OUTLOOK
Advice on wessina environmental toDics I
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The Environmental Studies Board of the NAS-NAE performs a tremendously important public service that only they can perform Without question, the most honorific professional clan in the U.S. is the august body of the National Academy of Sciences and the National Academy of Engineering. A recent reorganization of their structure is now expected to make the Academy more responsive to the needs of science and its problems in the U.S. The NAS-NAE serves a unique role in that it brings "experts" away from their everyday activity to perform a tremendously important public service that only they, "the cream of the crop" among the scientific and engineering talent, can render for this country. In that reorganization early this year, the NAS-National Research Council was restructured into five problem-oriented commissions and three discipline-oriented assemblies. Although only one commission-the Commission on Natural Resources (CNR)-has thus far been established, soon a Commission on societal Technology will be constituted, and some time later. Commissions on Human Resources, Peace and National Security, and International Scientific Affairs. The assemblies are organized along the lines of the scientific disciplines including chemistry. physics, mathematics, and so on. A first assembly, the Behavioral and Social Sciences, was organized in February. Before the year is out, a Life Sciences assembly (to include divisions of Medical Sciences and Biological Sciences) will begin operation, and then some time next year an assembly for Physical Sciences and Mathematics. One objective of the Commission on Natural Resources is to tie together the interrelationships between resources and environment. For example, you cannot have coal from strip mining without environmental tradeoffs. Nor can you burn the coal to produce electricity without producing some pollution as well. At present, this commission is a 13-member organization chaired by Gordon J . F. MacDonald, one of the three original members of the Council on Environmental Quality (CEO) 892
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In late August, the CNR held its first planning meeting at Woods Hole Oceanographic Institute (Woods Hole, Mass.). "The purpose of the commission is to coordinate the studies of the Boards and to identify the conflicting demands on resources and environmental quality," MacDonald says. "Of equal importance is the opportunity, in our overview, to use our own initiative to commence analysis in advance of a request from government or where no single agency may see the need." Further down in the organization, each commission is subdivided into a number of boards. Even before MacDonald was appointed to CEQ, he was chairman of the Environmental Studies Board (ESB), now a part of the CNR structure. Four other CNR boards are concerned with Energy Studies, Agriculture and Renewable Resources, Nonrenewable Resources, and Oceans and Atmosphere. The ESB is a 12-member board and its recently appointed chairman is Howard Johnson: "The environmental scientific questions today are posed with social and economic questions," Johnson says. "These interactions must be recognized from the start in our studies, or the answers will simply be a fragment of what decision makers really need." Richard Carpenter is executive director of the CNR; Theodore Schad is executive secretary of ESB. The current program of activities of the Academy is performed in some cases in response to inquiries from various agencies of the Federal Government. In other cases, a study program may be initiated by one of the boards or committees. The study program of the ESB usually takes one of two forms. Either it is a sort of technology assessment, or it involves a feasibility study or a validation study, according to Richa r d .Carpenter . Doings in ESB
Established in 1967 as a joint venture of NAS-NAE, the Environmental Studies Board has been involved in a number of major environmental proj-
ects. A grant from the Kellogg Foundation provided core support for ESB and its secretariat, a 10-man staff in addition to Carpenter, and a 3-year grant from the Scaife Family Charitable Trust made it possible for the ESB to begin studies on its own initiative. The Kellogg funds expire at the end of this month, and the Scaife grant runs to November 30, 1974. Perhaps from the outset, it is important to note in all of these study programs that members of the commission, the boards for the individual study programs, do not receive a salary from the Academy; they receive travel and per diem expenses and offer their expertise, time, and resources as a service to the nation. The study program may be spearheaded by a member of the Academy or any other eminently qualified leader who is recognized by his peers in their hierarchichal structure as the "expert" in the area. Currently, there are three programs under study. A first, on pest control strategies, is a broad-base cost-benefit analysis and goes beyond target 'organisms and the effect of pesticides on workers' health. On the benefit side of the equation, it gets into questions such as the current rising cost of food, world hunger, and the like. As an example of a study initiated by ESB, this program also gets into the aspects of rural sociology. For example, what effect did DDT use on cotton have on the life-style of a rural farmer? In what way was his life-style improved or diminished by such use? Under the chairmanship of NAS member Donald Kennedy of Stanford University, this 2-year study got under way July 1972; results are due next June. A funding of $300,000 was provided by the Ford Foundation, USDA, and EPA for this study. Where does the ESB input show up in such a program on pest control strategies, one might ask? In the past, the USDA Economic Research Service conducted a survey every five years to find out how much pesticide had been applied on a certain crop. Here specifically, the ESB study group last fall wrote an adviso-
ry opinion-type letter to the Secretary of Agriculture noting that this survey should be done on a more frequent basis, suggesting perhaps as often as every two years. I n this way, the group pointed out that the rapid transitions, such as the shift from the use of chlorinated hydrocarbon pesticides to the use of organophosphorus-type pesticides, could be correlated with the health of the individual farm worker, since the organophosphorus compounds are much more toxic to the people using them. A favorable reply was received; now, the
chairmanship of Norton Nelson of the New York University Medical Center, will be issued this fall. Typically, the chairman-who was selected because he is one of the best in his field-is not an Academy member but one of the other 8000 scientists and engineers who serve each year on NRC committees. The third program, which was just completed this March, has been published as the report, "Man, Materials and the Environment." Prepared for the National Commission on Materials Policy, this report details the en-
Planning session. MacDonaid, Johnson and Carpenter (/ to r j discuss obiectives of future studies
USDA survey will be performed at closer intervals of time. The second study program Is a contract with the EPA in anticipation of enactment of the Toxic Substances Control Act. This program is concerned with suggesting guidelines for testing procedures (or protocols as they are called stemming from use of the word in the pharmaceutical industry). For example, what series of tests must be performed before introduction of a new chemical on the market? As Carpenter points out, both the type and amount of testing will vary for different materials as well as different usages of the same material. Consideration must be given to the amount of material that might be released to the atmosphere, for example, whether it is to be used as a confined heat transfer fluid or in a paint formulation. The results of this $80,000 study under the
vironmental impact of materials used in the environment and cautions that both materials and environmental policy must be linked together in the same time span. Chairman Nathaniel Woolman of the University of New Mexico says that the study started in October, was funded 100% by the Commission to the tune of $100,000, and was completed in time for the final report of the National Commission on Materials Policy. In May, Howard Johnson became the new chairman of the ESB. His credentials include being chairman of the Corporation of the Massachusetts institute of Technology since 1971 and president from 1966-71. It is also important to note that Johnson is not a scientist but an economist and management specialist. Under his leadership, the ESB will continue existing projects and has launched three new ones-a first on
the development of certain environmental quality indicators, a second on recovery of oil and gas from the Outer Continental Shelf, and a third to assist the Senate Subcommittee on Air and Water Pollution in evaluating costs and benefits in pollution control. The idea that certain measurements may be useful in managing environmental quality has been suggested from time to time: to date no system has resulted. But in a new study program for ESB, Merrill Eisenbud, former director of the New York Department of Environmental Conservation. will be spearheading a 9month study to determine the possibilities for a more thorough and longrange development of the concept. Eisenbud plans a first meeting this fall; in this study the sponsors are CEQ, U.S. Geological Survey, and the Department of Commerce's Social and Economic Statistics Administration. The second new start, which did not have a chairman appointed at press time, involves the environmental impact of oil and gas recovery from the Outer Continental Shelf. This study stems from President Nixon's energy message of April 18, in which CEQ was instructed to use the Academy as a consultant in preparing an advisory report. The work was then assigned to the ESB. Exemplary of the type of studies ESB has performed in the past for various federal agencies are the following completed projects: Water Quality Criteria, an update of the so-called Green Book issued earlier by the Department of the Interior (ES&T, Sept. 1968, pp 662-3). ESB study chairman Gerard A. Rohlich of the University of Wisconsin says that the newer version was released in April and will be available from the Government Printing Office this fall. Biological Impacts of Increased Intensities of Solar Ultraviolet Radiation (1973). The study was sponsored by the Department of Transportation and Scaife funds: ESB study chairman was Kendric C. Smith of the Stanford University School of Medicine. Institutional Arrangement for, International Environmental Cooperation (1972). This study was sponsored by the Department of State, and Lynton K. Caldwell of Indiana University chaired the study group. Institutions for Effective Management of the Environment (1970). Sponsored by the Department of State, this study was chaired by Marvin L. Goldberger of Princeton and the new chairman of the Commission on Natural Resources, Gordon MacDonald. SSM Volume 7.Number 10.October 1973 893
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Plastics resource recovery dilemma Despite a number of experiences, neither the industry nor the public is satisfied with recovery technology Discoveries of plastic wastes on remote Alaskan beaches, of seagulls strangled from plastic carbonated beverage holders, and of bits of undigested plastic in the stomachs of other dead animals, all serve to dramatize the main problem in disposing of this material. Plastic in the environment is not biodegradable-a fact of which the industry and municipal solid waste treatment personnel are well aware. Ecologically. natural processes of decay are not available that would help reduce the volumes of waste plastics. Burning has been used and is still the most convenient method of disposal. But burning is not the ultimate disposal solution. For one thing, it can produce pollution problems of another kind. Landfill dumping is another method being used, but volume in this case far surpasses the need for landfill material. More and more, the plastics industry is turning to recycling, although at present the technologies are undeveloped. Still, the industry is optimistic. In a study conducted last year by the International Research and Technology Corp. (Washington. D.C.) it was concluded: "As sorting and property upgrading technology develops, and other materials in the municipal waste stream find greater return in reuse rather than combustion, similar technology in market mechanisms for waste plastics could develop." Plastics wastes comprise about 2% of the solid waste collection in the U.S. About 3 million tons were collected in 1970. According to the IRTC report, packaging accounted for two thirds of this total, industrial waste for one sixth, and household items, clothing. and construction for the remaining one sixth. Chemically, polyolefins accounted for approximately 70% of the total collected plastic waste: styrene polymers contributed 16%, and polyvinyl chloride about 12%. The three main sources of plastic wastes are the actual producers, fabricators, and users. The plastics industry. the producer of primary polymers, recycles part 3f its waste internally and sends the remainder to scrap processors fsr recovery and 894
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recycling. The fabricator, who molds the various products, recycles most of his waste internally. Finally, industrial, commercial and agricultural users, wholesalers and retailers, and private households usually have theirs hauled away to municipal disposal sites. The focus of most plastic recycling projects now under way is on thermoplastics, according to the IRTC report. These plastics, forming about 80% of the total, can be remelted again after forming. The remaining 2 0 YO-p he no I ic s, po Iye s t e r s , and epoxies-set permanently after forming and are labeled "thermosettings." These thermoset wastes, which cannot be remelted, have in the past been thrown away. However. recent experiments have shown that thermosets can be reduced and their polymers reconstituted. Experiences to date
One of the biggest and most efficient plastics in-plant reclamation systems in operation is at a Western Electric plant (Indianapolis. I n d . ) . The plant reclaims approximately 4.5 million pounds of acrylonitrile butadiene styrene (ABS) per year, and uses an additional 11 million pounds per year of virgin plastic. which the company molds by an injection process into various components for the manufacture of telephones. The process begins with the sprues, runners, and defective parts being dropped through a chute from the molding floor into a 1000-lb capacity container in the basement. At this central collection area, the ABS is packaged to avoid cross contamination with other colors or materials. The containers are stored until a need arises again for that specific material. Then. the boxes are emptied into the appropriate sorting and conveying line and automatically fed into a modified granulator. The system contains two automatic granulating devices. Of these. one is complete with a metal detector and an air clutch. I t removes the fines without the use of a separator or sifter. With equipment similar to that developed for ABS, Western Electric is also able to reclaim engineering thermoplastics, including
glass-reinforced materials, without a health hazard to operating personnel. A portion of the clean ABS regrind is immediately put back into the injection molding machine hopper. I f the material is contaminated, it is reprocessed through extruders and then pelletized. The company is finding that the amount of regrind that needs to be extruded and pelletized is slowly decreasing, while the regrind that can be fed directly into the mold hopper is steadily increasing. At present, the company sells approximately 1 million pounds of reground ABS per year to reprocessors. However, this figure will be reduced as Western Electric develops the capability of doing its own recoloring, The firm's technique, equipment, and ability to use dry colorants have reached a point where they can now stay within tight color specifications while maintaining the physical properties that are needed. Once this system comes into full-scale operation, it will recolor about 600,000 Ib per year. Typical of equipment used by reprocessors is the Vertruder of the Gloucester Engineering Co. In this system, ground plastic is melted, extruded through a screen. cooled, and pelletized.
Problems that concern most reprocessors: 0 Thermosets pack in the screens of the extruder and do not let thermoplastic materials through. Higher-melt temperature thermoplastic materials such as polycarbonates can be caught by the screen-pack in the extruder and cause the same problems as thermosets although not quite20 rapidly. Lower-melt temperature materials vaporize, go to gas, and act as filler in the extruded plastic with the resulting defects of weakness, brittleness, discoloration, and voids. Nonplastic materials such as wood, paper, garbage, and dirt reduce the quality of reprocessed plastic. Fines-tiny specks-caught in the material tend to flash in the extruder causing deep local burning points in the plastic. By introducing a reverse air flow in the grinding operation, more than 95% of the fines can be removed.
Plastic waste source. Plastic confainers are a convenience for the modern consumer, but eventually they present a serious disposalproblem
A large Vertruder system is in operation a l a Webster Industries plant (Peabody, Mass.), which reprocesses mainly scrap-polyethylene (PE) trash bag rejects from the company's blow molding operation. The operation has proved so successful that Webster now buys fairly clean scrap polyethylene film and bags to add to its own waste. At the Webster plant, recovered granulated pellets are added to the virgin input in the ratio of 5-10% scrap, although if sufficient clean scrap were available, this figure would rise to 15-20%. The firm says the cost of recovered polyethylene, including purchase of scrap and Vertruder process, is less than 50% of the cost of virgin material. Overall, however, there are problems that concern most reprocessors. These drawbacks are listed in the IRTC report (see box). Consumer plastics Projects to recycle "post-consumer" plastics have shown some promise but for the most part have failed. The Golden Arrow Dairy of San Diego, with the help of Dow Chemical Co., organized a demonstration recycling program in which the dairy's home delivery could be used simultaneously for collecting the plastic bottles. The bottles were
ground up and sent to the Ledco Co. (Brawley, Calif.) to produce plastic agricultural drainage tile by re-extruding the polyethylene. Unfortunately, local specifications prohibited the use of scrap for this purpose. At a later date, Roberts Irrigation Co. (Pauma Valley, Calif.) attempted to utilize the PE scrap to produce lawn sprinklers. This process involved grinding, ferrous metal removal by magnets, melting, and then molding by shots. However, there was so much contamination in the bottles that the hydraulic streams in the extruder were clogged in reprocessing this material. The production of these lawn sprinklers was then discontinued. The Golden Arrow Dairy demonstration, although discontinued, did potentially have commercial value. It is possible that a similar program can be undertaken elsewhere. (In both cases, the ultimate failure of the program is due to the lack of economically viable technology for cleaning waste plastics and intransigence on the part of specification engineers.) If new technology were to be applied, the program could be reinstated and be made commercially viable. Another project, undertaken in Waterville, Ohio, by the Owens-Illinois Corp. (Toledo, Ohio), achieved a certain kind of success, but left open the question of its full cost. Here the Boy Scouts collected and cleaned 5000 polyethylene containers, which were then turned over to Advanced Drainage of Ohio, Inc. (Malinta) to be remanufactured into 4200 ft of 4-in. drainage tile. The recycled material was mixed with virgin resins in a 3-2 ratio. This project demonstrated that PE can be recycled into useful products, but it gave no indication of the real economics involved. It was a oneshot program in which labor was free. And it is labor-for the most part collecting the material-that is the major stumbling block to this type of direct return plastics recycling project. The Mobil Chemical Co. (Macedon, N.Y.) successfully produces polystyrene foam egg cartons in which , it incorporates reprocessed polystyrene foam egg cartons returned by customers to the supermarket. But, again, the company can do this only because of special laborcost savings. Here the customer cooperates with market and supplier personnel by returning the original egg cartons. The cartons are then returned to the,supplier, who, in turn, supplies them back to the fabricating plant. The reclamation orocess that then
takes place includes: manual sorting, washing, melting, and extruding a spaghetti-shaped or steel material, which is chopped up into granular pellets. These pellets are mixed with virgin material and new cartons are molded. Currently the firm is recycling 500-1000 Ib of returned carbon per month. The new cartons could contain up to 25% reprocessed plastic. But the drawback again is in handling costs. Even with the assistance of the retail grocers, at no charge, indications are that widespread use of the program would be uneconomical because of the handling and transportation problems and attendant costs. What next? The problem remains, what can be done with plastic wastes? Some attention has been given to "prior treatment," or the development of plastics that will degrade after being discarded. This degradable material. if successfully developed, would reduce or even eliminate the need to recycle, not to mention eliminate the attending unsightliness of plastic litter, costs of collection, and the cost of degrading plastic articles in landfills. Such a product, however, might present disturbing side effects. According to the IRTC report. at leaSt four major questions arise when considering photodegradable polymers: Will they degrade prematurely? Is it desirable to make a complete line of plastic articles photodegradable for the sake of the small percentage that appears as litter? Are the subunits of a photodegraded polymer truly biodegradable? Is it advisable to release into the environment compounds that are otherwise locked into the plastic microstructure? Water-soluble polymers also have been mentioned as a possible s o b tion to the plastic wastes problem. Plastic developed from these compounds would "disaopear" after prolonged exposure to environmental moistures. However, the biodegradability and environmental impact of these compounds and solutions would likewise be a matter of m u c h concern. The problem, at this point, is one of safety. And whether the public and governmental regulatory agencies will accept degradable plastics is yet to be determined. Nevertheless, such potential "disposal" properties of plastics are being taken into account, and certainly should be taken into account, in determining the trend for future plastics recycling programs and technology. WSF Volume7, Number 10, October 1973 a95
Industry and air pollution control officials all want an
SO;!ambient air monitor with high sensitivity, unattended operation, and reliable record keeping, precisely why t h e .
..
Philips S02monitorfinds USuse In the January 1973 issue of Analytical Chemistry. it was reported that there were more than 60 SO2 monitors commercially available involving 13 different principles of operation. There are approximately 25 instrument manufacturing companies that offer a coulometric instrument for SO2 monitoring. One of these, referred to as "the Cadillac of SO2 monitors." the Philips PW 9700 SO2 coulometric monitor, is widely used for both enforcement agencies and industrial monitoring purposes. According to one conservative estimate. more than 400 Philips monitors are used in the U.S. and 1000 world-wide today. Of course, there are other instrument companies that offer coulometric monitors; some are mentioned in an earlier E S & T feature-Atmospheric surveillance: the current state of air monitoring technology" ( E S & T , August 1971, p 681). North American Philips Corp. (NAP) and its predecessor companies have been in the U.S. for more than 30 years. During the threat of Nazi takeover, N. V . Philips in the Netherlands safeguarded its American assets by creating what is now known as the U.S.Philips Trust in Hartford, Conn Consolidating some of its assets. the Trust soon formed North American Philips Co.. Inc.. now known as North American Philips Corp.: it is listed on the New York Stock Exchange Philips Electronic and Pharmaceutical Instruments (PEPI) is a division of NAP. PEPI, Inc.. was set up about 13 years ago. PEPI. a majority owned subsidiary of North American Philips, is listed on the American Stock Exchange. Recently, NAP announced a proposal to merge with PEPI. The present company. NAP, was the result of a merger on February 14. 1969 between NAP, widely known for its Norelco consumer and professional products, and Consolidated Electronics Industries Corp. Before the merger. the U.S.Philips Trust owned 100°/~ of NAP and 35% 896
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of Consolidated Electronics. Today, the Trust owns approximately 68% of the outstanding shares of NAP; the trust is entirely American-controlled, and its governing committee members are required to be both U.S. citizens and residents. Beneficiaries pf the Trust are the public shareholders (nonvoting) of N. V. Philips of the Netherlands. Why Philips coulometric?
In this age of instrument company one-upmanship, an endorsement by the federal EPA is the best of all possible recommendations. Perhaps the best endorsement came in a paper delivered at the 1970 APCA meeting, in which Robert K. Stevens, chief, Methods Development section of NAPCA wrote, "The Philips coulometric sulfur dioxide system is the most trouble-free, drift-free wet chemical method tested in our laboratory." He continued, "The system would be ideally suited to monitor SO2 in remote areas where technicians are not available for daily maintenance. This system has the potential of being an acceptable standard method for the measurement of SO2 in most urban environments." Subsequent to Stevens' paper, the Federal Register (Saturday, August 14, 1971. Vol. 36, No. 158) indicated that coulometry was an acceptable measuring technique. Studies funded by EPA (Contract No. CPA 70101) further established the equivalency of West-Gaeke and coulometry. The Philips instrument in particular gave the highest correlation with the official West-Gaeke method. Dutch network first After instrument development, the next step was the creation of a regional air monitoring network in the Netherlands for the monitoring of air pollutants. The Dutch national network comprises 250 remote monitoring stations connected by dedicated telephone lines to computers in nine regional measuring centers, which in turn. are connected by telegraph
lines to a master computer in the National Measuring Center in Bilthoven. Total cost of the system was 15 million guilders (about $5 million). I t is important to point out that all of this network was accomplished without legislation; it was a cooperative industry-government effort addressing a shared environmental concern. As part of the Dutch nationwide network, the Rijnmond network monitors the air for SO2 emissions in the heavily industrialized Rijnmond area
On site. Perhaps unnoticed by the pedestrians or in the industrial setting. monitors nevertheless keep watch on SO2 emissions in urban and industrial iocations to ensure a healthful ambient air
near Rotterdam. SO2 detectors are geographically located in such a way that with any wind direction eight out of a total of 31 monitors are located downwind of the pollution source. Based on mathematical modelings, 31 monitors were required in this area to obtain statistically significant data, independent of circumstances such as time of day or wind direction. By now, direct data links are planned between the Dutch National Measuring Center and its counterparts in West Germany and Belgium. The actual events leading up to the network go back several years. In 1966, Philips in cooperation with the Technical University of Einhoven, began research and preliminary contact into the development of a monitor capable of measuring SO2 in the air. In February 1968, the government-industry collaboration was made official when a development contract-the first of its kind in the Netherlands-was signed by N. V. Philips and the Dutch government for
Surely European experience with the Philips instrument was strong endorsement for the use in this country. The Philips SO2 monitor was first shown in the U.S. at the 1970 meeting of the Air Pollution Control Association. In 1971, technical personnel from PEP1 literally canvassed the U.S. for business. In this country, Philips SOs monitors have been put to use by the mining, chemical, and electric utilities industries, as well as the federal and various state and local air pollution dontrol agencies. Comments from these groups are testimony to the
the completion of the development of the SO2 monitor. I t was also during this time that a separate plan was conceived between the Rijnmond authority and Philips for the creation of a system for monitoring air pollution in this heavily industrialized Rijnmond area. That system was completed in October 1969 and was designed to measure actual air pollution levels for alerting purposes, potential air pollution levels, and trends for the purpose of long-term forecasting. It consisted of the 31. remote SO2 monitors, a transmission system, and a computer. Later. in 1970. another contract between Philips and the Dutch government, covering a threeyear period 1970-72, was entered into. I t concerned the general national network plus the development of a multicomponent air monitoring system for the measurement of NO, NO2, 0 3 , and SO2 in a single unit. A
fact that the instrument has gained wide acceptance in the U.S. The Allegheny County air quality monitoring network of the Allegheny County Health Department, Bureau of Air Pollution Control, is a completely integrated, automatic system consisting of a central control and data acquisition unit, seven remote monitoring stations including 31 sensors, and an interconnecting telemetry system linking the remote stations to the central station. Sensors in the present network include seven Philips sulfur dioxide monitoring instruments. One of the principal reasons for the selection of the Philips S O n monitor was minimum maintenance and the built-in calibration source, which provides the Bureau with the capability of having the computer command the sensor to perform a calibration check each day. The central unit consists of a real-
still later contract concerned the development of a CO monitor. Only this year, 1973, Philips introduced its multiparameter monitor capable of measuring the above pollutants plus hydrogen sulfide. Ultimately, Philips hopes to enter both the water pollution monitoring and the noise pollution monitoring fields.
U.S. track record
time on-line computer, which commands, receives, stores, and compiles data from the remote stations. Each station is polled and each sensor is checked for valid parameters every three minutes. The Bureau of Air Pollution Control has developed an Air Pollution Index (API) to provide the public with an understandable measure of daily air quality. During periods of adverse meteorological conditions, when air monitoring data for sulfur dioxide and fine particulates reach or exceed predetermined alert levels, source curtailment plans are implemented, and health warnings are issued to vulnerable residents. Neil O'Leary of the Massachusetts Bureau of Air Quality Control says that that state agency decided to go with the Philips monitor because of its good track record in Europe, meaning, of course, its good, reliable, and unattended operation. And while this reason may not be as important a consideration to a large electric utility complex, which in many cases always has a maintenance crew on hand, it may be a prime consideration to a staff-limited and growing state or local air pollution control agency. At present, the Massachusetts state air pollution control program has 15 Philips monitors and is programmed for a total complement of 25 monitors by the end of 1973 for its 50-station, statewide network. Data are telemetered to a central location, reduced to a usable form, and statistical summaries are compiled. In the national air quality standards, the Federal Government is interested in monitoring an annual average of 0.03 ppm Son. There is no 1-hr value specified in the federal standards. However, the Massachusetts standards specify both a 1-hr value of 0.28 ppm that is never to be exceeded and a daily average of 0.105 ppm in addition to its annual average of 0.025 ppm, tighter than the federal value. Lewis Potter of the San Francisco Bay Area Air Pollution Control District says that its agency has three Philips SO2 monitors. These units are installed in mobile vans that are maintained by the Bay Area control agency. All are used to measure SO2 ambient air concentrations around industrial perimeters or in complaint monitoring. Nearly all the heavy chemical and oil industry in the Bay Area is located in Contra Costa County. For example, Revised Regulation No. 2, dated Nov. 5, 1971, required an industrial network of 29 monitors, and a total of 38 are in operation today. There are eight industrial opVolume 7 , Number 10, October 1973
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erations in the Bay Area, mainly in Contra Costa County, using collectively a total of 29 monitors for record keeping of their industrial emissions. Surprisingly, 21 of the 38 are Philips monitors. Of course, if and when new industrial plants move into the area, then additional SO2 rnonitors would probably be needed. Most of these monitors are equipped with a recorder on each monitor. As a whole, there is no centralized telemetered readout for all 38 monitors, and Potter indicated that such a central telemetering network would not be needed for several reasons-cost plus the fact that any one company might be sensitive about its emissions. The Bay Area vans are also called into play to fill in gaps in the monitoring network and to sample and record emissions in any complaint area. Their revised regulation also requires urban air monitoring in addition to industrial perimeter monitoring. What was needed, and the Philips monitor qualified, was an instrument sensitive to 0.04 ppm on a 24-hr average SO2 and also one able to detect a 3-min. duration of 0.5 ppm Son, both of which are required in the indlistrial perimeter monitoring required by the Bay Area control agency. I t was also important that the monitor be able to distinguish between 0.02 and 0.04 ppm SO2 as well as be able $0 monitor unattended for long periods of time. The Bay Area Regulation No. 2 also requires monitoring for H2S emissions. The Philips monitor was useful for this purpose since the SO2 monitors can be readily adapted to measure H2S. For example, the SO2 monitor can be switched to a H2S mode and range simply by adding a filter to remove the SO2 from the gas sample stream. Incidentally, the filter for SO2 was developed by Dario Levaggi, director of the technical division of the Bay Area control agency.
building a new copper smelter, the Hidalgo smelter, which is currently under construction in southwest New Mexico. To be completed in the latter half of 1974, the Hidalgo will have several SO2 monitors. Currently, each of these monitors is equipped with a recorder and strip pen chart to obtain a permanent record of SO2 ambient concentrations. PD spokesmen indicated that the company is in the process of developing telemetering and data collection stations, one at Douglas and one at Morenci. In Arizona there are a number of ways that a company can comply with the state control agency regulations to meet air standards. One of the options is called closed loop or more correctly, the intermittent production curtailment method. I t is the latter option that PD chose for its Douglas and Morenci operations. For example, if and when certain ambient air concentrations of SO2 are exceeded, or predicted to be exceeded, then production cutbacks are put into effect. Another copper smelting operation uses the Philips monitors. J. R . Denny of the Newmont Mining Corp. (New York City) says that in early 1973 the company installed a sevenstation monitoring network. each with a Philips SO2 monitor, at the Magma Copper Co.'s mine at San Manuel, Ariz. This network is closely akin to the Rotterdam system. with visual light displays and other audible and visual w.arning devices. Another industrial user, Detroit Diesel, uses the monitor in two different ways. Dick Bourke of the Detroit Diesel Allison Division of General Motors which is geared for the production of gas turbine engines, diesel engines, and heavy duty transmissions tells E S & T that they put their Philips SOn monitor into use in early 1972. In the first mode of operation, the monitor is placed in the center of the Convincing industry industrial complex to measure on a continuous 24-hr. basis the concenExperiences include public electric trations of S O n from the manufacturutilities, mining operations at copper smelters, chemical operations at SUI- ing operation. The plants have both coal- and oil-fired boilers in their furic acid manufacturing plants, and power houses. In the other mode, an industrial plant site. Major copper Bourke says the monitor I S used in smelter users, for example, are the field to measure downwind conPhelps Dodge Corp. (PD) and Newcentrations of SO2 which are then mont Mining Corp. plotted as a function of distance from All told, PD has over 30 SO2 monithe power boilers. These data are tors, 29 are Philips monitors with a used in diffusion modeling. total of 10 SO2 monitors (not all PhilIn April 1972, Stauffer Chemical ips monitors) around its three copper placed eight Philips SO2 monitors smelters in Arizona at Ajo ( 1 ) . Dougaround its large sulfuric acid manulas ( 7 ) , and Morenci ( 2 ) . PD operfacturing plant, the Manchester ates another nine SO2 monitors in the south of Arizona in nonmining plant, in Houston, Tex.. to monitor SO2 emissions from its four acid areas to gather background data on ambient air that is not in the vicinity units, two regeneration units, and two recovery units. Data are telemeof the smelters. The corporation is 898
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tered over the telephone line, run into the control room of the Manchester plant, and to two multipoint recorders. Alarm systems, both visible and audible, are set off when certain SO2 concentrations are exceeded: then, plant personnel take corrective action at several different levels of emergency operations. Stauffer is so pleased with the Philips monitors that the company installed the same monitor at its other sulfuric acid manufacturing facilities throughout the U.S. Plants are located at Baton Rouge, La., Pasadena, Tex., Baytown, Tex., Axis, Ala., Martinez, Calif., and Fort Worth, Tex. Electric utility operations are also finding the SO2 monitor useful. George Titcomb of the Tennessee Valley Authority says that TVA has a total of 30 Philips SO2 monitors. About 25 were installed a bit earlier, and the remainder were to be installed by July 1 under orders from the Tennessee Air Pollution Control Board. The monitors were installed for ambient air monitoring at TVA coal-fired steam plants: most of them were installed during April-June this year. TVA operates eight coal-fired plants in Tennessee, two in Alabama, and two in Kentucky. And at each of the coal-fired plants in Tennessee, there will be three or four Philips monitors. Of course, there are other monitors from other instrument manufacturing companies that are used to monitor SO2 as well as other pollutants. In the next couple of years. TVA plans to collect all ambient air data by radio telemetry. A t each coal-fired plant, there will be a minicomputer controlled data logger which, in addition to recording SO2 data, will collect data from river temperature stations and from meteorological sensors. In the TVA case, the Tennessee air control agency gave T V A the options of monitoring either its ambient air concentrations of SO2 or total emissions from its stacks. TVA chose the former. In general, the offhand assumption is that the monitoring of the stack gases would result in tighter controls for the utility. Duquesne Light Co. operates three coal-fired and one oil-fired combustion turbine peaking power stations near Pittsburgh, Pa. ?he Pennsylvania utility acquired three Philips S O n monitors in February 1972 and uses them in semimobile vans along the perimeter of its new power plant, the Cheswick power station (outside Pittsburgh) which was available for full load in December 1970. SSM
Camping, environmental Rogers Environmental Education Center summer camping program aims at instilling environmental awareness Summer is the season for outdoor camping, and this past summer was no exception for about 200 youngsters who got a firsthand look at environmental problems at the Rogers Environmental Education Center in Sherburne, N.Y. Operated by the New York State Department of Environmental Education, the center conducted a series of four week-long environmental workshops for youngsters 13-16 years old designed to acquaint them with the major environmental problems confronting society today. The environmental camps are only one phase of the educational program of the Rogers Center which also includes teacher workshops, community education, survival training courses, and natural history programs.
ES&T goes to camp ES&T visited the Rogers Center during the week-long program for 13-14-year-old girls. The program was an ambitious one, consisting of half-day sessions devoted to the various ecosystems within the confines of the Rogers Center. Formerly a New York State game and fish farm, the center has a wealth of natural resources available. The focal point of the Rogers Center is a man-made marsh, a resting and breeding ground for several species of waterfowl, birds, and mammals. There are hardwood forests, open fields, fossil beds, and nearby rivers, ponds, and lakes. Using the various communities as starting points, the girls were introduced to stream and forest management, trees and animal identification, and the problems of mineral balance and natural resource use. They collected plankton and observed the effects of water pollution firsthand. They studied the elements of air pollution and solid waste management. And they had a ball. That, of course, was a major objective of the program, according to John Weeks, director of the Rogers
Center. Rather than burden the campers with a morass of factual material which they couldn't be expected to retain, the idea was to expose them to the interrelatedness of all life and help them form an appreciation of the role man plays in altering the environment. The campers quite literally got a taste of "environmental living" by feasting on edible wild plants and animals. They made clover tea, learned about cattail pollen biscuits, and collected wild onions. They sampled woodchuck legs and crayfish tails, the more adventurous campers eating the latter raw. The camping portion of the program was coordinated by Lauren Vredenburgh, chairman of the biology department of the Bainbridge-Gilford Central school in Bainbridge, N.Y. Vredenburgh, who often brings classes to the Center on field trips. is excited about the impact the Center can have on youngsters who might otherwise not have a chance to reflect upon the quality of their environment. "We get kids from all over New York-big city kids, small town kids -who for the first time are being introduced to the inner workings and beauty of nature." Vredenburgh says. " I t makes quite an impression on most of them." Indeed it seems to. Many of the campers ES&T talked with had been to camps of the Girl Scout-, YWCA-, 4-H-variety before. Almost to a girl, they preferred the Rogers Center experience. Suzanne Boyden, a ninth grade student from Dryden, N.Y., and a fledgling ornithologist, liked the informality of the camp and the opportunity to explore on her own. Helen Ray, a ninth grader from Delhi, N . Y . , who wants to be a computer programmer, agrees with Miss Boyden. " I t ' s more fun than the other camps," she says. "The counselors are freer and more open." Annette Kelley, a ninth grader from Hamden, N.Y., likes the fact that
Junior loggers. Campers learn to estimate the volume of timber in a tree with the help of a Biltmore stick she's learning something but having more fun than she might have in the classroom. "They don't push you here and they don't really force stuff on you," Miss Kelley says. What will the campers carry home with them and how much will they remember about timber management, wildlife conservation, or pollution control? Vredenburgh and Weeks don't really care whether they remember the specifics, but they're sure the campers will retain the big picture and a newfound sense of appreciation for the world around them. The new experiences in themselves will be rewarding, the camp staff feels. Miss Ray. who the day before had an eyeball-to-eyeball encounter with a rambling muskrat in the marsh, summed it all up enthusiastically, saying, "Wow! I've never seen a muskrat that close before." And ES&T's roving reporter felt much the same way as he stood at dusk in the Roger Center's glassed-in observation deck overlooking the marsh and watched a wood duck glide across the glassy water. HMM Volume 7 , Number 10, October 1 9 7 3
899
Rather than trying to treat vast amounts of waste water. canners are installing more pollution-free processes The fruit and vegetable industry in the U.S. is big business. According to estimates by. the National Canners Association ( N C A ) . some 170.000 persons are employed in 1800 canning and freezing plants. Each year, the industry eats up 26 million tons of raw products, discharges 83 billion gallons of waste water, and generates some 800 Pillion pounds of BOD. 392 million pounds of SS, and produces 800 millior tons of solid waste residuals. One of the vegetables which gets more processing than most and generates more than its fair share of pollution is potatoes. Potato processing uses enormous quantities of water. The water used in peeling alone may be 300-600 gal for every 1000 lb of potatoes peeled. On commercial lines, capable of peeling about 40.000 lb of potatoes per hour, that figures out to between 200-400 g a l l min. And because potatoes are so high in starch, the BOD of potato processing waste water is quite high. In some people's mind. at least, pollution from potato processing is complicated by the fact that potatoes are grown on marginal land which also just happens to be prime recreational land. An example often cited is the potato processing plants in the wild Snake River country of Idaho. Although some pollution potential arises from virtually every step of the canning or freezing process, two phases-peeling and blanching-are responsible for the I on's share of the trouble, according to Walter Rose of NCA Western Research Laboratory in Berkeley. Calif. Peeling is a must with some fruit and vegetables, including peaches, tomatoes. and potatoes. And the pollution from peeling arises largely from the chemicals that must be used to soften the peels so that they can be removed mechanically. Blanching is a process which uses hot water to inactivate enzymes and displace oxygen from the tissues of certain vegetables. Except for apples which are subject to oxidation, fruits are generally not blanched. But blanching is obligatory for frozen, and some canned, vegetables. To clean up pollution from fruit and vegetable processing, there's always 900
Environmental Science & Technology
the option of installing treatment plants. Unfortunately, however, biological plants which work fairly well for food processors on a small scale often run into difficulty at scale-up. I t seems to be something of a mystery to engineers just why the plants don't perform up to specifications. But an alternative which has been receiving increasing amounts of attention lately is to re-engineer the peeling and blanching processes. The object is to reduce hydraulic loading and at the same time cut BOD and COD. N e w processes Along those lines, two fairly new processes-dry caustic peeling and dry blanching-show great promise for the future. Indeed, dry caustic peeling is now in the first stages of commercialization for potato processing plants. And it looks as if the first generation of machinery for dry blanching will be off the drawing boards and on the cannery line in time for the 1974 processing szason, which runs from June to November. In the conventional potato processing plants, potatoes are peeled by first dipping them into a concentrated solution of sodium hydroxide. The sodium hydroxide softens the potato skin and the area of the potato immediately under it. The softened skins are then removed by water spray, giving rise to an effluent which is highly alkaline. But the dry caustic peeling process, pioneered by Arthur Morgan, Charles Huxall, R. P. Graham, M. L. Weaver, and M . R. Hart at the USDA Western Regional Laboratory (Albany, Calif.), promises to give a superior product and cut pollution at the same time. Magnuson Engineers Corp. (San Jose, Calif.) has developed the commercial machinery to put the process in operation, according to Traver Smith, Magnuson's vice-president. In the USDA-Magnuson process, potatoes are metered into vats containing dilute caustic solution. After a short period of time, potatoes go by roller conveyor through a gas-fired infrared unit. The infrared radiation dries the caustic solution and speeds up the peel-softening action. The potatoes then enter the Magnascrubber, a tumbling unit where stud rubber rolls
mechanically remove the peels from the potatoes. With the peels removed, the potatoes are washed briefly and placed in a holding tank to keep them from oxidizing. Cutting the costs The benefits of the dry caustic process are many, according to Smith (for a point by point comparison, see table, page 901). First of all, the amount of caustic used in the dry blanching process is about '/4 to '/3 of that used in the conventional caustic method. The time spent in the dip and the holding period after the caustic treatment is reduced drastically. The amount of peeling water used in the dry caustic method is about that used in the conventional method. And besides cutting pollution, the process costs less-somewhere from */3 to '/* as much as the conventional method. There are other advantages as well, Smith points out. In the conventional process, peels and water get mixed up together and the final solids concentration of the effluent is about 0.7-1.9%. The peel waste from the Magnascrubber unit, on the other hand, is a brown gluey substance about 15-20% solids (roughly the same solids content as the average potato). With the Magnascrubber, iup to 85% of the total peel waste solids are kept out of the plant water effluent. The remaining 15% from the washer is processed with other plant effluent. On the other hand, primary waste treatment recovers only about 50% of the solids from the conventional wet caustic peeling method. The rest must be removed by secondary treatment or perhaps discharged into streams, lagoons, or spray irrigation units. Since the peel waste can be recovered virtually in one step, it can be collected and disposed of in an environmentally acceptable fashion. The peel waste emerges as a sticky, hard-to-handle mass with a pH of about 12. The peel waste undergoes self-fermentation, however, dropping the pH to about 5.0, which makes it ideal as a blend with potato trim wastes-eyes, defective potatoes, spoiled or dropped potatoes-for animal feed. I f it's too expensive to ship
Comparison of peeling processes for french fry manufacture Measured characteristic
None
20,000 ib/hr 6-10% on new potatoes 10-13%,on old potatoes usually about 5% less than conventional caustic peeling 5-10% NaOH on new potatoes 10-1 2% NaOH on old potatoes , 30-45 sec on new potatoes 45-60 sec on old potatoes 180-200°F on new or old potatoes 2-3 ib NaOH/1000 Ib potatoes 14-21e/1000 ib potatoes 30 sec to 7 min max 90 sec exposure to 1650°F ir 8c/lOOO Ib potatoes
None None 30/1000 Ib potatoes
2,800,000 Btu/hr $1 60/hr 2c/ 1000 Ib potatoes
38-73t/lOOO ib potatoes
24-310/1000 Ib potatoes
Barrel washer with large volumes of water Heavy spray washing
200-400 gpm (for 40,000 Iblhr)
Dry scrubbing with soft studded rubbe? Soft polypropylene cylinder brushes with light water spray 25-30 gpm (for 20,000 Ib/hr)
300-600
75-90
2 5-5 0 Usually from 1/,6-1J4-in layer of gelatinized heat penetration over entire sur-
0 63-0 75 From none to 164-in(at 90 sec ir)
Typical line capacity Typical peel loss
40,000 ib/hr 10-15% on new potatoes 13-20% on old potatoes
Caustic solution strength
8-16% NaOH on new potatoes 16-20% NaOH on old potatoes 2-4 min on new potatoes 3 - 6 rnin on old potatoes 180-200°F on old potatoes 160-180°F on new potatoes 5-10 Ib NaOH/1000 ib potatoes 35-70&/1000 Ib Potatoes 3-10 rnin None
Caustic dip time Caustic solution temperature Caustic consumotion Caustic cost 0 7e Ib NaOH Holding time after caustic dip Infrared treatment
IR gas fuel cost 6 5.7c/ therm (one therm = 100.000 Btu) Total aas burned Gas cost on hourly basis Steam cost b 65c/lOOO Ib of steam Total cost of caustic, fuel and steam Peel removal method after caustic softening Final cleaning
Water used in peeling Drocess Water use rate in peeling Gal water/1000 Ib potatoes Lb water/ib potatoes Cook ring on potato surface
Dry caustic peeling process
Conventional caustic peeling process
face
Appearance of peeled potatoes
Usually yellowish-gray coior with gelatinous surface from cook ring
to feedlots, the sludge can be disced into the ground, returning nutrients. Developed for peaches The dry caustic peeling method was originally developed for peaches, according to NCA's Rose. In an experiment to prove out the process on commercial peeling plants for peach halves, the volume of water needed was cut to '115 of that required by the conventional process. The COD and SS contents of waste water from peach lines using the dry caustic method were about '/3 of those in the conventional process. But the dry caustic process has not made any great inroads in the fruit canning industry. The reason, says Magnuson's Smith, is that the pollution potential from peaches.
Very white appearance with surface texture normally associated with thin-skinned early-season, peeled potatoes
apricots, and the like is not nearly so great as that from potatoes. The peach peeling solutions, for example, use less caustic, and the canners have not really been under the gun in the way that potato processors have. The second most polluting process in the canning industry is blanching. Blanching, carried out to deactivate enzymes, is done by heating vegetables either with water or steam. Generally, vegetables pass on a conveyor belt to a high-temperature box or get dipped in water to raise their temperature above 155°F. Large volumes of water are needed, and the discharge water is high in BOD. A s a way past the problem, Jack Ralls, Western Research Laboratory of NCA, suggested that it might be possible to use the hot combustion
products from natural gas in place of water to blanch vegetables. In plant trials of the hot gasblanching process on spinach, freshly washed spinach was spread on a conveyor running through a box in which the combustion products of a 125,000-BTU/hr natural gas burner were blown through the spinach. The effect, according to NCA's Rose was to produce a fluidized bed of spinach. And the results were favorable. Tasting panels decided that the hot gas-blanched canned spinach tasted different from conventionally blanched spinach, but that the flavor was still good and would meet with consumer approval. Laboratory tests showed the spinach to be more nutritious than the conventionally blanched product, however. Although there were no major differences in phosphorus, calcium, or magnesium content, the hot gas blanching retained more ascorbic acid and destroyed fewer water-soluble vitamins. From the pollution control standpoint, waste water volume was reduced by 99%. And COD per ton of product was reduced by 96%. The process looks so good, according to Magnuson's Smith, that his company plans to engineer a prototype model for the production line during the 1974 canning season. More problems Apart from the successful inroads made in cutting pollutions from the peeling and blanching processes, however, there are still pollution problems to be licked by the food processing industry, NCA's Rose points out. First of all, a great deal of waste water is generated by the stringent cleanup rules imposed on the industry by the Food and Drug Administration (FDA). FDA requires a complete cleanup at each break, at meals, and at shift changes. This cleanup generates tremendous volumes of detergent-laden water. Even the more advanced high-pressure, low-volume washing systems still require significant quantities of water. Some work involving gamma raysterilization of the equipment has been done, but it is not yet very practical, notes Rose. Another process requiring large amounts of water is the cooling step following blanching. Work is now under way to develop a suitable air-cooling system which would replace hydrocooling with evaporative cooling. Preliminary work is encouraging, Rose says, and tests show that temperatures of about 200°F can be lowered to about 100°F on a 6-ft length of conveyor using a cooling system which blows air from a plenum under a vibrating HMM conveyor. V o i u m e 7 , N u m b e r 10, October 1973
901
Another lesson in resource recoverv ~~~~
~~
I
An integral part of all recycling operations, separation of'the various components of refuse may be accomplished by a variety of met hods In dealing with municipal refuse, whatever its final fate, ES&T learned that shredding is an important step ( E S & T , April 1973, p 300). Many experts feel that it is necessary, before ultimate disposal or recovery, to go a step further-classification of the refuse after shredding. "We believe that shredding and air classification are necessary first steps in any solid waste system where mineral recovery, fuel preparation, composting, or other resource recovery techniques are to be employed," explains Bert Hildebrand, manager of material recovery systems, Combustion Power Co., Inc. (Menlo Park, Calif.) However, as an industry, solid classification/separation is waste still in its infancy. Separation has been used in mineral, food processing, and other industries for years, but applying these techniques to garbage isn't a simple move. Most waste separation systems are laboratory projects or pilot plants at the most. The largest separation unit in the U.S. went on line last month in St. Louis, Mo., at the city's waste processing site. Union Electric Co. has been burning shredded garbage in its Power Plant boilers, but several problems occurred. The solid waste fuel is blown into the boiler through pneumatic tubes. However, when the solid waste shoots around bends in the pipe, the heavy material-glass and metals, for example-hits the outside of the bend in the pipe and erodes the pipe until holes appear. Another problem with the heavy materials is that they do not burn and therefore have no heating value and fill up the bottom ash pit faster than officials like. Union Electric sells its bottom ash for use in road construction, and the quality of the ash decreased with the appearance of unburned waste. However, by employclassification/separation, the ing heavy, mostly nonburnable materials will be pulled out of the trash to solve bbth problems. With the aid of an 902
Environmental Science & Technology
EPA demonstration grant, the City of S t . Louis installed the 45-t/hr air classifier built by Rader Pneumatics, Inc. (Portland, Ore.). The equipment began shakedown trials last month.
Air classification One of the most promising methods of separation is air classification. Generically, an air classifier is a piece of equipment that subjects a stream of solid waste to a stream of air with the theory that the heavier mostly inert items-metals, glass, dense plastics, rubber, stones, and organics-are unaffected by the air flow and fall through, and the lighter combustible items-paper, film plastic, fabric, and some wood-are entrained and flow with the air current. Air classifiers separate materials according to density and shape of the particles. The basic type of air classifier has a vertically rising airflow in a vertical column through which solid waste is dropped. The heavier items fall through the air flow to a bin in the bottom of the column, and the lighter materials are carried to the top and collected. The zigzag air classifier is a slight modification of the vertical air classifier in that rather than a straight column, the column zigs and zags or baffles are placed within the vertical column. The resulting turbulent atmosphere pulls the material apart so that each piece can be acted upon independently. Combustion Power Co., Inc., Stanford Research Institute (Menlo Park, Calif.) and Scientific Separators, Inc. (Denver, Colo.) have developed and tested zigzag air classifiers. In St. Louis, the simpler, less expensive vertical column air classifier will be initially used. If it does not separate the refuse adequately, the zigzag type will be installed. The zigzag classifier has the longest experimental track record but has not been implemented on a large-scale facility. The National Center for Resource
Recovery, Inc. (NCRR) (Washington, D.C.) has a 10-t/hr mobile air classifier (built by Combustion Power Co.) on a van that tours the country to acquaint people with techniques of resource recovery. The second basic type of air classifier is the horizontal air flow unit developed by the U.S. Bureau of Mine's Salt Lake City (Utah) Metallurgy Research Center. In the BuMines raw refuse pilot plant (Edmonston, Md.), solid waste is dropped vertically through a horizontal air flow. Lighter items-most paper, light plastics, and fabrics-are blown laterally past a divider and are pulled at the same time by a suction fan at the end of the column (to a IO-ft. diameter cyclone and are then collected). Materials blown past the divider but not affected by the suction fan or removed fall onto a conveyor that carries them to a rotating screen. These heavier wastes-glass, aluminum, food wastes, leather, plastics, wood, rubber, and heavy paper-can be further separated. Very heavy objects fall vertically through the stream of air to a conveyor which carries them to a container. The Bureau of Mines College Park Metallurgy Research Center operates a 5-t/hr pilot plant at Edmonston, Md., where ferrous metals, nonferrous metals, glass, plastics, and paper are reclaimed from unburned raw refuse. A flail mill coarsely shreds the refuse (rips open bags and boxes), which is taken by conveyor underneath a hood where suction pulls off the very light materiallarge pieces of plastic and big sheets of paper, for instance. The remainder of the refuse is conveyed for further separation. BuMines has another air classifier known as a three-stage aspirator. After passing through a shredder, light materials are pulled upward by suction through baffles, and heavier combustibles fall through an open bottom into a collecting bin. Another concept in air classificaz
Sorting. The horizont (above) separates so currents and suction (right) uses a mediun er than air; and in a I cess, paper and plast ciently separated (/eft)
tion is being developed by General Electric Co. (Schenectady, N.Y.). A 4-5-ft diameter cylinder is inclined and rotates on its axis. Solid waste is shredded and introduced into the cylinder by conveyor. Air is pulled from .the bottom of the cylinder up through the top into a large chamber in which the velocity of the air is reduced to the extent that anything pulled through the cylinder drops out. The rotating cylinder keeps the material mixed, and the lighter wastes gradually work their way up with the air flow into the top and are deposited in
the expansion chamber. The heavier materials, not picked up by the air flow, move countercurrently down the cylinder to the bottom where they are collected. A pilot unit is located in Shelbyville, Ind. Another type of research classification is termed ballistic separation. The Franklin Institute (Philadelphia, Pa.), in conjunction with an EPA demonstration grant, developed a system whereby solid waste is dropped on a revolving paddle wheel which projects the material laterally. The lighter material falls into the nearest bin while heavier materials are thrown farther away and land in other bins. Other types of air classification are modifications of these basic types. For example, three vertical air classifiers in a row can draw lightest materials from the first column into the second column which has a different air velocity. The next successive heavier items fall through, and again the lightest materials go into the third column.
The F8orest Products Research -...^_I_:_^ Laboratory. , -~, - Aw: - - -~ u %v~vI 8, :b^w. 1I :I> ~ wurntr8y . with air classification techniques to separate various paper commodities -wood, cardboard, white paper, newsprint. Such mixtures of paper have been a headache to paper recyclers. Wet classification Waste separation'can also be accomplished in a wet, rather than a dry, system. Wet classification takes place after refuse is wet ground, usually by a hydrapulper (as exemplified. by the Franklin, Ohio, solid waste facility--ES&J, Oct. 1971, p 998) which consists of a tank with blades in the bottom that pulp and mash the material as water is added from an opening in the side. One separation technique, the socalled junk remover, works ancillary to the hydrapulper's functioning itself. Beneath the blade is a screen with y4-in. openings. Materials ground small enough to pass through the openings do so and move to the Volume7, Number IO, October 1973
903
next separation unit. Other items, such as tin cans that are not able to pass through the screen, are thrown around the sides of the hydrapulper. Their density and speed are sufficient for them to work their way countercurrent to the incoming water flow: they then move down the water chute and are collected at the bottom. The screened slurried waste leaving the hydrapulper can be further separated by a liquid cyclone. The slurry enters the top of a conical cyclone and moves tangentially around the outside of the cone. At the bottom, the slurried waste reverses direction and flows up through the center of the flow that is going on around the outside of the cone-the phenomenon of vortex action. A t the bottom of the cone where flow velocity drops, heavier materials-stones. ceramics, glass, metal-drop, and the lighter items continue with the flow back up through the center and out for further processlng. The rising current or water elutriator, developed by BuMines, functions on the same principle as rising air classifiers except that the medium is water rather than air. Material is introduced to the top of a column with water flowing upward from the bottom. Glass and wastes heavier than the water flow pass to a lower portion in the column. while the food, paper, and lighter materials rise with the current and are skimmed off at the top. Heavier materials than glass then drop to the bottom. Finer separation All the techniques covered above are really gross separations-heavies and lights or noncombustibles and combustibles. Downstream from these operations, other separations may be desired or required; for instance, the heavy fraction contains metals, aluminum, glass, and rock. To separate these materials, various techniques have been refined. Perhaps the most straightforward is ferrous metal extraction, which is based on ferrous metals' attraction to a magnet. The heavy fraction of a waste stream is passed by conveyor near a magnet, and the fer.rous materials are pulled off while the unattracted items are unaffected. The incremental costs of adding the magnet are relatively small. Unfortunately, other components of the solid waste stream are not so easy to separate. D,fferent materials do n o t have characteristics sufficiently different to be used as a basis for separation. Screens can also be used to sort various segments of refuse. The BuMines pilot plant in Maryland also includes a rotating trommel screen 904
Environmental S c i e n c e & Technology
with 1-in holes. Glass, food wastes, and small amounts of other material pass through the holes, and large items are sent to be reshredded and classified. Froth flotation is primarily used to recover a clean glass fraction from a mixture of glass, stones, ceramics, brick, and metals. The waste mixture is put into a tub of water with a special chemical to make the glass particles attractive to air. Air is bubbled through the bottom of the tank. and the glass particles attract and hold air bubbles until they float. The result is a froth consisting of glass particles and air bubbles floating on the surface which are then skimmed off. Meanwhile, the other materials remain at the bottom of the tank. But froth flotation only works for glass particles that are too small for color sorting. BuMines has a froth flotation unit, and such a system is planned for the resource recovery plant at San Diego, Calif. Water jigging is another method to separate fine glass particles from metals and other wastes. A pulsating water bed causes glass particles to float to the top of the mixture while the heavier elements tend to go to the bottom. This technique has been developed by BuMines for separation of both raw refuse and incinerator residue. As a rule, 60% of the product from the liquid cyclone in wet separation is glass. This glass is too large for froth flotation but is large enough for color sorting (glass must be sorted into clear and colored fractions before it can be reused by glass factories). Sortex Co. of North America has developed a color sorter with which the BuMines is experimenting and which is in use in Franklin, Ohio. Simply, the glass is placed on a moving conveyor belt and is shot off the end so that each particle has a trajectory. In flight it passes between reference background and a light source. As the particle falls through this area, a sensing device determines whether the particle matches the reference background. I f so, nothing happens, and the particle falls into a bin. I f it doesn't match, the seFsing device activates an air jet that pushes the particle off its trajectory path and into a different bin. The speed of this system must be weighed against the accuracy of separation. To increase separation accuracy, the colored-sorted fraction could be run through the system again for optimum sorting of the clear and colored mixtures. Also, the colored (green-amber) mixture can be run through a color sorter with a different reference background to separate the two colors . After ferrous metals have been
picked from the waste stream, other metals may be removed by heavy media separation. The liquid medium is treated with ferro-silicon, or magnetite, or other organic fluids to give the liquid medium a certain specific gravity. The wastes are put into the tank, and those with a lower specific gravity than the liquid will float and those with higher specific gravity than the liquid will sink. The floating materials can then be skimmed off the top. There are a few problems, however, with heavy media separation. With extended use, the medium becomes more dense and surface tension increases. Therefore, an item which would normally sink may, indeed, float i f the surface tension is great enough. This problem may be solved by churning the medium or running the waste stream through a shredder to produce a particle size and shape to optimize heavy media flotation. Theoretically, all metals react to magnetic fields, although not in the same manner as ferrous metals, if the magnet is strong enough. Under an EPA demonstration grant, Vanderbilt University has developed this concept to separate various metals in automotive scrap-chromium, cast iron, aluminum, copper, and zinc. The wastes are put on a conveyor belt and passed over a high-intensity electromagnet. With a pulsating action the magnet increases the magnetic field intensity, and a certain metal will shoot right off the belt. Combustion Power Co. has a similar system to separate aluminum from other metals. BuMines has a laboratory device for separating paper and plastics called an electrostatic separator. When damp, paper conducts electricity and will "jump" from a rotating drum to an electrode and be collected. Plastic is brushed off from the drum and collected. Problems thus far are the low capacity of the unit and distribution across the drum. Where we stand The resource recovery plant at Franklin, Ohio, is perhaps the furthest along in materials separation technology, and it uses wet separation. I t is, in a sense, still a pilot plant handling 50 t/day. However, air classification, say the experts, is close behind, and all are waiting to see how the air classifier at Union Electric Co. functions. There are 4-5 times as many separation methods as those covered in this article, according to EPA's Resource Recovery Division, but few appear to be as technically and economically feasible for use in solid waste. CKL
