By John A. Pierson, P.E.
The initial treatment of processing facility effluents begins with primary screening to remove gross solids such as feathers, offal and other similar materials. Often secondary screens are employed to further remove finer solids comprised of fats and proteins. These steps serve to not only recover materials for rendering, but also reduce the costs for operating subsequent chemical dissolved air flotation (DAF). In practice low volume nozzle spray washes are used to continuously clean rotary screen surfaces. However, entrained particulate properties (size, density and miscibility) typically clog screen openings and diminish the volume passed through the screens over time (flux rates).
Thus, a critical need remains for both greater filter flux rates (L/m2*hr) and solids removal compared to a traditional secondary screening systems utilizing <300-micron filters. Previous U.S. Poultry & Egg Association research (Sellers, 2007) indicated that tertiary mechanical screening showed no significant difference in performance for any of the three screen sizes (212, 106, and 45 micron) examined. Authors noted that screen surfaces were quickly blinded, requiring that any full-scale system include an automatic backwash system.
The proposed project objectives focus on fully characterizing the scalability of a proof-of-concept dynamic filtration device. Results indicate that scaling the system to full-size is not an issue although care must be taken to adequately size piping. The system differs from other filtration systems in that an innovative process uses backflow of clean or processed waters for continuous or near real-time surface cleaning, depending on operational mode.
Preliminary data showed that the prototype system achieved suspended solids and protein removal efficiencies comparable to dead-end filtration. The prototype results were from processing chiller waters and margination using similar filter sieve and membrane fabric openings as compared to dead-end filtration but with longer filter runs. Material was concentrated in the filter backwash that comprised 20 percent or less of the overall flow. A patent is being finalized, a paper has been submitted and another manuscript is in draft form. Six different students were funded during the course of the effort.
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