What's up with manure foaming? Where are we at with understanding the causes of foam formation on deep pit manure storages

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 15^th, 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.