unbalanced cycle.