Phosphorus is an indispensable raw material, both for agriculture and industry. But it’s short. A newly developed process now makes it easier to sustainably recover the sought-after element from sewage sludge. The technology called FlashPhos makes it possible to extract white phosphorus and other useful substances from the sludge in an environmentally friendly, efficient and cost-effective way – and this is pure enough for industrial applications.
Phosphorus is scarce worldwide, but is urgently needed as a plant nutrient in agriculture, in the chemical and pharmaceutical industries and also in electronics. The phosphorus for this is obtained from phosphate-containing rock formations, but economically mineable phosphate reserves are distributed unevenly around the world. There are currently no mineable deposits in all of Europe, with the exception of smaller deposits in Finland. Because of its dependence on imports and limited resources, the EU classifies white phosphorus (P4), which is important for industry, as a critical raw material. This phosphorus variant is particularly reactive and is used as a raw material for the production of car batteries, flame retardants, catalysts and computer chips, among other things.
Sustainable recovery was sought – and found
One solution to the phosphorus shortage is recovery – for example from sewage sludge. Because it contains a lot of phosphate-containing organic material. That is why phosphorus recovery from sewage sludge will be mandatory in Germany from 2029. This will then be used primarily to produce fertilizers and ensure that less phosphorus has to be obtained through the energy-intensive mining of phosphate rock. In the EU project “FlashPhos”, coordinated by the University of Stuttgart, researchers have now developed a method with which the sought-after element can be recovered from sewage sludge as sustainably as possible.
“We want to ensure a sustainable supply of raw materials that are important for the economy, but are difficult to access and are only available to a limited extent,” says Markus Reinmöller from the University of Stuttgart. “But this can only be achieved if we produce these critical raw materials in a circular economy – like with the new FlashPhos process.” In addition to white phosphorus, the newly developed process also delivers other useful substances that can replace CO2-intensive raw materials, including a climate-friendly cement substitute, an iron alloy and a heavy metal concentrate for the metal industry. “This makes us more independent of imports and strengthens a sustainable circular economy,” explains Reinmöller’s colleague Christian Schmidberger.
Phosphorus extraction in three steps
Specifically, the FlashPhos process is based on three process steps. In the first step, a fine, almost water-free powder is obtained from the moist sewage sludge in a special dryer-grinder. In the second step, this powder is heated in a “flash reactor” to temperatures of 1,600 degrees. This creates a flammable gas and phosphate-containing sewage sludge within milliseconds. The positive thing is that the energy required for heating comes from the organic components of the sewage sludge powder. In the last process step, the so-called “refiner”, the sewage sludge slag is “refined” at also high temperatures. The main product produced is elemental white phosphorus.
Initial tests with prototypes of these systems have already been successful. Next, the researchers and their industrial partners plan to scale the technology to an industrial scale. For this purpose, the first large production facility is to be developed and built by 2028. To ensure that there is enough sewage sludge available, Reinmöller and his colleagues see potential locations for future FlashPhos systems, especially in densely populated regions. “Conurbation centers such as the Ruhr area, Barcelona, Madrid or Milan would be predestined for this,” says Schmidberger. According to the team’s estimates, FlashPhos systems could cover half of Europe’s P₄ needs by 2050.
Source: University of Stuttgart; FlashPhos project