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 × 10 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.