Carbonisation of sewage sludge

Drying and subsequent carbonisation produces a valuable material that can be used as a soil conditioner. Due to the operating temperatures in the range of 600 to 700 °C, the recovered phosphorus remains available to plants after carbonisation.

In several EU countries such as the Czech Republic, Denmark, Sweden and Australia, the carbonate is already officially approved as a soil conditioner and raw fertiliser material.

Drug residues, microplastics, PFAS and pathogens are eliminated through thermal treatment in the carbonisation process. You can find evidence of PFAS elimination here.

The lower temperature in the treatment process compared to conventional incineration influences the end product properties. The carbon contained in the sewage sludge is converted into biochar - and therefore CO₂ is sequestered. When sewage sludge is carbonised, the carbon it contains is not released as CO2, but is instead stably bound in the biochar and removed from the atmosphere.

Compared to incineration, carbonisation can save greenhouse gas emissions of around 198 kg CO2 per tonne of sewage sludge. In relation to the amount of sewage sludge produced in Germany, this amount of greenhouse gas emissions is equivalent to the binding capacity of a beech forest with around 48 million trees or a square forest area measuring 97 km by 97 km (Korrespondenz Abwasser, Abfall - 2020 (67) - No. 3).

The production of biochar is one of the "Negative Emission Technologies" (NET) urgently needed for climate protection. If the biochar is permanently incorporated into so-called carbon sinks (e.g. arable soil, building materials, asphalt), the sustainable storage of CO2 is successful in the long term.