Phosphorus circular economy of disposable baby nappy waste: Quantification, assessment of recycling technologies and plan for sustainability.

This study assessed the potential for minimizing human excreta bound phosphorus (P) loss through used disposable baby nappies, an area that remained unexplored for nations. Accordingly, it performed a substance flow analysis to assess the national P loss through used disposable baby nappies in the case of Australia. The analysis revealed that approximately 308 tonne P is lost through used baby nappies to landfills in Australia in 2019, which is nearly 2.5% of the overall P excreta as human waste. Although the quantity seems small in percentage term, it could result in the loss of a significant amount of P over several years, as assessed 5452 tonne P over the 2001-2019 period, which is concerning in the context of anticipated future global P scarcity. The review of peer-reviewed literature on available technologies/methods for recycling disposable baby nappy waste indicates that there are some technologies for recycling P particularly through co-composting with food and other organic wastes, while the majority of these are still at the lab/pilot scale. There are also various recycling techniques with purpose ranging from energy recovery to volume reduction, generation of pulp, hydrogel, cellulose, and polymer as well as to increase yield stress and viscosity of concrete, however, these are not effective in P recovery. The study implies that compost made of nappy waste can be used as fertilizer to produce bamboo, cotton, and maize plants to supply raw materials for producing biodegradable nappies, hence, to close the loop. The various product and system design options e.g., designing for flushing, designing for disassembling the excreta containing part, and designing for community composting suggested in this study could be further researched for identifying best suitable option to achieve P circular economy of disposable baby nappies. This study also recommends necessary interventions at various stages of the nappy life cycle to ensure sustainable management of phosphorus.