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)  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  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  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 5 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?  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 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 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  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 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?  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?  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 Cost estimates prepared for facility to manage 15, ,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  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  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