Results from a Full Scale UFAT VFA Generation Capacity Study

Primary sludge fermentation has long been used to generate volatile fatty acids (VFA) vital to biological phosphorus removal (BIO-P). At the Durham Advanced Wastewater Treatment Plant (AWWTP), the unified fermentation and thickening (UFAT) process was developed and has been in operation for eight years. This process consists of a static fermenter/thickener combination to produce and elutriate VFAs from primary solids before thickening.There are significant practical issues that can limit the capacity; such as inaccurate flow measurement because of rapid grease buildup, difficult inventory management, and the lack of automation. The achievable maximum VFA generation capacity depends as much on temperate and solids retention time (SRT), as it does from the ability to control the fermenter. In addition, prefermentation upstream of the UFAT system has proven to be a key factor in fermenter VFA yield.