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.