Wastewater sludge is a resource available wherever wastewater is treated. In the U.S., it comprises several million tons per year on a dry basis, with a typical fuel value of 20 MJ/kg (HHV). In the past, sludges have been disposed of at sea, incinerated, land-filled, and spread on land as a treated biosolids fertilizer. Because the sludge is available on a consistent basis, with an unchanging makeup, it might be considered to be a renewable fuel. Unfortunately, the sludge typically is available with a very high moisture content, rarely less than 85% by mass.

We have begun a small-scale research program to investigate the nature of sludge drying. Using a Thermogravimetric analyzer (TGA) with controlled humidity, experiments have been done to measure the equilibrium moisture content and to establish the governing mechanism of moisture mass transfer. The drying process is surprisingly complex, and serves to reinforce concepts of mass transfer.

Six undergraduate students have participated in the project, with tasks distributed between moisture control, TGA, and data analysis. Undergraduates are strongly attracted to work on projects with potential environmental and societal benefits. The students each wrote research proposals, three of which were funded by the campus undergraduate research program. Several participated in the project beyond the period of the original project. We are preparing a manuscript for submittal to a research journal.