Influence of H2O2 and Ni catalysts on hydrogen production and PAHs inhibition from the supercritical water gasification of dewatered sewage sludge

•Integrated H2 prodution and PAHs inhibition from SCWG of DSS.•Ratio of Ni:H2O2 affects the hydrogen yield and PAHs composition.•Mechanisms of effects of Ni/H2O2 additive on H2 yield and PAHs formation.

Dewatered sewage sludge was treated with H2O2 and/or Ni in supercritical water in a high-pressure autoclave (400 °C, 23 MPa, 60 min). The combined application of H2O2 and Ni was more effective than applying each separately for hydrogen production and for inhibiting the formation of polycyclic aromatic hydrocarbons (PAHs). The hydrogen yield (0.79-1.28 mol/kg organic matter) of combined additives with different Ni:H2O2 ratios was 21% to 35% higher than the calculated value of the hydrogen yield from the mixture. The Ni:H2O2 ratio affected the ring number composition of PAHs (proportion of 4-6 ring PAHs increased from 13% to 44% with increasing Ni:H2O2 ratio) considerably, but had little effect on the concentration of PAHs. The mechanisms of the Ni/H2O2 additive were also investigated from the viewpoint of combined action and intermediates. Overall, the method developed herein has the potential to promote hydrogen production in an environmentally compatible manner.

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