The extent of sludge solubilization allows to estimate the efficacy of ozonation for removal of polycyclic aromatic hydrocarbons (PAHs) in municipal sewage sludge

Ozone treatment has been proven as an effective technology for removing PAHs in municipal sewage sludge. However, given the complex interaction of PAHs with sludge extracellular polymeric substances (EPS), effective sludge disintegration is required to make PAHs more accessible to oxidants, which also affects PAHs partitioning. Here, we investigated two treatment systems, namely ozonation (ozone) and sequential hydrodynamic cavitation and ozonation (HC+ozone), under varied conditions, to determine whether the extent of sludge disintegration can estimate a measurable removal of PAHs. The results showed that both the PAHs removal efficiency and kinetics highly depended on pH and ozone dose. Although no significant removal of PAHs occurred during HC treatment, the observed rate constants for ?16 PAHs removal in HC+ozone system were 1.2?1.4-fold higher than those obtained in ozone system under the same condition. The accelerated PAHs removal could be attributed to the reduced flocs size (80% smaller) and increased soluble EPS concentration (5-fold higher) with HC pretreatment. Lastly, a positive correlation was noted between the PAHs removal efficiency and soluble EPS concentration (R2 = 0.85), indicating the important role of dissolved and colloidal matter (DCM) for PAHs partitioning between aqueous and particulate phases.

Automated summary

The study compared the removal effect of ozone treatment and hydrodynamic cavitation combined with ozone treatment on PAHs, finding that the removal rate of PAHs in the HC+ozone system was higher due to the reduced floc size and increased soluble EPS concentration from HC pretreatment, leading to enhanced solubility of PAHs.