Wastewater treatment biosolids, Sludge management, Thermochemical conversion technologies, Cogeneration system, Urban WWTPs (Wastewater Treatment Plants)


Wastewater treatment biosolids, commonly referred to as sludge, is a dilute suspension of micro-organisms, noxious organic matter, and mineral species in up to 99% water. Sludge is produced at about 250 mg/L of mixed municipal and light industrial wastewater treated. Management of this process stream can present a financial and environmental challenge for wastewater treatment plants (WWTPs), accounting for up to 15% of plant energy consumption. Operators of small urban WWTPs see the greatest challenge as their operations do not benefit from economies of scale, which permit larger facilities to absorb the costs or footprint of anaerobic digestion. This work considers small scale urban WWTPs, which serve sewage flows of up to 5 million gallons per day (MGD) (0.22 m3/s). A contemporary approach to sludge management considers sludge to be an incomegenerating, recoverable resource. On a dry basis, sludge has a lower heating value (LHV) similar to that of low- rank coal, about 15 MJ/kg (6449 Btu/lb). This suggests that the value of sludge might best be recovered as a fuel for on-site cogeneration of electricity and heat, with heat being used internally (i.e. for thermal drying). Thermochemical conversion (TCC) technologies subject sludge to chemical processes at high temperatures to convert the chemical energy in sludge into heat, more useful fuels, or both. Four candidate TCC technologies were looked at in this study. These include wet oxidation, direct combustion, pyrolysis, and gasification (air blown, steam blown, and supercritical water). Air and steam blown gasification were determined to be the most appropriate TCC technologies and were studied in depth. The present work intends to determine whether sludge fueled cogeneration is technically and economically feasible for decentralized urban WWTPs. We have reviewed the four TCC technologies, designed and simulated the performance of a cogeneration system, and evaluated the systems for technical and economic feasibility.

Original Publication Citation

N. Lumley, … J. Porter, Techno-Economic Analysis of Wastewater Biosolids Gasification, 2013 AIChE Annual Meeting, Nov 3-8, (2013), San Francisco, CA

Document Type

Conference Paper

Publication Date







Ira A. Fulton College of Engineering and Technology


Mechanical Engineering

University Standing at Time of Publication

Associate Professor