Author: Leslie Johnson

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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.

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Enhancing Phosphorus Recovery from Anaerobically Digested Dairy Effluent Using Biochar and FeCl₃ in a Rotary Belt Filter System

Purpose

This work aims to conduct pilot-scale trials using a rotary belt filter (RBF) with biochar to recover nutrients at a dairy anaerobic digestor and produce an upcycled bioproduct for soil amendment (Figure 1). Anaerobically digested (AD) effluents contain large quantities of phosphorus (P), nitrogen (N), and organic carbon, while biochar is a reactive material that has potential for use to recover nutrients and prevent nutrient loss. Biochar was used as a strategy to enhance phosphorus (P) recovery by improving total suspended solids (TSS) removal efficiency in the RBF system. This approach was further extended to include iron chloride (FeCl3) as a flocculant, which has potential to efficiently remove suspended solids as well as soluble phosphorus from wastewater.

Figure 1. Rotary belt filter removal of biochar and solids in anaerobic digest effluent.
Figure 1. Rotary belt filter removal of biochar and solids in anaerobic digest effluent.

To optimize P recovery, laboratory-scale experiments were conducted to evaluate biochar and iron chloride dosing rates. These experiments aimed to better understand the system’s performance and provide insights for pilot scale studies. The goal was to develop a lab setup that accurately represents field conditions and to identify cost-effective, practical solutions for large-scale applications.

What Did We Do?

Biochar dosing experiments were conducted using a jar test, in which 30 mL of AD dairy effluent was mixed with biochar (Biochar Now LLC., Loveland, Colorado) for 20 minutes at 200 rpm, with dosing rates of 1, 2, 4, 6, and 8 g/L. For the iron chloride dosing experiments, 6 g/L of biochar was mixed with the effluent for 20 minutes at 200 rpm, followed by the addition of iron chloride to achieve final concentrations of 0.25, 0.5, 1.0, and 2.5 g/L. The Fe-biochar mixtures were then stirred for 1 minute at 200 rpm and subsequently for 20 minutes at 40 rpm. After mixing, the samples were vacuum filtered using the same mesh of the rotating belt filter (112 mesh or 149 μm) on a 2” Buchner ceramic funnel. Since sedimentation time introduces variability to the flocculation process, a filtration setup was designed to allow simultaneous filtration of replicates. All experiments were performed in triplicate.

The solids retained on the mesh were collected, air-dried overnight, and digested using a modified dry ash method. Part of the filtrate was used for total suspended solids (TSS) analysis, while another portion was digested following the acid digestion method for sediments, sludges, and soils (EPA 3025B). The digested solid and filtrate samples were filtered through a 0.45 μm PES syringe filter and analyzed for elemental composition using an ICP spectrometer.

What Have We Learned?

The TSS of the AD dairy effluent can vary seasonally. In our experiments, the batch used contained approximately 25,000 mg/L of SS. The filtration system retains up to 15% of the SS when no biochar or Fe are amended to the AD.  The addition of 4 to 6 g/L of biochar increased TSS removal by 5%. However, higher biochar doses did not further enhance TSS removal efficiency.

Results indicated that most of the P in the AD dairy effluent is not in the soluble reactive form, which means that P removal in the rotary belt filter should be proportional to the TSS removal. Figure 2 shows the P concentration in the filtered effluent from the biochar dosing experiments, indicating that with biochar additions ranging from 2 to 8 g/L, the P concentration in the filtrate remains similar. Figure 3 shows that the P concentration in the solids decreased as the biochar dose increased. This is because the total mass of solids retained on the filter increased with the addition of biochar. These results showed that biochar has a dilution effect on P concentration because the phosphorus removal capacity of biochar during filtration is limited.

Figure 2. Total P concentration in the filtered effluent after biochar dosing experiments.
Figure 2. Total P concentration in the filtered effluent after biochar dosing experiments.
Figure 3. Total P concentration on solids retaining by filtration from the biochar dosing experiments.
Figure 3. Total P concentration on solids retaining by filtration from the biochar dosing experiments.

Figure 4 shows the P concentration on solids at different doses of FeCl3 added to 6 g/L of biochar. The results show that higher FeCl3 doses lead to higher P concentrations in the solids. Table 1 shows the relationship between FeCl₃ dosing rates and the estimated volume of iron chloride solution needed in a pilot scale field trial. With 6 g/L of biochar, achieving an increase in P concentration from ~3300 mg/L to 5000 mg/L would require 6 L/m³ of FeCl3 solution. pH adjustments would optimize iron promoted flocculation and significantly reduce the amount of iron dosing required, and thus process costs. However, due to the high buffering capacity of the AD effluent, large amounts of acid would be required, which would offset cost savings from the reduced iron amendment.

 

Figure 4. Total P concentration on solids retained by filtration from the FeCl3 dosing and 6 g/L biochar dosing experiments.
Figure 4. Total P concentration on solids retained by filtration from the FeCl3 dosing and 6 g/L biochar dosing experiments.
Table 1 – FeCl₃ dose and corresponding solution volume required in the field
Field scale
FeCl3 dose (g/L) FeCl3 (L/m3)
0 0
0.1 0.24
0.25 0.60
0.50 1.21
1.00 2.41
2.50 6.03

Future Plans

The next steps of this research are divided into two main topics. The first focuses on evaluating the effect of organic flocculants, such as chitosan and alginate, on TSS and phosphorus removal from the effluent. This includes analyzing their advantages and disadvantages compared to iron chloride. The second topic explores the oxidation of the effluent with ozone before flocculant addition. This approach aims to determine whether pre-oxidation can reduce the required flocculant dose per mg of TSS removed.

Authors

Presenting & corresponding author

Mariana C. Santoro, Postdoctoral researcher, Department of Soil and Water Systems, University of Idaho, marianacoelho@uidaho.edu

Additional authors

Daniel G. Strawn, Professor, Department of Soil and Water Systems, University of Idaho

Martin C. Baker, Research Engineer, Department of Soil and Water Systems, University of Idaho

Alex Crump, Research Scientist, Department of Soil and Water Systems, University of Idaho

Gregory Möller, Professor, Department of Soil and Water Systems, University of Idaho

 

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

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Impacts of Swine Carcass Preparation and Carbon Material on Effectiveness of Shallow Burial with Carbon (SBC)

Purpose

This project was conducted to increase our knowledge of the implications of using low-quality carbon feedstocks as the carbon layer within a Shallow Burial with Carbon (SBC) system. This system is also known as theTrench Composting and Above Ground Burial. SBC requires a 1-foot layer of carbon material in the bottom of the trench.  This carbon material serves three purposes: 1) absorbs and temporarily traps leachate released from the decomposing carcasses, 2) provides elemental carbon to the microorganisms that the system fosters to decompose carcasses, and 3) temporarily traps oxygen in the system.  To date, most applications of the SBC system have utilized wood products such as shavings, wood chips, and mulch. These products are generally effective at all 3 functions. While these carbon materials are successful feedstock for SBC, wood products are not widely available in parts of the country.

Regions with few woody carbon sources often have ready access to crop residues such as corn stover, rice hulls, straw, or hay.  These carbon feedstocks generally have a significantly lower carbon-to-nitrogen ratio than woody carbon sources.  For example, wood shavings typically have a C:N ratio of around 550:1 while the C:N ratio of straw is 100:1 or less. Materials with a higher C:N ratio may have more elemental carbon available for the metabolic activities of the microorganisms.  Crop residues tend to have a waxy cuticle layer that decreases their capacity to absorb leachate compared to woody materials.  Finally, crop residues tend to compress under the weight of the carcasses and the SBC system’s soil cover. This compression decreases the amount of oxygen trapped in the pore spaces between particles.  The degree to which these differences in the physical and chemical properties of woody products compared to crop residues impact their effectiveness as a carbon source in an SBC system has been unknown.

What Did We Do?

The study was conducted at the Horticulture Crops Research Station in North Carolina (Address: 2450 Faison Hwy, Clinton, NC 28328). This station is affiliated with NC Department of Agriculture and Consumer Services (NCDA&CS) and North Carolina State University (NCSU) is in the coastal plains region of North Carolina. The project site contained a weather station belonging to the state climate office (ECONET Station ID: CLIN) with continuous monitoring of primary weather variables such as air temperature, precipitation, wind speed, in addition to soil temperature, soil moisture content, and evapotranspiration.

Individual trenches were excavated for each treatment, ensuring each treatment combination (carbon material and carcass condition) was isolated to prevent cross-contamination. The placement of treatments was randomized to minimize bias and allow for a more rigorous comparison of outcomes. A total of 72 pigs of similar size were used, divided between whole and ground carcass treatments. Figure 1 below illustrates the site preparation.

Figure 1. Experimental site after excavating the individual plots and before carbon material placement
Figure 1. Experimental site after excavating the individual plots and before carbon material placement
Figure 2. (A) Carbon material after placement in plots: (1) hardwood mulch, (2) corn stover, (3) wheat straw, and (4) fescue hay;
Figure 2. (A) Carbon material after placement in plots: (1) hardwood mulch, (2) corn stover, (3) wheat straw, and (4) fescue hay;

Carcass decomposition was assessed using a five-point scale developed by Brown (2007), as adapted by Lochner et al. (2022) (Table 1). Observers scoring the decomposition were all trained and experienced carcass management subject matter experts, ensuring consistent and reliable assessments of carcass breakdown across all treatments.

Score Criteria
1 Large amounts of flesh, hide and hair present. Internal fluid is still visible. Carcass is still discernible.
2 Flesh, hide and hair are present in smaller amounts. Carcass is no longer discernible. No internal fluid visible.
3 Slight amounts of hair and hide present. Numerous large and small bones are present.
4 No hide present. Minimal hair visible. Flesh completely degraded and only large bones were present.
5 No flesh, hide, or hair present. Few to no large brittle bones present.

What Have We Learned?

Precipitation was analyzed in relation to evapotranspiration on a day-by-day basis. This was conducted by running a daily tally of precipitation less evapotranspiration for the entire study period; a positive value indicated a net water surplus (accumulation) while a negative value suggested deficit (or drying). Throughout the study period, the volumetric water content (VWC) fell between 25% and 35% which is close to the field capacity (FC) value for the site soil types. Collectively, these observations indicate the site soils experienced near-saturation conditions during the study period. Observers during each excavation activity reported noticeable soil wetness in the burial areas; but no pooled water.

Over the burial period, whole carcass decomposition was shown to gradually transition from a relatively low to higher decomposition score. Since these scores are ordinal but not continuous variables, we opted to avoid averaging them  avoiding confusion in interpretation.

The data indicates that all four carbon sources in this study (hardwood mulch, wheat straw, corn fodder, and fescue hay) provided an acceptable level of decomposition of whole swine carcasses after twelve months.  This trial used finishing hogs.  If larger breeding stock had been used the results may have been different.

Future Plans

Data analysis is ongoing to assess statistical significance in decomposition extent and ranking by observers. Also, downward movement associated with different treatments (different carbons, whole vs ground carcass) is currently being analyzed. Results provide guidance for site selection, carbon source screening, and relevant protective measures for water quality at the site. Future evaluation of the shallow burial with carbon (SBC) technology are planned in other sites/regions with results to be compared to this evaluation.

Authors

Presenting & corresponding author

Mahmoud Sharara, Associate Professor and Extension Specialist, Biological and Agricultural Engineering Department, North Carolina State University, Raleigh, North Carolina, msharar@ncsu.edu

Additional authors

Gary Flory, G.A. Flory Consulting LLC President, Director of Operations

Bobby Clark, Senior Extension Agent, Shenandoah County Office

Bob Peer, Agricultural Program Coordinator, Virginia Department of Environmental Quality

Mark Hutchinson, Professor Emeritus of Sustainable Agriculture, University of Maine Cooperative Extension

Acknowledgements

The authors would like to acknowledge Smithfield Foods for providing deadstock used in conducting this study. The authors also would like to acknowledge Hunter Barrier, Superintendent for the Horticultural Crops Research Station in Clinton, NC for providing space and resources needed for this work. The authors also would like to acknowledge Research Station crew for their timely support during project activities.

 

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

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Training Development for On-Farm Anaerobic Digester Operators

Purpose

This presentation documents the development of a new training program to be offered by North Carolina Extension (NC Extension), or other qualified entities, to serve on-farm digester operators in the state. This program was developed in response to increased adoption of on-farm anaerobic digestion (AD) systems in North Carolina, particularly on swine farms. With proliferation of on-farm digesters and the accompanying methane purification and transfer infrastructure, the availability of adequate training and support to ensure their safe and sustainable operation was a growing concern.

In North Carolina, the Water Pollution Control System Operators Certification Commission (WPCSOCC) was established, by NC General Statutes 143B-300 and 143B-301, to oversee training and certification of water pollution control system operators.  During their quarterly meetings, the commissioners discussed this need and engaged North Carolina State University (NC State University), the 1860 land-grant institution, to provide expertise and support over development and administration of this training program.

What Did We Do?

The training development proceeded over the following steps:

    • Need-to-know (NTKs) compilation: A team of five members representing NC Extension (the authors), NC Department of Environmental Quality (NC DEQ), and WPCSOCC met at regular intervals (three meetings in total, each 1.5 to 2 hours) to summarize key learning objectives that need to be met by the training program. External stakeholders representing animal industry, digester installers, and farm inspectors were consulted for input and comment on NTKs list (two one-on-one meetings). The NTKs were grouped by topic and divided into five (5) modules. Once finalized, the NTKs were submitted for approval by WPCSOCC during their regular meetings.
    • Training material development: Once the learning objectives were approved, NC Extension team started compiling resources (factsheets, PowerPoint slide decks) from existing NC Extension training materials on the topic, and resources made available by colleagues in peer institutions to prepare training content. Other training content delivered by land-grant and industry associations were consulted during this step. WPCSOCC and NC DEQ representatives also provided some input on content. The developed content was 3-hours in length.
    • Test offering: Once training material was developed, a group of 10 county extension agents with livestock training responsibilities were invited for the first offering of the training. They were encouraged to document impressions, comments, and provide feedback. Changes were made to address gaps, adjust pacing, and include more accessible graphics and data.
    • Official offering: Two sessions were held in September and October 2024 for the following audiences [1] NC DEQ inspectors and supervisors (28 attendees) in Raleigh, NC, and [2] animal producers/operators who operate AD systems, as well as those considering investing in AD systems in Kenansville, NC (36 attendees).
    • Feedback and continued learning: Feedback and questions by attendees were addressed in both sessions. In the second session, a county extension director facilitated compiling questions and shared them with the training leader to address. An open Zoom session was coordinated to bring expertise from regulatory agencies, the swine production sector, and AD technology installers to address these questions collectively. The answers were compiled into a frequently asked questions (FAQs) list that was reviewed by attendees before distribution and publishing on NC Extension portal, NC Swine Newsletter, and relevant trade magazines.

What Have We Learned?

Feedback and interactions with trainees showed growing interest in adopting on-farm anaerobic digesters primarily driven by the monetary value of biomethane sale as a renewable natural gas (RNG). Some cost-share programs further lowered the barrier to entry for many producers. Primary concerns/disincentives include profitability for small and medium size farms, impacts on nutrient management planning, and compliance. The training described above provides an opportunity to engage project developers/installers during the program to provide examples of adoption models without disclosing proprietary information. Clear delineation of responsibilities for the AD system between farm manager, operators, and project team supervision continues to be a priority.

Future Plans

Twice per year offering of the training is planned. Experiential and peer learning through field tours and testimonials by operators of ADs are planned for future offerings. A homepage for AD related content was developed on NC Extension portal including an opportunity to ask questions on the topic. The FAQ list will be continuously updated to answer new and emerging questions.

Authors

Presenting & corresponding author

Mahmoud Sharara, Associate Professor and Extension Specialist, Biological and Agricultural Engineering Department, North Carolina State University, Raleigh, North Carolina, msharar@ncsu.edu

Additional author

Mark Rice, Extension Specialist (retired), Biological and Agricultural Engineering Department, North Carolina State University, jmrice@ncsu.edu

Additional Information

Acknowledgements

The authors would like to acknowledge Dr. Bob Rubin, WPSOCC board member and retired NCSU faculty, Patrick Biggs (NC DEQ), Jeffrey Talbott (NC DEQ), Christine Lawson (NC DEQ), Gus Simmons (Cavanaugh and Associates) , and Smithfield Foods for feedback, assistance, and insights provided during training development.

 

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

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Bang for Your Buck: Developing Effective Anaerobic Digestion Policies for Carbon Emission Reduction

Purpose

Anaerobic digesters are an established technology for reducing methane emissions from livestock manure. In recent years, the rapid expansion of renewable natural gas (RNG) projects, driven by economic incentives such as Renewable Identification Number (RIN) credits, Low Carbon Fuel Standard (LCFS) credits, and Investment Tax Credits (ITC) from the 2022 Inflation Reduction Act, has spurred significant growth in RNG production. These incentives, while promoting the adoption of anaerobic digestion, may only sometimes be the most cost-effective way to achieve meaningful carbon reductions within the livestock sector. RNG production, electricity generation via biogas, and flaring biogas all mitigate agricultural greenhouse gas (sometimes referred to as carbon dioxide equivalence or CO2e) emissions from manure.  Nonetheless, electric generators are significantly cheaper than the biogas upgrading systems necessary for RNG production, and flares are significantly cheaper than electric generators.

Our analysis compares system costs and emissions reductions, and investigates the societal benefit featured by each system. The only revenue we analyze is RNG sales and electricity sales; we do not incorporate carbon credits into the revenue stream. Flaring biogas, or the process of burning the methane within biogas to produce the lesser potent greenhouse gas, CO2, greatly reduces agricultural CO2e emissions, though this process does not generate usable renewable energy. Electricity generation via biogas is cheaper than RNG production via biogas, but electricity can be sustainably generated with more efficient methods, such as wind turbines and solar panels. RNG is primarily created via anerobic digestion; additionally, RNG is the leading renewable replacement for conventional natural gas, a fossil fuel with increasing use, traveling within 3,000,000 miles of pipelines in the U.S. Nonetheless, RNG remains an expensive and technically complex process, requiring high capital investment and persistent, local, and skilled labor for effective operation.

What Did We Do?

This study compares the economic and carbon reduction potential of various anaerobic digestion biogas uses, including RNG production, electricity generation, and flaring. By evaluating the carbon savings and cost-effectiveness of these options, the study provides policymakers insights on optimizing public funding and incentives for the livestock industry. Furthermore, we provide livestock farmers with a decision support tool that balances the environmental benefits of anaerobic digestion with the most efficient use of financial resources to foster clean and sustainable livestock production system.

What Have We Learned?

Table 1 summarizes dollars per megagram (MG) of CO2e mitigated via RNG production, electricity production via biogas, and flaring biogas for both covered manure storages and constructed anaerobic digesters. Five scenarios were compared for farms featuring dairy cows, swine with lagoon manure storages, and swine with deep pit manure storages to analyze the carbon credit value (units of dollars per MG of CO2e mitigated) necessary to financially break even on the project. Flaring biogas featured the lowest necessary break-even carbon credit for dairy, swine farms with lagoon manure storage, and swine farms with deep pit manure storages. If a farmer wants to generate power, then generating electricity requires a lesser carbon credit value per MG CO2e mitigated compared to RNG generation. If a farmer wants to generate power via RNG, and carbon credits exist in units of dollars per energy, then a dairy farmer would be more profitable with a digester, whereas a swine farmer would be more profitable with a covered manure storage.

If a governing body is interested in maximizing its livestock manure CO2e reduction given a set amount of tax dollars, then the governing body may be most interested in incentivizing flaring systems. If a governing body is interested in both power generation via livestock manure and CO2e reduction, then the governing body may be most interested in incentivizing electricity generation. Nonetheless, renewable electricity can be generated more efficiently by a variety of methods, whereas RNG is the most prominent fossil natural gas replacement and primarily created via anaerobic digestion. Furthermore, as the electric grid “greens”, or as the CO2e emissions associated with grid electricity decrease, RNG generation will provide an overall greater percent CO2e reduction.

Deep pit swine farms generating electricity or RNG demonstrated CO2e reduction that was greater than 100%. Deep pit swine farms have less emissions than lagoon swine farms. By converting a deep pit swine farm to an outdoor covered manure storage or digester system, methane production increases, though that methane is now used for renewable energy generation, thereby offsetting fossil energy generation.

Table 1: Required Carbon Credit Value ($/MG CO2e mitigated) to Break Even
Head Dairy: 2,000 Swine – Lagoon: 14,000 Swine – Deep Pit: 14,000
Baseline CO2e (MG/yr) 10,654 10,179 3,980
Covered Storage Flaring CO2e Mitigated (MG/yr) 8,786 8,786 3,424
% CO2e Reduction 82% 86% 86%
$/yr Profit (10-year life) ($84,137) ($108,151) ($342,975)
Break-Even ($/MG CO2e Mitigated) Carbon Credit $10 $12 $100
Covered Storage Electricity CO2e Mitigated (MG/yr) 9,734 9,735 4,373
% CO2e Reduction 91% 96% 110%
$/yr Profit (10-year life) ($178,978) ($202,992) ($437,816)
Break-Even ($/MG CO2e Mitigated) Carbon Credit $18 $21 $100
Break-Even ($/kWh) Carbon Credit $0.08 $0.09 $0.20
Covered Storage RNG CO2e Mitigated (MG/yr) 9,913 9,914 4,552
% CO2e Reduction 93% 97% 114%
$/yr Profit (10-year life) ($780,801) ($795,726) ($1,030,551)
Break-Even ($/MG CO2e Mitigated) Carbon Credit $79 $80 $226
Break-Even ($/MMBTU) Carbon Credit $46 $47 $61
Digester Electricity CO2e Mitigated (MG/yr) 10,042 9,826 4,464
% CO2e Reduction 94% 97% 112%
$/yr Profit (10-year life) ($557,022) ($519,566) ($754,390)
Break-Even ($/MG CO2e Mitigated) Carbon Credit $55 $53 $169
Break-Even ($/kWh) Carbon Credit $0.14 $0.19 $0.27
Digester RNG CO2e Mitigated (MG/yr) 10,169 9,904 4,542
% CO2e Reduction 95% 97% 114%
$/yr Profit (10-year life) ($1,207,287) ($1,056,809) ($1,291,633)
Break-Even ($/MG CO2e Mitigated) Carbon Credit $119 $107 $284
Break-Even ($/MMBTU) Carbon Credit $39 $50 $62

Future Plans

The project life of biogas upgrading equipment, pipeline interconnects, electric generators, and flares are not always the same. We intend to further investigate the project lives of different equipment to calculate more accurate annualized costs and payback periods. Furthermore, we will analyze how the economies of scale compare between biogas upgrading equipment, electric generators, and flares by evaluating costs of equipment necessary for various farm sizes. Lastly, we would like to further define and quantify the overall societal impact created by RNG production, electricity production via biogas, and flaring biogas.

Authors

Presenting author

Luke Soko, Graduate Student, Iowa State University

Corresponding author

Dan Andersen, Associate Professor, Iowa State University, dsa@iastate.edu

 

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

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High Clearance Robotic Irrigation Impacts on Soybeans and Corn Yield and Nutrient Application

Purpose

This collaborative project between The Ohio State University, Iowa State University, and 360YieldCenter intends to demonstrate the in-season application of commercial and animal nutrient sources and water application as a unified strategy to reduce nutrient losses while improving profitability with increased grain yields. A new and innovative high-clearance robotic irrigator (HCRI) is being used to apply liquid-phase nutrients in-season beyond all stages of row crops. Replicated strip trials of Fall, Spring, and in-season application will occur using the HCRI (e.g., 360 RAIN Robotic Irrigator, Figure 1). The in-season application consists of traditional N and P application rates as well as reduced rates to take advantage of better matching nutrient availability to crop needs during the growing season. Data were collected to verify nitrate-nitrogen leaching loss using liquid swine manure as a nutrient source in Iowa, while total and dissolved reactive phosphorus losses with both runoff and leaching using commercially available nutrients were collected in in Ohio. Secondly, as climate shifts result in water scarcity during critical crop growth stages, robotic irrigation water applications will be used to meet the crop needs. Higher crop yields are anticipated via precision water management.

Figure 1: 360 RAIN Unit (HCRI)
Figure 1: 360 RAIN Unit (HCRI)

What Did We Do?

OSU is conducting two field demonstrations, one with a focus on water quality, and a second for comparison of nutrient management practices. The HCRI is being utilized to apply commercial fertilizer in-season via dilution in irrigation water with up to 12 applications per growing season (effective 4.5 in. of precipitation season dependent). Nutrient injection rates (N and P) are scaled to plant nutrient uptake and irrigator pass intervals. Both sites are farmed in accordance with existing crop rotation and standard practices.

Beck’s Hybrid Site (West 1A) – The Beck’s Hybrid site (78 ac) is subdivided in accordance with the sub-watershed boundaries and managed with two treatments: 1) conventional commercial fertilizer application in accordance with the Tri-State Fertilizer recommendations, and 2) in-season nutrient management (N and P) using the HCRI and Tri-State Fertilizer Recommendations with the exception nutrient application  matching with plant nutrient uptake rates as judged by growing degree days (GDD). This site is instrumented as a paired watershed for surface water and subsurface tile drainage. Further, these watersheds are monitored for precipitation, flow, and water quality (nitrate, nitrite, total phosphorus and DRP).

Molly Caren Agricultural Center (MCAC) Site 1 (Field 7) – Field demonstrations at this site (140 ac) are laid-out in a randomized complete block design (RCBD) strip trial design with treatments that include: 1) commercial fertilizer application (N and P) in accordance with the Tri-State Fertilizer recommendations, 2) in-season nutrient management (N and P) using the HCRI and Tri-State Recommendations with the exception nutrient application matched with crop nutrient uptake rates based on growth stages as determined by GDD, and 3) in-season nutrient management (N and P) using the HCRI and 67.7% Tri-State recommend application rates matched with crop nutrient uptake rates based on growth stages (GDD). Strip trials are 160 ft. in width and approximately 1,170 ft. in length (4.3 ac treatments) with eight replicates.

MCAC Site 2 (Field 8A) – Field demonstration site used to test HCRI and “sandbox” for other RCBD trials outside of NRCS CIG grant to discovery and planning for future projects. This site varies depending on studies each year, but trials are completed via RCBD strips.

Data Collection and Analysis – Demonstration sites are grid sampled each season on a 1-ac grid (Beck’s) and within treatments (MCAC site) to monitor soil fertility levels. Soil moisture and temperature in situ sensors (CropX) are placed in both study locations (three per treatment, 15 total sensors). Tissue samples are collected by treatment type to assess nutrient uptake at three stages of crop growth. Harvested crops are scaled by treatment to ensure yield monitor accuracy. Remote sensing imagery (RGB, ADVI and thermal) is collected 10 or more times during the growing season to evaluate crop growth and development. Data is analyzed using RCBD procedures in SAS.

Water Quality Assessment – Surface and subsurface (tile) monitoring capacity was established in 2016 at the Beck’s Hybrid Site. Two isolated subareas within a single production field were identified and the surface and subsurface pathways were instrumented with control volumes and automated sampling equipment. Surface runoff sites were equipped with H-flumes while compound weirs were installed at each of the subsurface (tile) outlets. Each sampling point (two surface and two subsurface) is equipped with an automated water quality sampler and programmed to collect periodic samples during discharge events. Once collected, samples will be analyzed for N and P. An on-site weather station provides weather parameters. Water samples are collected weekly from the field plots during periods of drainage and follow the same ISU protocol for NO3–N. Dissolved reactive phosphorus (DRP) and digested (total phosphorous) samples are analyzed using ascorbic acid reduction method.

What Have We Learned?

2023 Results

At the Beck’s Hybrid location field West 1A was planted to corn for the 2023 cropping season. There was an 8.0 bu/ac difference between irrigated and non-irrigated treatments. Nitrogen was injected using the rain unit and put on crop for the first application and use of the rain machine. Not having the rain unit in June made a significant difference in this study. The results of this location from 2023 should be taken lightly as complete implementation was not done until August. Location study information can be seen in Figure 2 and results in Figure 3.

Figure 2: Study information for Beck's Hybrid location in 2023 cropping season.
Figure 2: Study information for Beck’s Hybrid location in 2023 cropping season.
Figure 3: Results for Beck's Hybrid field location in 2023.
Figure 3: Results for Beck’s Hybrid field location in 2023.

In 2023, field 7 at MCAC was in soybeans and had no irrigation completed for this growing season.

Field 8A at MCAC was in corn for the 2023 cropping season. Irrigation had a statistically significant effect on yield over all treatments. Nitrogen had statistical significance from 120 versus 170 and 220 units on nitrogen treatments. The 170 units of nitrogen was the optimal amount of nitrogen for all treatments. Not having the irrigator installed in early June caused there to be less yield in irrigated treatments. The results of this location from 2023 should be taken lightly as complete implementation was not done until August. Location study information can be seen in Figure 4 and results in Figure 5.

Figure 4: Study information for MCAC 8A location in 2023 cropping season.
Figure 4: Study information for MCAC 8A location in 2023 cropping season.
Figure 5: Results for MCAC 8A field location in 2023.
Figure 5: Results for MCAC 8A field location in 2023.

2024 Results

Field 7 at MCAC was in corn for the 2024 cropping season. Irrigation had a statistically significant effect on yield over all treatments. There was a 48 bu/ac between irrigated two-thirds nutrients and non-irrigated and 44 bu/ac between irrigated and non-irrigated for the 2024 growing season. A total of 773 gallons of diesel was used to run the irrigator for this trial for 2024 cropping season across 71 acres. A total of 25,739 kWh was used to run the electric pumps, base station, and well for 2024 growing season across 71 acres. These are the initial results that were published in efields and further results will continue to be analyzed to meet all project objectives. This data will be used to help in evaluating HCRI versus traditional crop production and management practices to meet project objectives. Location study information can be seen in Figure 6 and results in Figure 8. In Figure 7, aerial imagery can be seen from the 2024 cropping season.

Figure 6: Study information for MCAC 7 location in 2024 cropping season.
Figure 6: Study information for MCAC 7 location in 2024 cropping season.
Figure 7: Aerial imagery of field 7 (Top l) and field 8A (Bottom left) from 2024 cropping season.
Figure 7: Aerial imagery of field 7 (Top l) and field 8A (Bottom left) from 2024 cropping season.
Figure 8: Results for MCAC 7 field location in 2024.
Figure 8: Results for MCAC 7 field location in 2024.

Field 8A at MCAC was in soybeans for the 2024 cropping season. Irrigation had a statistically significant effect on yield over non-irrigated. A total of 211 gallons of diesel was used to run the irrigator for this trial for 2024 cropping season across 11 acres. A total of 3,475 kWh was used to run the electric pumps, base station, and well for 2024 growing season across 11 acres. Location study information can be seen in Figure 9 and results in Figure 10. In Figure 7, aerial imagery can be seen from the 2024 cropping season.

Figure 9: Study information for MCAC 8A location in 2024 cropping season.
Figure 9: Study information for MCAC 8A location in 2024 cropping season.
Figure 10: Results for MCAC 8A field location in 2024.
Figure 10: Results for MCAC 8A field location in 2024.

Future Plans

During the next 12 months, we are planning for the HCRI operation at the two sites for cropping practices and irrigation for 2025 growing season. We will be aggregating weather data, agronomic data, plant samples, surface and ground water quality samples, and machine performance data for all years of the project with the current end date as spring of 2026. We are hoping to continue to perform testing with this technology and implementing the dry product skid for field operations for the 2025 growing and full-scale implementation across all studies in 2026. The results from the Iowa State portion of this funded project will also be reported in the future as well. There is a significant need to further develop programs for injecting macro and micronutrients in liquid and granular form for growers. The potential to significantly cut application rates exists with this technology. Also, implementing this technology with liquid livestock manure producers will change the paradigm of how manure is managed in the future.

Authors

Presenting & corresponding author

Andrew Klopfenstein, Senior Research Engineer, The Ohio State University, Klopfenstein.34@osu.edu

Additional authors

Justin Koch, Innovation Engineer, 360YieldCenter; Kapil Arora, Field Agricultural Engineer, Iowa State University; Daniel Anderson, Associate Professor, Iowa State University; Matthew Helmers, Professor, Iowa State University; Kelvin Leibold, Farm Management Specialist, Iowa State University; Alex Parsio, Research Engineer, The Ohio State University; Chris Tkach, Lecturer, The Ohio State University; Christopher Dean, Graduate Research Associate, The Ohio State University; Ramareo Venkatesh, Research Associate, The Ohio State University; Elizabeth Hawkins, Agronomics Systems Field Specialist, The Ohio State University; John Fulton, Professor, The Ohio State University; Scott Shearer, Professor and Chair, The Ohio State University

Additional Information

eFields On-Farm Research Publication 2023 and 2024 Editions – https://digitalag.osu.edu/efields

Acknowledgements

Natural Resources Conservation Service – Conservation Innovation Grant (NR223A750013G037)

Ohio Department of Agriculture – H2Ohio Grant

USDA, NRCS, 360YieldCenter, Beck’s Hybrids, Molly Caren Agricultural Center, Rooted Agri Services, Iowa State University, The Ohio State University

 

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

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System for Treating Livestock Wastewater Using Electrochemistry to Recover the Nitrogen and Phosphorus

Purpose

Conservation and recovery of nitrogen (N) and phosphorus (P) from livestock, industrial, and municipal effluents are important for economic and environmental reasons.  Therefore, a need exists for improved systems and methods for N and P recovery from wastewater, especially by using fewer chemicals.  A new method was developed using electrochemistry to enhance the gasification and rate of ammonia capture by a gas-permeable membrane and the solubilization and the rate of phosphate capture using P-precipitating compounds.  The process was tested using liquid swine manure.  It recovered 86% of the ammonia and more than 93% of the phosphorus contained in the manure.

What Did We Do?

This work aimed to develop new technology for simultaneous N and P recovery that eliminates alkali chemicals used to increase pH for quick N capture using gas-permeable membranes (Vanotti and Szogi, 2015), and also eliminates acid chemicals used to solubilize the P in the manure before precipitation with P-precipitating agents (Szogi et al., 2018).  The new N and P recovery system used in this example is described by Vanotti et al., 2024. It has a cathode chamber, an anode chamber, a stripping acid solution tank, and a phosphorus recovery tank (Fig. 1).  The cathode chamber is fitted with a gas-permeable membrane manifold. The cathode chamber is fitted with a gas-permeable membrane manifold and contains a salt solution. The wastewater containing ammonia and phosphorus is pumped into the anode chamber. The ammonium (NH4) in the anode chamber permeates into the cathode chamber through a cation exchange membrane placed between chambers.  The cathode increases the pH of the liquid and accelerates the rate of passage of ammonia through the gas-permeable membrane into an acid-stripping solution contained in a stripping tank/ reservoir and recirculated through the membrane manifold in a closed loop. The wastewater in the anode chamber is acidified by H+ released by electrolysis in the anode.  The anode chamber effluent, with most of the P solubilized, is passed through a centrifuge or filter to separate suspended solids without phosphorus and liquid filtrate/centrate with phosphate. Phosphorus precipitating compounds used were MgCl2 and Ca(OH)2.   After rapid mixing, the phosphorus precipitates as a solid.  This precipitation proceeds quickly as a result of the previous removal of the carbonate alkalinity in the anode chamber, which interferes with phosphate precipitation.

Figure 1. Schematic diagram of an embodiment of a nitrogen (N) and phosphorus (P) recovery system using electrochemistry (Vanotti et al., 2024).
Figure 1. Schematic diagram of an embodiment of a nitrogen (N) and phosphorus (P) recovery system using electrochemistry (Vanotti et al., 2024).

What Have We Learned?

In tests with liquid swine manure, the pH in the cathode chamber was increased due to the electrochemical production of OH-, from 5.8 to 12.5 (Fig. 2).  The wastewater’s ammonia was removed from the anode chamber and recovered in the stripping acid solution with 86% recovery efficiency (Fig. 3).

Figure 2.  pH in anode chamber, cathode chamber, and stripping acid tank.  
Figure 2.  pH in anode chamber, cathode chamber, and stripping acid tank.
Figure 3.  Ammonia-N mass removal in anode chamber and ammonia-N mass recovery in cathode chamber and stripping acid tank.
Figure 3.  Ammonia-N mass removal in anode chamber and ammonia-N mass recovery in cathode chamber and stripping acid tank.

The wastewater pH in the anode dropped from 7.9 to 3.5, and carbonate alkalinity dropped from 10750 mg/L to 0 mg/L (Figures 2 & 4).  The acid was produced by oxidation at the anode (2 H2O → O2 + 4 H+).  These conditions transformed the P from manure particles into soluble phosphates that were efficiently recovered in the phosphorus recovery tank.   For example, using the P-precipitating compound Ca(OH)2, the process recovered 93% of the total P in a P precipitate solid compared to only 4.6% in a control without electrochemical treatment (Fig. 5).  Using the P-precipitating compound MgCl2, the process recovered 95% of the total P in a P precipitate solid compared to only 6% P recovery in a control without electrochemical treatment (Fig. 5).

Figure 4. Reduction of carbonate alkalinity concentration occurring in the anode chamber. 
Figure 4. Reduction of carbonate alkalinity concentration occurring in the anode chamber.
Figure 5. Phosphorus is recovered in the solid precipitate using P-precipitating compounds Ca(OH)2 or MgCl2.  A) with a previous electrochemical step, and B) without an electrochemical step.  
Figure 5. Phosphorus is recovered in the solid precipitate using P-precipitating compounds Ca(OH)2 or MgCl2.  A) with a previous electrochemical step, and B) without an electrochemical step.

Future Plans

USDA-ARS seeks a commercial partner to bring this technology to market.  For more information on commercialization, contact: Mrs. Tanaga Boozer, Technology Transfer Coordinator, USDA-ARS, OTT Southeast Area, tanaga.boozer@usda.gov

Authors

Presenting & corresponding author

Matias Vanotti, USDA-ARS, Matias.vanotti@usda.gov

Additional authors

M.B. Vanotti, A.A. Szogi, P.W. Brigman, and S. Rawal, United States Department of Agriculture (USDA), Agricultural Research Service (ARS), Coastal Plains Soil, Water and Plant Research Center, Florence, South Carolina.

Additional Information

Szogi A.A., Vanotti, M.B., Shumaker, P.D. 2018.  Economic recovery of calcium phosphates from swine lagoon sludge using Quick Wash process and geotextile filtration. Frontiers in Sustainable Food Systems 2, 37, https://doi.org/10.3389/fsufs.2018.00037.

Vanotti, M.B., and Szogi, A.A. 2015. Systems and methods for reducing ammonia emissions from liquid effluents and recovering ammonia. U.S. Patent 9,005,333 B1. U.S. Patent and Trademark Office.

Vanotti, M.B., Szogi, A.A., Brigman, P.W., and Rawal, S. 2024. Systems for treating wastewater using electrochemistry. U.S. Patent Appl. 18/808,123. U.S. Patent and Trademark Office

Acknowledgements

This research was part of USDA-ARS National Program 212, ARS Project 6082-12630-001-00D. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.

 

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

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Novel technologies for dairy manure treatment: recovering ammonia with bioelectrochemical systems

Purpose

Animal manure is frequently applied to crop fields to supplement manufactured fertilizers, as manure is rich in many of the nutrients required for plant growth. Most nutrients in manure exist in organic forms, which must first be mineralized to inorganic forms before they can be used by plants. Direct land application of manure relies on in situ mineralization of nutrients by soil microorganisms, which is a slow and difficult-to-control process. In anticipation of limited immediate nutrient availability, manure is often applied to fields in excess of actual agronomic nutrient need. The excess nutrients can leach into water sources, causing accelerated eutrophication and threatening human and ecosystem health. As such, it is advantageous to investigate technologies designed to recover manure nutrients in inorganic forms, which can then be more easily regulated and applied to suit specific agricultural demand. Bioelectrochemical systems (BES) are a novel treatment option employing electrogenic microorganisms to drive operation and recover mineralized nutrients, making them an advantageous resource recovery mechanism.

What Did We Do?

This study investigated a BES for organic nitrogen mineralization and ammonia recovery from synthetic (e.g. prepared solution of organic nitrogen and acetate) and real dairy manure. The BES was custom fabricated and followed a two-chamber design as outlined in Burns and Qin (2023). Briefly, a cation exchange membrane separated a biological anode and chemical cathode in respective chambers. Electrodes were connected via a 10 Ohm resistor to allow for current flow, and synthetic or real dairy manure was fed to the biological anode depending on the experimental condition under investigation. The BES was operated in both fuel cell and electrolysis cell (applied voltage = 0.8 V) modes.

Figure 1. Schematic of the bioelectrochemical system used to treat dairy manure and produce ammonia fertilizer.
Figure 1. Schematic of the bioelectrochemical system used to treat dairy manure and produce ammonia fertilizer.

System performance was evaluated for organics removal (measured as chemical oxygen demand or COD), nitrogen removal, and total ammoniacal nitrogen production. We also calculate the nitrogen removal efficiency, RN, which measures how current is partitioned to drive nitrogen transport (as NH4+) across the cation exchange membrane. We modeled full-scale implementation of this technology on a theoretical Wisconsin dairy farm based on the experimental results obtained when treating real dairy manure. Results from the model (functional unit: tonne of manure treated, allocation: kg fat-and-protein-corrected milk (FPCM)) were used to investigate environmental impacts including greenhouse gas (GHG) emissions (in kg CO2eq tonne-1 manure), ammonia losses (in kg NH3 tonne-1 manure), and eutrophication potential (kg PO42- tonne-1 manure).

What Have We Learned?

In synthetic manure experiments, the BES consistently achieved excellent organics removal, exhibiting COD removal efficiencies well above 90%. Furthermore, total nitrogen removal efficiency averaged around 40% in electrolysis cell operation, and was seen to reach as high as 60% for some experiments. In fuel cell operation, nitrogen removal efficiency was decreased, averaging around 23%, indicating a slight advantage for nitrogen removal in electrolysis operation. RN exhibited interesting trends before, during, and after electrolysis cell operation. For the same system operational parameters, RN in fuel cell mode was around 1 mol N mol-1 electrons before electrolysis cell operation. However, during electrolysis operation and when the system returned to fuel cell operation after electrolysis cell operation, RN was and remained elevated at nearly 3 mol N mol-1 electrons with much more variability. This variability suggests that the microbial community was less tolerant to applied voltage conditions, and that there was perhaps some significant change during electrolysis operation that was difficult to recover from upon return to fuel cell operation. When treating real dairy manure, the system achieved average removals of 60% of total nitrogen and 58% of organic matter (Burns et al., 2024). The system exhibited similar nitrogen removal across multiple dairy manure feedstocks, however, a decrease in RN was observed with more complex dairy manure feedstock, likely due to the presence of competing ions (Burns et al., 2024).

Figure 2. Radar plots showing greenhouse gas emissions, ammonia losses, and eutrophication potential of three manure treatment scenarios: no processing/direct land application, solids-liquids separation (SLS), and microbial fuel cell (MFC) treatment for both surface and injection application of products. Results are reported per tonne of manure treated with an allocation of fat and protein corrected milk (FPCM).
Figure 2. Radar plots showing greenhouse gas emissions, ammonia losses, and eutrophication potential of three manure treatment scenarios: no processing/direct land application, solids-liquids separation (SLS), and microbial fuel cell (MFC) treatment for both surface and injection application of products. Results are reported per tonne of manure treated with an allocation of fat and protein corrected milk (FPCM).

We also investigated the environmental impacts of BES manure treatment when scaled up to a ~730 cow dairy farm. Impacts on greenhouse gas emissions, ammonia losses, and eutrophication potential were compared for surface and injection application of three manure treatment scenarios: (1) no manure treatment or processing, (2) solids-liquids separation (SLS) manure processing, and (3) BES manure treatment. Preliminary results from the model reported that BES manure treatment decreased impacts in all three categories when compared to the no treatment scenarios, and resulted in less ammonia loss when compared to the SLS treatment scenarios (Figure 2). For GHG emissions, BES manure treatment had slightly increased emissions when compared to SLS, mostly due to the added energy and freshwater inputs. However, BES manure treatment received more credits for P and N-based fertilizers than SLS treatment. For eutrophication potential, BES manure treatment had slightly less impact when compared to SLS treatment, despite the added impacts of freshwater, energy, and supplemental chemicals required for the treatment. Based on these results and those from experimental data, BES manure treatment is concluded to be a promising and competitive technology worthy of further development.

Future Plans

The results of this research prove bioelectrochemical systems to be a viable manure treatment alternative to current technologies. Our future work will involve investigating the organic nitrogen degradation kinetics in the BES treating dairy manure. Our goal is to determine reaction rate orders and calculate kinetic constants for degradation of COD, TN, and organic N within the cell, which can be used to develop more accurate full-scale models of the process. This analysis can be extended to investigate differing compositions of dairy manure based on the dairy’s variable feed compositions throughout the year. Additionally, we plan to expand the environmental impact analysis to include two other comparison scenarios which would be realistic at the industrial scale: (1) minimizing freshwater inputs for manure dilution and (2) harvesting electricity produced by the BES towards meeting pumping and aeration demands. Based on the model, BES manure treatment would require approximately 1,700 kWh of electricity per week to meet pumping an aeration demands, some of which can be provided by the microbially-generated electric current in the system. Furthermore, due to reactor size constraints at the lab scale, there is currently a large amount of freshwater used to dilute the manure prior to treatment with the MFC. This work will help to contextualize BES within existing manure treatment frameworks and will help both researchers and practitioners make informed decisions regarding manure treatment options.

Authors

Presenting author

McKenzie Burns, PhD Candidate, the University of Wisconsin—Madison

Corresponding author

Dr. Mohan Qin, Assistant Professor, the University of Wisconsin—Madison, mohan.qin@wisc.edu

Additional authors

    • Dr. Horacio Aguirre-Villegas, Scientist III, the Nelson Institute for Environmental Studies at the University of Wisconsin—Madison
    • Dr. Rebecca Larson, Associate Professor, the University of Wisconsin—Madison

Additional Information

Acknowledgements

The authors would like to thank the support from National Science Foundation CBET 2219089. In addition, the authors would like to thank the startup fund from the Department of Civil and Environmental Engineering, College of Engineering, the Office of the Vice-Chancellor for Research and Graduate Education (OVCRGE) at the University of Wisconsin–Madison, and the Wisconsin Alumni Research Foundation (WARF) for the support of this study. The authors gratefully acknowledge support from Jackie Cooper of the Environmental Engineering Core Facility at the University of Wisconsin–Madison for use of facilities and equipment. Finally, the authors thank Andrew Beaudet, Ethan Napierala, Katie Mangus, and David Xiong for their contributions as undergraduate researchers on this project.

 

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

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Liquid Dairy Manure in a Sugarbeet Rotation

Purpose

As large dairies move into western Minnesota, a consistent supply of manure is available that was not historically present. These dairies are using a new technology to separate solids from liquids in the manure, and the impact on nutrient availability in this region’s climate and soil types is unknown. Understanding this is particularly important for sugarbeet growers in the region as late season N availability in the soil affects sugar content of the crop (high late season soil nitrate levels typical result in reduced sugar production). Where in the crop rotation should this manure be applied to maximize the beneficial properties while minimizing risk?

What Did We Do?

A three-year crop rotation including sugarbeet, corn, and soybean was set up at two locations (west central and northwestern Minnesota) with each crop present each year (Figure 1) and then rotated accordingly in subsequent years. Two rates of liquid separated dairy manure from a nearby commercial dairy were applied in the first year (in the fall prior to planting of each crop) and compared with standard synthetic fertilizer-only practices (fertilizers were applied each spring prior to planting). The two manure application rates were approximately 15,000 gallons per acre, which supplied approximately 195 pounds first-year available nitrogen per acre, or approximately 10,000 gallons per acre, which supplied approximately 150 pounds of first year available nitrogen per acre. In following years, only commercial fertilizer was applied according to soil test phosphorus and potassium levels or state nitrogen guidelines, considering manure nitrogen credits if applicable, for each crop. At the end of each growing season, yield was determined for each crop. Sugarbeet was also evaluated for sugar content and quality.

Figure 1. Aerial photograph taken in July 2021 of the plot setup with each crop labeled. Each crop was replicated four times in a randomized complete block design.
Figure 1. Aerial photograph taken in July 2021 of the plot setup with each crop labeled. Each crop was replicated four times in a randomized complete block design.

What Have We Learned?

The manured treatments typically resulted in similar or higher yields than synthetic- fertilizer-only for corn and sugarbeet during all three years of the rotation. For soybean, yields were significantly decreased by manure application at one site in the first year and generally unaffected at the second site. In the second and third years, there were no differences in soybean yield across nutrient treatments.

Future Plans

This study was conducted in two fields that did not have a recent history of manure application. Since we know that manure is the “gift that keeps on giving”, we want to repeat this study to see if there are long-term effects of nitrogen release from repeated applications of manure. Thus, manure was applied after the third growing season of the rotation and the rotation will begin again at both sites.

Authors

Presenting & corresponding author

Melissa L. Wilson, Associate Professor and Extension Specialist, University of Minnesota, mlw@umn.edu

Additional Information

Search for manure research: https://www.sbreb.org/research/

Acknowledgements

Thanks to the Sugarbeet Research and Education Board of Minnesota and North Dakota for funding 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. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date.

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Changes in amount and location of US dairy manure production from 1970-2023

Purpose

We estimated milking cow manure production for US states from 1970 to 2023 with the aim to provide a broad perspective to stakeholders who manage and optimize the use of dairy manure. Stakeholders include producers and those working on their behalf such as agronomists, applicators, engineers, extension agents, researchers, governmental agencies, cooperatives, and markets.

It is hoped that with increased understanding of how manure production has changed over time and location stakeholders can better understand trends and historical conditions which impact their efforts.

What Did We Do?

We estimated milking cow manure production for 48 US states from 1970 to 2023 using an empirical equation estimating manure production as a function of milk production published by the American Society of Agricultural and Biological Engineer’s Manure Production and Characteristics standard. To apply this equation to each state we utilized two data sources produced by the United States Department of Agriculture’s National Agricultural Statistics Service (NASS), annual milk production and annual milking cow herd size. To gain further insight data sources reporting the number of dairy farms and land available for manure application in each state were additionally gathered from NASS and reported in combination with manure production. The workflow and references for combining this data are displayed in the following figures.

Figure 1. Workflow to estimate annual dairy manure production using ASABE’s Manure Production and Characteristics standard and NASS milk cow production and cow herd inventory data sources.
Figure 1. Workflow to estimate annual dairy manure production using ASABE’s Manure Production and Characteristics standard and NASS milk cow production and cow herd inventory data sources.
Figure 2. Workflow to estimate number of dairies and acres for manure application from NASS data sources.
Figure 2. Workflow to estimate number of dairies and acres for manure application from NASS data sources.

What Have We Learned?

Nationally annual dairy manure production has decreased from 1970-2023 by approximately 4% (2.2 billion gallons). From 1998 to 2023 annual dairy manure production increased by approximately 13% (6.4 billion gallons). Although national milking cow numbers generally declined from 1970 to 1998 then nearly remained constant until 2023, this trend was offset by continual increase in manure production per cow from 1970-2023 due to the direct relationship with milk production, which has continued to increase from 1970-2023. Also, the annual number of gallons of manure per dairy farm has increased from 1970-2023 due to a decrease in number of dairies combined with an increase in manure production per cow. It is accepted that the US dairy industry has consolidated over time, this data supports that its’ manure production has consolidated as well.  The author posits based on experience and this analysis that nationally, over time, manure systems in support of livestock production have contributed to an increase in volume of manure being managed to date. As dairy cows move to increasing levels of confinement, from pasture and lots which utilize land base as a manure system to barns with more engineered manure systems, greater collection of manure occurs and therefore must be managed. Regarding the impact of the specific type of engineered manure systems impact on volume of manure that must be managed the author posits this currently varies based on the kind of manure system selected, either adding or subtracting to the managed manure stream, which is a function heavily dependent on local climate (precipitation, evaporation, and length of storage period) and technology adoption (covers, flush systems, separation, and advanced treatment). In the upper Midwest with relatively high precipitation, low evaporation, and long winter periods dairy manure systems are predominantly collect and store only, overall adding to the volume of manure to be managed as additional precipitation is also captured by the uncovered nature of most storages in this region.

Figure 3. National change in manure and milk production, milking cow inventory, and number of dairies from 1970 to 2023.
Figure 3. National change in manure and milk production, milking cow inventory, and number of dairies from 1970 to 2023.

At the state level the change in manure production has varied. From 1970 to 2023, 12 states have increased manure production, the remaining 26 states have decreased manure production. This has resulted in a change in the location of where manure is produced. In 2023, most manure was produced in a few states. In 2023, 10 states produced 70% of the total annual US dairy manure production, with 6 states producing over 50%.

Figure 4. 2023 annual milking cow manure production, millions of gallons, and percent change of annual milking cow manure production from 1970 to 2023.
Figure 4. 2023 annual milking cow manure production, millions of gallons, and percent change of annual milking cow manure production from 1970 to 2023.

Future Plans

Authors seek to maintain this data analysis in a method available to stakeholders, additionally incorporating manure production from swine, beef, and poultry into it, and updating it as future NASS reports are published.

Authors

Presenting & corresponding author

Mike Krcmarik, Professional Engineer, mikekrcmarik@gmail.com

Additional Information

Email corresponding author for copy of all data and figures used in this analysis, including figures published on the poster only.

Acknowledgements

    • American Society of Agricultural and Biological Engineers, Engineering Practices Subcommittee of the ASAE Agricultural Sanitation and Waste Management Committee responsible for standard ASAE D384.2 Manure Production and Characteristics used in this analysis.
    • United States Department of Agriculture’s National Agricultural Statistics Service responsible for the various surveys and reports used in this analysis.
    • Allen Young, Eric County Soil and Water Conservation District (New York) providing valuable review and discussion.

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