Grantee Research Project Results

Final Report: Farm Waste to Energy: A Sustainable Solution for Small-Scale Farms

EPA Grant Number: SU834751
Title: Farm Waste to Energy: A Sustainable Solution for Small-Scale Farms
Investigators: Grimberg, Stefan J. , Rogers, Shane , Welsh, Joseph R.
Institution: Clarkson University
EPA Project Officer: Page, Angela
Phase: II
Project Period: August 15, 2010 through August 14, 2012
Project Amount: $74,544
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2010) Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Sustainable and Healthy Communities , P3 Challenge Area - Air Quality , P3 Awards , Sustainable and Healthy Communities

Objective:

Dairy manure management represents a major challenge at dairy farms. Manure contains pathogens and high nutrient concentrations. Manure waste also contributes significantly to the production of greenhouse gas emissions. The problems associated with manure are intensified by the rate at which it is produced on farms of all sizes. These concerns are represented most prominently on small farms that lack the technology to adequately treat dairy manure. Currently, dairy manure is most commonly used as fertilizer. Manure is spread over crop fields to increase the yield. In order to maximize this value, manure is preferably applied only in the initial growing season. Manure storage results in the emissions of significant methane (CH₄) and foul odors. Treating manure via anaerobic digestion represents a viable opportunity to reduce greenhouse gases exposed to the atmosphere, generate profitable renewable energy, while also reducing odors associated with manure storage. While anaerobic digestion has been promoted by the US EPA for large farms, no reasonable solutions are currently available for small farm systems. The objective of this project is to examine the feasibility of using small-scale anaerobic digesters to increase the efficiency of waste-stream management, utilize renewable energy, decrease emissions, and improve the economic feasibility of small-scale farming. Phase II of this project was broken into three major components:

1. The first part consisted of research conducted on a lab scale basis to help better determine a proper design for the pilot scale to be constructed later on in Phase II.
2. In the second part of Phase II the construction of a 1.2 cow scaled pilot digester was constructed and operated from Jan-Aug. Critical data obtained from this digester will be used in scaling up to our optimum design of a 25 cow digester.
3. In part three of Phase II, data collected from the operation of our pilot scale digester was used to determine the overall energy balance and economic feasibility of our modeled 25 cow system.

Phase II of this project commenced with the design and construction of the small-scale anaerobic digester at the Cornell Cooperative Extension Farm in Canton, NY. Given the range of waste-stream on a typical dairy farm, and of those surveyed in Phase I, it should be noted that Phase II focused on the methane production associated with the digestion of predominately cow manure. The scale of the digester built and assessed treated manure of approximately 1.2 cows. The digester was fed daily according to available participants and status of the digester. The samples collected were tested with respect to moisture content, volatile solids, ammonia, total nitrogen content and chemical oxygen demand. Upon installation of an effective control system complete with sensors that captured multiple data points, mass & energy balances were used to calculate the value of the energy offset. Future energy prices were predicted based on regression results of historical monthly average prices for diesel, propane, natural gas. Using these prices, the energy content of said energy sources was related to yearly biogas production, and its equivalent energy content to calculate the yearly energy offset. This offset was used in the calculation of the system's payback period.

A leachate system growing acidogenic and acetogenic bacteria will be constructed at approximately a 20 liter volume. This leachate system is much larger than the experimental leachate system built in Phase I and will have larger pipe diameters to eliminate clogging and pumping problems encountered with the first design. It will also be constructed such that different feedstock can be tested, including hay and silage. COD and VS data will be taken from the system over time. Monitoring and control should determine the optimum retention time, optimum liquid recycle rate, and the optimum volume of liquid to be taken out of recycle and put into the digester. Tests on the experimental leachate system in Phase I returned initial COD and Volatile Solids data, however not collected over time. Additionally, the pH of the leachate system was neutral, suggesting it was not optimized for fatty acid producing bacteria. Data from Phase I yielded a recycle rate and retention time that has thus far been successful, but not necessarily optimal. Hydraulic retention times from one to three months will be tested. This new leachate system will be connected to a laboratory sized digester such that the flow rate of liquid to the digester from the leachate system can be optimized. This data will be used to validate and improve the design for the pilot scale 5-cow digester.

While the leachate system undergoes testing, the pilot scale digester was constructed at the Cornell Cooperative Extension Farm in Canton, NY. The extension farm currently does not have dairy cows but raises beef cows, and grows energy crops. There are several dairy farms in close proximity to the extension farm that have agreed to provide the manure as a base feedstock for the digester. This plug flow digester has a liquid volume of approximately 5 cubic meters. It will be heated in the Mesophilic range at 35°C. The size of the leachate system will be approximately one and a half to two cubic meters. Once the digester was constructed it was put into operation and tested frequently. Students completed weekly sampling of influent and effluent COD, TS and VS data. Biogas and methane content are measured automatically using online gas meters and gas concentration sensors respectively. In terms of nutrient value, initial testing of nitrogen and phosphorous content of the effluent has been determined. Performance data was used as inputs for an economic model to determine the most cost effective operation of the system. The data collection from the digester will continue over a 10 month period. This will help to provide the most consistent information and will assure the digester can remain operating cost effectively through the entire year and not just through the summer months.

To determine if goals are being met once Phase II has begun, each group involved in Clarkson University's P3 team has specific criteria to conform to. In addition to a larger set of overarching criteria that cover the project as a whole, students in each individual group will use many of the same tools implemented in Phase I to analyze and correlate data towards these objectives. For the project as a whole, success can be defined in slightly more relative terms: staying within the designated budget, engaging the community as well as farmers on the benefits of anaerobic digestion, and demonstrating measurable progress towards the P3 goals of sustainability, increased prosperity, and helping members of the local community. Environmental, Civil, and Chemical engineers working to define the efficiency and environmental impacts of the digester will consider their work a success when the offset of fossil fuel use is quantified. Students studying business finance and economics working on defining the cost effectiveness of the digester will consider their work a success when the exact costs and revenues of the operating pilot scale digester can be defined and a business plan has been developed demonstrating the benefits of anaerobic digester for small farms.

Summary/Accomplishments (Outputs/Outcomes):

Over the course of the past two years during Phase II extensive laboratory testing was completed, along with the construction and operation of a 1.2 cow scaled anaerobic digester. Laboratory testing and results helped us gather a better understanding on how the pilot digester should be built and operated. This pilot digester produced biogas on an average of 84.15 cf/d. The biogas contained an average Methane concentration of 55.8% during May and 56.6% during July. When scaling up to the 25 cow modeled digester the real benefits start to become very apparent. During the months of July when heat loss is minimal the digester produced 21.20 GJ of energy that month after self-sustaining its heating demand. During the most energy intensive month of January the digester will still produce 14.55 GJ of excess energy. The total capital cost of the system was estimated to be $64,805. This would be broken down to where 25% would be paid for using a REAP Grant while the rest could be loaned through REAP requiring little to no upfront cash layout by the farmer. The scenario to pay back the loan the fastest was to use the biogas to offset propane all year. This scenario was determined impractical as propane demand during the summer months is low at small farms.  Therefore, the more realistic scenario was to use the biogas for propane offset 8 months out of the year and using the biogas in summer months to produce electricity. For this model the payback period would be 9.6 years.

Conclusions:

Overall this system shows promise for implementation on farms in Northern New York. The overall design has been improved significantly creating environmentally friendly energy while giving farmers another source of income even at the small scale. Farmers would benefit from the added income, while keeping a beneficial nutrient spread for their fields. Our planet would benefit from an environmentally friendly energy source while also helping control a pollution source by the disposal methods of raw manure. In the future we will be continuing our research in anaerobic digestion of farm waste to help optimize our system in further for the implementation on small farms.

Journal Articles:

No journal articles submitted with this report: View all 3 publications for this project

Supplemental Keywords:

Anaerobic digestion, biogas, digester, feedstock, hydraulic residence time, leachate, and reactor

Progress and Final Reports:

Original Abstract

2011

P3 Phase I:

Farm Waste to Energy: A Sustainable Solution for Small-Scale Farms  | Final Report