Mapping phosphorus hotspots in Sydney's organic wastes: A spatially explicit inventory to facilitate urban phosphorus recycling

Phosphorus is an essential element for food production whose main global sources are becoming scarce and expensive. Furthermore, losses of phosphorus throughout the food production chain can also cause serious aquatic pollution. Recycling urban organic waste resources high in phosphorus could simultaneously address scarcity concerns for agricultural producers who rely on phosphorus fertilisers, and waste managers seeking to divert waste from landfills to decrease environmental burdens. Recycling phosphorus back to agricultural lands however requires careful logistical planning to maximize benefits and minimize costs, including processing and transportation. The first step towards such analyses is quantifying recycling potential in a spatially explicit way. Here we present such inventories and scenarios for the Greater Sydney Basin's recyclable phosphorus supply and agricultural demand. In 2011, there was 15 times more phosphorus available in organic waste than agricultural demand for phosphorus in Sydney. Hypothetically, if future city residents shifted to a plant-based diet, eliminated edible food waste, and removed animal production in the Greater Sydney Basin, available phosphorus supply would decrease to 7.25 kt of phosphorus per year, even when accounting for population growth by 2031, and demand would also decrease to 0.40 kt of phosphorus per year. Creating a circular phosphorus economy for Sydney, in all scenarios considered, would require effective recycling strategies which include transport outside of the Greater Sydney Basin. These spatially explicit scenarios can be used as a tool to facilitate stakeholders engagement to identify opportunities and barriers for appropriate organic waste recycling strategies