From Grease to Green: Two FOG Case Studies
- Matthew P. Van Horne, T. Bruton, S. Hardy, C.M. Bullard, H. Long
Increasingly, wastewater treatment utilities are considering the dual benefits associated with fats, oils, and grease (FOG) receiving. Receiving this material can help to address the removal of a problematic material from the collection system by facilitating periodic grease trap cleaning and maintenance at food service establishments (FSEs) in their service areas. Through co-digestion of this material with traditional wastewater solids in anaerobic digesters, the utility can simultaneously realize benefits from increased digester gas production. This practice can be particularly beneficial where the excess digester gas can be beneficially used with little incremental capital investment and can be converted into electrical energy via a combined heat and power (CHP) system.
This presentation will review two case studies, the F. Wayne Hill Water Resources Center (FWHWRC) in Gwinnett County, Georgia and the Henrico County (Virginia) Water Reclamation Facility (HCWRF), and present the unique driving factors, design concerns and economic benefits from receiving FOG for co-digestion. The various drivers for the projects include both internal (collection and treatment system impacts from FOG, economics) and external (changing regulations, available grant funding opportunities) to the wastewater utility. Design concerns span the FOG receiving facilities, the use of existing anaerobic digesters for co-digestion and operation of the CHP system. Economic benefits include direct benefits from the electricity and heat produced by the CHP system and indirect benefits from the removal of the FOG from the collection and treatment systems.
The two case studies will be compared and contrasted to show how differing drivers, anticipated FOG volumes and digester gas production characteristics can vary greatly between multiple locations. One significant difference is the variations in projected digester gas production at the various flow rates between the two facilities. Figure 1 and Figure 2 show the digester gas projections for a range of flow rates for the FWHWRC and the HCWRF facilities, respectively. The projections for gas production for the FWHWRC generally exceed that projected for the HCWRF, especially as flow rates increase, which can impact the economic payback period for the two facilities. Gwinnett County is also performing bench-scale digestion studies through a local university to compare digester gas production impacts of adding a single and a mixture of high strength waste streams. Preliminary data will be available by the time of paper presentation.
Other comparisons between the facilities will be made including possibilities to increase digester gas production, impacts to the existing digestion processes and impacts of equipment sizing on payback periods.
The FWHWRC design-build project is scheduled for completion in early 2011 and the HCWRF project has completed the planning phase and various project delivery and funding mechanisms are being investigated to determine the next implementation phase.
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