Characteristics of Nuisance Odor Emissions from the Sludge Drying Process

Sludge drying from wastewater treatment can cause an odor nuisance for neighboring communities. This study characterized the nuisance odor emissions to begin to develop odor control strategies to minimize the malodor emission during a sludge drying process of digested wastewater sludge. The digested sludge used in the study was from Orange County Sanitation District (OCSD) Waste Water Treatment Plant (WWTP), at Fountain Valley, CA. This study examined the consistency of odor character, analyzes the relation between typical malodors and drying temperature and determine the pattern of the change of odors during the drying process. A new approach to understanding the odor produced by the sludge drying process was tried by replicating odors by creating artificial undigested and digested sludge recipes.The primary odors detected were consistent with a previous study, including the burnt odor. This study indicated that fecal and musty/earthy odors were also important odors. A caramel odor was detected as a new odor within the burnt odor category. The chemical(s) that contribute to each odor were more easily studied by simulating a sludge digesting recipe. Digested sludge (described as raw sludge) that was added into a sludge recipe containing fresh fats, protein, and carbohydrates successfully simulated the anaerobic digestion processes of the sludge. The odors produced were much closer to the actual odors from the sludge drying process than the recipes without adding digested sludge. The overall data for WWTP sludge shows that odors vary somewhat due to the fact that all of the incoming wastewater are not completely identical.