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Case Study: Pretreatment of Challenging Pork Rinds Manufacturing Wastewater

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Problem: Gaytan Foods facilities in City of Industry (Los Angeles, CA) manufacture pickled pork rinds, pickled pig feet and “cheese” puffs. The resulting wastewater is loaded with FOG's, proteins and salts. Wastewater varies hourly and daily. Drastic changes in amount and type of contaminants occur (two orders of magnitude). During some hours wastewater is loaded with proteins, and as it cools down, highly viscous gel is produced. Protein degradation produces hydrogen sulfide (odor problem).

Goals and Objectives: Local municipality complained about amount of FOG in wastewater and formation of gel in pipes. Reduction of BOD was also suggested. Odor problems (hydrogen sulfide) also had to be dealt with. The goal was to design and build wastewater treatment plant that will reduce amount of FOG, TSS and BOD and prevent formation of gel and hydrogen sulfide.

Solution: Wastewater treatment plant was designed and installed to deal with those problems. Rotating drum screen was installed to remove large particles and objects. Large equalization tank collecting 24 hours of produced wastewater with intense mixing was installed to prevent gelation. Equalization also helped reduce the salinity of the stream (dilution with low salinity streams). Following equalization, flocculation – flotation system was used for primary treatment. Individual samples were very difficult to coagulate and flocculate. Large amounts of flocculants were needed to achieve the flocculation. This made the process too expensive. However, equalization solved these problems. Equalized stream was easy to flocculate. Hybrid centrifugal - dissolved air flotation system reduces TSS to less than 50 mg/l and FOG to less than 5 mg/l. Dissolved BOD's are also removed, probably due to flocculation of some large protein molecules. Total BOD's reductions average around 75%. Aeration of the equalization tank prevents formation of hydrogen sulfide. This significantly reduces odor problems. Since the installation of the system, gel formation in pipes never occurred, either. Flotation produces sludge with over 25% of solids that is reused (pet food manufacturing). Municipal wastewater treatment plant has no problem with treatment of dissolved BOD's that remain in wastewater after the pretreatment. Fees and fines that Gaytan Foods faced in the past are significantly reduced or eliminated (fines). In the future, even more robust odor control will be attempted (deodorizing solutions).
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Keywords: FOG; flocculation – flotation; odor control; protein and BOD removal

Document Type: Research Article

Publication date: 2009-01-01

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