Pyrolysis of sewage sludge - upgrading atmospheric and vacuum distillation products

Although estimating proven reserves is an inexact science, most figures indicate that the depletion of fossil fuels will be evident before the middle of this century [LM02]. Therefore there is a growing need for alternative feedstocks to insure energy resources. There are several options available including wind, solar and nuclear as well as biomass. Other than long-term supply issues the main driver for moving away from fossil fuels are environmental considerations. Since pre-industrial times the level of atmospheric CO2 has risen from 280 ppm to 360 ppm, and whilst some observers believe this may be a natural cycle in the Earth\u27s history, most believe it is a direct consequence of burning fossil fuels. This additional CO2 is now thought to be the main cause of global warming via the greenhouse effect [LM02]. Biomass, an organic non-fossil material, can be the answer to the energy and the pollution problem. Additionally, some biomass treatments can result in the production of some speciality chemicals. Composting, direct landfilling, compression/concentration, liquid extraction and thermal treatment (incineration, gasification and pyrolysis) are possible methods for biomass treatment. Pyrolysis is the thermal decomposition of organic materials by heating in the absence of oxygen and water and is a promising technique, which has gained interest in recent years. The disposal of sewage sludge, which is a special kind of biomass, is produced by urban and industrial wastewater treatment plants, and is a matter of great concern. Pyrolysis is currently being investigated as an alternative solution to the problem of sewage sludge disposal, because it has certain advantages over other methods. The use of pyrolysis to treat sewage sludge results in a huge volume reduction and gives rise to the production of three products, viz charcoal, oil and gas with proportions depending on the pyrolysis method, reaction parameters and feed being used. Earlier research proves that bio oil derived from the pyrolysis of sewage sludge has good commercial value as a fuel to power diesel engines. However, the properties of the oil, such as its bad odour, high viscosity and its instability can be a disadvantage for marketing the oil [DA05]. This paper examines the possibilities of improving the characteristics of the atmospheric and vacuum distillation products from relatively old bio oil that is derived from sewage sludge. Herefore the chemical and physicochemical characteristics of the fractions will be examined. The characterization techniques applied are GC-MS, calorimetry, microscopic examination and adorption/desorption of N2 at 77K. The acid number and the water content (Karl Fischer-titration) of the different fractions can give additionally information. Some upgrading techniques such as esterification, hydrogenation, carbonisation and activation will be tested upon the atmospheric and/or vacuum fractions. All these tests were performed in the institute of Chemistry and Technology of Petroleum and Coal at the Chemistry Faculty of the Wrocław University of Technology in Poland