Our recent study explores an innovative approach to sustainable agriculture by combining dehydrated human urine with various organic wastes to create circular fertilizers. This research addresses a critical need: reducing reliance on inorganic fertilizers while managing nutrient cycles more effectively. By tailoring these fertiliser blends to meet the specific macronutrient demands of 15 major crops, we aim to provide a viable alternative that supports both crop yields and environmental sustainability.
We used a reverse blending modeling approach, analyzing data from 359 different organic wastes to simulate potential fertilizer combinations. The challenge was to identify materials that could balance the nutrient profile of dehydrated human urine, which is naturally high in nitrogen but lower in phosphorus and potassium. Through this process, biochars and ashes emerged as particularly promising blending materials due to their low nitrogen content and higher levels of phosphorus and/or potassium. This made them ideal for pairing with human urine, which helped offset the typical nutrient imbalances when used alone.
Out of the 359 organic wastes considered, 38 blends successfully met the macronutrient demands of the targeted crops. However, achieving an exact match for all nutrient requirements proved challenging, as most blends tended to slightly oversupply one or more nutrients, which poses a potential risk of overfertilization. For instance, while the nutrient content of these blends was comparable to conventional fertilizers, only a few precisely matched the crops’ nutrient needs, with some blends showing an excess of phosphorus or potassium. This highlights the need for careful management to mitigate the risk of environmental impacts, such as nutrient runoff, which can contribute to problems like eutrophication.
Another critical aspect of the study was assessing the heavy metal content in these blends. We found that most of the simulated fertilizers complied with European Union regulations, making them safe for use in agriculture. The inclusion of dehydrated urine played a crucial role in diluting the heavy metals present in organic wastes, which is a significant advantage of this approach. This safety factor enhances the potential for these blends to be adopted widely, as they align with both crop nutrient needs and regulatory standards.
The findings suggest that fertilizers made from human urine and organic wastes have the potential to replace inorganic fertilizers, supporting a transition to more sustainable agricultural practices. This approach not only recycles valuable nutrients that would otherwise be lost but also supports greater circularity in the global food and water sectors. However, there are still challenges to address, such as managing nutrient surpluses and ensuring that heavy metal content remains within safe limits. Future research should focus on identifying additional organic wastes that could be blended with human urine, as well as exploring combinations of multiple waste types to better align the nutrient content with crop requirements.
Overall, our study provides a promising outlook for the role of urine recycling in agriculture. By converting waste into a valuable resource, we can reduce our reliance on synthetic fertilizers and support a more sustainable and resilient agricultural system. For those interested in a deeper exploration of our methods and detailed results, we encourage you to read the full article available here: https://doi.org/10.1016/j.scitotenv.2024.175655