October 25, 2007 | General

Closed Loop System Takes Manure And Methane To Ethanol And Compost

BioCycle October 2007, Vol. 48, No. 10, p. 54
Anaerobic digestion, ethanol refinery and composting, team up to process manure, grains and other feedstocks into high value end products.
Robert Spencer

A CONVERSION plant in Mead, Nebraska is processing manure and methane to create ethanol and compost. According to Nebraska Governor Dave Heineman: “This plant sets a new standard for ethanol production in this state and our nation, and is an example of the innovation needed to take this industry to the next level. It lets America get its automotive fuel from the croplands of the Midwest instead of the oilfields of the Mideast.” The $80 million plant will produce about 20 million gallons of ethanol each year, eventually increasing output to 25 million gallons.
Major components of the Genesis Plant built by E3 Biofuels include:
o A 30,000-head cattle feedlot produces manure collected through slatted floors of cattle holding pens. The manure is continuously pumped to a storage lagoon.
o A 2,500-acre corn farm produces part of a special feed mixture for the cattle. About two million bushels of corn will be chopped up each year for the feed mixture.
o An additional eight million bushels of corn are expected to be bought for the ethanol plant’s production.
o A specially designed anaerobic digestion plant converts a mix of manure and a syrup-like stillage by-product from the refinery into methane gas.
o The ethanol refinery plant is fueled by the methane gas.
o The digestate is composted for use as fertilizer on the cornfields.
o Distilled grain and leftover corn, called “wet cake,” are incorporated into a cattle feed mixture.
o Process water from the plant is stored in lagoons and used to irrigate the fields in accordance with a discharge permit.
E3 BioFuels originally bought 880 acres for the plant site, and recently added another 1,400 acres that will be used for future expansion. The company does not own cattle in the feedlot, but instead has the cattle owners pay for the animals to be held and fed there for about 150 days before being taken to slaughterhouses, with at least two full turnovers in cattle during a year.
Dennis Langley, the company’s President and CEO, cites several advantages to the closed-loop system: “The largest water pollution problems are solved by removing manure from the feedlots. This system also helps reduce the greenhouse gas effect. And the process also helps reduce the odor associated with feedlot operations.”
In a recent interview with BioCycle, Langley emphasizes that the patented closed-loop system “combines three elements: ethanol refinery, anaerobic digestion, and animal feedlot. We can substitute in various gadgets such as different designs for the AD unit, but these three things put together are patented. As the technologies evolve we will substitute different components.”
He describes E3 Biofuels as “generation 2 technology,” and believes more energy efficient and environmentally friendly technologies will emerge with less dependence on a single feedstock. “E3 Biofuels will progress toward more thermal efficiency and the ability to process virtually all types of grains, potatoes, beets, and anything that can be distilled,” he adds. “As grain prices fluctuate, we want to be able to adapt to the most economical feedstocks. Generation 3 technologies will emerge and I believe we will get to 40 to 60 percent of the liquid fuel needs of the country through a combination of improvements, including energy conservation. We also want the highest and most beneficial uses of recyclable materials. For example, the material out of the Mead anaerobic digester is mixed with other materials and composted outdoors using the Brown Bear turning machine.”
Regarding the importance of transportation costs of feedstocks and fuel, and colocation of the ethanol refinery and a CAFO, Langley explains that E3 purchased the feedlot from the existing owners, and the plant is located on land owned by the feedlot to minimize the need to transport manure. Another significant benefit of locating next to the feedlot is that the distiller’s grain – a combination of protein, oils and fibers that comprises approximately one-third of the corn processed in the refinery – can be used for cattle feed. Since this grain is wet, if the refinery were not located adjacent to a feedlot, it would have to be dried to prevent spoilage during storage and transport. At a typical ethanol plant, the amount of energy needed to dry the grain constitutes almost one-third of the total energy requirement of the facility. Plus, much of the grain’s nutritional value is lost in the drying process. In contrast, wet cake from the Mead plant can be taken a short distance to the feedlot and fed to the cattle, another aspect of the operation’s “closed-loop” system.
E3 installed an anaerobic digester system manufactured by Biothane Corporation. Manure from the feedlot and thin stillage, a milky by-product of ethanol production, are digested to generate the biogas needed to operate the ethanol plant. Manure is transported to a 500,000 gallon storage tank via pipes or trucks, which then feeds the digesters, which consist of two 4-million gallon concrete vessels. Three types of bacteria work in sequence to convert manure into biogas: Stage one – Hydrolytic bacteria convert manure to fatty acids; Stage two – Acetogenic bacteria convert fatty acids to acetic acid; Stage three – Methanogenic bacteria convert acetic acid into biomethane gas.
Ted Mathews, manager of the anaerobic digester installation, has extensive experience in management of small and large dairies in New York and Wisconsin that have utilized anaerobic digesters. “The cattle manure and thin stillage are mixed in the 500,000 gallon influent tank, with the digestion process taking about three days,” he explains. “An ideal temperature is 100°F, which we maintain consistently. The manure enters the system at about 12 percent solids, and the resulting digestate has an impressive nutrient value.” Digestate is stored in another 500,000-gallon tank.
The portion of digestate to be used as bedding is sent to a nutrient recovery unit to make organic ammonia fertilizer, and extract potassium and phosphorus. The ammonia fertilizer can be injected below-ground to the roots of growing plants, instead of applied at the surface. before the nutrient-recovery unit extracts nitrogen, phosphorous and ammonium.
A 7-acre compost pad is located adjacent to the refinery and feedlots, and is used to compost digestate off the press. Some carbon material is mixed with the digestate to accelerate the compost process. A trailer hauls disgestate to the compost pad where a front-end-loader and a Brown Bear SC4912 compost windrow turner are used to form and turn the windrows. The turner is mounted on the articulated loader, and can process approximately 2,500 cy/hour. The unit is 12-feet wide and has a 49-inch paddle aerator that operates with windrows up to 5-feet tall. E3 plans to market the compost, possibly for use as bedding in a dairy operation, as well as for nurseries, golf courses and agriculture applications.
The total annual amount of manure from the Mead feedlot is 300,000 tons, equivalent to the solid waste generated by a city with a population of 350,000. Donna Garden, Supervisor of NPDES Permits and Compliance Unit at the Nebraska Department of Environmental Quality (NDEQ), explains that the Mead facility has a discharge permit from the NDEQ that addresses noncontact cooling water, as well as process and nonprocess wastewater from a lined holding lagoon. “This is a combination plant that crosses the boundaries of CAFO and industrial discharges, and it functions as a wastewater treatment plant,” she says. “The permit addresses both surface water and groundwater discharges.”
The permit allows water from the holding lagoons to be land applied at sites adjacent to the ethanol plant. Monthly monitoring is required for ammonia as nitrogen, nitrate as nitrogen, total Kjeldahl nitrogen, total phosphorous, total alkalinity, total dissolved solids, total chloride, and pH. The permit identifies the following sources of wastewater that flow to the storage lagoon, and are then land applied: ammonia stripper, washdown, biogas condensate from the anaerobic digsters, cooling tower blowdown, boiler blowdown, softener regeneration, reverse osmosis reject, filter backwash, emergency overflows from the filter and clarifier tower.
Prior to start of the land application process, E3 Biofuels must submit a plan to NDEQ that has been prepared in consultation with a professional agron-omist or certified crop specialist. The plan will evaluate site-specific plant-soil assimilation characteristics, and determine the pollutant from the wastewater that requires the greatest land application area, and application rates.
In addition to the NPDES permit, an air emissions permit was required for the anaerobic digester and the ethanol refinery. “We got no grace on obtaining permits,” says Langley. “The regulators were just as strict on our air permit as if we were burning natural gas or diesel to power the ethanol distillation process even though we don’t have sulfur or nitrogen oxide emissions, and we even offset those emissions.”
Langley anticipates that future permitting processes will be less involved after regulators become familiar with operation of the new technologies, and is hopeful that the regulatory requirements will be less expensive to implement. “I think there is wasteful capital that resulted from the permitting process, particularly some of the back-up in lagoon capacity,” he adds.
The $80 million Mead facility is financed over five to seven years, compared to petroleum refineries that can be financed over 20 to 30 years, explains Langley. “The biorefining industry is unbalanced compared to petroleum, and we are concerned about federal commitment to biorefining,” he says. “Financial markets have not matured to keep up with this rapidly growing biorefining technology. One thing that helped our financing at the Mead plant is that we are also a solid waste disposal facility and a sewage treatment plant, something the financing industry is familiar with, so that helps.”
No federal funding from the USDA was used, but it is possible for future projects, he adds: “There is also the possibility of generating electricity to sell to a third party, and that will provide additional revenue.”
Robert Spencer, a BioCycle Contributing Editor, is an environmental planner in Vernon, Vermont.

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