Wastewater Treatment Plants Dewater Dairy Manure



John Vrieze's on-farm wastewater treatment system starts with manure (left), removes the suspended solids to create low-P "tea water" (center), then filters out dissolved solids to yield clear water (right).

Graphic courtesy of Integrated Separation Systems


Wastewater Treatment Plants Dewater Dairy Manure

by Steve Werblow

Nearly half the weight of dairy manure is water. It's bulky, it's heavy and it's inconvenient to handle. Rising fuel costs make hauling that water component prohibitively expensive, and environmental protection measures push the cost of lagoons toward the half-million-dollar mark or higher.

And for dairy producers like John Vrieze of Baldwin, Wis., the problem grows with every rain. “Colleagues of mine in drier areas of the country can use the dry air to largely evaporate some of these problems,” he notes. “But when you live in a humid climate, the amount of water in your manure actually increases over time.” With 31.5 inches of annual precip, Vrieze says, accumulation easily exceeds evaporation – to the tune of 3 million extra gallons of extra water in his lagoon each year.

“It's getting to the point where it's cost-effective to dewater,” he says. “If we can dewater manure and further concentrate it, we can move it far greater distances, and we could double our herd without having to expand our lagoon.”

Vrieze's Emerald Dairy has been one of three pilot sites for an on-farm wastewater treatment plant that separates solids to an unprecedented level. Manure from the site's 1,600 cows feeds the system at 35 gallons per minute. At the end of the line, all suspended solids have been removed and 35 to 40 percent by weight has been filtered down into clear water, cleaner than treated municipal wastewater. Just as important, each of the other streams from his four-stage water treatment system can be allocated for a specific use, allowing him to target it to fields based on nutrient needs, hauling distance or irrigation system.

Industrial Technology
There are a variety of approaches to dewatering manure, from adding polymers to pressing out water with belts or screw presses. Vrieze's system uses filtration technology that would look familiar to workers in a municipal wastewater treatment facility, a food processing plant or a gas drilling operation. Integrated Separation Solutions (ISS) of Madison, Wis., the company that built the system, supplies water treatment systems to those industries and others. “We've had reverse osmosis and ultra-filtration for 30 years,” says Josh Vrieze, ISS vice president-agriculture and son of John Vrieze. “This isn't new technology, but it's new to the dairy industry.”

The industrial approach of ISS's NuWay system yields much more thoroughly cleansed water than the simpler solids separators that are becoming more common on the nation's dairies, says Josh. “Instead of trying to take one big cut as it goes from manure to water, we're taking three or four steps,” he says. Those steps include:

• A traditional, drum-type separator that pulls out fiber and other large solids;

• NuSpin, which uses centrifugal forces to remove sand, grit and small suspended solids (“Now we're down to pretty thin manure and solids with the consistency of clay,” says Josh.);

• An ultra-filtration membrane that removes the smallest suspended solids, creating a thick manure stream and a stream of “tea water” that contains only dissolved solids;

• A reverse-osmosis filtration system like those used in drinking water plants, which contains membranes that strain on the molecular level – water molecules will fit through, but larger molecules, like ammonia , can't.
Dividing Fractions
Each of the fractions created during the treatment process has its own value, says Josh.

“By the time we're at tea water, we've removed 90 percent of the phosphorous and about half of the nitrogen,” he says, explaining that most phosphorous resides in the manure solids, while nitrogen is about evenly split between solid and dissolved forms. “Because there are no suspended solids in the tea water, it won't plug nozzles, so it's great for irrigating. And the field you apply it on will probably cap out on nitrogen way before it caps out on phosphorous.

“The concentrated manure liquid – the other product that comes out of the ultra-filtration stage – has double the phosphorous of raw manure and 50 percent more nitrogen,” he adds. “If you've got fields you've got to haul manure to by truck, this is the manure to put in those trucks. You want to bring the highest nutrient concentration to those fields so you don't have as much volume to move.”

The large solids isolated by the separator in the first stage can be composted for bedding. The clay-like fraction – about 2 percent of the total manure by weight – is still something of a mystery. John Vrieze is working with researchers from the University of Minnesota to see how dry the solids would need to be to economically burn them to produce energy. He is also exploring ways to winnow it down further. “In theory, you could take one-third to one-half of the phosphorous that your farm produces in a day and haul it off in a 50-gallon drum,” he says. “That might be a great way to get rid of your phosphorus.”
Keeping it Simple
Beyond the technical challenges of dewatering manure is the logistical challenge of adding a new process to an already busy operation. Installing a three- or four-stage system involves signing a long-term maintenance and operation contract with ISS.

“I'm not trying to turn a dairyman into a wastewater treatment operator,” says Josh, who monitors the systems remotely via Internet links with key components. “We log onto each dairy every morning. We'll often see a problem before they do, and we can call them to let them know they need to check a particular valve or push a reset button. The system is actually smart enough to turn something off if there's a problem and email us. The dairyman just needs to be comfortable around the equipment, be able to check some valves and pumps, and be able to tell us on the phone what they see.”
Penciling Out Costs
Josh Vrieze says a four-stage system could run between $500,000 and $1 million, depending on the size of the dairy and existing infrastructure such as buildings and access to three-phase power.

That's a hefty price tag, but John Vrieze points out that it may be the most economical way for him to expand his operation. “For me to double my herd to 3,200 cows, I'd have to spend $500,000 to $600,000 on my next lagoon,” he says. “I believe you could run this system for less than that, and I'd rather put my capital into dewatering than into another lagoon.

“Right now, we distribute manure within two miles of the dairy,” he adds. “If we double the size of our herd, that circle gets out to five miles. It gets pretty cost-prohibitive to move raw manure five miles.”

The big hurdle now, says John, is securing a Wisconsin Pollutant Discharge Elimination System (WPDES) permit to discharge the clear, fourth-stage water into a local creek like municipal wastewater treatment plants do. Regulators are puzzling over how to write the permit, he says, because although the clear water is actually cleaner than treated municipal wastewater, confined animal feeding operations (CAFOs) are required to be zero-discharge facilities.

John Vrieze is confident that the regulatory hurdles will be addressed and dairy manure management will enter a new phase. “We don't store manure coming out of cities,” he points out. “We treat it and discharge it every day. But in the farm, we still handle manure the way my grandfather did. In any humid climate, dewatering our manure makes a lot of sense.”
The four-stage wastewater treatment plant at Emerald Dairy yields five distinct fractions by the end of the process. Here's how they measure up:

Product % of Total by Weight Use
Fiber/large Solids 3% Composted Bedding
Clay-type solids (high- phosphorous 2% Land Application
Concentrated Manure Liquid (high-P, high-N) 20% Land application through liquid systems
"Tea Water" 35% Irrigation
Clear Water 40% Permits pending for discharge

Reverse-osmosis membranes in these pipes separate molecules by size. Water molecules can fit; ammonia and most other large contaminants can't. This equipment is commonly used in drinking water treatment plants.

Photo courtesy of Integrated Separation Systems

A Systems Approach

Dewatering manure and managing the resulting fractions requires a bit of planning, notes Josh Vrieze, vice president-agriculture at Integrated Separation Solutions (ISS) in Madison, Wis.

Being able to discharge the water will require a pollution discharge elimination system permit from the state environmental agency. The challenge is that although municipal wastewater treatment plants routinely apply for those types of permits, permission for discharge from a confined animal feeding operation (CAFO) is unprecedented. Emerald Dairy in Wisconsin, a pilot site for ISS, has entered the process and hopes to receive a permit soon.

Other components of the process, both liquid and solid, are considered manure by regulators, he notes, and must be stored according to state and federal regulations.

When it comes to applying the by-products to fields, says Vrieze, “we'll work with the farm's crop consultant to make sure that the nutrients you're partitioning are going in the right directions and that the applications fit into your nutrient management plan.”

Ultra-filtration uses super-fine membranes to remove suspended particles - which contain nearly all of the P and about half of the N in manure - and creates "tea water" that dairy producers may apply through irrigation systems.

Photo courtesy of Integrated Separation Systems

Hope for Hogs?

The NuWay multi-stage wastewater treatment system by Integrated Separation Solutions of Madison, Wis., is geared toward dairy manure, notes Josh Vrieze, the company's vice president-agriculture. Further study will be required before the company can determine whether the system will be as efficient for managing hog manure. Differences in the percentage of solids and the size of the particles can impact the efficiency of the system, he says. Stay tuned.

About the Writer: Steve Werblow is a freelance agriculture writer based in Ashland, Ore.