May 17, 2011 | General

Tapping Digesters, Composting To Manage Manure And Food Waste

BioCycle May 2011, Vol. 52, No. 5, p. 28
Operating in a nutrient-sensitive watershed, no-till farming, anaerobic digestion and composting combine to make Oregon Dairy and its various enterprises a 21st century sustainable farm.
Dan Sullivan

George Hurst and his family have been leaders in demonstrating environmental stewardship in their Lancaster County, Pennsylvania dairy operation for more than 50 years. The Hursts installed an anaerobic digester in 1985, one of the early adopters of this technology for managing manure and generating renewable energy. Last fall, they partnered with Terra Gro, Inc. of Peach Bottom, Pennsylvania to install a manure and food waste composting facility. A strong impetus behind the move into composting was nutrient management. Oregon Dairy is located in the Chesapeake Bay watershed, which has been badly polluted by nutrient runoff from farms and urban and suburban development.
When the dairy switched to no-till farming to reduce soil erosion and nutrient runoff, it was left with a manure management challenge as it couldn’t easily incorporate the manure land applied on the fields. Nor did the farm need all of the nutrients. Composting was a logical solution to both manage the manure from the dry cow barn and export the nutrients in the form of compost for turf and landscaping applications. About 60 percent of the funds to build and equip the composting site came from public and private sector grants, including Chesapeake Bay watershed protection organizations.
On the renewable energy side of the picture, Oregon Dairy just expanded its anaerobic digestion capacity by adding a new unit. The expansion will make it possible to grow the dairy herd and generate more electricity to power farm operations and sell to the grid. The digesters also assist in managing odors, especially given the somewhat urbanized location of the dairy.
No-till farming, anaerobic digestion and composting combine to make Oregon Dairy and its various enterprises a 21st century sustainable farm. This article is divided into two parts – the anaerobic digestion operations and the composting facility.

When George Hurst initially installed an anaerobic digester 26 years ago, Oregon Dairy was home to about 250 cows. It now hovers around 400 milking cows and 500 young stock with plans to eventually expand to 600 milking cows. As the initial digester reached capacity, some of the manure was being sent straight back to the lagoon. Recently with funds made available from the American Recovery and Reinvestment Act (ARRA), Oregon Dairy added a second digester to accommodate current operations and projected growth. The two digesters combined will accommodate expansion targets and offer an additional 20 percent capacity for food waste to be taken in to boost biogas production and generate added income through tipping fees.
BioCycle visited Oregon Dairy in Manheim Township in early December 2010 as part of a daylong anaerobic digester (AD) workshop cosponsored by Penn State Cooperative Extension and the U.S. EPA’s AgSTAR program, just as the first phase of the new project was nearing completion. We caught up with Hurst for an update this spring, shortly after a manure separator had been added to the system and the farm had begun to take in food waste.
“The concept has basically stayed the same technology wise,” Hurst says, referencing more than a quarter century of experience with on-farm AD technology. “We’ve learned how to utilize the manure more efficiently with more frequent feeding and consistent heat – more consistency in the mix and also temperature leads to better methane production.”
What has changed significantly, he says, is the economic landscape, including increased government incentives for green power and on-farm nutrient management. “When we built the first digester in 1985, the only thing we had was a 10 percent tax credit,” Hurst recalls. “But the cost of installation was a lot less. We were able to pay that off even though we basically funded it all ourselves. Now the cost of construction is more than 10 times what it was – and electricity hasn’t gone up that much in these 20-plus years.”
Oregon Dairy currently utilizes all the electricity it produces through a virtual net metering arrangement that allows it to power all farm operations, two homes and a small portion of power utilized by its retail shop and restaurant under an arrangement it has had with Pennsylvania Power & Light Co (PPL) since 1995. Prior to that arrangement, the dairy sold excess power back to the utility. Over that timeframe, the farm also switched from a single-phase to a three-phase system, which is more efficient as it utilizes less conductor material to transmit power at the same voltage but which classified the entire operation as commercial rather than residential. This means Hurst pays a slightly higher rate for any electricity he purchases from PPL. “Right now we’re at a little over 13 cents a kilowatt,” he says.
For the first time in decades, Hurst says the economics are changing to favor producers who sell back to the utility. “Electricity prices did jump this past year,” he says. “I’m not sure where it’s going to level off. It went from nine or 10 cents a kilowatt to 11 or 12 cents this year, and it looks like it’s going to go up still more.” At some point, Hurst says, Oregon Dairy may be able to sell off carbon credits – as those markets develop – to industries that need them as well as renewable energy credits to other states needing to bolster their renewable energy portfolios by certain target dates.
Friendly regulations and reasonably cooperative utilities have combined to make the Keystone State third in the nation – behind Wisconsin and New York – in terms of the number of on-farm AD projects. Another plus for Hurst was the local pool of vendors and subcontractors from which to draw, including Martin Machinery with offices in Ephrata, Penn Jersey Products in New Holland (the local vendor of the new aboveground Slurrystore digester tank manufactured by Kansas City-based CST Storage, Inc.), electrical contractor C.M. High Inc. in Myerstown and Triple H Construction in Lititz, all within close enough distance to be considered neighbors. Another key partner is Stan Weeks, PhD, an agricultural engineering consultant in New York State and a veteran of on-farm anaerobic digester technology.

Hurst explains that the underground tanks installed for the first plug-flow digester more than 25 years ago are still being utilized along with the new aboveground tank. Tying the systems together meant that the project could utilize the existing tanks and increase capacity with the new tank without having to excavate new pits.
As with the old system, liquid manure is scraped from the free-stall barn and fed into a mixing tank. The only real difference is the addition of food waste, and since the cows in the free stall barn are now bedded on digested solids there is no longer any sawdust in the mix. “As food waste is mixed in, we pump it into the Slurrystore, and from there it’s pumped through a heat exchanger,” explains Hurst. The mixture then goes back into the aboveground tank and is kept in suspension through agitation every four hours. “As the manure heats up it immediately begins breaking down,” he adds.
The new digester is designed to handle 10 inches of water column, explains Weeks. “We’re talking pretty low pressure, but that’s what the silo will handle. There’s a relief valve at the top that will open up. It is set to 9 psi. If that doesn’t open up there’s an overflow with a trap in it once the pressure gets to 10. So the silo is protected in two different ways.” The silo tank has a conical bottom with a drain line that goes to the bottom with a valve outside, so periodically it can be drained out of the bottom for cleaning purposes.
Hurst says that Oregon Dairy is working toward 21 days total retention time in the digester system. “The digester is fed continuously every hour or two,” he explains. “The gas is pumped off the top of the Slurrystore and off the top of the older digester tanks into the engine generator set. We have a heat exchanger and try to utilize all the heat we can off this engine. Running 24/7 there’s a lot of BTUs that can be utilized. So what we don’t use for the manure, we use to heat the house and have the heat pipes going over to the barn to heat hot water for the milking facility.”

In order to scrub highly corrosive hydrogen sulfide (H2S) from the gas before feeding it to the 120 kW Mann genset, Oregon Dairy is utilizing new Energy Cube technology designed by Martin Machinery. The Energy Cube scrubs gas via a chemical process rather than through a biological process that requires air injection and colonization of bacteria. The system is designed to use effluent from separated manure solids, but when it was first installed at Oregon Dairy, it was using a water-based solution. “Over the past few weeks we’ve switched over to the manure separator and are using the effluent to scrub the gas,” says Hurst. “This Energy Cube is still a work in progress and a new concept. In terms of performance, the gas is being cleaned considerably better than with water – it’s done a super job of doing that. But with about 3 percent solids remaining in effluent, we’re having some trouble with the pumps as the solids kind of settle out in the scrubber.”
The Energy Cube has two chambers. In chamber one, the effluent is oxygenated with ambient air pumped through it. The oxygen is dissolved into the effluent and the remainder is vented to the atmosphere. The oxygen-saturated effluent is then transferred into the second chamber, where biogas is pumped through it. The H2S in the biogas reacts with the dissolved oxygen in the effluent and is oxidized to elemental sulfur. The product of this chemical reaction is suspended sulfur solid, which is flushed to the lagoon in the effluent. “The system is continuously regenerative, as effluent is drawn into the scrubber from the lagoon or separators and discharged back to the lagoon for eventual spreading on the fields,” explains Jere Martin of Martin Machinery. All of the gas is utilized by the genset immediately after it is scrubbed.

The combined digester system is fed from the manure produced by 400 cows in the free-stall facility. With the manure separator now operating, Hurst can bed all 400 cows on the digested solids at a projected savings of $20,000 to $25,000 annually (previously the cows were bedded on wood shavings). As inventory increases, Oregon Dairy may look to sell some of the digested solids to neighboring dairies. “We’re just starting, so we’re not sure how much more we’ll have that we can sell,” says Hurst, adding that some surplus is currently being bagged and sold via the farm’s retail store at $26 a cubic yard for use as landscape mulch and as a soil amendment for vegetable gardens.
Also by spring, the farm had begun to take in food processing waste – wash water from a molasses processor and Jello powder from nearby Kraft Foods. By adding just 5 percent food waste, methane production jumped 15 to 20 percent. While there’s still plenty of room in the combined system for more food waste, says Hurst, the motor was already approaching capacity before the new material was added. “We’re producing more kilowatts than anticipated and were almost maxed out without the food waste,” Hurst explains. “Our genset is designed for 120 kW. We will be able to go to 150 kW with this engine by making a few changes, and we will probably bring in more food waste as we bring in more cows.” If need be, he notes, a second genset will be added.
The tipping fee for the wash water is around $400 per 6,000-gallon trailer load and the dry Jello powder – which Hurst says works great in the digester but is difficult to handle – generates around the same per equivalent volume. “[Adding food waste] has had no effect on retention time that we can see,” he says. “But it’s only been a couple types over a couple months, so it might be a little premature to say for sure.”
Besides providing heat and power and helping the farm to better manage its nutrients, anaerobic digestion technology has also helped Oregon Dairy to be a good neighbor. “When the manure goes through the methane digester it takes a lot of the odor out, and we’re in an urban area,” says Hurst.

A new composting facility, Oregon Dairy Organics, opened last fall, adding another business to an enterprise that includes a dairy, restaurant and retail shop. It represents a collaboration between Oregon Dairy, technical partner and commercial composter Terra-Gro, Inc., of Peach Bottom, Pennsylvania, the Environmental Defense Fund (which oversaw development of the $1.5 million project), Chesapeake Bay Funders Network (CBFN), the nonprofit Chesapeake Bay Foundation and TeamAg, Inc., an agricultural consulting firm. These partners believe that manure composting managed well can help mitigate the nutrient runoff that plagues the Chesapeake Bay watershed and create a high-value landscape product.
“The compost facility is located on Oregon Dairy’s farm,” says Loren Marten, Terra-Gro’s general manager. “They own the site and all improvements to it. We formed an operating agreement with them where we are the day-to-day managers and we also do the marketing of the end product.” Funding for the project was comprised 60 percent of public grant and private foundation funds with the remaining 40 percent shared between Oregon Dairy and Terra-Gro. Funders included CBFN (a consortium of private grant funding foundations), the National Fish and Wildlife Foundation (operating through the Chesapeake Bay Foundation), the Pennsylvania Department of Environmental Projection (which awarded a composting infrastructure grant) and Pennvest. “The Pennvest funds are federal dollars coming directly to Oregon Dairy through the Chesapeake Bay Foundation related to manure management practices,” says Martin.
The 5-acre composting facility sits atop a hill overlooking the 850-acre Oregon Dairy farm, which also houses the anaerobic digestion facility just described. Pen-pack manure from the dairy operation’s dry cows is composted along with institutional food waste. “Farmers are under a lot of pressure right now with nutrient management,” says Martin. “We’ve been working with another farm in the south of the county and had the opportunity to do the same thing here with Oregon Dairy.”
Since Oregon Dairy, a longtime exemplar of sustainable farming practices, has transitioned to no-till farming, the bedded pack manure has become problematic, Martin explains. “They really don’t need all the nutrients in it, and it’s difficult to spread and run their no-till planters through that manure on the surface. For the most part we can take the manure from their barn and pretty much compost it as is.” But many times the manure is wetter than what is optimum for composting, so Terra-Gro mixes in amendments such as bedding from horse farms, sawdust or shavings and leaves from municipalities – and some bulking agent – so that the manure stacks better, facilitating composting. Carbon is already included in the bed pack manure in the form of corn fodder, sawdust, shavings, etc.
Food waste composting has become a growing part of the picture, he adds. “Franklin and Marshall College in Lancaster has gotten on board, as has the Lancaster County Convention Center. A few restaurants have started and a couple of retirement villages are getting pretty active with collecting all their food waste. We’re bringing that here and mixing it with the manure on the storage pad. It adds a lot of good microbial activity – some diversity in the feedstock. It really helps make a better compost and also provides a great opportunity to work with the community on organics recycling.” The addition of food waste also seems to help the manure break down, he notes.

Windrows are initially formed using a 35-yard box sitting atop a webbed floor mounted to the back of a tri-axle. “We load that truck with the right mixture of horse manure and dairy manure mixed with food waste so that it’s already somewhat premixed in the right ratio and then just back it into the building and walk it off in rows,” explains Martin. “The windrow turner really shapes the row, mixing everything together thoroughly.” Windrows are turned three times a week for about eight weeks. Temperatures are monitored to ensure the pathogen kill requirements are being met. From there, material is moved to a finished compost storage building where the compost cures.
Despite much tweaking and retrofitting, a conventional commercially available compost turner was not able to get the necessary air exchange. “So we started from scratch, worked with Pendu Manufacturing in nearby Farmersville, came up with our own design and had them build one,” recalls Martin. “It’s a much more efficient machine.” He adds that the turner has a big head on the front with angled teeth that actually pulls the material in from the outside and toward the center, puts it on a conveyor that goes up underneath the cab and tumbles it off the back and reshapes it into a row again. Terra-Gro has since ordered another machine to have at its other composting site.
Compost pads at Oregon Dairy are covered with fabric hoop structures supplied by Winkler Structures. Leachate from the storage pad is captured and added back to the windrow. “It keeps the nutrients in the pile, alleviates any environmental concern and actually hydrates the material,” says Martin. Another hydration technique that provides the windrows with additional microbes while mitigating potential nutrient runoff problems involves a system of underground pipes that run from the manure storage lagoon and eventually feed right into the custom-made compost turner.
“It gets covered right back up, and you don’t lose very much ammonia because you’re incorporating it immediately into the windrow and turning it in,” he explains. “And it also means we are not using clean water.”

At peak production, Oregon Dairy Organics will be producing between 16,000 to 18,000 cubic yards/year of finished compost from around 18,000 to 20,000 tons of manure and 2,000 to 3,000 tons of food waste. Looking for the most economical way to serve its institutional clients and other lower-volume organics generators, Oregon Dairy Organics contracted with local hauler Edie Waste, Inc.
For generators such as a college campus, Martin says, food waste might only represent 20 to 30 percent of the total volume of trash but could make up 80 percent of the tonnage. “If you can pull that out and not pay landfill fees of $75 or $80 a ton and we can take it in here at about $35 a ton, it gives us some revenue to help run our site and it also hopefully will be saving them enough money to at least offset any collection and handling costs.” Cafeterias and kitchens are equipped with wheeled toters for collection of all pre and postconsumer food waste (all source separated at the generation point). The toters are wheeled out to the loading dock where Edie Waste pulls in with a rear-load compactor truck. The food waste is incorporated with the manure and carbon material as soon as it is unloaded at the farm.

After curing, compost is screened through a Powerscreen trommel. The predominant end use for Oregon Dairy Organics’ finished compost is the athletic turf market, accounting for 70 to 75 percent of what the operation produces. “We have to make sure we are getting a complete pathogen kill, so we follow all the national standards with the temperature, time and turning requirements because it is going into markets where it’s used as high-end landscape and turf product,” Martin says.
Most of those customers require a fine material, he adds. “We screen it to 3/8-inch minus, and the overs are either put back into the process or we can rescreen them. The mid-range overs are often used for some other landscape application or for erosion control. We’ve been involved with some abandoned mineland reclamation projects and with some of the alternative BMPs for ground water recharge projects and rain gardens where they mix compost, sand and soil to percolate water through it and filter it. A lot of that material we end up screening a little more coarsely; that’s often more like 5/8- to 3/4-inch minus for those applications, because you want the water to filter through more quickly.”
Because specialty clients such as turf grass managers require an impeccably clean product, Martin says contaminant-free feedstock is critical. “So far the material coming in from the college is very clean,” he says. “The students were all really on board with this and pushed to see it happen. They’re taking a lot of initiative with the policing of the separation and collection process.” But that’s not always the case, he adds. “When we started out, the very first account we were working with was a local grocery store that liked the idea of composting food waste. But when it really came down to it, they weren’t committed to truly make it happen. There was some changeover in their management staff, and we were just really having trouble with trash in there.”
Plastic bottles and soda cans are bad enough, says Martin, but if glass is coming in, it gets crushed by the equipment, passes through the screen into the compost and ultimately out onto the athletic field. That, Martin says, is unacceptable. “So we have to be really careful about that type of thing coming in on the front end. We’re really optimistic that the colleges and probably the retirement villages and some of those types of operations will work out real well. Some of the grocery store chains seem to be really committed – some aren’t quite as careful with their waste streams, so it will be a learning curve.”
RALPH and Crystal Moyer of Myerstown, Pennsylvania held an open house at their 450-acre Mor-Dale Farms in March to showcase a new state-of-the-art robotic milking system as well as a new anaerobic digester (AD) featuring the same technology and partners as utilized at the nearby Oregon Dairy. Another common thread between the two projects is major funding from the American Recovery and Reinvestment Act.
According to Ralph Moyer, the dairy’s 500 cows – including dry cows and young stock – produce around 15,000 gallons of manure daily. That gets mixed in with about 10 percent DAF (dissolved air flotation) solids received from a nearby poultry plant. The blend is pumped into an insulated Slurrystore digester that sits atop a concrete pad outside the genset building, then circulated via piping that goes through the side of the building and into a heat exchanger, before going back out to the digester. Gas taken off the top of the Slurrystore is scrubbed with Martin Machinery’s Energy Cube technology before powering a 100 kW Mann engine genset to produce enough electricity to both run the farm and put an average of 1,000 kWh/day – about half of what the farm is producing – back onto the grid. “We figure we’re producing enough extra electricity for about 50 average houses,” says Moyer, whose bidirectional utility meter allows him to receive credit from the utility for the extra power he generates. Excess heat from the genset is captured to heat the Moyers’ home and various outbuildings and to generate hot water for the milking operation and other uses.
Moyer says the addition of the DAF has nearly tripled methane production. He’s also bedding the cows on digested manure solids rather than wood shavings, saving about $1,000 a month. He hopes odor problems associated with the dairy operation will be mitigated when the liquid effluent from the digester is applied to his field.
“The digester is fed 28 times a day with dairy manure and poultry waste,” explains Stan Weeks, an anaerobic digester consultant working with Mor-Dale. “The system is currently producing around 100 kW of power, more than double what it was producing before the DAF was added.” The digester was supplied by Penn Jersey Products, Inc., the local distributor of Slurrystore, a division of Kansas-based CST Storage. The company has now been involved with AD projects in New York, Vermont and Pennsylvania.

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