Manure Manager

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An oldie but a goodie

September 23, 2009  by Tony Kryzanowski

Dairy owners, Leo and Linda Langerwerf know how it feels to be a lightning rod for the well-funded and star-studded environmental activist crowd in California, but they have no regrets about their decision back in 1982 to be among the first to adopt anaerobic digestion as their primary manure management method.
Dairy owners, Leo and Linda Langerwerf know how it feels to be a lightning rod for the well-funded and star-studded environmental activist crowd in California, but they have no regrets about their decision back in 1982 to be among the first to adopt anaerobic digestion as their primary manure management method.

Solid compost by-product accumulates after processing through the Sweco Vibroscreen separator. Almost half is used as free-stall bedding, while the other half is sold to nurseries and landscapers. Submitted photos

“As a dairy farmer, you have a heck of a lot of crap to deal with and do you need that extra job? Probably not,” says Leo. “But if you are having some environmental or regulatory concerns, it is one way to combat some of that stuff.”

He adds that in any situation where there are a lot of animals being managed in a confined area, “it just doesn’t make any sense why people wouldn’t do something like this. I sell more power than I use, so why wouldn’t anybody else want to do that?”

A new gas bag was installed over the Langerwerf dairy plug flow anaerobic digester in the late 1990s, and that in turn was covered by a greenhouse enclosure.


One published estimate says that the entire methane recovery system at the Langerwerf dairy adds about $68,000 per year to their revenues.

In terms of return on investment, Leo says that it is likely that farms would build a manure collection, anaerobic digestion, and by-product disposal system comparable to the amount of manure that they generate. So a reasonably priced system could be designed depending on the circumstances.

In addition to providing a new income source, installing an anaerobic digester does benefit the environment.

“It makes you handle your manure on a daily basis,” Leo says. “It helps to keep your farm cleaned up of all your manure because you need that manure to put in the digester so that it’s digested down and creates gas. So, to keep that steady flow of gas, you have to take care of it. You have to be a better manager of your manure than you used to be.”

The need for hands-on involvement to properly manage the anaerobic digester is nothing new for dairy farmers.

“Whoever is doing this is going to have animals,” says Leo, “and it is just an extension of the animal. You have to take care of it every day, just like you do the animal every day, seven days a week, and there is no getting around it.”

Methane recovery from manure digestion to generate power is only one income stream. There are also the benefits of using the nutrient-rich liquid by-product for crop fertilizer, and the dry compost by-product for free stall animal bedding. It is also a marketable, weed free and pathogen free compost product that can be sold to landscapers and other dairy operations. The compost is weed free because the seeds germinate in the digester’s high temperature environment, but there is no oxygen. So the seeds die.

Once the methane is extracted and the nutrients broken down into a finer material through the anaerobic digestion process, Langerwerf believes it is a better crop fertilizer because it takes a lot less time for the soil to absorb that fine material versus application of a raw manure slurry. Then, there are the intangibles.

“It helps a great deal in fly control and smell,” says Langerwerf. “In fact, we hardly have flies at all like we used to prior to the digester.”

The Langerwerfs operate an 800-cow dairy on about 130 acres north of Sacramento and were among the first in North America to install a plug flow anaerobic digester for manure disposal. It measures 14 feet deep, 25 feet wide and 125 feet long. Of those early pioneers, the Langerwerf digester is the only one still operating in California. The dairy uses between a quarter and a third of the power it generates for its own operations and the rest is sold under contract to power utility Pacific Gas and Electric (PG&E). A study conducted in 1998 by RCM Digesters indicates that the farm saved $850 in one month alone from the electricity generated from burning the digester biogas.

The Langerwerf milking parlors are all concrete and the raw manure is scraped with a tractor and scraper into a collection tank, where it is mixed with water to achieve the proper consistency of about 14 percent solids and then pumped into a preheat tank.

“You never see it once you get it scraped,” says Leo.

The manure is warmed in the preheat tank with hot water coming off the methane-powered Cat 3306 engine. Then the slurry is pumped into the RCM Digesters plug flow digester where it is retained for 30 days at 97 degrees Fahrenheit. The water used to heat the slurry in the preheat tank is re-circulated to cool the engine so that the radiator fan isn’t running all the time.

As the manure digests, the gas collects in a gas bag and the weed-free slurry by-product discharged from the digester is processed through a Sweco Vibroscreen separator. The solid stream is collected and used as free stall bedding or sold, while the nutrient-rich liquid stream is collected in a lagoon and diluted with fresh water before being used to irrigate 120 acres of cropland. Langerwerf says he uses about 40 percent of the solid compost for bedding and sells the rest, usually without too much trouble.

During irrigation, the lagoon water is pumped at 200 gallons per minute and blended with irrigation water flowing at 5000 gallons per minute.

The biogas is suctioned through an underground pipeline from the gas bag to the 3306 Caterpillar engine. The engine generates about 40 kilowatts per day, and about 30,000 cubic feet per day of biogas is recovered.

Langerwerf has high praise for RCM Digesters as his anaerobic digester supplier.

“Mark Moser, the general manager at RCM, is a brilliant guy,” says Langerwerf. “He can tell you just about anything about a digester, when it’s happening, before it happens and after it happens. He has a track record in the United States and outside the United States. They are the only game in town, in my opinion, no matter where you are.”

RCM Digesters was involved in a study and refurbishment project that essentially dissected and rehabilitated the Langerwerf anaerobic digester in the late 1990s. It provided the company with an opportunity to determine what withstood the test of time over a 16-year period.

What they discovered is that while annual digester maintenance to that point had been estimated at about eight percent of capital cost, the annual digester maintenance costs based on this study was less than one percent.

Another interesting discovery is that the plug flow digester appeared to accumulate only about one percent of the volume of solids that would be expected in an anaerobic lagoon. More specifically, over a 16-year period, about 740 cubic yards of material accumulated in the plug flow digester, versus 85,000 cubic yards that would typically accumulate in a lagoon. In tangible terms, it would take 74 loads of a 10-yard dump truck to remove the solids from a digester versus between 5000 and 8000 truckloads from a lagoon.

“Eventually, the farm with the lagoon will have to manage 5000 to 8000 dump truck loads of sludge that a digester does not accumulate,” says RCM in its project report posted on the U.S. Environmental Protection Agency’s AgSTAR website.

The hypalon gas bag attached to the Langerwerf digester had degraded, largely through exposure to ultraviolet rays, but as a wear item that would need to be replaced over time, it is not a significant cost. There was only minor corrosion of concrete and steel.

Langerwerf believes anaerobic digestion is a viable option for many intensive farm operations – although this is one area where California may not be a forerunner as far as environmental leadership is concerned.

In his view, the “environmentalism gone wild” attitude within California and red tape are actually working against dairy farms in the state from moving in the direction of installing more anaerobic digesters, and some have as many as 6000 cows.

“The small handful of actors and people that have nothing better to do with their time but screw with somebody else’s livelihood are the ones that are swaying the vote because the squeaky wheel gets the grease,” Leo says. “As farmers, we don’t have time to go to every meeting to try to influence people on what’s going on.”

One other legislative wrinkle that ticks Langerwerf off is that he can not profit from marketing greenhouse gas emission credits from his anaerobic digester because it was built before 1999.

“This is BS,” he says, “because my green credits are worth just as much as anyone putting in an anaerobic digester tomorrow. I don’t need to be better than anybody else, but I sure as heck don’t need to be less than somebody else, and that is what they are doing to me.”


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