Turn sludge into value streams with pyrolysis

Yes. Pyrolysis can reduce greenhouse gas emissions by avoiding methane (CH₄) and nitrous oxide (N₂O) emissions associated with sludge storage and land application, while retaining part of the biogenic carbon in stable biochar.⁵

The stable carbon fraction in biochar can persist for centuries or longer.⁸ Life-cycle assessments indicate climate savings of approximately 1,000–1,500 kg CO₂e per tonne of sludge dry matter compared with conventional storage and direct land application.⁵

Yes. Pyrolysis combined with thermal oxidation of process gases can achieve substantial PFAS reduction. AquaGreen testing has shown PFAS below detection limits in biochar and flue gas under documented operating conditions.³

Published studies also report strong PFAS removal during pyrolysis, including full-scale and pilot-scale systems with subsequent thermal oxidation.²

The HECLA® process includes thermal oxidation, where pyrolysis gases are combusted at approximately 900–1000°C. Depending on the installed configuration, downstream gas treatment may include wet scrubbing and filtration to control acid gases, particles and other residual contaminants.³

Emission levels depend on feedstock composition, plant configuration and operating conditions, and compliance is assessed against the limits defined in the environmental permit for each site.

At high temperatures, microplastics and organic micropollutants such as pharmaceuticals are thermally degraded or removed from the solid phase.

Microplastics degrade at approximately 450–500°C⁴ , while pharmaceuticals have been reported below detection limits at temperatures above approximately 500–600°C.¹

Pyrolysis provides hygienisation and can substantially reduce organic contaminants.¹

Agricultural use depends on national regulations, biochar quality, contaminant testing and compliance with applicable heavy-metal limits. Phosphorus is largely retained in the biochar during sludge pyrolysis⁶, while heavy metals are not destroyed but can show reduced mobility compared with untreated sludge.⁶ ⁷

Typical return on investment (ROI) with HECLA® is 4–11 years, depending on sludge composition, disposal costs, energy prices and site-specific factors such as utilisation, regulatory conditions and available incentives.

Aside from faster ROI, utilities switch to integrated steam-drying and pyrolysis technology to reduce disposal costs, increase energy recovery and potentially receive revenue from carbon removal credit.

No. Organic pollutants are thermally degraded during pyrolysis, while heavy metals remain largely in the solid phase and can show reduced mobility compared with untreated sludge.¹⁶⁷ Process gases are oxidised and treated before discharge.³

Studies show substantial reduction of organic contaminants in the solid phase and reduced mobility of heavy metals after pyrolysis.¹⁶⁷ AquaGreen measurements have shown PFAS below detection limits in flue gas before and after scrubber treatment under documented test conditions.³

AquaGreen biochar is a stable, carbon-rich material with high phosphorus retention and low levels of organic contaminants under documented operating conditions. It is produced through controlled high-temperature pyrolysis, which substantially reduces organic pollutants¹², can lower the mobility of heavy metals⁶⁷ and stabilises carbon for long-term storage.⁵

Scientific studies show that at temperatures around 600°C and above:

• Organic micropollutants, including pharmaceuticals, PAHs and PCBs, are substantially reduced¹
• PFAS is substantially reduced during pyrolysis under documented operating conditions²³
• Microplastics are thermally degraded at high pyrolysis temperatures⁴
• Heavy metals are not destroyed but can show reduced mobility compared with untreated sludge⁶⁷

HECLA® operates at approximately 650°C with a residence time of around 20 minutes, followed by thermal oxidation of the process gases.³ These operating conditions are within documented temperature ranges for the degradation of plastics and many organic contaminants, while phosphorus is largely retained in the biochar.⁶  ¹⁰