Digester System Benefits:
offer potential economic and non-economic benefits. Actual benefits
will vary from farm-to-farm. Recovered biogas can be utilized in
a variety of ways.
Biogas is approximately
60 percent methane and 40% carbon dioxide, with a heating value
of approximately 600 Btu/ft3. Gas of this quality can be used to
generate electricity, as fuel for a boiler, space heater, or refrigeration
equipment; or it may be directly combusted as a cooking and lighting
fuel. Most equipment that uses natural gas, propane, or butane fuels
can be modified to operate on biogas.
can be generated for on-farm use or for sale to the local electric
utility. The most common technology for generating electricity is
an internal combustion engine with an induction generator. The predicted
biogas production rate and the operating plan are used to size the
electricity generating equipment.
For some dairies,
this may be the most cost effective option for biogas utilization.
Other energy use options may exist. For example, a nearby greenhouse
could be heated with the bio-gas, and carbon dioxide from the heater
exhaust could be used to enhance plant growth. These options need
to be evaluated on a case- by-case basis.
A system, which
includes equipment to remove course, suspended solids from the liquid,
may sell digested fiber for compost. Recovered digested solids may
be used for animal bedding offsetting the cost of bedding purchases.
Using solids separation equipment will reduce storage volume by
10 to 20% and the pumpability of the digested liquid is greatly
will greatly reduce the viability of seeds found in the waste stream.
Consequently, there is the potential that less herbicide will need
to be purchased.
A market is
developing in which a digester owner may be able to sell pollution
credits. The process would involve the sale of CO2 credits associated
with the production of electricity from renewable energy sources.
shown that anaerobic digestion does not lower the total amount of
nitrogen, phosphorus and potassium in the manure but does increase
the amount of ammonia nitrogen. The manure effluent will have a
higher nutrient availability and plant uptake may be improved with
digestion. Fertilizer purchases are expected to be reduced and crop
yields possibly improved.
greatest potential indirect economic benefit comes from the reduction
in risk of legal action and forced outright closure. Farm employees
as well as neighbors would prefer not to deal with odors associated
with manure management. After digestion, compounds, which usually
produce odors, are greatly reduced. Digester systems, properly designed
and operated, significantly reduce the odors associated with manure
storage and distribution.
on the operating conditions, pathogenic organisms may be reduced
by as much as 90%.