The fate of trace organic contaminants in sewage sludge during recuperative thickening anaerobic digestion

- Trace organic contaminants (TrOCs) were prevalent in primary sludge.
- High or excessive shearing cause a reduction in biogas production.
- Biodegradation of some TrOCs was enhanced by sludge shearing.
- Enhanced biodegradation is due to TrOC circulation between the water & solid phase.

The aim of this work was to study the fate of trace organic contaminants (TrOCs) in sewage sludge during recuperative thickening anaerobic digestion. Sludge shearing at 3142 s−1 for 5 minutes improved biogas production. By contrast, shearing at ≥6283 s−1 for 5 minutes caused a notable reduction in biogas production and the removal of volatile solids. Results reported here showed the prevalent occurrence of 17 TrOCs in sewage sludge and highlights the importance of assessing TrOC removal via mass balance calculation by taking into account partitioning between the aqueous and solid phase as well as biodegradation. Hydrophilic and readily-biodegradable TrOCs (caffeine, trimethoprim, and paracetamol) were well removed and were not affected by shearing. TrOCs such as carbamazepine, gemfibrozil, and diuron showed biodegradation only at high shearing. It is possible that shearing can facilitate the circulation of TrOCs between aqueous and solid phases, thus, enhancing the biodegradation of some TrOCs.