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.

Urban metabolism of phosphorus in the food production-consumption system of Bangladesh.

Anthropogenic disruption of the global phosphorus (P) cycle has already pushed it beyond the planetary boundary. Understanding P metabolism at global, regional and local scales is critical to close the loop of P for the safekeeping of mankind. Investigating the effects of urbanization-induced income growth on the natural nutrient (especially P) cycles contribute to that end. Bangladesh, a lower-middle-income agrarian economy seeing rapid urbanization and stunning GDP growth, presents itself as a good case for P-metabolism research. Past efforts to quantify P flows in the country have not addressed the effects of urbanization thereon. This time-series study quantifies the P flows in rural and urban Bangladesh using substance flow analysis after outlining the urbanization indicators (viz. GDP, income per capita, percentage of income spent on food, change in urban population and built-up area) which affects urban metabolism of P. Urbanization caused a dietary transition from cereal-based to animal-based diet resulting in 50% more P consumption from the latter by urban individuals than their rural counterparts in 2010. Comparing the P flows among the 19 expenditure groups of the urban population, an individual belonging to a higher expenditure group (USD 71-82) consumed 38% more P than one of the lower groups (USD 17-21) in 2016. Future forecasting was conducted for (i) future demand of P fertilizer using human appropriation of net primary productivity (HANPP) and (ii) P recovery potential from urban household food waste for the policymakers to get a glimpse of the future demand and recovery potential of P. The projections suggested approximately 145% rise in the national P inflow by 2030. Moreover, the universal adoption of source separation of household food waste in the two largest cities of Bangladesh can cycle back almost 1.2 × 103 tonnes of P to the system by 2030. As Bangladesh poises to faster economic growth in decades ahead, the study provides a basis for policy formulation for an appropriate P management plan to achieve circularity in nutrient use.

Magnitude of anthropogenic phosphorus storage in the agricultural production and the waste management systems at the regional and country scales.

Based on a systematic review of 17 recent substance flow analyses of phosphorus (P) at the regional and country scales, this study presents an assessment of the magnitude of anthropogenic P storage in the agricultural production and the waste management systems to identify the potential for minimizing unnecessary P storage to reduce the input of P as mineral fertilizer and the loss of P. The assessment indicates that in case of all (6) P flow analyses at the regional scale, the combined mass of annual P storage in the agricultural production and the waste management systems is greater than 50 % of the mass of annual P inflow as mineral fertilizer in the agricultural production system, while this is close to or more than 100 % in case of half of these analyses. At the country scale, in case of the majority (7 out of 11) of analyses, the combined mass of annual P storage in the agricultural production and the waste management systems has been found to be roughly equivalent or greater than 100 % of the mass of annual P inflow as mineral fertilizer in the agricultural production system, while it ranged from 30 to 60 % in the remaining analyses. A simple scenario analysis has revealed that the annual storage of P in this manner over 100 years could result in the accumulation of a massive amount of P in the agricultural production and the waste management systems at both the regional and country scales. This study suggests that sustainable P management initiatives at the regional and country scales should put more emphasis on minimizing unwanted P storage in the agricultural production and the waste management systems.