Connecticut Nutrient Management
Woodstock Nutrient Management Information
Woodstock Nutrient Management Feasibility Study
The Town of Woodstock is very supportive of its farmers and has been working with them to determine the feasibility of developing value-added products from excess dairy manure, both as a possible income source, and as a method to move nutrients to their fields. The Town and it's farmers are interested in investigating the development of a single farm or regional manure anaerobic digester to generate power, an in composting options either combined with a digester or as stand-alone processes. Both of these options have the potential to provide a source of income from the manure; however, only composting has the potential to move nutrients from the farms. The digestion process generates and captures methane gas produced by the manure and can convert it into heat and power which can be used on-site or sold to local users or the grid. Composting converts the manure nutrients into a form that can be exported off-site and can create an income stream for the farmer. The Town is also interested in the feasibility of incorporating other feedstocks such as food wastes or fats, oils and greases into the digester and composting options as they may represent an additional income stream due to tipping fees.
The feasibility study was completed by Wright-Pierce in July 2007 for Eastern CT RC&D and the study evaluated potential locations, configurations and technologies for both digester and composting alternatives. Specifically the study evaluated the following options:
In order to size the facility and estimate the quantity of available manure, the farms in the Woodstock region were interviewed and a survey of each farm was completed by Eastern CT RC&D. The data collected was used as the design basis of the digestion and composting facilities, equipment selection and cost estimates, including potential revenue sources.
The manure volumes used as the basis for the digester analysis are provided in Table 1-1 for an individual farm and for a regional facility. Digestion was found only to be feasible at farms with greater than 500 cows and the optimal complete mixed digester feed is approximately 8-10% solids. The digester influent would be diluted with the liquid stream from post-digestion dewatering to obtain the optimal percent solids. A complete mixed digester is the recommended digester technology if additional feed such as fats, oils, and grease (FOG) is to be added to the system. Only the largest farm was considered for single farm digestion.
Most of the Woodstock area farms currently use sand as the primary bedding material; however, none of the digestion processes are appropriate for sand laden manure. In order to consider a regional facility, a sand separator was included as part of the conceptual design. The regional facility was assumed to receive 65% of the manure from each farm. Transportation costs to several potential regional digester locations were also evaluated; however in order to minimize transportation and land purchase costs, it was assumed that the regional facility would be located at the largest farm. Since the regional digester would be located at the largest farm, it was assumed that 100% of the manure from that farm would be sent to the facility. The regional digester feed characteristics are also summarized in Table 1-1.
The compost facility feed quantities represented in Table 1-2 were used to predict the volume and quality of compost product that would be produced at the facility. Table 1-3 provides the expected quantity of marketable material under the design conditions.
Previous studies have shown that composted manure could be sold at approximately $17 per cubic yard. The potential revenue for each of the composting scenarios was estimated using this unit price. Windrow composting is a well proven method for composting, and all if the options considered were evaluated as windrow facilities. Containerized systems were also evaluated as part of this study and were determined to be cost prohibitive for manure composting due to the size of the containers and the number that would be required.
The important factors impacting the projected costs of the windrow composting options and the anaerobic digester options are listed below:
In assessing the feasibility of the manure management alternatives, additional feed sources and revenue factors were also considered, including:
• Fats, oils and grease (FOG): Revenue from FOG includes both sales of power from the additional digester gas produced and a tipping fee for disposing of the material.
The projected costs for the digester alternatives are summarized in Table 1-4. Only the individual farm, complete mixed digester alternative was found to be profitable without additional funding. The individual farm, complete mixed digester facility is estimated to generate enough income to fully cover the annual digester costs such that the facility could make a small profit. None of the other digester alternatives were found to be financially feasible without additional funding. In these other digester options, the annual costs of the digesters would exceed the income, even with an initial 50% grant.
The projected costs for the composting alternatives are provided in Table 1-5. Economically, the analysis indicates that none of the composting options would produce sufficient income to cover all of the costs of the operations. However, food waste and horse manure tipping fees would improve the feasibility of the composting options and if available in large enough quantities could allow the facilities to break even. Grant funding of 50% would also offset the annual costs enough for the proposed facilities to break even. The most feasible options are the single farm facility following a digester and the regional alternative that includes composting at each farm with shared equipment. Most of the on-farm options become cost effective when no building is required for housing the active composting phase of the process.
Table 1-6 presents the projected costs for the combined digestion and composting facilities. Neither of the combined regional facility options is profitable. Combining the individual farm digester with the composting of digested solids and whole manure from other farms has a low annual cost per cow, however, the economics of this option rely on the individual farm digesting system profits to offset the costs of the composting facility. The individual farm combined option would not be profitable since the cost for the composting portion is greater than the profit from the digestion portion. This combined case could be profitable overall if the building to house the active composting phase were not necessary for the composting facility. The individual farm case is more economically feasible than the regional facility with digestion option, primarily due to the absence of the need to transport the manure.
The study concluded that the best options to investigate further is the anaerobic digester on the individual farm and the regional facility combining the digester on the largest farm with composting the dewatered digested solids plus 20% of the other farms whole manure. If grants or other funding aids are available, these options would become even more economically feasible. Anaerobic digestion has the potential to produce renewable fuels; however, it would not provide a means to move nutrients off the farm. If there is a need to move manure nutrients to another non-farm market, then adding composting to the anaerobic digestion system could be relatively cost effective.
There are a variety of organizational and ownership structures that can be used for the manure handling options discussed. For the individual farm options the digester and/or composting facility would most likely be owned and operated by the individual farm on land it either leases, purchases or already owns. For the regional facility options, the ownership options include establishing a CO-op or farm group, a town owned facility or a privately owned facility.
The study noted that the first steps in developing a regional facility are to assess interest and to start building an organization to spearhead the project. In the earliest stages of organizing, it is useful to have an existing organization such as the Eastern RC&D, or the Town, that can "sponsor" the newly developing organization. The "sponsor" can provide basic office accessories such as an address, telephone and fax numbers, access to copying and word processing, and a space in which to meet. This approach avoids the initial expense of setting up an office specifically for the regional facility organization in the early stages of development.
Also early in the organization process, the focus should be on how to organize sufficiently to obtain "seed" funding to proceed to the next stage of development. While many ownership and organizational structures for the regional facility are possible, a focus on minimizing the farmers' costs quickly leads to a non-profit type organizational structure unless a developer is eager to spearhead the project. The ultimate organization will develop over time as the interim team (director or board of directors) develops the statement of purpose of the organization and the required funding is developed. It would be prudent at the early stages of forming the organization to involve a lawyer who is familiar with Connecticut State rules and regulations for incorporating a non-profit organization.
Critical factors in the success of regional manure handling facilities include farmer participation and support, long term commitment of manure feed sources and treated manure users, long term commitments for heat and electricity users, and transportation logistics. The project identified several areas where additional research of the issues presented in this report could potentially increase the economic feasibility of the considered alternatives. The areas to research should be completed as part of the next steps in identifying/developing possible manure management solutions for the Woodstock area farms. The areas of additional research include the following:
The above information comes from the Woodstock Nutrient Management Feasibility Study. To access the full report click on the following link Woodstock Nutrient Management Feasibility Study.
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