Spontaneous
foaming in swine manure pits is an ongoing challenge and has serious potential
danger. Methane gas is trapped in the bubbles and creates the
potential for fires and explosions, especially when the foam bubbles are
rapidly destroyed and a spark occurs. Conditions that are especially dangerous
are during agitation, pumping, or pressure washing or activities like welding
and hot work where slag might fall into the foam. If you are dealing with foam make
sure you take the appropriate precautions to ensure safety for you, your
employees, and your pigs. Below are a few best tips for working with foam, or
check out this video for a
refresher on dealing with foam.
·
Provide continuous ventilation
to prevent gas build-up. Increase ventilation during agitation to quickly
dissipate released gases.
·
Turn off heater
pilot light and other non-ventilation electrical systems, such as the feeding
system), that might produce an ignition spark.
·
When pumping pits
that are close to being full, pump without agitation until manure is about 2
ft. below the slats.
Research
Over the last three years, a collaborative
research project to understand and mitigate the causes of foam has been
conducted by Iowa State University, the University of Minnesota, and the
University of Illinois. A lot of information has been learned about foam and
its potential causes, and that information is briefly shared below.
Gas
Production
Methane is always produced during anaerobic
breakdown of manure, so when we store manure in a deep pit, we are going to
generate methane. However, it was determined foaming barns are consistently
producing methane at faster rates than their non-foaming counterparts, often
producing 2-3 times as much methane per day. This led researchers to start
asking why this might be happening. Through several dietary feeding trials, it
was discovered that diets higher in fiber tend to be less digested by the pig,
which results in more carbon entering the manure storage. To microbes, this
carbon is a food source, it’s the energy they need to grow and thrive. Researchers
believe this shows recent dietary changes, like feeding more DDGS (a feedstuff
high in fiber and protein) puts the fuel in the manure to build a more active
microbial community. For example, a study by Dr. Brian Kerr, of USDA-ARS,
tested how ration impacted the amount of carbon in the manure and found a diet
with 35% DDGS inclusion resulted in 40% more carbon in the manure than pigs fed
a corn-soybean meal based ration. However, just putting the energy in the
manure doesn’t guarantee foam, a microbial community needs to develop that
breaks it down quickly.
What’s this mean
for mitigation? Finding ways to get lower methane production should lead to
less foam. Items that reduce carbon in the manure lower the chance of foam by
reducing the microbial food supply. This could dietary change towards more digestible
feed ingredients (typically those lower in fiber content) or finding ways to
make currently utilized ingredients more digestible (including finer grinding
or feed treatments to improve digestion an incorporation in the pig). This also
indicate that treatments, such as ionophores (Narasin or similar),
that impact the methane production pathways can be effective treatments as they
lower methane production rates.
Foam Stabilization
The
second important part is the need for something to stabilize the bubbles to
help a foam form. Research has found the stabilizing agent are fine sized
particles (2-25 µm) that are enriched in proteins, but it takes something to
bind those proteins together. What’s that something? At this point researchers aren’t
100% certain, but best data suggests it is a microbially produced
poly-liposaccharide, aka microbial goo. This microbial goo causes the foam to
be very viscous, keeping the bubbles wet and making them last longer.
One
way of thinking about the chemistry of this stabilization is like comparing it
to making meringue for your lemon meringue pie. In that case you take some egg
whites (just the white, we want the proteins which have hydrophobic, or water
hating, and hydrophilic, or water loving, areas) and then start whipping it to
entrain air into it. This alone isn’t enough though; something needs to
stabilize the meringue. That’s where sugar comes in. Slowly add sugar and keep
whipping and you’ll end up with a tasty meringue that’s light and fluffy and
will persist for a long time. The sugars bond with the proteins and hold it all
together.
What’s
happening in the manure is surprisingly similar, the biogas moving through the
manure brings those bits of protein to the surface (just like when we separate
the whites from the yolk to make meringue), it also churns them up and causes
them to orientate themselves so their hydrophobic areas are towards the bubble
and the hydrophilic areas to the manure. When they react with some of that
microbial poly-liposaccharide, stabilized foam results.
What’s
this mean for foam mitigation? This tells us there are two parts we can focus
on to destabilize the foam, the protein or the microbial poly-liposaccharide. Research
has shown that treatments that destabilize the proteins, such as proteases, can
greatly reduce foaming capacity and foaming stability. Other treatments that
seed microbes, especially microbes known to produce proteases, into the manure
may be a viable treatment and are being tested both at the laboratory-scale and
in-the-barn. As proteins are an important component of the stabilized foam,
diets that lead to more protein excretion (typically higher protein contents)
would seem to have greater potential for foam formation. A swine feeding trial
focused how different levels of protein and sources of protein impacted manure
foaming properties. The results of this trial showed that higher protein diets
led to manures that had higher foaming capacity, greater foam stability, and
higher methane production rates – all characteristics of foaming manures.
The
second component that could be targeted as a mitigation approach is the
microibally produced poly-liposaccharide. Efforts to extract and better
characterize this substance are underway; however, at this time not enough is
known about material, or the microbe that produces it, to target this specific
aspect of foaming.
Microbes
How does
all of this explain when you have two barns that are treated the same; same
pigs, same diets, they are as similar as they can be, but one foams and one
doesn’t? It’s all about the microbial community that develops in the manure.
Certainly the dietary ingredients can influence microbial community, but other
factors seem to make as much of a difference. This was true both in the field
and with the feeding trials that were conducted; however, based on the feeding
trials it was clear that certain properties did influence the microbial
community that developed. In particular, our study showed that manure carbon
contents (microbial food) led to differences in microbial. Our evidence
suggests that in the field higher fiber diets, especially from DDGS, tended to
lead to foaming communities for to crusting.
In the case
of non-foaming manures, the microbial community tended to be focused on
lactobacillus and VFA processing. Within these barns the manures showed an
accumulation of volatile fatty acids, which lead to slightly lower surface
tension in the manure, and lower methane production rates. Foaming manures
exhibited microbial communities that were slightly correlated to higher added
oil in the diets and exhibited increased presence of ruminococcaceae,
ruminococus, and bateroidales and had a higher portion of the microbial
community from unclassified methanogens, which seemed to be correlated to the
higher methane production rates.
In terms of
mitigation we are currently working to better correlate why these microbes
become more prevalent as well as methods to alter and modify the microbial
community. In particular, we initiated a study to evaluate if increasing
lactobacillus in the manure can alter the amount of volatile fatty acids in the
manure and upset the unclassified methanogens in the manure to alleviate
foaming.
Leon’s Safety
Message:
September
15th, 2014…. This past year Leon Sheets shared the story, his story,
of a fire/explosion at his swine barn. His important message reminds us all the
importance of safety. “Farmers need to be careful whether they are pumping,
power washing, or doing maintenance, when it comes to these accidents, we want
no more, nobody else.” Take the time to hear Leon’s message.
