Vermont farmers visiting engine room at Pennsylvania farm in winter. It is heated at no cost by the farm digester’s CHP generator set.
Energy Sales and Offset Benefits
Nutrient Management Cost Benefits
Social and Environmental Cost Benefits
1) Energy Sales and Offset Benefits
- Digesters with CHP generators produce enough electricity to offset the farm’s electricity costs with additional to sell to the grid.
- Bedding solids from dairy digesters can offset the farm’s entire bedding cost. Actually, depending on how heavy the farm beds its cows the digester can produce as much as twice the bedding needed. This excess can then be sold to other farms as bedding or as organic compost and peat moss replacement. We have colleagues who can further “compost” these digesting solids to then be sold for much higher prices per cubic yard.
- We also work with a new technology that separates a portion of the farm’s liquid digestate a second time and converts it into a granular organic fertilizer currently sold to homeowners by Home Depot, Walmart, eBay and Etsy at high margins for the farm.
- Methane digesters with CHP generator sets can heat any buildings near the digester, offsetting those costs. Some farmers use this for other purposes, such as heating a greenhouse. In at least one state the government helps financially to replace a farm’s fossil fuel heat source with renewable, digester heating.
2) Nutrient Management Cost Benefits
Pennsylvania farm draglining liquid digestate which requires less time and fuel than raw manure.
- Digesters can be a solution to excess phosphorus runoff, which can lead to serious environmental problems in water bodies such as Lake Champlain in Vermont and New York. With a digester, manure management becomes more flexible. Phosphorous is somewhat concentrated in the solids separation process. Outlined here is our “Watershed Digester” concept.
- The liquid resulting from digesting plus the separation process has less phosphorus and total solids than separated raw manure and is also more plant available.
- When combined with modern field spreading techniques, like drag lining and injection, digesters can save the farmer time and fuel costs while providing major water quality benefit.
3) Social and Environmental Cost Benefits
Discussing revenue streams with farmer considering methane digester.
- Farms near population centers can co-digest food waste with their manure. This greatly decreases greenhouse gas emissions while increasing the digester’s biogas energy output and income. In addition, food haulers typically pay significant tipping fees. If the farm adds a “de-packager,” tipping fees will be much higher. Several American states now have laws mandating food waste be taken to environmentally friendly systems like methane digesters.
- Extremely large farms near pipelines can produce RNG (renewable natural gas). This currently provides higher profits for farmers and developers than electricity but has much higher capital costs. In addition, tax credits now only exist for electricity projects.
- Homeowners sometimes threaten legal action against nearby farms due to manure odors. An anaerobic digester system reduces these by as much as 90 percent, making the farm a good neighbor. One of our Vermont farms is building a digester to help the students next door concentrate on their studies.
A state-of-the-art, complete mix (CSTR) digester offered by Agricultural Digesters LLC.