Global nitrogen and phosphorus in urban waste water based on the Shared Socio-economic pathways

This paper presents global estimates of nutrient discharge from households to surface water based on the relationships between income and human emissions represented by protein consumption, degree of connection to sewerage systems, presence of wastewater treatment plants and their level of nutrient removal efficiency. These relationships were used to construct scenarios for discharge of nutrients with waste water based on the five Shared Socio-economic Pathways for the period from 1970 to 2050. The number of inhabitants connected to a sewerage system will increase by 2-4 billion people between 2010 and 2050. Despite the enhanced nutrient removal by wastewater treatment, which will increase by 10%-40% between 2010 and 2050, nutrient discharge to surface water will increase in all scenarios by 10%-70% (from 10.4 Tg nitrogen (N) in 2010 to 13.5-17.9 Tg N by 2050 and from 1.5 Tg phosphorus (P) in 2010 to 1.6-2.4 Tg P by 2050). In most developing countries, nutrient discharge to surface water will strongly increase over the next decades, and in developed countries it will stabilize or decrease slightly. A global decrease in nutrient discharge is possible only when wastewater treatment plants are extended with at least tertiary treatment in developing countries and with advanced treatment in the developed countries. In future urban areas that will be developed over the 2010-2050 period, options for recycling can be included in wastewater management systems. A separate collection system for urine can yield 15 Tg N yr^-1 and 1.2 Tg P yr^-1, which can be made available for recycling in agriculture. The SDG 6.3 about safely treated waste water by 2030 will be reached in the developed countries in 2030. In the developing countries, the goal will be reached by 2050 only under SSP1, SSP2 and SSP5.