Ash2Phos

From sewage sludge ash to clean phosphorous products

EasyMining is focused on creating circular material flows from waste. Phosphorus is an essential element for life as a key nutrient for agriculture. Via the food cycle, phosphorus ends up in sewage sludge. This sludge can be spread on agricultural land, used for soil production, or be incinerated. Incineration is today mainly used as a method to reduce the amount of waste to land fill, or destruction if the sludge quality is too low for other uses.

The phosphorus content of ash from incinerated sewage sludge is high, and through this unique patented process, we are able to extract clean commercial phosphorus products from the ash. In addition to the phosphorus, the Ash2Phos process can recover precipitation chemicals and remove heavy metals.

Background

Phosphate rock is the primary raw material source for phosphate production, but unfortunately is mineable phosphate rock a limited non-renewable resource. Large amounts of phosphorus end up in manures and in urban waste, mainly in sewage sludge and slaughterhouse waste. Today are EU countries re-circulating phosphorus by distributing 48% of the sludge back to farmland. The positive aspect is that phosphorus is re-circulated, but it’s not problem free. Sewage sludge can still contain viruses, heavy metals, and other substances that could be harmful to human health. Today 27% of the phosphorus is being transported to land fills or “other”, which are routes that rarely recover any phosphorus. 25% of the sludge is incinerated and the ash is mainly transported to land fills. The Ash2Phos process can in a near future transform the sludge ash to a raw material for phosphorus extraction and thereby be a part of a circular solution for phosphorus management.

Problem

Ash from mono-incinerated sewage sludge has a high concentration of phosphorus (7-10%), iron, and aluminium (5-10%), but also contains unwanted heavy metals such as cadmium. The high content of metal creates an obstacle for possible applications for the phosphate rich ash.

Solution

The Ash2Phos process consists of 3 steps: a first acidic step, a second alkaline step where intermediate products are produced, and finally a conversion step where the intermediates are processed into final products.

The main inputs of the process are

  • Ash from incinerated sewage sludge
  • Acid (hydrochloric acid, HCl)
  • Lime

The process consists of several successive chemical reactions undertaken at room temperature (though one process step may benefit from a temperature of 40 degrees C). There is no need for pressurized vessels or for exceptional materials to be used for the equipment. The mass balance of the process is favourable, since all input chemicals become part of the products.

Products

Monoammonium phosphate, MAP

  • Uses: Fertilizer in agriculture or horticulture. Animal feed ingredient.
  • Quality: Technical grade, 26,5% P (61% P2O5) and 12% N
  • Cadmium content: < 1 mg Cd/kg P (< 0.5 mg Cd/kg P2O5)
  • Efficiency in application: Very high, the product is fully water soluble and plant available

Dicalcium phosphate, DCP

  • Uses: Fertilizer in agriculture or horticulture. Animal feed ingredient.
  • Quality: Equal to currently available products with a phosphorus content of 18% P (41% P2O5)
  • Cadmium content: < 1 mg Cd/kg P (< 0.5 mg Cd/kg P2O5)
  • Efficiency in application: Equal to currently available products.

Phosphoric acid

It is also possible to produce phosphoric acid with the same low cadmium content of < 1 mg Cd/kg P (< 0.5 mg Cd/kg P2O5).

Superphosphates

A less likely alternative is to produce single or triple super phosphate. These products are lower grade phosphorus fertilizers which were common in the past, but have been mostly replaced by ammonium phosphates.

Circular economy