Holistic Approach to Residuals Handling at F. Wayne Hill Water Resources Center: Did the Upgrades Work?

In 2010 Gwinnett County Department of Water Resources (GCDWR) and Hazen and Sawyer (Hazen) performed a study at the F. Wayne Hill Water Resources Center (FWHWRC), a 60-mgd advanced resource recovery center, to assess the plant capacity and determine the capacity impacts from receiving solids generated at the county’s Yellow River Water Reclamation Facility. The study suggested improvements to the primary clarifiers to achieve reliable removals to maintain secondary process capacity and implement co-thickening of primary sludge and WAS to delay the expansion of the anaerobic digestion facility. These improvements have since been constructed along with a combined heat and power system, FOG/HSW receiving facility for co-digestion and nutrient recovery system.In 2015, Hazen performed a follow-up study to confirm that the above capital improvement projects were performing as intended and to optimize the processes to obtain the performance criteria, if required. The 2015 study showed that the primary clarifiers performance increased from negative total suspended solids (TSS) removals to averaging over 50 percent removal. The co-thickening of waste activated sludge (WAS) and primary sludge was slightly below the 5.5% TSS key performance indicator (KPI). This resulted in the plant evaluating a new polymer for thickening. Even with the thickening below the KPI, digester solids retention time (SRT) has averaged above 20 days. The CHP system along with their hour ahead rate structure, has decreased the annual electrical cost by over $3M in 2013. FOG/HSW receiving has contributed to the digester gas production; however, debris handling, chemical compatibility and clogging has created operational challenges. The Nutrient Reocvery System is producing about 1 ton of slow release fertilizer each day and has eliminated much of the struvite maintenance issues.