About phosphorus
Hydrochar is not the only good thing we can create with hydrothermal carbonization.
This newsletter will not focus on carbon for once, but on another important element: phosphorus.
Without phosphorus, there would be no life on earth, no plants or animals — no humans either.
Although this element is very widespread and occurs in all living matter, it is rarely concentrated in deposits for mining, e.g. for the production of fertilizer.
Making phosphorus circular
Since it has now been recognized that the resources of phosphorus are quite limited, we see increasing efforts, by the European Union among others, to recycle phosphorus and to start a circular economy.
Which material flows could be used for this? By far the most important raw material for the recovery of phosphorus is sewage sludge from sewage treatment plants. This is where all phosphorus-containing substances come through that we release again through our metabolic activities (vulgo feces).
In Germany alone, some 2.0–2.4 million metric tons of sewage sludge contain about 55,000 tons of phosphorus.
By a fortunate coincidence, about 90% of the phosphorus contained in wastewater accumulates in the sewage sludge during treatment — together with other macronutrients like potassium and chemically bound nitrogen.
Another benefit of using hydrothermal carbonization is that the water content of sewage sludge can be greatly reduced. Fresh sewage sludge contains about 20-25% dry matter. Transported and landfilled this sludge is expensive and energy-intensive.
With HTC, it is possible to increase this to 70% dry mass. Separation is easier, transportation is cheaper, and the product is perfectly hygienic. This advantage alone makes the use of HTC technology worthwhile, because it saves about 2/3 of the landfill costs.
Phosphorus and more
Are there other waste materials suitable for nutrient recovery?
Organic waste contains an additional 15,000 metric tons of phosphorus per year, and paper and cardboard waste 12,000 tons more. This adds up to about 82,000 tons per year that have yet to be recycled. But it is now mandatory in the EU to recycle phosphorus from waste streams, especially sewage sludge.
But what does all this have to do with hydrothermal carbonization? What the mentioned waste types have in common is that we can convert them effectively into hydrochar by means of the HTC technology.
But the process water used in HTC also contains considerable amounts of these nutrients. With HTC, we can also convert these waste streams into carbon, and not only contribute to carbon sequestration, but also recover the nutrients contained in the process water to produce fertilizers, and close the cycle of these nutrients.
In a way, two good deeds in one — or, as the business people call it, a win-win!
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