Pumpers are urged to look for creative ways to unlock the potential of what has been a challenging byproduct of the liquid waste industry
How do pumpers dispose of grease trap waste when municipal wastewater treatment plants accept fewer gallons — if they accept them at all — and counties ban land application?
A growing number of pioneers are recycling the grease into various products for a diverse market. Some even turn away customers anxious to get rid of it because their facilities can’t handle the demand.
To understand the best uses for grease trap residuals now and in the future, Pumper talked to A. Robert Rubin, Ph.D., senior scientist at the environmental engineering firm of McKim & Creed Consulting in Cary, N.C. Rubin, a former professor in the Biological and Agricultural Engineering Department at North Carolina State University, has been involved in recovering grease trap residuals for beneficial use since the mid-1970s.
What impact has the U.S. Environmental Protection Agency 527 regulations had on how the pumping industry handles grease trap waste?
They have provided standards for reporting and site monitoring. In essence, the regulations have professionalized the industry by requiring a paper trail of gallons pumped, gallons discharged, and where they were discharged. If regulators are going to accept what pumpers do as a permanent part of infrastructure, then the whole service industry must be professional.
Professionals are educated, licensed, certified, and regulations are making it happen. Many states or associations have, or are developing, educational programs. For example, (the National Association of Wastewater Transporters Inc.) has its Waste Treatment Symposium and the North Carolina Division of Waste Management provides training for every individual involved in pumping and land applying materials.
How do grease trap residuals differ from grease trap waste?
If a material has no inherent value, it’s waste. I will argue that the material we’re discussing has inherent value. People are converting grease trap residuals into fuel or land applying the material, taking advantage of its organic compounds to grow crops.
The challenge we face is recovering the beneficial value in all residuals, not just from grease traps. Recovering the energy in residuals is another huge challenge. Most people are somewhat familiar with biofuels, but we’re also dewatering residuals, composting the solids, and selling them as fertilizer. The fat, oil, and grease content of grease trap residuals is energy, the same energy that feeds the bacteria that make compost. It’s used on golf courses, athletic fields, Department of Transportation median strips, and is perfectly safe for residential lawns, gardens, and flowerbeds.
What’s behind the effort to recycle grease trap residuals?
We’ve always known what to do with the material: land application, digestion, or compost. Within the last 15 or 20 years, however, the focus has switched to managing it. Management is the driving force and its main component is energy production. For example, biogas is a gas produced through digestion (fermentation) using anaerobic microorganisms that live on carbon dioxide and hydrogen and give off methane. Biodiesel or biofuel is produced through some chemical treatment of the liquid stream.
What is your opinion of grease trap waste as a viable future energy source?
I think it’s a great source of energy. When crude oil is consistently $80 or more a barrel, then all kinds of alternative energy become viable. The U.S. government has subsidized the oil industry for so long that the private sector hasn’t thought about other energy sources: anaerobic digestion, biofuel and FOG-to-fuel. In FOG-to-fuel, power plants burn the dewatered, solidified material as a substitute for coal or wood. One pound of dewatered material has 7, 000 to 10, 000 Btus, which is equivalent to 2 to 2.9 kilowatt hours. As a comparison, a pound of wood has about 6, 500 Btu (1.9 KWh) and coal about 12, 000 Btu (3.5 KWh).
Digesters are sealed, heated containers that consume organic materials to produce biogas, usually hydrogen or ammonia, which is burned to power turbines. Some municipal digesters are using biogas in fuel cells, essentially large batteries, to drive the turbines. Fuel cell technology has tremendous potential, but it’s a little premature right now.
A pumper with a digester could heat his shop or generate enough electricity to sell the excess power back to the grid. Utilities are required to accept electricity generated through sustainable sources.
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