Heating Primary Sludge for Increased Fermenter Volatile Fatty Acid Production

The Durham Advanced Treatment Facility in Tigard, OR operates a fermentation complex that utilizes a Unified Fermentation and Thickening (UFAT) process to ferment primary sludge. Volatile fatty acid (VFA) produced through fermentation are used to support biological phosphorus removal (BPR). During cold weather months, solids retention time (SRT) limitations result in reduced VFA production, leaving BPR somewhat unstable especially in late spring when the plant effluent total phosphorus limit becomes more stringent. A sludge heating system was installed upstream from the fermentation complex to heat primary sludge, overcoming SRT limitations of the current system to increase cold weather VFA production. This improves BPR stability in the late spring and changes future fermenter design criteria, reducing the required footprint for future fermentation system expansion.