The most common waste management practice on hog farms in Eastern North Carolina are anaerobic lagoons. Lagoons contain three zones: [1] sludge storage zone at the bottom, [2] treatment zone for incoming manure in near the middle, and [3] a liquid (supernatant) storage zone at the top. The supernatant is land applied throughout the year as a nutrient source for growing crops on farms while the middle (treatment) zone is required to remain full to ensure effective treatment.
Considering the risk that hurricanes pose to North Carolina and the hog sector (particularly during late summer months), close lagoon management is critical to avoid risk of overflow or breach. Currently, regulations allow swine growers to lower the effluent level in their lagoons by applying part of the treatment zone effluent. Conditional to this allowance, however, is that the treatment zone contains at least 4-feet of depth that is sludge-free. This condition aims to ensure applied effluent is safe for application.
While this condition is helpful to reducing the risk of applying higher concentration of phosphorus, zinc, and copper to crops, many producers do not meet this condition due to excessive sludge buildup and would not be able to lower the lagoon level which poses a significant risk during intense rainfall events.
This study aims to quantify the impact of the sludge-free depth in the lagoon on the quality of supernatant during the drawdown period. Findings will help with precision nutrient application from swine manure and allow for further drawdown during necessary storm events.
What Did We Do
This study used a dataset representing 27 swine operations in Eastern North Carolina between 2016-2021. The dataset includes:
1. Monthly effluent/waste sampling analysis,
2. Annual sludge surveys, as well as
3. Lagoon level readings.
This dataset was analyzed using statistical methods to quantify the impact of seasonality (time of year), farm type (sow, finisher, or farrowing), and sludge level on nutrient concentration in the effluent.
Most growers use depth, in inches, to report volumes applied or available for storage. However, when comparing lagoons with different designs, this can be a challenge. As such, we developed two parameters to facilitate cross-farm, cross-lagoon comparisons. The first is “freeboard ratio” (FBR), which refers to the relative “fullness” of the storage zone in the lagoon. FBR value between 0 and 1 indicates the lagoon is currently within the storage volume (between start and stop pumps), values greater than 1 indicate the lagoon is in drawdown, and negative values indicate the lagoon level exceeded the storage volume and is currently in the rainfall/storm storage zone and must be lowered promptly. The equation used to calculate FBR is as follows:
TBR=
LFB-Lstart
, variables defined in Figure 2.
Lstop-Lstart
The second variable is “sludge level ratio” (SLR), which refers to the relative treatment volume available compared to the 50% treatment volume required. SLR values greater than 1 indicate that more than 50% of the treatment volume is sludge-free in the lagoon and therefore drawdown can proceed, and no sludge removal is necessary. SLR values less than 1 indicate that less than 50% of the treatment volume is available and drawdown might not be feasible. The equation used to calculate SLR is as follows:
SLR=
Lsludge-Lstop
, variables defined in Figure 2.
L0.5. Trt-Lstop
Figure 2. Anaerobic lagoon zones used to calculate study parameters FBR and SLR
What Have We Learned
In analyzing the dataset we observed that only 2% of the samples were collected while the lagoon level exceeded storage level (above the start-pump level). This suggests the majority of studied operations were successful in managing effluent despite the wet years observed between 2016 and 2021. By comparison, 22% of the samples were collected while the lagoon was at a draw-down state (the entire storage volume is empty and the treatment zone is partially emptied).
Additionally, 38% of the samples collected were associated with lagoons that needed sludge removal (SLR < 1). These results are summarized in Table 1, with 12% of samples collected from lagoons in drawdown (FBR > 1) and in need of sludge removal (SLR < 1). This latter group of samples represent the primary concern for lagoon drawdown.
Table 1. Summary of FBR and SLR Interactions
Lagoon Sample Class
Sludge Level Ratio (SLR)
No Removal
Removal Due
Freeboard Ratio (FBR)
Above stop-pump
40%
26%
In drawdown
22%
12%
The season was a significant predictor of the lagoon level (p < 0.001), with the late irrigation season (July – Sept) showing the least effluent volume in the lagoon. On average, 91% of the storage volume was unoccupied. This compares to the winter months (Oct – Feb) and the early irrigation season (Mar – June) with 81 and 69% of the storage volume empty, respectively.
For all seasons the mean ratio of N : P2O5 : K2O in the supernatant is 4 : 1 : 8.2. There was less variability for N and K content with the lagoon level than for P, Zn, and Cu. This can be attributed to the N and K being primarily in soluble forms in the lagoon supernatant compared to P2O5, Zn and Cu which are mostly bound to solids.
The analysis showed a greater variability in Zn, Cu, and P levels with changes in solid concentration in the supernatant as well as the amount of suspended solids as a result of wind or active lagoon agitation/sludge removal.
Overall, the results showed lagoon drawdown and existing sludge reserves to have a combined effect on nutrient concentrations in the supernatant, particularly for phosphorus.
Future Plans
This study will inform ongoing research to predict temporal variability in nutrient content in the lagoon due to weather, operational decisions, and time of year. Near term, these observations will help guide application rates to ensure P levels meet crop demands particularly during late-season drawdown without significantly increasing soil P levels. In addition, this work will be part of a larger study to predict the performance of anaerobic treatment lagoons under future climate conditions.
Authors
Presenting Author:
Carly Graves, Graduate Research Assistant, North Carolina State University
Corresponding Author:
Dr. Mahmoud Sharara, Assistant Professor & Waste Management Extension Specialist, North Carolina State University
msharar@ncsu.edu
Acknowledgements
Thank you to Smithfield Foods, Inc. for funding this research and providing datasets of sludge surveys.
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.
The purpose of this presentation is to provide a complete overview of ODA’s Division of Livestock Environmental Permitting (“ODA-DLEP”). ODA-DLEP regulates any livestock facility in Ohio that has the following number of animals or greater:
700 mature dairy cows
1,000 beef cattle or dairy heifers
2,500 swine weighing more than 55 pounds
10,000 swine weighing less than 55 pounds
82,000 layers
125,000 broilers or pullets
500 horses
55,000 turkeys
What Did We Do
Ohio Department of Agriculture’s Division of Livestock Environmental Permitting (“ODA-DLEP”) regulates the siting, construction, and operation of Ohio’s largest livestock facilities, referred to as Concentrated Animal Feeding Facilities (“CAFF”). ODA-DLEP’s primary objective is to minimize any water quality impacts, including both surface and ground waters, associated with the construction of new or expanding CAFFs, as well as implementation of best management practices once a CAFF becomes operational. These best management practices include management of manure, insect and rodent control, mortality management, and emergency response practices. ODA-DLEP issues Permits to Install (for construction) and Permits to Operate (for operations).
In addition, ODA-DLEP conducts routine inspections of each CAFF at least once a year, responds to complaints, and participates in emergency response. Inspections are conducted to review a CAFF’s compliance with Ohio Revised Code 903 and Ohio Administrative Code 901:10, the laws and regulations governing Concentrated Animal Feeding Facilities.
Finally, ODA-DLEP administers the Certified Livestock Manager program. Any individual in the State of Ohio that manages 4,500 dry tons of solid manure or 25 million gallons of liquid manure is required to be a Certified Livestock Manager (“CLM”).
What Have We Learned
Livestock operations continue to get larger and more concentrated and as a result, regulations are necessary to ensure proper handling and management of manure, particularly with land application of manure.
Future Plans
Over the past several years, DLEP has started to see more interest in manure treatment technologies. This could include, but is not limited to, anaerobic digestion, nutrient recovery, solids separation, and wastewater treatment. Technologies like this could greatly alter the landscape of the livestock industry by fundamentally changing the way manure is handled and how nutrients from manure are applied. DLEP does have regulations in place to account for manure treatment technologies. However, regulations, and specifically changes to regulations, cannot maintain the same pace as these technological advancements.
Authors
Samuel Mullins, Chief of ODA-Division Livestock Environmental Permitting
Samuel.mullins@agri.ohio.gov
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.
Dairy farmers and their key advisors, the balance of the dairy value chain, policy makers, government officials, non-governmental organizations (NGOs), and astute consumers value best available information about the greenhouse gas (GHG) emissions associated with milk production. In 2020, the Innovation Center for US Dairy set three 2050 environmental stewardship goals spanning from cradle to processor gate, including GHG neutrality. Further, they committed to reporting on progress towards the goals every five years starting in 2025.
Dairy farming economics will continue to drive production consolidation, a trend that substantially began in the 1960s. Consolidation results in fewer total farms yet only somewhat fewer total cows overall; thus, the number of cows per farm has substantially increased. The best management practice of long-term manure storage (LTS) was developed by USDA NRCS decades ago to protect water quality due to manure runoff and infiltration. The number of farms with LTS increased as the number of cows per farm increases. Overall, LTSs are largely anaerobic, resulting in the emission of methane (CH4) and in some cases nitrous oxide (N2O). It is generally understood that the 2nd largest cradle to farm gate CH4 emission source is LTS. Continued industry consolidation will result in more LTS over time.
Continued use of (LTS) to protect water quality, coupled with today’s use of manure treatment practices on-farm and the US dairy and other GHG reduction goals set are important reasons to quantify manure-based GHG emissions.
What Did We Do
To help dairy farmers and others understand the relative impact manure management (MM) has on GHG emissions, seven integrated MM systems that are utilized by farmers in the Northeast/upper Midwest were analyzed. The approach was to calculate the GHG emission impacts using best available information and procedures. The seven systems analyzed, each shown in process flow order, were:
1. Long-term storage (LTS)
2. Solid-liquid separation (SLS), LTS
3. SLS, LTS with cover/flare (CF)
4. Anaerobic digestion (AD) of manure only, SLS, LTS
5. AD, SLS, LTS with CF
6. AD of manure/food waste, SLS, LTS with CF
7. AD of manure/food waste, SLS, LTS with cover/gas utilization
The resulting net GHG emission values were compared to the baseline MM practice of daily spreading.
Impact of systems on GHG emissions associated with LTS and offsets from net energy production and landfill organics diversion (anaerobic digestion systems only) were included. Results were normalized on a metric ton of carbon dioxide equivalent (CO2e) per cow-year basis. A 100-year global warming potential (GWP100) value of 25 and a 20-year GWP20 (84) were used for comparative purposes in calculating CO2e. A sensitivity analysis was conducted to understand the impact of volatile solid (VS) biodegradability on GHG emissions and anaerobic digester system biogas leakage.
What Have We Learned
Not surprisingly, results show that the largest GHG reduction opportunity was from anaerobic co-digestion of dairy manure with community substrate (7. above). The net GHG emission from this system was -16 (GWP100) and -43 (GWP20) metric tons CO2e per cow-year (GHG avoidance). This is compared to the GHG emission of 1.9 (GWP100) and 5.6 (GWP20) metric tons CO2e per cow-year from the LTS (1. above). Sensitivity analysis results showed manure VS degradability had meaningful impact on GHG emissions, particularly for Scenario 4, and for the co-digestion scenarios, the most significant impact – 5% – resulted in a leakage increased from 1% to 3%. While using SLS with an impermeable cover and flare system on a separated liquid manure LTS reduces CH4 emissions as compared to uncovered long-term liquid manure storage, the practice does not provide an opportunity to achieve net zero or better manure enterprise GHG footprint because the energy in the biomass is wasted and diversion of organics from landfills cannot be effectively included.
Future Plans
Next step is to develop additional results for integrated MM systems that included advanced manure treatment technologies that further reduce the organic loading on LTSs. Further parallel work will focus on quantifying these same advanced manure treatment technologies on their partitioning of digester effluent nutrients for off-farm export.
Authors
Curt A. Gooch, Sustainable Dairy Product Owner, Land O’Lakes – Truterra
cgooch@landolakes.com
Additional Authors
-Peter E. Wright, Extension Associate, Cornell PRO-DAIRY Dairy Environmental Systems Program
-Lauren Ray, Extension Support Specialist III, Cornell PRO-DAIRY Dairy Environmental Systems Program
The Coalition for Renewable Natural Gas and the New York State Department of Agriculture and Markets provided financial resources to support this work.
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.
Manure lagoon systems are designed to hold and treat animal farm wastewater for a predetermined period and remain popular in many livestock farms. If the lagoon is properly designed and built, many years can go by without any significant maintenance requirements outside of water management, pumps and valves. Depending on the capacity and maintenance, additional manure solid removal is often required to reduce the amount of manure solids entering the lagoon storage. When excessive solids build-up or sludge was found, significant odor and low quality/quantity of flushing water would be the issues.
This study documents experience to prepare for and complete land application of lagoon effluent with heavy solids from a flush dairy lagoon in central Missouri. The free stall barn uses mattress bedding with supplemental cedar shavings and houses 140-160 lactating cows. Preparation included measuring lagoon sludge depth and lab analysis of sludge characteristics and scouting for crop fields for land application prior to contacting contractors for a bidding process. A contractor team utilized specialized equipment to dilute, agitate, pump and land apply approximately 8 million gallons of diluted lagoon solids in less than nine working days. Lagoon effluent was sampled throughout the process to monitor the mass of nutrients applied to specific plots of land. For effective lagoon solids removal and land application, proper preparation, specialty equipment and trained professional, timing of the crop fields, and adequate field working days are critical. Simple, non-mechanical technologies are available for even small to midsize dairy farms to reduce the cost of lagoon maintenance by preventing the bulk of solids from entering the lagoon.
What Did We Do?
We documented the process of lagoon solids removal for land application, considering the preparation (sludge and effluent sampling), specialty equipment and trained professionals, timing of the crop fields, and adequate field working days. The barn was flushed two to three times per day, with three times per day being typical. There was, at one time, an elevated screen that helped remove the large solids from the flush, but the screen system fell into disrepair several years ago and was abandoned. Solids in the lagoon were agitated and pumped out from May 21, 2020, through June 8, 2020, Figures 1 and 2. A total of 8 million gallons over 280 acres was applied to fields further away from the lagoon, including neighbor’s crop fields that were 1.5 miles away. Equipment needs and specifications were documented (Canter et al., 2021) and being prepared for an Extension publication.
Figure 1. PTO-drive lagoon agitators and agitation boat in operation.Figure 2. A dilution pump was used to pump water from the nearby lake (left) to the dairy lagoon (right) with agitation boat and lagoon agitation working in the background.
Daily lagoon effluent samples were taken multiple samples throughout the day on June 2 to gauge the consistency of nutrient concentrations. Results suggest that once completely mixed via agitation, the applied nutrient concentration from a single sample is a reliable estimate within a working day if the moisture content is consistent. The initial slurry had a 10-13 percent solids content, so a significant amount of dilution water was needed to dilute the solids content to the target range. The exact amount of dilution water used was unknown. Figure 3 shows the concentration and moisture data. In general, the higher the moisture content (less solids) in the slurry samples, the higher the concentrations of the important manure nutrients are. The team evaluated potential technologies based on historical experience and first-person interviews. A pull-plug sediment basin (PPSB) was selected after reviewing cost and visiting with a farmer who operated a PPSB and was satisfied with the overall operation and performance (Canter et al., 2021). The application rate of important manure nutrients did show variation during the several days of land application, suggesting an improvement to the real-time effluent nutrient measurement and land application rate adjustment could be improved to provide more consistent nutrients to the crop fields.
Figure 3. Concentrations and moisture content of slurry samples from the lagoon.
What Have We Learned?
Manure management can be a burden for animal feeding operations, which can potentially become a significant threat to the profitability and management of farms if not proactively managed. Owners would be well-advised to survey their lagoon yearly to track solid inventory and plan ahead for the amount of land needed for solids application. Proper solids removal from the lagoon, particularly if regular and effective solids removal has been neglected, requires specialized equipment to reduce liquid supernatant on an annual or semiannual basis. There can be significant variability of nutrient concentration and resulting mass applied. Testing for nutrient concentrations in the lagoon, whether supernatant or sludge, or both, can be misleading due to variance in concentrations due to moisture content as the applicators dilute and concentrate the solids during the land application process.
Daily sampling during land application could help but may not be practical due to the analysis time generally required by labs (5-10 business days). Sensors and probes are available that return instantaneous values and have been used in municipal and industrial wastewater treatment for over a decade. Companies have offered integrated sensors for land application equipment, combining them with their GPS and flow control system to give a complete and accurate summary of nutrient application. Simple, non-mechanical technologies are available for even small to midsize dairy farms to reduce the cost of lagoon maintenance by preventing the bulk of non-degradable solids from entering the lagoon. Implementation of a coarse solids separation system such as the PPSB could significantly reduce the long-term cost of manure management by allowing the operator to use more common equipment (e.g., a loader and spreader) to remove solids from the manure management system.
Future Plans
Continuous monitoring of the lagoon sludge level at a minimum of annual basis is needed to closely monitor the lagoon solid accumulation and performance of the PPSB. The authors are collaborating with NRCS team to improve the PPSB and ways to monitor the lagoon sludge level.
Authors
Teng Lim, Extension Professor, Agricultural Systems Technology, University of Missouri
Corresponding author email address
Limt@missouri.edu
Additional authors
Timothy Canter, Extension Specialist, Agricultural Systems Technology, University of Missouri
Joseph Zulovich, Extension Assistant Professor, Agricultural Systems Technology, University of Missouri
Additional Information
Canter, T., Lim, T.-T., and J. A. Zulovich. 2021. Field Experience of Removing and Land Application of Dairy Lagoon Solids. In International Symposium on Animal Environment and Welfare. Rongchang, Chongqing, China.
Lim, T.-T. 2022. Lagoon Solids Removal, Lessons Learned. Cleanout for Lagoons and Anaerobic Digesters, Jan 21, 2022. Webinar of Livestock and Poultry Environmental Learning Community (LPELC). https://lpelc.org/cleanout-for-lagoons-and-anaerobic-digesters/
Canter, T., Lim, T.-T., Chockley, T. 2021. Considerations of Pull-Plug Sedimentation Basin for Dairy Manure Management. University of Missouri Extension Publication. Retrieved September 25, 2021. https://extension.missouri.edu/publications/eq302.
Acknowledgements
USDA NIFA, Water for Food Production Systems Program A9101, for supporting the project. It is titled “Management of Nutrients for Reuse”, a multi-faceted project that involves professionals from the University of Arkansas, University of Nebraska, Colorado School of Mines and Metallurgy, Case Western University, and University of Missouri.
Joe Harrison, Professor, Livestock Nutrient Management program, Washington State University
Gilbert Miito, Postdoctoral Fellow, Agricultural Systems Technology, University of Missouri
Richard Stowell, Biological Systems Engineering, University of Nebraska
Farm crew and custom applicator team for their help.
Livestock and poultry manure are valuable sources of organic material and nutrients for crop production and pasture growth. Nonetheless, the trend away from diversified farms has disrupted the natural nutrient recycling of manure-fertilized cropping-systems. Meanwhile, inorganic fertilizer sales in Nebraska during 2020 reached a thirty-year high. This importation of nutrients, especially nitrogen and phosphorus fertilizer to areas rich in organic fertilizer products leaves an excess of nutrients that still must be utilized and leads to higher risk for nutrient contamination of surface and groundwater sources that would reduce quality of the water.
In areas where there is a high density of livestock production, utilization of manure nutrients may require additional cropland outside the livestock operations. Moreover, the transportation and application of manure has logistical challenges that remain critical to address to motivate the local recycling of organic nutrient amendments by crop producers and livestock owners.
The present research aims to bridge this gap of knowledge by developing a clearer understanding of nutrient utilization and supply capacities through exploration of county level geospatial data.
This analysis will have two main objectives:
Quantify livestock inventories, associated manure production, inorganic fertilizer imports, and potential crop nutrient utilization, and calculate nutrient surpluses or deficits in five Nebraska counties.
Identify and describe the suitable land for manure applications in each of the five target counties.
What Did We Do?
The research team selected five Nebraska counties (Scottsbluff, Cuming, Custer, Nemaha, and Antelope) for their agricultural importance and diverse geographical location and characteristics. The analysis of nutrients was realized using publicly available geospatial data and governmental databases.
Objective 1. Quantify livestock inventories, associated manure production, inorganic fertilizer imports, and potential crop nutrient utilization, and calculate nutrient surpluses or deficits in five Nebraska counties.
For this research, “livestock” includes poultry, pigs, and cattle (beef and dairy). The team used data from the USDA National Agricultural Statistics Service (NASS) (Table 1) to estimate the total animal units within each category based on NASS data for sales and end-year inventory.
The scope of this assessment was limited to include only commercial production livestock operations, which were operations with at least three animal units or with more than $2,000 in sales of livestock products. To obtain an annual average number of animal units at county-level two important assumptions, based on Kellog, Lander, Moffit, & Gollehon (2000) research: (1) different cycles of confinement for each animal category (according to its spans form birth to market) ; and (2) that sales throughout the year did not have seasonal variation. Algorithms for estimating animal units, average amount of recoverable manure, and its consequent rate for nitrogen and phosphorus levels were calculated using as reference the formulas and conversion factors adapted from Kellog, Lander, Moffit, & Gollehon (2000) and Gollehon, Kellog, & Moffitt (2016).
Table 1. Input data and formulas
Data/formula
Date
Source
Hogs and pigs inventory and sales.
2017
USDA- NASS
Cattle and Calves inventory and sales.
2017
USDA-NASS
Poultry inventory and sales.
2017
USDA-NASS
Estimated nutrients from commercial fertilizers.
2016
NUGIS- The Fertilizer Institute
Crop production Layer
2020
USDA-NRCS-NASS
Balance of nutrient
[Eq. 1]
Balance = Farm fertilizer nutrient used + Recoverable manure nutrient use – Nutrient in harvested crops
The balance of nutrients was thus determined using Eq 1 (Table 1); where farm fertilizer is estimated by fertilizer imports at county level (NuGis database, 2016). The nutrient in harvested crops is estimated with the yield report (USDA-NRCS-NASS), and average phosphorus and nitrogen uptake and fixation rate based on literature review [1].
Objective 2. Identify and describe the suitable land for manure application for each of the five target counties.
Six suitability factors were identified for manure application: land cover, potential for phosphorus uptake, proximity to road and streets, proximity to urban areas, slope, and proximity to water bodies (Table 2). Each factor class was weighted for their impact on manure application feasibility using the Analytic Hierarchy Process (AHP) and pairwise comparison method described by Doegan, Dodd, & McMaster (1994) where factors were given scores on nine objectives (A- Reducing surface water pollution, B-Reducing ground water pollution, C- Reducing soil contamination, D- Reducing runoff loss of nutrients, E- Reducing leaching loss of nutrients, F- Avoiding excessive use of manure, G-Increasing nutrient use efficiency, H-reducing cost of manure application, I- Reducing bad odor) through an objectives-oriented comparison (OOC) which values were adapted form Basnet, Apan, & Raine (2001) (Table 3).
Table 2. Input factors and constraints.
Input Factors
Data type
Excluded land
Land cover
National Land Cover Database
Other land cover besides cropland
Potential uptake of cropland-P2O5
Cropland Data Layer (CDL)
Grasslands, pastures, developed spaces, natural ecosystems.
Proximity to developed/urban areas
National Land Cover Database
Area less than 100 ft
Proximity to road and streets
TIGER Primary and secondary roads and streets
> 35 ft
Slope
DEM of Nebraska’s County
> 10%
Proximity to water bodies
National Hydrography Dataset
> 35 ft
Table 3. Weight distribution using an AHP process.
Land cover
Criteria Weight
Potential uptake of cropland-P2O5
36
Proximity to developed/urban areas
6
Proximity to road and streets
6
Slope
20
Land cover
26
Proximity to water bodies, rivers and streams
6
*Consistency ratio of weight distribution= 0.00 (This range is a measure if the reliability of the comparison and should be <0.1)
[1] (Warncke, Dahl, & Zandstra, Nutrient Recommendations for Vegetable Crops in Michigan, 2004)(Kang, et al., 2020)(Meena, Kumar, Dhar, Paul, & Kumar, 2015)(Grains Research & Development Corporation, 2018)(Fertilizer Canada, 2001)(Grains Reseach & Development Research, 2018)Manitoba Government. (2009).(Barker, 2019) and ((Barker, 2017)(Warncke, Dahl, & Jacobs, 2009)(Sullivan, Peachey, Heinrich, & Brewer, 2020)(Grains Research & Development Corporation, 2018)(Sullivan, Peachey, Heinrich, & Brewer, 2020)International Plant Nutrition Institute (2013)).
What Have We Learned?
Objective 1.
The total balance of nutrients for each county showed that even though none of the counties we assessed have a surplus of nutrients at the county level, some of them are very close to meeting or surpassing the capacity of the land in the county to utilize additional nutrients. Of the five counties, Cumming county has the lowest phosphorus assimilation available at the county level, followed by Nemaha, Antelope, Custer, and Scotts Bluff. Balance nutrients showed a lower assimilation capacity on phosphorus than nitrogen. Since phosphorus is a nutrient limiting the growth of aquatic organisms and reduction on water quality, it was important to represent the potential phosphorus sinks at the geospatial level for Objective 2 (Figures 1 and 2).
Figure 1. County level nitrogen balance.
Figure 2. County level P2O5 balance.
Objective 2.
The area suitable for manure application in the five counties was mapped (Figure 3) with the Weighted Overlay Raster tool, on ArcGis Pro 2.9.1. This allowed the researchers to incorporate multicriteria effects with a weight for each factor. The results are summarized in Table 4 and present the proportion of land in each county that is either not suitable for manure application, has a marginal (medium) suitability, or is very suitable (high). These classifications were determined by natural breaks (Jenks) classification which partitioned data into classes based on natural groups in the data distribution.
We recognize that land suitable for manure application is closely associated with acres in crop production, which for Custer and Scottsbluff Counties is less than 50% of the total acres. Whereas Cuming County had the highest percentage of area dedicated to crop production, which explains the high proportion of “High suitability land”. The category of “Medium suitability” has the lowest percentage for all counties because it is mainly driven by differences in low and medium potential phosphorus uptake, based on crop type and area destinated for crop production, which are regularly more spatially scarce in vegetation patches.
Figure 3. Suitable land for manure application.
Future Plans
Validate the model of suitable land for manure application by checking the available data for manure production, cropland areas and slope with other official sources, and taking random samples among the counties to compare the results under field conditions.
Incorporate a socio-economic analysis for manure transportation among and within different counties.
While the county level context and characteristics have value, it would increase the accuracy of the model if more information about individual and smaller scale farms and animal feeding operations could be geospatially available. Thus, where possible, it is the researcher’s goal to improve the current analysis with the addition of more accurate data on animal operations within each county to adjust the estimation of manure production, and the nutrients balance.
Promote Outreach efforts with farmers for making decisions based on a nutrient management approach that could decrease the importation of inorganic fertilizers, where possible.
Authors
Presenting author
María José Oviedo, Graduate Research Assistant, University of Nebraska-Lincoln
Corresponding author
A. Millmier Schmidt, Associate Professor & Livestock Manure Management Engineer, University of Nebraska-Lincoln
Corresponding author email address
aschmidt@unl.edu
Additional authors
A. Millmier Schmidt, Associate Professor & Livestock Manure Management Engineer, University of Nebraska-Lincoln; J. Iqbal, Assistant Professor, University of Nebraska-Lincoln; A. Yoder, Associate Professor, University of Nebraska Lincoln; and B. Maharjan, Assistant Professor, University of Nebraska Lincoln
Additional Information
Basnet, B. B., Apan, A. A., & Raine, S. R. (2001). Selecting Suitables Sites for Animal Waste Application Using Raster GIS. Environmental Management, 519-531.
Cassman, K., Dobermann, A., & Walters, D. (2002). Agroecosystems, Nitrogen-use Efficiency, and. Agronomy & orticulture– Faculty Publications, 356.
Fergunson, R. (2015). Groundwater Quality and NItrogen Use Efficiency in Nebraska’s Central Platte River Valley. Journal of Environmental Quality.
Gollehon, N., Caswell, M., Ribaudo, M., Kellog, R., Lander, C., & Letson, D. (2011). Confined Animal Production and Manure Nutrients. Washington, DC: Resource Economics Division, Economic Research Service, U.S. Department of.
Kellog, R. L., Lander, C. H., Moffit, D. C., & Gollehon, N. P. (2000, Diciembre). Manure Nutrients Relative to the Capacity of Cropland and Pastureland to Assimilate Nutrients. Retrieved from USDA: www.nhq.nrcs.usda.gov/land/index/publication.html
Nebraska Department of Agriculture. (2020). Nebraska Fertilizer, Soil Conditioner and Ag Lime Tonnage and Sampling Reprot Calendar year 2020. Lincoln: nda.nebraska.gov.
Spiegal, S., Kleinman, P., Endale, D., Bryan, R., Dell, C., Goslee, S., . . . Gowda, e. a. (2020, June). Manuresheds: Advancing nutrient recycling in US agriculture. Agricultura Systems 182, 102813. doi:https://doi.org/10.1016/j.agsy.2020.102813
Doegan, H. A., Dodd, F. J., & McMaster, T. B. (1994). A Statistical Approach to Consistency in AHP. Marh.Comput.Modelling., 19-22.
Barker, B. (2017, April 4). Moderate flax response to nitrogen. Top Crop Manager. Retrieved from https://www.topcropmanager.com/moderate-flax-response-to-nitrogen-19985/#:~:text=Generally%2C%20flax%20takes%20up%202.83,sensitive%20to%20seed%2Dplaced%20fertilizer.
Barker, B. (2019, December 3). Managing phosphorus in flax. Top Crop Manager. Retrieved from https://www.topcropmanager.com/managing-phosphorus-in-flax/
Fertilizer Canada. (2001). Phosphorus Management for Pulses. Canola Council of Canada. Retrieved from https://www.canolacouncil.org/download/2042/canola-watch/14659/cfi_nutrient_uptake_for_wcanada_2001
Grains Reseach & Development Research. (2018). Grownotes: Chickpea-Section 5. Grains Reseach & Development Research. Retrieved from https://grdc.com.au/__data/assets/pdf_file/0030/369444/GrowNote-Chickpea-West-5-Nutrition.pdf
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Kang, F., Wang, Z., Xiong, H., Li, Y., Wang, Y., Fan, Z., . . . Zhang, Y. (2020). Estimation of Watermelon Nutrient Requirements based on the QUEFTS Model. Agronomy, 1776. Retrieved from file:///C:/Users/Majo/Downloads/agronomy-10-01776-v2.pdf
Meena, B. P., Kumar, A., Dhar, S., Paul, S., & Kumar, A. (2015). Productivity, nutrient uptake and quality of popcorn and potato in relation to organic nutrient management practices. ICAR-Indian Agricultural Research Institute, 110 012.
Sullivan, D. M., Peachey, E., Heinrich, A., & Brewer, L. J. (2020). Nutrient and Soil Health Management for Sweet Corn (Western Oregon). Oregon State University. Retrieved from https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9272.pdf
Warncke, D., Dahl, J., & Jacobs, L. (2009). Nutrient Recommendations for Field Crops in Michigan. Michigan State University. Retrieved from https://www.canr.msu.edu/fertrec/uploads/E-2904-MSU-Nutrient-recomdns-field-crops.pdf
Warncke, D., Dahl, J., & Zandstra, B. (2004). Nutrient Recommendations for Vegetable Crops in Michigan. Michigan State University.
Many small and mid-sized dairy farms use flush systems for manure removal due to reduced chore time and increased barn cleanliness. Often, flush systems require greater attention to onsite water management and frequent lagoon maintenance. While anaerobic lagoons provide some digestion of manure solids and sludge storage, solids removal may help increase lagoon capacity and reduce costly lagoon sludge removal. A pull-plug sedimentation basin (PPSB) is a passive solids removal system that can reduce the operational time and cost of the overall manure management system by acting as both a sedimentation basin and pre-lagoon solids filter system.
Larger, denser particles accumulate on the basin floor, while buoyant particles (e.g., undigested fiber, waste forage, bedding, etc.) form a floating mat on the surface. The mat acts as a natural filter and retains some of the solids from the waste stream. The PPSB was developed as part of a collaborative effort between USDA NRCS and small dairy producers in Missouri. This abstract provides background and basic information on the PPSB, while more performance evaluation of the system based on nutrient retention, costs, and maintenance and operational considerations can be found in a University of Missouri Extension publication Eq302 (Canter et al., 2021).
What Did We Do?
Design details of a working PPSB were documented, and performance evaluation was conducted based on grab samples of the flush and PPSB locations. Critical design considerations for the PPSB including design, hydraulic loading, location of the pull-plug location, and construction details were reported in the Extension publication (Canter et al., 2021). The concrete entry ramp into the PPSB should have a maximum slope of 12:1 (or 5 degrees) (Figure 1) to minimize wheel slippage and potential for equipment overturns. The example provided in Figure 1 is of a typical PPSB design that serves a herd of ~150 milking cows with a single-flush volume of ~7,000 gallons but also represents the smallest recommended size of the system. A minimum depth of 6 feet is needed to keep settling solids out of the discharge stream.
Figure 1. Profile and plan views of typical PPSB (dimensions in feet).
Detailed discussion of the advantages and disadvantages of the PPSB system was reported in the Extension publication. Relatively little maintenance has been reported, while the pull-plug is the only moving part and may need to be replaced if damaged during cleaning or degradation, Figures 2 and 3. Details such as the management and sampling and analysis were discussed, and a case study was conducted to document the information of a PPSB system of a 120-hd dairy farm in Missouri, with a flush system and sand lane, as well as a performance evaluation.
Figure 2. A PPSB system in operation at a dairy farm.Figure 3. PPSB with liquid discharge pipe, after manure solid was removed.
What Have We Learned?
The owners are satisfied with the performance of the PPSB, which is considered a low-maintenance, low-technology option to efficiently manage manure solids within a flush system. The primary benefit of the PPSB is a reduction in time spent agitating and removing solids/sludge in the lagoon. When less capacity in the lagoon is used for solids treatment and storage, there is more room to store water and longer intervals between repairing or unclogging pumps and the water system. There are typically three to four clean-out periods per year, depending on PPSB and herd sizes and other factors.
The primary benefit of the PPSB is the removal of manure solids using a low maintenance system, resulting in longer intervals between lagoon agitation and land applications. Approximately 23,450 cubic feet of manure solids were prevented from entering the lagoon each year, along with 6,454 pounds of nitrogen (438 pounds as ammonia-nitrogen) and 2,415 pounds of phosphorous. These represent 13 percent and 28 percent of manure-based nitrogen and phosphorous, respectively, being retained in the PPSB.
Future Plans
Additional sampling just before or during clean-out is necessary for a more accurate performance determination. PPSB installed at larger dairy farms, and those using different bedding should be evaluated for performance and documented the cost savings as compared with other popular solid separation systems.
Authors
Teng Lim, Extension Professor, Agricultural Systems Technology, University of Missouri
Corresponding author email address
Limt@missouri.edu
Additional authors
Timothy Canter, Extension Specialist, Agricultural Systems Technology, University of Missouri
Troy Chockley, Environmental Engineer, Natural Resource Conservation Service, United States Department of Agriculture
Additional Information
Canter, T., T.-T. Lim, and T. Chockley. 2021. Considerations of pull-plug sedimentation basin for dairy manure management. University of Missouri Extension. https://extension.missouri.edu/eq302
Acknowledgements
USDA NIFA, Water for Food Production Systems Program A9101, for supporting the project. It is titled “Management of Nutrients for Reuse”, a multi-faceted project that involves professionals from the University of Arkansas, University of Nebraska, Colorado School of Mines and Metallurgy, Case Western University, and University of Missouri.
Joseph Zulovich, Agricultural Systems Technology, University of Missouri
Richard Stowell, Biological Systems Engineering, University of Nebraska
DUCTOR Corp. has developed a biological process that separates and captures nitrogen (ammonia) from organic waste streams. The biogas industry is a natural platform for this biotechnology as it solves the problem of ammonia inhibition, which has long bedeviled traditional anaerobic digestion (AD) processes. DUCTOR’s technology allows for stabilized and optimized biogas production from 100% high nitrogen feedstocks (such as poultry manure) and significantly strengthens the economics of biogas facilities: relatively inexpensive inputs, optimized gas production as well as new, higher value revenue streams from the organically produced byproducts—a pure Nitrogen fertilizer and a high Phosphorus soil amendment. DUCTOR’s mission is to promote biogas as a renewable energy source while securing efficient waste management and sustainable food & energy production, supporting the development of circular economies.
Purpose
Figure 1. High Nitrogen Feedstock
High concentrations of ammonia in organic waste streams have been a perpetual challenge to the biogas industry as ammonia is a powerful inhibitor of biogas production. In typical methanogenic communities, as ammonia levels exceed 1500mg/L Ammonia-N, the inhibition of methane production begins until it reaches toxic levels above 3000mg/L. Traditionally, various mechanical and chemical methods have been deployed to lower ammonia concentrations in high nitrogen organic feedstocks prior to or following biodigestion (Figure 1). These methods have proven cumbersome and operationally unstable. They either require dilution with often costly supplemental feedstocks, are fresh water intensive, waste valuable nutrients, or require caustic chemicals injurious to the environment. Without the application of these methods, nitrogen levels will build up in the digester and negatively affect the efficiency of biogas (methane) production. DUCTOR’s proprietary process revolutionizes ammonia removal with a biological approach, which not only optimizes the operational and economic performance of biogas production, it also allows for the ammonia to be recaptured and recycled as an organic fertilizer product (a 5-0-0 Ammonia Water). This biotechnical innovation represents a significant advancement in biogas technology.
What did we do?
DUCTOR’s innovation is the invention of a fermentation step prior to the classic anaerobic digestion process of a biogas facility (Figure 2). During this fermentation step in a pre-treatment tank, excess nitrogen is biologically converted into ammonia/ammonium and captured through a physical process involving volatilization and condensation of the liquid portion of the digestate.
Figure 2. Typical DUCTOR facility layout
We ran a demonstration biogas facility with these two steps in Tuorla, Finland for 2000 hours using 100% poultry litter as fermenter feedstock without experiencing ammonia inhibition of the methanogenesis process. While the control, a single-stage traditional digester, showed increased buildup of toxic ammonia, the fermented material coming out of the first stage of the DUCTOR process (having ~50-60% of its nitrogen volatilized and removed) exhibited uniform levels of nitrogen below the inhibition threshold (Figure 3). This allowed a stable and efficient digestion by the methanogenic microbial community in the second stage digester. The fermentation step effectively eliminates the need for co-digestion of poultry manures with other higher C/N ratio substrates.
Figure 3: Ammonium concentration & Methane quantities in treated and untreated substrates
What we have learned?
In addition to solving the problem of ammonia inhibition, DUCTOR’s innovation realizes the separation of valuable recycled nutrients in a manner that can produce additional revenue streams. The result of the fermentation process in the first stage digestion tank is an organically produced non-synthetic ammonia (NH4OH), which is condensed and collected. This ammonia water product can be marketed and sold as an organic fertilizer as it is the result of a completely biological process with no controlled chemical reactions. The non-synthetic ammonia produced comes from the digestion of poultry litter by ammonifying microorganisms in anaerobic conditions. Furthermore, this ammonia water is in a plant available form that can be metered onto fields based on crop demands and thus reduce the amount of excess nitrates leaching into the water table and surrounding watershed.
The solids byproduct that results from the completion of the anaerobic digestion process has a large fraction of phosphorus and potash. This digestate can be dried and pelleted to produce a high-phosphorus soil amendment. While recognizing demand for this product would vary by region based on existing phosphorus levels in the soil, it offers a transportable & storable way to return these valuable elements to the nutrient cycle.
Finally, the importance of gas production as a form of sustainable, renewable energy cannot be understated. With 2/3rds of the world’s greenhouse gas emissions coming from the burning of fossil fuels for energy or electricity generation,1 biogas derived from anaerobic digestion can displace some of those processes and reduce environmental greenhouse gas emissions.2 Currently, there are many state and federal policies focusing on renewable energy credits and low carbon fuel standards to incentivize this displacement.3 With the ability to unlock poultry litter as an additional AD feedstock, biogas facilities can offer greater volumes of biogas production per ton of manure than either dairy or swine.
Future plans
We have several commercial projects that will feature the DUCTOR technology at various stages of development in North America. The demonstration facility at Tuorla has been disassembled and shipped to Mexico where it will be reassembled as part of a larger commercial project there. In cooperation with our Mexican partner, we will demonstrate successful operations under a new set of conditions, including different climate and a new source of poultry litter from different regional growing practices. We further intend to demonstrate the highly efficient water use of the process in a drought-prone area.
Additionally, we have received approval from the North Carolina Utilities Commission for entry into their pilot program for injecting biomethane into North Carolina’s natural gas pipelines. Our first project there is expected to begin construction in Spring 2019 to be completed and operational by early 2020. These projects, and others in development, will bring a very attractive and new manure management option to poultry farmers, while recycling nutrients from the waste stream and returning them to the soil in a measurable and sustainable manner.
Author
Bill Parmentier, Project Development, DUCTOR Americas
3Methane is a potent greenhouse gas that is over 20 times more damaging on the environment than carbon dioxide. Anaerobic digestion stops the release of methane into the environment by capturing it and using it for energy production or transportation fuel.
Federal incentives include the Rural Energy for America Program (REAP), Alternative Fuel Excise Tax Credit, & Federal Renewable Energy Production Tax Credit to name a few. Examples of state level incentives include various states Renewable Portfolio Standards (RPS) as well as California’s Low Carbon Fuel Standard (LCFS) or Oregon’s Clean Fuels Standard (CFS).
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.
Nutrient loading of nitrogen and phosphorus in runoff and water leachate threatens Florida’s environmental and water resources. Of those nutrients, nitrate (NO3–) nitrogen is highly soluble and not strongly bound to soils. Consequently, nitrate is highly mobile and subject to leaching losses when both nitrate content and water movement are high.
Due to Florida’s sandy soils and humid subtropical climate, nitrate losses from leaching and runoff are high and creates concerns for animal waste handling1. Mitigating nutrient loading to ground and surface waters through proper management of horse manure and stall waste can help protect water quality. However, information regarding the relationship between on-farm equine manure management practices and water quality remains limited.
What did we do
The objective of this study was to address waste management challenges on Florida equine operations by developing methodologies for in-situ characterization of nutrient profile of pore and surface water runoff from stockpiled equine waste and waste that has been effectively composted. Two small-scale horse properties with 2-8 horses managed on 4-9 acres, and 1 larger scale operation with up to 70 horses managed on 300+ acres located within the Rainbow Springs Basin Management Action Plan (BMAP) were enlisted for the project. Lysimeters (soils enclosed in suitable containers and exposed to natural surroundings to capture leachates) were constructed of PVC and non-woven filter fabric suspended between a 4” and 2” PVC reducer with a total length of 24” and deployed 6” below ground2 (Figure 1).
Figure 1. Design details and image of lysimeters used for leachate collection. Each lysimeter was equipped with silicone tubing for effluent collection.
One hole was drilled between the 4” and 2” PVC reducer to insert the sampling lines to the bottom well of the lysimeter and secured with duct tape. For each lysimeter installation, the top 6” of the soil profile was removed using a 6” diameter core ring to ensure the soil profile was undisturbed. The remaining 6”-12” depth of soil was composited and repacked into the lysimeter container, layer by layer. An auger was used to achieve a total depth of 30 inches from the surface to secure the lysimeter in the ground. Following lysimeter installation, the top 6” of intact soil was replaced above the lysimeter and all lines were buried 6” in the soil and channeled to one central location. The collection trenches were fabricated from vinyl gutter material filled with river rock (pre-rinsed for removal of iron and sediment) and installed up and downgradient at stockpile systems and at the opening of each compost bin. A 5-gallon bucket attached to the downgradient gutter served as the water collection reservoir (Figure 2).
Figure 2a) Three bin manure compost structureFigure 2b) Manure stockpile structure
Figure 2. Placement of runoff collection trenches within the (a) compost and (b) stockpile manure bin structures. The trenches intercept any runoff during heavy rainfall and drain into a 5-gallon bucket. Once the bilge pump below the bucket is adequately submerged, the water is evacuated to the secondary collection bucket for sampling.
Figure 3. Arrangement of the eight peristaltic pumps on a hand truck dolly for ease of transport. The pumps with connected clear silicone tubing are attached to the lysimeter collection line for leachate collection.
For the lysimeter leachate sampling, eight peristaltic pumps were arranged in an array of 4 pumps wired together and controlled by an on/off switch connected to a sampling tube of the lysimeter (Figure 3). A grid of 4-5 lysimeters were placed under each compost bin for collection and compositing of samples. The lysimeters for the stockpile were arranged in a 3×3 grid across the stockpile bin with each row (3 lysimeters) representing a composited sample (Figure 4).
Figure 4. Pre-installation and arrangement (3×3) of the lysimeters within the manure stockpile structure.
The lysimeters were purged with deionized water after two weeks or after a heavy rainfall event prior to the first sample collection. For water runoff collection, a 12 volt (500gph) automatic bilge pump, powered by a marine battery, was used to pump water from the collection bucket to a 5-gallon sampling bucket. A 10% subsample was collected with the remaining 90% expelled to the ground surface using a 2-way restricted-flow Y connector. Runoff samples (collected immediately post rainfall event) and leachate samples (collected biweekly) were acidified and stored in scintillation vials at 4oC for nutrient analysis (NO-X, NH4+, TKN, and TP).
Outcome
The lysimeter and water runoff collection trench construction provide a cost-effective, easily deployed system for characterizing nutrient loading in leachate and surface runoff from manure storage and composting sites. The system has been successful in collecting samples for nutrient analysis, however, a few challenges have also been identified. (1) The runoff system requires periodic maintenance, primarily cleaning (re-rinsing) the gutter and river rock to remove any material lying above the trench. (2) Also, the Y connectors require calibration every month to remove leaf litter and other debris to allow water flow through the valves to ensure a 10% subsample is collected. (3) Suspended materials (fine soil or organic matter) have been observed in lysimeter leachate samples and runoff collection trenches. (4) A subset of lysimeter samples have emitted a sulfur odor when adverse weather conditions or other events delay sampling beyond the target 2-week interval.
Future plans
To assess potential nitrate losses due to sample retention time, the lysimeter effluent will be sampled at specific intervals (day 1, day 3, day 6, day 9, day 14) during a period of no rainfall. These measurements should help determine the optimal time interval for sample collection for analysis of nitrate levels. Additionally, runoff samples are being collected for analysis of fecal coliform and E. coli. The methodologies employed in this field level study represent an important step towards an improved understanding of the impact of manure management BMPs on water quality.
Corresponding author, title, and affiliation
Agustin Francisco, Graduate Student, University of Florida
Carissa Wickens, State Extension Horse Specialist, University of Florida Mark Clark, Wetland Ecologist, University of Florida; Caitlin Bainum, Extension Agent, Florida Cooperative Extension, Marion County, Ocala, Florida; Megan Mann, Extension Agent, Florida Cooperative Extension, Lake County, Tavares, FL
Additional information
1FDEP. 2013. Small Scale Horse Operations: Best Management Practices for water resource protection in Florida.
2Bergstrom, L. 1990. Use of lysimeters to estimate leaching of pesticides in agriculture soils. J. Environmental Pollution. 67:325-347
Additional information regarding this project is available by contacting Carissa Wickens (cwickens@ufl.edu), or Agustin Francisco (afran@ufl.edu).
Acknowledgements
The authors wish to thank the Southwest Florida Water Management District (SWFWMD) for funding support, the farm site cooperators Dave and Deb Kane, Jim and Merry Lee Bain, and Eli and Jeff McGuire. We would also like to thank Carol Vasco, Ellen Rankins, Ana Margarita Arias, Anastasia Reif for their assistance with site installation and 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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