Nutrient recycling: from waste to crop

Within the transition to a bio-based economy from a fossil reserve-based world, we face the vital dare of closing nutrient cycles and moving to a more practical and balanced resource management, taking into account not only the economical but also the environmental perspective. The manufacture and transportation of mineral fertilizers are activities that require large amounts of fossil energy. Therefore, the dependence that agriculture has on fertilizers based on mineral reserves (mainly P, N, and K) should be considered as a very serious threat to human food security and climate change. On the other hand, the existing forecast on phosphorus reserves is pessimistic. According to the latest published figures on population growth and estimated demand for nutrients in the future, depletion of this material is expected to occur within a maximum of 300 years. At the same time, the agricultural demand that exists for mineral fertilizers is constantly growing. The main reason is the increase in the world population, together with the increase in meat consumption and the popularity of energy crops. Despite these negative perspectives, the processing or elimination of waste streams causes uncontrolled dispersion in the environment of a large amount of minerals. Thus, a new global effort is needed to draw a new scenario where improved nutrient use efficiency and, at the same time, reduced nutrient losses provide the bases for a more circular economy, to produce more necessary inputs, as food or energy, as the same time as decreasing environmental impact. This paper will show the process options which can “upcycle” and recover residual nutrients to high-quality end-products, defined by efficient nutrient use and will reveal the key issues to face with novel biofertilizer products and changing policies.