Sewage Sludge Gasification as an Alternative to Incineration

While gasification had been used for many years as a means of converting carbonaceous fuels to useful heat and power, its use was largely phased out with the development and distribution of inexpensive and energy rich petroleum hydrocarbon fuels. However, there has been a recent renewed interest in gasification as a viable means to produce renewable energy while reducing the consumption of fossil fuels. Gasification can provide energy from renewable fuel sources while producing significantly less emissions than conventional combustion processes.Sewage sludge gasification utilizes dewatered and dried sewage sludge as a feedstock. The gas produced in the gasifier, referred to as syngas, is comprised of hydrogen and carbon monoxide which can subsequently be combusted in boilers for heat or engines/turbines for electrical power generation.Sewage sludge gasification as a process deployed at municipal wastewater treatment facilities is relatively new, with several pilot scale studies initiated between 2003 and 2007. Some of these initial efforts never advanced beyond a planning stage due to the absence of public support for implementation of technologies without an extensive proven operational track record (Stamford, CT). Others had started full scale operations, and subsequently shut down due to costs incurred to correct technical problems which could not be financially supported (Sanford, FL). However, there are two existing operational full scale sewage sludge gasification facilities in Europe (Balingen and Mannheim, Germany) and a third, the world’s largest, in Asia (Tokyo, Japan).The primary wastewater treatment facility in Anchorage, Alaska currently utilizes a multi-hearth incinerator to reduce the volume of wastewater solids which must be hauled to the local landfill. The city is considering sewage sludge gasification as a viable alternative to their incinerator to reduce their emissions, reduce sludge volume, and to operate their facility without being subject to the SSI Rule. In pursuit of that, the city is engaged in a full scale pilot project in which sludge from Anchorage is being dried on site, bagged, and shipped to a full scale operational gasifier for full scale testing. The results of this testing shall determine whether or not further steps towards the acquisition of a gasifier for the treatment plant in Anchorage will be taken.