Welcome to Dickinson College Farm Biogas!
What is Biogas?
Biogas digestion converts organic wastes into burnable methane gas, a versatile energy source for cooking, heating, and electricity generation. Since 2008, the College Farm has been experimenting with demonstration-scale biogas systems and laboratory research projects. Altogether this work includes numerous student projects, lab exercises, youth education programs, video and conference presentations resulting in international recognition for sustainability at Dickinson. Gas generated by the biogas digesters is used on the farm to fuel cooking appliances. In the near future, we will complete a farm-scale digester that will convert biogas to electricity and wipe out the farms power bill. Use of biogas on the farm replaces propane and other fossil fuels thereby contributing to the farm and College’s goal of net reduction of carbon emissions.
Table of Contents:
Commercial Digester Development
After over ten years of R&D with small scale biogas systems, the Dickinson College Farm is going big and building a farm-scale digester that will convert our waste into electricity! This initiative began in 2018 with a feasibility study. Our project gained support of the USDA Natural Resource Conservation Service with a generous cost-share grant in 2020. From there things really picked up steam with project development and fundraising to pull it all together. Our expected completion time is autumn of 2023. Watch this space for periodic updates on the progress of this exciting, innovative project!
Background: We’ve been making burnable biogas from cattle manure and food waste in our pilot scale (1000 gallon) digester since 2015. This system consumes only 150 lbs of food waste per week at full capacity, yet it already can produce more gas than we need for cooking and canning on the farm. Given that the College dining hall produces about 750 lbs of food waste per day, we knew we would need to convert the biogas into a more transferrable form of energy if we upsize to a full-scale project. By coupling a biodigester with a combined heat and power (CHP) generator, we can convert our biogas into electricity and heat. This electricity can be used on the farm or sold back to the utility (like a grid-tied solar project). However, while 750 lbs per day is a lot of food waste, it is not quite enough material to power the smallest commercially available grid -tied CHP system. So we started looking around for more waste in the neighborhood.
Through our feasibility study, we identified Triple L Farm dairy as a perfect partner for a shared digester. The Hoover and Charles families have rented the property directly adjacent to the College farm from Dickinson for over 20 years. Triple L Farm keeps about 150 dairy cattle on the property and expressed an interest in working with us to turn their waste into energy and fertilizer. Engineers from the USDA NRCS identified some manure management concerns at the dairy farm that made the project eligible for federal conservation funding, in the interest of improving water quality in the Yellow Breeches Creek nearby. The dairy farmers are excited to have a modernized barn to house their cattle, an improved manure system, and free bedding from extracted manure solids which will lead to substantial cost savings over conventional bedding.
Our feasibility study and discussions with our dairy neighbors, USDA engineers and experts in the digestion industry has resulted in the following plan:
We’re building a new structure that will serve as combined dairy cow housing and waste collection & processing system. The dairy farmers will push their manure into a collection pit each day, then College Farm staff will take over waste management from there. Food waste will be delivered to the site daily, chopped and mixed in a separate pit before blending with the dairy manure. The combined manure and food waste slurry will be pumped to the digester for processing into biogas and digestate (liquid fertilizer). Liquid effluent from the digester will flow back to the cattle & waste building, where it will be passed through a screw press to remove manure fibers which will be used as cow bedding. The liquid fraction of the effluent will flow to a final storage tank to await spreading on the fields or addition to compost piles. Biogas from the digester will be fed to a 50kW CHP engine which will produce electricity and heat. The heat will keep the digester warm through winter months (they operate best at cow body temperature, about 100F) or be used to heat greenhouses and dry grain and vegetables. Electricity will be used to power all machines on the project site, with excess sold back to the Met Ed utility. We anticipate energy output of 200-300,000 kWh per year of clean renewable electricity. To optimize productivity of the system we are seeking additional food waste from the Carlisle community and have thus far secured an additional 2000-3000 lbs per week of external waste from the local food bank, a commercial bakery, a restaurant and a craft brewery.
Overall beneficial attributes of this project include reduced manure odors, reduced water pollution through modernized manure management, reduced loading of landfills with food waste, and reduced greenhouse gas emissions. All the while we will generate renewable, carbon negative electricity, revenue for the farm, and strengthen the farm economy in the Cumberland Valley.
What makes our project especially exciting and unique is its modest scale. While 150 cows and 4000 lbs. per day of food waste seems like a lot to us, this is actually a small system as commercial biodigesters go. In the US most digesters are on farms with 500 or more cows due to economies of scale. However, in Europe, smaller “pocket digesters” have been proven effective on farms with herds as small as 50 cattle. So we are working with experienced Pennsylvania based manure management partners to build a smaller custom digester using domestic and European components. When complete, ours will be the smallest commercial digester in Pennsylvania. We will use this showcase system to teach and inspire farmers from around the mid-Atlantic to consider adding a small digester to their operations. There are about 5000 dairy farms in PA, with an average size of 85 cows. So the success of our project should pave the way for a lot more waste to energy digestion in our area.
Because we are building a lot of new infrastructure (cattle barn, waste pits, digester, final manure storage tank, new electrical service, new service road), our project will be costly with an expected total price tag of $1,600,000. Thankfully projects like this are eligible for lots of state and federal agricultural conservation incentive programs. To date we have secured over $1,300,000 in grants, donations and internal College funds to support development of the project. We are actively fundraising to complete the project – interested donors should contact firstname.lastname@example.org or the farm at email@example.com. The expected completion date of the digester project is autumn of 2023.
Food Waste Diversion
While most farms digesters run livestock manure, “co-digestion” has proven to be more effective and provide more burnable gas. Co-digestion is when multiple types of organic matter such as manure, food waste, or plant matter are digested in the same biodigester together. With this in mind, the digester can be used as a mean to divert food waste from landfills. Currently the farm collects 700 pounds of cafeteria waste every day as well as X pounds of food waste weekly from various establishments in the Carlisle, PA area with the goal of collecting X pounds for the commercial digester.
The goal of food waste collection is to divert organic matter from landfills, where they will release methane into the atmosphere and where their nutrients will be lost and become unviable for future usage in biogas but also in agricultural systems. Biogas is made up of carbon, hydrogen and oxygen, while the important plant nutrients needed for composting (nitrogen, phosphorus, potassium and trace elements) are passed through the system and come out in a more bioavailable form for future usage in agriculture.
Education and Outreach
A critical function of the farm’s biogas program is our education and outreach initiative. Since 2008 we have worked to inspire students of all ages through demonstration of sustainable organic waste recycling into energy and fertilizer. Beginning with plastic jugs of sheep manure in the farmhouse basement, we have progressed through several iterations of lab and homestead scale anaerobic digestion systems, all built by farm students and staff. At present we maintain a 1000-gal pilot-scale reactor for cooking fuel production, numerous lab-scale research units, and are in process of constructing a commercial-scale waste to electricity farm digester. These are used to educate Dickinson students and the public through lab exercises, hands-on internships, field trips and day camps for K-12 youth and clubs, farmer field days, and presentations at regional conferences. Our team is also available for direct support to teachers and school programs looking to add biogas and composting units to their curriculum. To support the in-person experiences, we also produce educational biogas videos targeted at audiences of all ages. Public education is fundamental to our objective of helping to increase deployment of biogas technology on farms, in schools and at homesteads across our region.
If you are a farmer, teacher, club leader, or student interested in learning more about biogas systems through tours, field trips, internships, presentations or virtual lessons, please contact project leader Matt Steiman for more information. The microbes and biogas await your inquiry!
Matt Steiman: E-mail firstname.lastname@example.org
College Farm Education & Outreach coordinator: email@example.com
Our ongoing research efforts have three components:
- Replicated lab-scale digestion for alternative feedstock analysis. In addition to cow manure and food waste, virtually all organic waste materials can be digested into biogas and fertilizer, so long as they are free of toxins and other contaminants. Combining multiple waste resources in one digester, known as co-digestion, can result in synergistic benefits such as diversification of the nutrients available to microbes and pH balancing, often resulting in higher levels of energy output compared to mono-substrate digestion. Taking advantage of locally available feedstocks enables a farm digester owner to increase revenue from additional energy generation as well as tipping fees for some externally produced wastes. Common questions facing digester operators are “what is the energy and nutrient value of a new feedstock”, and “what other operational impacts will occur if I add this feedstock to my manure digester?”. Establishing methane gas and nutrient production values for various feedstocks on a per kg basis is vital to successful extrapolation for planning and design purposes.
We are now completing our third season of focused lab-scale anaerobic digestion research mostly focused on the value of brewers spent grain as an alternate feedstock. During this period we developed and refined an effective yet inexpensive apparatus for lab digesters that simulate larger-scale conditions. At the core of our apparatus are 2.5 gallon Fort-Pak type square plastic containers that we modify into semi-continuously fed mini digesters. We like this particular container because it can produce a functional AD system at a cost of only $20-25 per unit. The large volume (by lab digester standards) and 1” diameter fluid piping readily accommodate high solids blends of cow manure and food waste without significant clogging. Each digester is connected to a floating cylinder gas collector equipped with a meter stick for recording accurate gas volume data on a daily basis. Daily service of the digesters includes feeding, releasing digestate, and recording biogas production. Collected biogas is analyzed at least once per week to assess methane content. The experiments are run for about 100 days to generate data that reflect the long-term performance of novel feedstocks in a farm digester. For a more detailed view of the lab digester system, please visit our DIY Research Digester video on Youtube.
Students’ roles in this experiment were fabrication and troubleshooting of equipment, feeding and data collection, and physical and chemical analysis of feedstock and effluent under in the Chemistry lab. Physical analyses of materials included loss on drying and loss on ignition tests to establish % total and volatile solids, respectively. Chemical analyses included titration for alkalinity and testing for total nitrogen, total phosphorus, and chemical oxygen demand. The newly developed digester set is user-friendly, accurate, spill resistant and productive. In 2022 we built a second set of six digesters to test blends of brewers grain, cow manure and campus food waste.
Click here for a brief fact sheet on the brewers grain digestion project.
2. Digestate value as fertilizer: Liquid effluent (digestate) from the biodigesters conveys plant nutrients from the starting feedstocks broken down into a more bioavailable form through the action of microbial decomposition. While carbon, hydrogen and oxygen leave the system as biogas, nutrients important to crop growth (e.g. nitrogen, phosphorus and potassium) pass through the system and reside in the digestate. It is common practice for farmers to use digestate as liquid crop fertilizer. Our objective with this portion of the study is to assess the value of digestate as fertilizer for field and greenhouse crops using bioassays and crop nutrient analysis in the chem lab. This objective builds on a study conducted by Max Lee ‘19 in 2018.
We set up two pilot studies in 2021. The first involved field application of digestate from the farm’s 1000 gal pilot unit to pasture grasses using a pump wagon pulled by a tractor. To calibrate the field application we used a large rectangular tub of known area to catch and weigh a sample of digestate as the pump wagon was pulled through the pasture. These data allowed us to estimate the quantity of digestate applied per acre to the larger pasture. However after several weeks of grass growth, it was determined that no significant difference in grass growth was observed in comparison to an adjacent area where digestate was not applied.
In the second pilot trial, we planted kale seedlings in 1-gallon pots in the Stafford research greenhouse and applied the following treatments:
1 digestate:2 water
1 digestate: 3 water
1 digestate: 6 water
Commercial fish fertilizer
Five replicate pots of each treatment were grown. Kale pots were checked daily and uniformly watered as needed. Once weekly all pots were fertilized with an equal volume (200 ml) of their designated treatment. This experiment was run for five weeks before we destructively harvested all kale plants. Plants were measured and photographed before placing them in freezer storage for further analysis for antioxidant content in the chemistry lab (this assessment will be carried out this fall). As seen in figure 4 below, the biomass production did not differ substantially between treatments. We suspect this was due to the quality of the potting mix used as a growth medium – note that the control plants which were not fertilized at all did not appear to suffer substantially due to lack of nutrients. We intend to repeat this experiment in the fall and spring semesters using a more nutrient-poor growth medium. A difference in concentration of antioxidants in the kale tissue may be discovered upon further testing in the chem lab later this fall.
The digestate as fertilizer trial was repeated in 2022 using red russian kale and beets as test crops. In this experiment we used a more nutrient-poor growth medium and only dosed the potting mix with digestate once prior to planting. From that point forward all pots were moistened only with tap water. Kale plants grew successfully under this system. Currently the harvested biomass is in frozen storage for analysis in the chemistry lab to assess differences in plant nutrient content across the treatments.
3. Impact of diversion of food waste to digesters on existing composting program. The majority of campus food waste collected is currently processed through a farm-scale composting system with the resulting compost used as a soil improving amendment in vegetable fields. A third set of experiments seeks to assess the impact of routing the food waste through an anaerobic digestion system for energy extraction before the nutrients are added to leaf compost piles as digestate. The results of this study will help us predict future impacts on the farm while potentially guiding other commercial composters who may consider adding a digester to their food waste recycling program. This study also continues the work of Max Lee ’19 from the 2018 summer research period.
We set up two sets of compost experiments in 2021. In each experiment, three replicates of 1 m3 compost piles were built for each treatment – Food Waste (FW) piles containing leaves, compost seed material and campus food waste, and Digestate (D) piles containing leaves, seed material and digestate. Food waste was added to the FW piles on the day of pile construction, while digestate was added to D piles at regular intervals throughout the experiment. The gradual addition of digestate was necessary to prevent liquid saturation of the D piles. Each time digestate was added to D piles, an equivalent amount of water was added to FW piles to control for moisture addition. Temperature of all piles was recorded three times per week throughout the summer, and piles were turned manually at regular intervals. When compost piles were deemed near to maturity (no longer heating up after turning) their CO2 respiration and ammonia production were measured using SOLVITA colorimetric compost testing paddles (Woods End Laboratory, Mt. Vernon, ME). At the end of the experiment a seed germination bioassay was run on the finished composts to assess suitability for use as potting soil.
The first round of this experiment yielded promising results that align with our expectations for compost behavior (the second round is still underway). While the FW piles attained higher average temperature than D piles during the initial weeks of composting, this pattern flipped in the latter weeks of the trial. This is likely explained by the timing of nitrogen addition. N is a limiting nutrient for microbial growth and is typically balanced with carbon at a ratio of 30C:1N in an ideal compost pile. The leaf base of our composts is mostly carbon, while N is applied as either food waste or digestate. Since the FW piles received their N allotment in the initial construction, it makes sense that they would heat up early, while D piles had their N dosed at intervals throughout the trial and thus maintained moderately high temperature for a longer period while the FW piles cooled off after exhausting their supply of nitrogen. No difference was seen between the finished piles using the SOLVITA testing paddles (both treatments displayed characteristics of normal maturing composts). Likewise there were no substantial
differences in germination rate of three crops (corn, bean, radish) between the FW and D piles, but both treatments exhibited faster germination response than seeds grown in a commercial potting soil control (fig 7).
While we had some experiments in 2021 that did not yield the results we expected, all efforts did add substantially to the experience of our team. As we continue to gain proficiency with the materials, equipment and procedures used to assess the performance of anaerobic digestion systems and associated components at the farm, we are confident in our ability to achieve results that are of interest to operators in this field and ideally publishable in environmental engineering and chemistry journals.
For K-12 audiences – intro to biogas and compost:
For science classes and interested farmers:
Build your own research digester:
For dairy farmers:
Beer to Biogas initiative:
Earlier versions of our project:
Papers and Articles:
If you want to dive deeper into biogas, here’s a list of papers and articles:
- Bucknell U. Digester Performance Study 2016
- Large Digester Feasibility Study 2018
- Digestate Research – Max Lee 2018
- Digestate Research – Full Paper
- Dickinson Digester Sustainability Analysis 2020
Commercial Digester Updates:
April 11, 2023
Construction has begun!!
We are so very excited to share the news that construction work has commenced on the farm-scale digester system. After almost five years of planning, fundraising, permitting and design work, we have finally broken ground on the overall project site. Phase one, which includes the new dairy barn with collection and blending pits for the cow manure and food waste, should be complete by June 30th. Our educational pavilion will also go up by the end of June. The second phase, to include the digester and final manure storage tanks, will proceed early this summer. The final phase (installation of the digester cover, combined heat and power genset, and all mechanical and gas connections) will wrap up this coming winter.
We’re grateful to all of the people, firms, agencies, and funders who have helped us reach this exciting point in the project. Please stay tuned for more updates in the near future! Here are a few photos from the start of phase one:
June 2023 Update:
Digester Construction Update June 28, 2023
Wow it has been a busy couple of months at the construction site! So much has been happening but we’ve been running hard just to keep up with project management and spring duties on the farm. Finally we’re getting a few rainy days and so are happy to update our construction page here on the blog. We are very happy with and grateful for all of the contractors who have brought their expertise and hustle to pull the project together. It is such a pleasure to work with all of these fine folks:
- Team Ag Engineering – site engineering, permits and project certification
- Barton Associates – electrical engineering and permits
- Weaver Hauling and Excavating – digging holes, grading, building roads, hauling rock, installing pipes
- Franklin Builders – Barn and pavilion structures, fixtures and concrete work
- Kurtzcrete – concrete tanks in the waste reception facility
- DML Poured Walls – round tanks for manure and digester
- Nutrient Control Systems – manure pumps, mixers, and digester kit.
That’s where we stand as of the end of June. Keep an eye out for more updates as we proceed to build the digester tank
and start installing mechanical equipment. Thanks for reading!!!
Prior Digester Updates:
10/3/22 Engineering for the digester project is virtually complete and the major hurdles are all behind us. Since 2020 we have been working with the excellent folks at Team Ag agricultural and environmental engineering. Team Ag has developed our civil engineering site plan and overall materials flow plan, as well structural engineering for the cattle barn and waste pits. This work was then used to secure site development and stormwater management permits from the PA Dept of Environmental Protection and to meet the standards of county engineers to ensure water pollution reduction in the nearby creek. Meanwhile we’re working with Barton Associates electrical engineers to develop a new service and interconnect agreement with the Met Ed utility as well as wiring plans for all buildings and major waste treatment components.
Experts from Nutrient Control Systems and Martin Energy have nearly completed the digester plan – we will post details in our next update.
Things are moving forward and we expect a ground-breaking ceremony late fall or early winter! Watch this space for another exciting update next month!