The Role of Shear in the Generation of Nuisance Odors from Dewatered Biosolids

Shear energy when in the presence of biosolids and polymer leads to the increased production of sulfur odors from dewatered biosolids. It is believed that the shear energy renders flocassociated proteins bioavailable. These proteins then interact with the polymer to form a proteinpolymer complex in which the bioavailable conformation of the protein is maintained. This assertion is supported by the fact that no increase in nuisance odor generation was noted when polymer was added after shearing of the biosolids. The odor production is not solely controlled by shear alone. Polymer dose as well as cake solids concentration impact peak sulfur odor generation. The underdosing of sludge with polymer results in a net reduction in odor production since there is insufficient polymer to coagulate the released proteins. Polymer overdosing also does not lead to an increase in odors due to the limited amount of bioavailable material released by shear. It was also observed that as the solids content of the dewatered biosolids increased, peak sulfur generation increased linearly. This is thought to be due to the inhibition of methylotrophic methanogens which normally reduce methylated sulfur compounds syntrophically with heterotrophic organisms. The results of this study, while preliminary do lay the groundwork for the development a method to mimic the odor generation of full-scale centrifuges using a laboratory method.