Why phosphorus recycling?
Phosphorus is mined as phosphate rock of which around 90% is processed into fertilizer. The remainder is converted into elemental white phosphorus as a feedstock for the chemical industry. Both as a fertilizer and as a chemical, phosphorus is indispensable for agriculture, the energy transition, electronics and pharma. Europe is highly dependent on imports from few countries. Moreover, elemental phosphorus is only available from Kazakhstan and Vietnam.
Since phosphorus is used in a non-circular way, reserves are expected to be exhausted in 50-150 years. The European Union declared phosphate rock and phosphorus critical raw materials. More than a third of the imported phosphate ends up in sewage sludge and is not directly reusable because of contaminants and the low plant availablity of phosphate. The sludge is disposed and the phosphorus is lost.
Some countries (Germany, Austria, Switzerland) set goals by law to recover phosphorus from sewage sludge. In other European countries (the Netherlands, Denmark, Belgium etc.) water authorities recognize their social responsibility and are fulfilling an active role in recovering phosphorus from sewage sludge circular. This also counts for the USA, Japan, Australia etc.
Routes to recover phosphorus
Many initiatives have been started to accomplish the goal to recover phosphate or phosphorus from sewage sludge in a sustainable and cost-efficient way (refer to the ESPP catalogue). This can be achieved locally at the waste water treatment plant and centrally after mono-incineration of sewage sludge. The most efficient starting point is considered to be incinerated sewage sludge ash, where the phosphorus content and volume are highest. Many processes are based on acid leaching of the ash and refining of the phosphoric acid formed. Few thermal routes are in development, of which only a few have elemental phosphorus as the main product.
All developments face common challenges, such as producing marketable products and limiting operational and investment costs.
Introducing Spodofos®, a patented out-of-the-box solution, producing high value products and showcasing maximum sustainability and an astonishing business case.
Chemistry of Spodofos
The core process comprises a thermite reaction of sewage sludge ash constituents with aluminium.
The lowest quality aluminium scrap can be used.
Aluminium acts as reducer and as energy carrier and therefore:
very less external energy is required;
reduction is carbon free.
The process is flexible in feedstocks.
Phosphate reduction is near complete.
Three step and compact processing
Limited preheating;
Mixture conditioning;
Conversion and products collection.
The maximum volumetric throughput equals the throughput of ash.
Products
White phosphorus; inherently purified by distillation from the reactor;
High aluminium oxide slag to be applied in civil works and refractory materials;
Metallic ferrophosphorus, directly applied or to be converted into a coagulant and a valuable P-product.
Total achievable P-recovery efficiency is unprecedented.
Sustainability
Zero waste, no waste water, no flue gas from conversion;
Zero fossil fuel possible;
Typical CO2 savings: 1.000 kg CO2/ton sewage sludge ash;
Immobilization of heavy metals;
Destruction of PFAS (expected, not yet proven).
Business case
Capex is low because of the few step, scaleable and compact processing;
All products are well marketable;
At usual price levels, a sound payback period is calculated.