Farming Magazine - October, 2012
Watershed Manure Management
On-farm phosphorus removal benefits sensitive ecosystems
Sean Jones with a prototype of the Multiform Harvest unit that converts phosphorus to struvite.
Photos by Sally Colby.
The Chesapeake Bay and the land that comprises the eastern shore of Maryland are among the most environmentally sensitive regions in the Northeast. The area was once dominated by farmland, but a growing population and concerns about water quality mean that farms in the watershed must come up with innovative solutions to manage the nutrients that come with manure.
The Jones family came to the eastern shore area of Massey, Md., in 1995 with several generations' worth of experience in the dairy business. They also brought new ideas about how to keep their dairy profitable while reducing its environmental impact on the sensitive Chesapeake Bay area.
The family is currently milking 1,190 cows, with 180 dry cows and 1,300 replacements. Sean Jones, who oversees daily operations at the three-generation family farm, says that they crop relatively few acres for the number of cows on the farm. "We farm about 1,170 acres, and of that, 700 acres can be irrigated," he said. "We grow corn on all of that acreage, and we'll grow small grains on most of it."
One of two large, lined lagoons designed to hold treated liquid for field application.
Due to drought conditions this season, Jones was forced to chop earless corn before the end of July. To maintain his feeding program and make up for the crop losses, Jones plans to plant MasterGraze (www.seedcorn.com
), a tillering brown midrib corn that should be ready to be mowed, wilted and chopped in early to mid-October, leaving a small window for winter wheat establishment.
Because diet has a direct role in manure management, Jones uses a precision feeding program centered on dry matter. "Feed is our highest cost resource, so we try to be as efficient as we can with all the resources we have," said Jones. "It doesn't make sense to overfeed phosphorus or protein. We want as little coming out in the manure as possible, so we concentrate on managing the crops, feed program and manure as a whole. It's all part of the big picture here - economically and environmentally. If we do a good job feeding the cow, there shouldn't be a lot of energy left in the manure - the cow already digested it once."
Even with precision feeding, manure still contains excess nutrients that must be carefully stored and managed for field application. The farm is in two watersheds, so nutrient management, especially phosphorus, is even more critical. The solution at the Jones farm includes a system that converts phosphorus to struvite (magnesium ammonium phosphate), which can be used in horticulture and landscaping as a slow-release fertilizer.
Prior to finalizing plans to install two Multiform Harvest (www.multiformharvest.com) units that will convert phosphorus to struvite, Jones tested a prototype unit on the farm. The fluidized bed process begins when manure slurry is pumped to the bottom of a cone and pushed through a bed of struvite crystals. The crystals separate and flow, allowing phosphorus to bond with and eventually coat the free-moving struvite crystals. Most of the crystals are harvested, with some left behind in the cone to act as seed crystals for the next batch of manure. Acid will be added as necessary to adjust the pH, and additional magnesium will help break the calcium/phosphorus bond.
The two phosphorus conversion units on the Jones farm will handle 60,000 gallons of manure per day. The harvested struvite, which looks and feels like damp sand, is dried, while treated manure enters one of the two-stage lined lagoons for future land application. Jones points out that a phosphorus recovery system simply for the purpose of obtaining phosphorus isn't economical. "From a bulk phosphorus standpoint, it costs about 10 times what the phosphorus is worth," he noted, "but the phosphorus form that we'll be getting is unique."
To complement the phosphorus conversion system, Jones is adding a complete mix anaerobic digester - a constant volume, flow-through, controlled temperature tank designed for methane production and recovery. Most farms that install digesters use post-digestion dried manure solids for bedding, but Jones, who beds freestalls with sand, doesn't plan to switch. "We want to stick with doing what we know how to do," he said. "It's what we have learned to manage. We're comfortable with sand; we recycle it, and it works. It wasn't a tradeoff option for us."
Slurry enters a series of sand settling cells after processing through a McLanahan sand separator.
Sean Jones, who oversees operations on the three-generation family dairy farm in Massey, Md., explains the prototype version of the Multiform Harvest unit that converts phosphorus to struvite.
Solids from the manure separation process will be kept wet and go into the complete mix digester as one of the substrate components. Additional substrate from local processing facilities will be brought in to increase gas production, and Jones anticipates having to pump additional liquid in. Once the digester is operating, the farm will actually have two digesters: the aboveground, complete mix digester tank and a covered holding pond that will collect gas. Although most on-farm digesters include a genset for energy conversion, most of the gas produced will be removed from the farm and used for transportation grade fuel. A small portion of the gas produced will stay on the farm and be used to operate stationary engines such as irrigation engines and pumps.
Manure processing at the Jones farm begins when slurry leaves the barn, passes through a McLanahan sand separator (www.mclanahan.com) and enters sand settling cells. "From there, it goes across a solids separator, then into a small settling cell that we clean daily, then into a larger settling cell, lagoon, and from there we will pull it to treat," Jones explains.
Post-processing struvite can be removed from the farm and used as a fertilizer component for the horticultural industry.
Although having property in two different watersheds was a potential complication for the entire process, Jones says that the Sassafras River Association, the Chester River Association and the Kent County Soil Conservation Service all provided assistance with the grant application process. Construction of the struvite recovery system is scheduled for this fall, with the goal of treating lagoon water later this year. "We got the results we wanted with the prototype: over 50 percent phosphorus removal," said Jones. "The lagoon had changed as a result of varying rainfall and pumping it down, but we were able to make the unit effective to the level we were hoping."
Jones' goal for the struvite recovery system and digester is to manage nutrients more efficiently while minimizing changes in the overall operation and keeping the operation cow-centered. "We're doing very little different," said Jones. "We're not changing the way we're handling manure. We should be able to maximize gas production and put it to good use. It'll be used here on the eastern shore and tied together with other environmental projects."
The author is a frequent contributor and freelance writer who farms and raises Great Pyrenees in south-central Pennsylvania.