Supercritical Water Gasification of Biowastes (Sewage Sludges)

Compared to other biomass gasifiers, supercritical water gasification is ideal for feedstocks with high moisture content (such as biosolid wastes ore sludge) as well as wastes with toxic or hazardous contaminants (such as heavy metals or halogenated compounds, etc). This high-pressure aqueous medium enables concentration and treatment of challenging feedstocks while providing in-situ scrubbing of hazardous materials. Nearly all the key process operations have been demonstrated. However, some technical data gaps are still real challenges and must be resolved (preliminary hydrothermal treatment, suitable catalyst, wall corrosion and salt separation). In addition, economic projections show that supercritical water gasification processing of sewage sludge provides with a cost-effective means for disposal of sludges, compared with current disposal costs, and for generating hydrogen and steam that can serve as potential sources of revenue to offset upstream treatment costs. The analyses also show that the supercritical gasification capital cost is comparable with those of alternativebiomass gasification methods, but that operating costs are much more favorable (i.e., negative). Furthermore, the favorable economics are fairly insensitive to the composition and hydrogen yield of the gasified product.