Model for projecting the generation of used disposable diapers in the era of depopulation and aging in Japan

Japan has entered a period of depopulation and aging ahead of any other country. One concern in an aging population is increases in the generation of used disposable diapers. The use of disposable diapers, which are largely composed of plastic, can be an important issue as we work towards building a carbon-free society and break away from using fossil-derived plastics. This study aimed to develop a model to project the future generation of used disposable diapers in each municipality in Japan through 2045 and to identify the effects on municipal solid waste (MSW) management. We revealed the per capita generation of used disposable diapers, distinguishing disposable diaper products, urine and faeces in an online survey of 2000 respondents. The generation of used disposable diapers was estimated to increase in general, but the amount was projected to decrease in rural areas where the population of elderly people would decline. The proportion of used disposable diapers in combustible waste was projected to increase by 2045 in almost all municipalities of Mie Prefecture. Based on the scenario in which disposable diaper products would become lighter in the future because of technical improvements, we concluded that the impact of the decrease in the lower heating value (LHV) of used disposable diapers on the incineration process cannot be ignored in the future.