6 former chicken houses with concrete pads 65 feet wide by 450 feet long, which may be suitable as a floor for some portion of a new AD facility
A 9,000 sf former egg processing/packaging/storage facility
Electrical building with 3-phase power
Existing padmount distribution transformer that is rated 1,000 kVA, sufficient to export the entire 848 kW output from the proposed anaerobic digester
Water supply wells
WET VS DRY TECHNOLOGY OR LOW SOLIDS VS HIGH SOLIDS
Project started by looking at both wet and dry fermentation systems
Decision to not pursue wet fermentation due to the fact that there is no sewer connection available at Mass Natural to handle the significant amount of liquid wastewater that would be generated by a wet fermentation system
Although the liquid wastewater can potentially be land applied, that scenario would have required construction of very large holding tanks, and then contracting for land application, something Mass Natural is not prepared to do at this point in time.
FEEDSTOCKS FOR HIGH SOLIDS ANAEROBIC DIGESTION
Approximately 52 tons/day
Solids Content 62%
Volatile Solids 88% of Total Solids
Ammonia/Ammonium Concentration: 3,777Mg/l
Biogas Generation: 480 m3/hour
Methane Content 62%
Electrical Output Potential 1,109kW
Based on engine-genset electrical efficiency of 36.3%
COMPARISON OF BIOGAS OUTPUT FROM TECHNOLOGY PROVIDERS
Because dry material is stackable, the digester can be loaded with a front-end loader, which is already at a compost facility
When the material is finished digesting, it still has a relatively high solids content. Therefore, the effluent can be composted without having to remove much liquid from it
Pumping liquid percolate is much easier than pumping slurries, which is the case in most commercial digestion systems. Pumping slurry requires significant horsepower, and the pipes are prone to clogging
To reduce the impact of reduced biogas production that occurs when the digester is re-filled, multiple digester “cells” can be employed so that several are operating at capacity at any one time
If one digester cell has an upset condition, the percolate from it is diluted by the percolate from the other cells, making it easier to re-start a “stuck” cell. In an extreme case, the percolate can be completely isolated and removed from circulation
Digestible, organic matter is loaded into a long, narrow gas-tight building
Once the building is sealed, it is saturated with percolate that contains anaerobic micro-organisms from an active digester
Percolate is periodically drained and re-sprayed into the digester over a period of approximately 28 days
Biogas is collected and a combusted in an engine-genset to produce electricity
Waste heat from the engine is used to maintain an ideal temperature within the digesters
After the prescribed retention time, the digester is opened, the organic matter is removed, and some of it (a third to half of it) is mixed with fresh organic material and loaded back inside the digester
Operating costs for the anaerobic digester system were estimated by the Brendle report to be approx-imately $130,000 per year assuming 1.5 full-time equivalent employees
Operating costs for the CHP operation are estimated at $137,000 per year
Total operating cost of $277,000 per year
MASS NATURAL PROJECT REVENUE AND FINANCING FOR $8.4 MILLION FACILITY
Project revenue is estimated at approximately $1.9 million in the first year of full operation. That revenue is based on an average tipping fee of $45/ton of feedstock, and receipt of $0.10/kwh of electricity generated.
Assumptions for project financing were based on 35.5% of total costs financed with solid waste bonds, 23% by investment tax credit, and the balance by equity investment. With this combination of revenue and financing the estimated return on investment, EBITDA (earnings before interest, taxes, depreciation and amortization), divided by pre-debt capital costs, is 13.4%
• Based on laboratory testing of many of these food wastes, it was determined that 20,000 tons per year of food wastes would generate sufficient quantities of biogas to power a 848 kW generator.
• Two technology vendors with numerous, successfully operating high solids anaerobic digestion technologies currently operating in Germany have technology that is technically feasible for implementation at Mass Natural.
• Sufficient types and quantities of industrial food waste are available within economical hauling distances of Mass Natural’s Westminster, Massachusetts composting facility to supply a 20,000 ton per year high solids anaerobic digestion facility.
• The electrical interconnection from a generator powered by an anaerobic digester is feasible and economical at Mass Natural.
• The Mass Natural site has sufficient space to locate an anaerobic digestion facility
• The current composting operation at Mass Natural would be a complimentary operation for an anaerobic digestion facility
• The regulatory approval process for an anaerobic digestion facility at Mass Natural was determined to be feasible.
• The capital costs for an anaerobic digestion facility at Mass Natural was determined to be between $5.5 and $8.4 million. For a 20,000 ton per year facility this was determined by Mass Natural to be a marginal investment.
• Mass Natural would like to conduct further evaluation to identify less costly high solids dry fermentation technologies.