The sludge eaters

The technology used to clean up oil spills is proving effective in mopping up sludge from the bottom of hog lagoons.

About 10 years ago, Ronnie “Geno” Kennedy began to wonder whether the same bacteria used to clean up oil spills would eat the sludge from the bottom of hog manure lagoons.

After all, petroleum and lagoon sludge both form under anaerobic bacterial conditions. They also form many of the same chemical compounds — methane gas, hydrogen sulfide gas, alcohol compounds, low-pH organic acids, and highly toxic phenols.

Kennedy was concerned because, in his line of work, helping North Carolina pork producers meet environmental regulations, he was seeing some problems with sludge buildup and a resulting lack of lagoon effluent capacity.

In 1995, he called a company in the Midwest that sold bacteria for oil spill cleanup and proposed his idea.

“They were busy selling huge amounts of their product to companies to clean up these big oil spills and hardly thought I was worth talking to,” he says. “But I told them about the hog industry in North Carolina and how many lagoons were out there. They got excited about the possibilities.”

The company brought a compressor and some diffuser lines to lay on top of the sludge to help stir the lagoon water, Kennedy explains. They also brought many buckets of their product, put it into the old lagoon and lowered the sludge from 5 ft. to 1½ ft. within just a few months.

“They used a lot of product,” he adds.

At that rate, Kennedy knew the biological process would not save much, if any, money above mechanical methods of sludge cleanout. So he began experimenting with lower bacterial rates, longer time frames, and higher rates of diffused air to stir the lagoon water.

Today, Kennedy believes he's arrived at a winning combination of time, bacterial supplementation, air movement and economics. His company, Agriment Services, Inc. (ASI) has 22 systems in operation in his home state of North Carolina.

He says his combination over a period of three to five years will reduce sludge volumes 25% to 75%, and reduce emissions of hydrogen sulfide, among the most offensive odors from lagoons. Kennedy also says lagoons undergoing his treatment will have lower levels of biological oxygen demand (BOD), chemical oxygen demand (COD), volatile fatty acid (VFA), ammonia, total suspended solids and volatile solids concentration, and a higher redox potential.

Cost comparisons

Kennedy offers two cost comparisons. In one, he says conventional stirring and pumping costs from 2-8¢/gal. of actual sludge removed. His biological/air mixture has driven system costs down to ¾-1½¢/gal. of actual sludge removed.

In another comparison, he offers cost estimates from a real lagoon. With a need to remove 44,400 lbs. of sludge, conventional removal would cost $10,384 compared to $3,248 with his process. Breaking it down further, conventional removal costs $233.87/1,000 lbs. vs. $73.15/1,000 lbs. with his process.

Kennedy's price estimate of $10,000 for conventional sludge removal via dredging, or agitating and pumping, may actually be low in North Carolina, says Patrick Fussell, an environmental specialist with one of the state's soil and water conservation districts.

The cost eight or 10 years ago for complete mechanical closure of a lagoon of the size required to serve two finishing buildings was $10,000. Today, the same size lagoon could cost $40,000 to $60,000 to close.

Fussell is careful not to endorse Kennedy's system because of the nature of his job, but says he's seen some positive results. “I can't endorse it, but I can't say anything bad about it, either,” he says. “I hope it works out because it will be a lot cheaper for the farmers.”

Several of Kennedy's customers see this process as a pre-emptive measure, a way to spend a little money upfront to avoid spending a large amount later.

“My sludge wasn't a major problem when I started, and I'm using the system more as a preventive maintenance program,” says Bud Rivenbark, a Rose Hill, NC, contract hog producer.

Rivenbark says he had 2.5 ft. of sludge in his lagoon when he started with Kennedy's biological program more than two years ago. Sludge levels have dropped 8-10 in., he says.

“I've seen some pretty positive results from it and it's certainly been worth the money,” he adds.

He plans to add the biological system to his other lagoon this year.

How it Works

Kennedy's system begins with the addition of compressor-driven air diffusers lying on or in the sludge layer of the lagoon. It oxidizes the hydrogen sulfide and turns it into sulfate. That initial process helps to detoxify the lagoon and prepare it for organic matter breakdown.

Next, he adds a proprietary blend of facultative bacteria to speed the breakdown of organic matter. Depending on the desired rate of sludge reduction, the lagoon operator will continue to add some amount of maintenance bacteria on a monthly basis.

The amount of air going into the lagoon is small — typically only 2-3 cu. ft./min. per compressor. That will be divided among two to four diffusers. “A little bit of air can move a lot of water,” Kennedy says.

Some caveats

The difficulty for those who need to reduce sludge accumulation seems to be in determining who has a viable method for reducing it. Some experts say even conventional methods of removal aren't always completely successful.

John Classen, North Carolina State University agricultural engineer, warns that many companies sell bacterial organisms. Be cautious, he says, with those requiring frequent application. Too often, this implies working against the natural system of bacteria already in place.

Kennedy offers five ideas about shopping for bioremedial lagoon sludge processes:

1. Note the bacillus count in billions/gram for the price.

2. Note the type of bacillus in billions/gram.

3. Seek products with a high concentration of anaerobic and/or facultative bacteria because you're treating an environment primarily anaerobic in nature.

4. If you use an enzyme product and your lagoon is already toxic to the naturally occurring bacteria, you're providing food for dead organisms — not an effective method of managing sludge.

5. Be wary of products you just pour into lagoons for quick results. Too often, the reason for lagoon sludge problems is lack of naturally occurring bacteria. Something is likely damaging the normal, anaerobic function, and that must be eliminated before spending money on more bacteria.

The bottom line would seem to be that any process you use should not hinder or work against the anaerobic lagoon system. It should improve it, Kennedy says.