Several studies were conducted to evaluate odors from biosolids that arise from upstream processes and from storage. One study that evaluated biosolids odors originating from upstream processes demonstrated that wastewater solids that was odorous prior to stabilization (such as from
back-ups during processing), would remain odorous after stabilization. The biosolids odors produced during high in-process sludge odor possessed a higher hedonic tone (with higher dimethyl sulfide production) than the biosolids odors from the low in-process sludge odor. In another study it
was found that cationic polymers used for conditioning in centrifuges may cause odors through breakdown of its constituents during post-lime operations. The odors produced from the breakdown of polymers were fishy odors related to the production of trimethyl amine. Trimethyl amine was produced
immediately and also over increase in storage time and appeared to persist. The fishy odors associated with trimethyl amine were observed in the biosolids after a month of testing. An increase in storage time resulted in an increase in production of odorous compounds. Further, a decrease in
lime dose promoted biological activity and production of odorous compounds. For the storage study, DMDS production peaked after 7 days, while methyl mercaptan and dimethyl sulfide continued to be produced over one month of storage. The 15 percent post-limed (dry weight) biosolids product produced
substantial odors after four days of storage and the odors increased over time. The 40 percent post-limed biosolids product was very stable, and the odors actually appeared to decrease over increase in storage time. A lime dose of at least 20–25 percent may be required to achieve a stabilized
product with low off-site odors.
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