A new venture looks to accelerate co-digestion of food waste as a way to divert organic material from landfills and increase renewable power generation.
Clean-water plants looking to boost biogas and energy production often explore co-digestion — adding food waste or other organic material to their anaerobic digesters.
Now, a Wisconsin company has launched a venture that takes a unique approach to co-digestion, essentially bringing sources of food waste and digester/energy producers together.
Grind2Energy is a business of InSinkErator, a manufacturer of the food waste disposers found under homeowners’ kitchen sinks and in the kitchens of commercial food establishments. The company offers a service in which a grocer or other business uses a commercial disposer to grind up food waste otherwise put in the trash and hauled to a landfill.
Instead, the ground-up material in slurry form is stored in a tank and later pumped out and trucked to a wastewater treatment plant or privately owned, stand-alone digester. Michael Keleman, manager of environmental engineering, marketing and business development, says the offering has a dual benefit in diverting organic waste from landfills while helping clean-water plants generate more biogas and more energy to help offset their operating costs.
Before joining InSinkErator eight years ago, Keleman was in the wastewater treatment profession for nearly 20 years, much of that time in plant superintendent jobs in Indiana. He still holds an Indiana Class 4 (highest) municipal wastewater treatment plant operator license, an Indiana Class C industrial wastewater license, and a Wisconsin Grade 2 wastewater operator license. Keleman talked about Grind2Energy in an interview with Treatment Plant Operator.
TPO: Why is it important to divert food waste and other organic waste from landfills?
Keleman: Organics in landfills result in emissions of the greenhouse gas methane. Landfills do a pretty good job of capturing that methane. The EPA Landfill Methane Outreach Program says about 600 landfills in the U.S. capture methane for energy. But when you put food waste in the garbage, it takes several days before it’s collected. Then it goes to a landfill where it may be weeks before it is covered. So most of the organic material decays before the methane can be captured. If you send that material to the sewer through a food waste disposer, it reaches the treatment plant within a few hours. It settles out in primary treatment and then can be converted to energy and soil amendment in anaerobic digesters.
TPO: Do you see a trend toward more diversion of organic wastes?
Keleman: Yes. There is a mega-trend toward diverting food waste from landfills and incinerators. It started in the European Union where they have a lack of space for landfills. Canada has many mandates focused on keeping organic waste out of landfills. Now states like Massachusetts, Connecticut, Vermont, Rhode Island and California are following suit.
TPO: How do food waste disposers fit into this picture?
Keleman: About 50 percent of food waste comes from residential sources. The other 50 percent comes from commercial, institutional and industrial sources. Massachusetts now mandates installation of at least one disposer in commercial locations serving at least 20 patrons. Philadelphia last December passed a mandate requiring residential disposers in all new construction. This suggests that commercial disposers should be embraced as one opportunity to manage organic waste.
TPO: Why can’t commercial food waste generators just install commercial disposers and send their material into the sewer system?
Keleman: If you are generating 1 ton or more of food waste per week, that’s quite a bit of material. Generally, using a commercial food waste disposer requires the use of up to 7 or 8 gpm of water while grinding to transport that material through the sewer. Grind2Energy uses 1 to 2 gpm to create a slurry that is pumpable and suitable for anaerobic digesters.
TPO: What kinds of establishments tend to generate that volume of food waste?
Keleman: Grocery stores certainly produce more than 1 ton per week. So do sporting venues, hotels, casinos and food courts. Restaurants typically don’t produce that much.
TPO: In basic terms, how does the Grind2Energy service work?
Keleman: We focus on areas where there are landfill mandates, to give those businesses an opportunity to divert material from the landfill. They process the waste in a 10 hp commercial-grade food waste disposer. The slurry is placed in a holding tank and ultimately removed and hauled by a vacuum truck directly to a digester. We contract with the haulers. Instead of selling the system at a capital cost to the customer, we enter a two- to three-year agreement where we charge them a monthly fee for the installation, maintenance, pumping, hauling and tipping fees at the digester, if any.
TPO: Is this cheaper than putting the material in a dump container and hauling it to a landfill?
Keleman: It can be, especially in jurisdictions where landfill tipping fees are $100 to $150 a ton, as in places like Massachusetts.
TPO: Other than to save money, why would a food business sign up for this service?
Keleman: Resource recovery can be a big part of a public relations message. They can tell customers they’re recovering resources by turning their waste into energy and fertilizer. Also, if you’ve ever walked outside a large commercial food enterprise where they have their dump containers, there are always odors, and there are pest issues. In our process, the material is contained in a vessel. The other benefit is labor savings. Instead of carting the material outside, they stand at a table and grind the waste and it’s gone.
TPO: What motivates treatment plants to accept the material?
Keleman: There is another mega-trend, promoted by the Water Environment Federation, to rebrand treatment plants as water resource recovery facilities. Progressive plants see an opportunity to use their digesters to boost biogas production, create energy to offset their costs, and in some cases become energy independent or even net energy positive.
It’s also an opportunity to generate revenue from tipping fees.
TPO: What are the obstacles to getting this material accepted at treatment plants?
Keleman: Almost every treatment wants to have its own evaluation. When we first call on them, they want a lab report. They want to see a sample of the material and have a sit-down discussion. There’s a perception that co-digestion will significantly increase the amount of biosolids they have to manage, so they have to evaluate that as well. They also need a receiving station — a way of blending the material directly into their digesters. And they have to establish a tipping fee for accepting the material.
TPO: Are treatment operators concerned about upsetting their digesters?
Keleman: To operate an anaerobic digester you have to keep the volatile-solids-to-alkalinity ratio in line. Food waste slurry does increase the volatile fatty acids, such as acetic acid, which is the building block for producing methane. If you were to overfeed the digester too quickly, you could go acidic, kill off the methane-generating bacteria and compromise your ability to process biosolids. However, a co-digestion study published a couple of years ago by the Water Environment Research Foundation said that until you get over the 25 percent hydraulic loading rate with outside organic waste, the risk is minimal.
TPO: What effect does accepting your material have on biosolids volume?
Keleman: In the range of 30 percent of the dry solids from food waste could become biosolids. So it’s not a significant incremental amount. In fact, there is some synergy to adding organic waste that has a high carbon-to-nitrogen ratio to sewage sludge in a digester, in that you get improved volatile solids destruction. We’re doing research at Western University to quantify that synergy, to show just how much incremental biosolids really is produced.
TPO: What is the reaction to your material from treatment plants that have accepted it?
Keleman: So far, the treatment plants that are accepting our food waste slurry simply say, ‘We want more of this.’ It has very high volatile solids content, greater than 90 percent, and it’s rapidly biodegradable. The methane potential testing we’ve done in-house shows that the organics are converted to methane in five to 10 days. It doesn’t take the 20- to 30-day detention time that a digester normally requires to process wastewater sludge.
TPO: How extensive is your network of food business customers and digesters?
Keleman: We have nearly 40 installations at commercial food service establishments, mainly supermarkets. That includes nine in the Massachusetts area, several in Cleveland and Columbus, Ohio, and 15 in southeast Wisconsin. Right now, we are delivering slurry to nine digesters. We deliver to the Nine Springs Wastewater Treatment Plant in Madison, Wisconsin, the South Shore Water Reclamation Facility in Milwaukee and the Downers Grove Wastewater Treatment Plant in Illinois. The others are stand-alone digesters.
TPO: What does your team at Grind2Energy consist of?
Keleman: My colleague Casey Furlong is an environmental specialist and worked in solid waste management operating landfills for over 15 years. We have a team of engineers who design our systems. We have a service department that monitors the tank levels and schedules the pickup and hauling. We also have a sales team. I attend trade shows and conferences to stay on top of the latest trends and technology in the wastewater space. I get to communicate with a lot of wonderful wastewater treatment professionals.
TPO: Do you have a concluding message for the operator community?
Keleman: Most people in the United States take the food waste disposer in their kitchen sink for granted. They probably don’t think twice about where that material goes. The idea that they could use their disposers to reduce what they send out to the curb and to the landfill, and help their local treatment plant become more energy independent — that is something I wish more operators would talk about.