WORKSHOP
Finding Solutions for Tough Environmental Problems At the frontiers of research, environmental engineers are using novel tools to obtain knowledge about complex environmental systems. BRUCE E. LOGAN AND BRUCE E. RITTMANN his January, environmental engineers and scientists (see Table 1, which lists workshop attendees) gathered in Monterey, Calif., to participate in an Environmental Engineering Frontiers Workshop sponsored by the National Science Foundation and the Association of Environmental Engineering Professors. Historically, the discipline has been focused on engineered process technologies built around a single medium, such as water or wastewater. The workshop participants agreed that these processes remain a foundation for future progress, but they also identified important research frontiers that emphasize a much broader scope of environmental concerns (see Table 2). A pervasive theme of the workshop was the inherent complexity of environmental systems. The workshop participants noted that although scientific investigation can unravel aspects of key issues related to pollution of air, water, and land, a more comprehensive, integrated view of these systems is needed to provide solutions to difficult environmental problems. Environmental engineers must seek to understand the nature and functioning of large and complex systems in order to protect whole ecosystems, produce new and sustainable technologies, prevent me outbreak. of discuses cicross global scales, and protect the environment from damage resulting from die production of new chemicals. Environmental gineers must take a leading role in directing projects as well as in investigating the different aspects of environmental systems As its central mission, environmental engineering is concerned with the analysis of environmental systems and the design of plans, criteria, and technological systems for the solution of environmental problems. The intellectual challenge for environmental engineers and scientists is the identifica-
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tion of critical environmental problems and the acquisition of scientific knowledge crucial to achieving effective solutions. Perhaps the greatest challenges will be in preventing, and not just removing, pollution and in conserving existing resources. Environmental engineers must do a better job of helping society anticipate adverse environmental impacts arising from the production of new chemicals before they become problems. A serious failure to anticipate impacts occurred when MTBE was added to gasoline to reduce air pollution without carefully considering the potential effects of leaks from tanks on groundwater quality. Although air quality improved in urbcin aresis, the threat of groundwater contamination increased significantly. Chlorofluorocarbons (CFCs) were eliminated in favor of hydrofluorocarbons (HFCs) to reduce ozone destruction in the stratosphere but this was done without sufficient knowledge of the potential environmental impact of refractory trifluoroacetic a-cid thcit Ccin form in the atmosphere and eventually rain down over the Earth The workshop participants advised that, once harmful chemicals are in the environment, environmental engineers must play a key role in determining the ability of natural systems to adapt to the presence of these chemicals. In pursuit of necessary information, engineers have gone to the frontiers of research, where, at the limit of current understanding, there are opportunities to advance knowledge in new and positive directions. New biological and chemical tools can be used for the analysis of complex environmental systems. The workshop attendees recommended that to take maximum advantage of these tools, environmental engineers would have to increase their interactions with a wide range of chemists and biologists. Moreover, they said, to ensure that scientific breakthroughs re0013-936X/98/0932-502A$15.00/0 © 1998 American Chemical Society
suit in practical advances in pollution prevention and treatment, engineers must cooperate more fully with applied and social scientists as well as with policy makers in government and industry. It was concluded that by working together, these groups could bring scientific and technological advances into widespread use for meeting the challenges of environmental sustainability.
A synthesis of issues Workshop participants considered a range of questions to identify and frame the fronUer challenges that environmental engineers will be called on to address. In the global arena of the 21st century, what are the most important environmental problems for which tliere are no known or easy solutions? Are these problems solvable with existing knowledge and technologies? If not, what new tools can be used to solve these problems? What science and technology breakthroughs provide the most promising opportunities to make a quantum leap in society's ability to understand and solve environmental problems? Important characteristics of chemicals that are released to the environment include tiieir volatility, adsorption and partitioning to minerals and organic matter, and their overall persistence. Critical to the issue of persistence is how these chemicals are degraded within a specific environment. • Are these chemicals degraded biotically or abiotically? • Are they subject to intrinsic biodegradability? • Can a variety of microorganisms degrade a chemical, or is its degradation limited to a particular species or redox environment? • Can the exchange of genetic information between microbial species make the ability to degrade these new chemicals more widespread among members of the microbial community? Little is known about die combined effect of these processes, but they are fundamental to the understanding of chemical fate and effects in the environment, and they affect decisions about when engineered solutions must be applied. Environmental problems, such as ozone depletion caused by CFCs and the prospect of global warming associated with release of C0 2 and other greenhouse gases, are global issues diat transcend political boundaries. Many environmental challenges are not limited to industrialized nations. For most of the world, the greatest need is for affordable, practical technologies— sanitation, drinking water supply, and wastewater collection and treatment—that can reduce the spread of infectious diseases. Moreover, world commerce and the intensified circulation of people bring an increased potential for the dissemination of infectious diseases throughout the developing world and into the developed world. Technology resources and knowledge, now mainly possessed in the developed world must be used to address environmental problems wherever they arise
Sustainable environmental resources Demand is increasing for use of limited environmental resources and will increasingly require multiple users of the same resource. The Colorado River,
TABLE 1
Workshop participants Participants of the Environmental Engineering Frontiers Workshop included ten members of the National Academy of Engineering, five members of the Association of Environmnental Engineering Professors, and the director of the Environmental Engineering program at the National Science Foundation. Participant
Affiliation
Edward H. Bryan Kimberly A. Gray Donald R. F. Harlemana'b Susan M. Larson Raymond C. Loehra Bruce E. Logan Richard G. Luthy Perry L. McCarty3 Charles R. O'Melia" James J. Morgan3 Bruce E. Rittmann Paul V. Roberts3 H. Gerard Schwartz3 Philip C. Singer3 R. Rhodes Trussell3 Walter J. Weber Jr.3
National Science Foundation Northwestern University Massachusetts Institute of Technology University of Illinois-Urbana-Champaign The University of Texas-Austin The Pennsylvania State University Carnegie Mellon University Stanford University The Johns Hopkins University California Institute of Technology Northwestern University Stanford University Sverdrup Civil, Inc. University of North Carolina Montgomery Watson, Inc. University of Michigan
a
NAE member; bemeritus.
TABLE 2
Research frontiers The research frontiers identified by the workshop participants were categorized into four general areas: sustainable environmental resources, complex environmental systems, new analytical tools, and engineered processes. Each category of frontier research was further subdivided. Category
Subcategories
Sustainable environment
• Safe, adequate, and sustainable water supply (reuse and conservation) • Terrestrial and coastal resources • Ecosystem stress • Assessment of chronic exposure to trace contaminants • Reduction of toxic materials used in industrial processes and consumer products
Complex systems
• Integration of components of complex, biogeochemical systems • Atmospheric systems • Ecosystem stability and diversity • Microbial ecology
Analytical and molecular tools
• Molecular biological tools • Chemical tools
Process technologies
• • • • •
Reactive separation systems Targeted chemical destruction Engineering subsurface systems Membrane technologies Process technologies for the nonindustrialized world
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source of 90% of San Diego's water supply, has 187 wastewater treatment plants discharging into it. Environmental engineers should concentrate on promoting resource sustainability, particularly of water and soil systems. Special attention should be given to the response of these systems to continued stress, long-term effects of chronic chemical exposure, and conservation of land and water resources. New methods are needed for defining and achieving sustainable systems, as is particularly apparent for water use and reuse. Although the human population has increased exponentially, total freshwater supply has remained constant. Water reuse is inevitable; the challenge for environmental engineers is to make it safe and economical. Overall, anthropogenic alteration has led to progressive declines in freshwater quality as it cycles through the Earth's geosystems. Environmental engineers must address the consequent realities of water quality and water quality demands and use by developing and applying new technologies that can transform any specific water supply to a level of quality required for a particular use. Technologies that eliminate pollution must be favored over those that simply transfer harmful materials from one phase or one environment to another, because all environmental resources are in high demand. To protect resources environmental engineers must partner with scientists from other disciplines to seek effective methods to eliminate toxic materials in industrial processes and consumer products
Terrestrial soil and coastal systems also remain heavily used. This has led to their damage and loss. Complete system protection through isolation is not achievable, and practices involving these systems must be modified to make the use of these environments sustainable. Two-thirds of world water consumption is for agriculture; water conservation and soil preservation to support the world's food supply will be pressing issues in the next century. Surface soils continue to be eroded through agricultural practices and lost to chemical contamination. New remediation technologies for contaminated soils continue to be needed along with methods to make the disposal of sludges and solid and hazardous wastes more sustainable. Prosfress in this arena will require interactions between hydrologists; soil crop and forest scientists; as well as environmental engineers engaged in scientific and applied research. There are other dramatic indications of severe ecosystem stress and a lack of system sustainabilitv The ecosystem disruption that resulted from the recent outbreak of Pfiprteria nUcicida is thoueht to he produced through increaspd Inadine of nutrients into surface waters. Toxic outbreaks, attributed to sevi A-te
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eral different dinoflagellates and other microorganisms, appear to be increasing worldwide. These mcidents are most often occurring in poorly flushed 1
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bays and lagoons subject to heavy runoff. Further evidence of a lack of system sustainability is found m the degradation of human health resulting from chronic exposure to trace contami-
Tools from molecular biology Molecular biology tools are enabling environmental engineers to conduct frontier research at very small scales and at very low target concentrations.
hybridization are viewed with a fluorescence microscope. Physical relationships among different microbial types can be observed.
Oligonucleotide probes. An ollgonucleotide probe is a small piece of DNA that is designed and synthesized so that its sequence of 15-25 nucleotide bases (C, T, G, and A) is exactly and uniquely complementary to a sequence of bases in target DNA or RNA. When the match is perfect, and under appropriate assay conditions, the probe chemically binds to the target DNA or RNA, a phenomenon called hybridization. The bound probe is then detected through a radioactive or fluorescent molecule (its marker) that was attached to it during its synthesis. Oligonucleotide probes provide several different types of information about cells, depending on what type of DNA or RNA is targeted:
Polymerase chain reaction (PCR)) PCR uses a apecial enzyme to make millions of copies of a particular piece of DNA. This amplification process is useful for studying or identifying DNA that is otherwise present in too small an amount. PCR requires a primer, which is an oligonucleotide that tells the PCR enzyme where to start copying.
Target
Information
Ribosomal RNA DNA
The phylogenetic identity of the cell The presence of a gene of interest, or the cell's genetic potential The expression of a gene, or the realization of the genetic potential
Messenger RNA
Fluorescence in situ hybridizatton (FISH). This technique involves using an oligonucleotide probe that is labeled with a fluorescent molecule. Hybridization takes place with cells that remain physically intact. The results of
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Denaturing gradient gel electrophoresis (DGGE). In DGGE, small DNA fragments (usually 200-700 base pairs) are electrophoresed through a gel under gradually increasing denaturing conditions, causing them to partally denature (melt) and reducing their mobility in the gel. Different base pair compositions and sequences have different melting points, making it possible to detect small differences in DNA and and providing a DNA "fingerprint" for a complex microbial community. Reporter genes. A reporter gene is inserted into the DNA of a cell in such a way that the reporter gene is expressed (its enzyme is produced) whenever the genes around it are being expressed. This provides a way to use an easy-to-detect measurement, such as light generation, to determine if the enzymes for hardto-detect reactions are being produced.
nants produced by industrial processes. Chemical releases into air or drinking water arise from leaking underground storage tanks, emissions of chemicals from cleaning agents used in the home, and applications of pesticides in the watershed. Chemicals about which there are health concerns may also be formed by processes used to purify the air or water. When chlorine is used to disinfect drinking water, disinfection byproducts, such as chloroform, can form and may be responsible for carcinogenic, reproductive, developmental, or other adverse public health outcomes. The level of exposure of humans to mese potentially harmful chemicals needs to be quantified so that health professionals can assess exposure impacts. However, the exposure level is often difficult to quantify for a given population. This results from an inability to obtain the number of measurements necessary to reliably assess overall ulation exposure at relevant temporal and spatial scales. Environmental engineers can help in determining levels based on their understanding of contaminant sources as well as their transport transformations and fate in the environment Complex environmental systems This century has produced remarkable advances in understanding components of natural systems at scales ranging from atomic to macroscopic. At the
frontier of research is the need to find ways to integrate this information and assemble it into models that better describe the behavior and dynamics of environmental systems. Given the complexities of natural systems and to assure a global societal benefit, advances must be coupled with more effective methods to communicate integrated information to the general public and to policy makers. As established from the topics of acid rain, urban smog, stratospheric ozone depletion, and climate change, the atmosphere, in particular, is a highly complex system, the dynamics of which are linked to land and water systems. Our understanding of anthropogenic influences on the atmosphere relies on quantitative descriptions of gas- and particlephase contaminant emissions; their optical, physical, and chemical properties; the transformation, transport, and fate of these species within the atmosphere; and exchanges with the land and water. Many ecosystems contain plants and animals of great interest to human society. Stewardship of the planet and its resources requires particular concern about die potential loss of species and tiieir genetic information. A better understanding of the functioning of complex natural systems will necessarily help guide choices of new chemicals and manufacturing processes and help preserve the health of various ecosystems.
Tools from molecular chemistry Microscopy techniques. The structure and composition of atomic-scale surface features and phases can be determined by high-resolution electron microscopy (HREM). Scanning electron microscopes provide details about surface morphology, size and shape analysis, local chemistry, as well as crystallography and texture. Analytical transmission electron microscopic (TEM) techniques provide surface characterization at scales less than a few nanometers. TEM applications include nanodiffraction/convergent-beam electron diffraction to probe the crystal structure and defects of surfaces and energy-dispersive spectrometry and electron energy loss spectrometry to determine local and electronic structure. Some instrumental systems combine these capabilities with the surface analyses provided by X-ray photoelectron and Auger electron spectrometers These systems typically require ultra-high-vacuum (UHV) conditions and model surfaces Atomic force microscoDv (direct contact; tannine] mode; electric field; and lateral shear and magnetic-force techniques) can be used to directly measure the topography and comnncitinn of a surface at atomic scales by monitoring the position of a tip relative to the surface. Synchrotron radiation sources A suite of in situ methods that ran detail atomir structure a ma t t r i ' l i e in am/ matriv / e n r h uc r* rwctsi 11 i c o anri nnn nrwo+'alliria ni irfo-noo
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