When Influent Sampling Goes Wrong: Averting Capacity Crisis

In 2008, the F. Wayne Hill Water Resources Center (FWHWRC), Gwinnett County's 60 mgd advanced wastewater plant, was operating below 50% of its design flow capacity. Based on influent flow to the FWHWRC, it was assumed that significant additional capacity remained. However, when the past several years of influent COD and TSS concentrations were analyzed, the County realized that, potentially, much of the remaining flow capacity was already consumed on a load basis since the influent concentrations far exceeded the original design concentrations. Secondly, the FWHWRC primary clarifiers historically experienced poor performance with low TSS and BOD removal rates, thus further reducing flow capacity to downstream processes. And finally, GCDWR planned to send primary and waste activated sludge from the upgraded Yellow River WRF (YRWRF) through the collection system to the influent of the FWHWRC, further increasing influent loadings.The combination of these three issues led to a potential capacity crisis at the FWHWRC. A study by an outside consultant determined that the FWHWRC capacity was now as much as half of the original design flow capacity (30 mgd instead of 60 mgd design flow capacity) based on the high influent concentrations and poor performing primary clarifiers alone, with additional reduction in capacity due to the planned YRWRF sludge transfer. GCDWR then hired Hazen and Sawyer to conduct a comprehensive study to confirm the influent loadings, evaluate the primary clarifier performance, calibrate a BioWin model, evaluate the impacts of the YRWRF sludge, and to verify unit process capacity based on the results. This paper will describe a comprehensive approach developed to reconcile the influent data and the primary clarifier performance issues, and will present the successful results of the study including maintaining the original flow capacity of the liquids processes.