Treatment of sewage sludge in supercritical water and evaluation of the combined process of supercritical water gasification and oxidation

Influences of temperature and oxidation coefficient (n) on sewage sludge treatment in supercritical water and its corresponding reaction mechanism were studied. Moreover, the combined process of supercritical water gasification (SCWG) and supercritical water oxidation (SCWO) was also investigated. The results show that ammonia nitrogen, phenols and pyridines are main refractory intermediates. The weight of solid products at 873 K and n = 4 is only 3.5 wt.% of the initial weight, which is lower than that after combustion. Volatile organics in solid phase have almost released at 723 K and n = 0. Highest yield of combustible gases was obtained at n = 0, and H2 yield can reach 11.81 mol/kg at 873 K. Furthermore, the combination of SCWG at 723 K and SCWO at 873 K with a total n = 1 is feasible for its good effluent quality and low operation costs.