Some days ago, I was trying to explain my work and my master thesis to one of my friends, that was about phosphorus recovery from different wastewater streams. After some minutes, she told me: It sounds like a nice topic, but why Phosphorus? It was interesting that she asked it while she was eating her dinner. Well, Phosphorus is a scarce and vital resource like Water. She replied, I did not know that, really? How, where and why?
Well the truth is that some years ago I was also not aware about the importance and criticality of this nutrient. Phosphorus (P) is an essential nutrient for all forms of life. We find Phosphorus in our DNA and all living organisms require daily phosphorus intake to produce energy, these includes all the plants and meat that we daily consume, and we usually call them “Our daily Food”. A study conducted in 2011 showed that 70% of Phosphorus global production is currently produced from reserves which will be depleted within 100 years and combining this with increasing demand in agriculture and industrial sector will result in a significant global production deficit, which by 2070 will be larger than current production. The bad new is that Phosphorus cannot be replaced and there is no synthetic substitute, which in other words means that there is no more alternative than to recycle it instead of losing it in form of food waste or wastewater disposed in water bodies. Which by the way just pollutes soil and water, but that is another story.
So here is how the Phosphorus’s challenge starts. Where can we find P and how to recover it? I would like to share an example. Germany, where I currently live, would require 364 000 t of P per year to implement a good fertilization practice (UBA, 2001 as cited in Weidelener et al.,2008). In a near future, this demand will be harder to meet, however, it could be supplied by recovered P from sewage sludge, the organic waste with the highest P source potential of around 50.000 t P per year. Sewage sludge, where to find it? This organic waste can be found in every city inhabited by humans, which household’s wastewater goes to a water treatment plant (WWTP). In other words, sewage sludge is a byproduct of the water treatment process.
Sewage sludge is just one example, however, P can also be recovered from food waste and animal manure, previous studies have already shown that P can be recovered up to 90% in form of high-quality fertilizers, that can be used in agriculture. I was recently in Berlin, where I found I good example to better describe how a recovery process works. The are many different options to recover P from organic waste or waste water, one of them is The AirPrex® technology originally developed by the ‘Berliner Wasserbetriebe’ (The wastewater treatment plant in Berlin) but since 2006 it is commercialized by the German company PCS (Pollution Control Service). The process consists in adding Mg2+ in the form of MgCl2 to a reactor that contains the digested sludge with sufficient concentrations of ammonium and phosphorus to form the fertilizer called struvite. Air is also applied to the reactor in order to increase the pH by stripping CO2 from the digested sludge. This can sound a bit complicated but not impossible, actually there are already two full-scale plants in Berlin and in Mönchengladbach. In these plants, 80-90 % of the Phosphorus is removed from the liquid phase of the digested sludge.
From this berlin experience, we can learn that similar or improved processes could also be applied to other organic waste with high P content, as many research institutes, universities and municipalities around the world are already doing. I share with you some links that might be helpful 😊 So the sky is the limit and we are not far to touch the sky and discover more ways of making the circularity a reality! I want to propose you which other forms of organic waste could be use as a source of P? and would you be interested in doing it at a small scale within your community? All suggestions are welcome and will contribute to continue generating new ideas around this topic.
Here the useful links:
-The future distribution and production of global phosphate rock reserves
-WWTP in Germany that recovers P at big scale http://www.bwb.de/de/4951.php
-P recovery from pig manure https://www.ars.usda.gov/ARSUserFiles/60820500/Manuscripts/2015/Man990.pdf
-P recovery from food waste