Water treatment plants are changing in both how they look and how they function. They’re becoming veritable wastewater recovery plants. They’re becoming major players in the circular economy in terms of energy. In just a few years, these treatment plants have been transformed into “wastewater recovery plants” that are able to offer new resources.
Phosphorus is a key mineral fertiliser in agriculture. In the Ancient Egyptian times, crushed bones were mixed with soil to enrich it. As phosphate, it helps plants to develop roots and ripen their fruit. It’s also a necessary ingredient in NPK fertiliser, nitrogen, phosphorus, potassium. Phosphorus also helps plants increase their resistance to low temperatures. It is used as a fertiliser in 90 % of marketing gardening. No phosphorus means no tomatoes, no salad leaves, no peas, and no wheat. Phosphorus is also used in food processing to preserve some meat and seafood.
A major challenge
The only phosphorus mine in Europe is in Finland, and supplies far from enough. Therefore, we have to import tonnes of phosphorus a year, mainly from Morocco, to grow crops and preserve food. Morocco provides 20 % of the world’s phosphate, it’s the number one exporter in the world and the main supplier to France. However, this rock powder, which is so essential to our crops, is not an unlimited resource. With increased demand every year and a growing population, there are only 50–100 years-worth of phosphate left. There is a huge risk that agricultural production will see a shortage, or at least a significant increase in the price, of phosphorus in the years to come. The idea is therefore to recycle the phosphorus that we consume. Once ingested through our diet, it can be found in our faeces and then in the wastewater going into treatment plants. This is a source of phosphorus that is just waiting to be harnessed.
Thanks to technological innovation, it is now possible to extract phosphorus from sludge that has been dried out and crushed down. This technique is called leaching. The waste is put into a reactor, it is chemically treated and the phosphorus is precipitated at the bottom of the reactor. A solvent is then used to dissolve the phosphorus in the sludge and it will then be turned into a solid element using precipitation. Heavy metals are removed in the same stage so that they do not end up on the crops. Using this process, 90 % of the phosphorus in our wastewater can be recovered. Phosphorus is found in the form of small white granules called struvite. It’s a real gem since it can be turned into fertiliser and sold to farmers. There are multiple savings since the treatment plant will see a reduction in energy consumption, use fewer chemical products, spend less on treating the sludge, and increase the lifespan of the equipment.
Every year in France, around 1.8 billion kilos of dry sludge is produced by the industrial sector and urban wastewater treatment plants.
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