Optimization of Biological Nutrient Removal Processes at Long Creek and Crowders Creek WWTPs

The City of Gastonia, North Carolina, owns and operates two wastewater treatment plants (WWTP) for biological nutrient removal. Until the late 1990s, most of the wastewater came from industrial sources, primarily textile dying companies. More recently, the industrial fraction of the flow has decreased significantly, to about 30% of the total flow treated. A master planning project completed in 2004, that included comprehensive facility evaluations and operations optimization assessments, identified a number of operations optimization opportunities. Among the optimization opportunities implemented by the City over the last several years are chemical optimization, use of alternative carbon sources, use of “swing zones”, increasing nitrified mixed liquor recycle flows, replacement of aeration diffusers, optimization of blower operation, and control of the anaerobic digester supernatant stream that is routed to the head of the plant. This paper will discuss each of these optimization measures and the resulting savings in chemical use and energy, and enhancement of performance reliability.