When
you travel through Vermont, tree-lined farms and hills dominate the
landscape. Throughout this patchwork lies hundreds of producers that,
until now, have been cut off from the advancing world of manure
digestion, simply because people have said their operations are just
too small. With the backing of a renewable energy company, Avatar, and
a desire to prove everyone wrong, Dr. Guy Roberts is about to change
the face of anaerobic digestion and its implications for smaller
operations.
“My interest into digesters was piqued when I
attended a conference in Syracuse, New York,” Guy said. “There were
five farmers who were asked why they built digesters and the first
answer from each one of them was for odor control. That is when I
realized that farmers are under all kinds of pressures and it is kind
of ridiculous to concentrate on only biogas for energy. There are all
kinds of benefits for farmers, from odor control to gas for heat and
electricity. Nutrient management and air quality also come into play
with digesters, so finding a way for every farmer to take advantage of
this kind of technology became my focus.”
But getting from an
idea to a working model and from a model to a full-scale operating
system has proven to be quite a challenge. But, as Guy explained, the
journey has been enlightening and helpful in creating the final product.
“I
have met with several people familiar with digester technology and most
of them have said that a small-scale digester isn’t feasible. They
continue to go back to the need to produce electricity, forgetting
there are so many benefits to a digester beyond electrical output.
Something didn’t strike me about the whole economy of scale argument
that kept coming up in the conversations.
“As I kept looking
into current technologies, it finally came to me that the real economy
in creating digesters was to come up with a model that would work for
just about any situation” Guy added. “We needed to come up with a sort
of kit that would work into any situation, any size. The economy didn’t
come in making it bigger, but rather making it fit into the system in
place – something smaller, leaner and easier for everyone involved to
work with.”
Guy’s desire to make a digester that not only
worked, but was easy to work with was also at the forefront of his
planning. He realized that unless he could create a process and
products that works for the farm, you really haven’t helped anyone.
“Another
reason for developing this model was to find a way to make it simple
and easy to work,” Guy said. “Producers are already tasked beyond what
they can do in a day without adding the hassles of digester maintenance
on top of it. It had to be easy to put together, easy to work and easy
to maintain.”
With those desires has come the need to
completely rethink traditional digester design. The final design is
something totally new, yet captures the main ideas needed for a good
digester to work.
“The first thing that struck me was to make the
digester above-ground. I had seen too many examples that showed
in-ground digesters were too prone to problems that required excessive
time to clean and maintain. They also had the tendency to develop leaks
that went too long undetected. Getting everything above-ground would
give people a first-hand account of what was going on all the time, not
to mention the ease of keeping it maintained.”
“The
hardest part of the design was the control system and the elevated
tails to keep the pressure for gas production and consistent gas flow,”
Guy added. “The choice of materials was also a learning curve for us,
but we have found a mix of materials that look to handle the continual
processing of manure. While it has been a long road to go down, what we
have seen has been very promising and working well for us.”
Although
this digester system produces methane as other systems do, it is the
treatment and use of the effluent that starts to set this system apart
from the others.
“One of the biggest discoveries in looking
at the bacteria within the system and the effluent was what happens to
the nitrogen once methane has been produced,” Guy added. “We realized
that through the digestion process, a lot of nitrogen was being
converted over to ammonia. This ammonia was quickly dissipating from
the effluent, resulting in a tremendous loss of nitrogen as a
fertilizer while adding volatile compounds back to the atmosphere.
Neither result was something we wanted to see happening.
“We
have tested and are now implementing a simple aerobic process after
digestion that allows us to take the effluent and run it through a
bacteria-sustaining medium,” he said. “This allows the microbes to
convert ammonia to nitrate, allowing the nitrogen to remain in the
system and not escape to the atmosphere. I am not aware of any
digestion system out there that allows for this type of nitrogen
control from beginning to end.
“Most recently, we have been
looking at phosphorus removal systems that could easily be added after
the nitrification process,” he continues. “In essence, with both
systems added to the back of our digester, producers would have a very
effective tool in knowing what type of effluent they had to return to
their fields and be able to make adjustments according to their needs.
Since the nitrogen is in a nitrate form, there is the potential for
runoff from the farm. But it will also allow producers to apply
nitrogen throughout the growing season, giving them the opportunity to
match crop needs and growth with a readily accessible nutrient source.
Any excess nutrients could be sold off to other farmers or homeowners.
It just makes the system, as a whole, a much better management tool.”
Because
of its above-ground, tubular design, the digester is scaleable to
nearly any farm with 100 or more cows. This innovation, not considered
before in digester designs, is something that can truly make a
difference for farms across the country. When asked about the future
and how soon this system would be available, Guy responded: “We are
seeing it now, today. The system is in and working well. We have in
place what we need to begin placing these systems on dairies throughout
the U.S. I am excited with what I have seen, what the possibilities are
and that what I had hoped for is becoming a reality in this building.
It is only up from here.” ANM
