State/EPA agreements They could be very useful management tools f o r ensuring that regions and states accelerate compliance with environmental laws and regulations, especially in priority areas
In order to optimize the use of available financial and technical resources for solving priority environmental problems in the various regions and states, EPA evolved the system of State/EPA Agreements, or SEAs. Even though the program was voluntary in the beginning, fiscal year 1979, seven regions and 32 states executed agreements. They became mandatory this fiscal year (ending September 30). Indeed, SEAs must encompass all states, for a state which refused to sign one would become ineligible for grant funds authorized by the Clean Water Act (CWA), the Safe Drinking Water Act (SDWA), and the Resource Conservation and Recovery Act (RCRA). Since last fiscal year’s effort was somewhat of a “pioneering” effort, SEAs were generally limited in scope to water programs and were processor program-oriented. Now that they are mandatory, the scope has expanded to cover C W A , S D W A , and R C R A , and emphasis has shifted to environmental/problem-oriented priorities. Moreover, some regions and states are including air programs, even though they are not yet mandatory. FY 1981 could see consideration of virtually all EPA programs, if everything goes according to plan. Indeed, as a Region 111 spokesperson told ES& T, the regional administrator would like to see SEAs in his jurisdiction expanded to cover pesticides, noise, and many other problems, on the broadest possible scale.
\ 1
Q C T O E l l l 22 ‘9’8
A management tool The basic purpose of any S E A is to enhance environmental resource management by coordinating and integrating the planning, management, and implementation of all programs covered. T o achieve this aim, it is necessary to have a clear understanding of EPA’s and a state’s (or region’s) respective obligations and priorities, and to spell out what resources are available. Other steps consist of: more effective coordination and integration in program planning, priority setting, reporting, and accountability processes the greatest possible reduction in
1
“red tape,” delay, paperwork, and program duplication. more efficient use of each program’s resources. Another purpose of SEAs, according to various EPA documents, is to coordinate the administration of grant money with EPA and state agency leadership on what are perceived to be the most important environmental and management problems. The idea is also to set plans delineating what each federal and state agency will do, and according to what schedule. The general feeling in EPA is that SEAs should be strengthened as a management tool. I n order to move toward this objective, certain strategies are envisioned. Among them are: focusing on priority issues-for the present, mainly water and hazardous-waste problems including all EPA programs as eventual candidates for S E A coverage using S E A priorities to “push” or “drive” program grant activities giving special emphasis to problems that cross program lines “tracking” specific EPA and state commitments and progress in carrying them out making the negotiation and implementation of SEAs a top-level, personal priority task of EPA regional administrators (RAs).
Division of tasks At EPA’s Washington headquarters, SEAs are handled by the Office Volume 14, Number 8, August 1980
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of Water and Waste Management’s Division of Water Planning, and are generally supervised by Peter Wise. However, beginning October 1 , this function will move to the Office of Planning and Management. At regional offices, SEAs are managed through the RA and a special S E A contact that the RA designates. On a state level, state environmental and perhaps other agencies would share responsibilities. EPA headquarters sets national priorities, develops appropriate regulations and guidelines, finds ways to ease paperwork, reviews actual SEAs and their operations, and furnishes grant funds. Although the “ground rules” come from Washington, regions and states are given considerable discretion in adapting programs and procedures to meet needs in their respective territories. Among the RA’s missions are evaluating regional problems, finding ways to integrate financial and technical resources, negotiating priorities with states, resolving priority conflicts, and assuring that EPA’s and states’ commitments are met. As a federal grant recipient, a state must, of course, comply with applicable federal laws and regulations. However, through SEAs, it can negotiate priorities of compliance within their annual work grant plans. A state and EPA can also address issues that may call for application of time and resources across program lines. Other state responsibilities include making best efforts to integrate resources, activities, and grant work plans; conducting public involvement activities; and, together with the R A , making sure that program commitments are met. Normally, when an S E A is signed, the R A signs for EPA, and the governor signs for the state. A sample SEA One example of an S E A is an agreement, for this fiscal year, between EPA Region 111 and Delaware, signed last October. It set forth seven priority needs. Among these needs were detection/control of toxic and hazardous substances, and their abatement through state and federal pollutant discharge elimination and permit systerns. Special emphasis is on pretreatment of industrial wastes sent to municipal wastewater treatment (wwt) systems. Other perceived priority needs encompass water supply protection, correction of drinking water standard violations, identification of toxicants and organics in public water 900
Environmental Science & Technology
supplies-generally, state laboratories would carry out the identification task-and construction of municipal wwt plants, with delegation of EPA construction grant responsibilities to the state of Delaware. For EPA, the functions of headquarters and of Region 1 1 1 are as described earlier. State missions are handled by the Department of Natural Resources and Environmental Control ( D N R E C ) , and the Department of Health and Social Services (DHSS). Within DNREC, oversight is given to the Division of Environmental Control; within DHSS, to the Division of Public Health. Other state entities, such as the University of Delaware, Solid Waste Authority, Division of Soil and Water Conservation, and others, will also have roles to play.
By the beginning of this month, preparation and revision of annual program plans, mainly addressing SDWA, RCRA, and C W A (especially “1 06”, or enforcement/compliance, and “208”, or grant planning), should have been completed. Final approval should be accorded shortly before September 30.
What if no SEA? A typical program under the EPA/Delaware S E A involves hazardous-waste management. For instance, at the end of last year, EPA was to advise the state of the adequacy of Delaware’s hazardous-waste laws, and the state was to have organized a hazardous-waste committee. T h a t committee would include state and industrial representatives. By March I , a joint EPA/state plan to integrate hazardous- and solid-waste portions of
RCRA compliance programs was to have been completed. By next March I , in harmony with federal requirements, Delaware must develop a hazardous waste management process to provide a manifest system: hazardous waste identification; permitting systems for generators, transporters, and for treatment, storage, and disposal facilities; and any other activities that RCRA may require. On a continuing basis, EPA provides the state guidance and assistance. ‘‘Surel), these programs would be carried out even if there were no SEAs,” one may say, and quite correctly, for federal law requires these programs. But with the Delaware SEA, for example, EPA Region 111 representatives could meet with Delaware legislators and give them the time and expertise to help to write or rewrite laws that would harmonize with federal legislation, regulations, and guidelines. This joint effort would help the state to meet or beat deadlines, Paul Ambrose of Region I I I told ES& T . Ambrose handles Delaware and Maryland SEAs for EPA. In fact, he noted, SEAs give states a better “crack“ at negotiating and satisfying reasonable compliance deadlines; with the close liaison provided through SEAs, legislation and subsequent regulation would “come out right the first time,” with a minimum need for redoing them and, thereby, losing time. Even without SEAs, EPA would have to provide guidance and assistance to a state on a continuing basis. But as Ambrose explained it, with SEAS, such guidance and assistance can be much tighter than it would be otherwise. Also, there is a better “meeting of the minds,” leading to better-ordered priorities and allocations of financial resources. Ambrose also explained how S E A priorities may differ from state to state. For instance, hazardous waste is a top priority everywhere; however, acidic mine drainage may be of high priority in West Virginia, but of lower priority in Maryland, since only the western part of the latter state is affected. In Delaware, of course, that problem does not arise. With expanded programs and emphasis tailored to the perceived needs of the various regions and states, the S E A system should come into “full bloom” next fiscal year. By the end of FY 198 1 there should be some idea of how well the agreements are working, hopefully as measured by the yardstick of an enhanced rate of environmental quality improvement. -Julian Josephson
Biological contributions to air pollution Are they considerable? Or negligible? The a nswt?r remains shrouded in uncertain extrapolations and some complicated atmospheric chemistry
Evidence has been accumulating for the last 15 years that the natural workings of the earth’s biota could be responsible for a substantial portion of the hydrocarbons and sulfur compounds observed in the air. Although at first it had industry elated, the EPA worried, and scientists intrigued, it now seems to have everyone mainly confused. “Some issues thought to have been resolved are really still unresolved, and new issues have been raised,” said Basil Dimitriades of the E P A in a paper presented at the Air Pollution Control Association meeting held June 22-27 in Montreal. Inconsistent data are the rule in this field of “biogenic” emissions; attempts to resolve the inconsistencies bring into question measurement techniques, extrapolations, and our understanding of atmospheric chemistry. Much more research needs to be done, and no one is now taking bets on which way the answers will finally fall.
Tree exhaust Inconsistencies are most apparent in studies of natural organic emissions. It has been known for some time that vegetation gives off terpenes, isoprenes, and other hydrocarbons; recent work has suggested that these compounds are emitted, worldwide, at a rate as much as 20 times that of hydrocarbons from man-made sources. Dimitriades cited a number of regional emissions inventories which estimated natural contributions to hydrocarbon emissions to be as much as 58% in urban areas. But when the EPA attempted a review of the subject in 1977, it found a glaring inconsistency: “Despite their reportedly high emission rates,” Dimitriades said, “terpenes do not occur in ambient air a t significant concentrations.” Attempts to resolve this contradiction have not been conclusive. Dimitriades, and D. L. Flyckt of Washington S t a t e University, who also pre-
r m o v e d from the atmosphere much faster than are anthropogenic hydrocarbons. Terpenes are apparently more reactive than anthropogenic hydrocarbons, and do indeed disappear faster. Their faster reaction rate, however, is not great enough to account for the discrepancy between emission data and ambient concentration data. Ambient measurements overlook some natural organics. Dimitriades cited evidence that some naturally emitted alcohols “escape sampling and detection.”
sented a paper a t the A P C A session, suggested several possible explanations: Natural emission rates are overestimated. A commonly used measuring method is to encldse a tree branch in a plastic bag, which collects the emissions over a set interval. “The drawback of the method is that use of the bag enclosure creates environmental conditions that are different from those in the real atmosphere, and which affect the emission rate strongly,” said Dimitriades. An EPA study released in January found imprecision of about an order of magnitude in emissions rates calculated this way. Extrapolation of local emission rates results in an overestimate. “Such extrapolation is bound to cause large errors,” according to Dimitriades; the reason is that the conditions under which a sample was taken will not be applicable to different places and times. A second possibility, suggested by Brian Lamb of Washington State, is that “emission rates measured at ground level [may] not [be] representative of emission rates near the canopy top where ventilation effects may be more important.” Anthropogenic emission rates are underestimated.
Local chemistry The concern about hydrocarbon pollution rests primarily on its role in generating ozone through the photochemical smog reactions. The different reaction rates between natural and anthropogenic hydrocarbons mentioned above may thus mean that a simple comparison of the two emission rates does not reveal their actual relative effect on air quality. Dimitriades stressed another factor in determining the effect: “The one thing we have come to learn is that the contribution of an organic pollutant to ozone formation depends on the type of atmosphere to which it is emitted.” Rural atmospheres, which are loaded with a greater proportion of natural hydrocarbons than are urban atmospheres, have relatively low concentrations of NO,. Under these circumstances, hydrocarbons tend to act as ozone scavengers rather than producers. So where terpenes make their greatest showing, they have the least effect. The upper troposphere, on the other hand, may be quite sensitive to all emitted hydrocarbons, natural or anthropogenic. Methane, produced by the activity of anaerobic bacteria found in marshes and rice paddies, and carbon monoxide, produced by initial breakdown of more complex hydroVolume 14, Number 8, August 1980
901
curbons, react in the upper troposphere with the hydroxyl radical, O H . The OH radical plays a key role in the self-cleansing process of the troposphere. Pollutants such as bromine and certain chlorohydrocarbons, in addition to most hydrocarbons, react with O H as the first step either towards oxidation to COz or formation of water-soluble compounds which are then rained out. Consumption of O H by natural hydrocarbons would thus seem to limit this cleansing ability. Which numbers? The need for more time to reconcile emissions data with ambient concentration data must unfortunately be balanced against the immediate need for input data for air quality simulation models (AQSMs). Dimitriades comes down on the side of ambient concentrations: “ I f an assessment must be made at this time of the environmental impact of natural organics, such assessment should be based preferably on the ambient concentration data.” And: “Natural organic emission rate values needed for use in AQSMs should be back-calculated from ambient concentration data.” He also pointed out that since current AQSMs predict ambient ozone concentrations “reasonably well” without considering natural emissions, “we could altogether ignore biogenic organics in urban AQSMs, as a first approximation.” That view brought a sharp attack from Reinhold A. Rassmussen of Washington State University, who argued that we should at least base our work on observations, rather than inference. But there was widespread agreement with Dimitriades’ observation that both kinds of data-emission and ambient concentration-are probably in error, and that a combination of the possible causes listed above is at the root of the discrepancy. Cycling sulfur While the key to pinning down biogenic hydrocarbons may be better measurements, for biogenic sulfur compounds it may be a better understanding of the atmospheric chemistry of the sulfur cycle. Atmospheric sulfur exists in many different forms, and understanding the transformations between them is fundamental to reconciling observed concentrations with emissions-and even in knowing what sorts of emission sources to look for. For example, early investigators believed that hydrogen sulfide (H2S) was the primary carrier 902
Environmental Science & Technology
Sulfur fluxes
09 08
07
. x
1 .0 6 c 3
05
E
? 04
u
03 0.2 01 n
”
Global average (high budget)
Global Salt average marshes (low (Aneja) budget) I
Calculated
us
(Adams)
average hemisphere average average
J
I
Observed
of sulfur from the biosphere to the atmosphere. When emission measurements implied a global source strength for H2S far short of the contribution needed to balance the predicted sulfur-cycle budget, attention turned to other possible sulfur carriers, including carbonyl sulfide (COS), dimethyl sulfide ( D M S ) , carbon disulfide (CS2), and dimethyl disulfide ( D M DS) . Even so, “at least experimentally, it has not been possible to balance the global sulfur cycle,” said Viney P.‘ Aneja of General Electric, one of the cochairmen of the APCA session. Paul A. Steudler of the Ecosystems Center a t Woods Hole agreed: “Emissions of sulfur compounds to the atmosphere from natural sources are still a major unknown in the sulfur cycle.” Aneja, Steudler, and Donald F. Adams of the Univeristy of Idaho, the other cochairman, all reported on efforts to measure fluxes of various sulfur compounds from biological sources. Aneja found average fluxes of approximately 0.5 g of sulfur per square meter per year (g S / m 2 / y ) from fresh and salt water marshes in North Carolina. Dry inland sites showed no sulfur emissions above the detection limit of his analytic method (0.01 g S/ m2/y). He was able to detect H2S, COS, CS2, and DMS at the salt water sites, but only H2S at the fresh water
sites. Taking into account the global marshland area. Aneja concluded that emissions from marshes contribute only about 10% to the natural tropospheric sulfur cycle. But there is, inevitably, a difference of opinion over just what the contribution of biological sources needs to be in order to balance the cycle. Aneja quoted a figure of 0.4-0.7 g S / m 2 / y , averaged over the earth’s surface; this corresponds to 200-350 Mt/y. Adams, on the other hand, compared his average measured flux-based on a study of 27 locales in the southeast US.-of 0.03 g S / m 2 / y to the “low” budget figure of 0.08 g S / m 2 / y , or 40 Mt/Y. Adams is continuing an extensive survey, perhaps the only approach to obtaining a truly representative average biogenic flux. A multitude of factors affects the biological production of sulfur compounds, and, as in the case of natural organic emissions, extrapolations of a few measurements may lead to large errors. Adams pointed to soil temperature, moisture, organic content, oxygen content, and solar insolation as factors affecting the sulfur flux. The variability from site to site-and even within a single sitecan be enormous: Adams found sulfur fluxes in salt marshes to vary 0.021940 g S / m 2 / y . “What we’re attempting to do,” Adams said, “is see how the actual
Model of natural S-cycle
field measurements compare with the circumstantial reasoning” of the sulfur-cycle budgets.
Chemical models Still, the “circumstantial reasoning” is what will likely supply some of the vital missing pieces in our knowledge of the sulfur cycle and the biogenic contribution. Chemical models of the cycle have already-as noted earlier-pointed the way to studies of compounds other than H2S. Ultimately, chemical models will provide the test for the completeness of the source emission inventories, and will be a key to understanding the environmental effects of biogenic-and for that matter anthropogenic-sulfur. This is particularly so because of the complex network of reactions which link the many sulfur species in the atmosphere. Comparing emission rates with observed concentrations is futile without a knowledge of the chemical transformations that have occurred; likewise, linking emission rates to environmental effects depends on a knowledge of the ultimate fate of the emitted species. Some work by N. Dak Sze and coworkers at Atmospheric and Environmental Research, Inc. (Cambridge, Mass.), and earlier at Harvard University-not reported on at the APCA meeting-have pointed up some intriguing possibilities concerning the
transformation and fate of atmospheric sulfur compounds. One is that oxidation of C O S can give rise to Sol. The suggested mechanism is: O H COS SH COl
+ + S H + 0 2 + SO + O H so + 02’S02 + 0 -+
Sze has suggested that CS2 may in turn be a precursor to C O S in the atmosphere through the reaction:
+
-,C O S HS Thus release of both CS2 and C O S into the air may lead to production of
sol.
Although the estimated amounts of SO;?produced in this manner are relatively small-12 Mt S/y, compared with 65 Mt S / y for anthropogenic emissions-this biogenic contribution is nonetheless significant, for it may explain a number of peculiar atmospheric phenomena. The key piece of additional information is that COS is relatively inert in the troposphere, but reactive in the stratosphere. Thus the biogenic contribution to SO1 does not occur in the troposphere, where it would be minor in comparison with the
anthropogenic component, but rat her in the upper troposphere and stratosphere. The notably constant concentration of SO2 observed in these upper regions might thus be attributed to biologically produced CS2 and COS. Similarly, the persistent and widespread stratospheric sulfate layer-at first ascribed to volcanic activity, but observed even during periods of low activity-might be attributable to oxidation of this SO2 of ultimate biological origin. In a paper due to appear shortly in Atmospheric Encironment, Sze presents calculations from a one-dimensional atmospheric model of the natural sulfur cycle; the principal finding is that a “relatively low flux of reduced sulfur compounds [COS, CS2, DMS, HlS]”-about 28 M t S/y-“may account for much of the observed global burdens of SO2 and SO4*-.”
Work needed Confirmation of this calculation by direct measurements would be of course by a major step toward constructing a modern picture of the sulfur cycle. Sze also pointed to a need for better data on removal of SO2 and sulfates by wet deposition, for simultaneous atmospheric measurements of O H , H2S, and DMS, and for better laboratory data on reactions of the reduced sulfur compounds with OH. -Stephen Budiansky Volume 14, Number 8, August 1980
903
Wanted= fugitive emissions Methods for identifying and measuring nonpoint sources of air pollution were discussed at a session held during the annual meeting of the Air Pollution Control Association They are called fugitive emissions, pollutants that escape to the air by evading control devices. Leaking valves, holes in ductwork, even unpaved roads and cattle fiedlots are responsible for millions of tons of gases and particles that reach the atmosphere each year. Originally viewed merely as nuisances, these sources are now seen as major contributors to the observed air pollution in many regions. “Control of point-source emissions has not produced the anticipated improvement in ambient air quality levels in certain areas of the United States and Canada,” said A. John Chandler of Beak Consultants (Mississauga, Ontario). “The reason would appear to be fugitive emissions.” A recent EPA study of 14 cities concluded that fugitive emissions of particulate matter account for 30 l.(g/m3 of observed average concentrations. John Cooper and co-workers at the Oregon Graduate Center have estimated that all but 20 Mt of the 400 Mt of particles emitted each year in the country a r e from nonpoint sources. Fugitive hydrocarbon emissions may also play an important role. Thomas R. Blackwood of Monsanto cited a study which put fugitive hydrocarbon emissions a t 12.8 M t per year-42% of the total. But Blackwood pointed out that the particles will be the greater problem: “Volatile organic carbons will probably tend to decrease themselves. People will be looking everywhere to save those Btu’s.” Lost hydrocarbons mean lost money. How can these vast and diffuse sources be tamed? The problem is first one of identifying and measuring the sources. “It is difficult even to quantify such a source, much less regulate or control it,” Blackwood said. “The actual mass of emissions is not all that well established.” 904
Environmental Science & Technology
The problem appears to be fundamental. The major source of fugitive particles is unpaved roads; obtaining an accurate source strength for a hundred-mile stretch of dirt road approaches the impossible. Other large nonpoint sources pose similar difficulties. Blackwood cited harvesting operations, animal feedlots, coal mines, mill tailings ponds, and unplanted agricultural lands as signifiint sources of particles. A first
step, said Blackwood, would be to “look at the air quality impacts and develop the measuring methods at the same time,” thereby reducing the task to one of measuring the most needed data only.
Getting the numbers Henry J. Kolnsberg of T R C Environmental Consultants (Wethersfield, Conn.) reported on some of the direct measurement methods available. The
Nonpoint-source particulates
300
250
200
150
100
50 25 0
Source, Cooper et ai EPA Report EPA-600 7-79 186 (August 1979)
most accurate--and also the least generally applicable-is given the dubious name of “quasistack” sampling. A hood is placed over the source area and a blower moves the air past particle and gas sampler intakes. This approach has been used successf u l l y to measure emissions from welding in a shipyard and molding in a steel foundry. A similar, but less accurate method is to “take advantage of the hood provided by an enclosure” with a roof monitor. For line sources, an “exposure profiler”-an array of samplers stacked vertically-can be placed a few meters downwind from the source to measure concentrations in the plume as it begins to spread out. The least accurate, but most widely applicable method is “upwind-downwind sampling.“ The upwind sampler is assumed to respond to the background concentration, which is subtracted from the reading a t each of the downwind samplers. This method has been applied to stone-crushing operations, open-pit coal mines, and chemical plants.
terest was emphasized by John s. Kinsey of AeroVironment, Inc. (Pasadena. Calif.), who injected a strong warning about using published emission factors for nonpoint sources. “Sometimes perfectly valid factors are extrapolated over and over again without benefit of substantive data. The emission factors themselves can also vary for the same type of source. depending on the measurement techniques used to formulate them and variations in process conditions. The accuracy by which emission f.‘1 c t o r s actually predict real-life conditions can vary from plus or minus a factor of two to as large as an order of magnitude depending on the particular conditions.” Published reports of the effectiveness of various control strategies are subject to similar uncertainty. “ I f you don’t happen to like a particular number, you can go back in the literature and find whatever number you’re seeking,” Kinsey said. “ I f we’re going to develop good regulations,” he concluded, “ u e need good data.” -Stephen Budiansky
A number of statistical methods can also reveal contributions of nonpoint sou r c es to o bs e r v cd at ni os p h e r i c loadings. The most powerful is the method of chemical element balances, applied by Cooper and others. By establishing the characteristic elemental “signature” of different classes of sources, the relative contribution of each class to a sampled mass of particles may be determined. ( A complete discussion appeared in E S & T , July 1980, p. 792). Less refined techniques, such as comparison of particle samples obtained on wet days-when nonpoint emissions from roads and wind erosion a r e suppressed-with samples obtained on dry days, can reveal the bulk contribution of fugitive emissions. Monthly and seasonal variations in total suspended particulate levels and differences between weekday and weekend levels may also reveal the influence of nonpoint emissions.
Caution about emission factors But the need to carry out detailed measurements at specific sites of in-
Measuring fugitive emissions
.
/
-
Plant
Source
“Quasistack” sampling
Roof monitoring
Upwind sampler
W \
\ \
\
Plume boundary \
\ I
Line source
f2
‘a\
Downwind sampler array
Exposure profiling
Upwind-downwind sampling
Volume 14, Number 8, August 1980
905
Hazardous wastes here and there A New Jersey meeting heard how Canada, Poland, the United Kingdom, and West Germany are tackling this problem When one looks at hazardous waste management problems and possible strategies to control them, it is interesting to see how different countries approach the matter. After all, the types of wastes and management techniques can vary widely. At the National Conference on Hazardous and Toxic Wastes Management, representatives from Canada, Poland, the United Kingdom, and West Germany told of experiences in their countries. The conference was sponsored by the New Jersey Institute of Technology (Newark, N.J.) and held in Newark in June. In the U S . , of course, the federal government is attacking the hazardous-waste problem mainly through the Resource Conservation and Recovery Act of 1976 (RCRA) and related regulations issued. The sheer volume of regulations which appear in the Federal Register is quite impressive; for instance, Book 2 of Volume 45, Number 98 (there will be three books in all), issued May 19, contains 522 pages covering hazardous waste and consolidated permit regulations. Samples of data and forms to be submitted to EPA are included. Another hazardous-waste strategy in the US.is the “superfund” legislation now working its way through Congress. “Superfund” money would be used to render “orphaned” waste sites safe, from health and environmental standpoints. What final form this legislation may take, and how it may stand up in the face of whatever resistance industry may bring to bear, remains to be seen. Hazardous-waste strategies and “superfunds” are an especially cogent topic in New Jersey where the conference was held. That state has had considerable problems of its own, what with the recent Chemical Control fire a t Elizabeth and an old site found in Jackson Township, that are severely threatening underlying aquifers. In 1976, New Jersey passed the 906
Environmental Sciences & Technology
Spill Compensation and Control Act. This March, that act was amended to include a mini-“Superfund” to finance the effort of cleaning up or inactivating abandoned sites such as that in Jackson Township. The amount of the fund, initially, would be at least $ 3 million/y for cleaning up abandoned dumpsites, with a $1.5 million ceiling on one site. Jerry English, commissioner of environmental protection for New Jersey, told the conference that her department has so far cleaned up eight sites since January. One is still in the process of being cleaned up. English is very aware, however, that more such abandoned sites will be found. She also expressed strong support for a federal “Superfund.” New Jersey is a special case within the U.S. because of its heavy industrialization and the environmental and hazardous-waste problems that industrial concentration may have brought about. But what is happening outside the U.S. in the way of mitigating the threats of hazardous wastes?
Canada In Canada, there is an Environmental Contamination Act, and a Transportation of Dangerous Goods Act is working its way through Parliament. However, it could be several years before the latter law passes and regulations are drawn up, according to estimates by Hans Mooij of H. Mooij and Associates (Kingston, Ont.). Meanwhile, the Canadian federal government has certain authority concerning hazardous wastes on an interprovincial basis, but provincial governments have primacy within their boundaries. Mooij said there is, at present, no comprehensive hazardous-waste legislation for all of Canada, but there are hopes that the federal government will coordinate these matters in the future. Meanwhile, the problem is handled in
varying ways by different provinces. Probably the most action is being taken by Ontario, which, as of last January 1, started a seven-point program that outlaws disposing liquid wastes to land. Ontario also has a manifest system, much like what R C R A requires, and New Jersey has required since May 1978. Ontario may also build its own special facilities for managing hazardous wastes and may set up a mini-“Superfund”; indeed, as of January 1 some funds were allocated. The Atlantic and Western Provinces, as well as Quebec, require a hazardous-waste inventory, Mooij explained. Alberta may take regulatory action where public health is involved. The Atlantic Provinces and Ontario are developing site criteria, Quebec has liquid waste management regulations which cover permits for recycling or incineration. Qutbec, incidentally, has run into a situation frequently found in the U .S.-the N I M BY (not - in- my backyard) syndrome. Apparently, there were plans to do a test burn of PCBs in that province. This resulted in strong protests from citizens living in the vicinity of proposed burn sites. To date, the incineration test has not taken place.
The United Kingdom In England, the Department of the Environment has more of a legislative and advisory function than a regulatory/enforcement one, Ray Osmond of that department explained to the conference. Actual hazardous waste control authority is normally vested in waste-disposal authorities of the various county councils. Nevertheless, Parliament has passed laws with respect to hazardops-waste management. One is the Deposit of Poisonous Wastes Act, which came about after several sites, especially in the Midlands, were found to contain cyanide in 1972. A provision of this act
outlaws depositing poisonous wastes, or causing them to be deposited, without notifying the authorities before and after deposit. The Control of Pollution Act of 1974, particularly Part I, also deals with waste disposal. In addition, Osmond said that because England is a relatively small country, there have been land-use controls for 30 years, and public health laws in effect since the last century.
“fines” for high-temperature incineration. However, when it comes to incineration, strong N I M B Y protests are encountered a t County Council town meetings; so while the technology is there, social problems prevent application, Osmond observed. Another option under examination is salt-dome burial a t the Kali und Salz AG site in West Germany. There have been several hazardous-waste incidents that led to legislation and action. One was the cyanide case mentioned earlier, for which some fines were imposed. Another was a Derbyshire tanker leak believed to have been caused by vandalism. About 50 old fill sites presented threats to surface and groundwater. However, Osmond said that the U.K. never had “biggies” such as Love Canal or the Valley of the Drums, as the U.S. had.
detailed plans. For example, for a landfill, the quality and quantity of wastes must be listed; surface and groundwater protection schemes must be explained, along with contingency plans for bad weather; and full lists of equipment and personnel must be included. Pest control, firefighting, and long-term care plans are also required. The long-term care plans include ways of minimizing leachate, estimating possible chemical reactions of codisposed wastes, and even landscaping of closed fill sites. Suitable geological/hydrogeological site selection is also a matter of importance.
Commissioner English a mini- “superfund”
Sometimes referring to hazardous wastes as “special” or “notified” wastes, Osmond said that 3.5 million metric tons (mt) of such wastes were generated in 1978, about the same expected for this year. Most goes to landfills, but about 250 000 mt are organic wastes incinerated under contract, and another 250 000 mt may be disposed of in the ocean. Material placed in a fill may not threaten groundwater, nor may it spread overland. The present British strategy looks to licensing all waste disposal, and to have each county survey all wastes within its jurisdiction, pursuant to Section 17 (“special” wastes) of the 1974 act. Handling such wastes will involve a “cradle-to-grave’’ system with prenotification and manifesting. These procedures will meet European Economic Community standards, which, Osmond said, resemble those of the U S . RCRA, but are “more comprehensive.” H e also said that Section 100 of the 1974 act restricts the manufacture of chemicals that could give rise to disposal difficulties. Persistent chemicals are an example of such materials.
No “biggies” Osmond said that his department has allocated $4-5 million for “special” waste research and development over the last several years. Among R & D objectives are improving methods of inactivating wastes through solidification and combination with coal
The IMP’S Kunicki
aim is low-waste technology
Nels of West Germany
“some bureaucracy needed” Perhaps the worst British case was one in which wastes reacted to form hydrogen sulfide, and caused one fatality. For the future, Osmond sees efforts a t enhancing public awareness of the need to manage hazardous wastes properly, and that somewhat differing approaches may be taken by different counties. There will also be the need to address the N I M B Y syndrome. Finally, on the legal and technical side, there may be an increasing trend toward waste treatment and material recovery, and toward evolving a more complete definition of how Section 17 of the 1974 act will address “special” wastes.
West Germany Here, both a transporter and disposer of hazardous or “special” wastes, whether from the public or private sector, must be licensed. Moreover, licensing criteria are “very tough,” Christian Nels of the Umweltbundesamt (approximately equivalent to a federal environmental authority) said. There must be very
A list of wastes deemed hazardous was published by the federal government on May 5, 1977. However, individual Lander (equivalent to states in the U.S.) can add to the list to meet special conditions, but they must meet certain minimum uniform national standards. When a waste is to be treated or disposed, the generator, shipper, and treater or disposer must file notifications with cognizant authorities. Data from waybills are computerized and are important parts of the “cradleto-grave’’ record. This notification procedure is known as the “tripticket” system. Nels said that pharmacies, medical facilities, and residences are excluded from these “special” waste requirements, even though some of their wastes may be hazardous. A reason given is that each generator puts out very small amounts, and that going through the “tripticket” system would lead to inordinate costs. Pharmacy and medical wastes, rather, can be properly treated and codisposed with residential wastes.
Control at source Nels told the conference that in West Germany, control and separation of individual wastes at the source are Volume 14, Number 8, August 1980
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considered an ideal way to go. This is especially the case when wastes are to be stored at the deep, geologically stable Kali und Salz AG site. He noted that changing economic and technological situations may make it feasible to recover and use such wastes as feedstocks in the future. Indeed, there has already been one case of waste recovery for feedstock use for these reasons a t Kali und Salz, Nels noted. Another control approach that the West German authorities encourage is
pretreatment at the plant site. First of all, as Nels put it, “industries should pretreat, because they, more than anyone else, know what wastes they have.” Secondly, pretreatment can reduce or obviate the need for relatively scarce landfill sites and can cut disposal costs. Another way to treat on-site, and avoid the need for fills is incineration of substances from which heat could be recovered for plant use, Nels suggested. Temperatures must be able to
Underground disposal in Germany There are two principal sites in West Germany for deep underground disposal and storage of wastes. In most cases, any wastes stored at those sites must be separated and labeled according to strict rules laid down by the authorities. The idea is to be able to retrieve and possibly reuse them should the need arise, or technology permit. The actual disposal sites are old salt mines in geologically stable parts of
the country. One is the Kali und Salz site at Herfa-Neurode, established by the firm Kali und Salz AG. It is about 700 m deep, and has been in existence since 1972. The other site is at Asse and is operated by Gesellschaft fur Strahlen und Umweltforschung mbH (Munich). Although wastes are stored down to approximately 750 m, space is available as deep as 800 m.
Underground depository at Herfa-Neurode
Alluvium
Middle and lower colored sandstone
Depth (meters)
1--
401.3 1,437.0 448.0 471.7 505.0 520.8
-530.0
Crumbled shale Upper Zechstein level Dolomite level Lower Zechstein level Salt layer Salt clay Upper rock salt
656.5 Upper potash layer Middle rock salt 704.0 706.5 Lower potash layer 756.8 Lower rock salt -800 -820 Sulfateicarbonate Lower red sandstone
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Environmental Science & Technology
break down toxic materials-about 1200 OC, for instance. Nels reminded the conference that avoiding the need for land disposal automatically is a means to protect groundwater.
Other approaches Another possibility Nels brought out was shipment of wastes to the Dutch vessel Vulcanus ( E S &T , March 1977, p. 236) for incineration with proper air and water pollution controls. Fixation and inactivation of hazardous wastes in fly ash are also under consideration. West Germany has about 100 recycling plants to handle hazardous wastes, plus facilities that employ other techniques, all strictly licensed, Nels said. The government is directly involved in financing these facilities, and, along with private persons, holds shares in waste-handling concerns. “It avoids much argument to have this arrangement. We realize that government involvement can sometimes discourage private investment and motivation. But in this business, you need some bureaucracy if the system is to work,” Nels said. For the future, the aim will be to get around the hazardous-waste problem by accelerating development of lowand no-waste technology as much as possible. Also, over the next few years, hazardous-waste laws and regulations will be tightened even more and will be “harmonized” with those of other EEC countries, Nels forecast. Poland Poland has some rather specialized hazardous-waste problems in that the great majority comprise heavy metals, largely because of the large electroplating, metal-finishing, and metalworking establishment. Synthetic organics are a small problem, originating mostly from paint and pigment works; even those will contain metals, explained Wojciech Kunicki of the Instytut Mechaniki Precyzyjnej (IMP, or Institute of Precision Mechanics, Warsaw). Thus, in Poland, the hazardouswaste situation is one that addresses water protection as the main effort. Poland has effluent limitations that divide water into three classes: Class I-potable, recreational, and special industry uses Class 11-generally “fishableswimmable” Class Ill-general industrial use, but still required to meet certain national pollutant limits (ES&T, August 1978, p. 896). Water protection is governed by the Water Conservation Act, which was
amended this year to define “best protection.” Hazardous wastes are very broadly defined; even so, under Clause 53 of the act, improper discharge of such wastes can result in penalties. However, penalty imposition does not clean the environment; scientific and technical work does. Such work in Poland has as its chief aim low- or nowaste technology, not only for environmental reasons, but also to reduce costs of importing mineral raw materials, Kunicki said. In any case, the object is to extract what metals can be extracted and then to store the balance of any waste safely. What organics there are after the metals are taken out-some can be very toxic, such as pyridine-would go to an air pollution-controlled incinerator for hightemperature destruction. One option in this direction being considered is fluidized-bed combustion. A t present, of the hazardous waste Poland generates about 80% (approx. 30 million tpy) is metallic. Most is presently in lagoons and fills-about 150 million mt; little goes to what in the U S . would be called “publicly owned treatment works.”
What the metals are Lead, manganese, nickel, and zinc, along with lesser quantities of others, come from the ferrous metals industry, Kunicki pointed out. The metal-finishing industry generates small quantities of very dangerous wastes. From some sources, such as paints/pigments, metals and organics can be mixed, with toxic substances concentrated from about 0.1% up to several percent. Among nonferrous metals in the waste stream are chromium (also from tanneries), copper, and others normally expected from such industries. Given the types of industries involved, cyanide (CN-) is another waste with which to contend, as is slag. The I M P is responsible for finding ways of abating hazardous wastes, especially with a view to water protection, Kunicki said. Among R & D thrusts in this direction are waste exchange; minimization of water use; changes in process methods, including ways of avoiding C N - use; detoxification; and material recovery. Among techniques being tested for metal and other material recovery are ion exchange, electrodialysis, reverse osmosis, oil-metal coagulation, and ultrafiltration. Reputedly, the I M P has made notable advances in ion-exchange and reverse-osmosis technology. Other R & D efforts are being exerted in the direction of “zero-discharge” electroplating technology, and
materially reducing the amount of rinse water needed, yet still recovering metal from the rinse water that must be used. Other approaches would involve “mining” sludges as low-grade “ores,” with safe disposal of mixed sludges that cannot be “mined.” Resource “mining” could also be tried a t existing landfill sites as well, the idea being to reduce danger to groundwater. In other words, where possible, certain hazardous wastes will be regarded as potentially useful raw materials. Where they cannot be, as with certain wastes containing mercury, chlorinated organics, or other such materials, disposal in special sites would be the route taken, Kunicki foresaw. For several years, Poland’s I M P has been researching metal waste as a joint “venture” with EPA. This project is still ongoing.
Similarities and differences Thus, there are numerous differences in hazardous-waste problems and attempts at solutions among the countries represented a t the Newark conference. Most have many different kinds of organic and inorganic wastes with which to contend, while one
seemed to have wastes of a somewhat more specialized nature. Also, some countries have a whole system of hazardous-waste management in existence, or soon to come, with “cradleto-grave” recordkeeping and manifest requirements; in others, there are only preliminary efforts that vary from region to region. Some similarities or points of agreement were brought forth, however. One is that technology exists, or can be developed in the fairly near future, to handle hazardous wastes in ways that would protect public health and the environment. The main problems, then, are economic and social ones, not technological ones. The economic problems are rather straightforward; ultimately, they boil down to costs of developing the needed technologies, putting them into practice, and maintaining them. The social ones will be more difficult to address, especially the N I M B Y syndrome and particularly in countries where the authorities cannot easily ride roughshod over the citizenry. Yet solutions must be found because, to put it simply, hazardous wastes will not obligingly go away on their own. Only human efforts can accomplish that aim.
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Volume 14, Number 8, August 1980
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Adsorption on carbonr theoretical considerations Based on an interview with Dr. Georges Belfort, an assessment of equilibrium theories is presented in this first part of a two-part article The great mathematician Alfred North Whitehead wrote, “An unflinching determination to take the whole evidence into account is the only method of preservation against the fluctuating extremes of fashionable opinion.” To date, granular activated carbon has been used in drinking-water treatment to remove organic compounds that cause taste and odor and/or color problems. Now, activated carbon is being considered for the removal of synthetic organic chemicals from upstream discharges or runoff, the removal of organic compounds (precursors) that react with disinfectants to produce “disinfection byproducts,” and the removal of organic chemicals that are the disinfection by-products themselves. Various theories and models have wolved to explain, on a scientific basis, the removal of organic solutes from dilute aqueous solution on granular activated carbon. To learn the scientific base for these theories and models, ES& 7”s Stan Miller spent a couple of days with Dr. Georges Belfort, associate professor of chemical and environmental engineering at Rensselaer Polytechnic Institute (Troy, N.Y.). His explanation is an attempt to “take the whole evidence into account,” as the mathematician advised. After introducing the equilibrium and dynamic aspects of adsorption, the variables affecting adsorption, the best-known adsorption models for single- and multicomponent systems are presented in detail. Overall process of adsorption The ultimate adsorption capacity of a continuous activated-carbon process for a single- or mixed-solute system is usually measured as the time or volume processed for which the carbon can be exposed to the fluid before breakthrough of the solute(s) occurs. This breakthrough time or volume is determined by the equilibrium isotherms of the particular solutes alone, or together if in competition, and their 910
EnvironmentalScience & Technology
Dr. Georges Belfort taking the whole euidence into account
rates of diffusion into the adsorbent particles. Thus it is not only important to understand and predict the equilibrium adsorption for single- and multisolute systems, but it is also necessary for design purposes to describe the dynamics of the adsorption process. In this regard, Weber and Snoeyink and their respective co-workers in the U S . , and Liapis and Rippin in Switzerland have developed detailed dynamic models incorporating equilibrium adsorption models with film-, pore-, and surface-diffusion phenomena. In describing this dynamic process, three consecutive steps have been proposed for porous adsorbents such as activated carbon: transport of the solute through the external film from the bulk solution to the exterior of the adsorbent granule solute diffusion within the pores in the interior interstitial fluid and on the internal porous surface, except for the small amount of adsorption that occurs on the exterior surface of the adsorbent adsorption of the solute on the interior surfaces, filling up the pore and capillary spaces of the adsorbent. These dynamic models are thus directly based on the efficacy of the equilibrium adsorption isotherm models.
Weber, in his text (“Physicochemical Processes for Water Quality Control,” W. J. Weber, Jr., Ed., Wiley-Interscience, 1972) and in a recent review with M. van Vliet (in chapter 1 of the Ann Arbor Science proceedings book based on the Miami A C S Adsorption Symposium), summarized in detail the important factors considered to influence adsorption from aqueous solutions. These include the nature of the adsorbent (activated carbon), the adsorbate (in this case, dissolved organics), and the intensive and extensive conditions of the aqueous solution. Variables affecting adsorption Adsorption capacity for specific single organic solutes of a homologous series is thought to be a direct function of 1) the adsorbate properties, such as functionality, branching or geometry, polarity, hydrophobicity, dipole moment, molecular weight and size, and aqueous solubility 2) the solution conditions, such as pH, temperature, pressure, adsorbate concentration, ionic strength, and presence of background and competitive solutes 3 ) the nature of the adsorbent (activated carbon), such as surface area, pore size and distribution, surface distribution, and surface characteristics (Le., number of OH- sites/A*, ash content). Little quantitative information is known about the surface characteristics of carbon and its influence on organic adsorptive selectivity. Important physical characteristics include poresize distribution, surface heterogeneity, porosity, hydrophilicity, surface area, etc. Clearly these parameters influence the degree and type of adsorption possible. Characteristics of activated carbon It is important to understand the physicochemical characteristics of activated carbon. Activated carbon is the term used to describe a range of materials similarly prepared from
different raw materials (wood, lignite, coal, bone, petroleum residues, and nut shells) that exhibit a high degree of porosity and extremely large (internal) surface areas (500-2000 m2/g carbon). Because of its ability to adsorb a wide range of solutes from the gas and liquid phase, its ease of production and reasonable cost, and its regeneration capability, activated carbon has found wide commercial application as an adsorbent. I n addition to surface area and porosity, the surface characteristics of activated carbon are also particularly important with respect to adsorption of specific solutes. Here it is sufficient to point out that essentially two types of surface interactions are thought to predominate. The first type of surface interaction, which occurs on a majority of the surface (on basal planes), can be characterized by van der Waals physical interactions, and is hydrophobic in nature. The second type of surface interaction, which occurs at the more reactive edges of the microcrystallites, can be characterized by positive physical (and maybe even chemical) attractive interactions due to hydrogen bonding and electrostatic forces. Although the second type of surface interaction probably occurs at a small fraction of the total surface area, these specific adsorptions result from the surface heterogeneity and to the presence of oxides, hydroxyls, and other groups on the surface. Activated carbons produced by different processes probably differ in their adsorptivity as a result of their different energy potential and extent of these heterogeneous sites.
Hydrophobic interactions can play a dominant role in activated carbon adsorption of nonpolar (or nonpolar moieties of) solutes, and this is used as the starting point to develop Belfort’s generalized solvophobic thermodynamic theory for adsorption. This will be discussed in detail in part 2 of this series. Single-solute adsorption Belfort pointed out that “most of the early attempts to describe microscopically the mechanism of adsorption in the gas phase ran up against the very difficult problem of how to define the extent and properties of the ill-defined adsorbed phase.” A modern description of how J . Willard Gibbs approached this problem is presented in detail in Hendrick C. Van Ness‘ review article entitled “Adsorption of Gases FIGURE 1
Gas phase
*-Activated
carbon
The well-known adsorption diagram by Polanyi showing equipotential or equal compression lines (after M. Polanyi 2 Nectrochem , Vol 26. 1920 p 371)
on Solids. Review of the Role of Thermodynamics” from the A C S publication Chemistry and Phjjsics of Interphases-11 ( 197 I , pp. 12 1 132). Belfort continued, “Gibbs got around this problem by proposing an imaginary mathematical surface which can be treated as a two-dimensional adsorbed phase. He then assumed that this hypothetical 2-D phase was in phase equilibrium with the bulk (gas) phase, and that the molar interfacial area, A , was an independent variable uninfluenced by temperature, pressure, composition, or the amount of material adsorbed. With these assumptions, Gibbs derived analogous thermodynamic expressions for the 2-D phase to those for homogeneous 3-D fluid phases. “Of course, he had to define an analogous pressure which Gibbs called the spreading pressure, x. Thus pressure and molar volume for a 3-D phase were replaced in the equations by spreading pressure and molar area A .” This is the basis of the now famous Gibbs adsorption isotherm derived from the Gibbs-Duhem equation and the fundamental property relation (Table I ) . Other models were proposed during the early part of this century. These include the monomolecular theory proposed by Langmuir in 1915 in which it is assumed that adsorptive forces, similar to those needed for chemical combination, are able to hold or fix adsorbed atoms on the surface in a monomolecular layer. Brunauer, Emmet, and Teller (BET) extended this model to a multilayer adsorption
Volume 14, Number 8, August 1980
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isotherm model. Both the Langmuir and BET isotherms can be derived using either kinetic or thermodynamic approaches. Belfort pointed out that “other theories were out of favor as early as 1932, as described in J. W. McBains’ text entitled The Sorption of Gases and Vapors by Solids and published by George Routledge & Sons, Ltd., London. 1932.” These theories include
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Environmental Science & Technology
the capillary-condensation model which could not explain either sorption on truly planar surfaces or the sorption of gases. Another model, based on de Saussure’s (in 1814) idea that as molecules approach a surface they are strongly attracted toward it, is called the thick compressed-film model or, more popularly, the Eucken or Polanyi adsorption potential theory. This model presupposes a changing poten-
tial and therefore a changing pressure as the solutes approach the surface during adsorption. See Polanyi’s diagram (Figure 1 ) showing equipotential lines or equal compression of the adsorbed solute in the sorption space. Investigators have suggested that enormous pressures, of the order of thousands of atmospheres, exist near the adsorbent surface. The same
problem that Gibbs faced has plagued the quantification of this model. As Belfort put it, “With such an enormous ill-defined pressure gradient across the sorption region, how does one define the extent, the state of aggregation, and the density needed for comparing the experimental isotherm with the model’?” “With much difficulty,” he answered rhetorically. Thus, the basic problem with the Polanyi potential theory is one of defining the adsorbed space region and its associated properties. Polanyi’s distinctive contribution, however, is the suggestion that since the attractive influence of the solid is assumed to be independent of temperature, experimentally determined isotherms can be used to predict the adsorption of others for the same system by merely applying the equation of state. Berenyi, improving on Polanyi‘s first attempts, recalculated in 1920 many of the results in the literature. He also obtained empirical curves for the isotherms connecting adsorption potential with sorbed volume, assuming that ordinary density at the adsorption temperature and a t atmospheric pressure could be used to convert amount to volume adsorbed. “Of course, this assumption contradicts the model itself,’’ Belfort commented. Berenyi found that for different temperatures all the empirical curves coincided for a given solute and sorbent. This is called the characteristic curve of adsorption. Polanyi extended this by comparing characteristic curves for different solutes (he used gases and vapors), pointing out their similarity in form. Quoting from page 457 of McBain, they “must be [similar in form], since sorption curves in general are similar.” The scaling factor used to align the characteristic curves was molal volume. This approach seemed to work quite well when dealing with a homologous series of gases. Major probletns remain concerning the validity of the tnodel. Contrary to the model, for example, sorption of h’l in highly porous bodies was found to increase instead of decrease as a function of pressure. Belfort quoted from McBain’s monograph, “This disproof of any compressed film hypothesis applies with certainty to active charcoal. . .” In 1928, Polanyi explicitly modified his compressed-film theory by making the film two dimensional like Gibbs’. Even with this modification, the model of a compressed film has problems. “The untruth of Polanyi’s latest hypothesis of the compressed monomolecular film obeying the equation of
state arises presumably from the tacit assumption therein involved that all planes on a surface are indifferently alike so that further pressure merely squeezes the molecules more closely together. This neglects the molecular constitution of matter,” said Belfort. quoting McBain again. The modern adoption of this theory to the experimental adsorption of solutes from liquids has been mainly due to Manes and co-workers since about 1962. Using scaling factors (of molal volume and refractive index, which represents polarizability of the solute), they too have followed Berenyi’s and Polanyi‘s approach for comparing single-solute isotherms. This formalism has been used to correlate the adsorption of organic liquids and solids from trace concentrations to saturation and to study competitive adsorption of binary and ternary solute mixtures. The fit between theory and experiment was not always as good as desired. A central problem encountered was that the maximum adsorption of all solutes should have been the same on a volume basis, but it was not. Manes and co-workers accounted for this discrepancy as being caused by variations in molecular packing within the pore space of the activated carbon. Nonetheless this method is extremely useful and simple to apply. I n spite of this, very few workers have chosen to use the model. According to Belfort, “This may be because, although the plotting procedures are useful, the physical model has just not added to our detailed understanding of the interactions involved in the adsorption process.” I n 1922, Freundlich revived the e.uponential empirical equation, which has since been called the Freundlich equation. This was meant to apply to that portion of the adsorption isotherm beyond the region of Henry’s law. Belfort remarked, “Since the asymptotic behavior of the Freundlich equation at infinite dilution does not obey the necessary thermodynamic boundary condition of proportionality between solute adsorbed (per unit mass of adsorbent) and solute concentration in the aqueous liquid, this model can only represent a narrow range of the adsorption isotherm curve. Many investigators have incorrectly extended this empirical model beyond its valid experimental range. “ I n fact, much of the experimental work on the adsorption of toxic organics in water has been conducted at a solution concentration of several orders of magnitude higher than that actually found in water. After fitting the Freundlich equation to these data,
many investigators have incorrectly suggested that the parameters calculated from fitting the model at such high solution concentrations also apply at the very low actual concentrations. “With this limitation, it is unclear to me w h y so many investigators persist in using this equation. The fact that higher correlation coefficients for a linear regression analysis are obtained with the Freundlich equation than with the Langmuir or other thermodynamically consistent equation is misleading. After all, it is not entirely unexpected that a log-log plot [for the Freundlich] gives a relatively good fit.” In addition to the isotherm models (Table 2), several less well known three-and-more-parameter isotherm equations have been used. Their ability to represent the data in dilute aqueous solutions have been evaluated by Prausnitz et al. in their 1978 paper which appeared in Chemical Engineering Science (Vol. 3 3 , pp. 10971 106). They rejected the Freundlich and Dubinin-Radushkevitch equations because of their thermodynamic inconsistency at infinite dilution and the Langmuir equation because of its restriction to homogeneous surfaces. They compared the Toth, RedlichPeterson, and Newman (three-parameter) equations with a new threeparameter isotherm containing an exponential function. Belfort explained, “Evidently this latter equation and the Toth equation represented the data best. Toth’s equation is little known in the West and was first published for gas-phase adsorption in the east European literature.” Competitive adsorption So far everything discussed has to do with representing adsorption isotherm data for a given single-solufe compound in the gas, vapor, or aqueous phases. What about the relative adsorption of different or even similar (homologous) solutes from the aqueous phase? Can we predict a priori which solutes will be preferred by carbon adsorption? In other words, can we rank-order the solutes‘? Experimentally, this can be accomplished by comparing the single- or mixed-solute adsorption isotherms for different solutes on the same activated carbon. “A significant leap in the ability to predict multicomponent adsorption equilibria from dilute solutions occurred with the publication of Radke and Prausnitz’s calculation procedure (in AlChE Journal, Vol. 18, No. 4, 1972. pp. 76 1 -768), which extended Volume 14, Number 8, August 1980
913
the method of Myers and Prausnitz from mixed-gas to multisolute adsorption. The method, which uses the Gibbs adsorption equation, requires single-solute isotherms (or any representative model) for reconstructing the multisolute competitive adsorption isotherms,” said Belfort. Because of the model’s mathematical complexity for more than two competing solutes, it has recently been modified to include a much simpler calculation by DiGiano et al. (Chemical Engineering Science, Vol. 33, 1978, pp. 1667-73). Other approaches to describing multicomponent adsorption generally have been empirical. This includes the Polanyi approach of Manes and coworkers at Kent State University and various best-fit equations. ‘Fritz and Schuliinder from the University of Karlsruhe, West Germany, proposed in Chemical Engineering Science (Vol. 29, 1974, pp. 1279-1282) a general empirical equation for calculating the adsorption equilibria of organic solutes in aqueous solutions. Under certain simplifying assumptions, the equation reduces to some well-known relationships as special cases. These include for bisolute adsorption the Langmuir and the Jagar and Erdos equations, and for single-solute adsorption, the Radke and Prausnitz, the Freundlich, and the Langmuir equations. Belfort summarized, “The underlying point of all this is that giuen single-solute or multisolute adsorption equilibrium, a reasonably good mathematical description of multicomponent behavior is attainable. However, what has been missing is the development of an equilibrium adwrption theory which specifically accoilnts for the presence of the aqueous solvent and which apriori can predict, without experimental observations, the preferential adsorption of organic compounds onto activated carbon from dilute aqueous solutions.” In the second part of this two-part article, a detailed discussion on the latest developments including Belfort’s new theoretical approach of a comprehensive theoretical basis for predicting a priori the preferential adsorption of organic compounds onto activated carbon from dilute aqueous solutions will be presented. McGuire and Suffet’s application of the solubility parameter approach to adsorption will also be presented. -Stanton Miller
Water-treatment chemicals The newly established NAS committee will study the potential problems and health impacts of chemical additives to drinking water In the U S . approximately 60 bulk chemicals are used as additives in the collection, treatment, or delivery of drinking water. At present there are no data, let alone federal standards, for the use of these chemicals. Dr. Robert E. Rehwoldt, staff officer of a two-year N A S study requested by the EPA, said that the potential problems and health effects of additives to drinking water were first looked a t in 1958 when the Public Health Service began a system of advisory statements on coagulant aids. Even though this advisory service was subsequently expanded, it never considered the problems and effects for the majority of bulk chemicals in use today. In order to carry out this study, N A S assembled a committee of nine experts representing the technical areas of water supply, water treatment, toxicology, chemistry, engineering, analytical testing, and manufacturing procedures. Housed in the Food and Nutrition Board in the N A S Division of Biological Sciences, the Committee on Water Treatment Chemicals is comprised of three academic representatives, three nonindustry representatives, and three industry representatives.
Chairman of the committee, Dr. William H . Glaze is professor of chemistry a t North Texas State University, Denton, Tex. The two other academic representatives are Dr. Carrel Morris, professor of sanitary engineering a t Harvard University, and Dr. Ronald Shank, a toxicologist from the University of California at Irvine. Nonindustry representatives include Mr. Charles Buesher of the St. Louis County Water Co. (Missouri); Dr. Rhodes Trussell, a member of the ES&T advisory board who is with James M. Montgomery Engineering (Pasadena, Calif.); and Dr. Nina McClelland, National Sanitation Foundation (Ann Arbor, Mich.). The industry representatives are Mr. Robert Bryant, Stauffer Chemical (Conn.); Mr. Gerald Stobby, Dow (Midland); and Dr. John Mahon, Calgon (Pittsburgh). Rehwoldt told E S & T that drinking water i s considered a food and hence the study falls within the purview of the Board of Food and Nutrition. Considering drinking water a food, the FDA transferred to the EPA, in an interagency agreement, the responsibility of learning what the health impacts are of chemicals that come in contact with water in the process of
Staff Officer Rehwoldt
Committee Chairman Glaze
Additional reference “Activated Carbon Adsorption of Organics from the Aqueous Phase,” Suffet, I. H.; McGuire, M. J., Eds.; Ann Arbor Science Publishers, Inc.: Ann Arbor, Mich., 1980; VOl. 1. 914
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making potable water. This N A S committee is trying to form guidelines for the use of these reagents and, more importantly, to establish analytical tests for impurities in the bulk chemicals. Some problems with the chemicals are the presence of chloroform in chlorine used for disinfection; fluorides as well as arsenic in phosphates and heavy metals such as chromium; and manganese and lead impurities in iron salts. There is also the chance of organic contamination from coagulant aids, which often are polymers. These polymers contain monomers which tend to be leached out in the process of water treat m e n I:,
The activity of the committee is divided into four major groupings which represent user categories of these chemicals. The individual chemicals in each group are shown in Table 1 . Each group has two representatives from the committee; Shank, the toxicologist, is involved in all four groupings. There is a first section on coagulants and flocculants as a major grouping of chemicals; Glaze and Stobby are the responsible committee members. A section on disinfectants as a major use group is represented by Morris and Trussell; Bryant and Buesher represent a third section on softeners and precipitants as a major use group. The last
TABLE 1
The four major use groups of chemicals in the NAS study Activated silica Aluminum ammonium sulfate Aluminum chloride Aluminum potassium sulfate Aluminum sulfatea Bentonite Chlorinatedferrous sulfate
Ammoniaa Ammonium chloride Ammonium hydroxidea Calcium hypochlorite a Chlorinea Chlorine dioxidea Chlorinated lime Hydrochloric acid Calcium hydroxidea Calcium oxide Carbon dioxide Dolomitic hydrated limea Dolomitic limea Dolomitic limestone Activated alumina Calcium f Imide Copper sulfate Disodium phosphate Fluorositicicacida Hydrochloric acid Granular activated carbona Monosodium phosphate Substances to be given priority attention
Ferric sulfate a Ferrous sulfate Ozone Sodium aluminate Sodium silicate
ea
Sulfur dioxide Sulfuric acid Magnesium carbonate Magnesium hydroxide Magnesium oxide Sodium bicarbonatea
is a miscellaneous categor)' including adsorbents. activated carbon. and phosphates, and is represented by Mahon and McClelland. Rehwoldt explained the protocol that the four subcommittees will be following in their two-year study. They will: establish sources and manufacturers of the particular chemicals look at the ways the chemical is used in water treatment. (For example, calcium hydroxide is used as a precipitant as well as a chemical to regulate acidity; the dosage is different in these applications.) recommend purity levels for the bulk chemicals. Committee guidelines prohibit making the recommendations more strict than the drinking water standards, nor may they decrease the quality of the existing standards. In cases where there are detrimental health effects or toxicological implications associated with the impurities, the committee will formulate minimum-quality specifications for the bulk reagents and recommend impurity levels based upon consideration of maximum allowable exposure to the impurity. Most important is the fact that all standards will include analytical test procedures, not only for the bulk reagent but for the likely impurities. EPA has estimated that 100 gallons of processed water are used per person per day, including water for swimming pools and food processing. in addition to ingestion. About 10% of total lime production goes for water treatment: this amounts to 450 000 tpy. For sodium carbonate, the use figure is 23 1 000 tpy. I n 1978, activated-carbon use was 18 300 tpy with a 5% per year increase projected: caustic soda and sodium bicarbonate amounted to 13 000- 15 000 tpy. The projected 1985 figure for iron salts is 93 000 tPY. The A W W A has issued its own standards for many chemicals used in potable water. Rehwoldt indicated that these quality standards were concerned primarily with an assay. i.e., proof that the chemical reagent worked. On the other hand, the N A S committee intends to look into the chemistry of the materials and will come up with analytical procedures for measuring the impurities in these bulk chemicals. There is certainly no intention to supplant the A W W A standards, which EPA recognizes as invaluable. Ultimately what is envisioned as a product from this committee is a manual analogous to the Food Chemicals Codex, 1974. -Stanton Miller Volume 14, Number 8, August 1980
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