Conversion of faecal sludge to liquid fuels. Why and how could it work for small-scale application? : a paper presented at the second conference on...

Waste to energy conversion is a promising route for reducing the fossil fuel dependency of the world. Fermentation, chemical processing, pyrolysis and gasification have been the main processes used for transforming biomass and other “burnable” wastes into useful fuels like ethanol, methanol, biogas, bio-diesel, bio-oil, bio- hydrogen etc. Most works on the subject are focused on power generation or on the production of alternative fuels, while few consider the option of producing gasoline or diesel. Gasoline and diesel can be produced from bio-waste through gasification, a process that produces a mixture of hydrogen and carbon monoxide known as syngas, and a method known as the Fischer-Tropsch (FT) process. FT has been implemented by some companies (Sasol, PetroSA, Shell,...) for the production of high value hydrocarbons from coal and natural gas. These plants are normally large with production capacities of thousands of barrels per day. But for a plant with such production rates, converting high water content biomass such as faecal sludge into hydrocarbons would require large quantities of sludge to be transported to the processing plant. At a smaller, local scale it may be economically attractive to process faecal sludge for the production of liquid fuels. Although small scale FT has not yet been commercialized, there are new developments in reactor technologies that can offer economically viable small-scale FT processing. [authors abstract]