Anaerobic digestion of industry waste sought Although anaerobic microbial digestion plays an important role in municipal sewage treatment, the technology really hasn't caught on—in the U.S., at least—for treatment of i n d u s t r i a l wastes. That may be changing, however, as environmental concerns make the anaerobic approach increasingly attractive for industrial applications. One organization working to promote the adoption of anaerobic digestion (among other things) is the Iowa Biotechnology Byproducts Consortium (BBC). BBC consists of faculty members from the University of Iowa and Iowa State University and staff from the Cedar Rapids water treatment system. What brings them together is a common interest in winning valuable materials from the by-products of biotechnology and agribusiness operations. BBC is governed by a triumvirate: Rex Montgomery, professor of biochemistry and associate dean at the University of Iowa's College of Medicine; Richard R. Dague, professor of environmental engineering at Iowa State; and George Milligan, in charge of water pollution control for the city of Cedar Rapids. They note that the U.S. Department of Agriculture has provided more than $2 million for the consortium and its work. Anaerobic treatment of biotechnology by-products is only one part of a BBC program that also encompasses characterization of waste streams, bioseparations, bioremediation, microbial transformations, and livestock and soil amendment applications. However, it was anaerobic treatment that was the subject of a recent two-day symposium, "Anaerobic Methanogenic Processes Applied to Industrial By-Products," organized by BBC and held in Cedar Rapids. A l t h o u g h t h e symposium addressed an Iowa problem, the topic is one of national and even international significance: Overloading municipal water treatment plants is a matter of concern wherever there are biotechnology industries. And the symposium was international in scope, with several speakers and
participants coming from European and Latin American countries. In many instances, the organic components of industrial waste streams are too dilute to be worth recovering. However, they may be present in amounts worth converting to methane, using an appropriate bioconversion process. Solid byproducts from food processing, livestock slaughtering, and livestock feeding operations can also be suitable feeds for bioconversion. The methane, even if not produced in commercial quantities, can provide energy and thus reduce the overall costs of waste treatment. Several symposium speakers pointed out the advantages of anaerobic treatment. These include the ability to treat a great variety of organic wastes, low sludge production (compared with aerobic digestion), low energy requirements, an enclosed system that facilitates odor control, low nutrient requirements, and a high-grade energy by-product. Indeed, anaerobic digestion has been used successfully to stabilize wastewater sludges for more than 60 years, according to Gene F. Parkin, a professor of civil and environmental engineering at the University of Iowa. But, he adds, the process is still considered by some to be unreliable. Part of the problem is that plant engineers and personnel don't understand the process well enough and haven't been trained sufficiently, resulting in unsatisfactory operations. There's more to it than that, however. During most of the preceding 60 years, anaerobic digestion was used largely to stabilize raw domestic
sewage sludge accumulated during primary sedimentation. Lately, Parkin says, the process has been increasingly used on chemically treated sludges, biological sludges produced by aerobic digestion processes, and sludge mixtures containing industrial wastes, each application presenting different problems for system designers. Reduced to essentials, anaerobic digestion of organics takes place in three stages. The first involves hydrolysis, liquefaction, and fermentation, which are needed to convert complex wastes to simpler materials that can pass through bacterial cell walls. In the second stage, hydrogen and acetic acid are formed. Finally, those substances are converted to methane. According to Parkin, five groups of bacteria are thought to be involved in the various reactions. One of the main aims in design of anaerobic digestion plants is to achieve rapid flow-through of liquids but at the same time maximize solids retention time. As the liquid flow rate increases, however, there's an increasing tendency for solids (including the bacteria that are doing the work) to wash out of the reactor. Several symposium presentations dealt with ways of preventing solids washout in continuous-flow systems. The approaches include baffled reactors, anaerobic filter reactors (which immobilize the bacteria on some heavier medium), the upflow anaerobic sludge blanket process (which depends on the development of dense granules that settle rapidly), and hybrids of two or more of these and other approaches.
Batch reactor prolongs solids retention time Biogas recycle Biogas
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Science/Technology Iowa State's Dague and associates have taken a different tack, going to a batch approach. Dague notes their "anaerobic sequencing batch reactor" operates analogously to simple anaerobic contact reactors, except that biomass separation and liquid clarification take place within the reactor, not in an external clarifier. The sequence has four steps: feed, react, settle, and decant. The internal clarification step obviates the need to degasify the effluent, Dague says. Since the partial pressure of the biogas remains constant within the reactor, the tendency for biomass solids to float is minimized. That leads to rapid solids settling and the ability to process large liquid volumes while maintaining long solids retention times. Dague notes that the project was initiated to provide an economically viable solution to the difficult problem of treating swine manure. Adding value to pigs is, after all, one of Iowa's biggest biotechnology-based industries. But decaying swine manure smells awful. "Lawsuits arising from environmental problems associated with confinement swine-feeding facilities are becoming common,"
Dague observes. However, the batch reactor should also be useful for other industrial applications. Other symposium speakers addressed the increasing use of anaerobic processes for industrial wastewater treatment outside the U.S. For example, Peter Weiland, an engineering professor at the Technological Institute of the German Federal Agricultural Research Center in Braunschweig, noted that the number of anaerobic industrial treatment plants in Germany grew from only 12 in 1982 to more than 60 in 1990. Similarly, Adalberto Noyola, a civil engineering professor at the National Autonomous University of Mexico, Mexico City, reported that the number of modern anaerobic digesters in Latin America has risen from essentially zero in 1983 to more than 100 in 1990. Brazil has been the leader in installing anaerobic digesters, Noyola says. Ross E. McKinney, an environmental engineering professor at the University of Kansas, pondered the future of anaerobic treatment in the U.S. Most of the theory and studies on high-rate anaerobic treatment
systems (HRATS) came out of U.S. universities, says McKinney, who is one of the pioneers in the field. But most of the "real-world" HRATS action is in Europe and Latin America. The U.S. has fewer than 10% of the world's full-scale HRATS plants. And U.S. equipment makers are "still not sure it's here to stay." Much of the reluctance of industry to switch to anaerobic methods results from the way the municipalities do business. Typically, municipalities have to deal with separate consulting engineers, equipment suppliers, and building contractors. Industry doesn't want to deal with separate entities, McKinney says; it wants turnkey systems. And it finds the consultants "don't really understand how industry works." But, McKinney concludes, "the vise is starting to squeeze," and industry will be forced to go to anaerobic treatment process to meet ever stricter regulations. Moreover, the field could provide a golden opportunity for chemical and process engineers, "if they'd only learn the microbiology and biochemistry." Ward Worthy
U.S. Postal Service launches stamp set depicting planetary exploration At a ceremony in Pasadena, Calif., earlier this month, the U.S. Postal Service introduced a set of 10 commemorative stamps depicting planetary exploration. The ceremony was held at Jet Propulsion Laboratory—which has played a central role in U.S. planetary exploration efforts—and featured remarks by JPL director Edward C. Stone and postmaster general Anthony M. Frank. The stamps are sold in a $5.80 booklet containing two panes of 10 29cent stamps. Each pane shows the nine planets in the solar system and
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Earth's Moon, all but one planet accompanied by an unmanned spacecraft that has explored it. The planets are depicted in order of increasing distance from the Sun. In the top row (left to right) are the Mariner 10 spacecraft approaching Mercury's orbit, Mariner 2 encircling Venus, Landsat orbiting above Earth, Lunar Orbiter exploring the Moon, and Viking Orbiter speeding toward Mars. In the bottom row (left to right) are Pioneer 11 collecting data from Jupiter, Voyager 2 photographing Saturn and racing on to
encounters with Uranus and Neptune, and Pluto "Not Yet Explored." Stamps depicting space-related topics are among the most popular with the public, and the Postal Service is promoting sales of the new set as a focus of National Stamp Collecting Month in October, under the theme "Journey to a New Frontier—Collect Stamps!" It has enlisted as spokesman Leonard Nimoy, who played Mr. Spock in the original Star Trek science fiction TV series and movies. "Stamp collecting is logical," Nimoy notes.
