Tag: dairy manure

Posted on

Can Cover Crops Help Nutrient Management in Idaho Dairy Systems?

Purpose


This research aims to determine the effectiveness of cover crops (CCs) to improving nutrient uptake and soil health in a corn silage-cover crop system. Nutrient accumulation in soils from years of dairy manure or compost applications has increased the level of soil nutrients, creating environmental concerns. The study tests the feasibility and performance of different management strategies using CCs to mine nutrients from agricultural soils and reduce the negative environmental impact of manure or compost application.

What Did We Do?

In one study, two CC mixes (low height or tall) were inter-seeded (dual cropping) with corn silage at two different dates, near the corn planting date and later in the vegetative development. Two post-harvesting management strategies were used by either keeping the CC during the next season or terminating the CC in the spring, before the next corn silage planting. The control had no CC, only the corn silage. In an additional study, a fall CC mix was planted after corn silage harvest (double cropping). Different management strategies were used, including harvesting the CC, simulated grazing, green manuring the CC, and control with no CC. Both studies received the same amount of dairy manure compost annually, plus synthetic fertilizers. All other parameters, including corn planting and harvesting times and irrigation, were the same for both studies and all treatments. Weed management was adjusted using mowing as a method on plots with CCs, and herbicide on plots with no CCs.

What Have We Learned?

This study will continue for two more years. The first year of data collection was 2021. The inter-seeding (dual cropping) study results show very few significant differences in soil analysis comparing CC treatments. There were, however, statistically significant differences between some treatments and the control. This situation indicates that having an actively growing CC influences the soil nutrients and nutrient uptake compared to not having any CC when growing corn silage. The short CC mixes, either planted near the corn planting date or later during the corn vegetative development, tend to have the highest increase in soil OM, especially under reduced or no-till conditions, and reducing soil nitrates, ammonium, and total nitrogen. This can be explained by the better growth of the low mixes that continued growing after the corn silage harvest, compared with the high mixes that were harvested with the corn and rarely regrew after harvesting. CC establishment and growth was a challenge each year due to the corn silage shade. The low CC mix was the only one that was not terminated and continued to grow until after planting the corn silage the following spring. This treatment has proven challenging due to the aggressive CC regrowth and low growth of the corn with the CC competition, even when using strip tillage.

In most years, the previous season CC needed to be terminated to allow for the corn to grow and to reduce weed pressure before replanting the CC again. Soil phosphorous (P) did not show significant differences across treatments and control on the surface level. Phosphorus levels kept increasing during the study, indicating that the application rate far exceeded the crop uptake. In the case of nitrogen, even when CC showed increased nitrogen (N) uptake for all N species, nitrates have accumulated in soils, especially at lower depths, indicating leaching processes in all treatments and much more in the control (Figure 1). Cover crops can uptake some of the excess nitrogen, especially on the soil top layer, reducing the impact of N leaching (Figure 2). Under nutrient overapplication conditions, CCs that have not developed to their full potential cannot handle all the nutrients’ load, thus leaching can still occur. Overall, inter-seeding CC may have a positive impact on nutrient management when managed properly. This positive effect may be complex to quantify when comparing different CC practices with lower-than-ideal CC growth and under nutrient-overapplication conditions.

The second trial with double cropping with a single fall CC mix after harvesting the corn silage was more successful in most years in growing much more CC mass than the inter-seeding CC. The greatest differential was present only for a short period in spring before harvesting or terminating the CC for corn planting. Weed management during the corn growing season was simplified in the double (fall) cropping system. Results on the impact of fall CC and the different treatments compared to the control have not been fully analyzed.

Figure 1. Soil NO3-N estimated marginal means at 0-30 cm, 30-60 cm, 60-90 cm, and 90-100 cm depths across all sampling points in an inter-seeding corn silage-cove crop system receiving annual applications of dairy compost and synthetic fertilizer.
Figure 1. Soil NO3-N estimated marginal means at 0-30 cm, 30-60 cm, 60-90 cm, and 90-100 cm depths across all sampling points in an inter-seeding corn silage-cove crop system receiving annual applications of dairy compost and synthetic fertilizer.

Figure 2. Estimated marginal means of soil nitrate at 0-30 cm depth by CC planting timing, CC height, and CC vs control in an inter-seeding corn silage-cove crop system receiving annual applications of dairy compost and synthetic fertilizer.

Figure 2. Estimated marginal means of soil nitrate at 0-30 cm depth by CC planting timing, CC height, and CC vs control in an inter-seeding corn silage-cove crop system receiving annual applications of dairy compost and synthetic fertilizer.

Future Plans

There is additional data to analyze in both studies, including other soil chemical parameters, corn silage and CC yields, and feed quality. In the last year, moisture sensors were installed in some plots, measuring and recording soil moisture and temperature at different depths up to three feet. This moisture data at various depths could be correlated with nitrate values and other soil chemical parameters data to determine nutrient leaching, irrigation efficiency, and what role CC may play. Two additional seasons of data will be included to the dataset.

Authors

Presenting & corresponding author

Mario E. de Haro-Martí, Professor and Extension Educator, University of Idaho, mdeharo@uidaho.edu

Additional authors

Linda Schott, Assistant Professor, Extension Specialist, University of Idaho

Miguel Mena, MS Graduate Student, SWS Department, University of Idaho

Steven Hines, Professor and Extension Educator, University of Idaho

Anthony S. Simerlink, Assistant Professor and Extension Educator, University of Idaho

Clarence Robison, Research Support Scientist, University of Idaho

Additional Information

Idaho Sustainable Agriculture Initiative for Dairy website: https://www.uidahoisaid.com/

Acknowledgements  

The research team thanks the USDA-ARS Kimberly, ID personnel for their support with machinery and assistance with this project.

Funding for this project was provided by a USDA-NIFA Sustainable Agriculture Systems (SAS) grant #2020-69012-31871.

 

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.

Posted on

Economic feasibility of dairy manure and food waste co-digestion at small, medium, and large farms

Purpose

Anaerobic digestion (AD) of dairy manure with and without food waste has mainly been implemented on a large scale in the US. The installed cost of these systems have economies of scale, and operations and maintenance costs need to be outweighed by adequate revenues from accepting food waste and/or producing energy, as well as reducing greenhouse gases (GHG). Scaling down AD systems is now technically feasible even on a micro-scale, but economic feasibility is still largely a challenge at small scales.

Local markets with competitive value structures for AD energy output and GHG reduction are needed to facilitate successful small and moderate scale AD systems. Analysis of energy values and consideration of food waste co-digestion with manure, as a way to expand revenues needed for economic feasibility at various scales, can help farmers and policymakers navigate opportunities.

What Did We Do?

We investigated the economic feasibility conditions of small, medium, and large AD systems processing dairy manure from 300 cows, 1000 cows, and 2,000 cows, respectively, in combination with varying amounts of food waste. The Cornell Manure-based Anaerobic Digester Simulation tool was further developed and then utilized to model the mesophilic, vessel-type AD of various food wastes and amounts in combination with varying dairy cow manure volumes to assess performance and associated economics. The breakeven capital cost of the full project was computed for each scenario (nine per dairy farm size) of manure to food waste ratio, tip fee revenue, energy output and revenue value. These were compared to estimated project costs based on multiple case studies to evaluate whether or not the breakeven cost was high enough to be considered an economically viable project.

What Have We Learned?

Key results from modeling these scenarios included that an AD to biomethane system can be economically feasible for a 300-cow dairy (300 lactating cow equivalents) only when food waste is co-digested in an equal volume with the manure and when tip fees reach $20 per ton and biomethane is valued at $25 per million BTU (MMBTU) or more. Biomethane sell price data collected from our collaborator, Energy Vision, was found to be as high as $70 per MMBTU if sold in the California transportation market (manure only AD), and between $12 and $28 in voluntary markets.

Additionally, a dairy farm with 1,000 lactating cow equivalents (e.g., 725 milk cows and 650 heifers), was found to achieve economic feasibility with 25% or more of food waste ratio to manure co-digested as long as both tip fees and energy revenue were high ($40 per ton tip and $35 per MMBTU biomethane). When food waste ratios increased to half the digester’s feedstock, economic feasibility was achievable at more moderate rates. The economic feasibility of manure-only AD continues to be challenged at small and moderate scale, while the addition of food waste with manure enables significantly higher revenues from substantially more energy production and tipping fees.

Future Plans

This project included detailed analysis of a small-scale co-digestion application at Cornell’s smaller Teaching Dairy operation to evaluate available equipment and biogas utilization options. A preliminary design is developed, capital funding secured, and initial operating period research and extension defined. The project is scheduled to be completed later this calendar year and will be utilized for various food waste and manure anaerobic digestion to energy system research and educational programming.

Authors

Presenting & corresponding author

Lauren Ray, Sr. Extension Associate, Cornell University – PRO-DAIRY, LER25@cornell.edu

Additional author

Peter Wright, Agricultural Engineer, Cornell University

Additional Information

https://cals.cornell.edu/pro-dairy/our-expertise/environmental-systems/manure-energy-systems

Acknowledgements

Funding was provided by the New York Farm Viability Initiative.

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. 

Posted on

Using ManureTech Decision-Support Tools to Aid in Manure System Selection

Purpose

The purpose of the ManureTech Decision-Support Tools (DST) for Dairy and for Swine is to assist farmers, consultants, and others in the dairy/swine industry in optimizing the management of manure from collection to land application. By providing data-driven recommendations based upon customizable inputs and priorities, the ManureTech DST help users make informed decisions about manure management systems in consideration of the economic, environmental, and operational needs of farm management.

What Did We Do?

A multi-state team has developed Excel-based decision-support tools for selecting technology and systems for managing manure on dairy and swine operations as part of a USDA NIFA-funded project.

During this workshop, participants will be introduced to the ManureTech DST for Dairy and the ManureTech DST for Swine and will be provided with hands-on training in using the decision-support tool for dairy.  Major aspects of the tools that will be addressed in the workshop include an introduction to the user interface; entering primary inputs; prioritization of economic, environmental, and operational metrics; and reporting of results, including the ranking of manure system scenarios.

What Have We Learned?

In terms of learning, this effort has provided the project team with a fuller grasp of the complex nature of manure management!  In terms of accomplishments, the team has assembled a tool that considers the multi-faceted benefits and challenges of various manure management systems and presents users with a ranked list of systems for consideration, which should help expedite and enhance system selection.  Users of the ManureTech DST can provide farm-specific weight to economic, environmental, and operational criteria which allows ManureTech DST to rank alternative manure management scenarios in close alignment with individual priorities.

This visual illustrates what a user of the ManureTech Decision-Support Tool sees when weighing economic, environmental, and operational priorities of a farm, so that the rankings of the manure management systems reflect these farm priorities.  In the illustrated case, the user preferences favor economic priorities over others.
This visual illustrates what a user of the ManureTech Decision-Support Tool sees when weighing economic, environmental, and operational priorities of a farm, so that the rankings of the manure management systems reflect these farm priorities.  In the illustrated case, the user preferences favor economic priorities over others.

Future Plans

Future plans include completing beta testing / pilot-testing of the ManureTech DST and conducting additional training on using the tool.  Over a longer-range timeframe, the team would like to add some additional specialized capabilities and functionality, as a phase II effort.

Authors

Presenting authors

    • Erin Scott, Project/Program Manager, University of Arkansas
    • Varma Vempalli, Wastewater Treatment Specialist, City of Meridian (ID)
    • Jacob Hickman, Systems Analyst, University of Arkansas
    • Rick Stowell, Extension Specialist in Animal Environment, University of Nebraska-Lincoln
    • Teng Lim, Extension Professor and Engineer, University of Missouri

Corresponding author

Rick Stowell, Extension Specialist in Animal Environment, University of Nebraska-Lincoln, Richard.Stowell@unl.edu

Additional authors

    • Erin Scott, Project/Program Manager, University of Arkansas
    • Jacob Hickman, Systems Analyst, University of Arkansas
    • Jennie Popp, Associate Dean and Professor, University of Arkansas
    • Varma Vempalli, Wastewater Treatment Specialist, City of Meridian (ID)
    • Greg Thoma, Director of Agricultural Modeling and Lifecycle Assessment, Colorado State University
    • Teng Lim, Extension Professor and Engineer, University of Missouri

Additional Information

The ManureTech DST and related articles can be accessed at Decision-Support Tools – Livestock and Poultry Environmental Learning Community.

Acknowledgements

The authors acknowledge funding from the USDA NIFA AFRI Water for Food Production Systems program, grant #2018-68011-28691.

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.

Posted on

Measured methane emission rates relative to the chemical composition of dairy manure samples

Purpose

Methane emissions from liquid manure storage systems contribute a significant portion of methane emissions from the US agricultural sector (EPA, 2024). There is a need for more farm-level methane emission values to guide decision-making activities within the dairy industry and by government agencies. Cost, time, and labor constraints are challenges related to on-farm methane emission measurements. There is a need for simpler emission measurement methods.

The purpose of this work was to investigate relationships between methane emission rates (MER) in a laboratory assay and commonly measured characteristics including total solids (TS), volatile solids (VS), ash, and total Kjeldahl nitrogen (TKN). The relationships were also examined in conjunction with storage type, season, manure type, and storage duration.

What Did We Do?

We collected dairy manure samples from manure storages at 27 farms in Minnesota and Wisconsin at 2 to 4-month intervals throughout 2024. These samples represented various storage types, storage durations, and manure temperatures. To date, a majority of these samples have been processed for TS, VS, Ash, and TKN using standard methods for manure chemical analyses (American Water Works Association, 2017; Wilson et al., 2022). Additionally, MER were estimated in triplicate with a 3-day in vitro assay (Andersen et al., 2015). Relationships between MER and these manure chemical constituents were examined using Spearman correlation analysis and bivariate plots across all manure samples and with respect to other manure management characteristics. These include storage type, season, manure type, and storage duration. Manure chemical constituents were treated as numerical data whereas storage characteristics were treated as categorical data in the analysis. It is important to note that many samples may only have a partial set of manure analyses completed at this point. This resulted in varying counts of available samples used in the statistical analyses below (Table 1-3). Summary statistics (mean, median, range) are also presented for the different manure chemical constituents.

What Have We Learned?

Table 1 shows summary statistics of dairy manure samples processed for this work (wet basis). There was a wide range of concentrations observed for each manure chemical constituent; however, average values were comparable to American Society of Agricultural and Biological Engineers (ASABE) manure characteristics values (ASABE, 2019).

Table 1: Summary statistics of dairy manure chemical characteristics (% wet basis) (n = 148 for TKN, n = 155 for other manure constituents)

Mean Median Min Max
TS 5.92% 4.98% 0.53% 17.89%
VS 4.39% 3.50% 0.27% 16.60%
Ash 1.53% 1.21% 0.26% 11.12%
TKN 0.31% 0.29% 0.08% 0.83%

Generally, overall correlations (Table 2) and correlations within categories (Table 3) were not strong, however there were some exceptions. These exceptions were observed in TS and VS relationships with MER for flush water and long-term storage duration (Table 3). Here, both positive and negative correlations that were at least moderately strong (rs ≥ |0.5|) were observed. Since methane emissions are a product of organic matter degradation, positive correlations between VS and MER were expected, but not always reflected in the results. Other trends in relationships between other manure constituents and MER are not well understood. However, manure management factors may also influence other microbial activity with respect to TS, Ash, and TKN content, which may have indirect effects on MER that cannot be discerned from a correlative relationship.

Additionally, given the wide range in the concentrations of all manure constituents and MER, it may be difficult to distinguish these relationships when comparing across the aggregate values. Instances where the strongest correlations were observed (Table 3) describe samples from a single farm, which suggests conducting a similar analysis within individual farms to better understand these relationships.

Table 2: Overall Spearman correlation values (rs) between manure constituents and MER

Total solids Volatile solids Ash Total Kjeldahl Nitrogen
MER 0.060 0.052 0.137 -0.046

 

Table 3: Spearman correlation values (rs) between manure constituents and MER by manure storage type, manure type, storage duration, and season

TS vs MER VS  vs MER Ash vs MER TKN vs MER
Manure storage type Transfer pit (n = 169) 0.150 0.124 0.271 0.075
Underfloor pit (n = 34) -0.103 -0.121 -0.125 -0.153
Manure type Raw manure (including bedding (n=36) 0.270 0.267 0.312 0.369
Raw manure (including bedding + others) (n = 140) 0.042 0.047 0.094 -0.093
Liquid separated manure (n =24) -0.213 -0.297 -0.025 -0.156
Flush water (n = 9) 0.800 0.800 0.883 0.833
Storage duration Short term (< 1 month) (n = 176) 0.082 0.090 0.117 -0.020
Long term (> 1 month) (n =6) -0.771 -0.771 -0.143 -0.200
Point sample (not a storage) (n= 29) 0.029 -0.078 0.350 -0.136
Season Winter (n= 23) 0.013 0.081 -0.011 0.132
Spring (n= 57) 0.406 0.399 0.411 0.238
Summer (n = 46) -0.268 -0.291 -0.165 -0.436
Fall (n =66 -0.188 -0.198 -0.023 -0.011

 Future Plans

We plan to conduct a stepwise regression analysis to better understand the significant independent variables (manure constituents) that influence MER. Correlations between manure constituents and MER using measurements from samples within individual farms will also be conducted.

Authors

Presenting author

Noelle Soriano, PhD candidate, University of Minnesota

Corresponding author

Erin Cortus, Associate Professor and Extension Engineer, University of Minnesota, Ecortus@umn.edu

Additional author

MaryGrace Erickson, Postdoctoral associate, University of Minnesota

Additional Information

Andersen, D. S., Van Weelden, M. B., Trabue, S. L., & Pepple, L. M. (2015). Lab-assay for estimating methane emissions from deep-pit swine manure storages. Journal of Environmental Management, 159, 18-26.

American Water Works Association. (2017). Standard Methods for the Examination of Water and Wastewater. American Water Works Association.

ASABE. (2019). Manure Production and Characteristics (ASAE D384.2). ASABE.

EPA. (2024). Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2022 (No. EPA 430-R-24-004). U.S. Environmental Protection Agency. https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-andsinks-1990-2022

Wilson, M., Brimmer, R., Floren, J., Gunderson, L., Hicks, K., Hoerner, T., Lessl, J., Meinen, R. J., Miller, R. O., Mowrer, J., Porter, J., Spargo, J. T., Thayer, B., & Vocasek, F. (2022). Recommended Methods Manure Analysis (M. Wilson & S. Cortus, Eds.; 2nd ed.). University of Minnesota Libraries Publishing.

Acknowledgements

We are grateful to the farms that participated in this research for providing samples and for sharing their observations with us. We are also grateful to Kevin Bourgeault, Seth Heitman, Sabrina Mueller, and Jacob Olson for contributing to sampling and laboratory analysis.

This research is supported by through USDA NIFA Award 2023-68008-39859, and the Minnesota Rapid Agricultural Response Fund.

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. 

 

Posted on

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. 

 

Posted on

Turning Dairy Manure Into P-rich Hydrochar, a Conceptual Design of Continuous-Flow HTC System

Purpose

Dairy manure was once considered a waste, but it can be transformed into a valuable resource. As demand for sustainable waste management grows, innovative ways for converting dairy manure are being actively researched to enhance both dairy productivity and environmental sustainability. One such method, hydrothermal carbonization (HTC), has recently garnered significant attention due to its ability to convert wet biomass into value-added products. HTC involves treating wet biomass, such as dairy manure with high water content, at moderate temperatures (180℃-250℃) and pressure. The outcome of HTC is hydrochar, a solid product with high carbon and nutrient content.

Hydrochar has strong potential as a means of soil amendment, carbon sequestration and/or biofuel. Our lab scale experiments showed that hydrochar retains more than 90% phosphorus (P) from dairy manure.  For hydrochar production to become a viable technology for dairy farms, a continuous system is essential. Such a system would offer numerous benefits, including increased production, enhanced efficiency, and greater potential for commercialization. The purpose of this study is to design a pre-commercial conceptual process for the continuous production of hydrochar from dairy manure.

What Did We Do?

Manure management consists of collecting manure from the floor to utilize it in the best possible way. Most dairy farms treat manure through anaerobic digestion to produce energy, separate the solids for use as a bedding material, and/or apply directly to field applications. To explore alternative ways of handling the large quantities of manure in a quick chemical method and recycling nutrients back to the cropland, dairy manure is processed into P-rich hydrochar via an HTC process. Based on the results of our laboratory experiments, a conceptual process was developed, which is capable of treating dairy manure from a mid-size farm with 1,000 lactating cows and equates to 38,000 tons of manure per year with 8-10% solids. The process design includes engineering designing details of manure preparation and handling, feeding and discharge mechanisms, main equipment (such as HTC reactor and heat exchangers), heating and temperature controls, and schemes for post-HTC process wastewater (post-water) handling. Figure 1 is the schematic of the conceptual process with major process equipment, where the thick, black lines indicate the flow of dairy manure slurry containing solids, while the thin, blue lines represent the flow of post-processed water.

Firstly, dairy manure collected from the dairy barns (approx. 10% solids) is stored in a storage tank (T-101) before being pumped into the feeding tank (T-102), where it is heated to 167°F (75°C) by the recycled post-water from preheater I (E-201) through internal heating coils. The feeding tank is equipped with a marine-style impeller for agitation to maintain solid suspension. Two preheaters (E-201 and E-202) are used to further heat the slurry to the required HTC temperature before entering the reactor (R-301). Preheater I is a shell-and-tube heat exchanger to heat the slurry up to 320°F (160°C) by heat recovery using the hot post-water from post-water tank (T-304).  Preheater II is a tubular electric heater and is to finish the last stage of heating to 437°F (225°C). A continuously stirred tank reactor (CSTR) with agitation is the main equipment to thermochemically process dairy manure into hydrochar. After a 30-minute retention time in the reactor, the resulting product mixture is collected in the receiving tank/separator (T-302). Then the hot post processed-water is separated from the solid (the wet hydrochar cake) and collected in a storage tank (T-304) before being used as a heating medium for heat recovery. The wet hydrochar cake coming out of decanter centrifuge (T-303) is dewatered through an air-drying unit (C-305) to a water content of 12% or less, which can be used directly for land applications or packaged and transported to other markets.

Figure 1 Schematic of the conceptual process with major process equipment.
Figure 1 Schematic of the conceptual process with major process equipment.

What Have We Learned?

Continuous hydrochar production holds great potential for recycling phosphorus from dairy manure back into the cropland as a soil amendment and for sequestrating carbon back to the soil. The conceptual process represents a significant step towards practically promoting this alternative manure treatment technology and creating a value-added product for nutrient cycling. This process is capable of producing approximately 5 million pounds (2,300 metric tons) of air-dried hydrochar per year, a yield of about 60% of the solid matter from dairy manure, and with a phosphorus concentration of approx. 1.4 lb/100 lb. Hydrochar is hydrophobic and can be sufficiently dried by ambient air. The air dried hydrochar contains a moisture content of 12% or less (as low as 5% per laboratory results due to hydrochar’s hydrophobic characteristics) and is suitable for long term storage and/or distance transportation. Because the raw, wet dairy manure can be processed directly from the farm without any pretreatment, the HTC process offers a good possibility for a cost-effective waste management alternative while producing valuable hydrochar for phosphorus recycling.

Future Plans

Upon completing this continuous flow process design, we will conduct a techno-economic assessment (TEA) to provide insights into the system’s economic feasibility, cost structure, and profitability. The TEA study will also offer a better perspective on the economic viability, technical challenges, and potential profitability of adopting and investing in the continuous hydrochar production system from dairy manure for waste management and nutrient cycling.

Authors

Presenting author

Imran Hussain Mahdy, Graduate Student (Ph.D.), University of Idaho

Corresponding author

Brian He, Professor, University of Idaho, bhe@uidaho.edu

Acknowledgements

USDA AFRI, UADA NIFA and Idaho Agricultural Experiment Station are acknowledged for their financial support through Sustainable Agricultural Systems (SAS) program (Grant 2020-69012-31871), and hatch project of IDA0-1716 (Accession number1012741).

 

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. 

Posted on

Pilot-scale Composting System to Measure Air Emissions from Dairy Manure and other Byproducts

Purpose

The overall objectives of this research are to investigate the design, implementation, and evaluation of a pilot-scale composting system for dairy manure. This composting system was developed because of the significant quantities of dairy manure produced in Idaho and the need to improve dairy compost quality while reducing air emissions during the composting process. This composting system provides the ability to simulate on-farm composting in Idaho while measuring and regulating key composting parameters, gas emissions, and implementing changes during operation.

What Did We Do?

This pilot-scale composting system was developed by adapting a home composter to simulate a mechanically turned windrow system. The composters were modified to include aeration control, air monitoring equipment (Gasmet), and measure key composting parameters throughout the process. Ten compost reactors were built, which allowed for several combinations of treatments and multiple replications. Each reactor is connected to a plenum with the capacity to interconnect several reactors or isolate each one and regulate airflows and chamber pressure. During the initial trial, two replications of each amendment: control, biochar, pumice, wood chips, and zeolites were evaluated. A follow-up trial will repeat the two replications per treatment, for a total of four replications. Modifications of the composting system during the trial addressed challenges with moisture control, odor, temperature regulation, air velocity, and compost balling.

Figures 1 and 2 define the blocking pattern and layout of the composting system for all ten compost reactors. The blocking pattern was generated for two primary reasons: Create replications for each treatment and compensate for a temperature differential between both ends of the research space caused by the cooling method in the greenhouse.

Figure 1. Diagram of air plenum that hangs above the compost reactors. Source: Authors

Figure 2. Diagram of gasmet tubing color coded with three separate lengths of PTFE tubing to each reactor. Source: Authors

What Have We Learned?

We learned that the pilot-scale composting system can effectively simulate different types of on-farm composting methods, demonstrating its adaptability for research. During the composting trial, the aeration was regulated to simulate forced and natural airflow composting systems. The ability to continuously measure the headspace size confirmed a significant decrease in composting volume, as expected in a full sized composting system. The temperature monitoring showed we were able to reach thermophilic composting for the first two weeks of the trial and showed temperature increases at each turning event. These findings indicate that this system can be a valuable tool for developing more efficient on-farm dairy manure management practices at the pilot-scale.

Future Plans

The design and implementation of this composting system have only completed one trial run. The immediate next step is to complete another round of the compost trial. Each resulting compost mix with the corresponding amendment will be tested in a crop-testing greenhouse trial. The amount of compost, or any other products, handled by these reactors allows for further tests in the lab, at the pilot scale, or in a greenhouse.

In the short term and beyond the dairy manure trials, the reactor system will be tested for other processes, including different composting techniques and amendments. Other processes to be tested include soil amendments and their impact on air emissions, anaerobic digestion without mixing, emissions from diverse waste streams and amendment combinations, among others.

Authors

Presenting author

Anthony Scott Simerlink, Assistant Professor, Extension Educator – Power County, University of Idaho

Corresponding author

Mario E. de Haro-Martí, Professor, Extension Educator – Gooding County, University of Idaho, mdeharo@uidaho.edu

Acknowledgements

Funding for this project was provided by a USDA-NIFA Sustainable Agriculture Systems (SAS) grant #2020-69012-31871.

 

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. 

 

Posted on

Phosphorus Recycling from Dairy Manure via Hydrochar – Experience from the Lab-Scale to Pilot-Scale Hydrothermal Carbonization Prototype

Due to a technical glitch, the beginning of the recorded presentation was not recorded. Please accept our apologies.

Purpose

To address the depletion of phosphorus resources and the environmental issues associated with phosphorus enriched runoff from the application of raw manure, a strategic and sustainable approach is to recycle phosphorus from dairy manure using innovative and efficient methods. Hydrothermal carbonization (HTC) has been considered one of the sustainable techniques, which can transform dairy manure into phosphorus-enriched hydrochar at relatively low temperatures, typically ranging from 180 to 250 °C. This process not only recovers valuable phosphorus but also converts organic waste into a stable, nutrient-rich product that can be used as a soil amendment or phosphorus fertilizer.

Despite the massive experimental activity performed to characterize the HTC process, the design and development of a validated bench-scale model is crucial for scaling up. While numerous studies have explored the HTC process at the laboratory level, only a limited number of studies have assessed the technical feasibility and performance of implementing this process on an industrial scale. In this context, the purpose of this study was to provide a detailed and systematic examination of phosphorus recovery from dairy manure using a lab-scale HTC reactor and illustrated the basis of the design of a bench-scale processor and evaluated its performance in terms of hydrochar yield (HY) and phosphorus recovery (PR).

What Did We Do?

Fig. 1. Scale-up of the hydrothermal carbonization (HTC) reactor from lab-scale to bench-scale. (a) Lab-scale HTC reactor with a 300 mL capacity, used for small-batch experiments. (b) Scaled-up bench-scale HTC reactor with a 9 L capacity. 
Fig. 1. Scale-up of the hydrothermal carbonization (HTC) reactor from lab-scale to bench-scale. (a) Lab-scale HTC reactor with a 300 mL capacity, used for small-batch experiments. (b) Scaled-up bench-scale HTC reactor with a 9 L capacity.

In this study, the HTC of raw dairy manure with a 7.9% of total solids was first conducted using the lab-scale reactor to optimize the process parameters, including temperature and reaction time, and then scaled up at a scale of 30 times larger (Fig. 1). The HTC-derived hydrochar samples were named according to the temperature and reaction time. For example, HC200-30 represents the hydrochar sample obtained at 200 °C and 30 min. The scaled-up reactor was designed and operated at the optimized conditions obtained from the lab-scale study, which was 225 ºC and 60 min of reaction time. The HY, which also reflects the mass reduction of dairy manure (on a dry weight basis), and PR were the two main parameters evaluating the HTC of dairy manure. We additionally evaluated the energy required for hydrochar processing in both lab- and bench-scale processors.

The HY and PR expressed as a percentage were determined by the following equations:

What Have We Learned?

Fig. 2 shows the effects of HTC processing temperature and reaction time on the HY and PR using the lab-scale reactor. It was observed that the HY decreased gradually as the processing temperature and time increased, which is attributed to the temperature and time dependent degradation of organic matter during HTC. The highest PR was observed at 225 ºC and 60 min.

Fig. 2. Hydrochar yield (%) and phosphorus recovery (%) efficiency under different hydrothermal carbonization conditions.
Fig. 2. Hydrochar yield (%) and phosphorus recovery (%) efficiency under different hydrothermal carbonization conditions.

As shown in Fig. 3, the scale-up of the hydrothermal carbonization (HTC) process demonstrated that HY and PR remained consistent between lab-scale and bench-scale systems, indicating that the transition to a larger reactor did not compromise HY or PR. Notably, the energy input per mass of hydrochar was significantly reduced in the bench-scale system, improving overall energy efficiency. These findings indicate that scaling up HTC can enhance process feasibility while maintaining similar nutrient recovery.

Fig. 3. Comparison between lab-scale and bench-scale HTC systems. (a) Hydrochar yield (%), (b) phosphorus recovery (%), (c) Energy input (kwh/kg-HC), and (d) specifications of the scale-up reactor.
Fig. 3. Comparison between lab-scale and bench-scale HTC systems. (a) Hydrochar yield (%), (b) phosphorus recovery (%), (c) Energy input (kwh/kg-HC), and (d) specifications of the scale-up reactor.

Future Plans

We plan to further develop a continuous-flow HTC system at pilot-scale as a potential advanced manure processing pathway. We will also conduct technoeconomic and environmental assessments to verify scalability and sustainability.

Authors

Presenting author

Mohammad Nazrul Islam, Postdoctoral Fellow, University of Idaho

Corresponding author

Lide Chen, Professor, Dept. of Soil & Water Systems, University of Idaho, lchen@uidaho.edu

Additional author

Brian He, Professor, Dept. of Chemical and Biological Engineering, University of Idaho

Acknowledgements

This work is supported partially by USDA NIFA (award number 2021-67022-35504) and the University of Idaho P3R1 grant.

 

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.

Posted on

Ammonia Recovery from Anaerobically Digested Dairy Manure Using Electrodialysis Coupled with A Hydrophobic Gas-permeable Membrane for Stripping

Due to a technical glitch, the beginning of the recorded presentation was not recorded. Please accept our apologies.

Purpose

Nitrogen is considered an essential macronutrient for plant growth and development. Ammonia, a key part of the nitrogen cycle, arises through two main pathways: naturally through biological nitrogen fixation bacteria and artificially through the Haber-Bosch process. The Haber-Bosch is an energy-intensive process relying on fossil fuels and contributing to greenhouse gases emission. Recovering ammonia from anaerobically digested dairy manure offers a more sustainable alternative to this energy-intensive process, reduces reliance on fossil fuels and mitigates environmental impact. Furthermore, the recovered ammonia can be used as a value-added product to improve soil health and sustainable agricultural productivity. Various technologies have been applied to recover ammonia from dairy manure. However, these technologies were not very efficient in terms of energy consumption, resource recovery, and treatment time.  The purpose of this research was to develop a hybrid system where electrodialysis and membrane stripping were applied simultaneously to enhance ammonia recovery from anaerobically digested dairy manure within a shorter treatment period. This approach promotes circular economy through transforming dairy waste into a valuable resource.

What Did We Do?

We developed a three-chamber electrodialysis and membrane stripping (ED-MS) combined system, in which the anode and the cathode chambers were separated by a cation exchange membrane (CEM), and the cathode and trap chambers were separated by a hydrophobic gas-permeable membrane (GPM). The GPM was used for membrane stripping. The authigenic acid in anolyte and the authigenic base in catholyte have been utilized as absorbents and stripping agents to improve ammonia recovery in the ED-MS system. We have applied different current densities ranging from 0 to 150 A/m2 to observe the effect of ammonia removal and recovery efficiency within an 8-hour treatment period. We also observed the maximum rate of nitrogen flux passing through the CEM and GPM for a specific energy consumption.

What Have We Learned?

From this research, we have learned that with increasing current density the removal and recovery efficiency of ammonia also increased. The presence of ammonia in the trap chamber increases with increasing treatment time (Figure 1).  This ED-MS treatment process demonstrated a broad range of effectiveness for current densities ranging from 0 to 150 A/m2, achieving ammonia removal efficiencies of 42.97% to 99.49% and recovery efficiencies of 11.7% to 75.9% over an 8-hour treatment time. The main reason for this increment is to accelerate the electrolysis process and increase the rate of acid production in the anolyte and base production in the catholyte (Figure 2). The product recovered was ammonium sulfate which can be used as a fertilizer. The highest nitrogen flux through CEM and GPM was identified as 616.1 and 207.6 g-N m-2d-1, respectively, with a specific energy consumption of 45.3 kWhkg-1N-1 (Figure 3). Therefore, this research supports the idea that the ED-MS technique could be a viable solution for sustainable ammonia recovery from anaerobically digested dairy manure on a large scale.

Figure 1. Ammonia distribution in three chambers at different treatment times.
Figure 1. Ammonia distribution in three chambers at different treatment times.
Figure 2. Changing pH with different current densities in anolyte and catholyte.
Figure 2. Changing pH with different current densities in anolyte and catholyte.
Figure 3. Effect of current density on nitrogen flux and specific energy consumption.
Figure 3. Effect of current density on nitrogen flux and specific energy consumption.

Future Plans

To continue this research, we have a plan to investigate the reaction kinetics of this ED-MS hybrid system. Further, we will develop a novel electrochemical reactor to recover nitrogen and phosphorus simultaneously from dairy waste.

Authors

Presenting author

Ashish Kumar Das, Ph.D. Student, Environmental Science Program, College of Natural Resources, University of Idaho

Corresponding author

Dr. Lide Chen, Professor, Department of Soil and Water Systems, Twin Falls Research and Extension Center, University of Idaho, lchen@uidaho.edu

Acknowledgements

This research was funded by the USDA Sustainable Agricultural Systems Initiative through the Idaho Sustainable Agriculture Initiative for Dairy (ISAID) grant (Award No. 2020-69012-31871).

 

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.

Proudly powered by WordPress