Environmental t News How green is ethanol?
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both [the ES&T and Science] studies is that those [ethanol studies] that have found negative returns are decided outliers from a very large and solid set of alternative studies,” says Nathaniel Greene, a senior policy analyst for the environmental group Natural Resources Defense Council, which provided funding for Hammerschlag’s study. “We need to move on now and start figuring out how we [can] use this technology and advance it to get as much out of it as possible.” Large-scale ethanol production raises other environmental concerns, including water pollution and soil quality problems, but by far the biggest are the air quality issues associated with using ethanol, Greene says. The “low blends” predominantly used today, which contain only 5–10% ethanol and are mixed with regular unleaded gas, have higher evaporative emissions than regular gasoline in warm climates, and this contributes to ozone problems. “The best way to mitigate that is to use ethanol in high blends,” such as E85 (which contains 85% ethanol), Greene says. “So, from our perspective, the question is: How quickly can we make [the] transition to really using ethanol as an alternative fuel as opposed to just a fuel additive?” The U.S. EPA’s newly established Renewable Fuel Standard final rule will help. It requires nearly 3% of gasoline sold this year to be produced from renewable fuels, with a doubling by 2012. And President Bush has promised additional research funding into methods of producing ethanol. —KRIS CHRISTEN jupiTerimages
E
ven as ethanol production is sons why the debate has been so ramping up in the U.S., enermurky,” Hammerschlag says. Widegy policy analysts are at odds ly varying assumptions were made over whether fueling cars with the about farming practices. He found biologically derived fuel is better a particularly glaring difference in for the environment than gasoline. one of the cellulosic studies: The Now, research published in this isresearchers obtained a higher fossue of ES&T (pp 1744–1750) attempts to put this debate to rest. Assessing the benefits of ethanol over gasoline is complicated by the fact that this biofuel is produced in a series of steps that themselves require energy. A wide range of studies have come to different conclusions about whether more energy is saved or wasted in the complete Sawdust is one of the energy materials scientists are process, which starts with looking at for producing cellulosic ethanol. the cultivation of the various crops that can be used to produce the fuel. sil-fuel investment than anyone By first normalizing and then else because they assumed that comparing the data used in 10 of coal or natural gas would be used the most prominent studies, Roel to power the facility converting the Hammerschlag, president of the cellulose material to a liquid fuel. Institute for Lifecycle EnvironmenIn practice, though, one of the bigtal Assessment and author of the gest reasons cellulosic ethanol has ES&T paper, draws a much clearer a much better energy balance than picture: Producing and burning corn ethanol is that the whole plant ethanol are better for the environcan be used, Hammerschlag notes. ment than producing and burning The cellulose or fermentable comgasoline. However, not all ethanol ponent is separated from the ligis created equal. nin or nonfermentable component, Fuel produced from corn via which itself has a high energy valthe more traditional approach ue. Consequently, the lignin can be may yield only marginal renewburned to power the facility, so no able-energy returns. But the ethaexternal power source is needed. nol obtained from cellulose with Hammerschlag’s results are sima developing technology that uses ilar to those recently published in fibrous materials—such as wood Science (2006, 311, 506–508). Howchips, switchgrass, or farm resiever, the ES&T paper goes further dues—as opposed to corn kernels in showing the advantages of celhas a clear advantage over gasoline. lulosic ethanol over corn ethanol, “Unfortunately, there’s no single says Lee Lynd, a biochemical engiitem that you can pin the differneer at Dartmouth College. ences on, which is one of the rea“What you see very clearly from
© 2006 American Chemical Society
SAMER ADHAM, MWH
At a time when freshwater is growing ever more scarce throughout the world, the prospect of creating drinkable water by removing the salts from seawater has increasing appeal. The main disadvantage of using reverse osmosis (RO) membranes for desalinating seawater has been its cost, which is 2–3 times more than conventional treatment mainly because of high membrane fouling rates. But research published in this issue of ES&T (pp 2037–2044) indicates that a new approach to pretreating the seawater by using microfiltration (MF) membranes could significantly lower the overall treatment costs. “It’s counterintuitive, because membrane pretreatment is much more expensive than conventional pretreatment,” says Manish Kumar, who is a senior engineer with MWH, an environmental engi-
The polymeric fibers inside these microfilter membranes remove particles down to 0.1 µm in diameter from the water. By doing so, they ensure that such particles won’t foul the reverse osmosis membranes that remove salt from seawater.
neering firm, and the paper’s lead author. But better pretreatment leads to less fouling and therefore more efficient operation of the RO membrane, which is the most expensive part of the process because that’s where most of the energy costs lie, Kumar says. Fouling is caused by a number of things, including biological growth on the membrane, suspended solids in the seawater, and the precipitation of salts, explains Kevin Price, manager of the U.S. Bureau of Reclamation’s water treatment, engineering, and research group. “They add a layer of resistance to the membrane, making it harder to push the water through, which means higher energy and cleaning costs, and in some cases the fouling can even be irreversible.” Consequently, fouling prevention is key to making RO technology more suitable for seawater. In one of the first systematic studies of how seawater RO membranes become fouled, Kumar and his colleagues performed benchscale experiments with seawater from San Diego Bay. They found that particulate matter >1 µm in diameter—representative of what gets past many conventional pretreatment systems—caused most of the RO membrane fouling. Conventional pretreatment usually involves coagulation, followed by flocculation and sedimentation, and then filtration with media filters, such as sand. San Diego officials plan to build a seawater RO plant to increase the reliability of the region’s water supply, according to Cesar Lopez, a senior water resource specialist with the San Diego County Water Authority. Kumar and his colleagues observed a significant reduction in fouling rates when they prefiltered
News Briefs Sick-stream diagnosis
The U.S. EPA has developed a new web-based tool to ascertain why a stream is contaminated. Diagnosing sick streams has been troublesome because scientists had to untangle several complex parameters that interact to impair stream health. The new system, the Causal Analysis/Diagnosis Decision Information System (CADDIS), guides users through a process to pinpoint the cause of poor health. Users first complete worksheets to eliminate obvious problems and then take a strength-of-evidence approach to make a defensible case for attacking a stressor. The final diagnosis is the first step before drafting a Total Maximum Daily Load report of any pollutant flowing into the water body. To access the conceptual models, sample worksheets, case studies, and information on CADDIS, visit http://cfpub.epa.gov/caddis.
Cadmium linked to cancer
Environmental exposure to cadmium, a byproduct of zinc smelting and a common industrial pollutant, increases the risk of cancer, according to a study published in The Lancet Oncology (2006, 7 [2], 119–126). For the study, the researchers enrolled 521 people who lived close to 1 of 3 zinc smelters in northeastern Belgium and compared them with 473 controls. The risk for lung cancer was 3 times higher in people who lived close to zinc smelters compared with those who did not. The results also showed that a doubling of urinary cadmium was associated with a 30% increased risk of all cancers and a 70% increased risk of lung cancer. The International Agency on Cancer Research has recently classified cadmium as a carcinogen.
March 15, 2006 / Environmental Science & Technology n 1723
paul D. thacker
Pretreatment lowers desalination costs
Environmentalt News the feed water by using MF membranes (0.1-µm pore size) and ultrafiltration (UF) membranes, which are an order of magnitude smaller. They didn’t see much difference between the two membranes in the final flow through the RO system, an indication that the higher cost of using UF isn’t worth the small benefit. These findings “confirm assumptions that a lot of people have been making and put some
quantifiable numbers on the type of advantage that’s expected,” says Craig Bartels, vice president of research and development for Hydranautics, a leading RO membrane manufacturer. A number of seawater systems currently run well with conventional pretreatment, he notes. But for sites that don’t, “membrane pretreatment will help resolve much of the fouling problem and thereby extend the life of the RO membranes.”
To date, “very few seawater plants are being built with MF/UF pretreatment, and I believe it’s because people still feel it’s too expensive,” Price notes. He adds that as MF and UF are becoming more common in drinking-water treatment, however, costs are coming down, and in the future, “I think we’re going to see membranes pretreating, followed by membranes doing desalination, as a cost-effective way to go.” —KRIS CHRISTEN
OMB proposes to harmonize risk assessments
latory protections themselves,” he says. Experts also note that the bulletin defines “an adverse effect” as implying “some functional impairment or pathologic lesion that affects the performance of the whole organism or reduces an organism’s ability to withstand or respond to additional environmental challenges.” This significantly affects a determination crucial in risk analysis, says Harvard Center for Risk Analysis director James Hammitt. “Reference doses and other limits are often set on the ‘most conservative’ [i.e., smallest] dose that shows an ‘adverse effect’ in laboratory animals,” he points out. “So defining what measurable effects count as adverse can be very important.” But Andrew Maier, the assistant director for the nonprofit group Toxicology Excellence for Risk Assessment, says that this is an ongoing problem for all risk assessments. “We are getting better at understanding the biology, but that doesn’t make it easier to understand the risk. Often, it is not as simple as, ‘Yes, it does cause an adverse effect’ or ‘No, it doesn’t,’” he says. Maier notes that most of the bulletin is consistent with evolving best practices in risk assessment, which present risk numbers along with upper and lower bounds. He adds that such an assessment is “intellectually honest” but that what’s missing is guidance on how risk managers should use the range or interpret the number. —REBECCA RENNER
On January 9, the White House Office of Management and Budget (OMB) released a draft bulletin outlining, for the first time, proposals on how federal regulatory agencies should assess the likelihood and severity of risks before they issue rules, policies, or recommendations. The draft proposals would apply to many controversial U.S. EPA risk assessments, such as the reference dose for the rocket-fuel contaminant perchlorate and national air quality standards. The new guidelines would also encompass EPA’s Integrated Risk Information System data and the U.S. Food and Drug Administration’s tolerances for food contaminants. The bulletin’s proposals specify that independent analysts must be able to reproduce government assessments with the same data and models. The changes would also place more emphasis on scientific uncertainty and genetic variability and intensify the focus on “middle” estimates of risk—the most likely scenario for most people— rather than a worst-case scenario for small numbers of people. For low-dose-chemical risks, the bulletin asks federal agencies to make a stronger case that an actual adverse effect is observed and not just a subtle marker of exposure. The bulletin focuses on the technical aspects of risk assessment, rather than risk management or risk
communication. OMB plans to finalize the guidelines later this year after a National Academy of Sciences review and public comment period, which ends on June 15. The proposals follow new guidelines for peer review, data quality, and cost–benefit analyses of regulations, which have been put forth since well-known risk assessment expert John Graham became the administrator of OMB’s Office of Information and Regulatory Affairs 5 years ago (Environ. Sci. Technol. 2003, 37, 365A–368A). Public-health interest groups and advocates of government efficiency call this draft bulletin “significant”. Former OMB official Jim Tozzi, who is now president of the conservative policy analysis group Center for Regulatory Effectiveness, says that the bulletin’s recommendation will make it harder for agencies to make risks sound scarier than they really are. “Agencies will have to compare the risk they assess to a risk that is familiar to most people,” he says. “[That] reduces an agency’s flexibility to pick and choose to suit their agenda.” But regulatory analyst Robert Shull with the liberal group OMB Watch calls the bulletin troubling. “It is also the latest element in a sequence of policy changes designed to undermine protective policies by shifting attention away from polluters and onto the regu-
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