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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.
(continued on next page)
Western Dairy News is a collaborative effort of Dairy
Specialists from:
March 25, 2010 W-43
HOARDSWEST
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.
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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
March 25, 201044
HOARDSWEST
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at:http://animalscience-extension.tamu.edu/dairy/wdn.html
For further information contact:Dr. Ragan Adams, Editor
ILM, CSU-VTH300 W. Drake Road
Fort Collins, CO 80523970-297-0371
[email protected]
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cow power . . .(continued from previous page)
