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.

Pumper:

What impact has the U.S. Environmental Protection Agency 527 regulations had on how the pumping industry handles grease trap waste?

Rubin:

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.

Pumper:

How do grease trap residuals differ from grease trap waste?

Rubin:

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.

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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.

Pumper:

What’s behind the effort to recycle grease trap residuals?

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Rubin:

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.

Pumper:

What is your opinion of grease trap waste as a viable future energy source?

Rubin:

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.

Pumper:

How strong is the market for biogas and biofuels?

Rubin:

I can’t answer that. I do know some people who have done a really good job of marketing. Others still don’t view what they do as part of the local infrastructure. Lyle Estill of Piedmont Biofuels in Pittsboro, N.C., has a large used oil collection business. Dean Brooks of Brooks Contractor in Goldston, N.C., added large-scale composting to his operation and is turning away customers because he’s run out of room. Jim Lanier of Stanley Environmental Solutions in Stanley, N.C. (see a profile story on Stanley Environmental in this issue of Pumper) is solidifying and composting grease trap residuals.

All these people are selling the product. Stormwater utilities use it in bioretention ponds. Duke Energy in North Carolina burns the material in place of coal. Landscapers use it as fertilizer. The market depends on what is available in your area for compost, fuel, or digester gas.

Pumper:

How can pumpers identify these markets?

Rubin:

Look for the opportunities. Successful people are not content to just pump and discharge at a facility or land-apply it. They continue to look for better ways to manage it. For example, North Carolina limits pumpers to 30,000 gallons per acre per year liquid loading on land application sites for grease trap waste. Jim Lanier and other pumpers didn’t like that and looked for a better way. They purchased dewatering boxes, mixed the dewatered material with wood waste or other byproducts, and composted it. By removing the nutrients, they increased the liquid loading on their sites to 200,000 gallons per acre per year.

Pumper:

Why are more wastewater treatment plants rejecting grease trap waste?

Rubin:

First, community and industrial growth has diminished plant capacity. Second, because of the strength of grease trap waste and septage, plants can only co-mingle about 10 percent of it into their waste stream before violating their discharge permit limits. Third — and here’s what many people forget — those limits keep dropping.

When pollution control regulations were established in 1972, the target was secondary treatment with a BOD of 30 mg/L. However, each new permit imposes higher levels of pollutant removals, because the goal is the elimination of pollutant discharge to surface water. The BOD numbers are fairly low now, so the focus has switched to nitrogen and phosphorous levels.

Pumpers can’t operate the way they did 50 years ago and expect to stay in business. For example, they may have to build dewatering facilities to separate the nutrients from the liquid. Lowering the concentration levels opens the door for municipalities to reassess its assimilation into their waste stream.

Pumper:

What side effects, if any, are you seeing from the regulations requiring grease traps to be pumped?

Rubin:

On the positive side, it’s bringing more intensive professional management. The negative side occurs when regulations are based on a length of time rather than a percentage of tank capacity. Tank management frequency should be based on the characteristics of that business or industry, and pumpers can do something about it. If a tank doesn’t need pumping as often as specified, gather the data to prove it, then take it to the permitting agency. If pumpers work with officials in a professional manner, most are willing to switch the tank to a different maintenance cycle.

Pumper:

Is it cost effective for pumpers to add grease trap pumping to their list of services?

Rubin:

It is if they have a place to go with the residual. Again, know your market area. Septage is different from grease trap waste. They’re regulated differently and managed a little bit differently. Loadings for septage are generally higher than loadings for grease trap residual. For example, if I go into the grease trap business, my 10-acre land application field will handle only 50 percent as much liquid load unless I first dewater the material. Pumpers must know the capabilities of their systems before adding or subtracting components.

As energy costs continue to escalate, alternative fuel opportunities will become better and better. Pumpers should look at their market, figure out the opportunities, and seize them.

A. Robert Rubin may be reached at 919/233-8091.

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