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King County & Brown Grease. Local sewer agencies have a need to address restaurant grease trap waste. In response, there is the potential of a renewable energy fuel source and opportunity to invest in sustainable waste management technologies. Wastewater Treatment Division (WTD).

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King county brown grease

King County & Brown Grease

Local sewer agencies have a need to address restaurant grease trap waste. In response, there is the potential of a renewable energy fuel source and opportunity to invest in sustainable waste management technologies.


Wastewater treatment division wtd
Wastewater Treatment Division (WTD)

  • 34 local jurisdictions feed wastewater to King County WTD’s system

  • 3 major treatment plants serve 1.5 million across 420 sq. miles

  • 600 employees manage the treatment of about 175 million gallons of sewage each day

  • Our challenge: integrating sustainability into urban sanitation systems


In evaluation of emerging technologies
In Evaluation of Emerging Technologies

  • Level of technology development

  • Applicability to WTD system

  • Potential benefits to WTD facilities or environment

  • Potential impacts to WTD facilities or environment

  • Potential for recovery of valuable resources

  • Consistency with King County policies & directives


A business need for energy management
A Business Need for Energy Management

  • WTD represents 58% of all King County government’s facility energy use

    • Target #1: Achieve a 10% normalized net reduction in energy use

    • Target #2: Produce, use or procure renewable energy equal to 50% of use

    • Target #3: Maximize the cost-effective conversion of waste to energy

2010 Wastewater Treatment Energy Use by Type


Wtd already produces 610 000 mmbtu s of digester gas
WTD Already Produces 610,000 MMBtu’s of Digester Gas

South Plant

  • Digester gas scrubbed. 20% of it used on site for process heat. 65% sold directly to PSE [85% use, 15% flared]

    West Point

  • New cogen plant expected to generate 18,000+ mega-watt hours of ‘renewable energy’ every year, nearly 1/3 of the plants yearly electricity consumption

  • Plant will use 60% of digester gas to produce electricity for sale to SCL – two engines, capable of producing 2.3 MW each (combined 4.6 MW installed power)

  • 44% of digester gas energy used on-site for process needs including raw sewage pumping [total adds to >100% as cogen process also generates all process heat required for the plant]


Why south plant for brown grease
Why South Plant for Brown Grease?

  • Relatively easier plant access for trucks visiting brown grease receiving site - must be self serve

  • Centrally located in Renton

  • Digester capacity


Local sewer agencies proposed p referred p umper p rogram
Local Sewer Agencies’Proposed Preferred Pumper Program

If PPP moves forward:

  • Potential for “new” brown grease coming on market

  • Standardization and improved record-keeping helpful

  • Would need public & private involvement to leverage resources/support beneficial reuse


2006 food waste co digestion study
2006: Food Waste Co-Digestion Study

Benefits:

  • Increased energy production

    Concerns:

  • Uncertain supply with private composter contracting for restaurant food waste

  • High onsite cost to unload and store incoming waste; screen out metals and glass; mix and grind

    Conclusions:

  • 2006 report recommended looking at liquid waste as potentially more cost-effective


Wtd approach to study
WTD Approach to Study

  • Experience available: nationally, agencies/consulting firms have implemented full-scale grease co-digestion projects

  • Plants currently accepting brown grease by truck (partial list):

Riverside, CA

East Bay Municipal Utility District, CA

Millbrae, CA

Oxnard, CA

Watsonville, CA

So. Bayside Authority (Redwood City), CA

Lincoln, NE

Pinellas County, FL


2012 brown grease co digestion study
2012: Brown Grease Co-Digestion Study

Q1: How much brown grease can the current wastewater processing facilities manage?

Q2: How much would an appropriately-sized brown grease receiving facility cost?

Q3: What are the estimated operating costs and revenues?


Q1 how much grease can current wastewater processing facilities manage
Q1: How much grease can current wastewater processing facilities manage?

  • Capacity of solids processing facilities (digesters, biosolids mngt., etc.) - OK

  • Capacity of biogas handling systems could be limited by waste gas burners - ??

  • Capacity of biogas-to-energy systems - OK

  • Practical operational limit to daily truck deliveries onsite - maximum 10–20 trucks/day


Q2 how much would an appropriately sized brown grease receiving facility cost
Q2: How much would an appropriately-sized brown grease receiving facility cost?

  • Representative site selected

  • Identified facilities needed

    • Truck offloading facilities, grease receiving tanks

    • Screening, heating, mixing, pumping

  • Modular design to facilitate expansion if needed

  • Capital cost estimate: $2M


Q3 identify estimated operating costs and revenues
Q3: Identify estimated operating costs and revenues

Cost estimates prepared for facility to manage

15,000 - 30,000 gpd (10 – 20 trucks/day)

Costs

  • Cap’l recovery: ~$135,000/yr

  • O&M cost: $400,000/yr to $500,000/yr

    Revenues

  • Energy revenue: $100,000/yr to $200,000/yr

  • Tipping fee required to break even


Next steps
Next Steps

  • Market assessment

    • How much brown grease is currently being collected by haulers?

    • Can a sufficient quantity of grease be secured to recover costs?

    • Is the PPP moving forward?

  • Further verify key grease co-digestion process assumptions

  • Seek grant funding


Wtd considerations moving forward
WTD Considerations Moving Forward

  • Must be cost-effective for ratepayers

  • Ability to help WTD meet energy targets

  • Need assurances that supply won’t disappear

  • Is this something better done by private sector?

  • Brown grease can create storage and pumping issues

  • Must be O&M cost neutral

  • Ensure trucks don’t create safety & security issues

  • Digester and scrubber capacity is not unlimited


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