ES&T
OUTLOOK Water research needs and trends The emphasis is on improving and refining existing technologies, rather than developing new ones Most, if not all, of the fundamental technologies of water and wastewater treatment have been known for several decades; some have been in use since before 1900. In recent years, fundamental research in the field has not developed new technologies, nor does it appear headed in that direction. Current research seems to be leading toward materially improved knowledge and use of existing technologies. For example, filtration, disinfection, and anaerobic digestion have been known and used for a long time. But fundamental research is producing a new understanding of the biological, chemical, and physical principles underlying these processes and more sophisticated ways of applying these principles. Scientists discussed research needs at a recent conference on water and wastewater systems. Walter Weber, Jr., of the University of Michigan, suggested that "Few if
Weber: "new understanding of principles" 0013-936X/83/0916-0069A$01.50/0
any truly new water treatment technologies have been developed over the past 20 years. Rather, there have been many adaptations, modifications, and refinements of existing techniques. Changes in the field relate to a better understanding of process fundamentals—this through an active program of basic and exploratory research." Weber listed several examples. "Filtration is almost as old as the water supply field itself, but we have learned more in the past two decades than in the preceding several hundred about mechanisms, pretreatment, and advantages of direct filtration." Weber also pointed out that "each of the variety of disinfectants we use today was available in 1962, but we now know more about the relative effectiveness of each as both bactericide and viricide." He noted that activated carbon was used for taste and odor removal before the turn of the century, "but only in the last 20 years has there evolved a base of technology sufficient to carry this process toward optimum and routine use for the removal of a broad spectrum of hazardous organic compounds." (The large-scale use of activated carbon for water treatment, especially in drinking water, did not get under way to the extent originally expected. EPA regulations governing the use of activated carbon to remove synthetic organic compounds, for example, have not materialized to date.) Weber refutes the claim that fundamental research has produced no new knowledge over the past 20 years. "Research has enhanced and refined our level of sophistication regarding process mechanisms and dynamics and has provided insights which foster more imaginative and creative engi-
© 1983 American Chemical Society
neering in the development of advanced treatment systems. Were it not for fundamental research, environmental engineering would not have evolved to the necessarily more sophisticated practice it is today." 100th anniversary The notion that basic research in water and wastewater treatment is a matter of refinement and more sophisticated approaches was also supported by Perry McCarty of Stanford University. He pointed out that 1981 marked the 100th anniversary of the first recorded application of the anaerobic process of wastewater treatment and that much knowledge was gathered between 1775 and 1900. In 1775, Alessandro Volta showed that "combustible air" was formed in sediments in natural waters; by 1900, scientists had defined routes of methane formation.
McCarty: "more sophisticated approaches" Environ. Sci. Technol., Vol. 17, No. 2, 1983
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A main theme of the Conference on Fundamental Research Needs for Water and Wastewater Systems was that water and wastewater research essentially is an effort to imbue known technology with new ideas and practices. Sponsored by the Association of Environmental Engineering Professors, with support from the National Science Foundation (NSF) and cooperation from EPA, the conference took place in Arlington, Va., in December; a previous workshop had been held in 1977. At present, about 70% of U.S. wastewater facilities use anaerobic biological stabilization and digestion, James Gossett of Cornell University (Ithaca, N.Y.) told the conference. But anaerobic digestion has, over the years, developed a reputation for being susceptible to upset and, thus, unreliable. Gossett explained that while failures may have occurred as a result of introduction of inhibitory materials, such as heavy metals or toxic organics, more often, design and operation errors have been the culprits. He called for fundamental research to enhance the understanding of ecological relationships among anaerobic microbes, especially thermophilic ones important for the generation of methane. And Stanford's McCarty said that anaerobic system performance would be much improved with more knowledge of nutritional needs and enzyme biochemistry, process kinetics, reactor design, and amenable substrates. Gossett observed that "the physical appearance of anaerobic sludge digestors . . . has changed little in the last 40 years." He added that "novel process schemes and configurations need further examination and development," but saw "promise in the many varieties of the anaerobic filter process which are now being proposed" (ES&T, Vol. 16, No. 7, 1982, p. 382A). Still, new things are being learned about how anaerobic digestors could work better. McCarty gave several examples. For instance, trace amounts of certain metals, such as iron, cobalt, and nickel, are now known to be necessary to activate methanogenic microbe enzymes. This knowledge, together with new reactor designs developed over the past few years, has allowed anaerobic treatment of industrial wastes with reactor COD loading rates as high as 10-50 kg/ m3· d. Also, anaerobic treatment can now degrade aromatic compounds such as phenol, catechol, and benzoic acid, and can mineralize certain hazardous halogenated aliphatics (for 70A
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example, chloroform and trichloroethylene) under proper conditions. Under aerobic conditions, these halogenated compounds are considered to be biorefractory. "Diverse viewpoints are imperative" The view that fundamental research in water and wastewater treatment should lead to a better understanding of existing technology, and thus to improvements in its application, was also expressed by C. P. Leslie Grady, Jr., of Clemson University (South Carolina). However, he added that the objective of such research is to create "new technology which will either solve existing problems more effectively, or will provide the means for solving new problems which are as yet unforeseen." As an example of improved understanding of existing technology, Grady cited better ways of controlling microbial interactions associated with sludge bulking, as a result of enhanced knowledge of these interactions. Deeper insights into the kinetics of nitrification and hydrodynamics of fluidization led to the "new technology" of biological, fluidized-bed reactors, he observed, noting that "the payoff from fundamental research is often unforeseen." Grady emphasized the importance of investigator-generated (unsolicited) research. "While a degree of direction within research programs is necessary for timely progress, the breadth of vision generated by diverse viewpoints is imperative for the success of a fundamental research program," he said. To illustrate his views on new technology, Grady cited two areas that he feels are especially worthy of intensive investigation—exploitation of "unconventional" organisms and natural genetic engineering. The first approach could consist of the use of algae, cyanobacteria, photosynthetic bacteria, fungi, and certain other organisms to transform trace amounts of chemicals into forms more amenable to attack by "conventional" microbes. Some unconventional microorganisms can bioaccumulate hydrophobic compounds, Grady noted. Genetic engineering applies the principle that the outcome of the natural evolutionary process can be accelerated by sharply increasing opportunities for DNA exchange in a mixed culture placed under selective stress. Unlike the microbe acclimation procedure normally practiced by wastewater treatment engineers, this culture is continually seeded with a variety of organisms known to carry
certain DNA elements (viruses, plasmids, transposons, insertion sequences), thereby maximizing the potential for desired DNA exchange sequences. Grady said that this technique was used to develop organisms capable of degrading the chlorinated phenoxy herbicide 2,4,5-T, for example. But certain questions still need to be answered, he added. Could this method be effective over a wide range of organic contaminants? Is it really more advantageous than conventional acclimation and enrichment techniques? How stable are any chemical breakdown pathways that may evolve? Grady observed that answers must come from fundamental research, but if they indicate advantages and efficiency of natural genetic engineering, "there may be great potential for the development of specialized cultures for both industrial wastewater treatment and cleanup of toxic spills." Pollutant fate The "fate" of a pollutant is its position in time and space, Gerald Orlob of the University of California (Davis) reminded the conference. Research concerning pollutant fate addresses four principal areas: • transport processes, • reaction kinetics, • state transformations, and • hydrosphere / atmosphere / biosphere reactions. Orlob counsels that a water body receiving pollutants can never be regarded as a "continuous stirred-tank reactor" or as a "steady-state" system, regardless of the engineering convenience of these two assumptions. In the real world, it is neither of these. Orlob advocates a better understanding of hydromechanical properties, such as nonuniform advective flow; lateral, longitudinal, internal, and wind-induced mixing; flow in densely stratified water bodies; and propagation of hydraulic transients associated with such large pollutant emissions as accidental spillages. Can any generalization be made about the values of reaction rate coefficients? Orlob cited that problem as one needing further research under the heading of reaction kinetics. Also, what happens when a pollutant's state changes? For example, how might metals such as cadmium, copper, iron, manganese, or mercury, in ionic form, either remain that way, or be changed through adsorption on sediment, complexation in various forms, or ingestion and metabolism by aquatic organisms? What oxidation-reduc-
ability to describe the physical behavior of subsurface phenomena quantitatively, Pinder said. He explained that "by borrowing some of the established theoretical tools of continuum mechanics, and developing several new ones, experts found themselves capable of formulating equations governing some very complicated porous-flow problems." Pinder added that not only could the problems be expressed in mathematical formulas, "but, thanks to computers, the resulting equations could be solved numerically for rather general physical situations."
DiGiano, Bryan, Clesceri (/. to r. ): organized the conference
tion, pH, or anoxic conditions could solubilize or otherwise mobilize metals from sediments, or, on the other hand, precipitate or otherwise immobilize them? How, and in what forms does aquatic vegetation take up, metabolize, and excrete toxicants? These are examples of many questions to which fundamental research may help to find answers, Orlob suggested. However, he proposed that in the absence of adequate direct support for fundamental research, perhaps some of this effort might be attached to programs otherwise oriented toward application and operation. Groundwater hydrology With increasing dependence upon groundwater for public and private industrial water supply, the need for fundamental research in subsurface water phenomena has grown. Problems are encountered in effective field sampling procedures, and because of a lack of understanding of the fundamental porous media physics involved. Proper sampling is very important, given the high toxicity of certain groundwater contaminants in parts per billion, or even in parts per trillion, George Pinder of Princeton University observed. Addressing field sampling, Pinder explained that "one must unravel the microhydrology of an area. Local variations in stratigraphy, reservoir properties, and fluid potential gradients can profoundly affect the direction and rate of movement of a contaminant plume." Pinder called for "technology to detect contaminants in the field, measure groundwater velocities, and determine reservoir properties." A less recognized, yet equally im-
portant problem is that there is no established protocol for investigating reservoir lithology and sampling groundwater formation fluids. "Most field programs," Pinder said, "are designed and executed only through a combination of experience, ingenuity, and insight" on the part of those involved. He added that a determination of how much data are needed and an optimal strategy for their collection require the scientific and engineering community's attention for several reasons. First is the need to "reconstruct and forecast" contaminant movement. This understanding is necessary for fixing liability and for designing remedial measures for containment and rehabilitation of groundwater reservoirs, Pinder pointed out. More insight is needed concerning the transport of volatile organics and of water-miscible and -immiscible compounds in porous and fractured media. We also need to know more about the chemical behavior of water and contaminants at the pore level and about associated reaction kinetics. Finally, Pinder observed that no efficient, generally applicable approaches for modeling and simulating groundwater phenomena exist. Moreover, "there appears to be no mathematical apparatus [equations] available to provide the theoretical underpinnings for such a methodology." Pinder expressed concern about the identification of "uncertain parameters" (the groundwater medium being inaccessible to human eyes), but he believes that this latter problem can be attacked "with suitable field techniques." Despite these concerns, there has been "a virtual revolution" in the
NSF support At the time of the first water and wastewater research needs conference in 1977, NSF was funding 18 basic research projects and 36 applied research projects oriented toward problem solving. During fiscal year 1982, ended Sept. 30, NSF made about 60 new and continuing awards to projects dealing with groundwater, erosion and sediment transport, hydrology, water and wastewater treatment, fate of pollutants, and several related fields, Edward Bryan of that agency explained. Along with Francis DiGiano of the University of North Carolina (Chapel Hill) and Nicholas Clesceri of Rensselaer Polytechnic Institute (Troy, N.Y.), Bryan helped to organize the December research needs conference. "It seems apparent that NSF support of research on a strictly numerical [number of projects] basis has held steady over the past five years," Bryan estimated. But he said "the emphasis has clearly shifted from a preponderance of problem-focused projects in 1977 to support of research that is more basic in its approach to environmental engineering." Bryan added that NSF's Program in Water Resources and Environmental Engineering was divided into two new programs: environmental and water quality engineering, and hydraulics, hydrology, and water resources engineering. The former program covers water supply, water/ wastewater treatment, and pollutant fate, while the latter is concerned with groundwater, erosion and sediment transport, and coastal and ocean engineering. "The objective," Bryan said, "is to obtain a better understanding of the natural phenomena and fundamental principles that underlie the empirical practice and procedures used in environmental and water resources engineering." —Julian Josephson Environ. Sci. Technol., Vol. 17, No. 2, 1983
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