Coverage of biosolids and co-digestion supported by Anaergia
Located in Carlsbad the Encina Wastewater Authority (EWA) operates an advanced wastewater treatment facility with an average flow of 20 million gallons per day. Founded in 1961, Encina is a joint powers authority owned by six public agencies who provide wastewater services for approximately 400,000 people.
Long an innovator in the wastewater sector, Encina has focused on resource recovery for several decades and produces beneficial products for their community including Pure Energy (cogen power), PureGreen (pelletized biosolids fertilizer); and Pure Water (recycled water). The focus is so important for the agency they’ve written resource recovery into their mission statement: “EWA provides reliable and fiscally responsible water resource recovery services to the communities of Northwest San Diego County.”
In recent years Encina’s leadership started examining how to implement the co-digestion of grease and food waste at Encina. According to James Kearns, EWA’s Capital Improvements Manager, they decided to take a unique approach to designing the waste receiving facility:
- Form a public-private partnership (3P) with one waste-grease supplier
- Be innovative/unique/first of its kind
- Select a design-build (DB) project model
“We started out with a project charter that clearly outlined the goals of the project. We set a primary goal for this project to be innovative and to be unique – the first of its kind,” said James.
The project was completed and started-up in April 2015. Earlier this year, the Encina Alternative Energy Facility won the Engineering Achievement of the Year Award from CWEA’s San Diego Section.
We recently toured the facility and had a chance to talk co-digestion with Michael F. Steinlicht, General Manager; Octavio Navarette, Operations Manager and James Kearns, Capital Improvements Manager.
What are the project specifications?
Octavio – The Encina energy recovery system receives about 80,000 gallons of FOG (fats, oil and grease) each week from one supplier – Liquid Environment Systems (LES). We screen and grind all incoming material to remove large inorganic debris, then we store and mix the grease in two storage tanks.
Each day we feed the FOG into our digesters at about 12 gallons per minute (gpm). We consume the 80,000 gallons in one week and then clean and flush the system over the weekend. One Monday morning we’re ready for the next week of grease deliveries.
The alternative fuels receiving facility has a high level of automation and is reliable so minimal operations assistance is required when the drivers are offloading. Since we have only one supplier – LES – their drivers are familiar with the facility and we allow them to offload 24 hours a day.
Encina has a 3 MW facility and we’re producing about 1.1 mW with our co-gen engines – a combined heat and power system. We are limited by our regulatory permits for CO2 from our co-gen engines. We produce approx. 70-75% of the energy required to run the treatment plant. The additional biogas produced is used to fuel our biosolids heat dryer dryer when it is running.
Who designed and built the facility?
James – We decided to complete this project as a design-build project. Kennedy/Jenks completed the 30% Design and developed the bridging documents. The Design Build Team selected was HDR and Filanc. The facility was started up on April 10, 2015.
This LES 8-year supply agreement is EWA’s first ever public-private partnership. When we started the project we issued a Request for Qualifications for Alternate Fuels Providers. The LES proposal prevailed. LES pays an annual Capital Contribution for use of the facility and also pays a tipping fee for each gallon of FOG delivered. Communication with LES has been fantastic.
What are the advantages of contracting with just one firm for grease deliveries?
Michael – We issued a Request for Proposals and through this competitive process LES prevailed. We quickly realized they were the premier choice to partner with in this critical program. LES has a strong reputation in the industry and has demonstrated effective and professional operations over the last year. Our Member Agencies are making a significant investment in processing renewable resources and, as such, the firm we chose to partner with continues to deliver and provide value. This arrangement was the best choice for our rate payers.
James – Working with LES really works for us – it is the same drivers each week and they know how to operate the facility and they know their way around the plant.
Octavio – Another advantage of the relationship with LES is if the facility is offline for any reason, we have just one company to notify and work with. They also have a very high standard – their business model is focused on pumping grease traps on a regular preventative schedule rather than a reactive basis. For EWA this means consistency in deliveries and in the type and quality of grease they deliver.
How did you decide on the design for this grease receiving facility?
James – We visited several current grease receiving facilities in California and we learned a lot from those sites.
- We’d need hot water flush for the FOG feed piping to the digesters
- We wanted a user friendly graphical interface to make the unloading process easier
- Screening out inorganics is important
We wanted the project to be user friendly, easy to operate and maintain – operations, equipment and only one grease delivery company.
After a year of operation what are some of the lessons learned?
Michael – Some of the lessons learned include:
- We included room for an automated screening system that will reduce the labor effort of staff (EWA is looking at purchasing and installing this screening system in the near future)
- The truck delivery area will require a concrete pad that will provide for easy cleanup of truck/system leaks and spills
- Installing a permanent steam cleaner installation near the truck delivery area to assist in cleanup activities would be helpful
- Connecting this facility into our plant hot water system for periodic pipe flushing would assist with pipe cleaning
- We will require more effective tank mixing of both the upper and lower portions of the tank
- Even though we live in Southern California with a temperate climate, the FOG receiving tanks will require heat tracing to prevent solidification of product
- We will need to evaluate our digester feed pumps to provide a more effective feed rate for product
- Like all wastewater facilities siloxanes can be troublesome and effective management is required. Siloxanes originate from food, soap, detergents and other consumer products
What’s next for Encina’s Pure Energy program?
Michael – We look to be 100% energy self-sufficient and a reliable net-energy provider for the community – that’s a win for our member agencies and ultimately our rate payers. We’re just scratching the surface of what’s possible with organic waste recycling.
AB1826 (‘Mandatory Organics Recycling’) calls for more food waste to be diverted away from landfills in order to reduce the carbon footprint of solid waste management. This facility has opened the door for us to receive not only fats, oil and grease but liquefied food waste as well.
For Encina we always strive to find that nexus that links environmental stewardship with fiscal responsibility. While there’s a cost for building this facility we are now producing real value for our rate payers by recovering resources, generating electricity and producing soil amendments.
Our mission is to protect public health and the environment, and if we can do that and lower our operating costs, that’s a win-win for our community.
If you’re ever in or near Carlsbad be sure to request a tour of the Encina Wastewater Facility. It is an outstanding facility and well worth the drive or flight!
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