Christian Wieth

The management of sewage sludge is increasingly challenging due to the presence of persistent organic micropollutants such as PFAS and pharmaceuticals. In Denmark, 20% of sewage sludge is PFAS-contaminated, with disposal costs rising by a factor of 5-10. This study explores the AquaGreen HECLA technology at a full-scale plant at Fårevejle in Denmark —an innovative sludge drying and pyrolysis process that not only eliminates micropollutants but is also climate- and energy-positive. The process incorporates autothermal drying and pyrolysis with after combustion of all pyrolysis gas achieving over 95% degradation of organic micropollutants. PFAS in the biochar is reduced by 99.9%, leaving no detectable residues in the resulting biochar or flue gas. Pharmaceuticals are also eliminated at rates exceeding 97%, alongside LAS, nonylphenols, DEHP, and microplastics. The resulting biochar complies with regulatory standards, including PAH thresholds for soil use, and captures approximately 1 tonne CO₂e per tonne of biosolids biochar.

Complementing this, Aarhus University has shown that the biosolids biochar produced are potentially a sustainable and cost-effective alternative to activated carbon for wastewater filtration. A year-long column filtration study using wastewater from Hillerød Utility (Denmark) demonstrated effective pharmaceutical removal—bringing concentrations below predicted no-effect concentration (PNEC) levels over 500-2000 bed volumes. Additionally, equilibrium studies with six PFAS compounds showed a 50% reduction in PFOS and PFOA concentrations at a 1g/l dosage of biochar and sorption on par with activated carbon for four of the six PFAS compounds, highlighting the technology's dual utility in both sludge treatment and for cheaper sustainable effluent polishing via the biochar produced