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Applying Rheological Techniques to Upgrade Anaerobic Digesters and Handle High Solids Concentrations

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The Orange County Sanitation District (OCSD) is implementing a Capital Improvements Program that includes upgrading their wastewater treatment Plant No. 1 in Fountain Valley, California to full secondary treatment. The expansion will increase both primary and secondary solids production. OCSD prepared a Long-Range Biosolids Management Plan that concluded the waste solids should continue to be anaerobically digested to produce Class B biosolids. The Plan also investigated the capacity of the existing anaerobic digestion facilities and concluded that the digestion volume would be adequate for future loading conditions; however, to maintain the 15- day hydraulic retention time for meeting EPA 40 CFR Part 503 Regulations, it would be necessary to thicken the feed solids. Preliminary estimates indicated that feed solids solids concentrations would need to be approximately 6 percent dry solids resulting in the digesters operating at solids concentrations of about 4 percent.

The paper presents the results of a preliminary design engineering study carried out for Plant No. 1. Sludge samples were collected and tested to determine site-specific sludge rheology data. The rheology data were used to scale model the digester mixing system and calibrate a computational fluid dynamics computer model for assessing digester mixing.

Document Type: Research Article


Publication date: 2006-01-01

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