7/30/2019 Making Smart Choices about Cow Power
By Sarah Lupis, SybilSharvelle, Catherine Keske,and Jessica Davis
Institute for Livestock and theEnvironment, Colorado StateUniversity
Across the Western UnitedStates over $150 million may belost every year in untapped ener-gy generation. Not from solar orwind or natural gas sources, butfrom cow manure.
An interdisciplinary team of re-searchers from Colorado StateUniversitys Institute for Live-stock and the Environment isworking to help dairy producersdecide if and when to use tech-nologies that convert manure intouseable energy and, thus, increasecow power.
Although dairies in the Western U.S.have an ample supply of manure, producershave been reluctant to adopt anaerobic di-gestion technology that would convert itinto methane-rich biogas which could po-tentially be used to power farm operationsor heat on-site buildings, thereby decreas-
ing operating costs. It could also be sold asa replacement for natural gas, thereby di-versifying revenue for dairies at a timewhen milk prices are often fluctuating. Inaddition to these financial benefits, recy-cling manure would help to reduce green-house gas emissions, decrease unpleasantodors, and improve water and air quality.
The technology is out there, says SybilSharvelle, an associate professor in CSUsDepartment of Civil and EnvironmentalEngineering and an expert on biologicalwaste processing. Farmers just need toolsto help make smart choices about how andwhen to use it.
In collaboration with economist Cather-ine Keske and biowaste specialist JessicaDavis, all from CSUs Institute for Live-stock and the Environment, Sharvelle is de-veloping an on-line decision-support tool forproducers considering on-farm bioenergyconversion. The web site will guide themthrough a series of yes/no questions de-signed to help determine if the technologyis technically and economically feasible andmeets their needs. Users will also receiveadvice on selecting the right technology,finding an equipment provider, and how tooperate and maintain the equipment.
The Environmental Protection Agencyestimates there are 140 anaerobic digestersoperating at commercial livestock opera-tions across the U.S.; 126 of which generateelectrical or thermal energy from the cap-tured biogas. Of the 17 Western states, 10(Washington, Oregon, California, Idaho,Montana,Wyoming, Utah, South Dakota,Nebraska, and Texas) have anaerobic diges-
tion projects in place, generatingnearly 150,000 combined mega-watts of electricity per year.There are 29 dairies in the West-ern U.S. with systems installed,16 in California alone. Nation-wide, dairies account for 116 ofall anaerobic digestion projects.
Decision support tools similarto the one being developed atCSU have been developed forEastern dairy farmers to help ad-vance the use of this technology,
especially in Vermont whereseven dairies now provide elec-tricity generated from manure-derived methane gas to thestates utility customers.
In a recently published study,University of Texas at Austin re-searchers estimated that convert-
ing manure into renewable energy couldmeet up to three percent of electricity con-sumption needs in North America, leadingto a substantial reduction in greenhousegas emissions.
Part of the reason why Western dairyproducers have been slow to adopt anaero-bic digestion technology is that unlike their
Eastern counterparts, Western dairies typi-cally collect manure by scraping drylotsrather than flushing indoor barns, whichrequires a high volume of water. Add tothat a naturally dry, moisture-evaporatingclimate and what do you get? Manure thatis too dry for traditional technologies.
How dry is too dry? Conventional anaer-obic digestion technology (complete mix,plug flow, fixed film, and upflow sludgeblanket) all require inputs to be over 85percent liquid. In Colorado, for example,dairy manure scraped from dry lots cancontain as much as 88 percent dry solids.
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Western Dairy News is a collaborative effort of Dairy Specialists from:
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for the West, about the West, from the West
March 2010Vol. 10, No. 2
Making smart choices about cow power
In a two-stage anaerobic manure digestion sys-tem the process is separated into distinct por-tions, mirroring the biological process. Highsolids waste are placed in a concrete bay where
water is passed through, effectively leachingout organics that are later converted intomethane gas.
7/30/2019 Making Smart Choices about Cow Power
To use conventional anaerobic digestiontechnology, waste products would have tobe diluted with water. For example, to di-gest 1,000 metric tons (2.2 million pounds)of waste with 90 percent total solids, a con-ventional digester would require the addi-tion of almost 2.4 million gallons of water.Not only would the expense associated withpumping and heating that much water beenormous, but that much water is simplynot there to use. In addition, clean water iscontaminated by the process.
Sharvelle is also developing new anaero-bic digestion technology that can help makethe process of converting animal waste intoenergy more efficient. She is studying thefeasibility of using a multiple-step processin which a small amount of water, typicallyfrom existing on-site wastewater, is perco-lated through dry manure until it hasleached out as much organic material aspossible.That water, now saturated withenergy-rich organic compounds, is then con-verted into methane gas using microbes.
Having tested this new technology at asmall scale, Sharvelle, in cooperation withCSUs Kenneth Carlson and Stacey Simmsof the Governors Energy Office, is nowworking to develop a plant scale demon-stration version. It will be built at the Col-orado Correctional Facility in Cannon Citywhere horse, cow, and aquaculture wastesare all readily available and on-site facili-ties exist to manufacture all of the materi-als needed to set up the system.
Conversion of manure to methane is amulti-step process. First, in a process calledhydrolysis, enzymes released from mi-croorganisms naturally present in the ma-nure break down the organic compounds inmanure (in this case, organic means thecompound at the molecular level contains acarbon atom) into simpler compoundswhich dissolve more readily. It is this initialstep that is often the biggest hurdle toanaerobic digestion in the West because ata molecular level it requires water to breakapart chemical bonds.
In the second step, called acidogenesis,the simple organic compounds are chemi-cally converted into organic acids such asacetic, formic, and butyric. In the third step,the organic acids produced during acidoge-nesis are consumed by bacteria that pro-duce methane as a waste product.
Unlike conventional technology, two-stage anaerobic digesters can handle mate-rial that is anywhere from zero to 50 per-cent solids, opening up new possibilities forWestern waste-to-energy conversion en-deavors. Several scenarios are possible.
Dairies with on-site two-stage anaerobicdigesters could accept waste materials, in-cluding crop residue, leaves, and organicmunicipal wastes for processing, potentiallyprofiting from both drop-off fees and the en-ergy generated. Alternatively, independentlarge-scale digesters could be establishedthat would handle diverse dry wastes frommunicipal and agricultural sources, andthen pipe the biogas back to their regional
communities as an alternative to homeheating natural gas.
The potential for co-digestion is onething that makes anaerobic digestion moreeconomically attractive in the West.
Although new technologies are creatingnew possibilities for those who are thinkingabout adopting anaerobic digestion, econo-mist Catherin Keske offers a word of cau-tion. She recently completed a feasibilitystudy of anaerobic digestion sponsored bythe Governors Energy Office in Colorado,to evaluate the experiences of those whohave tried the technology, determine if andwhen anaerobic digestion makes economicsense for producers, and identify whatcould be done to make it more accessible inWestern states.
Based on the technology currently avail-able (two-stage digestion was not includedbecause it is still in development and notyet widely available) and the current eco-nomic climate, her report concluded thatWestern dairy producers cannot makeenough or save enough money from on-siteuse of biogas to generate electricity to makethis a good decision.
It also said that adopting existing tech-nology with the hope of turning a profit byselling carbon credits isnt realistic either,at least not until the market price of carbongoes up. She did say, however, that Thereare situations that would make anaerobicdigestion economically attractive.
One of these is when a producer is facedwith nuisance lawsuit related to odor. Ac-cording to case studies in Keskes research,producers can expect to pay on the order of$100,000 in legal fees to fight a lawsuit,and could potentially be ordered to paydamages of $50 million. Under conditionslike this, installing anaerobic digestersstarts to look good. In situations where thetechnology is primarily used for mitigation,generating electricity is merely an addedbonus rather than a true cost savings.
In general, Keske determined that gen-erating electricity from anaerobic digestionisnt a smart move for a couple of reasons.In the West, electricity rates are not veryhigh, so generating your own electricitydoesnt create huge cost savings. Similarly,supplying it to the grid is not a profitableoption. Secondly, methane is a relatively
dirty gas that often clogs generators,causing them to break down and need fre-quent maintenance or repair.
The best use for methane biofuel gener-ated from anaerobic digestion appears to beas a heat source replacing natural gas, es-pecially when it can be used on-site orpiped to a nearby location. For example, adairy with a neighboring facility that canuse the biofuel to heat buildings.
But the most economically attractive op-tion for anaerobic digestion at the presenttime and with currently available technolo-gy, according to Keskes report, is a region-al-scale conventional digestion facility thatrelies on co-digestion.
As stated earlier, anaerobic digestion inthe West is severely limited by the avail-ability of water. Co-digestion overcomesthat hurdle because by using a variety ofinputs from agricultural and municipalsources, some with high solids content (likemanure or grass) and some with low solidscontent (like paunch, the material left overfrom meat processing) ensures that inputsto the system will reliably have enoughwater content for the multi-step anaerobicdigestion process to work.
Projections are that the entrepreneurialindividual who decides to invest in a re-gional co-digestion facility could make be-tween $700,205 and $8.9 million, represent-ing between three and 46 percent return onthe initial investment. But under a worst-case scenario the investment could loseover $5 million.
To maximize returns, Keskes report rec-ommends using the biogas product on-site.For the Colorado Correctional Institutionthats what makes investing in anaerobicdigestion so attractive it has on-site in-puts from a dairy herd and a horse trainingand boarding facility, and it can use themethane biogas to heat buildings, includingits goat nursery and tilapia barn.
The development of a separate stageanaerobic digester capable of processingdry wastes is expected to make this processmore affordable, reliable, and practical forproducers, industry, and municipalities inthe Western U.S. As new technology be-comes available, current technology is im-proved, and as markets change to makeelectricity or carbon more valuable, produc-ers will need to know how to respond.
Remember the on-line decision-supporttool we talked about earlier? Thats wherethe web site designed by Sharvelle, Keske,and Davis to guide prospective investorsthrough a process of identifying existing re-sources, potentially suitable technology, andanticipated outcomes, will be most helpful.Before taking the plunge and investing inanaerobic digestion technology, producersand others will be able to use it to assesstheir current situation and receive adviceand estimates about conditions that couldresult in a profitable, positive endeavor.
Additional information on anaerobic di-gestion, with links to the reports and stud-ies described in this article, can be foundthrough the Institute for Livestock and theEnvironment at www.livestockandenvi-ronment.info
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