Grantee Research Project Results

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

EPA Grant Number: SU834293
Title: Farm Waste to Energy: A Sustainable Solution for Small-Scale Farms
Investigators: Grimberg, Stefan J. , Gibson, Shannon L , Welsh, Joseph R. , Booska, B , Klotzbach, C , Laush, C , Maley, C , Dissanayake, D , Gilman, Falisha , Desing, G , McCrum, I , Labelle, J , Matteson, K , Reddinger, M , Rogers, Shane , Page, T , Boyd, V , Armington, W
Institution: Clarkson University
EPA Project Officer: Page, Angela
Phase: I
Project Period: August 15, 2009 through August 14, 2010
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2009) RFA Text |  Recipients Lists
Research Category: P3 Awards , Sustainable and Healthy Communities , Pollution Prevention/Sustainable Development , P3 Challenge Area - Sustainable and Healthy Communities , P3 Challenge Area - Air Quality

Objective:

Dairy manure management represents a major challenge at dairy farms. Manure contains pathogens, high nutrient concentrations, and may contribute significantly to the production of greenhouse gas emissions. The problems associated with manure are exacerbated by the rate at which it is produced on farms of all sizes, but is especially true for small farms that lack the technology to adequately treat dairy manure. Currently, the most common use of dairy manure is fertilizer where it is spread over crop fields to increase their yield. In order to maximize the fertilizer value of manure, it is preferably applied only in the initial growing season. Manure storage, results in the emission of significant methane and odor emissions. Treating manure via anaerobic digestion (AD) represents a viable opportunity to reduce greenhouse gas emissions, to generate renewable energy, and to reduce odor associated with manure storage. While AD has been promoted by the USEPA for large farms, no solutions are 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 and the utilization of renewable energy, to decrease emissions, and to improve the economic feasibility of small-scale farming of livestock.

This project was broken into two major components:

1. Small farms within driving distance of Clarkson University were surveyed while samples were collected of potential substrates for testing small-scale co-digestion with manure.
2. Analyze the samples collected; conduct research into the economic feasibility/impacts, process design, and mass balances; design and conduct experiments testing the value of co-digestion, operating temperature, and hydraulic residence time.

Phase I of this project commenced with the surveying of eight local farms to determine the types and quantities of substrates available as well as to collect samples of said feedstocks. Given the range of waste-stream on the farms surveyed, a model farm size was developed on which the remainder of the Phase I was focused. While the farms surveyed were very diverse, the dairy operation was the predominant manure source. Surprisingly little additional waste feeds were identified at the surveyed farms. Additional waste included hay, waste feed, milk waste, and some minor other organic compounds. Overall, the available extra feed at the surveyed farms was approximately 10-15% of the total waste feed.

 

The samples collected were tested with respect to moisture content, volatile solids, ammonia, total nitrogen, and chemical oxidation content. Given the results, mass and balances were developed. Bench-scale anaerobic digesters were operated for more than one month to investigate the effects of temperature, hydraulic residence time, and feed composition on biogas generation rates and methane content.

The estimated biogas production of the system then was used to calculate the value of the energy offset. A regression of historical monthly average prices for energy sources such as diesel, propane, natural gas, etc., then was used to project average monthly prices for the next 20 years. Using these prices, the Btu value of said energy sources, yearly biogas production, and equivalent Btu value of biogas produced, a yearly energy offset was calculated. This offset was used in the calculation of the system’s payback period.

Summary/Accomplishments (Outputs/Outcomes):

Through this project, it was determined that the utilization of anaerobic digestion on small farms for the purpose of managing varying waste streams and odor issues and decreasing fossil fuel consumption and cost was feasible. The feedstocks necessary to run the digester are readily available on farms where this system would be implemented. Although quantities of feedstocks may not be exactly equivalent to that of this project’s experiments, it was proven through lab experiments that in most cases any additional organic waste added to the reactor could increase the biogas production of pure manure. Furthermore this system gives farmers a solution for any disposal issues they currently may be facing given their current waste stream and techniques for managing it.

Through the lab experiments it was determined that any of the co-digestion mixtures tested resulted in a significantly higher rate of biogas production than dairy manure alone given all other variables were constant. Furthermore, the warmer of the two reaction temperatures and the shorter of the two hydraulic residence times tested both resulted in increased biogas production rate. A separate reactor was designed to treat fibrous, high solids wastes. This leachate system proved to be a positive influence on the digester as it eliminated the need to incorporate materials with high solids content in the digester while not forfeiting the energy value of these wastes. Given these results, co-digestion, a reaction temperature of approximately 37°C, and a hydraulic residence time of 15 days proved to be the most sensible course of action.

The economic analysis demonstrated that the anaerobic digestion of farm wastes would positively influence the economics of farming on all scales. Given the regression analysis, projection of future energy prices, and estimated offset yearly energy, it was determined that the two most productive uses of the biogas produced were to generate electricity and to burn it as a substitute for propane. Given the cost of power generation equipment, the production of electricity is not a feasible option for this system as it would greatly increase the capital investment and extend the payback period. Therefore, it was decided to use the biogas produced as a substitute for propane, which for the model farm provided revenues of approximately $10,429 per year ($6,491 in profit) and would completely pay off the cost of the system in 5.2 years.

The successful development of a small-scale anaerobic digester that can be efficiently operated on the many small scale dairy farms in the United States would have many benefits. The people that would benefit from this technology include both farmers and their surrounding communities. This technology would present fossil fuel savings and provide a method for small farms to treat wastes efficiently, which they were unable to do in the past. This increases prosperity as farmers and communities can see a cost savings along with the reduction in fossil fuel use. This technology also benefits the planet in that it helps treat many different organic wastes and helps prevent pollutants, including harmful pathogens, from entering the environment. The reduction in fossil fuel use helps to reduce greenhouse gas emissions as the biogas produced is carbon neutral. The treatment of dairy manure also helps in preventing methane, a potent greenhouse gas, from entering the atmosphere.

Conclusions:

Based on the findings of this project, the construction of small-scale digesters on farms with 60 cows or less has the potential to bring about drastic changes in waste stream management, decreased fossil fuel dependency, and increased utilization of renewable energy on said farms. Given the scalability of this design, it can be used as a solution on farms of any size through scaling up or down or implementing as a series of units operating in tandem.

This system will decrease, if not completely offset, some or all of the fossil fuel demands on farms where it is implemented. Furthermore, this will decrease the greenhouse gas emissions, waste volume, and increase the nutrient density in the effluent in comparison to manure. Farmers who implement this system are expected to be able to pay off the system in a reasonable amount of time and generate profit, thereby improving the outlook of their economic future. By funding Phase II of this project, the system can be optimized such that it will have the maximum effect on the environment and prosperity of the agricultural sector of the world economy.

Proposed Phase II Objectives and Strategies:

Phase II of this proposed anaerobic digestion project will build on the empirical and experimental research conducted as part of Phase I. The basis for the continuation of this project’s experimental research will be a scaled-down version of the proposed reactor on which studies will be conducted over the course of the next 18 months. Focus areas for continued research include: (1) system heating requirements, (2) co-digestion, (3) optimization of the leachate system, (4) optimization of effluent waste utilization, and (5) pathogen reduction. Four major tasks have been outlined for Phase II of this project: (1) design, construct, and test a larger laboratory leachate system to develop operating parameters; (2) test and optimize this leachate system interaction with a laboratory digester; (3) construct a 5-cow scaled version of the current 15-cow design, (including plug flow reactor and leachate system); and (4) test and optimize this completed system.

A more detailed evaluation of the leachate system and effluent composition is essential to the project in Phase II. The added value of the leachate process will be quantified such that it can be specifically addressed in proposals to farmers. Similarly, the effluent composition will be evaluated with regard to nutrient composition, mass reduction, and utilization.

Phase II involves the implementation of a model digester at the Cornell Cooperative Extension Farm in Canton, NY, where the public and students can observe and evaluate the performance of individual components as well as the overall efficiency of the system. Given a prototype unit, students will collect data that will be incorporated in a detailed study of the proposed system. With this study, a complete business plan for an optimized system will be presented to local farmers.

The work proposed for Phase II of this project develops each of the primary aspects of the P³ program; the local community benefits from the reduction of problem odors, the farmer benefits economically from the biogas and effluent wastes, in addition to promoting sustainability through the utilization of waste to generate renewable energy while decreasing fossil fuel dependency and greenhouse gas emissions.

Supplemental Keywords:

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

Relevant Websites:

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P3 Phase II:

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