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Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

Waste To Biogas Mapping Tool

The Waste to Biogas Mapping tool (W2B) has been updated!

There’s new and updated information for the following existing categories: Food processing Facilities, Fat, Oil, and Grease (FOG) Collection Sites, Dairies, Dairies with digesters, and Wastewater Treatment Facilities. Two new categories have also been created: FOG Haulers and Landfills. Please note W2B only has landfill information for CA, and hauler information for CA, AZ and NV.

The most substantial changes were made to the following categories: Dairies, Dairies with Digesters and Wastewater Treatment Facilities (WWTF). EPA Region 9 has estimated total technical energy potential for CA dairies and WWTFs throughout Region 9. To demonstrate how one facility’s energy potential compares to others region-wide, the updated W2B mapping tool graphically represents energy potential with blue flames. The number of blue flames symbolizes a given range of total technical energy potential. Please see the chart below:

Total Technical Potential
Number of Flames kWh/year
images/icon_flame_sm.png 1 - 9,958,992
images/icon_flame_sm2.png 9,958,993 - 19,918,761
images/icon_flame_sm3.png 19,918,762 - 29,878,166
images/icon_flame_sm4.png 29,878,1672 - 39,837,558
images/icon_flame_sm5.png 39,837,559 - 49,796,953
images/icon_flame_sm6.png 49,796,954 and up

For Dairies, estimates for Total Technical Potential (expressed in kWh/year) were based on the following assumptions and data:

  • Assumption #1: In 2006, the Central Valley Regional Water Quality Control Board provided EPA Region 9 with data from the 2005 General Waste Discharge annual reports; these reports included information on dairy herd size for over 1,500 dairies throughout the Central Valley. Estimates for Total Technical Potential are based on 2005 herd sizes.
  • Assumption #2: Typically, dairies designate three roles for cows—Milking Cows, Dry Cows, and Support Cows—and, based on her role, a cow will produce more or less manure. Typically, cows reside in different types of structures based on their role. Each structure collects manure differently, some more effectively than others. Inasmuch, a cow’s role determines how much manure she will produce, and the type of structure the cow resides in determines how much of that manure can be collected. Calculations for total dairy manure production were based on the following assumptions:
    • A ‘Milking Cow’ spends 75% of her time in a flushed milk barn, which can capture 100% of the manure. The calculations assume a 75% manure capture rate.
    • A ‘Dry Cow’ receives less feed than a milking cow and would produce 50% less manure; typically dry cows reside in feeding lanes, where manure is flushed or scraped, with 42% collection efficiency. The calculations assume a 21% (.50 x .42) capture rate.
    • A ‘Support Cow’ (i.e. a calf) produces 25% of the manure that a ‘Milking Cow’ does; typically support cows reside in feeding lanes, where manure is flushed or scraped, with 42% collection efficiency. The calculations assume a 10.5% (.25 x .42) capture rate.
  • Assumption #3: To calculate how much manure a dairy could produce, a model cow—called a ‘Manure Equivalent Milker’ or MEM—was conceived; an MEM represents the weighted average manure capture rates of Milking- , Dry- and Support Cows. For example, Manual Azevedo Dairy #2 in Denair, CA—which according to the 2005 CVRWB waste discharge report—maintains 85 milk cows, 16 dry cows, and 118 support cows—would have 79.5 MEMs:
Milk Cows Dry Cows Support Cows MEMs
Cows 85 16 118
% Manure Produced 100 50 25
% Manure Captured 75 42 42
Total 63.75     + 3.36     + 12.39       = 79.5

  • Assumption #4: After collection, the manure would be digested in a Continuous Stirred Tank Reactor, mesophylic anaerobic digester.
  • Assumption #5: 130 cubic feet of biogas would be produced by each MEM’s manure.
  • Assumption #6: The biogas would have a BTU content of 550 BTU per cubic feet (55% methane).
  • Assumption #7: That the biogas would run through a standard high efficiency internal combustion engine generator with full SCR emission control suitable for SJVUAPCD (<0.15gm Nox/bhp.hr); its heat rate would be 9800 BTU/kWh.
  • Assumption #8: The dairy biogas to energy project would operate with 75% efficiency.

California Bioenergy (CalBio) helped calculate the total technical potential for each California dairy. The estimates are a work in progress and EPA welcomes comments.

For Dairies with digesters, Current on-Site generation (expressed as kWh/year) information was obtained from the EPA AgSTAR digester database.

These data were compiled from a variety of sources. AgSTAR cannot guarantee the accuracy of these data. AgSTAR encourages farm operators, project developers, financers, and others involved in the development of farm digester projects to provide updates and corrections to these data by contacting AgSTAR.

For Wastewater Treatment Facilities (WWTF), Total Technical Potential was estimated for two different scenarios: biogas energy yield with the co-digestion of Fats, Oil and Grease (FOG), and biogas energy yield without. The number of blue flames for WWTFs represents the total technical electricity potential WITH the co-digestion of FOG. For each scenario, Total Technical Potential for electricity (expressed in kWh/year) and for heat (MMBtu/year) were based on the following assumptions and data:

Biogas energy yield without co-digestion of FOG:

Biogas energy yield with the co-digestion of FOG:

  • Assumption #1: Average Dry Weather Flow (Columns B & C) based on information contained in Region 9’s annual biosolids reports.
  • Assumption #2: The co-digestion capacity estimate (Column H) is based on the experiences of the four Wastewater Treatment Facilities (WWTF) analyzed in Environmental Engineering & Contracting, Inc.’s (EEC) Grease to Energy Assessment Report (2007). Industry experts confirmed that a WWTF could reasonably handle a volume FOG equal to 1/10% of their Average Dry Weather Flow (ADWF). Column H = 0.001* Column C.
  • Assumption #3: Methane production potential (Column I) is based exclusively on the experiences of the Millbrae WWTF in California, which suggests that 11 cubic feet of methane can be produced by co-digesting one gallon of FOG. Inasmuch, the potential volume of co-digested FOG was calculated by multiplying the co-digestion capacity estimate (Column H) by 1,000,000 (to convert from MGD to gallons) and then multiplied again by 11 (from gallons to cubic feet). Column I = H*1,000,000*11.
  • Assumption #4: Energy Content (Column J) is based on the standard assumption that 1 cubic foot of methane yields 1,027 British Thermal Units (BTU).
  • Assumption #5: The estimates presented in Columns K through R are based on the USEPA's CHP program performance standards for four engine types: Rich Burn Engine/CHP, Lean Burn Engine/CHP, Microturbine/CHP, and Fuel Cell/CHP. Those standards can be reviewed in Table 6 (on page 11) of Opportunities for Combined Heat and Power at Wastewater Treatment Facilities: Market Analysis and Lessons from the Field linked document (PDF) (57 pp, 1.21MB).
  • Assumption #6: The thermal and electrical outputs for the four engine types were averaged; those estimates appear in Columns S and T.
  • Assumption #7: Column U—Total Technical Potential (kWh/year) of co-digesting the volume of FOG specified in Column H—was calculated assuming an engine with the average electrical capacity (Column S) would run 90% of the year, i.e. Column S * 8760 * 0.9 = U.
  • Assumption #8: Column V— Total Thermal Potential (MMBtu/year) of co-digesting the volume of FOG specified in Column H— was calculated assuming an engine with the average thermal output (Column T) would run 90% of the year, i.e. Column T * 365 * 0.9 = V.
  • Assumption #9: Column W represents the combined Total Technical Potential with FOG (Column U) and without (Column E), i.e. W= E + U.
  • Assumption #10: Column X represents the combined Total Thermal Potential with FOG (Column V) and without (Column G), i.e. X= G + V.

Click here to see the Total Technical Potential estimates for each facility. The estimates are a work in progress and EPA welcomes comments.

Click here to view the UC Davis Biomass Collaborative's estimates for current on-site generation.

What is 9,958,992 kWh/year of biogas-derived electricity equivalent to? The greenhouse gas equivalencies calculator can help you understand just that, translating abstract measurements into concrete terms you can understand, such as the "CO2 emissions from the electricity use of 856 homes for one year.
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