Quantifying and demonstrating scrubbing H2S from farm-based anaerobic digestion systems

Final report for LNE15-341

Project Type: Research and Education
Funds awarded in 2015: $216,879.00
Projected End Date: 10/31/2018
Grant Recipient: University of Maryland
Region: Northeast
State: Maryland
Project Leader:
Stephanie Lansing
University of Maryland
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Project Information

Summary:

Anaerobic digesters (AD) process waste, such as manure, food waste and wastewater sludge, into renewable energy in the form of methane (CH4)-enriched biogas. During this microbial-mediated process, greenhouses gases, odors and pathogens are greatly reduced, while enhancing the fertilizer value for crop production. In the US, more guidance and evaluation is needed for anaerobic digestion (AD) adopters, especially in light of the large capital investment needed for AD (averaging $1-1.5 million for a 1000-cow dairy). According to EPA’s AgSTAR, there were 265 new on-farm digesters built in the US since 2000, but many AD systems lack biogas scrubbing systems. Biogas scrubbers remove hydrogen sulfide (H2S) from the produced biogas to protect the expensive equipment used for transforming biogas into renewable energy, i.e. broilers for heat and engine generator sets (EGS) for electricity production. To benefit existing AD system operators and new adopters, this project documented and reported on existing H2S scrubber systems and developed relevant educational outreach materials. The produced information can be used by farmers and AD operators to make informed decisions about what biogas scrubbing technology is right for them and possibly increase the output of electricity from their EGSs by reducing overhaul and EGS downtime costs.

This research quantified H2S scrubber operating costs and efficiencies in reducing H2S in biogas from anaerobic digestion systems in the Northeast US. Five case studies were published detailing the efficiency of each on-farm scrubber system studied over a 12-month period, with information on capital and operating costs. A 100+ page, ‘Technical Reference Guide for Dairy-Derived Biogas Production,’ was published for this project and is available at: https://go.umd.edu/FarmerBiogasHandbook. Eleven Fact sheets were published on AD technology and H2S in biogas, and six field days/AD operator courses were attended by more than 300 people in Maryland, New York and Vermont as part of this effort. The farmers who participated in these efforts gained a better understanding of AD operation and the different kinds of biogas scrubbers and need for scrubber maintenance.  With greater adoption rates, widespread implementation of AD systems could result in large increases in on-farm energy production, increased opportunities for on-farm greenhouse gas reductions, and increased opportunities for nutrient reductions from manure, as digestion allows for post-treatment harvesting and transport off-farm of nutrients or more appropriate application of nutrients on-farm. This work provided famers with unbiased information about the efficacy and economics of H2S scrubbing systems for AD, and trained and provided holistic background materials on AD operation, planning and maintenance through our workshops and the Biogas Technical Reference Handbook.  

Performance Target:

Project Objectives from Revised Proposal:

  • Evaluate biogas scrubbers operating on five NE farms to document: a) efficacy of different H2S scrubbers b) effect of H2S on EGS operation, c) determine the extent of differences in on-farm sulfur concentration, d) economic cost/benefit of scrubber operation, and e) practical aspects of daily operation and maintenance of AD systems and biogas scrubbers;
  • Create a Farmer’s Guide to Dairy-Derived Biogas: Production, Scrubbing and Utilization;
  • Host five field days in the NE;
  • Develop and deliver extension/outreach materials including at least 4 Fact Sheets, 5 Case Studies, 6 popular press article/newsletters, journal articles, and field day presentations to ≈ 150-200 dairy farmers, installers, government agents, and NGOs, with all materials available free on Cornell’s PRO-DAIRY Environmental Systems program website, extension and Livestock Learning Center.

 

Performance Targets from the Revised Proposal:

By project conclusion, biogas scrubbing performance and cost benefits will be determined on five dairy farms with digesters. By project conclusion, 10 dairy farmers with 5,000 total cows will install new biogas scrubbers and 10 additional farmers (with 2500 cows) will improve/update their existing scrubbers. As a result, these 20 farms will realize a total of 6 MW of additional generation capacity with a value of $4,500,000/year. The results and recommendations from the study will be written into the Biogas Guide, Fact Sheets, Case Studies, and popular press and journal articles. The results and recommendations will be used by at least 10 dairy farmers (>5,000 total cows) to guide new scrubber installation and/or improvements to existing units, resulting in enhanced engine-generator set output, i.e. higher capacity factors.

 

Challenges to Meeting Performance Targets:

The price of milk is currently at all-time lows, with many/most dairy farmers in the NE losing money every year. The 30% federal tax break for renewable energy installations, which many digester operators use (including one of our collaborating farmers that submitted for upgrade his H2S scrubber and EGS), expired at the end of 2016 and is not expected to be renewed with the new political climate. The largest H2S scrubber installer and operator in New York went out of business last year, leaving many farmers with existing H2S scrubbing systems without any technical support or periodic calibration capabilities. These challenges are beyond the control of the grant PIs, but are very real challenges to the entire AD industry.

Introduction:

Anaerobic digestion (AD) systems reduce GHG emissions, odors, pathogens and solids, while producing renewable energy. AD is a microbial-mediated process in which microorganisms utilize organic matter, carbon dioxide, and hydrogen to produce biogas. Biogas is generally comprised of methane (60%), carbon dioxide (35%), water vapor (4%) and some trace gases, most notably hydrogen sulfide (H2S).

One of the main technical barriers to large-scale adoption and long-term operation of AD systems is the unreliability of biogas-powered engine-generator sets (EGS) due to H2S damage. Experience from the PDs and other experts within the industry have shown that EGSs are frequently down due to high levels of H2S in the biogas fuel. Engine-generator sets are designed to operate on cleaner fossil fuels, and their reliable use over prolonged time duration still remains an issue.

Proper H2S scrubbing is vital to continual operation of EGS and improvement in economic viability. Hydrogen sulfide reacts with water vapor present in the biogas producing sulfuric acid, which is corrosive to brass, copper, bronze, cast iron, carbon steel, lead, and several types of stainless steel. As many components of EGS are composed of these metals, the presence of H2S has a deleterious effect on EGS infrastructure, piping, and fittings. The H2S content of biogas generated from animal manures typically ranges from 1000-8000 ppm (0.10-0.80 %). Biogas end use dictates the extent to which the H2S must be removed prior to usage. When burning biogas in a boiler for heat generation, the H2S concentration should be below 1000 ppm (0.10%). In an EGS, the H2S concentration should not exceed 100-500 ppm (0.01-0.05%) to prevent corrosive damage. 

There are many types of H2S scrubbing systems on the market, including: (1) biological conversion using sulfur-oxidizing bacteria to oxidize H2S to elemental S and sulfuric acid and elemental sulfur, (2) chemical oxidation and precipitation with Fe or Zn compounds, and (3) injection of air in the vessel airspace to react with H2S.

At this point, one type of system has NOT emerged as preferable due to lack of unbiased data on: 1) year-round H2S reduction, 2) on-going operational and maintenance costs, and 3) the relationship between increasingly utilized co-digestion food waste substrates and H2S production. The importance of proper biogas treatment in order to grow the ADS field cannot be over emphasized. Reliability of biogas end-use equipment is a major concern amongst farmers, both current ADS adopters due to EGS downtime/maintenance and future adopters due to these uncertainties. This project is innovative because no previous studies have focused on scrubbing efficiencies for biogas, while practitioners have expressed that biogas cleanup is integral to EGS performance and system lifetime.

Long term scrubber efficiencies and cost information on H2S scrubbing systems does not exist in peer-reviewed literature, with limited information online in the form of dissertations, theses, presentations, and online reports, which is a large part of the motivation for generating this data through this proposed project.

Cooperators

Click linked name(s) to expand
  • Traci Jackson
  • Abhinav Choudhury (Researcher)
  • Gary Felton (Educator and Researcher)
  • Curt Gooch (Educator and Researcher)
  • Stephanie Swann

Research

Hypothesis:

Based on the limited literature available, it is predicted that of the four H2S scrubber systems outlined for testing, the air injection system will be the least effective in terms of removing H2S in the biogas, but will have the lowest maintenance time and capital costs, while the physical scrubber will be the most effective H2S removal mechanism but have the highest time and cost commitment.

Materials and methods:

The treatments chosen represented a diversity of existing H2S scrubbing systems that were evaluated for 3 to 6 months over an 18-month period using our two previously purchased continuous monitoring system.

 

  1. Kilby Farm has a covered lagoon digester with food waste co-digestion on 600-cow farm in Colora, MD with a biological-chemical H2S scrubber and 110 kW EGS.
  2. Sunny Side Dairy Farm in Venice Center, NY is a 3,300 milking cow and 1,400 heifer farm with a plug flow digestion system for a 1000 kW EGS and 1.5 mmBTU boilers, with a biological scrubber.
  3. Spruce Haven Farm in Auburn, NY processes manure from 2,000 cows with an innovative, low cost anaerobic digester that includes a 450 kW EGS and a biological scrubber.
  4. Reinford Farm in Mifflintown, PA has 550 cows and an RCM complete mixed digester co-digested with culled produce from supermarkets for a 140 kW EGS with air injection H2S scrubbing.

 Methods

There were four AD systems and three types of H2S scrubbing installations in which the biogas scrubbing efficiency and ADS costs/maintenance were accessed. Biogas composition pre- and post-biogas cleanup were measured for 3-6 months to capture seasonally variations using two custom-made assemblies consisting of a portable continuous gas analyzer for CH4, CO2, O2, and H2S (Siemens Model # 7MB2337-3CR13-5DR1), a data acquisition system (Campbell Scientific), and a Sage gas meter (Model # SIG-05-15-SVA-05LP). The assembly allowed for continuous measurement and logging of all parameters before and after H2S scrubbing. The Reinford Farm with in-vessel air injection only used the monitoring assembly as a standalone unit and only quantified the biogas composition (CH4, CO2, O2, and H2S) leaving the digester.

Economic analyses were performed for each AD system by collecting and analyzing: 1) annual cost and cost savings for each scrubbing system, 2) biogas utilization and electricity sales, 3) maintenance and on-going AD operational costs, and 4) valuation of time spent operating the AD using an annualized cost-benefit analysis (AgSTAR Protocol, 2011).

 Data collection

The two equipment assemblies were rotated among the four project-collaborating farms in order to reduce expensive equipment costs while still allowing for determination of the effect of scrubbing on biogas quality over time and carrying temperatures. Collected data included biogas production, composition and utilization, H2S reduction, temperature, and all economic cost items for owning, operating and maintaining the H2S scrubber system. All monitoring equipment was calibrated, installed and used per the manufacturer’s recommendations. Meter data was continuously logged. Information collected by the biogas system was downloaded at regularly scheduled monthly visits or transmitted to Cornell daily, if internet was accessible on-site.  Data was managed and analyzed in a custom developed MS Excel spreadsheet for this project. Collected data was reviewed in accordance with QA/QC procedures, with ANOVA and Tukey-Kramer post-hoc statistical analyses of the reviewed data.

 Farmer input

The collaborating farms and PDs have worked together previously and were eager to gain information on improving their H2S scrubbing and biogas utilization efficiency. The farmers operated and maintained their AD systems and scrubbers and supplied records of time and costs spent on their AD system. Farms received at least two reports during the project, with graphs/charts on their system performance and optimization strategies.

 Additional information: Other relevant features of the proposed research

The research was the first encompassing quantification of H2S scrubber operating costs and efficiencies in the Northeast (and US). One advantage of our approach was that without construction or experimental manipulation the likelihood of project delays was greatly reduced. The AgSTAR “Safety Practices for On-Farm Anaerobic Digestion Systems” was used as a guide for the producers and project team. In addition, the Advisory Board created for this project included the AgSTAR Program Manager, the head of the Energy Innovation at Green Mountain Power and the Deputy Chair of the USEPA Farm, Ranch, and Rural Communities Federal Advisory Committee.

Research results and discussion:

Pennsylvania Farm Summary:

The results from the study showed that the average methane (CH4) concentration was found 56.2 ± 0.1%, with a high of 61% and low of 49% CH4. During the same time, the average hydrogen sulfide concentration (H2S) was found to be 1938 ± 23 ppm. The range of hydrogen sulfide concentrations varied from a high of 3300 ppm to below 200 ppm H2S due to inconsistent treatment with the air injection system, possibly due to clogging, insufficient air injection to create a suitable micro-aerobic environment for biological desulfurization, or variability in the feedstock sulfur concentrations. The highest concentration of oxygen (0.5%) in the biogas corresponded to the lowest hydrogen sulfide concentration (~ 100 ppm), indicating effective desulfurization. During the remainder of the study period, the oxygen concentration in the biogas output was nearly 0%, but complete desulfurization did not take place. Furthermore, it was observed that liquid food waste addition, instead of solid food waste, led to a positive effect of higher biogas production with a higher methane percentage due to the higher ease of degradability of the liquid feedstock. However, this also contributed to a higher concentration of hydrogen sulfide in the biogas. Biogas flow rates varied from 72,000 – 79,200 scf/day before the feedstock change and increased to 96,000 – 120,000 scf/day after the feedstock change. The farm produced a total of 689,656 kWh of electricity from June ’16 to April ’17, at an average of 2071 kWh/day. Micro-aeration had the lowest capital ($450) costs, maintenance costs ($120/year) and maintenance time (15 mins/week) of all the scrubbers monitored during the study. The air injection scrubbing technique was also only effective (91% lower than the overall average H2S concentration) on one instance during the entire study period.

Detailed results can be found in the Hydrogen Sulfide (H2S) Removal at a Northeastern Dairy Farm Digester using Micro-aeration: Case Study.

Maryland Farm summary:

The results from the study showed that in the first three months of the study period, no major differences were seen between the hydrogen sulfide (H2S) concentrations in the pre-scrubbed (715 ± 58 ppm) and post-scrubbed biogas (695 ± 58 ppm). The inefficient scrubbing media coupled with the low biogas residence times substantially affected scrubber performance. The average methane (CH4) concentration was 65.1 ± 0.3 % in the pre-scrubbed biogas and 66.2 ± 0.2 % in the post-scrubbed biogas. The scrubbing media was changed twice in the following three months to induce a treatment effect. It was noticed that a change in the media led to a cleaner product after scrubbing (41 ± 9 ppm H2S compared to 66 ± 13 ppm H2S before scrubbing). The biogas had a low concentration of H2S during this time, due to lower temperatures in the winter months as the digester was unheated, and it affected both biogas and H2S production. The methane concentration during this period was consistent in the pre (62.7% ± 0.2) and post scrubbed (62.8% ± 0.3) biogas. The average daily biogas flow rates varied from a high of 42,450 scf/day from June to October 2016 to a minimum of 1,788 scf/day during January – February 2017. The farm produced 47,158 kWh from August to December 2016 at an average rate of 360 kWh/day. Overall, the biogas was of high quality due to the high methane content and low concentrations of H2S. The methane concentrations remained largely unchanged during the entire study period, while the biogas quantity fluctuated with temperature. The scrap iron scrubber had a capital cost of $525 and required 2-3 hours of labor every two weeks for changing the media for a yearly cost of $650. For the steel wool media, the media needed changing every month for a yearly cost of $960. Overall, the scrubbing technique was only 3% efficient, but the use of a commercially available iron-oxide or iron-sponge scrubbing media would have led to a much higher efficiency.

On average, the H2S concentrations in the biogas at the MD farm were an order of magnitude lower than the PA farm due to differences in the manure management. The MD farm used digester effluent as the flush water and it resulted in a more dilute feedstock, whereas the PA farm used fresh scraped manure mixed with food waste and added it daily into the digester.

 

Detailed results can be found in the Hydrogen Sulfide (H2S) Removal at a Northeastern Dairy Farm Digester using Iron Oxide: Case Study

 

New York Farms Summary:

 

The pre-treatment H2S concentration at Farm 1 averaged 2,640 ± 350 ppmv over the course of the monitoring period. Post-treatment H2S concentration was consistent throughout the monitoring period (150 ± 110 ppmv), with a gradual increase in concentration observed toward the end of the monitoring period which was likely due to build-up of solid sulfur on the biological scrubber/biotrickling filter (BTF) media. Over the course of the monitoring period, overall H2S removal efficiency averaged 94.5%. Biogas flowrate over the monitoring period was 0.19 ± 0.03 m3/s. Pre-treatment average methane content of the biogas was 56.3 ± 0.5%, and post-treatment average methane content was 50.7 ± 0.7%. The decrease in CH4 content was likely due to increases in N2 gas in the gas scrubber with air injection.

The pre-treatment concentration of H2S at Farm 2 averaged 2,350 ± 315 ppmv over the course of the monitoring period. Post-treatment performance was consistent throughout the monitoring period (450 ± 190 ppmv). Over the course of the monitoring period, overall H2S removal efficiency averaged 80.1%. Biogas flowrate over the monitoring period averaged 0.04 ±0.01 m3/s. Pre-treatment average methane content of the biogas was 63.7 ± 4.4%, and post treatment average methane content was 55.4 ± 3.2%, which also reflected the increases in N2 in the post-treated biogas.

The BTF annual maintenance and repair costs (averaged from cost data observed over the 18-month monitoring period) for each BTF system is presented in Table 1. Labor for each system was typically 15 minutes per day, which consisted of checking the recorded system logs to ensure proper BTF operation, which was punctuated with longer periods when system maintenance or repairs were required.

Over the course of the monitoring period, it was determined that the total annual cost of owning/operating the BTF on Farm 1 was $71,621 per year. Of that, costs for labor alone totaled $10,323 per year. The economic benefit of reduced oil change frequency was a savings of $10,028 per year. The net benefit of -$61,593 (benefit/cost ratio of 0.14) indicates that the benefit of reduced oil change frequency alone is not enough to economically justify owning/operating the BTF at Farm 1.

The total annual cost of owning/operating the BTF on Farm 2 was $35,593, of which labor totaled $4,340. The estimated annual economic benefit of reduced oil change frequency was a savings of $5,500, with a net benefit of -$30,093 (benefit cost ratio of 0.15). As at Farm 1, the benefit of reduced oil change frequency alone is not enough to economically justify owning/operating the BTF at Farm 2.

Detailed results can be found in the journal article “Performance and Economic Results for Two Full-Scale Biotrickling filters to remove H2S from Dairy Manure-derived Biogas” accepted for publication by ASABE and in the two case studies from the NY farms.
Hydrogen Sulfide Removal at Spruce Haven Farm Case Study
Hydrogen Sulfide Removal at Sunnyside Farms Case Study 

Research conclusions:

Even though commercial H2S scrubbers require expertise and are expensive to maintain and operate, it is still an important part of AD systems in order to maintain H2S concentrations within recommended limits. Our hypothesis about the in-vessel air injection for biological desulfurization having the lowest capital and time investment was accurate but the biological scrubbing systems had the most consistent performance out of the three systems monitored. The biological scrubbers also required the most time investment to ensure maximum efficiency. The use of scrap iron and steel wool instead of commercially available iron oxide or iron sponge scrubbing media also affected the results of the study and use of the appropriate scrubbing media would have increased the scrubber performance on the MD farm. It is also important to understand the economic and technical factors after taking the end use of the biogas into account before purchasing an H2S scrubber. The study showed that even though the biological scrubbers had the best performance, the savings on oil changes was not enough to justify the added costs and longer studies may be needed to account for major engine generator overhauls that that are infrequent but are also more expensive. The study also showed a substantial effect of scrubber operation and management on its performance. The two BTFs on the NY farms were better managed with more time and labor investment compared to the other scrubber systems studied, which resulted in more efficient and consistent scrubbing performance for these two BTF systems. While the iron-oxide scrubber had a much lower time and labor investment, the performance was the most inconsistent of the three tested H2S scrubbing technologies, likely due to this low capital and labor investment made in this specific system.

Participation Summary
4 Farmers participating in research

Education

Educational approach:

Through our survey, we have received contact information for > 40 interested participants in ADS workshops and/or scrubbing installation/upgrading. We delivered workshop advertisements to > 1,000 dairy farmers in the Northeast through extension meetings, newsletters (i.e. Livestock and Poultry Learning Center), and e-mail networks (i.e. Dairy Farmers of America and Northeast Dairy Producers Association). Recruitment materials also included a link to an additional online survey about current ADS practices and ADS learning objectives to guide our extension programming.  Our Advisory Board assisted in steering farmers interested in installing/upgrading scrubbers to us in order to meet our performance targets.

Delivery methods

We integrated performance and cost results into a 100+ page, ‘Technical Reference Guide for Dairy-Derived Biogas Production,’ which was published for this project and is available at: https://go.umd.edu/FarmerBiogasHandbook. Originally named (in the proposal), a ‘Farmer’s Guide to Biogas Production, Scrubbing and Utilization,’ this Handbook is written in easy-to-understand language with detailed and practical information for anaerobic digestion processes, factors affection biogas composition, increasing biogas production, assessing biogas cleanup feasibility, and biogas effect on maintaining successful end-use equipment. Overall, such a comprehensive publication was not in existence before and is a welcome resource by current and future ADS owner/operators.

We developed and delivered educational materials through producing the Biogas Handbook, eleven published Fact sheets (while only 5 were proposed), four case studies, two peer-reviewed journal publications, and six field days (two in Maryland, two in New York, and two in Vermont) to dairy farmers, policy makers, governmental agencies, extension educators, lenders, and NGOs to disseminate lessons learned. We delivered oral presentations at dairy industry meetings, academic conferences, and other related events in the Northeast. All materials are posted on UMD’s website: https://enst.umd.edu/people/faculty/stephanie-lansing under the Extension tab, as well as Cornell Pro Dairy’s website: https://ecommons.cornell.edu/handle/1813/36497

Curriculum topics

The ‘Technical Reference Guide for Dairy-Derived Biogas Production,’ provided the necessary information to: (1) factors affecting biogas composition, (2) determine biogas production potentials under a range of scenarios, including with co-digestion, (3) determine biogas scrubbing needs and capabilities with various scrubbing systems, (4) provide predictive capabilities for biogas production and scrubbing throughout the year, and (5) document operating costs for a range of sophistication in biogas scrubbing systems to better understand capital and labor needed for on-going operation.

The field days covered a range of topics with lessons learned from collaborating farmers, including general anaerobic digestion ABCs, methods for increasing biogas production (co-digestion), H2S scrubbing, and operating more efficient EGS for electricity production.

Beneficiary support

In addition to regular updates to collaborating farmers, additional farmers interested in upgrading or installing new H2S scrubbing systems were provided with one-on-one support by the PDs and part-time extension agent by phone, e-mail, or in-person. The information from the collaborating farms were consolidated into Fact Sheets and Case Studies, which were published online and widely distributed. In addition, sections of the Field Day presentations were recorded and posted online for widespread access to the presented information: https://enst.umd.edu/about/opportunities-and-challenges-anaerobic-digestion

Milestones

Milestone #1 (click to expand/collapse)
What beneficiaries do and learn:

Milestone 1: Initial meetings with Advisory Board and farmers within four months of contract execution to: 1) receive feedback on project commencement and the developed logbook to record generator performance, maintenance efforts and costs, and 2) determine project baseline for capital costs, maintenance time and maintenance expenses.        

Proposed number of farmer beneficiaries who will participate:
4
Actual number of farmer beneficiaries who participated:
4
Proposed Completion Date:
October 31, 2018
Status:
Completed
Date Completed:
October 31, 2018
Accomplishments:

A meeting was held with each farmer at the start of the project to explain the project, objectives, and milestones. Additional informal meetings were held with the farmers as we collected data to update them on our progress and gather information on their system operations and expenses. One New York dairy farm with a H2S scrubber listed on the project proposal was replaced with a different farm with an H2S scrubbing system from the same manufacturer due to AD system shutdown at the original farm.  Ten months of biogas data was collected from this replacement farm’s scrubbing system.

An Advisory Board was held in April 2016, with all Advisory Board members participating (in person or by phone). During the meeting, we received feedback on the project commencement and possible improvements and discussed current scenarios of anaerobic digestion in Northeast US. In addition, Advisory Board members discussed different dairy groups they are associated with in their area (VT, NY and PA) that could be targeted for extension events. In addition, new information on permitting for air emissions implemented in various states that have implications for digester operators was discussed. Eleven (11) total Fact Sheets were published as part of this project. These included a series of ten (10) H2S scrubbing Fact Sheets that were posted on the Cornell PRO-DAIRY Dairy Environmental Systems web site (http://www.manuremanagement.cornell.edu/Pages/Popular_Pages/Fact_Sheets.html). An additional (1) Fact Sheet on in-vessel micro-aeration for biological desulfurization is posted on the UMD website (https://enst.umd.edu/people/faculty/stephanie-lansing under the Extension tab).  All fact sheets are listed below:

HYDROGEN SULFIDE REMOVAL FROM BIOGAS Part 1A: Hydrogen Sulfide and Biogas – Basics
HYDROGEN SULFIDE REMOVAL FROM BIOGAS Part 1B: Measuring Hydrogen Sulfide
HYDROGEN SULFIDE REMOVAL FROM BIOGAS Part 1C: Available technologies for hydrogen sulfide removal from biogas
HYDROGEN SULFIDE REMOVAL FROM BIOGAS Part 1D: Partial Budget Analysis
HYDROGEN SULFIDE REMOVAL FROM BIOGAS Part 1E: Hydrogen Sulfide and Sulfur Emissions
HYDROGEN SULFIDE REMOVAL FROM BIOGAS Part 2A: Microbial underpinnings of H2S biological filtration
HYDROGEN SULFIDE REMOVAL FROM BIOGAS Part 2B: Biotrickling filters for H2S – Overview of configuration and design
HYDROGEN SULFIDE REMOVAL FROM BIOGAS Part 2C: Biotrickling filters for H2S – Improvement opportunities
HYDROGEN SULFIDE REMOVAL FROM BIOGAS Part 3A: Iron Sponge Basics
HYDROGEN SULFIDE REMOVAL FROM BIOGAS Part 3B: Iron Sponge Design Considerations: Vessel Sizing

The information from these Fact Sheets were incorporated into the extension efforts and workshops detailed below.

Capital, operational, and maintenance costs for the scrubbing systems, as well as hours spent on the scrubbing systems, were collected from the farms involved in the study. Briefly, the collected data showed that the in-vessel micro-aeration system had the lowest costs and maintenance time, while the bio-trickling filters had the highest costs and maintenance time A full summary of the costs can be found in Table 1 and 2 (See Milestone 2 below). Detailed information for each system is available in the four (4) published Case Studies:

  1. Hydrogen Sulfide (H2S) Removal at a Northeastern Dairy Farm Digester using Micro-aeration: Case Study
  2. Hydrogen Sulfide (H2S) Removal at a Northeastern Dairy Farm Digester using Iron Oxide: Case Study
  3. Hydrogen Sulfide removal at Spruce Haven farm, LLC: Case Study
  4. Hydrogen Sulfide removal at Sunny Side farm, LLC: Case Study

Overall, the targets for this milestone were met. The initial Advisory Board meeting occurred within eight months of project commencement, and the initial meetings with each participating farmer took place within a month of project commencement. The baseline for capital costs, maintenance time and costs were also obtained and published by the project completion date.

Milestone #2 (click to expand/collapse)
What beneficiaries do and learn:

Milestone 2: Provide quantified information to four dairy farmers on their biogas- scrubbing performance and cost-benefit, specifically for two farms with external biological scrubbers, one with an in-vessel system using air injection. The four farmers will receive information on their H2S scrubbing evaluation, their economics, and improved scrubber and ADS maintenance/optimization within 24 months of contract execution. Dozens of farmers will also receive this information during field days hosted on their farms in order to impart this knowledge to fellow farmers.

Proposed number of farmer beneficiaries who will participate:
4
Actual number of farmer beneficiaries who participated:
4
Proposed Completion Date:
October 31, 2018
Status:
Completed
Date Completed:
October 31, 2018
Accomplishments:

New York Systems

The financial costs and the scrubbers’ characteristics and performances for the two NY farm systems over the course of the data collection period are shown in Table 1 and published in Shelford et al. (2019). Both farmers were provided with reports containing all the information about their scrubber systems. Farmers were also advised on how to manage and improve the performance of the H2S scrubbing equipment on their farms. The two biogas scrubber systems studied in NY were both biological scrubbers. The system at Farm 1 performed better of the two systems studied. On Farm 1, there was an advantage in that the digester supplied two EGS, and therefore, biogas flow through the scrubber was maintained during routine EGS maintenance, as one EGS could still be working during this time.  In addition, Farm 1 has a solid cover over their digester, while Farm 2 has a flexible cover that posed problems during the winter months when snow and rain would build up on top and restrict the collection and flow of biogas, resulting in system slowdowns or shutdowns.  This difference in scrubber performance was verified by examining the capacity factor (how much power was actually produced divided by how much power could have been produced over the same period) of the two farms, as shown in Table 1.  The capacity factors were less than one due to system shutdowns for maintenance or outages as well as the system operating below design capacity due to inadequate biogas flow or other maintenance problems (overheating of engine heads, etc.).

Maryland and Pennsylvania Systems

Scrubber performance and the cost information for the MD and PA farm systems are shown in Table 2.  Both farmers were provided with reports containing all the information about their scrubber systems.  Farmers were also advised on how to manage and improve the performance of the H2S scrubbing equipment on their farms.  An important observation for MD and PA farms compared to NY farms was the time and effort spent in scrubber maintenance.  The MD and PA farms were smaller and did not have a dedicated operator for the digester. The owners found it easier to change the oil in the generators regularly instead of troubleshooting the H2S scrubber during periods of inefficient performance.

Table 1: Financial and Operational Summary for NY systems (Shelford et al., 2019)

System

NY Farm 1

NY Farm 2

Size

Average number of milking cows

4,200

1,500

Engine Generator Capacity (kW)

1,000

502

Average
Performance
based on the
Study period
for each farm

Average untreated H2S concentration (Avg ± Std. Err)

2,640 ± 6

2,350 ± 6

Average treated H2S concentration (Avg ± Std. Err)

150 ± 2

450 ± 3

Overall Removal Efficiency (%)

94.5

80.1

Capacity Factor

0.93

0.68

Avg Mass of H2S removed (lbs/hr)

5.22

0.78

Cost Estimates
(based on one year of data, if available)

H2S Scrubber system capital cost ($)

304,724

133,500

H2S Scrubber yearly maintenance ($/yr)

5,772

3,120

H2S scrubber cleanout labor ($/yr)

4,551

1,220

H2S scrubber yearly nutrients ($/yr)

3,300

7,800

H2S scrubber yearly trickle media replacement ($/yr)

5,600

1,600

 

 

Table 2: Financial and Operational Summary for MD and PA systems

System

MD Farm

PA farm

Size

Average number of milking cows

450

650

Engine Generator Capacity (kW)

110

140

Average
Performance
based on the
 Study period
 for each farm

Average untreated H2S concentration (Avg ± Std. Err)

603 ± 51

N/A

Average treated H2S concentration (Avg ± Std. Err)

585 ± 50

1,938 ± 23

Overall Removal Efficiency (%)

3.0

N/A

Capacity Factor

N/A

0.76

Avg Mass of H2S removed (lbs/hr)

0.001

N/A

Cost Estimates
(based on one year of data, if available)

H2S Scrubber system capital cost ($)

525

450

H2S Scrubber yearly maintenance ($/yr)

1,110

120

H2S scrubber cleanout labor ($/yr)

N/A

0

Generator yearly maintenance and repair cost ($/yr)

N/A

28,708

Data was not collected from any additional farms, including the fifth planned farm in PA dairy farm that used both micro-aeration and a separate biological scrubbing system due to the breakdown of the CH4 and H2S monitoring system.  Due to the high levels of H2S in the biogas, we had to replace the H2S sensors multiple times in the monitoring system, which resulted in gaps in the biogas collection period.  The corrosiveness of the H2S in the biogas and failure of the equipment over the 2-year study highlights the difficulty of quantifying H2S concentrations in un-cleaned biogas due to the damaging levels of H2S.  Eventually, the high levels of the H2S in the pre-scrubbed gas damaged the equipment beyond repair over two years of testing.

Data was collected over two years at the four farms involved in the project. The farmers were updated on how to improve scrubber performance and how their practices affected the composition of the biogas. In addition, the presence of the project biogas monitoring systems demonstrated the importance of properly maintaining and calibrating the equipment used to measure gas quality; particularly H2S. Often, farmer owned monitoring equipment was either not working at all, or generally, under-reporting values of H2S when compared to project measured calibrated values.

The targets for Milestone 2 were met for four farms.  The farmer operating the 5th farm-based scrubbing system was consulted throughout the project and troubleshooting of this H2S scrubbing system occurred, as needed, but monitoring of this 5th system could not occur due to breakdown of the monitoring equipment.  All five farmers received information on their H2S scrubbing systems, the economics, and improved scrubber and ADS maintenance/optimization by the project completion date.

Hundreds of farmers (not dozens, as predicted) also received information on the importance of H2S scrubbing, pros and cons of different systems, economic evaluation, and full study results during the four (4) field days that were hosted by University of Maryland and Cornell University in MD and NY and two (2) additional VT workshops in which we participated. These events helped impart this knowledge to farmers, with a total of 314 participants in the six (6) field day/workshop events, which included farmers, consultants, academics, industry representatives, state representatives, and students.  The participations from these events exceeded our expectations.

Milestone #3 (click to expand/collapse)
What beneficiaries do and learn:

Milestone 3: Provide 700 people, including farmers, essential information on scrubbing and biogas performance through the publication of a Biogas Guide, nine Fact Sheets, five Case Studies, and two journal articles by October 2018. The farmers will be able to use the Guide to determine: (1) factors affecting biogas composition, (2) biogas scrubbing materials and capabilities for different types of scrubbing systems, (3) operating costs for five ADS, and (4) managing and operating guidelines for EGS with different scrubbing system types. This comprehensive farmer-friendly guide currently does not exist, nor are publicly developed data available on H2S scrubbing efficiencies and operating costs for maintaining ADS. This will be a welcome resource by current and future digester owner/operators. A preliminary outline of the Biogas Guide will be circulated to ten NE farmers for review and input.

Proposed number of farmer beneficiaries who will participate:
700
Actual number of farmer beneficiaries who participated:
200
Actual number of agriculture service provider beneficiaries who participated:
50
Proposed Completion Date:
October 31, 2018
Status:
Completed
Date Completed:
October 31, 2018
Accomplishments:

The “Biogas Guide for Dairy farmers,” now renamed “A Technical Reference Guide for Dairy-Derived Biogas Production, Treatment and Utilization” has been finalized, edited and reviewed by members of the Advisory Board and others. The final Guide is now available online on the UMD website (https://enst.umd.edu/people/faculty/stephanie-lansing under the Extension tab).
A Technical Reference Guide for Dairy-Derived Biogas Production, Treatment and Utilization

From this project, eleven (11) Fact sheets and five (5) case studies were published and are available online, with ten (10) Fact Sheets and three (3) case studies posted to the Cornell PRO-DAIRY website and are attached as PDF documents to this report and one (1) Fact Sheet and two (2) case studies posted to the UMD Extension website and all attached to this report.

The ten (10) Fact Sheets and three case studies posted to the Cornell PRO-DAIRY website. The Fact Sheets are part of a series entitled, “Hydrogen Sulfide Removal from Biogas.” This Series includes the basics of H2S production from biogas (#1A), the different types of equipment available for measuring H2S (#1B), available technologies for removing H2S from biogas (#1C), a tool that enables a farmer to determine the financial implications of proposed AD and H2S scrubbing systems (#1D), and the basics of H2S and sulfur emissions (#1E). There are three Fact Sheets related to biological trickling filters (BTF), including the basic biology of biological desulfurization (#2A), configurations and design for BTF systems (#2B), and improvement opportunities (#2C). Finally, there are two Fact Sheets that focus on iron sponge scrubbers, including iron sponge basics (#3A) and design considerations and vessel sizing (#3B).  The title of each Fact Sheets is listed below.

1A: Hydrogen Sulfide and Biogas – Basics
1B: Measuring Hydrogen Sulfide
1C: Available technologies for hydrogen sulfide removal from biogas
1D: Partial Budget Analysis
1E: Hydrogen Sulfide and Sulfur Emissions
2A: Microbial underpinnings of H2S biological filtration
2B: Biotrickling filters for H2S – Overview of configuration and design
2C: Biotrickling filters for H2S – Improvement opportunities
3A: Iron Sponge Basics
3B: Iron Sponge Design Considerations: Vessel Sizing

The case studies on the performance and economics of the two BTF filters on the NY farms studied in this project were posted to the Cornell PRO-DAIRY website (titles listed in Milestone #1). Another case study titled “Anaerobic Digestion at Twin Birch Farms, Inc.: Case Study” that discussed the AD system, biogas utilization, H2S scrubbing, and economic information for the farm was updated in 2016.

An additional (1) Fact Sheet and two (2) case studies were posted on the University of Maryland website. The Fact Sheet discussed the basic chemistry, biology, and control parameters of micro-aeration as a biological scrubbing technique for biogas desulfurization.

  1. Micro-aeration for Hydrogen Sulfide Removal in Biogas

The two case studies on the performance and economics of the two scrubbing techniques used on the farms in MD and PA (physical-chemical scrubber and in-vessel micro-aeration for biological desulfurization) were posted to the UMD website (titles listed in Milestone #1).

The contents of the Fact Sheets and the data from this study on H2S scrubber performance was distributed/presented at the following workshops and field days: the VT Digester Operator’s Group with 60 participants (Dec 2016), an AD workshop held at Sunny Side Farm in Venice, NY with 12 participants (Jan 2016), a digester operator’s workshop at Enosburg Falls, VT with 28 attendees (March 2018), the University of Maryland Dairy Field Day with 59 attendees (Oct 2017), an Cornell AD Short Course with 66 attendees (Dec 2017), and the Opportunities and Challenges in Anaerobic Digestion: Maryland and the Northeast US Experience workshop with 89 attendees (Oct 2018). For a total of 314 attendees for our presentations on the importance of H2S scrubbing and FactSheet and Case Study distribution.

An updated draft of the Biogas Guide was distributed to all 89 attendees (including farmers) at the MD workshop in October 2018. It is expected that the now published Biogas Guide, the Case Studies, and Fact Sheets have likely reached at least 700 people online, with this number expected to rise over time.

Three journal articles were written as part of this project. One article was published, one is accepted for publication and waiting final printing, and another manuscript is currently being prepared for publication. The published article was titled “Effect of liquid surface area on hydrogen sulfide oxidation during micro-aeration in dairy manure digesters” and published in PLOS One in 2017 (attached), with 1,123 views to date. This study focused on increasing the efficiency of micro-aeration and investigating digestate liquid surface area as one of its controlling parameters. The journal article titled “Performance and economic results for two full-scale biotrickling filters to remove H2S from dairy manure-derived biogas” has been accepted for publication in the journal for American Society of Agricultural and Biological Engineers. This article focused on the performance and economic analysis of the two New York State BTF systems studied during this project. Another manuscript, entitled “Evaluation of hydrogen sulfide scrubbing systems for anaerobic digesters on dairy farms” discusses how management of scrubbers affect their performance is under preparation and part of the PhD student dissertation. This dissertation will be defended in May 2019, with subsequent publication of the associated article. In addition, a popular press article on micro-aeration was published in Biocycle magazine in 2017: Microaeration Reduces Hydrogen Sulfide In Biogas

Overall, the targets for this milestone were met and, in some cases, exceeded with 314 participants directly obtaining essential information on scrubbing and biogas performance through in-person presentations, distribution of the Biogas Guide, ten new Fact Sheets, and five new or updated Case Studies at the workshops and conferences held in MD, NY and VT and reaching thousands of more people online. It was decided that instead of six popular press articles, it would be more beneficial to create more Fact Sheets to provide more factual information to farmers and AD practitioners. 

The Biogas Guide (104 pages long) was also published and contained valuable information on the: 1) factors affecting biogas composition, 2) biogas scrubbing materials and capabilities for different types of scrubbing systems, and 3) managing and operating guidelines for EGS with different scrubbing system types. This type of extensive Guide has not been available before this project and is a valuable resource for farmers, industry and policy makers. There will be more opportunities to advertise this Guide to farmers and the industry, and it is expected to be used by hundreds of people moving forward. A Technical Reference Guide for Dairy-Derived Biogas Production, Treatment and Utilization is located at:  https://go.umd.edu/FarmerBiogasHandbook and can also be found at: https://enst.umd.edu/people/faculty/stephanie-lansing under the extension tab.

Milestone #4 (click to expand/collapse)
What beneficiaries do and learn:

Milestone 4: Host five field days to allow producers to see biogas scrubbing technologies and learn general information on ADS operation, biogas production, and H2S scrubbing options, and specific information on H2S scrubbing performance and economic viability for 100 farmers and their advisors for five the field days combined by August 2018.

Proposed number of farmer beneficiaries who will participate:
100
Actual number of farmer beneficiaries who participated:
200
Actual number of agriculture service provider beneficiaries who participated:
50
Proposed Completion Date:
October 31, 2018
Status:
Completed
Date Completed:
October 2, 2018
Accomplishments:

We hosted two workshops in Maryland, two in New York and contributed to two workshops in Vermont by providing planning assistance, presenting talks, and disseminating project extension materials.

1) In 2017, we hosted a field day at the University of Maryland Dairy in Clarksville. The event was held on October 18th, 2017 with a total of 59 participants. The effects of H2S in the farm setting was presented, as well as potential ways to control H2S production, and safety concerns with H2S production from digesters and lagoons. The produced Fact Sheets were provided at the event and available digitally on the event page.

2) The Opportunities and Challenges in Anaerobic Digestion: Maryland and the Northeast US Experience workshop was held on October 2, 2018 in Annapolis, MD with 89 attendees comprised of consultants, farmers, academics, industry representatives, state representatives, and students. All the Fact Sheets and case studies from this study, along with a draft of the Biogas Guide was presented and shared at the workshop, which has its only individual website will all presentations and associated FactSheets (https://enst.umd.edu/about/opportunities-and-challenges-anaerobic-digestion). Dr. Curt Gooch also presented a talk on “Use of Biogas: Scrubbing, RNG, Gen-sets, Reclaimed Heat” where he discussed the monitoring and use of surplus heat from AD systems for greenhouses. The basic technological and economic aspects of biogas use and clean up technologies for H2S and CO2 removal were also presented. 

3) The first workshop in NY was held at Sunny Side Farm in Venice, NY on January 7, 2016. This workshop was a hosted industry group meeting with 12 participants to discuss the implications of the closing of the largest H2S scrubber operator (ABC Scrubbers). Following the workshop, site visits were held at the operators affected by the ABC Scrubbers closure from January 19th – January 21st, 2016.

4) In 2017, Cornell hosted an AD Short Course. The event was held from December 12th – December 14th with 66 participants at the three-day workshop. The information from the Fact Sheets was presented during the Short Course and shared in the proceedings. 

5) The VT Digester Operator’s Group was held at Rosie’s Farm in Middlebury, VT on December 8th, 2016 with 60 participants. At this workshop, controlling H2S was a presented topic, and our work on H2S scrubbers was highlighted using preliminary performance and economic data from the two NY farms. The project methodology and goals, including future monitoring of H2S scrubber systems on PA and MD farms were also presented (Quantifying and Demonstrating Scrubbing H2S from Farms 2016).

6) The VT Annual Anaerobic Digester Operator’s Meeting was held at Enosburg Falls, VT on March 22nd, 2018 with 28 digester operators. We were involved with the planning of the workshop and presented a talk titled “Hydrogen Sulfide Solutions” that highlighted the different H2S removal options from biogas.

The H2S scrubbing performance and economic results for the participating NY farms were presented in the form of a paper presentation titled “Monitoring on-farm Dairy Anaerobic Digestion Biogas H2S Scrubber Performance and Economics” at the American Society of Agricultural and Biological Engineers (ASABE) annual conference at Spokane, WA, 2017. The final results from the project highlighting the H2S scrubber performance and economics from all participating farms in NY, PA and MD were presented as a poster titled “Scrubbing H2S from Farm-Based Anaerobic Digestion Systems” at the “SARE : Our Farms, Our Future” national conference at St. Louis, MI, 2018.

Overall, the targets for this milestone were met/exceeded with six field days/workshops being hosted that provided information on biogas scrubbing technologies and general information on AD operation, biogas production, and H2S scrubbing options. Our materials and project outcomes reached the 314 participants (AD practitioners, industry representatives and farmers) who attended the six field days/workshops, exceeding our expectations.

Milestone #5 (click to expand/collapse)
What beneficiaries do and learn:

Milestone 5: PDs will consult and assist 25 farmers on implementing H2S scrubbers on dairy farms or improving their existing scrubbing systems, work with collaborating farms to optimize their systems, and continue to implement advisory board suggestions, as appropriate, by project conclusion.

Proposed number of farmer beneficiaries who will participate:
25
Actual number of farmer beneficiaries who participated:
45
Proposed Completion Date:
October 31, 2018
Status:
Completed
Date Completed:
October 31, 2018
Accomplishments:

We were able to assist all the farmers involved in the project through on-site regular meetings.  Through our assistance, the farmers at one PA farm were able to solve their scrubber clogging problems and were able to save $20,000 by not having to install a new micro-aeration pump for their digester.  Now, the farm is maintaining their pump in order to prevent further clogging. The PA farm has also decided to construct a new digester with a biological scrubber. The construction is expected to be completed in 2019. They have also been able to restart the biological scrubber connected to their old digester after changing the nutrient media, which was discovered during consultation with us.

The MD farmer sold his farm to new owners, who are retrofitting the digester with a mixer and heating equipment to improve digester performance and have also purchased a new scrubber to be installed to protect their new combined heat and power system, as their old generator stopped working during our study.  We have consulted with them on this new system and worked with them on the new scrubber and digestion system.

During this project, we confirmed that accurately measuring the concentrations of H2S over sustained periods on farm is challenging, even with industry leading equipment from Siemens.  Frequent calibrations and diligent maintenance of the measuring equipment is essential to ensuring confidence in measured values.  Siemens requires monthly calibrations and yearly replacement of the H2S sensor, which we conducted, yet, the sensors failed from the high H2S concentrations in the biogas and harsh temperature conditions during wintertime operations. Both of the NY farms use Inca gas analyzers (Union Instruments GmbH), and their manufacturer requires annual replacement of the H2S sensor, but does not specify a calibration schedule. The MD and PA farms did not have on-site analyzers outside of our monitoring schedule.

The two NY farm systems that have their own gas analyzing equipment installed had taken advantage of an incentive program by the New York State Energy Research and Development Authority (NYSERDA), which rewards farms for maintaining an H2S concentration below 300 ppm in order to receive the performance-based payments from NYSERDA.  It was clear from comparing the measurements of the two systems (PI-owned Siemens instrument and the farm-owned instrument) that in one case (NY Farm 2) the Inca analyzer was rarely working at all. NY Farm 1 better maintained and monitored their equipment (replacing sensors etc.), however, it appeared that values measured by the farm owned equipment were lower than those measured by the project equipment. This is likely due to our more frequent calibrations.  It seems clear that NYSERDA should require a validation/calibration check to ensure that their goal of incentivizing reduced H2S concentrations is actually met.

Overall, the targets were exceeded for this milestone with 45 farmers, industry representatives and AD practitioners consulted in MD, PA, NY, VT, and VA.  Regular meetings were held with the five farmers collaborating on this project to provide them with more technical information about AD and H2S scrubbing systems to improve/optimize its performance.  Consultations were also held with farmers and industry officials who were planning to install new AD systems and scrubbers, including a poultry farmer with an existing AD system, multiple farmers who did not have an H2S scrubbing system on their digesters but were interested, as well as parties involved in constructing new digestion systems for food waste and manure substrates.

We also collaborated with industry representatives who were interested in testing new additives for H2S removal. We were able to test this product in our lab and provided them with a comprehensive report on the results by conducting a biochemical methane potential (BMP) test on the additives with dairy manure to determine the effect of the product on H2S removal when added to the dairy manure digesters.

It should be noted that the written Fact Sheets, Case Studies, and Biogas Guide will help convey the information from this project to the public beyond the individual farmers that we consulted with during this project.

Milestone Activities and Participation Summary

45 Consultations
17 Curricula, factsheets or educational tools
2 Journal articles
2 On-farm demonstrations
1 Published press articles, newsletters
3 Tours
13 Webinars / talks / presentations
6 Workshop field days

Participation Summary

200 Farmers
50 Number of agricultural educator or service providers reached through education and outreach activities

Learning Outcomes

45 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

The farmers who participated in the study and attended the workshops/field days had a better understanding of the different kinds of scrubbers and their function, along with improved scrubber maintenance. The study also illuminated the importance of regular biogas monitoring to ensure efficient operation of the digester and the H2S scrubber.

As this project progressed, the PA farm owner started regular cleaning of the air pump lines used for micro-aeration to prevent clogging. The farmer also showed increased interest in learning more about scrubbers that led to a successful troubleshoot of their original scrubber. Regular consultations with the farmer also showed an increased interest in obtaining additional equipment for increasing the biogas production and experimentation with additional feedstocks. The farmer also bought an industrial food de-packaging system to introduce a new stream of waste organic materials into the digester and receive additional tipping fees.

The new MD farm owners discussed the results of the study and identified the problems with the current setup that needed to be addressed. As a result, they obtained a grant that will help them upgrade their digester, and add a full-scale H2S scrubber, which they did not currently have, and purchase a new generator, as their old generator had to be decommissioned.

This information was obtained from personal communication with the farmers at their farm on sampling visits and at the Opportunities and Challenges in Anaerobic Digestion: Maryland and the Northeast US Experience workshop.

Performance Target Outcomes

Target #1

Target: number of farmers:
20
Target: change/adoption:

By project conclusion, 10 dairy farmers with 5,000 total cows will install new biogas scrubbers and 10 additional farmers (with 2500 cows) will improve/update their existing scrubbers.

Target: amount of production affected:

These 20 farms will realize a total of 6 MW of additional generation capacity.

Target: quantified benefit(s):

The 6 MW of additional generation capacity will result in a $4,500,000/year value

Actual: number of farmers:
3
Actual: change/adoption:

A 499 kW generator in PA and a 225 kW generator in MD are being planned and constructed, with direct impacts from information coming from this grant helping their system adoption and consultation with project personnel on scrubber and generator adoption. Additionally, an upgrade of a poultry litter H2S scrubber in MD.

Actual: amount of production affected:

This is new renewable energy production of 724 kW

Actual: quantified benefit(s):

The 724 kW of additional generation capacity will result in a $543,000/year value

Performance Target Outcome Narrative:

Two farmers who participated in the study have made changes to their scrubber/digester/generator. The MD farm was sold to new owners, who have received a new grant to completely overhaul their digester, scrubber, and generator. We had a meeting with the new owners to discuss the current problems with the scrubber and the digester and provided them with the results from the study. They are currently constructing a 225 kW generator and biological scrubber.

The PA farmer also decided to construct a new digester with a biological H2S scrubber that will have a generator capacity of 499 kW. The construction is expected to be completed in 2019. The farmer was also able to troubleshoot and restart the biological scrubber for their first digester by changing the nutrient solution this year.

Another farm in MD had submitted designs and applied for grants to construct a digester, but they were unsuccessful in obtaining the funds required and had to abandon the project.

An additional poultry litter digester upgraded their H2S system based on consultation with this group.

It was difficult to ascertain the additional revenue from the construction and improvement of H2S scrubbers since some farmers in MD and PA did not have records of expenses prior to scrubber construction. While our study showed that for the two NY farms the scrubber installation and maintenance costs did not offset the costs from the decrease in oil change frequency, however, major generator overhaul costs were not taken into account and longer studies (5+ years) that incorporate these costs may justify the costs associated with biological scrubbers.

The low milk prices for the last four years have changed how farmers make investment decisions and affected lender’s decisions on project investments. It was clear during project proposal development that farms were not achieving high capacity factors for energy generation and H2S in biogas was a major reason for this issue on most farms with AD systems. Renewable energy prices for biogas has stayed low (often less than $0.06/kWh), and these low electricity prices for biogas combined with 4 years of sustained low milk prices (occurring during the course of our study) led to lower AD and H2S scrubber adoption rates than projected. In addition, American Biogas Conditioning, the company that supplied scrubbers to five NYS farms, went bankrupt and the farms had no industry support for their H2S scrubbing systems. Luckily, through this project, we were able to provide assistance to all of these farms, as the scrubbers had no Operation Manual or Customer Support from the manufacturer.

3 Farmers changed or adopted a practice

Additional Project Outcomes

2 Grants applied for that built upon this project
1 Grant received that built upon this project
$14,950.00 Dollar amount of grant received that built upon this project
2 New working collaborations
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.