What is ethanol and how is it used?
Ethanol is an alcohol that is produced through the fermentation of sugars in plants such as the one proposed in Bridgewater Township. Corn is most commonly used as the source of these sugars, although other plants may be used depending on the fermentation process that is used. Ethanol is combustible, doing so via the reaction C2H5OH + 3 O2 --> 2 CO2 +3 H2O. In this reaction ethanol (C2H5OH) gives off energy, carbon dioxide, and water. The energy given off by this reaction can be harnessed, making it a suitable fuel. Currently, ethanol is used as a gasoline additive in fuels such as E85 (85% ethanol, 15% gasolinel) and E10 (90% gasoline, 10% ethanol). Fuels that include ethanol produce fewer harmful emissions when burned than pure gasoline, making ethanol a popular gasoline additive in areas concerned with air pollution. Ethanol alone can also be used as a fuel, although it produces 30% less energy than the same volume of gasoline.
What does ethanol production have to do with water?
Ethanol plants require large amounts of water for the production of ethanol. Most of the water consumed by ethanol plants is used for cooling machinery. In some older plants, a process know as "wet-milling" is employed, in which grains are soaked in water. This process is becoming less common because most modern plants use a more-efficient new method known as "dry-milling".
How much water do ethanol plants consume? How much would the Bridgewater plant consume?
In general, the production of ethanol consumes roughly four gallons of water for every one gallon of ethanol produced, although the figure ranges from 3.5 to 6 in Minnesota ethanol plants. This figure varies from plant to plant depending on the processes that each plant uses to produce the fuel. In general, newer plants have been growing more efficient with their water use.
The company proposing the plant in Bridgewater Township, Advanced BioEnergy, stated in a June 25, 2006 news release that the plant would produce 100 million gallons of ethanol per year. If this is the case, the plant would accordingly consume around 400 million gallons of water per year, or an average of 761 gallons of water per minute.
Are there any other ways in which ethanol production might consume water?
Possibly. If an ethanol plant were built in Bridgewater township, corn production in the surrounding area would probably increase since it is more efficient to produce ethanol from corn that is locally grown than to ship it from far-off places. This could lead to an increase in irrigation, which would increase consumption of water in the area. Additionally, side products of ethanol production known as "wet-cake" and dried distillers grains with solubles (DDGS) are often used as animal feed. Feedlots sometimes become more common in areas near ethanol plants because they create a cheap and plentiful supply of feed. If feedlots were developed near the Bridgewater plant, their water use would increase the overall water consumption in the area. Feedlots also have major implications for groundwater quality because of all the animal waste they produce. This represents another potential problem for the water supply in Bridgewater Township.
Where would this water come from?
The water used by the plant would very likely be pumped from the major underground aquifer in the area, the Jordan Aquifer. The Jordan sandstone, one of the bedrock units in the area, contains large amounts of water in the pore spaces between the individual sand gains that compose the unit. Sometimes included in the Jordan aquifer is the water contained in the Prairie du Chien formation, a unit composed primarily of dolostone, a rock similar to limestone but with higher amounts of magnesium and less calcium. In some areas the Prairie du Chien unit acts as a confining layer because because dolostone is fairly impermeable when it is not fractured. In other places, however, the unit is highly fractured and contains significant amounts of water and is lumped with the Jordan and called the Prairie du Chien-Jordan aquifer. The water located in the Prairie du Chien where it is considered an aquifer is contained in fractures and cavities within the unit.
Could the pumping of groundwater from the Jordan Aquifer be harmful to surface water in the area?
It is certainly possible. In most areas, including south-eastern Minnesota, surface waters are directly interacting with groundwater. When this is the case, surface water (in the form of streams, ponds, rivers, and lakes etc.) tends to form where the water table intersects low points in the land. When this happens, groundwater flows into surface water. Excessive pumping can cause the water table to lower as the amount of water leaving the aquifer (the discharge) exceeds the amount of water entering the aquifer (the recharge). This is especially true in the area directly surrounding the pumps, which create a “cone of depression.” When the water table is lowered it may decrease to the point that it no longer intersects low points in the land. When this occurs, surface water often flows into the groundwater, instead of the other way around.
Obviously, in the case of the proposed plant, an important question is to what extent pumping will lower the water table. If pumping lowers the water table too much, surface waters in the area will likely be affected.
Will the plant produce wastewater? If so, what will be done with it?
The plant will produce some waste water. How much exactly is unclear. It might be possible for the plant to discharge its used water into holding areas, where it would have the chance to cool and percolate back into the Jordan Aquifer, assuming those areas are located within the recharge zone of the aquifer. Another less likely option would be for the plant to discharge wastewater directly into surface waters such as the Cannon River or Wolf Creek; however, this would likely have harmful consequences because the discharge would affect both the temperature and volume of these waters. In any surface water, a change in temperature will alter the water's oxygen-holding capacity (which decreases with increasing water temperature) and therefore the ecosystem supported by the water body. Although some distance from the proposed plant, temperature pollution is a particularly major concern for Rice Creek because a change in water temperature could disrupt the steam's trout population. For whatever means of disposal is used, any chemical contaminants the water had gained would have to be removed by a treatment facility first.
Sources
Water Use by Ethanol Plants: Potential Challenges (Institute for Agriculture and Trade Policy, October 2006)
Advanced Bioenergy press release for Northfield, MN