Submitted to: Water Environment Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 15, 2002
Publication Date: November 1, 2003
Citation: Murtry, S., Kim, H., Peot, C., McConnell, L.L., Strawn, M., Thomas, S., Dolak, I. 2003. Evaluation of odor characteristics of heat-dried pellets. Water Environmental Research. 75(6):523-531.
Interpretive Summary: Wastewater treatment facilities are under increasing pressure to invent new ways of utilizing the biosolids materials created from the wastewater treatment process. Some facilities are creating a fertilizer product by heat drying the biosolids material into lightweight pellets. However, these pellets can be odorous and can become more odorous when they are wet. This project was designed to evaluate the relative differences in key odorous chemical concentrations in the headspace over pellets created from different types of biosolids. Results showed that anaerobically digested biosolids had lower levels of these key compounds than undigested material.
Heat drying of wastewater solids from municipal wastewater treatment plants is becoming prevalent as biosolids management regulations become more restrictive since the material can typically be classified an (EQ) product. Although odors are not the only characteristics that describe product quality, it can be one of the important criteria that describe the characteristics of the pellets. The product from heat drying is sometimes odorous as dry pellets or as 'wetted' pellets. The odors, although not regulated, can be important for marketability and public acceptance of the product. The reasons for the odors are usually a result of upstream processing and management of wastewater solids prior to drying. The goals of the study were to determine the odor characteristics and to compare the odors produced from different types of heat dried pellets and to relate this data with the odor characteristics of Blue Plains oven-dried to validate the decision making process for future facility design. This study evaluated the odors from four types of heat dried biosolids, 1) All undigested, 2) Primary digested, waste activated sludge (WAS) undigested, 3) All digested, and 4) WAS lime stabilized. The odors from these pellets were substantially different for olfactometric response (qualitative descriptors, hedonic tone, odor intensity and persistence) and analytical characteristics (type and relative concentrations) in the gas phase. The Blue Plains digested product exhibited much lower odor characteristics than the undigested blend product when related against each other and against the bench-mark heat dried products. This comparison against benchmarks allowed for a validation of a decision making process that provides for anaerobic digestion of wastewater solids at this particular plant.