Environmental Engineering Reference
In-Depth Information
ago, inserting an essentially “new” greenhouse gas into the modern
world. Existing biomass, however, releases carbon dioxide that is largely
balanced by the carbon dioxide captured in its own growth.
Most biomass use in the United States today involves some form of
incineration to produce electricity or fermentation to make ethanol and
biodiesel fuels. Biofuels supply about 3 percent of the energy we consume,
thanks primarily to waste biomass from the paper industry, forest indus-
try residues, and municipal solid waste used to generate electricity.
7
Energy from Manure
Livestock in the United States produce almost 2 trillion tons of manure
annually, most of which is left to rot.
8
If it were collected and converted
to methane in anaerobic digesters, it could generate a signifi cant percent-
age of annual U.S. electricity demand. It is a stable and reliable source
of fuel. A typical lactating cow produces about 100 pounds of “pies”
and 50 pounds of urine each day. There are about a hundred methane-
producing cattle farms today.
9
Typically a minimum herd of 300 dairy
cows or 2,000 swine is needed to make such a system feasible.
10
It takes
twenty to thirty days to turn the manure into heat and power.
Questions have been raised about the economic viability of such proj-
ects.
11
Calculations by several investigators indicate that large biodigester
operations will need federal subsidies to be economically viable and that
proposing to build them is therefore inadvisable. Particularly problem-
atic is the site-specifi c nature of cattle feedlots, which produce four-fi fths
of the manure. The low energy density of manure makes transporting
waste to centralized digesters diffi cult, and large cattle feedlots are often
located in areas far from where the energy is needed.
However, as is usual with calculations that indicate alternative energy
sources are uneconomical, no consideration is given to the enormous
amounts of money given to the fossil fuel industries in the form of mili-
tary protections and domestic subsidies and the undependable character
of the nations that supply America's imported fossil fuel (see chapter 6).
The federal government has provided many billions of dollars in subsi-
dies for the fossil fuel industries, and subsidies in rich countries world-
wide for fossil fuel energy were estimated to be about $73 billion a year
in the late 1990s, with an additional $162 billion spent in other coun-
tries.
12
In an age of climate change and air pollution, these subsidies are
like giving money to drug addicts to fuel their life-destroying habit. When
these facts are inserted into the fi nancial calculations, most alternative
energy sources seem cheap.
