There are a number of possible reasons to put digester gas to work — to further sustainability goals, to reduce harmful greenhouse gas emissions, to conserve energy and save money.

The Victor Valley Wastewater Reclamation Authority in Victorville, Calif., goes a step deeper. To general manager Logan Olds and his team, it’s about getting the most from the resources customers have paid for with their rate dollars.

To that end, the authority has entered a public-private partnership with resource recovery company Anaergia on a project to become energy independent by producing and using more biogas, ultimately saving an estimated $9 million over a 20-year term.

The initiative involves retrofitting old digesters, allowing co-digestion of food waste, fats, oils, grease and other organic materials with biosolids. That will yield enough biogas to fuel generators that can fulfill all power needs at the 18 mgd (design) activated sludge tertiary wastewater treatment plant.

Construction is to be complete by February, according to Olds, who heads an independent entity governed equally by leaders from member agencies that include the communities of Apple Valley, Hesperia, Victorville, Oro Grande and Spring Valley Lake.

Financing is structured so that the authority incurs no up-front cost. The project also may enable the authority to open new revenue streams by charging companies to drop off waste and by selling excess energy to the utility grid. Olds and Arun Sharma, Anaergia president, talked about the project in an interview with Treatment Plant Operator.

TPO: What is the Victor Valley Authority doing with biogas now?

Olds: We use about 70 percent of the biogas we produce to fuel three Waukesha 450 hp engines driving Turblex blowers, producing 9,200 scfm airflow to provide oxygen for our aeration basins. We capture the engines’ waste heat to keep our digesters heated. The issue we have is that we’re still flaring gas, and that’s money.

TPO: What was the origin of the goal to make the plant energy self-sufficient?

Olds: In 2008 we completed an expansion to 18 mgd and built two new million-gallon anaerobic digesters that replaced three 300,000-gallon units. The initial plan was to decommission the old digesters, but I considered that a pretty significant waste of resources, given that they are paid for and still work fine. Our project with Anaergia initially will repurpose one of the old digesters for our food-waste-to-energy program. We could potentially use the other two for that as well.

TPO: Does your agency have any previous experience with co-digestion?

Olds: We did a full-scale test of food waste digestion with Waste Management. We didn’t want to have to reach out and manage dozens of waste haulers and whatever waste they might bring. In a public-private partnership, you want to use each party’s strengths to mutual benefit. Waste Management had access to every doorstep and every business for collecting material, while we had the ability to process it and produce energy from it.

The project ended a couple of years ago, and it was a great learning experience. We found where the issues were with our system and how we could improve the efficiency of it. What we wanted was a slurry that we could inject into our digestion process without having to process it. Anaergia will bring that in as part of our contract with them.

TPO: How will you change the plant’s cogeneration system to handle the additional gas production?

Olds: We will decommission our existing biogas engines so that all the biogas we produce will be burned in two 800 kW engine-generators [Caterpillar], which will provide electricity for a high-speed turbo blower [Piller TSC Blower Corp.].

TPO: As a matter of philosophy, why are you doing all this?

Olds: I am relatively obsessive about performance efficiency. I hate to see waste, and when I saw that methane flare going, I knew we could do a better job with the gas. We may be a public agency, but we need to think just like we’re a business. The bottom line is how do we provide the best value to our customers?

We do that by being proactive rather than reactive and by identifying what resources we can use to reduce costs and improve efficiency. Every time we have to build something or meet a new regulation, we don’t want to hold our hand out to our ratepayers and say, “Now we’ve got to do this.” What we should do is operate as efficiently as possible, so that when we do ask to increase rates, we can fully justify it.

TPO: Will this project have benefits beyond increased energy production?

Olds: Yes. Now that we do nitrification-denitrification for nutrient removal, we need to be smarter about how we apply oxygen to our process. By having high-speed turbo blowers with variable-frequency drives, our staff can dial in a specific point to meet our oxygen requirements at any given time — there’s no waste.

TPO: What is the nature of material that will be co-digested? Where will it come from? How will it be collected, processed and fed to the digesters?

Sharma: There are two basic classes of material. One is relatively clean, like fats, oils and grease, which do not need much processing before they are put into the digester. The other is source-separated food waste, such as from grocery stores and restaurants. These would require a certain amount of processing because they contain grit and a certain amount of plastics. We have technology called the Anaergia Dynamic Cyclone that extracts those items from the material.

TPO: What sort of volumes are you expecting for the co-digested materials?

Sharma: The volume depends on the type of material available. For example, FOG is very high-strength material and will produce a lot more energy than food waste, which is rich in carbohydrates.

TPO: What is the timetable for getting this system up and running?

Sharma: There are two separate projects. The power generation project is separate from the biogas enhancement project. Right now, they are proceeding concurrently, and both should be up and running no later than the end of 2014.

TPO: At what point do you expect to achieve energy self-sufficiency or become a net energy producer?

Olds: The first goal is to meet all our on-site energy needs, and the second is to export energy. We have a ready customer, because the Victorville Municipal Utility Services [VMUS] power plant is directly next door to our facility.

We’re now doing a survey with a third-party firm to determine how much FOG is being generated in our community, so we can see if that is enough to inject into our system and get the additional energy we need. Right now, we need about 20 to 30 percent more biogas to fulfill all our energy needs — that is to produce about 1.4 to 1.5 MW. It’s my hope that by as early as June 2014, we could be energy-neutral. I expect us to be in a position to export power to VMUS within six to eight months after we complete our project with Anaergia. Part of the plan is to leave a slot for a third engine-generator.

TPO: How does your facility manage biosolids from the digestion process?

Olds: We produce a Class A exceptional quality product that is used in cement kilns and on land application sites. Because we get so much sunlight here, the material is completely air-dried. We put it in drying beds that cover many acres and get our solids content up to more than 80 percent. We do not rely on mechanical dewatering.

TPO: How did Victor Valley Authority and Anaergia form this partnership? 

Olds: On projects like this, you’re dealing with a commodity, and the margins are extremely important. We were fortunate to obtain a free energy audit through a U.S. EPA Region 9 program in which University of San Diego engineering students did the evaluation.

The other critical element was to write a request for proposal [RFP] that would get us exactly what we needed for our facility. A specific requirement we put in the RFP was that the partner we selected must be able to self-fund the project. They could not submit a proposal that would require us to sell bonds at municipal bond rates, as that would undermine the economics of the project. Anaergia met that requirement.

TPO: How would you quantify the economic benefits of this initiative?

Olds: It gives us a reliable long-term energy cost, rather than wondering what Southern California Edison is going to charge us year to year. We’re now paying 11.7 cents per kWh for electricity. We calculated that after all our generating costs are included, we will save $50,000 to $150,000 in the first year.

We have a fixed-price contract with Anaergia, so that every year Edison increases its rates, we will experience additional savings. Over the 20-year term of the contract, we expect to save about $9 million, not counting savings on natural gas. That translates to cost savings to our member agencies and customers.

As public agencies, we’re all cash-strapped, yet we continue to face new regulatory requirements that come with additional costs. We need to be smarter about how we leverage the resources we have.