Tag: hydrogen sulfide

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Short-term bio-electrochemical pretreatment of dairy manure for efficient sulfide remediation prior to anaerobic digestion

Purpose

According to the latest estimation of Food and Agriculture Organization of the United Nations, the global dairy cattle stocks reached over 265 million in 2019. The massive stocks of dairy cows excrete an enormous amount of manure, which is a huge burden to the environment if unproperly disposed of, thus necessitating proper manure treatment. As such, anaerobic digestion (AD) has been widely adopted as a practice to manage dairy cattle manure. Within the United States, digesters at dairy farms started to be widely constructed after 2000, and the number of these on-farm digesters in operation or under construction has increased to over 400 in 2024. During the AD treatment of dairy manure, the sulfate-reducing microorganisms are active under anaerobic conditions, therefore high levels of hydrogen sulfide (H₂S) are common in biogas because of the degradation and conversion of sulfur-bearing organics in feeding materials and sulfate-bearing minerals in bedding materials within the manure stream. As an extremely toxic gas with an acute rotten egg odor, H₂S is one of the leading causes of workplace gas inhalation deaths in the US according to the Bureau of Labor Statistics. In addition to the health risks, high H₂S levels can be also very corrosive to the equipment and infrastructure: long-term exposure to concentration of H₂S greater than 1 ppm reduces the lifespan of structural materials, equipment, and electronic devices inside the facilities. Therefore, it is an urgent task to mitigate the H₂S emissions in manure management.

Conventional H₂S removal technologies typically include two categories, namely ex-situ and in-situ. The ex-situ biogas cleaning technologies (e.g., biofilters, aqueous solutions, iron sponge, etc.) require a separate unit to house the facilities and are chemical- and energy-intensive. In-situ H₂S mitigation methods usually require less energy and chemical input as well as an easier operation. In our previous study which employed bio-electrochemical (BEC) treatment concurrently with AD of dairy manure, a H₂S removal efficiency of over 95% was successfully achieved, thus offering a very promising in-situ H₂S remediation method. Nonetheless, it was operated in a continuous mode with electrodes inserted into the digester, which would require significant modification of existing AD systems when scaled up. Therefore, developing new strategies that can advance the application of BEC H₂S remediation within the conventional AD system is critical.

What Did We Do?

Most large sized farms collect liquid manure and slurry in a reception pit (or transition pit) before manure is pumped to the anaerobic digesters. This pit is usually open to the air, thereby offering a great opportunity to integrate the BEC treatment in dairy manure management. In the present lab-scale study, a BEC unit was applied to pretreat the dairy manure collected from the transition pit. On the basis of our previous study, a combination of low carbon steel (LCS) anode and stainless-steel cathode was selected as the electrode pair. At the applied voltages of 1.0-2.5 V, the dairy manure was pretreated for 24 hours prior to AD tests. After the BEC pretreatment, the peak H₂S concentration in the biogas was reduced from approximately 6,000 ppm (in the control without BEC pretreatment) to below 420 ppm in the groups at the applied voltages over 1.5 V. The total H₂S removal efficiencies reached 48.9%, 89.1%, 98.5%, and 100% at 1.0 V, 1.5 V, 2.0 V, and 2.5 V, respectively, equivalent to the sulfide removal of 18.6, 33.4, 36.9, and 37.4 mg S²⁻/g wet dairy manure. Nonetheless, higher voltages did not trigger higher biogas production. Besides, due to the anodic oxidation that released some CO₂ and the precipitation of carbonate (e.g., CaCO₃) in BEC pretreatment, the CH₄ contents in the yielded biogas from BEC groups (64.5-65.6%) were all slightly higher than that from the control (63.4%). Moreover, it was noteworthy that the technical digestion time (T80) (i.e., the time needed to produce 80% of the maximal digester gas production) was shortened to 28.0-29.3 d in the BEC groups at 1.5-2.5 V as compared to 32.8 d in the control. This suggests that the BEC pretreatment can remarkably accelerate biogas production in addition to the H₂S remediation. Groups using non-sacrificial electrodes (e.g., graphite sheets and rods) were also established for the 24-h BEC pretreatment of dairy manure. However, in subsequent AD tests, a large quantity of gaseous H₂S was still emitted. The comparison between the groups with and without sacrificial LCS anodes indicates that the formation of insoluble ferrous sulfide (FeS) was the main route of sulfide removal, whereas the contribution of anodic sulfide oxidation to sulfate and elemental sulfur was relatively limited.

With all the selections and optimizations above, a pilot-scale electrochemical unit was accordingly designed and then installed and operated in the dairy manure pit in a local dairy farm in Minnesota for over two months (as shown in Fig. 1), and its effects in in-situ H₂S remediation in a real application scenario were documented. This pilot-scale BEC system reduced the headspace H₂S level from 1,808 ppb to 390 ppb with a removal efficiency of 78.4%.

Fig. 1 Pilot-scale BEC system installation and operation in dairy manure transition pit
Fig. 1 Pilot-scale BEC system installation and operation in dairy manure transition pit

What Have We Learned?

This lab-scale success as well as the pilot-scale implementation supports BEC as a promising method for integration into existing on-farm AD systems treating dairy manure. With its incorporation of a BEC unit into the open-air manure transition pit, the operation could be simplified to a large extent without the considerable modification of existing AD systems, whilst the H₂S remediation and the improvement in biogas production (in both CH₄ content and technical digestion time) could be simultaneously achieved at an optimum applied voltage. In summary, this proposed BEC system can successfully reduce the H₂S and improve the safety of a dairy farm during manure storage and treatment.

Future Plans

In our future research, we will further assess the sulfur distribution and microbial community changes after both lab-scale and pilot-scale BEC treatment and also optimize the BEC strategy to reduce anode consumption. Besides, a techno-economic analysis and a life cycle assessment are now under evaluation, based on the data obtained through both the lab-scale tests and the pilot-scale demonstration, to further explore the feasibility and applicability of a full-scale BEC system in a real dairy farm scenario.

Authors

Presenting author

Lingkan Ding, Researcher Pro 5, University of Minnesota

Corresponding author

Bo Hu, Professor, University of Minnesota, bhu@umn.edu

Acknowledgements

The authors greatly appreciate funding support from USDA NRCS Conservation Innovation Grant (NR213A750013G029) and the assistance of Dennis Haubenschild for on-site work on the farm.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7-11, 2025. URL of this page. Accessed on: today’s date. 

 

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Emission of ammonia, hydrogen sulfide, and greenhouse gases following application of aluminum sulfate to beef feedlot surfaces

Purpose

Alum has been successfully used in the poultry industry to lower ammonia (NH3) emission from the barns. However, it has not been evaluated to reduce NH3 on beef feedlot surfaces. Additionally, it is not known how it would affect other common emissions from beef feedlot surfaces. The purpose of this study was to determine the effect of adding aluminum sulfate to beef feedlot surfaces on NH3, hydrogen sulfide (H2S), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions.

What Did We Do?

Eight feedlot pens (30 animals per pen) at the U.S. Meat Animal Research Center feedlot were utilized. The pens had a central mound constructed on manure and soil and 3 m concrete apron by the feed bunk and cattle were fed a corn-silage based diet. Four pens (30 cattle/pen) had 10% (g g-1) alum applied to the 6 meters immediately behind the concrete bunk apron and four did not receive alum. The amount of alum added to the area was determined on a mass basis for a depth of 5 cm of feedlot surface material (FSM) using the estimated density of feedlot surface material for Nebraska feedlots (1.5 g cm−3). On sampling days, six representative grab samples were collected from the feedlot surface from the six-meter area behind the bunk apron in each pen; samples were combined within pen to make three representative replicates per pen (N=24). Each of the three pooled samples per pen were measured for pH, NH3, H2S, CH4, CO2, and N2O using petri dishes and wind tunnels in an environmental chamber at an ambient temperature of 25°C (77°F) and 50% relative humidity. Flux measurements for NH3, H2S, CH4, CO2, and N2O flux were measured for 15 minutes using Thermo Fisher Scientific 17i, 450i, 55i, 410iQ, and 46i gas analysis instruments, respectively. Samples were analyzed at day -1, 0, 5, 7, 12, 14, 19, 21, and 26.

What Have We Learned?

Addition of alum lowered pH of FSM from 8.3 to 4.8 (p < 0.01) and the pH remained lower in alum-treated pens for 26 days (p < 0.01). Although the pH remained low, NH3 flux was only lower (p < 0.01) at day 0 and day 5 for alum-treated pens compared to the pens with no alum treatment. Nitrous oxide emission was not affected by alum treatment (6.2 vs 5.7 mg m-2 min-1, respectively for 0 and 10% alum treated pens). Carbon dioxide emission was lower for alum-treated pens than non-treated pens from day 5 until the end of the study (p < 0.05), perhaps due to suppressed microbial activity from the lower pH. Hydrogen sulfide emission was higher (p < 0.05) from alum-treated feedlot surface material (0.8 mg m-2 min-1) compared to non-treated feedlot surface material (0.3 mg m-2 min-1), likely due to addition of sulfate with alum. Methane emission was also higher in alum-treated pens (173.6 mg m-2 min-1) than non-treated pens (81.4 mg m-2 min-1). The limited reduction in NH3, along with increased H2S and CH4 emission from the FSM indicates that alum is not a suitable amendment to reduce emissions from beef feedlot surfaces.

Table 1. pH, ammonia (NH3), hydrogen sulfide (H2S), methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) emission from feedlot surface material treated with 0 or 10% alum (g g-1 mass basis).
pH NH3
(mg m-2 min-1)		 H2S
(mg m-2 min-1)		 CH4
(mg m-2 min-1)		 CO2
(mg m-2 min-1)		 N2O
(mg m-2 min-1)
Day 0% Alum 10% Alum 0% Alum 10% Alum 0% Alum 10% Alum 0% Alum 10% Alum 0% Alum 10% Alum 0% Alum 10% Alum
-1 8.1 8.3 229.6d 515.9c 0.3 0.4 136.3 x 73.4w 4,542 3,234 3.1 4.2
0 8.3a 4.8b 163.0c 32.4d 0.2 f 1.8 e 43.1 x 193.8w 4,372 5,294 2.9 1.8
5 8.5a 6.3b 279.5c 83.6d 0.4 0.5 84.1 x 309.5w 404y 1,347z 6.0 6.8
7 8.6a 6.7b 120.2 130.0 0.6 f 1.2e 53.4 61.7 468 y 1,903z 15.3 10.9
12 8.6a 7.2b 418.0 320.3 0.3 0.3 104.5 145.7 3,742y 1,939z 3.3 8.0
14 8.9a 7.6b 229.0 145.5 0.2 0.4 25.4x 180.7w 4,203y 2,018z 11.5 9.3
19 8.6a 7.5b 228.0 225.1 0.1 f 1.1e 132.3x 254.7w 5,999y 3,116z 6.9 5.8
21 8.4a 7.2b 232.0 257.0 0.5 0.8 81.9x 250.0w 4,324y 2,477z 2.2 1.9
26 8.6a 8.0b 584.5c 319.9d 0.1f 0.7e 72.2 92.9 5,534y 3,540z 4.7 2.9
Within a parameter and day, different superscripts indicate a significant difference (p < 0.05) between the emissions from the feedlot surface material treated with 0% and 10% alum.

Future Plans

Future research will evaluate the use of aluminum chloride instead of aluminum sulfate to lower pH of FSM and retain nitrogen. Additionally, microbial amendments are being evaluated to determine if they can reduce gaseous emissions from the feedlot surface.

Authors

Presenting author

Mindy J. Spiehs, Research Animal Scientists, USDA ARS Meat Animal Research Center

Corresponding author

Bryan L. Woodbury, Agricultural Engineer, USDA ARS Meat Animal Research Center

Corresponding author email address

bryan.woodbury@usda.gov

Additional Information

For additional information about the use of alum as a feedlot surface amendment, readers are direct to the following: Effects of using aluminum sulfate (alum) as a surface amendment in beef cattle feedlots on ammonia and sulfide emissions. 2022. Sustainability 14(4): 1984 – 2004. https://doi.org/10.3390/su14041984

Acknowledgements

The authors wish to acknowledge USMARC technicians Alan Kruger and Jessie Clark for their assistance with data collection and analysis.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2022. Title of presentation. Waste to Worth. Oregon, OH. April 18-22, 2022. URL of this page. Accessed on: today’s date.

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NAEMS: How It Was Done and Lessons Learned

Building Environment and Air Quality – Presented by Al Heber

Development of Draft Emission Estimating Methodologies for AFOs: Process Overview – Presented by Ian Rumsy

National Air Emissions Monitoring Study Status Update – Presented by Bebhinn Do

Purpose

The National Air Emissions Monitoring Study, or NAEMS, was conducted from 2007 – 2010 to gather data to develop scientifically credible methodologies for estimating emissions from animal feeding operations (AFOs). It followed from a 2002 report by the National Academy of Sciences that recommended the development of the emission models. NAEMS was funded by the AFO industry as part of a 2005 voluntary air compliance agreement with the U.S. Environmental Protection Agency (EPA). The goals of the air compliance agreement were to reduce air pollution, monitor AFO emissions, promote a national consensus on emissions estimating methodologies, and ensure compliance with requirements of the Clean Air Act and notification provisions of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), and the Emergency Planning and Community Right-to-Know Act (EPCRA). Thus, the design of the study was based both on principles set forth by the National Academy of Sciences and on the needs of EPA and the AFO industry to satisfy the compliance agreement.

What Did We Do

NAEMS monitored barns and lagoons at 25 AFOs in 10 states for approximately 2 years each to measure emissions of ammonia, hydrogen sulfide, particulate matter, and volatile organic compounds. University researchers conducted this monitoring with EPA oversight. The types of AFOs monitored included swine, broiler chickens, egg-laying operations, and dairies. Participating AFOs made their operations available for monitoring for two years and cooperated with the researchers, industry experts, and EPA during the study.

In 2012, EPA used information gathered in NAEMS, along with information provided as part of a 2011 Call for Information, to develop draft emission models for some of the AFO sectors that were monitored. The EPA Science Advisory Board (SAB) conducted a peer review of these original draft emission models and made suggestions for improving the models. Since 2017, EPA began applying the SAB suggestions and developing new draft emission models for each AFO sector. The models estimate farm-scale emissions using information that producers already record or is easy to get (like weather data). The models are not “process-based.” However, the approach aims to estimate emissions from sources based on statistical relationships between air emissions and the meteorological and housing parameters collected that are known to affect processes that generate emissions. The development of process-based models remains a long-term goal of the agency, as we acknowledge process-based models improve the accuracy of emission estimates for the livestock and poultry sectors.

What Have We Learned

During the workshop, panelists will discuss in more detail the lessons learned at various stages of the NAEMS project and how those lessons could inform future work.

Future Plans

The EPA team continues to develop draft emission models using the NAEMS data. It is anticipated that the AFO emission models will be finalized after incorporating input from a stakeholder review period.

Authors

Presenting Authors

    • Albert J. Heber, Professor Emeritus, Agricultural and Biological Engineering
    • Ian C. Rumsey, Physical Scientist, Office of Research & Development, U.S. Environmental Protection Agency
    • Bebhinn Do, Physical Scientist, U.S. Environmental Protection Agency

Corresponding Author

Bebhinn Do, Physical Scientist, U.S. Environmental Protection Agency
do.bebhinn@epa.gov

Additional Information

For updates on NAEMS, please see: https://www.epa.gov/afos-air/national-air-emissions-monitoring-study

Acknowledgements

U.S. Environmental Protection Agency – Office of Research & Development Emission Estimating Methodology development team: Maliha Nash, John Walker, Yijia Dietrich, Carry Croghan

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2022. Title of presentation. Waste to Worth. Oregon, OH. April 18-22, 2022. URL of this page. Accessed on: today’s date.

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Manure emissions during agitation and processing

Purpose

Recent deaths associated with hydrogen sulfide exposure from manure systems have highlighted the need for increased awareness to reduce health risks. While information on some aspects of hydrogen sulfide release from manure are available, there is limited information on the characteristics when agitating manure storages and in manure processing buildings that result in concentrations that are dangerous to human health. This project aimed to gather data on emissions from manure storages and processing to assess risks and develop mitigation strategies for these risks.

What Did We Do?

Our research team acquired over 20 days of field data (at multiple livestock farms) to assess the air concentrations from manure storages with and without agitation, for hydrogen sulfide, methane, ammonia, and particulate matter. The emissions were measured over the course of eight hours using numerous sets of sensors around the manure storage during agitation for each sampling event. Each sampling event had one backpack that was worn by a researcher with a set of sensors to represent the concentrations relevant to someone working in the area. Five additional sensor sets were placed around the manure storage. Some sensor sets remained in the same position throughout sampling (e.g., at the location of the agitation equipment controls) while others were moved around the storage.  Researchers also measured the concentrations of these gases inside a manure processing room to assess the concentration changes with different air exchange rates. During each event manure samples were collected as well as weather data to relate to the manure emissions data.

What Have We Learned?

This research assessed the environmental and design conditions of manure systems that may lead to increased concentrations of gases that have human health implications. The results indicate critical operating parameters on how to manage manure systems to limit risk from gases produced from manure processing and storage areas. More details on the study results will be available soon and will be presented at the conference.

Future Plans

This information is also being integrated into an existing fact sheet, https://learningstore.extension.wisc.edu/collections/manure/products/reducing-risks-from-manure-storage-agitation-gases-p1865, to provide an updated resource which integrates this new data. This information will be shared in a variety of settings to increase awareness and guide practices to reduce health risks to those working with livestock manure.

Authors

Rebecca A. Larson, Associate Professor & Extension Specialist, Biological Systems Engineering, University of Wisconsin-Madison

Corresponding author email address

rebecca.larson@wisc.edu

Additional author

Anurag Mandalika, Assistant Professor, Audobon Sugar Institute, LSU AgCenter

Additional Information

Reducing Risks from Manure Storage Agitation Gases

Acknowledgements

This work is supported by Foundational Program CARE 2019-68008-29829 from the USDA National Institute of Food and Agriculture.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2022. Title of presentation. Waste to Worth. Oregon, OH. April 18-22, 2022. URL of this page. Accessed on: today’s date.

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Production of Greenhouse Gases, Ammonia, Hydrogen Sulfide, and Odorous Volatile Organic Compounds from Manure of Beef Feedlot Cattle Implanted with Anabolic Steroids

Animal production is part of a larger agricultural nutrient recycling system that includes soil, water, plants, animals and livestock excreta. When inefficient storage or utilization of nutrients occurs, parts of this cycle become overloaded. The U.S. Beef industry has made great strides in improving production efficiency with a significant emphasis on improving feed efficiency. Improved feed efficiency results in fewer excreted nutrients and volatile organic compounds (VOC) that impair environmental quality. Anabolic steroids are used to improve nutrient feed efficiency which increases nitrogen retention and reduces nitrogen excretion. This study was conducted to determine the methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O), odorous VOCs, ammonia (NH3), and hydrogen sulfide (H2S) production from beef cattle manure and urine when aggressive steroid implants strategies were used instead of moderate implant strategies.

What Did We Do?

Two groups of beef steers (60 animals per group) were implanted using two levels of implants (moderate or aggressive). This was replicated three times, twice with spring-born calves and once with fall-born calves, for a total of 360 animals used during the study. Both moderate and aggressive treatment groups received the same initial implant that contain 80 mg trenbolone acetate and 16 mg estradiol. At second implant, steers in the moderate group received an implant that contained 120 mg trenbolone acetate and 24 mg estradiol, while those in the aggressive group received an implant that contained 200 mg trenbolone acetate and 20 mg estradiol. Urine and feces samples were collected individually from 60 animals that received a moderate implant and 60 animals that received an aggressive implant at each of three sampling dates (Spring and Fall 2017 and Spring 2018). Within each treatment, fresh urine and feces from five animals were mixed together to make a composite sample slurry (2:1 ratio of manure:urine) and placed in a petri dish. There were seven composite mixtures for each treatment at each sampling date. Wind tunnels were used to pull air over the petri dishes. Ammonia, carbon dioxide, and nitrous oxide concentrations were measured using an Innova 1412 Photoacoustic Gas Analyzer. Hydrogen sulfide and methane were measured using a Thermo Fisher Scientific 450i and 55i, respectively. Gas measurements were taken a minimum of six times over 24- to 27-day sampling periods.

What Have We Learned?

Flux of ammonia, hydrogen sulfide, methane, nitrous oxide, and total aromatic volatile organic compounds were significantly lower when an aggressive implant strategy was used compared to a moderate implant strategy. However, the flux of total branched-chained volatile organic compounds from the manure increased when aggressive implants were used compared to moderate implants. Overall, this study suggests that air quality may be improved when an aggressive implant is used in beef feedlot animals.

Table 1. Overall average flux of compounds from manure (urine + feces) from beef feedlot cattle implanted with a moderatea or aggressiveb anabolic steroid.
Hydrogen Sulfide Ammonia Methane Carbon Dioxide Nitrous  Oxide Total Sulfidesc Total SCFAd Total BCFAe Total Aromaticsf
µg m-2 min-1 ——–mg m-2 min-1——–
Moderate 4.0±0.1 2489.7±53.0 117.9±4.0 8795±138 8.6±0.1 0.7±0.1 65.2±6.6 5.9±0.5 2.9±0.3
Aggressive 2.7±0.2 2186.4±46.2 104.0±3.8 8055±101 7.4±0.1 0.8±0.1 63.4±5.7 7.6±0.8 2.1±0.2
P-value 0.01 0.04 0.01 0.01 0.01 0.47 0.83 0.05 0.04
aModerate treatment =  120 mg trenbolone acetate and 24 mg estradiol at second implant; bAggressive treatment = 200 mg trenbolone acetate and 20 mg estradiol at second implant; cTotal sulfides = dimethyldisulfide and dimethyltrisulfide; dTotal straight-chained fatty acids (SCFA) = acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, and heptanoic acid;  eTotal branch-chained fatty acids (BCFA) = isobutyric acid and isovaleric acid; fTotal aromatics = phenol, 4-methylphenol, 4-ethylphenol, indole, and skatole

Future Plans
Urine and fecal samples are being evaluated to determine the concentration of steroid residues in the livestock waste and the nutrient content (nitrogen, phosphorus, potassium and sulfur) of the urine and feces.

Authors

mindy.spiehs@ars.usda.gov Mindy J. Spiehs, Research Animal Scientist, USDA ARS Meat Animal Research Center, Clay Center, NE

Bryan L. Woodbury, Agricultural Engineer, USDA ARS Meat Animal Research Center, Clay Center, NE

Kristin E. Hales, Research Animal Scientist, USDA ARS Meat Animal Research Center, Clay Center, NE

Additional Information

Will be included in Proceedings of the 2019 Annual International Meeting of the American Society of Agricultural and Biological Engineers.

USDA is an equal opportunity provider and employer. 

Acknowledgements

The authors wish to thank Alan Kruger, Todd Boman, Bobbi Stromer, Brooke Compton, John Holman, Troy Gramke and the USMARC Cattle Operations Crew for assistance with data collection.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2019. Title of presentation. Waste to Worth. Minneapolis, MN. April 22-26, 2019. URL of this page. Accessed on: today’s date.

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Production of Greenhouse Gases and Odorous Compounds from Manure of Beef Feedlot Cattle Fed Diets With and Without Ionophores

Ionophores are a type of antibiotics that are used in cattle production to shift ruminal fermentation patterns. They do not kill bacteria, but inhibit their ability to function and reproduce. In the cattle rumen, acetate, propionate, and butyrate are the primary volatile fatty acids produced. It is more energetically efficient for the rumen bacteria to produce acetate and use methane as a hydrogen sink rather than propionate. Ionophores inhibit archaea forcing bacteria to produce propionate and butyrate as hydrogen sinks rather than working symbiotically with methanogens to produce methane as a hydrogen sink. Numerous research studies have demonstrated performance advantages when ionophores are fed to beef cattle, but few have considered potential environmental benefits of feeding ionophores. This study was conducted to determine if concentrations of greenhouse gases, odorous volatile organic compounds (VOC), ammonia, and hydrogen sulfide from beef cattle manure could be reduced when an ionophore was fed to finishing cattle.

What Did We Do?

Four pens of feedlot cattle were fed an ionophore (monensin) and four pens received no ionophore (n=30 animals/pen). Samples were collected six times over a two-month period. A minimum of 20 fresh fecal pads were collected from each feedlot pen at each collection. Samples were mixed within pen and a sub-sample was placed in a small wind-tunnel. Duplicate samples for each pen were analyzed. Ammonia, carbon dioxide (CO2), and nitrous oxide (N2O) concentrations were measured using an Innova 1412 Photoacoustic Gas Analyzer. Hydrogen sulfide (H2S) and methane (CH4) were measured using a Thermo Fisher Scientific 450i and 55i, respectively.

What Have We Learned?

 

Table 1. Overall average concentration of compounds from feces of beef feedlot cattle fed diets with and without monensin.
Hydrogen Sulfide Ammonia Methane Carbon Dioxide Nitrous  Oxide Total Sulfidesa Total  SCFAb Total BCFAc Total Aromaticsd
µg L-1 —————-mg L-1—————-
No Monensin 87.3±2.2 1.0±0.2 4.3±0.1 562.5±2.2 0.4±0.0 233.4±18.3 421.6±81.9 16.8±3.1 83.7±6.4
Monensin 73.9±1.4 1.1±0.2 3.2±0.2 567.1±2.1 0.5±0.0 145.5±10.9 388.9±32.5 20.3±2.3 86.4±5.6
P-value 0.30 0.40 0.01 0.65 0.21 0.01 0.79 0.48 0.75
aTotal sulfides = dimethyldisulfide and dimethyltrisulfide; bTotal straight-chained fatty acids (SCFA) = acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, and heptanoic acid;  cTotal branch-chained fatty acids (BCFA) = isobutyric acid and isovaleric acid; dTotal aromatics = phenol, 4-methylphenol, 4-ethylphenol, indole, and skatole

Total CH4 concentration decreased when monensin was fed. Of the VOCs measured, only total sulfide concentration was lower for the manure from cattle fed monensin compared to those not fed monensin. Ammonia, N2O, CO2, H2S, and all other odorous VOC were similar between the cattle fed monensin and those not fed monensin. The results only account for concentration of gases emitted from the manure and do not take into account any urinary contributions, but indicate little reduction in odors and greenhouse gases when monensin was fed to beef finishing cattle.

Future Plans

A study is planned for April – July 2019 to measure odor and gas emissions from manure (urine and feces mixture) from cattle fed with and without monensin. Measurements will also be collected from the feedlot surface of pens with cattle fed with and without monensin.  

Authors

Mindy J. Spiehs, Research Animal Scientist, USDA ARS Meat Animal Research Center, Clay Center, NE

mindy.spiehs@ars.usda.gov

Bryan L. Woodbury, Agricultural Engineer, USDA ARS Meat Animal Research Center, Clay Center, NE

Kristin E. Hales, Research Animal Scientist, USDA ARS Meat Animal Research Center, Clay Center, NE

Additional Information

Dr. Hales also looked at growth performance and E. coli shedding when ionophores were fed to finishing beef cattle. This work is published in Journal of Animal Science.

Hales, K.E., Wells, J., Berry, E.D., Kalchayanand, N., Bono, J.L., Kim, M.S. 2017. The effects of monensin in diets fed to finishing beef steers and heifers on growth performance and fecal shedding of Escherichia coli O157:H7. Journal of Animal Science. 95(8):3738-3744. https://pubmed.ncbi.nlm.nih.gov/28805884/.

USDA is an equal opportunity provider and employer.

Acknowledgements

The authors wish to thank Alan Kruger, Todd Boman, and the USMARC Cattle Operations Crew for assistance with data collection.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2019. Title of presentation. Waste to Worth. Minneapolis, MN. April 22-26, 2019. URL of this page. Accessed on: today’s date.

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Evaluation of current products for use in deep pit swine manure storage structures for mitigation of odors and reduction of NH3, H2S, and VOC emissions from stored swine manure

The main purpose of this research project is an evaluation of the current products available in the open marketplace for using in deep pit swine manure structure as to their effectiveness in mitigation of odors and reduction of hydrogen sulfide (H2S), ammonia (NH3), 11 odorous volatile organic compounds (VOCs) and greenhouse gas (CO2, methane and nitrous oxide) emissions from stored swine manure. At the end of each trial, hydrogen sulfide and ammonia concentrations are measured during and immediately after the manure agitation process to simulate pump-out conditions. In addition, pit manure additives are tested for their impact on manure properties including solids content and microbial community.

What Did We Do?

Figure 1. Reactor simulates swine manure storage with controlled air flow rates.

We are using 15 reactors simulating swine manure storage (Figure 1) filled with fresh swine manure (outsourced from 3 different farms) to test simultaneously four manure additive products using manufacturer recommended dose for each product. Each product is tested in 3 identical dosages and storage conditions. The testing period starts on Day 0 (application of product following the recommended dosage by manufacturer) with weekly additions of manure from the same type of farm. The headspace ventilation of manure storage is identical and controlled to match pit manure storage conditions. Gas and odor samples from manure headspace are collected weekly. Hydrogen sulfide and ammonia concentrations are measured in real time with portable meters (both are calibrated with high precision standard gases). Headspace samples for greenhouse gases are collected with a syringe and vials, and analyzed with a gas chromatograph calibrated for CO2, methane and nitrous oxide. Volatile organic compounds are collected with solid-phase microextraction probes and analyzed with a gas chromatography-mass spectrometry (Atmospheric Environment 150 (2017) 313-321). Odor samples are collected in 10 L Tedlar bags and analyzed using the olfactometer with triangular forced-choice method (Chemosphere, 221 (2019) 787-783). To agitate the manure for pump-out simulation, top and bottom ‘Manure Sampling Ports’ (Figure 1) are connected to a liquid pump and cycling for 5 min. Manure samples are collected at the start and end of the trial and are analyzed for nitrogen content and bacterial populations.

The effectiveness of the product efficacy to mitigate emissions is estimated by comparing gas and odor emissions from the treated and untreated manure (control). The mixed linear model is used to analyze the data for statistical significance.

What we have learned?

Figure 2. Hydrogen sulfide and ammonia concentration increased greatly during agitation process conducted at the end of trial to simulate manure pump-out conditions and assess the instantaneous release of gases. The shade area is the initial 5 minutes of continuous manure agitation.

U.S. pork industry will have science-based, objectively tested information on odor and gas mitigation products. The industry does not need to waste precious resources on products with unproven or questionable performance record. This work addresses the question of odor emissions holistically by focusing on what changes that are occurring over time in the odor/odorants being emitted and how does the tested additive alter manure properties including the microbial community. Additionally, we tested the hydrogen sulfide and ammonia emissions during the agitation process simulating pump-out conditions. For both gases, the emissions increased significantly as shown in Figure 2. The Midwest is an ideal location for swine production facilities as the large expanse of crop production requires large fertilizer inputs, which allows manure to be valued as a fertilizer and recycled and used to support crop production.

Future Plans

We develop and test sustainable technologies for mitigation of odor and gaseous emissions from livestock operations. This involves lab-, pilot-, and farm-scale testing. We are pursuing advanced oxidation (UV light, ozone, plant-based peroxidase) and biochar-based technologies.

Authors

Baitong Chen, M.S. student, Iowa State University

Jacek A. Koziel*, Prof., Iowa State University (koziel@iastate.edu)

Daniel S. Andersen, Assoc. Prof., Iowa State University

David B. Parker, Ph.D., P.E., USDA-ARS-Bushland

Additional Information

  • Heber et al., Laboratory Testing of Commercial Manure Additives for Swine Odor Control. 2001.
  • Lemay, S., Stinson, R., Chenard, L., and Barber, M. Comparative Effectiveness of Five Manure Pit Additives. Prairie Swine Centre and the University of Saskatchewan.
  • 2017 update – Air Quality Laboratory & Olfactometry Laboratory Equipment – Koziel’s Lab. doi: 10.13140/RG.2.2.29681.99688.
  • Maurer, D., J.A. Koziel. 2019. On-farm pilot-scale testing of black ultraviolet light and photocatalytic coating for mitigation of odor, odorous VOCs, and greenhouse gases. Chemosphere, 221, 778-784; doi: 10.1016/j.chemosphere.2019.01.086.
  • Maurer, D.L, A. Bragdon, B. Short, H.K. Ahn, J.A. Koziel. 2018. Improving environmental odor measurements: comparison of lab-based standard method and portable odour measurement technology. Archives of Environmental Protection, 44(2), 100-107.  doi: 10.24425/119699.
  • Maurer, D., J.A. Koziel, K. Bruning, D.B. Parker. 2017. Farm-scale testing of soybean peroxidase and calcium peroxide for surficial swine manure treatment and mitigation of odorous VOCs, ammonia, hydrogen sulfide emissions. Atmospheric Environment, 166, 467-478. doi: 10.​1016/​j.​atmosenv.​2017.​07.​048.
  • Maurer, D., J.A. Koziel, J.D. Harmon, S.J. Hoff, A.M. Rieck-Hinz, D.S Andersen. 2016. Summary of performance data for technologies to control gaseous, odor, and particulate emissions from livestock operations: Air Management Practices Assessment Tool (AMPAT). Data in Brief, 7, 1413-1429. doi: 10.1016/j.dib.2016.03.070.

Acknowledgments

We are thankful to (1) National Pork Board and Indiana Pork for funding this project (NBP-17-158), (2) cooperating farms for donating swine manure and (3) manufacturers for providing products for testing. We are also thankful to coworkers in Dr. Koziel’s Olfactometry Laboratory and Air Quality Laboratory, especially Dr. Chumki Banik, Hantian Ma, Zhanibek Meiirkhanuly, Lizbeth Plaza-Torres, Jisoo Wi, Myeongseong Lee, Lance Bormann, and Prof. Andrzej Bialowiec.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2019. Title of presentation. Waste to Worth. Minneapolis, MN. April 22-26, 2019. URL of this page. Accessed on: today’s date.

 

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Additive to Mitigate Odor and Hydrogen Sulfide Gas Risk from Gypsum Bedded Dairy Manure

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Purpose

Dangerous levels of hydrogen sulfide (H2S) gas released from gypsum-bedding-laden dairy manure storages have imposed risks to animal and human health, as demonstrated both on-farm and in bench scale studies (Fabian-Wheeler et al., 2017; Hile, 2016). Gypsum bedding is popular with some producers for advantages to cow comfort and health along with agronomic benefits. This project demonstrated the effect of iron oxide (FeO2) as a promising additive to dairy manure storages on mitigating H2S releases and odor.

What did we do?

Two bench-scale trials comprised three replicates each (15 kg manure each vessel) of three treatments: (1) control (dairy manure only), (2) manure with gypsum added 0.35% by weight, and (3) manure with gypsum and iron oxide added at a 1:1 molar ratio with gypsum. Headspace gas concentrations were measured using a Fourier transform infrared analyzer (FTIR model 700, California Analytical, Inc., Orange, CA) from each experimental vessel prior to and during manure agitation. Nutrient analyses were performed upon initial mixing and at the end of the incubations (PSU Agricultural Analytical Laboratory and Fairway Laboratories). Final incubation of the first trial included an odor evaluation of headspace gas according to international standard EN 13725 using qualified human assessors at the Penn State Odor Assessment Laboratory (abe.psu.edu/research/natural-resource-protection/odors). Odor quality testing on undiluted headspace gas used the labelled magnitude scale (LMS), Odor Intensity Referencing Scale (OIRS) and Hedonic Tone (pleasantness).

What have we learned?

High total sulfur in gypsum-laden manure confirms that gypsum provides the sulfur source that is converted to H2S. However, introduction of iron oxide maintained 98.8% total sulfur of manure sample by the end of incubation. The H2S concentrations remain low (below 5 ppm) in static conditions until gases are immediately released as soon as manure is agitated. Maximum H2S concentrations were reduced 83% to 96% in gypsum-laden manure by adding iron oxide (Figure 1). Despite anecdotal field reports of increased malodor associated with gypsum bedded manure, odor detection threshold (DT) did not increase with addition of gypsum compared to the control (manure only). However a 1:1 molar ration of iron oxide reduced the DT by approximately 50%. Odor quality results show that gypsum-laden manure created a less pleasant odor when compared to control manure.

Figure 1. Analyzer H2S concentrations from vessel headspace for each treatment evaluated sequentially over time during three agitation events at day 17, 24, and 31 manure age

Future Plans

Field-scale research would strengthen these findings and document management and economics associated with the iron oxide treatment use on farm. Additional odor surveys would confirm odor intensity reduction via iron oxide.

Corresponding author, title, and affiliation

Eileen E. Fabian (Wheeler), Professor in Agricultural and Biological Engineering (ABE) at Penn State (PSU)

Corresponding author email

fabian@psu.edu

Other authors

Long Chen, Ph.D. Candidate in ABE at PSU, Dr. Michael Hile, Project Associate in ABE at PSU and Dr. Mary Ann Bruns, Associate Professor in Ecosystems Science & Management at PSU

Additional information

Fabian-Wheeler, E., M. L. Hile, D. J. Murphy, D. E. Hill, R. Meinen, R. C. Brandt, H. A. Elliott, D. Hofstetter. 2017. Operator Exposure to Hydrogen Sulfide from Dairy Manure Storages Containing Gypsum Bedding. Journal Agricultural Safety and Health 23(1): 9-22.

Hile. M. L. 2016. Hydrogen sulfide production in manure storages on Pennsylvania dairy farms using gypsum bedding. Ph.D. dissertation. University Park, PA.: The Pennsylvania State University, Department of Agricultural and Biological Engineering.

Acknowledgements

This work was a partnership of Penn State College of Agricultural Sciences graduate student competitive grant program, Penn State Extension, and USA Gypsum

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2017. Title of presentation. Waste to Worth: Spreading Science and Solutions. Cary, NC. April 18-21, 2017. URL of this page. Accessed on: today’s date.

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Natural Resources Conservation Service Reaction to the Final H2S/ Gypsum CIG Study Report


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Purpose            

The Natural Resources Conservation Service (NRCS) and partners worked with Eileen Fabian-Wheeler of the Pennsylvania State University to study the manure gas risks associated with gypsum bedding at dairy farms. This was a NRCS Conservation Innovation Grant (CIG) project. As a result of the information gathered and the published final report, NRCS has taken the following actions which are described below.

What did we do? 

1. The NRCS National office has published National Bulletin 210-15-9 dated 7/14/15 detailing safety risks from manure storages of dairy cows bedded with gypsum.

2. The NRCS National Standard 333 for Amending Soil Properties with Gypsum Products has included a safety reference warning about adding gypsum to liquid manure storage facilities.

3. Pennsylvania NRCS has led and participated in numerous safety programs discussing the relationship between gypsum added to liquid manure storage facilities and the production of hydrogen sulfide (H2S). Within Pennsylvania (PA), NRCS and agency partner employees have been made aware of the risks of gypsum and excessive H2S production through the repeated use of a wide variety of educational medium.

4. Pennsylvania NRCS developed a new safety sign titled, “During Agitation, Deadly Gases Possible”. The sign was developed in direct response to the new Penn State Conservation Innovation Grant report that H2S is proven to be released during the agitation of manure with gypsum. There are possible ties to other high sulfur materials.

5. Pennsylvania NRCS developed a new PA Fact Sheet #5 titled, “Under Barn Storage Facilities, (Pros and Cons)”. The factsheet was developed to increase awareness of safety risks with under barn manure storages including extreme risks with H2S coming from high sulfur manure/bedding additives. (Can also include other high sulfur feed materials)

6. Pennsylvania has added safety requirements and clarifications to the PA 313 Waste Storage Facility Standard including;

a. requirements for agitation signs at covered/uncovered manure storages,

b. gypsum cannot be added to solid covered or under-the-barn waste storages (known to produce excessive H2S gas production),

c. silage leachate or other materials containing high sulfur cannot be stored in covered under-the-barn storages.

7. Pennsylvania NRCS has added safety warnings and clarifications to the PA 634 Waste Transfer Standard; “Gypsum bedding, silage leachate, and other waste components containing high amounts of sulfur can produce excessive amounts of manure gases…can create dangerous manure gas situations….”

8. Pennsylvania NRCS has rewritten the PADEP/PSU Fact Sheet MM2, to include up-to-date safety information, especially highlighting known H2S gas origins and hazards. Now titled PA NRCS Fact Sheet #10, this is a ready reference available to be supplied to producers at time of manure storage planning and design.

9. Pennsylvania NRCS engineers and others are currently on alert for the proper reporting of manure gas accidents.  They are investigating H2S as a probable most significant cause of manure gas accidents.  Hydrogen sulfide should be the first manure gas suspected and investigated.

10. Pennsylvania NRCS is alerting our field employees and partner agency field employees about the high sulfur content in ethanol by-products, which is different than brewer’s grain by-products. The ethanol production process normally includes the addition of significant amounts of sulfuric acid into the ethanol process for multiple purposes including chemistry, sanitation, pH control, and others, but leaving behind significant sulfur, which can cause unexpected H2S production with by-product reuse.

11. Pennsylvania NRCS has purchased 4 multi-gas meters for in-state training use. Meters measure 4 gases. The NRCS meters are intended for educational / awareness use and encouraging landowners / manure haulers to purchase for their own use.

Corresponding author, title, and affiliation        

W. Hosea Latshaw, PE, USDA NRCS Pa State Conservation Engineer

Corresponding author email    

hosea.latshaw@pa.usda.gov

Acknowledgements       

Manure Gas Risks Associated with Gypsum Bedding at Dairy Farms, Final Project Report, USDA NRCS Conservation Innovation Grant, Pennsylvania State University, Project Manager: Eileen Fabian-Wheeler, December 2017

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2017. Title of presentation. Waste to Worth: Spreading Science and Solutions. Cary, NC. April 18-21, 2017. URL of this page. Accessed on: today’s date.

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Hydrogen Sulfide Release from Dairy Manure Storages Containing Gypsum Bedding


Why Look at Potential Connections Between Gypsum and Hydrogen Sulfide?

Gypsum, a recycled product from the waste streams of the manufacturing and construction industries, provides ideal bedding for livestock because it absorbs moisture keeping the animals dry, is non-abrasive, and discourages bacterial growth as it is inert and non-organic. Gypsum is calcium sulfate (CaSO4•2H2O) and provides a sulfur source material that potentially increases H2S production from the manure storage due to the high generation of H2S levels. The goal of this research project is to compare H2S concentrations among Pennsylvania dairy farms that use traditional bedding, gypsum bedding and gypsum bedding with an amendment. Related: Manure Storage Safety | 2013 Waste to Worth conference proceedings by these authors “Gypsum Bedding – Risks & Recommendations for Manure Handling“

Information from this gypsum bedding project was recently featured on a pre-conference webcast More…

 

What did we do?

Ten farms were observed during 19 fall and spring agitation events. Portable multi-gas meters (models MX6, M40 and Tango, Industrial Scientific, Pittsburgh, PA) were place around the perimeter of each manure storage, 10 meters downwind of the storage perimeter and attached to the operator for the duration of the event to monitor exposure. Each meter recorded gas measurements every minute during the first hour of manure agitation. Wind speed, wind direction and air temperature were recorded every minute during these events using a weather station (Kestral Communicator model 4500, Nielsen-Kellerman, Birmingham, MI). Manure storage design and manure handling practices were characterized. Manure was characterized according to general chemistry (temperature, pH and oxidation-reduction potential) as well as submitted for a full nutrient analysis content including total nitrogen, sulfur, calcium, percent solids and phosphorus source coefficient.

What have we learned?

Figure 1 shows cumulative H2S concentrations versus gypsum application rate. Gypsum and non-gypsum farms represented by the diamonds show a significant increase in cumulative H2S concentrations with increasing gypsum application rate. The observations depicted by the squares represent farms that use Vital™ Breakdown (manufactured for Homestead Nutrition, New Holland, PA), a treatment reported to reduce H2S emissions. One of the farms observed, also pointed out in Figure 1 by the triangles, uses OK-1000 (manufactured by Pro-soil Ag Solutions, Hawkins, TX) as a manure additive. Though it appears that these manure additives reduce cumulative H2S concentrations, the reduction was not statistically significant because not enough observations were recorded to provide statistical power.

Movement of manure prior to the storage location appears to allow H2S to escape before entering long term storage (shown in Figure 1 as prior agitation), lowering H2S concentrations released during agitation of the manure storage. Wind flowing into proximate buildings inhibited the dissipation of H2S thereby increasing cumulative H2S concentrations as shown by the observation pointed out by the image of wind direction in Figure 1. Four observations of operator exposure (out of 19 observations including non-gypsum, gypsum and gypsum with additive) yielded H2S concentrations above 20 ppm (above the Occupational Health and Safety Administration’s (OSHA) recommended exposure limit. Of the four operators above 20 ppm H2S, three were working over the rim of the storage, which increased risk of exposure. Downwind H2S concentrations above 20 ppm ten meters from storage occurred for eight out of the fourteen observations from farms that use gypsum, showing that children and animals within ten meters of the storage are at risk.

Figure 1. cumulative hydrogen sulfide concentrations for first 60 minutes of agitations versus gypsum application rate

Future Plans  

Bench scale work will be performed in hopes of finding a manure additive that reduces H2S production from farms that use gypsum. A new product (Dri Mat) formulated from its precursor, VitalTM Breakdown, will be mixed with manure and analyzed to determine the efficacy to reduced H2S emissions. Iron oxide, a by-product of acid mine drainage passive treatment lagoons will be one of the treatments for this work as well.

Authors  

Hile, Michael, Ph. D. Candidate in Agricultural and Biological Engineering (ABE) at Penn State (PSU) mlh144@psu.edu

Dr. Eileen E. Fabian, Professor in ABE at PSU, Dr. Herschel A. Elliott, professor in ABE at PSU, Dr. Robin Brandt, Senior Lecturer in ABE at PSU, Dr. C. Alan Rotz, Agricultural Engineer at USDA-ARS and Dr. Ray Bryant, Soil Scientist at USDA-ARS.

Acknowledgements      

This project would not have been possible without the support from Natural Resources Conservation Service’ (NRCS) Conservation Innovation Grant (CIG) program, USA Gypsum and Industrial Scientific.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2015. Title of presentation. Waste to Worth: Spreading Science and Solutions. Seattle, WA. March 31-April 3, 2015. URL of this page. Accessed on: today’s date.

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