Combined steam drying and pyrolysis unit

Gallery Combined steam drying and pyrolysis unit 1
Gallery Combined steam drying and pyrolysis unit 1
March 2021
Headquarters 4000 Roskilde, Danmark

Combined steam drying and pyrolysis unit - Carbon storage and P recycling in biochar and renewable energy by combined steam drying and pyrolysis allowing better sludge management

There is a growing concern about what to do with sewage sludge due to concerns of environmentally unfriendly pharmaceuticals, microplastic and chemical compounds (PAHs, furans, dioxins, NPE, LAS etc). In many countries, sludge is now incinerated instead of spread on land due to public health concerns. This creates a problem of locking Phosphorus in the ash making it very difficult and expensive to recycle it into the soil. Sludge can only be spread on land 3 months a year and the prolonged storage gives considerable GHG emission. AquaGreen dries and pyrolyses (heat to 650 °C) the sludge turning it into useful resources - energy and biochar w. phosphorus - solving environmental and climate problems of sewage sludge. It the farmer to better yields and the climate by storing CO2 in the ground when biochar is used as a fertilizer. It also supports future generations ability to grow plants by recovering phosphorus - an element which is listed as a critical scarce raw material by EU.

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Key features

  • One 350 kW unit capture and store 550.000 kg CO2-eq per year in the biochar treating the sludge from a city with 40.000 people
  • Recycle 80 % of the phosphorus in the sewage sludge
  • Biochar is recognised by UN IPCC in 2019 as one of three ways to capture and store carbon to avoid climate change
  • Sewage sludge volume reduced with 90 % and pyrolised sludge (biochar) is sterilised and decontaminated and odor free
  • Carbon storage via the biochar - 50 % of the carbon in the sewage sludge is captured in the biochar saving 1.1 kg CO2 eq per kg of biochar.
  • The phosphorous of the biochar is plant available to a very large degree whereas today's standard sludge incineration process is very problematic for phosphorus' plant availability


  • ROI for the waste water plant after 2-6 years - due to sludge handling/incineration cost savings
  • Avoiding cost of extracting phosphorus from the sludge after incineration - currently estimated in Germany to 300 €/ton (per ton sludge on dry matter basis)

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