Odor Classification of Biosolids to Mitigate Nuisances : A Québec Approach

Odors from biosolids are generally considered to be nuisances, not something that requires regulation for protection of public health and the environment. However, there is evidence that malodors may trigger health effects, and malodors are the most commontrigger of public concerns regarding biosolids land application programs. In Quebec, Canada, the Ministry of Sustainable development, Environment and Parks (MDDEP) developed an odor classification system for biosolids and other fertilizing residuals (FRs) that are applied on farm land. This system was developed from a survey of a diversity of individuals' subjective perceptions of the odors from various FRs in comparison with farm manures.The Ministry uses the classification scheme in its regulations of biosolids and other FRs. Thus, odors are classified just as are levels of trace elements (metals) and pathogens. Specifically, 38 different types of typical biosolids and FRs are given a default odor designation of O1 (smells less offensive than dairy manure) to O3 (smells more offensive than dairy manure, but less offensive than hog slurry) or “out of category” (more offensive than hog slurry). Increasingly stringent management requirements, such as increased setbacks, are required for each classification from O1 to O2 to O3. “Out of category” biosolids / FRs cannot be land applied without further treatment for odors. The regulatory system allows for land application program managers to have their biosolids or other FRs reclassified based on olfactometry applied to the specific material.Quebec's regulation of biosolids and FRs odors is unique and has proven effective in reducing odor complaints. It is a simple system, easily understood by practitioners and the public. However, it has led to elimination of land application in the province of some biosolids that were deemed too odorous, and for some biosolids management programs, it has added costs for odor reclassification through olfactometry.