Nutrient leaching puts a strain on both the natural environment and economy, and the increasing world population highlights the need for circular solutions for nutrients in the feed, food, and animal system. Nutrients in waste from human food nutrients are to a high extent excreted into wastewater and nutrients are leached from the arable land to both ground water and environment. This cause unwanted impact on the environment, but minerals, especially phosphor is a limited resource and needs to be recycled. The potential economic value of increased utilization and recycling of nutrients is therefore high. 

Therefore, the questions are: 

• Can we reduce leakage enough? And how do we quantify leakage? 

• Should we focus on increased re-utilisation instead of reducing losses? 

• Plant species, growing conditions, farm management 

• Demand and utilization of nutrients by plants 

• Demand and utilization of nutrients by farm animals 

• Can we create “sinks” for some of the components and through that allowing a degree of leakage in other places? 

• Can we re-utilise nutrients from urine/sewers for input in food production? 

• How do we make food fertilised with nutrients from wastewater plants acceptable for the consumers? What food types will consumers accept? 

• Are there any unexploited side streams? 

• Can single cell protein be a solution? 

• Circular solutions for nutrients, feed, food, animals, energy, and wastewater 
• Filtration methods, such as direct membrane filtration, adsorption, and dynamic sand filters 
• Microbial collection of nutrient salts from sludge/wastewater treatment plants 

• Use of perennial crops on the fields 
• New farming methods/practise for annual crops 
• Nutrient utilization by plant and animals 
• New EU regulations will cover bio-based fertilisers enabling this being put into practice 
• Focus on nitrogen and phosphorous with carbon circularity as a minor focus

People from social sciences are essential in defining the significant challenges, and engineers as part of coming up with innovative, technical solutions.