Polycyclic aromatic hydrocarbon formation from gasification of sewage sludge in supercritical water: The concentration distribution and effect of sludge properties

• The PAH concentrations in sewage sludge before and after SCWG were measured.
• The effects of sludge properties on the PAH distribution were investigated.
• The PAH concentrations increased significantly during the gasification process.
• High volatile matter and low pH value can promote PAH concentrations increase.
• The organics composition had a high impact on the form of the PAH distribution.

The changes in the polycyclic aromatic hydrocarbon (PAH) concentration and distribution in 10 different types of raw sewage sludge and gasified residues were investigated, and the effects of the sludge properties and the organic matter composition were determined. The results showed that the concentrations of 2-ring and 6-ring PAHs increased significantly during the gasification process. The PAHs in raw sludge were dominated by 3-ring and 4-ring PAHs, and those after gasification were dominated by 2-ring and 3-ring PAHs. The total PAH concentration increased with the increasing volatile matter content and decreased with the increasing pH value. Phenols have been considered to be important precursors for PAH synthesis. The crude fat and carbohydrate content can promote lower-molecular-weight PAH formation, while lignin and humic substance content can promote higher-molecular-weight PAH formation, which indicates that the organic matter composition in raw sludge has a high impact on the PAH distribution.

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