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

Dewatered sewage sludge was treated with H 2 O 2 and/or Ni in supercritical water in a high-pressure autoclave (400   °C, 23   MPa, 60   min). The combined application of H 2 O 2 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:H 2 O 2 ratios was 21% to 35% higher than the calculated value of the hydrogen yield from the mixture. The Ni:H 2 O 2 ratio affected the ring number composition of PAHs (proportion of 4–6 ring PAHs increased from 13% to 44% with increasing Ni:H 2 O 2 ratio) considerably, but had little effect on the concentration of PAHs. The mechanisms of the Ni/H 2 O 2 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.