North Harbor Dairy

A digester, energy recovery and value-added product system (e.g., micro-cheese) is being designed and installed at the 500-cow North Harbor Dairy Farm in Jefferson Co., New York to capture valuable biogas that will be used as heat and power for value-added products. This will be among the first anaerobic manure digesters operating in Northern NY State and is intended to be a showcase operation for future installations at farms utilizing sand bedding or in cold regions (9 ºF in January). Innovative designs are being employed to separate the sand from manure solids within the digester to be reused as near-pathogen-free bedding material.

A study to determine the feasibility of  anaerobic digestion at NHD was conducted by Environomics,  Inc., of Salt Point, Maryland ( New York). The project was deemed to be feasibile, with an estimated annual owner return on investment of 6% and an NPV-based payback of 5.85 years.

The laboratory scale anaerobic digesters shown in the accompanying photograph are used to digest dairy manure. The digested manure and biogas characteristics are measured as a function of manure feedstock characteristics. Measurements include chemical oxygen demand, total organic carbon, total volatile solids and biogas composition. Currently, the digesters are producing both methane and carbon dioxide in increasing amounts.

Many farmers use sand for bedding because of their perception that it increases cow comfort, and therefore milk production.  However, digesters have failed because sand is inert and tends to fill up digesters. Therefore, the laboratory digesters are also used to observe the separation and build-up of bedding sand within them. 

Pilot Plant

A small-scale pilot plant will be temporarily placed at the NHD to study the effectiveness of the sand separation design. It will also incorporate instrumentation allowing measurement of biogas production, heat loss to the surroundings, and the energy required to keep the manure at 100 °F, the optimum digestion temperature.

The pilot plant will be built by: MTARRI/VARANI, LLC

The Mathematical Model

A mathematical model that integrates mass, energy, revenue and cost flows throughout the digester-energy recovery system is under development. Data quantifying gas quantity and composition, heat and energy production, and economic return will be compared with model predictions for calibration and verification. The verified model can be used to determine economically optimum operating conditions as a function of feedstock composition, loading rates, temperature, electricity costs, net metering legislation and heating costs to maximize revenue from the system. A software package will allow the economic tradeoffs and potential incentives to be examined. The model will be invaluable to the regulatory community to identify incentive structures needed to promote this technology, for the designer to evaluate design and operational parameters and for the farmer to optimize his/her system to adjust for seasonal variations in temperature, changes in manure composition or other farm management practices.

Life Cycle Study

A detailed lifecycle environmental analysis, including the fossil fuel energy displacement, greenhouse gases emissions, soil health and water contamination by nutrients is being quantified for the North Harbor Farm and used to predict the environmental benefits and ease in meeting CAFO (Contained Animal Feed Operations) legislation across Northern New York. The Figure below illustrates the system that is included within the life cycle environmental analysis.

Gasification of Dairy Manure

The feasibility of gasifying, rather than digesting, dairy manure was examined by Skill Associates, of Kaukauna, Wisconsin. Gasification of some waste biological materials, such as wood chips, is feasible. However, the moisture content of dairy manure is typically 87% by mass, too high to gasify. Therefore a drying process must be introduced in order to lower the moisture content to at or below 40%, the break-even point in the energy cost of drying. The Skill Associates process, which is more accurately described as manure burning, incorporates extensive manure drying facilities and mechanical sand separation. The cost estimated for the system was $1.7 million (much higher than the digester system) with a payback period of 9.4 years and was considered infeasible by the CBG when compared to our available funds.  

Despite these conclusions, manure from Fisher Dairy has been sent to North Carolina State University to be experimentally gasified. The results of this work will contribute information on the energy costs of gasifying wet manure.