Assessing Feasibility of Bio-acidification to Reduce On-farm Ammonia Volatilization from Dairy Manure, Digestate and Urine

Progress report for ONE21-402

Project Type: Partnership
Funds awarded in 2021: $29,939.00
Projected End Date: 03/31/2023
Grant Recipient: Rich Earth Institute
Region: Northeast
State: Vermont
Project Leader:
Abraham Noe-Hays
Rich Earth Institute
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Project Information

Project Objectives:

This project will assess whether bio-acidification of manures using high-carbon substrates is a potentially feasible method for reducing ammonia emissions on Northeast farms. If successful, the method could generate increased farm revenue through whey or short paper fiber disposal fees, as well as reduced fertilizer purchases and/or higher yields from retained manure N. 


We will address the following questions: 

Lab research questions:

  1. Does the addition of whey and/or paper fibers induce fermentation in liquid dairy manure, digestate, and/or human urine?
    1. What pH changes are achieved by different volume ratios?
    2. Is there any benefit from adding starter cultures?
    3. How long do the pH changes of different mixtures last at different temperatures? 
  2. Does bio-acidification reduce ammonia volatilization when manure, digestate, or urine are applied to soil? 


Farmer research questions:

  1. What challenges do farmers have managing ammonia loss from manure? How feasible would bio-acidification be on farms with liquid manure? 
    1. We will interview 10-15 farmers managing liquid manure to understand their concerns around manure N content and loss, and manure storage / management capacity
    2. Using lab trial results, we will conduct a detailed analysis with two farmer-partners of whether and how bio-acidification could be added to their operations, and additional research needs.

Ammonia volatilization from manure is a significant source of environmental N pollution and an economic loss for farms. UVM Extension Nutrient Management Specialist Laura Johnson has found that farmers in the Northeast are concerned with ammonia loss, both from the perspective of neighborly relationships (i.e. reducing odor), and reducing fertilizer costs (PC, 10/14/20). According to the Vermont Agency of Agriculture, this is a key issue for the farmers they work with because fertilizer is one of their biggest farm expenses (PC, 10/19/20). A common issue noted in previous farmer interviews conducted by Rich Earth was expressed by long-time Vermont dairy farmer Peter Miller, whose several hundred cows do not produce sufficient manure to fertilize his 700 acres (Noe-Hays, 2020). Retaining the N in that manure could significantly reduce his overall costs. 

In Europe, acidification of liquid manure is used to reduce ammonia emissions; however, this requires hazardous concentrated inorganic acids, limiting wider-scale adoption. An alternative is to acidify slurry using fermentation by adding high-carbon waste material to liquid manure stores. In addition to reducing N pollution and purchased inputs, this may indirectly help reduce P overapplication and runoff, if manure is used to meet crop N demand. These benefits could potentially be achieved for lower cost than other ammonia retention methods like injection equipment, tank covers, or biochar. Additionally, with adequate pH reduction, bio-acidification likely prevents methane generation in slurry stores, reducing greenhouse gas impact. This method could benefit any farmer using liquid manure, digestate, and/or urine fertilizers. 

Using data from USDA (2020) and EPA (2020), we estimate that there are approximately 8,000 liquid dairy and swine manure storage facilities in the Northeast (including tanks, lagoons, and pits). These are primarily located in New York and Pennsylvania, with several hundred in Vermont.

Whey and short paper fibers are two waste products that are produced in large quantities in the Northeast and present disposal challenges to the dairy and paper industries. In New York alone, “over 1.2 billion pounds of whey are produced annually” and “[f]inding economical, environmentally protective means to manage the whey is crucial to the viability of the industry and is needed to support the expansion of yogurt manufacturing in the State” (Ketterings et al, 2018). 

Both paper fibers and whey are currently applied directly to farmland in the Northeast region. Adding these substrates to manure stores before land application could be a relatively simple way to reduce manure NH3 and methane emissions. In cases where whey is already added to manure stores, benefits could be realized with an even smaller change in current practices. 


Click linked name(s) to expand/collapse or show everyone's info
  • Joshua Allen - Technical Advisor
  • Tom Beaudry - Technical Advisor
  • Leon Corse - Producer
  • Pete Stickney - Producer


Materials and methods:

Lab Research: Materials and Treatments  


(More detail on treatments is provided in the attached spreadsheet.)


Fermentation substrates: 

  • Sweet whey or lactose powder
  • Acid whey 
  • Short paper fibers
  • Mixture of paper and whey:
    • 25 - 75
    • 50 - 50
    • 75 - 25
  • Control (untreated)



  • Liquid dairy manure
  • Digestate from an on-farm anaerobic digester
  • Source-separated, pasteurized human urine


Starter culture: 

  • To be determined, likely a combination of sauerkraut juice, silage, and/or yogurt 


Each substrate will be tested on each manure type, and each of those mixtures will be tested with and without starter cultures. Fermentation substrates and manures were all chosen based on their availability in the Northeast region. 


Short paper fibers

Short paper fibers are a paper manufacturing byproduct and are produced in large quantities in the Northeast region. The Soundview paper mill in Putney, VT generates 90-120 tons per day (PC, Adams, 10/9/2020). Finding a way to incorporate this material would add organic matter to fields while being valuable to the paper industry. Because of its low nutrient content, SPF could be safely added to manure stores on farms with excess P accumulation in soil. 

Subair (1995) tested bio-acidification using short paper fibers, adding 2.5% and 5% paper fiber to liquid hog manure by wet weight. At these addition rates, the final pH was reduced from 7.2 to 6.5 after 56 days, and a minor reduction in ammonia volatilization was observed. We will try higher proportions of paper fiber, and mixing paper fiber and whey to test the synergistic effects of a labile and recalcitrant material mixture. 



There are two types of whey: sweet and acid (Ketterings et al., 2017). Sweet whey is produced from cheesemaking and has a higher pH (5.6 or greater). Acid whey has a lower pH (around 4.1) and is a co-product of Greek-style yogurt, cottage and cream cheese production. Although there are some re-use markets, both wheys present disposal challenges. For example, the Grafton cheesemaking plant in Brattleboro, VT pays 5 cents per gallon to dispose of sweet whey (Grafton Cheese, personal communication).

Prado et al. (2020) tested bio-acidification of liquid dairy manure using cheesemaking whey (whey pH 4.8), at whey:manure ratios from 1:5 to 1:2. They found that a 1:2 whey:manure ratio was needed to temporarily acidify below pH 5, with a net reduction in NH4 emissions. We propose to test a range of whey:manure ratios, up to 1:1. Whey has approximately 5-6% dry matter content, most of which is lactose (Ketterings et al. 2017, Lievore et al. 2015), so a 1:1 mixture would produce a sugar concentration approaching 3%. 


Whey-paper fiber mixtures

Other bio-acidification studies have shown that mixing labile and recalcitrant substrates can have a synergistic effect (Subair, 1995, Nykänen et al., 2010), and this may reduce the overall substrate volume needed. In one study, a half-maltose half-flour treatment had the same results as the all-maltose treatment, but greater effect than all-wheat (Nykänen et al., 2010). One possible explanation for this is that acid generated by the labile materials speeds hydrolysis of the more recalcitrant materials; acidification with sulfuric acid has been shown to increase hydrolysis (Hjorth et al., 2013).

By mixing whey and paper fibers, we hope to achieve an acidification effect as strong as that achieved using whey alone, but with a smaller volume of fermentation substrate.



Liquid dairy manure was also chosen due to the prevalence of dairy in the region. Digestate and urine are not as common, but are becoming more so.  Urine is already in use and in demand among farmers in the Brattleboro area, and may be a valuable source of N fertilizer in the heavily populated Northeast region in the future. Both digestate and urine have a higher pH and NH4+ content than typical manures, meaning they have a high potential for ammonia loss. 


Lab Research: Procedures

  1. Test a wide range of substrate:manure mixtures to identify best “recipe” for each manure/substrate combination

pH Pre-trial 

  • Prepare mixtures at different substrate:manure ratios in 50 mL Falcon tubes (see research plan). Total = 210 tubes
  • Store tubes at 24°C for 2 weeks. 
  • Data collection: measure pH at time 0, after 7 days, and after 14 days. 
  • Analysis: identify recipes that reach a pH below 5. Of these, identify the lowest effective substrate:manure ratio.

pH Long-term Trial: 

  • Prepare 3 recipes for each substrate/manure combination, using ratios identified as effective in the pre-trial. Total treatments = 39 x 3 replicates =  117 tubes
  • Two sets prepared for a total of 234 samples. Store one set of samples at 4°C, the other set at 24°C
  • Data collection: measure pH at time 0, then every 2 days for the first 8 days, then every week for 1 month, then every 4 weeks for 5 months.
  • Analysis: identify the mixture that requires the least substrate addition while maintaining pH below 5.5 throughout the storage period.

2. Test ammonia volatilization following simulated surface application

  • For each combination, use the best recipe identified in the long-term trial. 
  • Total treatments = 15 x 3 replicates = 45 jars
  • Place 5mL of mixture in a container inside an airtight jar. Add separate containers with 2mL of NaOH to absorb CO2 and 2mL boric acid to absorb NH3
  • Change boric acid trap and titrate daily for 5 days, then every other day for 20 days, to measure ammonia caught.  


Data analysis

We will test data for homogeneity of variance and normality; non-normal data will be transformed and reanalyzed for normality. Data will then be analyzed for significant differences using a one-way analysis of variance (ANOVA) and a post hoc test, with significance determined at p<0.05. We will use R and RStudio to do the analyses. 


On farm feasibility evaluation and wider farmer engagement

  1. Farmer Interviews: For initial input on the research design, we will re-engage several of the livestock farmers we interviewed in 2018 (SARE ONE 18-318) to ask follow-up questions concerning their N loss challenges; their interest and motivation for increasing N content of manures; and the potential economic benefits of reducing N-losses through this approach. We will also seek input on the time and labor costs potentially involved in adding inputs to current manure storage, and cost estimates for acquiring additional storage capacity if needed. We will also engage several additional farmers who use liquid manure and have manure storage facilities on their farms. We anticipate a total of 10 - 15 farmers will be contacted.

  2. Farmer-partner feasibility study: Our two farmer partners will be closely involved with the project to review and document their current manure collection, storage, and field application systems, and how they currently manage N volatilization. We will share the results from the lab trials and evaluate with them whether and how whey or paper fibers could be used on their farms. Specifically, we will strategize about how we could potentially implement a bio-acidification strategy with existing practices and equipment and/or determine what additional equipment/infrastructure would be needed. We will evaluate the potential costs and financial benefits from implementation. If the results are promising, they will help plan and design follow-up field trials for a subsequent research proposal.  
Research results and discussion:

This project is in preliminary stages and there are no results yet to report.

Research conclusions:

This project is in preliminary stages and there are no conclusions yet to report.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

Webinar: Near the conclusion of the project we will host one participatory webinar to share results from the lab trials and farmer-partner assessment of the bio-acidifcation concept. The event will involve a panel with our farmer-partners and collaborators, as well as Rich Earth researchers. In addition to presenting our results, we will invite participants to offer feedback and highlight any concerns or additional research needs to include in followup research. 

We are excited about the webinar format because it enables participation from a much wider geographic area than our past field day events. Since there isn’t a field component of this trial for participants to view in person, it seems like a good opportunity to share information with and get feedback from a wider group than we could with an in-person event. 

We hope to engage farmers and service providers from throughout the Northeast region. Outreach for the event will be conducted via our collaborators as well as other Northeast farmer and agricultural educator networks.

Our intention is for this project to provide the groundwork for a larger study, including field trials, perhaps to be funded through the SARE Novel Approaches program. For this reason, the somewhat limited outreach planned for this Partnership grant will be followed with a more robust outreach to a larger farmer and academic audience once we have done more comprehensive additional tests of this method and field trials at farm scale.

In addition to the webinar, we will share our findings with an academic audience by submitting our results for publication to journals such as the Journal of Environmental Quality or Agrosystems, Geoscience and Environment.

Learning Outcomes

Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

This project is in preliminary stages and there are no learning outcomes yet to report.

Project Outcomes

Project outcomes:

This project is in preliminary stages and there are no project outcomes yet to report.




Assessment of Project Approach and Areas of Further Study:

This project is in preliminary stages and cannot yet undergo a project assessment.


Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.