Innovative technologies for nutrient recycling

Dwindling deposits of mineral phosphorus and eutrophication are major challenges that affect Outotec’s customers – and also our whole planet. Outotec offers a wide-ranging portfolio of comprehensive sludge treatment solutions for energy production and nutrient recycling, complemented by partnerships.

The phosphorus fertilizers currently used in agriculture today are a non-renewable resource mined from finite mineral deposits. Mineral phosphorus is becoming increasingly rare, and the food supply in some regions of the world is already completely dependent on imported phosphorus.

We believe that nutrient recycling will help to combat eutrophication and shortages of phosphorus. By using the right technology, it is now possible to recover phosphorus from sewage sludge for use as a fertilizer.

“When municipal energy and sewage treatment companies can recover valuable nutrients and sell them to fertilizer producers, this benefits society as a whole,” says Tanja Schaaf, Senior Product Engineer, Thermal Processing.

Old technology – for a new purpose

The basic ASH DEC technology is a thermochemical process for separating heavy metals from ash generated during the combustion of industrial and municipal waste. The combustion of sewage sludge also produces electricity and heat usable for district heating. Combustion also produces ash, from which we can recover phosphorus. In addition to turning waste into new raw materials or even directly into products, ASH DEC can also reduce hazardous landfill volumes and ash-handling costs.

Nutrient recycling

Partnerships for driving nutrient recycling

In 2016, Outotec partnered with Thermo-System GmbH, a German based global leader in low-energy drying technology. Such technology is mainly used for pre-drying sewage sludge or wet peat before incineration. Part of the resulting pre-dried sludge can now be mixed with incineration ash to produce valuable raw materials rich in phosphorus, nitrogen and potassium.

In May 2016, Outotec and Ecolan, the leading Finnish forest and organic fertilizer producer, won the first prize in a Sitra competition looking for solutions for nutrient recycling. The companies’ solution, Fullrec, combines three technical processes: Outotec’s DeBugger and ASH DEC processes, and Ecolan’s granulation process. Through this tested and proven approach, digested sludge is not burned, but dried and mixed with ash. The resulting mixture is then granulated to create a product that can be transported cost-efficiently.


“Together with Ecolan, we have been developing this concept in the new industry zone ECO 3 in the Finnish city of Nokia,” says Juhani Anhava, Director, Energy & Environment Business Development. “The goal is to develop a thermal treatment plant for sewage sludge. The project is currently in the construction phase, and expected to become operational in the first quarter of 2017.”

Support for challenging conditions

In 2016, Outotec secured a contract with the Italian engineering company Desmet Ballestra S.p.A Milano, to  design and deliver a solvent extraction plant to purify fertilizer phosphoric acid before evaporation.

The customer’s operations in a desert area in Egypt face several challenges affecting the viability of fertilizer production, including:

  • The isolated location of the plant
  • The low phosphate content of the ore body
  • The relatively large throughput of the plant
  • Impurities created in the process

Outotec’s basic design for the solvent extraction facility is based on scalable modules, making it ideal for application to diverse customer needs. Such a modular solution enables the creation of a closed system, reducing emissions of volatile organic compounds (VOCs). The modules are easy to transport and install, which reduces the total delivery time dramatically, and also brings safety benefits. As the life-cycle of the plant comes to its end, the modules can be transported to other locations, avoiding the expenses that characterize conventional plant closures. Outotec provides the customer with VSF®X technology, a license, equipment for crud  treatment, and a cooling tower.

Scalable modules are ideal for diverse customer needs

Outotec will also deliver two sulfuric acid plants for the same project. The technology offered by Outotec improves the sustainability of NCIC’s fertilizer plant by:

  • minimizing fugitive emissions of sulfur dioxide from the acid plant
  • generating carbon-free energy by applying our HEROS heat recovery technology
  • reducing the plant’s consumption of raw water