This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Agriculture depends on a reliable supply of nutrients. Phosphorus, nitrogen and potassium, for example, are indispensable for agricultural crop production.
However, natural reserves are limited, vary greatly in regional availability or are very energy-intensive to extract. Resource-oriented sanitation systems (ROS) offer a sustainable solution for managing these raw materials: they collect nutrient-rich material streams from human excreta separately and, as far as possible, undiluted with water. After targeted treatment, the plant nutrients they contain can be made available for agricultural use again.
A research team has studied this treatment process, compiling extensive international data on various ROS-based recycled fertilizers for the first time in a recent study. For 13 types of recycled fertilizers, sufficient data were available to characterize their properties in detail. The study is published in the journal Frontiers in Environmental Science.
Many can be classified into known categories of mineral, organic or organic-mineral fertilizers in terms of nutrient composition and function. The results show that the recycled products are just as effective agronomically as conventional fertilizers. "Our findings provide an important scientific basis for their application, as they show that recycled fertilizers derived from separately collected material streams are not second-class fertilizers," says Martina Winker of the Institute for Social-Ecological Research (ISOE), a co-author of the study.
"What matters is what properties a fertilizer brings to the specific agricultural application, not whether it comes from a conventional or a recycled material stream." Research is now being conducted worldwide to determine how well such ROS-based fertilizers perform and what requirements they must meet. "For the study, we compiled more than 450 data sets from over 200 sources across 32 countries and analyzed them at the product level. Our findings on individual fertilizer products show that nutrient recycling from human waste has long been a scientific topic at the international level," says Ariane Krause of the Network for Sustainable Sanitation (NetSan), also a co-author of the study.
"Until now, however, there has been no comprehensive overview of the wide variety of products, processes and application conditions. We wanted to highlight what can actually be deduced from this broad body of evidence and where gaps in knowledge still exist." The nutrients contained in a ROS-based fertilizer—as well as their form and concentration—depend largely on the raw material and the specific processing method. Physicochemical properties such as pH, salt content or the proportion of organic matter also vary among products and influence their potential applications.
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