OCAMM Seminar Series
Manure to Energy


      Click on title to view summary.  Presentation date in parenthesis.

Anaerobic biological treatment of manure: Full scale operations in Europe
Dr. Christian Kaendler and Dr. Gerhard Langhans, Linde Biowaster Technologies (2000)
Energy from livestock manure and other organic materials
Folker Hemman, Farmatic Biotech Energy Corp. (2002)

Shelled corn as an agri-fuel: Direct combustion vs ethanol
Dr. Harold Keener, Ohio State University (2006)

Thermochemical converstion of swine manure to oil
Dr. Yuanhui Zhang, University of Illinois at Urbana-Champaign (2006)


Anaerobic biological treatment of manure:  Full-scale operations in Europe
Dr. Christian Kaendler and Dr. Gerhard Langhans, Linde Biowaste Technologies

Anaerobic digestion in a closed system is an alternative treatment for liquid manure which produces biogas, approximately 60% methane and 40% carbon dioxide.  Digestion also reduces odors and the chemical oxygen demand (COD) of the manure.  In Europe, high COD levels have been associated with disruption of the microbial ecosystem in soils due to reduced oxygen levels during rapid degradation of manure.  Within the digester, mixing occurs by circulation of biogas and injecting a small amount of oxygen into a central tube reduces hydrogen sulfide.  During digestion, the characteristics of the manure are changed so that when sprayed as a fertilizer, it is less “sticky” and absorbs more quickly into the ground.  While the initial investment in a digester may be high, as the capacity of a plant increases the cost of treatment per ton of manure decreases.  Costs may also be offset by charging tipping fees for co-substrates and by producing biogas for use in the operations or sale to a power grid.

Fred Michel (OSU) asked if feedstocks  could be liquid or solid.  Kaendler replied that the system is a wet digester and needs less than 10% total solids.  Manure is usually liquid and a suspension is created for biosolids.

Alice McKenney (Tuscarawas SWCD) noted that the production of hydrogen sulfide is normally a problem with anaerobic digesters as it affects equipment.  Kaendler explained that the small amount of oxygen injected into a central tube in the digester disrupts the bacteria that produce H2S.  Because the amount of oxygen is small and limited to the tube, anaerobic conditions are maintained.

Brian McSpadden-Gardner (OSU) asked how a mixture of air and biogas is optimized.  Kaendler responded that the oxygen flow is determined by measuring the H2S being emitted.   The amount permitted often depends on regulations.

McSpadden-Gardner questioned whether generalizations about the percentage of power requirements that can be met by the biogas exist.  Kaendler responded that it depends on the equipment needed for treatment.  Example:  A  2,500 cow dairy produces about 125,000 metric tons of manure per year.  If the dairy manure is mixed with poultry manure (approximately 9 tons/year) biogas (65% methane) would be expected with an energy output of 13.1 kwh/ton of input.

Ted Short (OSU) asked if nutrient problems still exist after treatment and if so whether the product is stabilized for easier transport.  Kaendler noted that if nutrients are the only problem, anaerobic digestion is not the best alternative.  The benefit of digestion is that it can reduce nutrients and improve the handling characteristics of manure while creating a source of energy.  The product is hygienized (elimination? of pathogens) which meets regulations and improves marketability.

Maurice Watson (OSU) asked if digestion concentrates the nutrients.  Kaendler replied that it does not because the low total solids result in less than a 5% reduction in mass.

Michel asked whether the phosphorus and potassium end up in the solids or liquids.  Kaendler said that the amount of these nutrients that stay with the liquids depends on pH, temperature and other factors as well as separation methods. In general, solid separation with a screw press, results in 50% separation efficiency while separation with decanter and polymers results in a 90% efficiency.

McKenney asked if any digesters in operation are decanting dairy manure with polymers.  Kaendler responded at this time none are as the cost of spreading liquids as fertilizers is a more economic alternative.

John Smith ? (OSU) asked the cost per cow for this type of treatment.  Kaendler noted that it varies depending on the material available.  Also, U.S. and European standards for manure production vary.  As estimate for a digester system for 2,500 dairy cows is about $4 to 5 million.

Jody Tishmack (Purdue) requested the final pH of the liquid from the digester.  Kaendler: 7.5.

Michel asked if these systems are being used on cooperatives or single farms.  Kaendler noted that in Germany, farmers tend to be independent and do not respond to a shared system.  However, in Denmark it is more acceptable for farms to cooperate.

McKenney asked how the manure is transported to a central treatment facility and what distance is economical.   Langhans responded that 20 cubic meter trucks are used and that transport of the manure up to 20 to 30 km is cost efficient.

McKenney asked if manure treatment systems are subsidized in Europe.  Kaendler noted that the European Union recently agreed to minimum price guarantees for electricity generated from renewable resources (biogas).  Otherwise, subsidies vary with the country.  Langhans added that in Denmark, both the Ministry of Energy and of Agriculture support digestion as the country has no natural energy resources.

Michel explained that the philosophy behind composting is to reduce the volume of manure and stabilize it for transport.  The compost is a value-added product that can be used in the ornamental, crop and container markets.  Kaendler noted that the liquids can be evaporated at the end of the digestion process and the material composted.

Short commented on the evaluation of nutrient balance on the OARDC campus.  To meet the nitrogen standard, approximately 1/4 to 1/5 acre is needed per dairy cow.  To meet the phosphorus standard, approximately 1 acre is needed per dairy cow. 

Energy from livestock manure and other organic materials
Folker Hemman, Farmatic Biotech Energy Corp.

Seven times more efficient than a human-designed anaerobic digester, a cow’s stomach provides the ideal conditions – anaerobic conditions, constant temperature, regular addition of finely chopped food, neutral pH, and effective mixing - for the fermentation of organic materials that produces biogas.  The basic process in anaerobic digesters consists of mixing organic materials to form a highly liquid (3-10% solids) slurry which is heated for pasteurization (70o C) or sterilization (130o C).  Afterwards, the slurry is pumped to the fermentation tank for 12-20 days then to a storage tank where the fermented solids are removed.  The biogas generated ranges from 60 to 75% methane, depending on inputs and temperature, and requires drying and removal of sulfur dioxide before it is used to generate electricity or heat.  In addition to producing energy from a renewable resource, digesters produce fermented solids which have little odor and can be used as a soil amendment.  Although anaerobic digesters require significant up front costs, they have the potential to reduce energy costs and produce income through the sale of green electricity, methane, fermented solids and carbon dioxide credits.


Harold Keener (OSU) asked if power plants are tied into other waste industries or only manure.  Hemman noted that in Germany, there are usually additional organic materials.  In Denmark, an anaerobic digester may not use additional materials as they are often centralized with several farmers contributing manure.

Fred Michel (OSU) asked if Farmatic has a system for small dairies (approximately 200 cows).  Hemman responded that larger systems are more efficient and allow for a constant input of material which increases efficiency.  According to the EPA’s website, AgSTAR (http://www.epa.gov/agstar/index.htm), of the 71 systems installed in the US, approximately 50% were closed because of poor management and/or designs that did not meet the needs.  A possible solution for smaller farms is to form a coop which utilizes a single digester.

Floyd Shanbacher (OSU) asked how changes feedstock mixes affect the composition of the biogas.  Hemman replied that the percentage of methane in the biogas typically varies from 60 to 70%.  However, the quantity of biogas produced varies with feedstocks.  While animal manures generate a relatively small volume of biogas, the addition of other feedstocks can significantly increase production.

A Columbus participant questioned how contaminants such as plastics or sharps are handled by the digester system.  Hemman explained that the when the slurry is pumped into the system, cutters shred it but some contaminants may require other means of separation.  For dairies using sand bedding, the sand must be removed first either by settling or a mechanical separator.

To an inaudible question in Columbus, Hemman replied that, theoretically, there is no smallest capacity for a digester system.  The size is more often determined by economics.  However, if the goal is only to reduce odor, a small system that flairs the methane or heats a boiler may be effective.

Mike Lilburn (OSU) referred to the impact of feeding a cow too much fat.  The bacteria in the rumen are affected, reducing its effectiveness as a “digester.”  If processing plant waste is added to the slurry, wouldn’t the high lipid content have a similar impact?  Hemman responded that the bacteria can adjust if the material is added slowly into the system.  Management for such feedstocks is critical, including testing the slurry and accurately dosing (adding organic material) to the digester.

A Columbus participant asked if the dosing is determined by a formula as materials are received or whether sensors regulate it.  Hemman noted that, when the feedstock is consistent, sensors are effective in monitoring the system.  The Farmatic system is computer controlled and will alert technicians if a problem arises.  However, if a change in the feedstock requires an adjustment in the dosing, the technician will have to determine the adjustments.

Shelled Corn as an Agri-Fuel: Direct Combustion vs. Ethanol
Dr. Harold Keener, Ohio State University

Current agricultural issues, including low product prices and high energy costs, are similar to those faced thirty years ago.  Research at that time documented the viability of using shelled corn as an agri-fuel based on crop and energy yields and initial studies were conducted using an atmospheric fluidized bed combustion (AFBC) system to generate heat energy from corncobs and other biomass.  The AFBC system uses forced air to fluidize a bed of sand-like particles, resulting in a churning mass that absorbs and stores heat, allowing fuel to heat and ignite rapidly as it is introduced.  Although the economic analysis in 1975 did not support development of the AFBC for small-scale use, evaluation based on current corn and fuel prices indicate that it is competitive with petroleum fuels.  In a comparison of shelled corn to other fuels based on the cost per Btu, shelled corn provided heat for $13.45 per million Btu, using a corn price of $3.24/bu, which was less than natural gas, propane, fuel oil, electricity and ethanol.  Analysis of the potential liquid fuel savings realized by burning shelled corn in place of fuel oil compared to using ethanol determined that combustion of shelled corn has the potential to save 2.4 to 3.9 more fuel oil than does the use of ethanol.  Additional analyses that accounted for the dairy rations produced as a by-product from ethanol production indicated that the potential fuel oil savings was 2.7 to 3.2 times more for corn combustion than for ethanol.  Based on these assessments, if half of the 2 billion bushels of shelled corn currently exported were combusted, 4.58 billion gallons of #2 fuel oil would not be needed for heat energy but could be used for transportation.  Realization of the potential of the AFBC system will require additional testing to optimize the burner configuration as well as collaboration with the grain industry to develop a shelled corn delivery system and with industry to develop manufacturing capacity.


John VanKeuren (OSU) asked who developed the coal-burning AFBC system used at Cedar Lane Farms and if it is used elsewhere.  Keener noted that the prototype was developed by OARDC/OSU but the current system is the result of two phases of modifications during which Cedar Lane worked with the Ohio Coal Development Office and engineering firms.  Will-Burt Company, a manufacturer in Orrville, Ohio, is interested in commercializing the system.

Larry Brown (OSU) questioned whether using shelled corn for combustion would eliminate government price supports for corn.  Keener responded that no calculations have been made but an impact on price supports would be expected.   World trade and European Union concerns would also be impacted as the corn exports from the U.S. would be reduced significantly or, possibly, eliminated.

A participant in Columbus asked how many ethanol plants are currently under construction in the U.S. and how much is too much.  Keener responded that in Ohio there are two planned for construction in 2006 and up to five planned for the near future.  According to the Renewable Fuels Association’s Ethanol Industry Outlook 2006 (http://www.ethanolrfa.org/objects/pdf/outlook/outlook_2006.pdf), 95 ethanol facilities nationwide produced 4 billion gallons of ethanol in 2005.  As of January 2006, 29 new facilities were under construction and 9 facilities were expanding, adding an additional capacity of 1.5 billion gallons annually.  To date, there has been no assessment of the limits of ethanol production; however, some concerns have been raised about the potential for an oversupply of distiller’s dried grain (DDGS), an ethanol by-product used for animal feeds, which would negatively impact the economics of ethanol production.

Maurice Watson (OSU) noted that combustion of shelled corn will produce an ash by-product that may have more value as a fertilizer than the DDGS does as a feed.  Keener commented that distribution of shelled corn for combustion could be built on the infrastructure in place for fuel oil delivery.  The cooperative could deliver the shelled corn then pick up the ash and market it.

A participant in Wooster asked if corn cobs could be combusted with the shelled corn.  Keener responded that in the 1980’s, Minnesota was successful in using the cobs in different burner systems and have been used in the prototype AFBC.  However, corn cobs do not have the same energy density as shelled corn and would require a reduction in particle size before combustion in an AFBC system.

Dianne Borger (OSU) asked if the potential energy in corn varies for different varieties.  Keener noted that no evaluation has been completed but it would be expected to be true as the protein and oil content varies.  Varieties with lower nitrogen levels would reduce nitrous oxide emissions.

Keener noted that the expected cost for manufacturing a 150,000 Btu AFBC systems is estimated at $5,000 to $8,000 with greenhouses and the rotation molding plastic industry markets being targeted initially.

Brown questioned whether the economics for the energy required to produce corn needs to be re-evaluated due to changes in farming practices.  Keener responded that modifications could be made due to savings from new equipment and conservation tillage.  However, the energy reduction is estimated to be less than 15 percent.

Themochemical Conversion of Swine Manure to Oil
Dr. Yuanhui Zhang, University of Illinois at Urbana-Champaign

The thermal chemical conversion (TCC) process is “a chemical reforming process in a heated and pressurized enclosure, in the absence of free oxygen, where long-chain organic compounds (solid waste) break into short-chain molecules (liquid oil).”  Initial research using the TCC process to convert fresh swine manure to oil was conducted on 230 different batches.  Optimum operating conditions were identified as 275-305 oC, 900-1500 psi, 20% solid content, 30-120 minute retention time, 1:7.5 ration (by weight) of carbon monoxide to volatile solids and 6.5 pH.  The products formed from the conversion of the volatile solids averaged 70% oil, 15% gasses, 6% inerts and 8% water.  Development of a continuous bench scale TCC reactor (CTCC) required the addition of a pre-processing shear mixer to reduce particle size and increase homogeneity, a oscillating/rotating feeder to permit additions of manure to the high pressure tank, a continuously stirred tank reactor and a separation vessel.   Analysis of the oil produced indicated a low sulfur, heavy oil (low boiling point) that could be burned for heat or electricity or used as an alternative for crude oil products such as plastics.  Collaboration with industry is underway to develop a pilot plant but additional research is needed to assess the effect of aging of the manure as well as to optimize the system for other materials such as dairy manure or biosolids.  The TCC has the potential to provide up to 50 million barrels of oil per year from the hog manure produced in the US while improving the profitability of livestock producers and reducing the potential of negative environmental impacts from manure handling

To read about Dr. Zhang’s work in more detail, click here.


Betty Ayslworth (OSU) asked if the University of Illinois had any patent protections on the process or if companies have funded the research.  Zhang responded that the only patents at this time are on some of the engineering processes for the continuous system.  The TCC process itself has not been patented and the primary funding for the research has been from public sources.  There is a licensing agreement between UIUC and an Bioenergy industry based on ‘know-how’. 

David Munn (OSU) asked how much energy must be input, both theoretically and based on the batch tests, to create a kilogram of oil.  Zhang noted that for every unit of energy put into the systems, three units of energy based on the optimum conversion rate. The energy yield also assumes that no energy required to produce the manure as it is a by-product.  Additional work is needed to add a heat exchanger to the system to recapture the heat. 

Participant in Lima requested a comparison of the “fingerprint” of the TCC oil to standard heavy petroleum crude oils produced in North America.  Dr. Ocefemia, a post-doc working on the TCC project, responded that the oil is very heavy but lighter than oil from tar sands.   While it has not been fingerprinted, analyses indicate approximately 40% asphaltenes.

Mark Smith (NRCS) asked about the potential for having a CTCC reactor on site at a swine operation.  Zhang replied that two options have been discussed:  1) an on-farm reactor and 2) a central reactor site requiring transport of manure.  The preference is on-farm, especially if a furnace-size unit that could fractionate the oil on-site was developed, allowing on-site use of the products.  Another alternative would be to transport the oil off-site for processing.  If constructed as modules, the size of the reactor could be increased as needed by adding additional units.

Harold Keener (OSU) asked if the by-products from the TCC process contain nitrogen, phosphorus and/or potash.  Zhang responded that the oil is low in sulfur but has is approximately 4% in nitrogen than petroleum sources of oil.  The phosphorus and potassium are primarily in the solids that remain which could be used as a soil conditioner.  The gas produced by the system is approximately 98% carbon dioxide.