Anaerobic Digester Performance

Dan Andersen begins the episode with manure gases and road safety reminders for fall manure application. Later in the episode, Luke Soko, a graduate student at Iowa State University, joins Dan to discuss his research, which focuses on anaerobic digester performance between covered lagoons and heated digesters.

Hydrogen sulfide safety publications mentioned in the podcast are linked below:
Hydrogen Sulfide Safety - Manure Agitation
Hydrogen Sulfide Safety - Monitoring
Hydrogen Sulfide Safety - Barn Ventilation at Cattle Facilities
Hydrogen Sulfide Safety - Swine Barn Ventilation

Transcript

Dan Andersen  00:06

Hello and welcome to Talkin' Crap, a podcast by Iowa State Extension and Outreach, where we discuss insights into the science, technology and best practices surrounding manure management. Our objectives are to build awareness about the challenges farmers and the broader agricultural industry face around manure, and to demonstrate solutions in areas of innovation.

Dan Andersen  00:28

Welcome to this month's Talkin' Crap podcast. I'm your host, Dan Andersen. As always, I'm thankful to have you join us. And I think we have a lot of great crap on tap for you this episode, depending on when you are listening to this application season is rapidly approaching. So our plan for today is to start out with a review of some manure safety tips, especially related to manure gases, and road safety. We'll take a brief look at some carbon that we talked about last time, and then we'll bring in Luke Soko, a PhD student working with me here at Iowa State. He's been doing some great work looking at different types of anaerobic digesters and covered including covered lagoons and heated digesters to understand what the data says for how effective they are. So with that, we'll get started for today. 

Dan Andersen  01:19

As we so often do, I wanted to start out today with a manure fact. So today's fact is timing is everything. We say that all the time in life, timing really matters. And while I don't have exact data for this, and there is a year to year variability, depending on the weather, and when we get the crop harvested. From the best we can tell from the surveys we do about 70% of the manure in Iowa is fall applied with the remaining 30% applied in the spring. Again, that varies by region manure type, and year, but as a good starting point for conversation, I think that's about where we are. I've been told I talk about manure application timing a lot. And there's a reason for that. I think it's really important. It's also a complicated issue. One that I don't want to tell you do this, do that, because lots of factors come into play. So what's that mean for us? Well, as we embark on another agricultural season here in Iowa, it's time to delve into this critical aspect that often goes unnoticed -application timing. It's really critical for our success, we know that manure is a valuable fertilizer. And our ability to get the most out of it is dependent on making sure that those nutrients, especially nitrogen is still there, when our crops are up and growing. So for applying in the fall, that means that those nutrients have to make it a longer period of time before they can be taken up by the crop. On the other hand, there are some advantages to maybe fall application. As you've probably noticed, this year is a little bit on the dry side and those drier soils often are great for minimizing things like compaction, and giving us longer windows, greater opportunities, to get our manure application done. And I'm gonna try and hit on these, as I talk us through some of the things that I think about when we figure out when should we be putting on manure. 

Dan Andersen  03:08

So with manure application timing, the early bird gets the worm and by that I mean spring application. As the frost thaws out, and fields become workable in the spring, many Iowa farmers opts to apply manure. This timing aligns with planting making it convenient to incorporate manure into the soil before sowing our seeds, right. And that means that those nutrients are there and ready for the crop to use. Spring application that allows the crops to access the nutrients as they need them throughout the growing season, promoting healthy development. And it also reduces the opportunity for those nutrients to be lost because they were sitting in the root zone for our crop to take up and haven't had as much time to transform and move. However, with that said, spring application does come with some challenges. Manure can be challenging to get applied if the soil is wet. Manure application equipment is oftentimes relatively heavy and we can cause compaction, especially as we just saw this last year, spring can be a tight time for time crunch. This last spring was cold, cold, cold, and then nice and warm and we should have had everything planted. And that's hard to predict and doesn't often give great windows for getting the work done. So what I like to say is Iowa's temporary climate well, great for crop production is also a little unpredictable about what's going to happen in the spring and that always brings in some risk. When we think about fall application, it allows farmers to often take advantage of the drier field conditions and that can help reduce the risk of nutrient loss from runoff at the time of application. It also allows for at least in certain manures to have more time to break down and help those nutrients become crop available while in manures that are relatively high in ammonium nitrogen, that break down isn't necessary. So when I think of ammonia rich manures I'm often thinking of swine manure, dairy manure, especially dairy manure with salads that have been separated, layer manure. But if I contrast that with some other types of manures, that we have especially bedded pack manures, from cattle facilities, or turkey litter, where there's been bedding incorporated into that litter, where there have higher carbon and nitrogen ratios, that breakdown can be an advantage to us, at least in some cases, so that those nutrients are available right when the crop needs them at the beginning of the season. Now, there are other ways to handle that challenge, some starter fertilizer to supplement manure, things like that. But it is something that we have to think about and be cognizant of. 

Dan Andersen  05:38

However, if we are putting on manure early in the fall, there's a trade off, some of that nitrogen may be lost the environment, it's sitting there, sometimes for longer periods of time, four or five, six months, in some cases, before the crop is really up and growing and rapidly incorporating that nitrogen. If there's water movement through the soil during that time from rainfall moving down towards or tile lines, or just moving down through that soil profile, it's probably taking some of the nitrogen with it. Because of that timing of manure application is really a balancing act. And it's not one size fits all, it's really important to figure out what your your needs are for your crop, your soil, the weather patterns we're experiencing, and also your labor availability. So I've really pushed towards, we'd love you to wait for the soils 50 degrees and cooling or at least approaching that 50 degrees mark, or trying to wait until spring to get manure application done. But I understand that that might not fit all your operations. With that said, if you haven't done much spring application, historically, I encourage you to give at least a little bit of a try, especially if you have your own manure application equipment, give it a try and just one field, a couple passes and see how it compares to your fall application. And that might give you an idea of how you're doing in terms of holding that nitrogen for when we really need it. I think that's a topic we'll dive into greater detail in a future episode, we have some great research data from some of the years where we've been doing some timing of application. And I know there's a lot of other great research around the country going on on a similar topic. So we'll try and get some of that shared to you to make sure that you're up to date on the latest science of what's happening. 

Dan Andersen  07:13

 Next up, I promised a little bit of banter on safety. And we, Iowa State University, and I, especially, care about you. After all, you're listening to this podcast, so you must like manure almost as much as I do. So let's talk about things to keep you safe. And we're really gonna focus on two areas here, manure, gas safety, and some road safety tips. So safe manure transport, a crucial aspect of sustainable agriculture. And I know that's funny thing to say we don't normally think about moving manure as as part of sustainability. But we want to get that manure, it's a complete fertilizer with nitrogen, phosphorus, potassium, sulfur, and so many micronutrients to the places we need it, and to get it to where we need it, transport is a crucial issue. So transporting the manure to the right place at the right time really does help make us more sustainable. We know that manure is a valuable fertilizer resource, and getting it to the right field really plays a key role in that. So what are some things that we can think about or be doing to help make manure transport a little bit safer. So the first thing I like to think about is secure loading. Proper loading and securing of manure on the vehicle or trailer is paramount. This prevents spills, which can lead to accidents or soil and water contamination. For solid manures, consider tarping loads where appropriate, or loading in ways that minimize spills. And what I mean by that is if you have manure that is really dry coming from one part of the operation, sometimes putting manure that's just a little bit wetter, on top of that can help add some mass, help keep dust down, and do a better job of holding it on the trailer. That's something that I think we all need to assess how far are we moving that manure? What's the condition? How fast are we going to be going? What sort of loss of load might we be dealing with. For liquid manures I think a couple things that play a key role especially as we get larger equipment and have been trying to haul manure a little bit further is baffles within our manure transport tanks. Baffles are internal partitions or barriers strategically placed within the tank to manage the fluids movement and behaviors. And a lot of work has been done to show that oftentimes, good use of baffles can improve braking and handling of equipment. And it also reduces risk of surging or spills. So thinking about how fill our tank is what sort of road conditions are we going to have to go around? How fast do we have to go do we have to stop and speed up, any sharp turns, things like that, that might lead to some fluid surges, but really making sure that our equipment is in good repair to handle that. Going with that good repair, regular vehicle maintenance is important and that starts with routine inspections of transport vehicles. Make sure the brakes lights tire suspension system are all in good wear working order to ensure safe transportation. And then while you're hauling check periodically to ensure that these items remain clear and functioning. Every now and then we are dealing with a dirty substance - manure it might splash, making sure that our signs or reflectors are still showing up, as well as our lights, especially at certain periods of day, continue to work and operate as they should. 

Dan Andersen  10:22

Signage and communication, displaying appropriate signs on our manure vehicles, making sure they have those slow moving vehicle signs, the flashing lights is extremely important to communicate to other drivers. I know that more and more, we're dealing with some distracted driver issues out in the countryside, and anything we can do to help alert them that we're there we're working so that they slow down, understand the situation and do their best to mitigate struggles for our movement of manure, I think is useful. Load distribution, manure should be evenly distributed to maintain a stable vehicle. So if you're loading that solid manure truck, make sure we're getting it relatively spread out or as best we can. Proper weight distribution helps prevent swaying or tipping during transit. Be aware of the weather. Adverse weather conditions like rain or snow, require some extra caution. Oftentimes, if we've had that, we might be tracking some mud out of the field onto the road that can make things slick. So it's just something to be aware of, especially as it can make shoulders of roadways a little bit softer and a little bit more of an issue. I think the other thing that I wanted to mention there is just being attentive to different periods of the day. As we get later into the fall the sun's location, especially at certain periods of the day might severely limit our visibility. I know that that certain periods, I need my sunglasses more and more to help with those rays of the sun that seem to be blinding me when I'm driving certain directions. Along with that thinking about route plannings where possible, trying to choose routes that avoid steep hills, sharp turns, narrow roads, roads without shoulders, places where we might struggle to get by. I know that in all cases, we're trying to get to specific fields that may not be possible as some challenges are unavoidable. But knowing the route, mapping the route, making sure that everyone's aware of the biggest risks on that route, I think are a good way to to help mitigate some of those issues. Protecting the environment is a shared responsibility, and transporting manure is a big part of that. It's essential to prevent spills and waterways. Using tarps or covers to avoid losses during transport can be a great tool in some cases. But really making sure that you're familiar with the terrain, the route you're taking, getting to the right field, and helping others be aware of what we're doing will hopefully help keep you safe on the roadway. 

Dan Andersen  12:47

Okay, so with that I wanted to move into manure gases. This is something that I talk about a fair amount because we do want to keep you all safe when it comes to manure, when manure is breaking down in anaerobic conditions, which just means without oxygen, which is really the condition we have anytime we're dealing with liquid manure, we are going to make some gases. There's really four gases that I think about ammonia, methane, hydrogen sulfide and carbon dioxide. When it comes to your personal safety, they all do matter, but there's really three of them that jumped to the forefront to me. The first is ammonia. Ammonia is a pungent gas it can irritate your eyes, nose and throat. In high concentrations, it can cause respiratory problems. Sometimes you might get a hoarse voice if you've been in a livestock facility, or have been working around manure, oftentimes that's related to ammonia and dust. While we sometimes see spikes of ammonia coming off when we're agitating manure, it tends to not be as large of issue at least from my perspective, as maybe being in a barn or facility that's relatively closed off with low ventilation in the winter, and then the ammonia might be a little more bothersome. The second one is methane. Methane is colorless, odorless and flammable. And the real issue with that is it can be explosive. In certain situations. It's explosive between 5 and 15%. Generally for ventilating the barn, we avoid those conditions. If you have something like foam on your manure where we break that foam rapidly, oftentimes will be in that 5 to 15% range. And sometimes when we're agitating that manure below the slats will will be in that explosive range and because of that we want to avoid sparks or, or things that might ignite that manure. 

Dan Andersen  14:27

Then the final gas hydrogen sulfide, to me, that's really the one that is the most dangerous. Hydrogen Sulfide is a colorless gas, it has a distinctive rotten egg odor. So your nose is a good detector of it at low concentrations. Unfortunately, as that concentration goes up, we often go nose blind, and it doesn't tell us when we have a safety risk. Hydrogen Sulfide is more dense than air. So especially on cooler days where the atmosphere and the air are staying pretty cool. It doesn't tend to rise away from us but rather sinking into those low spots around the barn and that's part of what it makes it a little bit more dangerous. This is the one that it does come off every time we're agitating manure. The manure will often have hydrogen sulfide stored in it at beyond levels that are what we'd expect. And that's partly because micro bubbles of hydrogen sulfide stick to the solid particles in the manure. When we start agitating or mixing that manure, we knock those bubbles together, they coalesce, they get a little bigger, and then they pop out of that manure, sometimes relatively rapidly. Our agitation practices have some some play on that, how we're ventilating the barn building at that time, is really important for what keeps us safe. So some things to think about are common risks. First, anytime we have a pit, a manure pit or a lagoon, we are going to make some of these gases. They often trap and concentrate the gases and our normal ventilation systems, where we're ventilating for animal comfort in the bar typically keeps them at a pretty good range unless something's happening that causes those gases to come up quickly, or we really have low ventilation rates because the winter temperatures are very cold. So the time that really is more important is anytime we're disturbing that manure, so agitation and pumping. Agitation and pumping, the liquid manure releases those gases from the newer much more rapidly. So that's the time we really need to be cautious. If we're agitating manure storages stay out of the barn, I recommend wearing some detectors for hydrogen sulfide, they beep at you when you hit certain concentration thresholds and give you a idea of the risk that you're facing. Finally, when we're spreading manure, we can sometimes have some of these gases released. Again, most of the time, there's enough dilution air in the field from wind blowing the open space to not cause an issue. But it is something that we should be aware of, at least a little bit. But really, it comes down to me at that building facility is really the the place where we tend to see the highest concentrations when we're agitating and pumping. So some safety measures on this, there are certain things we can do with the diet of livestock to help mitigate both ammonia concentrations in the manure and hydrogen sulfide concentrations in the manure. Many times, While that is useful, it's something that is often either outside of our control, or that given the economics of feeding animals, we have a limited opportunities to make meaningful changes. We kind of have to feed what we have available corn, soybean distillers grains, some roughages if we're feeding cattle, and oftentimes while we can change the concentration somewhat, they're still going to be in ranges where if we're agitating that manure, enough can come out that we should think of it as a potentially dangerous situation. So that means there's really a couple of things we have to think about right. And the first one is proper ventilation, ensure that good ventilation in of the manure storage areas use exhaust fans vents, openings to allow those gases to escape while we're ventilating. I'm not going to get into details for tunnel ventilated versus curtain ventilated barns. Iowa State has some extension pubs out there, if you're interested to take a look at on best recommendations for ventilation practices. But the one thing I'm going to comment on is make sure your ventilation system is working. I've been to a few sites where people have had issues with hydrogen sulfide. And then you go look and say what was happening, what could have we done differently, and sometimes you see pit fans that aren't working properly, right, or they have cones or dampers on them that didn't function properly. So really just checking over that equipment, make sure it's in good working order, and then getting the barn set up appropriately goes a long way for that. 

Dan Andersen  18:27

The second things I wanted to talk about were just some personal protective equipment. Obviously, we're thinking about biosecurity, so boots, gloves, sometimes goggles if we're dealing with splashes are useful. Along with that a gas monitoring system. They make a lot of single gas monitoring systems for hydrogen sulfide that you can get between $100-200; they'll oftentimes beep or buzz when you hit certain concentration thresholds like 10-20 parts per million. While those concentrations aren't what I would think of as lethal, my experience at sites have generally been if you move a step or two, you'll find yourself in better air and it's at least an indicator that you know hydrogen sulfide is coming out and we should be thinking about how we're agitating and ventilating that barn. The next part I wanted to talk about was aggressive agitation. I know at times we have crusting and we want to surface agitate to break it up, but all the research shows that if we are doing aggressive agitation, especially surface agitation, hydrogen sulfide comes out much more rapidly. So if at all possible, avoid that. If you feel like you have a crust that you need to work a little more aggressively to agitate, thinking about human safety and animal safety trying to get animals away from the area that were agitating, either out of the building out of the barn, or at least to the other side of the barn where we're not agitating, can be useful. Avoid things like rooster tailing and just be aware of where that agitator is pointing. If it's at a pillar or a corner, especially if we're getting splashing as it hits things in there, more hydrogen sulfide is coming out. And then the last two are really just about awareness. Make sure that you are reminding your co-workers that there are dangers of manure gases, talk through some safety measures and response plans appropriate for each facility and for you as a company. So if you have meters, make sure you're using them, explain to people why they're important. And explain to them how you'd respond. So I see this meter is reading, take a moment, make sure that the ventilation system is still operating the way we were hoping it would. Take a moment to check over our agitation systems do we see some of that manure running into a pillar or something happening in there that might be causing more hydrogen sulfide to come out than what we'd otherwise anticipate. 

Dan Andersen  20:33

With that, we're gonna get Luke on to talk about digesters and digester efficiency. But I do want to wish you all a safe and happy hauling season as we get into that time of year. So as we get Luke on, he's going to be talking about methane, how we would want to try and generate it, why we would want to try and generate it, some of the options we have and how effective they are. But as we do that, I wanted to give you a reminder of something we've talked about before the carbon footprint of pigs. We know that for every pig, we raise here in Iowa, the carbon footprint is about half a ton per year. And in some ways, that's an abstract tracked measure. But we know that a larger percentage of that carbon footprint, global warming potential comes from the methane we generated. And I just wanted to give you sort of a sense or a scale of, of carbon flows throughout the barn. So as we think about a pig that we're trying to raise from maybe 25 pounds to 277 pounds. To do that, we might feed him on the neighborhood of 280 pounds of carbon. So 280 pounds of carbon go in, of that about 120 pounds of that carbon is going to come out as CO2 that he exhales, now that CO2 was in the atmosphere, we turned it into plant matter, we're just turning it back into CO2. Neither here nor there, right, it's we just borrowed it for a short period of time. Another about 70 pounds of that carbon ends up in the pig, right? So that that wonderful pork comes out to the supermarket and we all consume it. But right there, we're talking somewhere around, you know, almost 190 pounds of the carbon. So a lot of the carbon that we said the pig is ending up in those two components. Only about 90 pounds is excreted from the pig in the form of manure. Of that 90 pounds, somewhere in the neighborhood of 13 pounds of that carbon turns into methane, nine pounds turns into carbon dioxide while we're storing that manure, and the remaining 70 pounds of carbon make it out to the field for land application, where a lot of it will be turned into CO2, but some of it is stored in our soil helping improve soil health, soil tilth and the water holding capacity of our soils. So when you think about it, you know, we started out with on the neighborhood of 280, 290 pounds of carbon, and we're talking about a pretty small amount of it right somewhere around 9-10 pounds of it that are ending up in that methane form. And that isn't a large percent of the carbon, but it is a large issue that we're all taking a much closer look at these days. And hopefully some of what Luke is going to share here with us will help give us some better insight into what that means and what opportunities and options might be in store.

Dan Andersen  23:18

I'm joined by Luke Soko, PhD student here at Iowa State working with me on anaerobic digestion to get us started. Luke, could you tell us a little bit about yourself?

Luke Soko  23:26

Yeah, hi, my name is Luke Soko, I went to undergrad here at Iowa State University, I majored in Biosystems Engineering. I'm a second year PhD student, Dr. Dan Anderson and I we investigate the feasibility of biogas projects. We're hoping with the advent of carbon credits continuing to arise on the market, and new technology being developed along with centralizing biogas facilities, centralizing biogas upgrading and anaerobic digesters, that we can increase feasibility of anaerobic digesters in America and reduce greenhouse gas emissions.

Dan Andersen  24:02

Great. Thanks, Luke. And I wanted you to tell us a little bit about what got you interested in anaerobic digestion?

Luke Soko  24:07

Absolutely, anaerobic digestion, does two things that I think is very unique for our system. It reduces pollution and it also creates energy. And I don't know many systems that can do that feasibly. There are hundreds of industrial biogas facilities across Europe. It's a technology that works. It's a technology that we know can produce renewable natural gas, biogenic natural gas, and it's something that I find very interesting. I think we know this technology works. It's something we should be utilizing to reduce our carbon footprint. As dairy and swine manure emissions continue to rise to about 700,000 metric tons per year of carbon dioxide equivalents, we should definitely look into reducing those emissions using anaerobic digestion.

Dan Andersen  24:59

Thanks. And then so at a broad level, could you tell us just a little bit about what you've been working on, and specifically what we're going to talk about here today? 

Luke Soko  25:07

Yeah, so there are different types of anaerobic digesters, there's the covered lagoon anaerobic digester, which is the most simple, covered lagoon, or sometimes used interchangeably covered manure storage, where you have some storage filled with manure, it could be a lagoon, it could be a covered storage, and it's not heated. It's not mixed. It is simply there, the manure is there, and it is generating biogas during warmer times of the year. It's generating biogas all the time, but specifically during warmer times of the year, and the cover is used to catch the biogas. And typically, if you catch the biogas, you'd like to convey it to something to either make renewable natural gas or electricity. And that's the most simple type. It's just a manure storage that's covered. And then there are heated anaerobic digesters. And sometimes there are heated and mixed anaerobic digesters. And the reason you would heat and or mix an anaerobic digester is to increase the digestion efficiency to increase the amount of methane that you're producing, increase the amount of biogas and subsequently the amount of methane as well. So what we're looking at is, we know if you do a biochemical methane potential assay, you can figure out how much methane a substrate can make a manure, corn stover, but you're not going to actually get that in practice, you're going to get some fraction of that potential. And what we're here looking at is, what kind of digester system what kind of anaerobic digester system makes sense, a covered lagoon or a heated digester. A heated digester generally is accepted that it's going to increase your efficiency, increase the amount of methane you're producing, although at what cost? And so we're going to talk about anaerobic digestion efficiency.

Dan Andersen  26:57

Perfect. And so you mentioned efficiency. What do you mean by that term? What is anaerobic digestion efficiency?

Luke Soko  27:03

There is, so there's a potential of methane that can be produced from a substrate, there's a maximum potential. In practice, we're going to see some percentage of that maximum potential actually achieved. If you're heating and mixing, it's generally accepted that you're going to make more methane per gram of volatile solids, which we'll talk about because its on a, it depends how much you're gonna get more methane, depending on how much you're putting in. But you're gonna make more methane per gram of volatile solids, typically, if you're heating, and so we're going to evaluate that efficiency of heating it versus not heating it.

Dan Andersen  27:39

Great. So you mentioned a couple of things. One is volatile solids, volatile solids are really the amount of organic material that's in a substance. Is that fair? 

Luke Soko  27:50

Yes. 

Dan Andersen  27:51

How would you measure volatile solids?

Luke Soko  27:53

You'd measure,  it by you take your sample, and you dry the samples so that there's nothing left but solids. And then you essentially, when there's no liquid left, you would bake your sample at around a little over 400 degrees Celsius. And what you'd be left with is ash after you bake your sample long enough. And the difference between your ash and how many solids you have is your volatile solids, or the amount of solids that are not recalcitrant enough to stay as a solid form at high temperature.

Dan Andersen  28:29

Yeah, so it's kind of what burned off. And yeah, that stuff that burned off is organic material or carbon based material. 

Luke Soko  28:35

Yeah. 

Dan Andersen  28:35

And that's really the stuff that we were talking about that we can transform. The other thing you mentioned was the biochemical methane potential. Could you talk a little bit more about that, and maybe how they measure it?

Luke Soko  28:45

Yeah, so the biochemical methane potential is your maximum potential, how much methane you're going to make. And that's typically measured by you take a sample, and typically use some sort of inoculum or something, or you can use an inoculum, or just to give the correct bacteria to the substrate. And you would put that in an incubator over time. And you would measure what's the maximum amount of methane that that incubated sample is going to be able to produce per gram of volatile solids. 

Dan Andersen  29:18

Great. So inoculum, he used the word there that I think we want to talk a little bit, but it's really just a fancy way of saying, I have this group of bacteria, this community of bacteria that is primed to make methane, and I'm going to feed them a little bit of this organic matter, and see how much methane they can make from it. And then nothing that they make, that's the maximum amount by definition these with the BMP, we're going until methane production stops or ceases. So, we got all of it that we could, we use just a little bit of organic matter, lots of bacteria, so we're trying to make sure they consume it all, and then we go and tell it staff, so roughly 30-40 days somewhere in there, but we've really manipulated the system to make sure we get it all. In practice in a real digester, or even in a covered lagoon, it's rare that we get to that level. Oftentimes in just covered manure storages, maybe the retention time isn't sufficient or even in a heated digester, since we don't want to make them huge, oftentimes we'll shorten retention times. Right? And, and that's why it's important to understand maybe what your efficiency is. Okay. So can you talk a little bit about where you found data to start looking at efficiency?

Luke Soko  30:18

Absolutely. The EPA AgSTAR publishes, has published the livestock anaerobic digestion database. This database features reported values for herd size, something we're looking at specifically for herd sizes, dairy and swine as those projects are more common. But they list projects and they list the herd size. And they also, if reported, list of the biogas generation for the project, and/or the electricity generation for the project. And this allows us to essentially use this data and measure how much biogas is being made per animal, how much methane is being made per animal, and we can assume, we assumed about 60% methane by volume, which is pretty typical among anaerobic digestion of manures, 60% methane per volume of biogas to be specific. And so we can measure the amount of methane per animal. And that's what we're looking at.

Dan Andersen  31:17

Roughly how many projects did you find in their database that were in a format that you could use? 

Luke Soko  31:22

We found 100 dairy covered manure storage anaerobic digestion projects, with an average anaerobic digestion efficiency of 50%. So that means that they these projects are achieving 50%, of what we think the maximum methane potential is. And we see that as about 0.86 cubic meters of methane per day per cow. And we see the maximum amount of methane that could be made as 1.71 cubic meters of methane per day per cow.

Dan Andersen  31:59

Great. So about 50%, in that case, and that's for a relatively simple digester system, it was out there, there was a storage, maybe lagoon, we put an impermeable cover over the top of it so that we can catch gas, and we're really just offsetting the amount of emissions that it would have made rather than watching that gas go into the air. We're capturing it and better able to use it. 

Luke Soko  32:18

Yeah. 

Dan Andersen  32:19

And then you also looked at heated digesters, did you separate heated in mixture? Do you consider them all together?

Luke Soko  32:24

We considered all the heated digesters together. We did not find a significant difference, well, there's not a tremendous amount of data, and we did not find a significant difference between biogas generation of plug flow versus mixed digesters, some digesters are considered both plug flow and mixed, and it gets kind of hairy in that situation. And so with the covered manure storage, we really only had 100 digesters for dairy to analyze, and we had nine for swine to analyze. So we got 100, for dairy for covered storage. And for dairy digesters, we found 82 usable data points. And we add an efficiency of 77% for those digesters, so you get an increased efficiency from 50% for covered manure storage, up to 77% for a heated digester.

Dan Andersen  33:21

So that sounds pretty good to me. I mean, if I'm using some heat, which unfortunately means that the some of the product and making some of that methane, presumably to heat up my digester, and really still increases the amount of gas I was making. And that's a good thing. But there are some some complications to this. Digesters are a little bit more costly to build, they're definitely more sophisticated to own and operate. And then the other part of that is hydraulic retention time. So when you have a covered manure storage, it's a manure storage, our primary function is still to get that manure out to the landscape. We're applying manure every six months every year, somewhere in that range. With a designed heated digester, oftentimes, you're really shortening the retention time, maybe 30 to 40 days. So even with that much shorter retention time, the efficiency is still 27% higher than those long efficiencies of covered lagoon, right. 

Luke Soko  34:10

Yeah. 

Dan Andersen  34:11

For sure. Yeah

Luke Soko  34:11

Yes, that's exactly right. Some complications about this, as well as the location of covered lagoon projects. So if you were interested in doing a project that generates renewable natural gas, you would likely be  interested in California's low carbon fuel standard credits. Our modeling thus far has shown that low carbon fuel standard credits can generate the majority of revenue in a project more so than D3 RINs. And a covered lagoon project further south in the United States where it's warmer is going to have a larger efficiency, a greater efficiency, than if it's a project further north. So we also analyzed the California Air Resources Board has published their tier one simplified CI calculator for bio methane from anaerobic digestion of dairy and swine manure. This was published by the California government in 2018, and they're currently working on another model. But using this, we had found that as you as you go south, the California model does predict that you're going to have a larger efficiency with your anaerobic digestion, which complicates it. So you have this, EPA study, according to the EPA data, you have a 50% efficiency for a covered manure storage, and you have a 77% efficiency for a heated digester. Although as the CARB model shows, as you move south a cover, manure storage is going to have a greater efficiency.

Dan Andersen  34:41

And the EPA dataset doesn't, it gives you location, but you didn't necessarily have enough data points in any spot to say, as I move north, there's is a lower efficiency,

Luke Soko  35:57

Absolutely. Something that could be improved in the future of the EPA databases, those values are reported values to the EPA. We don't necessarily know the mechanism of their data collection. It's not a ton of data points. Most of the EPA's data was in California, was from California, although California has a mixed range of weather as you go throughout the state. So the data, the data is what it is, it could be better and it could be worse. 

Dan Andersen  36:31

And that's something as we see more projects we'll definitely collect more data. But I think what you calculated from these datasets is really close to what I had been using as rules of thumb for a long time, you mentioned that there is a temperature variation in the United States and that really impacts covered lagoon performance,  less so heat did digester performance, since we're controlling temperature. A good rule of thumb has always been that microbial activity, essentially the right that will make methane doubles for every 10 degrees Celsius that we increase. So as I think about that, did you do any sort of calculations to say, how would a digester in maybe a covered lagoon digester in Iowa comparing performance to maybe one in Missouri or further south?

Luke Soko  37:13

Absolutely, absolutely. So I've developed a map using the California Air Resources Board model. Calculating anaerobic digester efficiency of covered manure storage is covered lagoons. Something to note as well is another large factor, besides temperature, is how often you empty the manure storage. If you empty the manure storage more often, the California Air Resources Board predicts that you're going to have a significantly lower efficiency and your digestion overall throughout a year, you're going to have lower digestion throughout the course of a year, if you're emptying your manure storage more often. How often you empty your manure storage was not reported in the EPA database. So there's no frame of reference to really explain the discrepancy between often you empty your manure storage with the EPA database. So according to the California Air Resources Board, if you are having a digester system in Iowa, and you empty your manure storage once a year, and you're going to have a 67% digestion efficiency. If you empty your manure storage twice a year, we're going to have a anaerobic digestion efficiency of 43%. Now the EPA predicts that you're going to have an anaerobic digestion efficiency of about 50%. Now, based on our experience, we believe that dairies typically empty more often than once a year, we think dairies lean towards emptying closer to twice a year. And we feel as though that 50% I mean, it's nice that it's between the 43% and the 67%. But it's even nicer that it's closer to 43%. So that's just an Iowa, but if you were to have a dairy farm in say, Bakersfield, California, the California Air Resources Board predicts you'll have an anaerobic digestion efficiency at a covered manure storage of 74%. If you empty once a year, and 58% If you're emptying the manure storage twice a year. And that's where things get kind of hairy. So if you're emptying your manure storage once a year, and you're getting 74%, anaerobic digestion efficiency, then you might think, why would I build a heated storage if I'm only going to get 77%, 75% anaerobic digestion efficiency? Because it's warm here. So that's where it gets more complicated on whether you should have a covered manure storage or a heated digester. It depends where you're at in the country, depends the temperature, and it also depends on how often you're emptying that manure storage.

Dan Andersen  39:45

I think that's really great logic. And one of the things that I think we've seen a lot of is we've seen a fair amount of investment in covered lagoons in areas that have historically had lagoons, California, Missouri, North Carolina, and that's left the upper Midwest where we haven't used that type of manure storage, where we've been more a slurry storage or concrete basins, a little bit harder to implement a project. And, and it sort of makes sense. We built lagoons where you're saying that covered lagoon performance will be much better and, and we're covered lagoons wouldn't have been as effective within historically build lagoons, and that means we have to think a little bit different about how to put these systems together. But there are a lot of variables that come into play. And I think you mentioned a lot of key ones retention time, especially when you're not heating, more retention times good, we're never going to get to that 100% efficiency. But more time for microbial activity helps us get at least a greater percentage of that, that gas production. I think I only have a couple more questions here for you today. What do you think your biggest take home from analyzing the EPA dataset, that CARB model for how well a covered lagoon or a digester would perform? What did you learn from them?

Luke Soko  40:54

I think the biggest takeaway is that the CARB model, which you can download on the California Air Resources Board website, and it's called Tier One simplified CI calculator for Biomethane from Anaerobic Digestion of Dairy and Swine Manure, is a fair mechanism to estimate methane production. On one of the pages of that Excel spreadsheet, it will give you a total manure emissions value, and that value seems to be fairly by manure emissions, methane emissions from manure, it's going to give you a methane emissions value. And that value seems relatively close within the ballpark of what the EPA has. Now, another takeaway message is the EPA database needs more data. And it needs the best data, it can be everybody wants more data and better data, but with better data that we could provide a much better analysis of the EPA database. But for right now, it seems as though CARB has a fair estimate. And also, if you're moving, if you're in the southern part of the United States, a covered manure storage might be a thing that you should investigate. And if you have the ability to store large amounts of manure, and you want to put in a covered manure storage project, and then you should investigate emptying your manure storage less if you can. There are a lot of factors of how often can you empty manure storage that are much more important than just I'm trying to make more biogas for this project, but if you can empty less, then you, we see that you'll make more methane, you could make more money.

Dan Andersen  40:57

Yeah, and one thing we didn't get into detail about today, and we'll talk more about in the future is some of these economics, what does it cost to just cover manure storage versus having to go build a heated gigester. And that definitely has to play a large role in what a facility would ultimately choose. But looking at your facility, seeing what resources you have, what do I currently have for storage? Is this an option? Do I have to go to a digester? What makes me decide a digester is better for my operation, than covering that existing manure storage? Definitely important considerations. And I think you did a really nice job summarizing a lot of data for us to understand sort of what those efficiencies are. But a good rule of thumb, if you are thinking about a covered storage, you told us probably estimate about a 50% efficiency on digester efficiency of the amount of methane you could make. If we're leaning towards maybe one of those heated digesters, hopefully somewhere in the neighborhood of 75%, 77% efficient. So there is an efficiency gain to be had, and it's important to determine when that extra gas production would pay for a project or make a project more feasible.

Luke Soko  42:26

Yeah, and it's something I'd like to add as well as the cover manure storage project sounds very simple, you're covering the manure storage. But keep in mind, if you want to make LCFS credits and RIN credits, you need to inject renewable natural gas into the pipeline, or you need to be making renewable fuel currently. So that means that you're going to likely have to invest millions of dollars into a biogas upgrading system and some way to inject the natural gas into a pipeline. So both projects, it's not both projects will require significant capital investment, even though the covered manure storage project sounds much simpler than a heated digester. 

Dan Andersen  43:26

Perfect. I think that's a great, great spot for us to end, but it really is a component of a system. Right. We talked specifically about just the digester, but there's a lot more that goes into making these projects successful. Thanks for taking a little time to talk to us today, Luke.

Luke Soko  44:18

Absolutely, thank you.

Dan Andersen  44:22

Thank you for joining this installment of Talkin' Crap. Be sure to take a look at the show notes on our website for links and materials mentioned in the episode. For more information or to get in touch, go to our website, Iowa Manure Management Action Group, which you can find at www.extension.iastate.edu/immag/. If you found what you heard today useful, or it made you think we hope you'll subscribe to the show on your podcast app of choice, signing off from a job that sometimes smells, but never stinks, keep on talkin' crap.