Balancing nutrient flows between human settlements and the rest of nature within planetary boundaries is essential for life on earth and for safeguarding biodiversity and ecosystem integrity, notably healthy water bodies and soils. Recirculating nutrients in human excreta and other organic residuals to agriculture can make important contributions to more circular nutrient flows and improved food security.
The Problem
Linear nutrient flows
Human activities are profoundly altering critical nutrient flows that underpin productive ecosystems and life on earth. Factors such as the rise of waterborne sanitation and synthetic fertilizers, increased urbanization, as well as globalization and industrialization of food and farming systems have brought about a linearization and globalization of nutrient flows.
Orange solid arrows: linearization and globalization of nutrient flows. Grey solid boxes: associated drivers. Orange dotted boxes: associated environmental problems. Green dotted arrows: opportunities for nutrient recirculation. Adapted from: Harder R, Wielemaker R, Molander S, Öberg G. 2020.
Nutrient Pollution and Dissipation
The increasing linearization of nutrient flows has led to nitrogen and phosphorus emissions crossing planetary boundaries beyond the threshold considered safe. Dead-zones in oceans and large lakes are among the most tangible effects of nutrient pollution in water bodies.
Dependence on Mineral Fertilizers
Today, global agricultural production largely relies on high inputs of, among others, nutrients mined from finite reserves and produced using fossil fuels. In light of continued nutrient dissipation and the geopolitical tensions related to the progressive depletion of high-quality resources, increased insecurities related to future nutrient supplies are anticipated.
The Challenge
Balancing nutrient flows
One of the key prerequisites to achieving and maintaining global food security is improved nutrient management along the entire food chain, which includes farming practices, food processing, consumer behavior, and waste management. Better nutrient management also includes the recovery and reuse of nutrients in human excreta and wastewater, using approaches and solutions that ensure products are free of harmful contaminants.
New and Innovative Recovery and Reuse Solutions
Research and development related to the recovery and reuse of nutrients and carbon in human excreta and other organic residuals has intensified over the past years, continuously unfolding new knowledge and technologies. Nevertheless, research impact, knowledge transfer, and practical application at present are limited. In particular, uptake, implementation, and upscaling of new and innovative solutions remain a key challenge.
Knowledge Synthesis and Transfer
The messy and sprawling nature of existing knowledge is one of the obstacles to taking full advantage of the potential for nutrient and carbon recovery and reuse. Wastewater managers and food producers have clearly expressed the difficulty of staying up to date and sifting through available knowledge. There is a need for better knowledge synthesis and transfer.
Acceptance and Implementation
Issues of environmental and resource management are often related to governance and subject to cultural, economic, institutional, and regulatory barriers. Therefore, increased acceptance and endorsement of innovative and sustainable solutions to recirculate nutrients and carbon from human excreta and other organic residuals to agriculture requires social innovation to overcome societal and institutional inertia.