Harvest to harvest : Recovering nutrients with New Sanitation systems for reuse in Urban Agriculture

To maintain the city as a viable concept for human dwelling in the long term, a circular metabolism needs to be adopted that relies on recovering, reusing and recycling resources, in which output ('waste') from one metabolic urban conversion equals input for another. Urban Agriculture (UA) and source-separation-based New Sanitation (NS) are gaining momentum as measures for improved urban resource management. UA aims to localize food provisioning while NS aims to reorganize wastewater and organic waste management to recover valuable and crucial resources. The objective of this paper is to assess the match between the supply by NS systems and the demand from UA for nitrogen, phosphorus and organic matter, in terms of quantity and quality, to foster a circular metabolism. The research is contextualized in the city of Rotterdam. The methodology used is based on the Urban Harvest Approach (UHA), developed previously for the urban water cycle. Novel to this research is adapting the UHA to nitrogen, phosphorus and organic matter loads for two practiced UA typologies (ground-based and rooftop) and four NS concepts for the treatment of domestic urine, feces and organic kitchen waste. Results show that demand for nutrients and organic matter from UA can be minimized by 65-85% and a self-sufficiency of 100% for phosphorus can be achieved, while partial self-sufficiency for nitrogen and organic matter. This research reveals that integration of NS and UA maximizes urban self-sufficiency.