The increasing population and urbanization have led to a greater need for treating wastewater and addressing concerns about the disposal of sewage sludge. At the same time, there is a growing need to recover nutrients from sewage sludge due to food scarcity and the reduction of fossil fuel-based fertilizers.
Text: Ali Saud
This study thoroughly explores the feasibility of extracting resources from sewage sludge, with a focus on recovering nitrogen, as well as considering phosphorus and energy.
Treatments and hazardous materials
One of the main challenges in dealing with sewage sludge is the presence of potentially hazardous materials like pathogens, pharmaceutical residues, and microplastics. This has led to the exploration of thermal treatments such as pyrolysis and combustion, along with post-treatments like adsorption, stripping, and scrubbing to recover nitrogen from reject water, condensate, and drying fumes resulting from thermal drying.
The research involved conducting economic and environmental analyses of these approaches to provide insights for sustainable waste management practices. The study achieved its objectives through process modeling, mass and energy calculations, and using a life cycle assessment methodology.
Focus on comparing technical possibilities
The research focused on comparing technical possibilities for recovering ammonia from exhaust fumes of thermal drying, finding optimal integration approaches to maximize ammonia recovery in wastewater and sewage sludge treatment processes, and assessing the environmental impacts of different ammonia recovery technologies.
Multiple studies were conducted, each addressing specific aspects of the research. One focused on recovering ammonia from drying fumes during sewage sludge thermal drying. Another studied heat and nutrient recovery through pyrolysis and combustion with gas scrubbing. A life cycle assessment evaluated composting, combustion, and pyrolysis options for sewage sludge digestate. Lastly, an LCA investigated the environmental impact of nitrogen recovery for fertilizer from sewage sludge treatment.
Promising results
The results of these studies are promising, showing high efficiency in recovering ammonia and the potential to generate valuable products such as ammonium sulfate fertilizer, district heat, and biochar.
Economic estimates suggest significant investment costs, but also projected product revenues. The environmental impact assessments showed varying results based on different scenarios and impact categories. Notably, the study also highlighted the potential environmental and health benefits of wastewater systems that incorporate integrated resource recovery.
Overall, this research provides valuable insights into the potential of recovering resources from sewage sludge while addressing environmental concerns, laying the foundation for more sustainable waste management practices in the future.
See some figures of the research here.
Dissertation Sustainable recovery of nitrogen from sewage sludge of Ali Saud was completed in December 2024. He received a scholarship from Waste Management Finland.
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