Dynamic simulation of phosphorus flows through Montreal’s food and waste systems

Abstract

Phosphorus (P) is an important nutrient, essential to plant growth and agricultural production, however it can also act as an aquatic pollutant. Anthropogenic activities have impacted global P flows—causing increased mobilization of P to waterways and accumulation of P in landfills. Cities play a unique role in P management because they tend to concentrate demand for P-rich products and subsequent waste production. After developing a substance flow analysis of current P flows in Montreal, we use a system dynamics model to explore the flows of P on the island from 2008 to 2050 under four scenarios. The scenarios are based on existing trends, impending policies, and possible social change. We found that presently over 80% of P imported onto the island ends up in landfill, another 17% flows to the Saint Lawrence River, and less than 3% is available for recycling. There is significant potential to recover P from both wastewater and solid organic waste on the island of Montreal, and to reduce P flows to landfill by up to 95%. Given that existing policies in Montreal support organic waste diversion and wastewater treatment, information gained through our study can be utilized to make P policy and management decisions that fit readily into these current policies. This study shows leverage points where Montreal has the most potential to improve its P management, reducing the use of synthetic fertilizers and reducing P pollution. Furthermore, this model can be used to guide future research analyzing P flows in urban settings.