When we first hear about the word “nutrient”, the idea of human nutrition comes to our mind, however, this expression has a much deeper meaning. To understand a little bit more about this idea we need to think about the context of the chemical components that are playing the role of nutrients. Among these chemical components we have nitrogen (N), phosphorus (P), magnesium (Mg), and metals such as calcium (Ca) which are plant food plant constituents consumed by every living being. Therefore, talking about “nutrients” can take us to think about fertilizers.
It is well known that food crops need fertilisers as a nutrient source, especially phosphorus, which unfortunately is only obtained by limited rock phosphate mining centres around the world (Morocco with >70% of reserves). This reality can trigger geopolitical risk of interest, and stress within the countries that are dependent of this resource. To make things worst, rock phosphate reserves are dropping over time with less than a century to be completely depleted. In this context, some companies around the world are recovering nutrients from wastewater streams with technologies that especially capture three nutrients (N, P and Mg) to form solid particles and crystals known as struvite (Mg.NH_4.PO_4.6H_2 O).
One of the advantages of nutrient recovery technologies lies in “Closing the Loop” of nutrients. This means that nutrients (N, Mg, P, etc.) that are usually just removed during wastewater streams (without the possibility of their reuse as fertiliser because of the addition of metals such as Aluminum (Al)) are being captured to be reused as fertilisers. “Closing the loop” also has financial advantages due to the production of a slow-released fertiliser (struvite), which has the quality of not burning the crops if they are accidentally added in excess. Of course, struvite is not the only nutrient source that can be produced, but just one of different solid phases depending on the chemical composition of the initial wastewater stream source. Research in nutrient recovery nowadays comes along with energy recovery trends in wastewater treatment plants, forming the expression “Resource Recovery”. New technologies, processes, and model simulators are being implemented and studied around the world with the goal of optimising current systems and bringing a positive change in world societies. Just imagine for a second, living in a world in which are own domestic residues can be easily transformed in fertilisers being used to produce the fruits and vegetables in our house garden. Perhaps previous idea is still far from reality, but some people are still working to make that happen into reality.
