biofuels: promise and problems

The October 2007 issue of National Geographic includes an informative article on biofuels. A couple points come to mind. If you compare the fossil fuel energy used to make the fuel with the energy that is released by burning it, corn ethanol is not a very efficient way to go: for each unit of energy required to create the ethanol, you get 1.3 units of energy by burning it. Contrast that with ethanol derived from sugar cane: for each input unit you get 8 output units of energy. (Sugarcane ethanol is widely used in Brazil. For us, the cost would be higher since it would have to be shipped to North America). (Bourne, 2007)

Corn ethanol: 1:1.3
Sugarcane ethanol: 1:8
Biodiesel: 1:2.5 (make from soy or canola)
Cellulose-derived ethanol: 1: (anywhere from 2 to 36)

Another factor to consider is greenhouse gas emissions that result during production and use of various fuels. The article compares several alternative fuels to gasoline:

Corn ethanol: 22% less
Sugarcane ethanol: 56% less
Biodiesel: 68% less
Cellulose-derived ethanol: 91% less (however, this is still in experimental stages)

The downside of biofuels is that they consume either food crops (corn, soy, etc.) or take up the land that could otherwise be used to grow food crops. So, there's a fuel-food nexus that must be carefully managed.

Some researchers are evaluating using the stalks of food crops as a fuel source. The issue here is how to avoid degrading the soil, since the stalks are typically tilled back into the ground providing nutrition for the soil and future crops. How much of the plant material can be removed without harming soil fertility? (Wilhelm, 2004)

Another possible fuel source that is being researched? Algae. If somebody can figure out how to harvest this energy source it has several potential advantages. "Algae not only reduce a plant's global warming gases, but also devour other pollutants. . . . Best of all, algae in the right conditions can double in mass within hours. While each acre of corn produces around 300 gallons of ethanol a year and an acre of soybeans around 60 gallons of diodiesel, each acre of algae theoretically can churn out more than 5,000 gallons of biofuel each year." (Bourne, 2007, p57)

The potential of algae is also exciting from a water reuse point of view. It will grow in wastewater and in the process will also partially clean the water. (Hoffman, J P, 1998)



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Biofuels: Boon or Boondoggle? National Geographic. Bourne, Jr., J K. October, 2007. pp38-59.

Wastewater treatment with suspended and nonsuspended algae. Journal of Phycology [J. Phycol.]. Hoffmann, J P. Vol. 34, no. 5, pp. 757-763. Oct 1998.

Crop and Soil Productivity Response to Corn Residue Removal, A Literature Review. Published in Agron. W. W. Wilhelm, W W, Johnson, J M F, Hatfield, J L, Voorhees, W B and Lindene, D R. J. 96:1-17 (2004).

water footprint

Here's an interesting site. Check it out:

http://www.waterfootprint.org/?page=files/home

"People use lots of water for drinking, cooking and washing, but even more for producing things such as food, paper, cotton clothes, etc. The water footprint of an individual, business or nation is defined as the total volume of freshwater that is used to produce the goods and services consumed by the individual, business or nation."

This website is maintained by the University of Twente in collaboration with the UNESCO-IHE Institute for Water Education, the Netherlands.

can your drinking water be too clean?

We're all familiar with how vaccines work: you get a small dose of a nasty virus or other pathogen, your body works out how to fight it, and then you're pretty much protected against coming down with the illness that the virus causes.

This semester, as part of the Water Resources Program at UNM, I am studying water reuse with Dr. Bruce Thomson. He assigned us an article by his colleague, Floyd J. Frost. Dr. Frost hypothesized that exposure to small doses of some pathogens in drinking water can actually provide a protective immunity against that particular disease.

Cryptosporidium is a persistent water borne protozoan that can cause serious gastrointestinal illness, even death. There have been a sufficient number of outbreaks of cryptosporidiosis in the U.S. in the last 15 years, that the EPA has published new rules under the Safe Drinking Water Act requiring water utilities to specifically implement treatment methods to remove this organism.

In response to this concern, Floyd developed a study to test whether people who are exposed to small doses of Cryptosporidium oocysts on a regular basis might be less susceptible to the gastrointestinal distress caused by a Cryptosporidium infection.

He studied people who got their drinking water from a good quality surface source. He tracked episodes of gastrointestinal illness among the sample populations and correlated those with levels of two antigens believed to be produced by the human body in response to Cryptosporidium. He found that those exposed to subclinical doses of Crypto as evidenced by moderately high levels of the antigens experienced significantly less outbreaks of gastrointestinal distress episodes.

More research is needed to fully understand what is happening. The study suggests that "a moderately strong serological response to a Cryptosporidium antigen group is related to a lower risk of enteric illness." (pp 812-813) The implication is that "[i]f future improvements in water treatment reduce serological responses for users of surface water, then the risk of cryptosporidiosis will likely increase. Thus, reducing low-dose waterborne exposures may increase rather than reduce the risks of diarrheal and gastrointestinal illnesses." (p813)

Obviously, this raises some difficult questions for those responsible for developing policy on water treatment standards. Can your drinking water be too clean?


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Special thanks to Dr. Bruce Thomson for his review and comments on this post. LRK.


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Floyd J. Frost, Melissa Roberts,Twila R. Kunde, Gunther Craun, Kristine Tollestrup, Lucy Harter, and Tim Muller. How Clean Must Our Drinking Water Be: The Importance of Protective Immunity. The Journal of Infectious Diseases. 2005. 191:809-14.