Seeking Least-CostApproaches BY JULIAN JOSEPHSON erhaps fewer hazardous waste sites and aquifers would need to be remediated today if industrial managers had heeded these words of the late professor Don Bloodgood during the mid-1940s: “We need to minimize, recycle, and reuse waste.” Bloodgood said that when he organized and chaired the first Purdue University Industrial Waste Conference in 1944. But from the heady days after 1945 until the early 1970% little thought was given to environmentally friendly ways to manage industrial waste; most was simply disposed to land, and in many cases it began to contaminate eroundwater and soils. From the 1940s to the ” early 198Os, conferences such as the Purdue University Industrial Waste Conference stressed improved methods of landfilling and, later, incineration. Partly because of legislation passed in the 1970s
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thrust of the conference has become the development of innovative, least-cost alternatives for remediating hazardous waste sites and contaminated aquifers. Alternatives include in situ remediation by biological and chemical methods, waste minimization, and pollution prevention. The 48th Purdue Conference, held in West Lafayette, IN, in May, emphasized these alternatives. Researchers from industry, government, and academia hope that in situ treatment of contaminated sediment, soils, and groundwater will prove to be a leastcost technology. They believe such treatment would minimize environmental disturbance and have cost advantages over incineration, pump-and-treat methods, and landfilling under strict federal and state laws and regulations. Actually, waste minimization and pollution prevention could be the most cost-effective approach because it would reduce the need for waste treatment and site remediation by any technique. E S b T Associate Editor Jerald Schnoor, keynote speaker at the conference, speculated that incineration could become moribund as an approach to dealing with hazardous wastes. “Maybe it’s not the right decision because of a lack of public acceptance,” he said. “For instance, it is difficult to site even new medical and infectious waste incinerators [although incineration of such wastes] would seem to make a lot of sense.” On the other hand, Ron Wukasch of Purdue University, a successor of Bloodgood’s in the conference chairmanship, told E S b T , “Incineration will not be-
will continue to be the focus of small specialty workshops.
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Bioremediating groundwater Ralph Moon of Geraghty & Miller (G&M, Tampa, FL) described a , biotreatment program for remediating contaminated groundwater that has been under way since 1991. Groundwater at an industrial site was contami-
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toluene, ethyl ether, benzene, ethylbenzene, xylenes, and methyl tert -butyl ether. Reduced sulfur compounds such as hydrogen sulfide, dimethyl sulfide, and mercaptans also were present. Moreover, the freshwater aquifer to be treated lay atop a saltwater aquifer, so the system had to be designed to prevent the saltwater from being pulled up into the freshwater layer. G&M set up an in situ bioremediation system that uses aerobic bacteria to degrade the organic compounds and oxidize the H,S. The first step was to introduce ambient air into the subsurface by soil vacuum extraction. The next was to install 13 recovery wells, 10 injection wells, and an aeration-bioenhancement unit (ABU). The ABU promotes bacterial growth, raises the dissolved oxygen concentration, and adds nutrients to contaminated groundwater drawn up through the recovery wells. The microbe-laden groundwater is reinjected through the injection wells so the bacteria may “feed” on the contaminants. Moon says that after one year of operation, groundwater monitoring showed that contaminant levels dropped to less than 10% of their original concentrations. The area of the plume of contamination decreased by more than two-thirds. Subsequent monitoring showed 9599% removal of contaminants by aeration and biological treatment. In addition, no intrusion by the underlying saltwater was detected. Decomposing PCBs Since the early 1980s, research has been under way to develop ways of decomposing polychlorinated biphenyls (PCBs) in situ. Back then, scientists at General Electric (GE) were examining biological alternatives to expensive dredging and incineration of PCBcontaminated sediments in the upper Hudson River (ESbT, Feb. 1984, p. 44 A). Bacteria examined as possible PCB degraders included Corynebacterium and Alcaligenes spp. This research continues at GE and elsewhere. Ronald Unterman of the bioremediation firm of Envirogen (Lawrenceville, NJ) estimates that more than 1.25 billion pounds of PCB“much still in use”-eventually will have to be broken down. Much of these PCBs have been or are being used in electric transformers, although they may no longer be used after 1997. He told a plenary session of the Purdue Conference that a ma2300
jor financial goal of R&D is to be able to biodegrade PCBs microbially in situ at a cost of $100-$150 per ton of soil or sediment treated, Unterman said that as of mid1993, no biodegradation system was available commercially to decompose PCBs. He expects, however, that by late 1994 to mid-1995, such systems will be available. The first systems probably would use aerobic species of microbes that will consume other aromatics and cometabolize PCBs. Different classes of PCBdegrading microorganisms are able to attack the various PCB molecules in different ways, thereby allowing a greater extent and breadth of PCB degradation. Unterman sees biodegradation working in sediments and soils containing 10-1000 p p m PCBs; for more contaminated sediments and soils or for the destruction of the highly chlorinated Aroclor 1260 (60% Cl), incineration or other alternative technologies still would be necessary. In the future, anaerobic PCB degradation may become feasible. Unterman says that naturally occurring anaerobes have been found that can alter PCB molecules. By breaking chlorine-carbon bonds, they would reduce chlorinated PCBs to lower chlorinated congeners and eventually to monochlorobiphenyl. Unterman speculated that even the in situ reduction of Aroclor 1260 with specially developed anaerobes may become possible. Currently, extensive research is under way to develop a two-stage biotreatment system whereby anaerobic degradation removes one or more of the chlorine atoms from the PCB molecule. This would be followed by aerobic attack on the biphenyl nucleus. Envirogen has begun the first of several field trials at a PCB-contaminated site in Pennsylvania. The company also is conducting other research and development work at its laboratories in New Jersey. Other nonincineration technologies being examined for destroying PCBs include nucleophilic substitution reactions, ultraviolet (UV) radiation, ozonation, oxidation with supercritical water, and pyrolysis, Data on emerging technologies for the destruction of PCBs, other chlorinated chemicals, and other hazardous wastes are available at EPA’s Alternative Treatment Technology Information Center (ATTIC). ATTIC is accessible by a computer database network where titles and abstracts can be searched online.
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Chemical approaches Volatile organic c o m p o u n d s (VOCs) can be removed from contaminated soils by in situ vapor stripping. Hazardous waste researchers at the conference discussed ways to develop in situ technologies for removing nonvolatile organic compounds (NVOCs) by chemical means such as oxidation. One approach being investigated at Michigan State University (East Lansing, MI) under the leadership of Susan Masten is the decomposition of NVOCs with ozone, a powerful oxidant. Her team wants to answer the questions: What may be the inhibiting influence of adsorbed VOCs, such as toluene, and naturally occurring organics (e.g., humic acids) in the soil? What is the role of pH? Would the oxidation of NVOCs be more efficient in moist soils because of the formation of hydroxyl radicals (OH) through the reaction of ozone with water? For the treatment of contaminated groundwater, would ozone work better alone or with UV, with hydrogen peroxide, or with both? One “recalcitrant” class of NVOC contaminants is polycyclic aromatic hydrocarbons (PAHs). According to Masten and her team, some members of this class, such as phenanthrene, are suspected carcinogens. One of the team’s objectives is to determine the potential of ozone for in situ treatment and for treating excavated soils. Currently, using glass-soil columns, team members are testing the ozonation of PAHs in soils with 0-20% water saturation (the water is used to determine the role of OH in PAH oxidation). Their 50-g test samples are contaminated with 500 ppm of chrysene, phenanthrene, and pyrene. Gaseous ozone concentration is monitored in column influent and effluent using a flow-through cell and a UV-VIS spectrophotometer. Unreacted residual PAHs are analyzed by means of gas chromatography According to the MSU researchers, the mechanism by which ozone reacts with PAHs is not understood, but it is believed that the dose of ozone and the degree of saturation of the soil control the degradation. One reason suggested is that ozone reacts with water to form OH radicals, an even more powerful oxidant than ozone. OH radicals might degrade those PAHs only partially oxidized by ozone, which suggests that PAH degradation would pro-
not? Some answers to this question are in a National Academy of Sciences report ( E S b T , Oct. 1993, p. 1974). If in situ remediation is the Metals way to go, does one use biological methods, chemical techniques, or Robert Peters of Argonne National Laboratory (ANL, Argonne, IL) is in- some combination of them? And if vestigating the use of chelating in situ remediation is not indicated, agents to remove metals from con- what approach should be used? “When considering in situ remetaminated soils. The primary focus is on lead. Peters’ study deals with diation of contaminated soil and soil from shooting ranges and a groundwater, you have to underhand grenade range at a military stand the nature of the site; how the training site in Germany, where the geology, hydrology, and chemistry soil is heavily contaminated with interact; then add in human health lead. Extraction agents included risks and, of course, regulatory facdeionized water and the chelating tors,” advises remediation engineer agents ethylenediaminetetraacetic Stan Zagula of Woodward-Clyde acid (EDTA) and citric acid. Con- Consultants (Chicago, IL). A similar centrations of the EDTA and citric approach may be applied to in situ acid ranged from 0.01 to 0.05 M and treatment of contaminated sedithe pH range was 3-8. Flushing was ments. “Sometimes, the best envidone by batch-shaker and columnar ronmental and cost-effective approach may be just to cap the site, flooding methods. For batch-shaker studies, Peters isolate the contaminants, or restrict observed that EDTA at 0.01 M re- access to the site,” he said. “If rememoves cadmium, copper, lead, and diation must be done, then you zinc from soil more effectively than want to develop a strategy that imcitric acid does. The two chelants plements the most cost-effective are equally effective, however, at method. This may mean selecting extracting barium and chromium. one technology or integrating a seExtraction seems to be more effec- ries of technologies. Biotreatment, tive at pH of about 5. “With the for example, may be used successbatch-shaker method, chelant ex- fully at one site; however, it may not traction appears to be a promising be able to meet the specific cleanup alternative for removing heavy met- objectives at another site,” Zagula als from soils on site,” Peters says; suggested. “Choosing the best remehe adds that removal “generally ex- dial strategy for a site depends on ceeded 70%.” understanding the effectiveness, By t h e c o l u m n a r f l o o d i n g limitations, and costs of technolomethod, Peters used 0.05 M EDTA gies, then integrating them into an or citric acid. With EDTA he ob- overall system.” tained a maximum lead removal of Currently, pump-and-treat, stabi50.6% and an average removal of lization, and incineration technolo17.6%. EDTA also removed Cd, Cr, gies are used routinely at many SuFe, and Pb more effectively than cit- perfund sites; nevertheless, many ric acid did, but citric acid worked innovative technologies also are bebetter for Cu and Zn. Because a ing demonstrated, according to Zasmall percentage of metals were gula. But he believes the trend will mobilized and extracted by colum- be away from incineration and nar flooding, Peters does not see co- pump-and-treat and that alternative lumnar flooding as a viable means techniques such as in situ biological of remediating soils contaminated treatment, vapor extraction, and with metals on site. chemical extraction will be more Using columnar flooding with widely used. In many cases, in situ deionized water, Peters achieved a remediation is being demonstrated maximum solubilization for cad- to be the most economical strategy, mium of 3.72%. Mobilization of Zagula says. He adds, however, other metal ions generally was “Treatment, whether in situ or not, < 1.7%. On the basis of these re- is still after the fact. The most effecsults, Peters suggests that metals in tive strategy is to use the three R’s: the soils at the study site in Ger- reduce, reuse, and recycle.” many are tightly bound to the soil and pose no serious threat to the groundwater. ceed more efficiently in moist than in dry soils, according to the researchers.
Choosing strategies When is in situ remediation appropriate for a site and when is it
Julian Josephson is an associate editor on the Washington staff of ES&T.
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