Conversion of horse manure into valuable products using hydrothermal carbonization

The project is motivated by the need for sustainable waste management and circular economy practices to address the challenges of degraded soils and climate change. In addition, with the production and use of synthetic fertilizers being resource-intensive and resulting in significant greenhouse gas emissions, there is a need to find alternative materials with negative carbon emissions, for soil improvement.

Horse manure is considered a valuable organic fertilizer for soil because it contains high concentrations of nutrients such as nitrogen, phosphorus, and potassium, as well as organic matter that can improve soil structure and water-holding capacity.

Sweden has approximately 360 000 horses, and the number is increasing, leading to a growing amount of manure that needs to be managed. Current horse manure management practices, direct spreading or composting, have disadvantages, including nutrient leaching and greenhouse gas emissions. Although there is an increasing interest in anaerobic digestion of horse manure, potential difficulties in digestion when soft wood is used as bedding material, as well as the fugitive methane emissions associated with the process, pose significant challenges.

In addition to these environmental challenges, transporting horse manure to waste management facilities can also be costly for horse farmers. Moreover, while digestate can be a good way to circulate the nutrients back to the soil, it lacks the capacity to promote the formation of stable organic matter in soils, which is crucial for soil health. In contrast, hydrochar, produced via hydrothermal carbonization (HTC), not only contains humic substances that enhance soil properties but also has the potential to capture and store carbon in the soil, making it a more sustainable alternative for horse manure management. Therefore, this project aims to evaluate the potential of horse manure-derived hydrochar as a soil amendment, including the identification of optimal process conditions and the evaluation of its effectiveness as a soil amendment.

The project also includes an analysis of the composition of the HTC liquid and its potential as a fertilizer. Additionally, the greenhouse gas emissions from horse manure storage will be compared with those from the HTC process.