Water to Grow Corn
Corn is currently
the primary feedstock for ethanol production—and accounts
for the largest volume of water required in the overall
ethanol production cycle. While much of this water is
returned to the atmosphere through plant evapotranspiration
(4,000 gallons per acre per day!), corn (like all crops)
must have water at critical times of its development.
Depending
on soil type and growing conditions, a corn plant requires
up to 14 inches of water to produce satisfactory yields.
Corn ethanol opponents suggest that corn farmers
artificially supply this water. In reality, 90-93% of the
nation’s corn but relies solely on rainfall (USDA).
Water use
regulations, coupled with the increasing fuel costs to
irrigate, are leading to innovation and dramatic increases
in water efficiency on the 7-10% of corn acres that rely on
irrigation. Sophisticated management and monitoring
practices boost water efficiency and cut water consumption
by up to half. Electronic monitoring of ground moisture
levels and crop evapotranspiration are now commonplace and
even required in some areas. This technology measures how
much water the crop is using and losing, which enables
farmers to know exactly when,where and how much to irrigate.
Crop
rotation and no-till practices allow soils to retain
moisture and nutrients. Drought resistant corn hybrids are
being developed that will reduce the amount of water needed
to achieve optimum yields.
It is in
farmers’ best interests to use water as efficiently as
possible—and they are implementing innovative methods that
are having a dramatic effect on reducing water use without
impacting yields.
Water Use in
Ethanol Plants
Like virtually all
manufacturing and processing facilities, ethanol plants use
water to do what they do. Depending on plant design and
process, water use ranges from 1.5 to 4 gallons for each
gallon of ethanol produced. The overall industry average is
between 3.0 and 3.5 gallons—down from nearly 6 gallons just
a few years ago. Older plants tend to be toward the top of
this range, but many are making significant investments in
key processing equipment to reduce water demand.
Newer plants have
more sophisticated, water-conscious designs that put them at
the lower end of the water demand scale. Additionally, the
water discharged from ethanol plants is heavily regulated,
assuring that water is environmentally neutral when it
leaves the plant.
Water availability
and allocation is a critical factor in siting an ethanol
plant, a process that also involves government water
agencies and municipalities.
In an ethanol
plant, water is primarily related to energy production: the
boiler system that drives the plant and the cooling of
process water and equipment. The U.S. Department of Energy’s
National Renewable Energy Laboratory estimates 70% of the
water demand at an ethanol plant goes to these functions,
with the rest entering the fermentation process.
If distillers
grains are dried, the water is returned to the atmosphere
through evaporation. If the distillers grains are shipped
wet to local livestock operations, the moisture in the
product helps reduce additional water requirements of the
animals.
Because the
quality of water coming into a plant can vary, it’s more
efficient to focus on managing and reusing the wastewater
generated during the ethanol process, which is more
consistent and reliable. This is typically "blow down"
residual water from boilers and cooling towers or from
centrifuges that remove some water from wet distillers
grains before shipment.
Some plants are implementing
creative ways to reduce water usage including use of "gray"
municipal wastewater, return of water to farmers for crop
irrigation, management of mineral levels in water
supplies—even the development of zero-discharge technology
that eliminates waste stream disposal issues altogether. In
many areas, ethanol plants must purchase water rights from
other users in order to achieve a net-zero increase in water
demand.
