National Hog Farmer March/April 2022
We take great pleasure in welcoming you to another digital edition of National Hog Farmer.
We take great pleasure in welcoming you to another digital edition of National Hog Farmer.
Every other month, we aim to bring the latest in market insight, swine research and pork production content to life — dynamically.
We will be doing so through a unique audience experience, with content packaged like print but with digital benefits such as video, podcasts, slideshows, animation and more. You also will have the opportunity to engage, share and download content.
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Your National Hog Farmer Team
Latest from Farm to Fork
Stonestreet addresses consumer misconceptions through Real Pork
By National Pork Board
More than half of pork producers rank promotion and telling the industry’s story as extremely important to the future success of the industry1. Real Pork is the industry’s trust and image brand differentiating pork from the alternatives. It is the identity of the industry, from farm to fork, that celebrates everything authentic about pork.
Coupled with Checkoff- funded consumer insights showing nearly 40% of consumers want to know more about where their meat comes from2, National Pork Board (NPB) is leveraging Real Pork to increase consumer confidence in pork and help protect producers’ freedom to operate.
The producer-led Real Pork Barriers Task Force set out to understand top consumer concerns and questions about pork production and found there is a spectrum of consumer myths, which could be barriers for consumers.
Stonestreet and Real Pork
Real Pork puts an emphasis on an emotional connection to pork and its ability to unite people through food. It is the answer for consumers who are questioning what they can trust within a cluttered food environment.Checkoff-funded consumer research indicated 25% of pork consumers are at risk of decreasing their pork consumption3, citing concerns around the health, safety and ethics of pig farming as their rationale.
NPB partnered with Emmy-award winning actor Eric Stonestreet as a credible spokesperson to address these misconceptions.
“Farmers are my people. Pig people are my people,” says Stonestreet in a Pork Checkoff online seminar in July 2021. “I knew when this came across my plate that it was an opportunity to re-tether myself to where it all started for me.”
Stonestreet, a Kansas native and former pig farmer, helped NPB launch the Real Pork Mythbusting campaign through a series of five videos and digital content that (re)define common pig-related idioms and phrases. For example, “pig-sty” may refer to a mess, but today’s pig barns follow significant biosecurity and cleanliness practices.
The campaign targeted consumers in urban areas with kids at home who prioritize criteria like health and sustainability in their food decisions. Research shows 48-54% of consumers are more favorable for the pork industry and 34-36% more likely to buy pork after viewing the content4.
Stonestreet participated in a media day during National Pork Month in October 2021, speaking with mainstream broadcast, print, radio and digital media about his passion for the pork industry, support for pig farmers and why he was compelled to participate in the campaign.
“Our personal story is very valuable, and we should be loud and proud about what we do,” says Rich Deaton, a NPB board member and producer from Ohio. “Having somebody outside of the industry say, ‘listen to these guys’ makes the impact exponentially bigger; I could not be more excited to have someone speak the truth.”
This landed positive coverage in outlets like People and Fox News. NPB tested two of the videos to see how people felt after viewing; more than 86% felt Stonestreet was a very effective spokesperson.
Scientific research from Pork Checkoff
The We Care® Ethical Principles ensure producers uphold the highest standards and constantly strive toward improvement. Real Pork brings the principles to life for consumers who want to know where their food comes from and show how pork is produced by a transparent, trustworthy and genuine industry.
"Pigs are crowded and mistreated," "producing pork is bad for the planet" and "producing pork is bad for society" are more specific and need evidence to address consumer concerns.
NPB partnered with state associations and used Checkoff funding to invest in scientific evidence and provide accurate information to decision-makers and the public.
This research is especially important since nearly 4 in 10 consumers who indicate they spend more on brands and products that are better for the environment5.
Two examples for Pork Checkoff-funded public health research include:
- NPB collaborated with researchers at the University of Minnesota to re-evaluate a widely cited 2018 study raising concerns about the public health impacts of pork production. The study is expected to be published in a peer-reviewed journal soon.
- NPB partnered with Michigan State University to develop a database of research on potential public health outcomes of live animal production allowing producers, researchers and the public access to this scientific information.
Two examples for Pork Checkoff-funded water quality research include:
- North Carolina State University conducted a fecal speciation study that identified the source species of fecal material present in water samples. In the past, fecal material was either present or absent without a tie to species contribution.
- In partnership with Northwater, an environmental and geosciences consulting firm, NPB used checkoff funds for a ground water study design. The design lays the groundwork for how to effectively study water quality around pig farms.
Real Pork is not a marketing campaign
Real Pork shows up differently, and allows producers, state associations and NPB to address consumers’ questions and concerns to build trust in pork production and add value by increasing affinity for pork.
Real Pork is the industry’s trust and image brand; Mythbusting, We Care and Checkoff-funded research are examples of Real Pork for consumers and decision makers. They exhibit how Real Pork is about Real Farmers who live on Real Farms raising Real Pigs to produce Real Pork that is Real Nutritious and Real Sustainable.
1. National Pork Board Annual Producer Survey, 2020
2. Pork Checkoff “At Home Meat Tracker,” Q2 2020
3. Pork Checkoff-funded Barriers Tracking Research, Consumer Online Poll, conducted by PSB, May 2021
4. Pork Checkoff-funded Barriers Tracking Research, Consumer Online Poll, conducted by PSB, September 2021
5. Pork Checkoff “At Home Meat Tracker,” Q3, 2021
Goes beyond good nutrition, takes team effort
By Ann Hess
From antibiotic resistance and environmental sustainability concerns, the pressure on the swine industry to go “antibiotic-free” has been continuous. However, before removing all antimicrobials from animal systems, Iowa State University Assistant Professor Laura Greiner says the industry needs to have better grasp on the cost and the impact of doing so.
“When we think about antibiotic-free programs, I think a lot of us have been very hesitant in the past. Myself, I know when I've worked with producers who took antibiotics out of the nursery, I've seen a reduced growth rate by about a kilo over a six-week period of time,” Greiner says. “When we listened to some other people talk in the past, we've heard estimates of $5 to $11 loss per pig.”
Changing or removing a technology can also create additional challenges. In a nursery, this could mean issues with diarrhea, infection, decrease in production weight, reduced water and feed consumption, and susceptibility to stress and disease, and all will most likely involve additional diet reformulations.
For diarrhea alone, Greiner says she would be looking at possibly adding prebiotics or probiotics, adjusting ingredients to use different fiber sources such as oats or rice hulls, changing the lactose percentage or working with zinc, copper or organic acids.
“This is not an all-inclusive list, but as nutritionists, these are the first things we're going to run to and start thinking about if somebody approaches us,” Greiner says.
Adjusting diets isn’t the only solution though for addressing herd health chaIlenges in ABF production. Greiner suggests the industry needs to start thinking more outside the box, “first about genetic selection of parents that have high survivability rates in the expected environment that we're placing them in.”
“We're looking for immunological diversity and function, so this is not nutrition, but this is selecting the animal that is going to be more appropriate for the environment that we're putting them in, and we need to understand the maternal influence to disease management,” Greiner says.
In researched funded by the Iowa Pork Producers Association, Greiner and associates are examining the microbiome differences between gilts and sows, knowing that piglets that come from gilt litters generally have a higher mortality rate and are more susceptible to disease. One of the things they have discovered is a shift in an organism called, "Clostridium Sensu Stricto 1."
“What's interesting about this organism is that we find that pigs that are born as IUGR (intra-uterine growth retardation) pigs, they have a decreased level of Clostridium Sensu Stricto 1, and they actually have reduced harvest weights,” Greiner says. “If we look at some of the data that we have, we can see that in gilts, we have a lower level of Clostridium Sensu Stricto 1. So, does that mean that's part of the reason why our piglets that come from those litters are slower growing and not as thrifty by the time they get to market?”
Another organism to consider is "Ruminococcus 2," Greiner says. Research at the University of Minnesota has shown that if animals have a higher level of Ruminococcus 2 in their gut, they have reduced lung lesions when they are exposed to Mycoplasma Hyopneumoniae.
In the research that Greiner and her team at Iowa State are doing, they also found that the gilts actually had a higher level of Ruminococcus 2. While the herd was going through a mycoplasma break at the time, the naive animals did have a higher level, indicating a higher rate of protection.
“We might need to go farther back in the animal to prepare ourselves to run an antibiotic-free program, back to this, with practices in the field,” Greiner says.
Have you previously worked with or are currently working with swine being raised without antibiotics?
- Yes, currently
- Yes, in the past
- No, only conventional
It’s the practices and the players involved that are needed to make a robust, thriving ABF or no antibiotics ever program, says Steve Kitt, swine nutritionist with First Choice Livestock.
“It can’t just be hung on the veterinarian or a nutritionist,” Kitt says. “When these tools that get taken away from us, really the people in the barns taking care of pigs, making sure ventilation's right, feed's right, water delivery, and caretaking of the animals is a big piece of that program.”
Kitt echoes Greiner’s sentiment in understanding the cost and value of NAE/ABF production before implementing.
“Which of these are fads versus here to stay, because if we go spend a lot of time on research, and those sorts of things, is all of that for naught in five years and has the consumer changed their mind?” Kitt says. “As tools are taken away for programs such as NAE and ABF, but it could be lack of zinc oxide, we have to understand the cost of production.”
Kitt cites Aaron Gaines’s presentation at a recent Allen D. Leman Swine Conference, where he estimated 14 to 21% increased COP with a NAE or ABF program. COP comparisons that need to be considered include weaned pig cost, geography and associated transport cost, space cost, burden on other production, staffing needs, milling/feed costs, vaccine and medication costs, as well as the percentage of animals not marketed in the program.
Kitt says producers also tend to take their best flows, growers, people and turn it into NAE production, which is likely to make the conventional portion of their business ( the majority) less successful, and to it’s important not to misinterpret results that might be an effect of people versus lack of antibiotics.
Health and hygiene
While the focus is often on gut health when removing antibiotics from a system, Kitt questions if respiratory health should be given more weight, especially with porcine reproductive and respiratory being a major issue.
He also thinks more research needs to be done with biofilms and how they can be impacted by detergent, temperature and washing time.
Kitt points to one case study early in his career, with brand new nurseries and the exact same pig flows and barns.
Over time however they started seeing an extreme uptick in mortality. The ultimate solution ended up being an industrial detergent that could take down the biofilm.
Another hygiene area in the barn is the use of hydrated lime, not limestone, for an effective whitewash program. For good disinfection, Kitt says it’s important to have the right chemical.
Both Kitt and Greiner agree successfully going to a sustainable, cost-productive ABF or NAE system, involves many stakeholders.
“We have to learn that one size does not fit all, and we need to recognize that this is going to be a concerted effort with the veterinarians, nutritionists, production managers and caregivers,” Greiner says.
“It’s going take more than nutritionists and veterinarians to meet the needs of what we're being asked to do with less tools in our toolbox, and clearly management is going to play a big role in that I believe,” Kitt says.
Greiner and Kitt were part of a panel discussion along with Ben Keeble, vice-president of U.S. Production, Sunterra Farms, at the 2020 International Conference on Swine Nutrition.
Raise the profile of your new/redesigned product for the hog industry. Join the 2022 New Product Tour and showcase your product at the Global Hog Industry Virtual Conference.
To light or not to light
Advancing the potential of UV light for the swine industry
By Peiyang Li, Jacek Koziel, Jeffrey Zimmerman, Jianqiang Zhang and William Jenks
Ultraviolet (UV) light is invisible yet ubiquitous in our daily life. UV light has a shorter wavelength than visible light, so it is more energetic and can be used for germicidal purposes. The sun is a natural source of UV light. Artificial UV sources come from different types of UV lamps (e.g., mercury bulbs).
Generally, UV is categorized into four wavelength ranges:
- vacuum UV (VUV), 100-200 nm
- UV C (UV-C), 200-280 nm
- UV B (UV-B), 280-315 nm
- UV A (UV-A), 315-400 nm
UV-C light, often referred to as the germicidal wavelength, can be absorbed by nucleic acids and proteins to cause damage. It has been found effective for disinfection in various areas, such as drinking water disinfection, air disinfection and medical applications.
The commercially available, inexpensive UV-C mercury lamps have a peak at around 254 nm. In recent years, there have been some developments in costly far-UVC excimer lamps (207 – 222 nm), which are germicidal while at the same time claiming to be harmless to mammalian skin and eyes.
UV-C LED products are also commercially available. They have a much longer lifespan and energy-saving while the cost is much higher than mercury bulbs.
However, UV-C light cannot penetrate through standard glass or non-transparent materials. Its irradiation also reduces significantly as distance from the UV source increases (Figure 1).
Figure 1. UV light irradiance (I) decreases proportionally to the inverse square of the distance (d) between the lamp and the target.
Currently, the UV applications in swine farms are mostly pass-through chambers for the decontamination of items (shipment deliveries, lunch boxes, small tools) that cross the biosecurity line.
There is a potential to expand the UV-C application to air treatment in the future to mitigate airborne transmission of diseases.
Maintaining good, common-sense safety practices is essential while using UV light. That means, avoiding direct exposure of skin and eyes to UV and wearing protective gear such as UV safety goggles, UV face shields and proper clothing under direct irradiation.
The information above is documented in a white paper funded by Swine Health Information Center (SHIC) and was peer-reviewed and published recently.
Porcine reproductive and respiratory syndrome (PRRS) has been one of the most economically impactful diseases for the pork industry. Properly treating the barn inlet air can mitigate the spread of airborne PRRS virus (PRRSV) from one barn to another.
In a recent project funded by the National Pork Board (NPB #18-160, PI: Dr. Koziel) (Paper 1, Paper 2), we tested the effectiveness of UV in inactivating aerosolized PRRSV, specifically with UV-A (365 nm), ‘excimer’ UV-C (222 nm), and conventional germicidal UV-C (254 nm) lamps in a laboratory setup (Figure 2 and 3).
Figure 2. A lab-scale setup of UV treatment on aerosolized PRRSV in fast-moving air. UV doses were estimated to inactivate PRRSV with different types of UV lamps.
The key advancement was the testing of a recently developed excimer UV-C light (222 nm) that is less harmful to people and livestock while germicidal for MSRA and the H1N1 influenza virus.
This research bridged the knowledge gap by comparing UV treatment effectiveness of three wavelengths (222, 254, 365 nm).
We quantified the surviving PRRSV titer after UV irradiation and estimated the UV-C dose to inactivate PRRSV in fast-moving air. We found that UV-C (254 & 222 nm) lamps are very effective at inactivating PRRSV aerosols with short treatment times (<2 s).
Scaling up research on UV-C treatment of aerosolized pathogens is warranted based on its effectiveness and reasonable costs compared to HEPA filtration.
The indoor air quality became an important part of mitigating the outbreak of the COVID-19 pandemic.
UV-C can play a significant role in the decontamination and disinfection of air and surfaces in public areas. However, UV agricultural applications are still limited.
We are currently collaborating with Kryton Engineered Metals Inc. (Cedar Falls, Iowa) and CIRAS of ISU on advancing UV treatment for large indoor spaces.
We upgraded an existing air purification scalable prototype, FastAir (~2,200 CFM), with the addition of UV-C light that can treat indoor air and maintain a healthy environment.
The prototype has been tested in animal production facilities, and data such as particulate matter concentration and airborne pathogens are collected.
Current data showed that the prototype could mitigate the airborne particulate matter (PM1, PM2.5, PM4, and PM10) and almost 100% of airborne pathogens between inlet and outlet. Its long-term, continuous effect on indoor air quality is being tested.
We believe that this research will be beneficial to industrial applications (air cleaning on manufacturer floors, etc.) and also to animal production facilities where UV treatment may be useful for mitigating the transmission of airborne pathogens.
Figure 3. The FastAir (Kryton Engineered Metals Inc.) was upgraded with UV light.
We established collaboration with a major UV lamp manufacturer to scale up the work of UV-C to application in swine housing.
Li is a graduate research assistant; Koziel is a professor in the Department of Agricultural and Biosystems Engineering department; Zimmerman is a professor and Zhang is an associate professor, both in the College of Veterinary Medicine; and Jenks is a professor in the Department of Chemistry, all at Iowa State University.
Lessons learned from unexpected
M. hyopneumoniae PCR results
How can we do better?
By Albert Canturri and Maria Pieters
Accurate diagnostics are the cornerstone in which disease prevention and control interventions lay on. Every diagnostic investigation should start with two simple questions: "what information do I need to obtain?" and "how will I interpret and use the obtained information?"
For the first question, producers and practitioners in the field most likely seek to determine the presence or absence of a pathogen of interest in a sample, whether it is a clinical specimen from individual pigs, aggregated samples, such as oral fluids, or even environmental samples.
In the case of Mycoplasma hyopneumoniae, the intrinsic difficulty of this pathogen to grow in bacterial culture dampens its use for routine diagnostics. Thus, the most practical tool that diagnosticians have in their hands to investigate the presence of M. hyopneumoniae in a sample is polymerase chain reaction (PCR), which targets and amplifies the DNA present in a sample and gives an approximation of bacterial quantity.
For the second question mentioned above, it is generally understood that techniques based on PCR are widely used in swine disease diagnostics, mainly due to their high sensitivity and specificity, and their cost-benefit advantage over other tests.
However, current PCR testing for M. hyopneumoniae is far from perfect and possesses important features that need to be taken into consideration, as interpretation of the obtained results can be challenging at times.
One example of the latter has been the recent detection of unexpected positive results in non-traditional sample types, such as the processing fluids (PF)1.
Detection of M. hyopneumoniae in PF was an unforeseen result since the pathogen is thought to be restricted to the respiratory system. Researchers and practitioners were therefore puzzled and were set up to figure out this perplexing finding by expanding the sampling in farms with different health status and management conditions for an extended period.
Results from such studies study showed that M. hyopneumoniae was consistently detected in PF in positive farms and that, at least in part, the origin of the detected genetic material could be traced down to vaccine products, which clearly illustrates that environmental contamination of samples is not to be ignored.
Indeed, a study2 presented at the most recent Allen D. Leman Conference (2021) reinforced the importance of this issue, showing that post-vaccination environmental contamination of samples was possible even with tracheal secretion swabs, the preferred sample type for ante mortem detection of M. hyopneumoniae.
These two above-mentioned diagnostic challenges recently experienced emphasize that, for an appropriate interpretation of M. hyopneumoniae PCR results, producers, practitioners and caretakers collecting samples in the farm should center their efforts at minimizing the chances of pre-analytical error, that is, all the procedures that occur before the sample arrives at the laboratory for testing.
A meticulous sampling methodology should be exercised, paying special attention to details. For example, it is good practice to differentiate between a clean and a dirty zone in the cart or the surface in which tubes and catheters or swabs are placed, both before and after sampling. Sampling materials, such as mouth speculums or laryngoscopes should be cleaned and disinfected between sampled pigs, and gloves should be changed often.
These measures should be maximized in high-risk scenarios, such as in the monitoring of gilts for introduction into a naïve herd, especially when gilts have been vaccinated prior to sampling at the gilt development unit (GDU). It is important to clarify that vaccinated pigs will not result positive to M. hyopneumoniae by PCR due to inoculation with bacterins, however, vaccines can be unintentionally sprayed into the surroundings and become a source for environmental contamination.
Additionally, farm management practices should be considered when implementing measures to minimize risks of environmental contamination. For example, there is a hypothetical risk that farm personnel who vaccinate pigs at weaning carry vaccine-derived genetic material on their hands and coveralls, and cross-contamination can eventually occur when they handle piglets at processing or when aid at restraining gilts and sows for tracheal testing in gestation or farrowing.
In summary, nucleic acid detection of M. hyopneumoniae by PCR testing is a great diagnostic technique because of its extremely high sensitivity of detection. Nevertheless, because of the same reason, care should be taken when collecting, handling and transporting samples to the laboratories, always aiming at minimizing both cross- and environmental contamination.
1. Vilalta C, Sanhueza JM, Murray D, Johnson L, Pieters M. Detection of Mycoplasma hyopneumoniae in piglet processing fluids. Vet Rec. 2019 Oct 26;185(16):510. doi: 10.1136/vr.105475. Epub 2019 Aug 13.
2. Hensch M, Kellen M, Maschhoff A, Gauger P. Diagnostic problems with unexpected positive PCRs. 2021 Allen D. Leman Swine Conference Proceedings, Saint Paul, Minnesota, USA.
Canturri is a graduate student and Pieters is an associate professor, both in the Department of Veterinary Population Medicine at the University of Minnesota.
Solar sludge drying
North Carolina solar energy powers nationwide distribution of hog manure nutrients
By Mahmoud Sharara, Christopher Hopkins, Sanjay Shah and Joseph Stuckey
Lagoons are critical to swine production in North Carolina as they provide cost-effective manure storage and treatment. The temperate climate in the southeastern United States keeps the microbial communities active and improves manure digestibility. Over years of operation, however, lagoons accumulate a solids residue, known as sludge (Figure 1), which cannot be further digested.
On average, sludge accumulates in the lagoon at an annual rate of 0.36 gallons per pound of live animal weight2. This means that for a 3,000-head finishing farm, around 145,800 gallons of sludge accumulates in the lagoon annually. If left in the lagoon, the sludge reduces the treatment capacity of the lagoon leading to higher odor emissions, and increases risk of lagoon failure under extreme rainfall events.
The North Carolina Department of Environmental Quality (NCDEQ) requires that sludge removal to maintain at least 50% of the lagoon treatment volume sludge-free at all times.
Figure 1. Cross-view of anaerobic manure treatment lagoon.
Sludge, unlike manure, contains a high concentration of minerals relative to nitrogen (Table 1). As a result, sludge requires more acres for land application to avoid over-application of phosphorus (P), zinc (Zn), and copper (Cu).
Today, many swine producers are facing a challenge finding acres that can accept and beneficially utilize sludge nutrients. The high density of hogs and poultry production across North Carolina, and the reliance on feed imports, has led to regional nutrient accumulation. A recent study by ARS researchers3 identified the Carolinas among the largest sources of manure P in the continental United States that can benefit from a wider distribution of nutrients. For North Carolina hog producers, identifying a cost-effective technology to concentrating sludge nutrients and allow export is a priority.
Why dry sludge?
To remove sludge, lagoons are typically agitated to suspend sludge solids before the slurry is loaded into spreaders for land application.
More recently, growers resorted to sludge dredging and dewatering using on-site permeable bags (Figure 2).
Figure 2. Dewatering bags with swine lagoon sludge (at 20% solids) on a North Carolina hog farm.
This approach was adopted to concentrate the sludge and make it more transportable. For comparison, the agitation approach removes sludge at 6% solids, compared to 20% solids with dewatering.
Even with after dewatering, finding suitable land base for the dewatered sludge remained a challenge, in addition to the cost involved in the dewatering step. Hence, drying offers a great opportunity to concentrate nutrients and create a product that is easy to store, transport and apply using existing equipment.
Through funding from the NC Department of Agriculture and Consumer Services - Bioenergy Research Initiative (BRI) and Smithfield Foods, we set out to investigate opportunities for sludge removing, drying and utilizing sludge as a renewable nutrients and energy source.
Table 1. Typical nutrient content in fresh swine manure, lagoon liquid, and lagoon sludge in pounds per 1,000 gallon (not-for-use as planning guide).
a: Chastain, J.P.; Camberato, J.J.; Albrecht, J.E.; Adam, J. Swine Manure Production and Nutrient Content; South Carolina Confined Animal Manure Managers Certification Program; Clemson University: Clemson, SC, USA, 1999; Chapter 3; pp. 1–17.
b: Manure Nutrient Content, Nutrient Management in North Carolina – NC State University guide. Online at: https://nutrientmanagement.wordpress.ncsu.edu/
c: NCDA&CS Agronomics Laboratory, swine lagoon supernatant samples submitted between 2010 and 2019/
d: Sharara, M and Owusu-Twum, 2020, Sludge Sampling in Anaerobic Treatment Swine Lagoons (Factsheet). NC Extension Factsheet. Online at: https://content.ces.ncsu.edu/sludge-sampling-in-anaerobic-treatment-swine-lagoons
Industrial drying is commonly used to handle sludge in municipal wastewater treatment plants, particularly in large metropolitan districts.
We evaluated four commercial systems currently in use in municipal sludge drying, using technologies such as rotary drums (Option 1), steam moving beds (Option 2), belt drying (Option 3), and high-velocity cyclones (Option 4).
We used a one dry ton of sludge (1 ton at 10% moisture content) as the basis for comparing the cost of the drying technologies, with an annual throughput of 20,000 dry tons for each system. Such a scale is common for these technologies and often provide economy of scale to the drying and processing.
The first barrier we identified is the logistical planning and cost involved in aggregating sludge to satisfy the system capacity. The typical scale for such dryers makes them too large for a single farm or a small cluster of farms. On the other hand, aggregating wet sludge involves significant hauling cost and increases the risk of spill during transportation.
The second barrier we identified is the significant energy cost involved in producing a dry sludge product (Figure 3). The energy inputs, both heat and electricity, represent between 35% and 50% of the cost of drying. Due to these barriers, we began investigating the use of low-input drying technologies such as ambient air-drying and solar drying.
Figure 3. Sludge drying cost using different technology options at a 20,000 ton/year capacity. The cost estimates include share of capital cost (CAPEX), labor, and energy needs (heat, and electricity).
Solar drying opportunities
Solar energy is an abundant resource particularly in the south and southeastern United States. In North Carolina, solar radiation provides between 4.5 and 5 kWh of energy per square meter per day (equivalent to 1.4 to 1.6 MMBtu/sq.ft.-day)4. This resource is already being harnessed by the solar energy sector across North Carolina, less so in thermal applications such as drying.
Open-air drying is the lowest cost option but not suitable for the Southeastern United States due to high rainfall; year-round rainfall that averages 48 inches in Eastern North Carolina where hog production is clustered. As a result, we adopted greenhouse designs to both utilize solar energy and avoid rainfall interference. We conducted preliminary studies to quantify the rate of sludge drying for swine lagoon sludge in greenhouse structures.
For the first tests, we utilized a greenhouse system on NC State University campus (Figure 4) to dry freshly dredged lagoon sludge. The sludge was dredged from the on-campus swine unit and were introduced to the greenhouse at an initial solid content (TS) of 7.9%.
Two tests were conducted during summer 2021 utilizing two loading rates: 2.85 lb. and 5.80 lb. of sludge per square foot.
During both tests, we observed a daily drying rate between 1.1 and 1.2 pounds of water removed per square foot.
Under the high loading rate, the sludge reached 91% total solid content after 102 hours. The dried product N: P2O5: K2O equivalent to 5: 15: 1, with 72 pounds of N, 229 pounds of P2O5, and 14.5 pounds of K2O per dry ton.
Figure 4. Greenhouse drying structure on NC State University campus (left) and drying a thin-layer (0.5-inch) of dredged sludge in the greenhouse (right).
In summer 2021, Smithfield Foods built two greenhouse-drying units in Duplin County, North Carolina (Figure 5). The long axis of these greenhouses are east-west. These units (5,000-sq.ft area each) will be used to dry on-site dewatered sludge currently in geobags as well as off-site material.
Our team was funded by the Virginia Pork Council to collect yearlong data on the performance of this technology and identify opportunities to improve its performance.
Figure 5. Solar drying greenhouses for lagoon sludge in Duplin County, North Carolina.
The greenhouses are operated as deep bed drying units with a loading rate of 34 pounds of sludge per square foot. The sludge is loaded into greenhouses at a total solid of 20%.
The material is regularly turned using a tiller to avoid crusting which was observed to slow drying.
The greenhouse ventilation is managed using a controller equipped with temperature and humidity sensors inside and outside both greenhouses.
A key priority is avoiding operating the ventilation system during high humidity conditions in the summer and during rainfall events. Our team started the data collection/monitoring during winter 2021.
We observed significant heat gain during winter due to the greenhouse effect (Figure 6). This thermal gain has a dual benefit of increasing the rate of drying as well as deactivating any remaining fecal communities in the sludge to ensure safe handling and use.
During December-January 2022, the daily rate of drying was between 0.5 and 0.6 pounds of water removed per square foot, requiring 40 days to reach desired total solid concentration.
The seasonality of solar radiation and temperatures play a large role in the observed rate of drying in these systems. We plan to continue comparative evaluation of solar drying on thin-layer and deep-bed sludge under different weather conditions to develop management recommendations.
Figure 6. IR image of solar drying greenhouse showing temperatures between 9 and 25.7°C (48 to 78°F) with outside air temperatures at 5.2°C (41.4°F).
A key question is how the economics of solar drying compare to industrial dryers discussed earlier. To answer this question, we utilized data collected so far from solar greenhouse drying (during winter 2022) and compared it to commercial-scale systems reviewed earlier.
Using one ton dried sludge as a comparison basis, the energy consumption associated with industrial drying ranged from $49.3 and $69.2 per ton. By comparison, the energy expenditure for solar drying ranged between $9.4 and $11.9 per ton of dried sludge.
Energy consumption for solar drying is primarily associated with ventilation power consumption. We are currently working to complete a year-round performance assessment of solar greenhouse sludge drying and compare it to the systems reviewed earlier.
Using winter drying performance as basis for comparison shows that solar drying energy cost is 18% to 22% of the cost associated with the most energy-efficient industrial dryer. In addition, reducing energy consumption by adopting solar drying also lowers greenhouse gas (GHG) emissions, which aligns with the priorities of the hog industry nationwide.
The team is continuing to study these systems to improve drying performance, reduce energy use and identify value-added uses for dried products using post-processing technologies such as pelleting and formulating the dried product with other nutrients. These technologies could be centralized once sufficient farms adopt the concept of sludge drying.
Interest by industry groups in this technology and the entrance of commercial developers that are already installing sludge drying systems5 indicate the need for such technology and its fit with North Carolina hog production context.
This move is projected to greatly improve manure nutrient use and increase the sustainability of hog production in the United States.
1. US Department of Agriculture, Natural Resources Conservation Service (USDA-NRCS), Agricultural Waste Management System Component (Chapter 10), in Part 651 – Agricultural Waste Management Field Handbook. Available online here.
2. Bicudo, J. R., Safley Jr, L. M., & Westerman, P. W. (1999). Nutrient content and sludge volumes in single-cell recycle anaerobic swine lagoons in North Carolina. Transactions of the ASAE, 42(4), 1087.
3. Spiegal, S., Kleinman, P. J., Endale, D. M., Bryant, R. B., Dell, C., Goslee, S., ... & Yang, Q. (2020). Manuresheds: Advancing nutrient recycling in US agriculture. Agricultural Systems, 182, 102813.
4. National Renewable Energy Laboratory (NREL), Department of Energy (DOE), Solar Resource Maps and Data: Global Horizontal Irradiance. Available online here.
5. [Press Release] Could NC Export Poop For Profit? Crop and Soil Sciences News - February 9, 2022.
Sharara is an assistant professor and Extension specialist and Shah is a professor and Extension specialist, both in the Biological and Agricultural Engineering Department; Hopkins is a research associate in the Department of Forest Biomaterials, College of Natural Resources; and Stuckey is a research operations manager at the Animal Poultry Waste Management Processing Facility, Prestage Department of Poultry Science; all with North Carolina State University.