Production of bio-oil from sewage sludge by thermochemical liquefaction

The increasing demand for petroleum by emerging economies, the predicted shortage of fossil fuels, as well related environmental concerns, are spurring the search for new sources of liquid fuels. It is expected that a significant part of future renewable fuels will be represented by biomass resources. A good feedstock could be the urban organic wastes, among them the municipal wastewater treatment sludge. The management of the sewage waste is a difficult and expensive problem to solve for many countries. The common disposal processes for sewage sludge include landfilling, land application and incineration. However, these conventional processes have certain technical limitations or increasing environmental restrictions. Conversely a liquefaction process, that allow the direct use of wet sludge without particular pretreatment, represents a valuable and sustainable tool in order to produce liquid organic products from a biomass not in competition with food and without land use or change. The liquid products, i.e. the bio-oil, could in principle be used to produce biofuels. In the present study, the direct liquefaction of sewage sludge was investigated in order to maximize the bio-oil production. The effects of liquefaction operative conditions were studied. All the yields were calculated versus dry sewage sludge basis.