Historical trends, roles, and future challenges of sewage sludge thermal treatment in Japan

In Japan, almost all sewage sludge is not sent to landfills due to the country’s limited land availability and the need to prevent global warming. Most sludges undergo thermal treatment. Sewage sludge incineration is popular. Recent technological advancements include fluidized bed and step grate stoker incinerators. Energy-saving and recovery technologies have been gradually developed. Currently, sludge thermal drying, melting, carbonization, and gasification are commercially implemented; energy-saving and recycling strategies are steadily progressing. In particular, the conversion of sewage sludge into fuel and fertilizer has increased in recent years. These new technologies enhance energy efficiency, reduce CO₂ emissions, and, notably, decrease N₂O emissions. Each technology and its applications are distinct. Thermal treatments are expected to continue as a measure against organic pollutants in sewage sludge. Continued technological development will contribute to achieving a carbon-neutral society, promoting a circular economy, and ensuring food security.