Manure Agitation Tips for Hydrogen Sulfide Safety

Hydrogen sulfide gas continues to be a serious issue both in and around barns with liquid manure storages. The decomposition of organic matter in manure results in the release of several gases, ammonia, carbon dioxide, methane, and hydrogen sulfide among them. Most of the time these gases are emitted slowly, but any time manure is being agitated, pumped, or the surface is disturbed, hydrogen sulfide can be rapidly released. Although all are potentially dangerous, hydrogen sulfide tends to be the one of most concern in these cases. Hydrogen sulfide has an intense rotten egg smell, so it is relatively easy to detect its presence, even in very low concentrations. However, since we can smell it at such low levels, there is not a clear indication of when it reaches a potentially hazardous conditions that we can detect without the use of analytical instruments.

Hydrogen sulfide can spike quickly and without warning during pit pumping.

People should NEVER enter a building or facility while agitation is occurring. Use yellow caution tape to mark barn entrances and alter everyone that manure agitation and pumping is occurring. Consider lockout tags during pumping.

If possible, remove animals before pumping. For barns with multiple pits move cattle out of the room with the pit being agitated to reduce risk.

Agitation Strategy

·         Don’t agitate until manure the manure level is 1 ½­ to 2 feet below the slats.

o  Hydrogen sulfide is denser than air and as a result will tend to pool on the manure surface, sufficient separation is required to minimize hydrogen sulfide in the animal breathing zone

·      Avoid aggressive agitation when animals are in the building (no rooster tailing).

o  Surface agitation causes more turbulence and greatly increases the release of hydrogen sulfide

·      Do not direct agitator nozzles toward pillars, walls, or towards a corner.

o  Pillars and walls stop flow quickly and cause the manure to churn, increasing the rate hydrogen sulfide is off gassed from the manure.

o  Corners are often dead air zones; releases off hydrogen sulfide in this area are more likely to result in animal loss

·      Stop agitating when bottom nozzle is less than 6” below the manure surface.

o   Keep the agitation below the surface at all times.

·      Avoid sudden changes in agitator depth and intensity.

o Quick changes can result in large amounts of solids that haven’t previously been agitated and result in rapid gas release.

o Slower changes in both power, flow direction, and depth, allow slower, more continuous release that is safer for animals and workers.

Can nutrient separation reduce manure application costs?

The nutrient density of the manure is one of the most important factor influencing transportation costs. As the largest part of the manure slurry is water, it is natural to consider separation and partitioning strategies that divide the slurry into different fractions. One fraction would be nutrient dense and could be more economically transported away from the animal production facility, and the other fraction would have a low nutrient content that would be applied at high rates on land nearby the production facility. However, if a producer is going to add a nutrient partitioning technology to their manure management system, the costs associated with the installation and use of the system need to be recovered. Potential economic benefits associated with nutrient partitioning technology could include reduced transport and land application costs, smaller manure storages (if a system where the low nutrient fraction could be irrigated onto the land more frequently could be developed), or potentially the recovery of a bedding product that could be recycled for on farm use. Although all three of these factors could be important in justifying the added costs of the nutrient partitioning/separation systems, the work presented here will only focus on the cost modification occurring to manure transport and land application.

The original cost of manure transport and land application can then be compared to the costs of transport and land application when differing levels of manure treatment were obtained. This then gives the performance and cost relationship the nutrient partitioning systems would have to achieve to be a viable option to implement in the farm’s manure management systems.

To do this a model of how application costs vary with manure application rate and transport distance is needed. The first objective of this work was to develop a relationship to describe the costs associated with applying manure and the manure application rate. Our data for this is from Mulhbauer et al. (2008) and are shown in figure 1. In addition to the land application costs, an additional 0.001 $/gallon-mile for every additional mile the manure is transported away from the farm beyond the first mile was assumed. These costs are specific to a farm and more complex than these assumptions I’m using, but offer a useful starting point for the discussion. In many cases the actual costs are strongly influenced by distance from the barn to the field driveway, as well as variables like the size of the field, and how a drag hose could be routed or the path that tank wagons would have to take to get the manure from the storage to the land application area, or even the number of times the drag hose would have to be set and moved to cover the application area, along with numerous other things.

Figure 1. Impact of manure application rate on manure application cost per liter of manure; also illustrated is the differences between broadcast application and manure injection.

Rather than going through the nitty, gritty details of what I’m trying to do instead I’m just going to look at an example. Assume a 4,000 head grow-finish operation. This operation completes 2.5 production cycles per year and has pigs that excrete manure at a rate and nutrient content in line with those suggested in the ASABE manure production and characteristics standard (2005), i.e., 4.5 L/head-day and the manure has nitrogen and phosphorus contents of 0.47% N and 0.18% P (approximately 40 lbs N and 15 lbs P per 1,000 gallons) after storage in a deep pit. Thus at this operation 6,570,000 L of manure are generated per year and 30,879 kg of N and 11,826 kg of P that need to be land applied. Assuming manure application occurs at a nitrogen application limit and 168 kg N/ha are applied (roughly the recommendation for corn following soybean in Iowa), then 184 ha of land application area are required for manure application. The resulting manure application rate would be approximately 35,745 L/ha. Using our previous assumptions (50% of farmable land in corn and 60% of the land farmable) then 613 ha of total land area would be required. Based on these calculations, this example farm would apply about half of the manure within 1 km of the farm and the other half would be applied within the second km. Manure applied within the first kilometer would cost about $0.00458/L for application, while manure within the second kilometer would cost about $0.00478/L. Of the manure, 3,368,857 L would be applied at the $0.00458/L rate and the other 3,201,143 L at the $0.00478/L rate; thus total cost for land application would be $36,475 or about $198.44 a hectare or $0.004675/L.

The results of this analysis (figure 2) indicated that nutrient partitioning techniques could lower the cost of land application with the effectiveness of nutrient partitioning (in terms of total nutrient capture and the volume these nutrients are concentrated in) resulting in different cost reductions. On this graph, the x-axis represents the simple separation index (shown as equation 1) and the y-axis represents the estimated cost of land application, in dollars per liter of manure applied. Each series on this graph represents the percent of total manure volume that ends up in the nutrient enriched fraction. In general, the cost reductions were minimal until either extraction efficiency (the percent of total nutrients captured) was relatively high or nutrients were extracted into a relatively small volume. This figure provides information on what a farm could pay for the nutrient partitioning process; for instance, if they obtained equipment that could partition 60% of the nitrogen in 10% of the manure mass it would reduce the application cost by approximately $0.00068 per L, or the manure application bill by $4,460 per year.

Figure 2. Evaluation of a nitrogen partitioning technology with differing performances to impact the costs of transport and land application of the manure.

So what this method does is provide a quick an easy way to tell if a nutrient separation system would be useful on our farm if we are trying to use it to lower our manure application costs. Next time I’ll take a look at a couple of technologies that are available and see how they’d do at paying for themselves.

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.

Are you taking your safety seriously when dealing with manure?

Hydrogen sulfide gas and foaming continue to be a serious issue in and around barns. But don't take my word for it. Hear Leon Sheet tell about what happened to him and why you need to take this issue seriously. Your safety is important to us and we are always humbled to hear our messages makes a difference. Hear Kris Kohl talk about his recent experience when a farmer told him about remembering hearing about hydrogen sulfide in training and how to react. We all on the manure team here at Iowa State feel the same way, and hope you take the time to educate yourself about ways to keep yourself safe and check out some of the resources below for altering you of H2S dangers.

Hydrogen sulfide is especially concerning when agitating or pumping the manure. As the amount of distiller’s grains in feed rations has increased, so has the amount of sulfur excreted by the animal. Over the past ten years, sulfur concentrations in swine manure have increased from 3 pounds per 1000 gallons to 9 pounds per 1000 gallons. When manure is agitated, hydrogen sulfide gas can be quickly released. Exposure to low concentrations of the gas for even a short period of time can cause health issues and at high enough concentrations can cause near instant death. A list of symptoms to different hydrogen sulfide exposures is provided in Table 1.

If you work around manure, monitors can be purchased to help keep you and your employees safe. A monitor, which is small enough to wear, ranges in cost from $99-$800 and will alert you if the situation is dangerous. This year as part of the manure applicators program participants were asked if they currently use any type of hydrogen sulfide monitoring equipment. On the commercial applicators survey, 5 percent of workers reported using a hydrogen sulfide monitor compared to 1 percent of confinement applicators survey. When asked about the likelihood of purchasing a monitor, 25 percent of commercial applicators and 31 percent of confinement applicators said it was likely that they would purchase a monitor (for a summary of this information see Figures 1 a and b below).

There are numerous options available for monitoring hydrogen sulfide levels when working with manure. Below are links to four meters for you to take a look at and some pictures of what they look like.

1. Honeywell GasAlertMax XT II
2. BW Honeywell GasAlert Clip Extreme GA24XT-H
3. BW Honeywell GasAlert Micro Clip XL 4-Gas Monitor
4. Draeger Pac 3500 H2S Monitor
5. RAE Systems ToxiRAE II

In addition to considering purchasing a monitor, other practices to follow when agitating or pumping manure include:

• Check to ensure all ventilation fans are working prior to pumping and that air inlets are open
• Place a tarp over pump-out to help protect the applicator
• Communicate with farmer and crew and never enter a barn during agitation and pumping
• Listen for pig distress
• Always be aware and alert as dangerous situations can develop quickly.