Modeling and optimization of biofiltration for odor control

Odorous air emissions (H₂S and other volatile reduced sulfur compounds) from wastewater treatment and other processes (e.g., composting, animal feeding operations, paper manufacturing, petrochemical refining, etc.) exert toxic impacts on human health and corrosive effects on infrastructure and equipment and therefore require treatment. Biofiltration has been found to be an ecologically and economically favorable alternative for odor control. Unfortunately, removal of reduced sulfur compounds from a waste air stream in a biofiltration unit has not yet been well studied and the systems in the field are prone to unknown upsets. Although mathematical modeling is an efficient method for design and optimization, no biofiltration model is currently available to support design and optimization of biofiltration for odor control.; In this dissertation, a dynamic model was developed to aid design and optimization of biofiltration for odor control. Removal mechanisms include advective flow, mass transfer from the bulk phase to the biofilm, biofilm internal diffusion, and biological reactions in the biofilm. Compared to the existing biofiltration mathematical models, the model developed in this study has the following advantages: (1) It was developed especially for biofiltration of odorous compounds. (2) The mass transport of the target compound at interfaces was modeled as a dynamical process instead of assuming equilibrium. (3) The active biomass concentration was modeled as a function of axial position (x), biofilm depth (z) and time (t) instead of assuming a uniform concentration. (4) It was incorporated into a user-friendly software called Biofilter™.; The model was calibrated and validated with H₂S data obtained from pilot- and full-scale lava rock biofilters at Cedar Rapids Water Pollution Control Facilities (Cedar Rapids, IA), and then its applications in design and optimization of biofiltration for H₂S removal was demonstrated. The model was also applied to evaluate a full-scale two-stage biofilter at the Western Lake Superior Sanitary District (Duluth, MN), which was packed with a different packing medium than lava rock (i.e., a mixture of compost and wood chips), and treated a mixture of H₂S, methyl mercaptan (MeSH), dimethyl sulfide (Me₂S), and dimethyl disulfide (Me ₂S₂). The results demonstrate that the model is also applicable for organic odorous compounds and/or organic packing media.