Immobilizing Liquid Organic Laboratory Wastes Using Granular Activated Carbon Amos Turk, Harry Karamitsos, Khizar Mahmood, Jahangir Mozaffari, Rivka Loewi, and Vicky Tola The City ~ o l i e ~ e , York, ~ e wNY 10031 The dis~osalof chemical wastes from academic and industrial faboratories can be a demanding and expensive task (1. 2). The ~roblemis ereatlv mamified when the che&ch identitiof the w a s c i s urknowk. This paper presents our fmdings on the application of eranular activated carbon (GAG) as a medium for im&&ing liquid organic laboratory wastes of known characteristics (but not necessarily known identity). The paper also reviews the U. S. Federal regulations concerning the identification and listine of hazardous waste. In brief. the immobilization method wnsists of adsorbine the organic liquid on a sufficientmass of carbon so that the resulting solid satisfies the following criteria: (a) It is no longer wet; (b) when it is exposed to the environment and subjected to the worst expected conditions of wetting (acid rain), its leachate does not add any detectable pollution to surface runoff or to groundwater; (c) it has little or no odor. When federal and local regulations allow such wastes to be disposed of with ordinary municipal garbage, the potential savings compared with other methods of disposal can the federal regulations are strinbe very &eat. gent and complex, and the chemist should not assume that the method described here conversion - - is - a ~ catch-all for the ~--~ - -~of all organic liquids to nonhazardous solids. A summary and interpretation of these regulations appear later in this paper. Furthermore, local regulations may be even more strineent than federal ones. For dis~osal. . bv" whatever rout< of a large variety of small of organic liquids, it may be economically advantageous to immobilize each of the liquids separately, then wmbine the resulting solids to form a single batch. As will be noted later. mimation of immobilizedadsorbates from granule to granuik is so slow that such mixing is permissible.
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ow ever,
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~~
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Granular Activated Carbon (GAC) The activated carbon to be used should be granular rather than powdered, to avoid dusting during the mixing procedure. The size (largest dimension) available will be typically between 2 and 7 mm, and the particles may be rough granules or extruded cylindrical pellets. For most applications, unimpregnated virgin"^ carbon is the best choice because it offers the highest udsorptive capacity (3,.
The carbon we used in this study was a coal-based pelletized product. The pellets were 3-3.5 mm in diameter and 5-7 I&long. The adsorptive capacity of activated carbon is generally r a t e d by i t s carbon tetrachloride activity (4), i t s chlorofluorocarbon activity (5), or its iodine number (6). The first two measures are used for quality control ot'gasphase activated carbons: the chlorofluorocarbon procedure was develo~edto avoid the toxicitv of cnrhon tetrachloride. -but restrickons on use of chlorofl~orocarbonsmake many laboratories stav with the CCL method. The iodine number is a generd indicator of the porosity of an activated carbon and is used for oualitv control of carbons intended for aqueous-phase appiicati&s. The carbon used in this study had a CCl, activity of 64% and an iodine number of 1056, attributes typical of a good commercial product (3). Commercial sources of activated carbon are listed in Thomas Register under "Carbon: Activated." The carbon used in this study was obtained from COH Corporation, Argonne Road, Brewster, NY 10509.
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Immobilization Procedure For organic liquids of known identity, the organic liquids for which this method is applicable are those whose boiling points are above about 45 'C. The liquid may be a single substance or a solution with liquid or solid solutes. However, the method is NOT applicable to liquids that contain any shock-sensitive or strongly oxidizing components. Lists of these cateeories of inadmissible substances amear in various texts ( f 8 ) . Cautions for Working with Hazardous Chemicals Protect your eyes with safety goggles. Wear a lab apron and gloves. Work in a fume hwd.
Have a separator? or d r o ~ ~ i funnel ng on hand. Alternawhose tip is restricted so tively, a lon&stem& 60° that liquid flows down from it a t about 100 mumin can be used. h e capacity of the funnel should be no more than about 500 mL. Place the required amount of carbon in a plastic, glass, or metal dish. The data of Table 1 suggests a ratio by weight of carbon to organic liquid of 3:l to 10:l for the liq-
&a
Volume 69 Number 11 November 1992
929
uid not to be leached out by water. However, we suggest that initial conservative practice would be best served by usine the 10:l ratio. Later exoerience mav make the ooeratormore cornfurtable with oiher ratios. . O ~ e the n container of liouid to he immobilized. and set it and its cap near the carbon. Position the funnel vertically in the carbon, holding it by hand so that the bottom of the stem extends about half way into the carbon granules. Pour the organic liquid into the funnel, which should not be filled beyond about half its capacity. If you are using a separatory funnel, adjust the stopcock so that the liquid runs into the carbon a t the desired rate of about 100 mumin. While the liquid is running in, move the funnel through the carbon so that the liquid is distributed as uniformly as practicable among the granules. When all the liquid is in, stir the carbon with a sturdy rod for a minute or so to homogenize it. If the liquid is viscous, more thorough stirring will be helpful. Invert the funnel so that its mouth rests on the surface of the carbon. Do the same for the empty container and its cap. Any remaining liquid in these items that vaporizes will fall into the carbon and be adsorbed. The carbon will bewme warm from the heat of adsorption. Leave the inverted funnel, container, and cap on the carbon. close the hood sash. and continue to run the hood exhaust for about an hour. Let the mixture stand overnight to cool to mom temoerature. It is not necessarv to run the hood exhaust overnight. The next day, remove the items resting on the carbon. Many liquids will have vaporized completely, When the carbon with its immobilized liquid has woled, it should have little or no odor. If for any reason you think that your ratio of carbon to liquid was too low, you can add more carbon to the mixture and stir it. There will be no significant temperature rise at this point. The mixture can now be transferred to a plastic bag or other suitable container for disposal. For organic liquids of unknown identity but known characteristics, a given organic liquid may be known to be, for example, a mixture of hydrocarbons boiling above 45 'C, or a solution of phenols in toluene. If the characteristics of the organic liquid conform to the requirements cited above, the carbon method is applicable. If such information is not Table 1. Capacity of Carbon for Organic Liquids Organic liquid
Capacity of carbon for liquid (liquidicarbon ratio by mass)= For dryness
Acetic acid (100%) n-Hexane Toluene lsopropyl alcohol Phenol (melted) Aniline Amyl acetate thy^ acetate Methyiene chloride Methylethyl ketone Cyclohexanone Methyiisobutyl ketone
For purity of leachate
0.70 0.40 0.59 0.46 0.50 0.45 0.55 0.67 1.60 0.59 0.56 0.45
The three liquid-ta-carbon ratios were 0.33.0.20,and 0.10. %ith both pH 7 and pH 3 leachates.
930
Journal of Chemical Education
0.33 0.33 0.33 0.33 0.33 0.20~ 0.20 0.10~ 0.20 0.20 0.10~ 0.10~
known, the liquid must he examined to establish whether or not its characteristics are acceptable. Specifically, the organic liquid should not boil when heated in a water bath a t about 50 -C, and should not show a positive test for peroxides. Fortunately, most laboratories are unlikely to harbor unknown liquid explosives such as nitroglycerin or ethylene glycol dinitrate, but if there is any possibility that the unknown organic liquid is a n explosive, the carbon method should not be used. How "Immobile" Are the Adsorbed Organic Liquids? If a drop of, say, amyl acetate falls on a 6&70 mg granule of activated carbon the initial visible wetness on the surface disappears within about three seconds. The granule is now dry to the touch, so the objective of immobilizing the liquid so that it is no longer wet has been achieved. However, if you hold the granule to your nose you can smell the amvl acetate. This liauid-to-carbonratio therefore does not mekt all the objectiv& cited earlier. However, it is interestin^ to auantifv the maximum amounts of oreanic liauids that c& be imrnobilized in this way. We testez 12 sucL liquids, each immobilized on 20 g of carbon. Our findings, displayed in the first column of data in Table 1, show that GAC can "dry" from about one half to more than its own mass of various organic liquids. Are the Immobilized Liquids Leached Out by Water? In the US EPAExtraction Procedure (91, which may simulate the acid-rain leaching of waste in a municipal landfill, a sample of waste is extracted with water to which 0.5 M acetic acid added in sufficient quantity to reduce the pH of the mixture to 5.0. The filtrate is then analyzed. We applied the following adaptation of the EPA procedure to the 12 organic liquids of Table 1.The liquids were immobilized in 100 g samples of carbon, each a t three liquid-to-carbon ratios. Each sample was then soaked overnight with about 200 mL of pure water a t pH 7. Since the pH of acid rain may be lower than 5.0, some samples were soaked with dilute sulfuric acid in sufiicient wncentration to make the filtrate reach a pH of about 3.0. These choices involved a total of 48 tests. We extracted 75-mL aliquots of the aqueous filtrates (leachates) with 2-mL portions of CC14 and analyzed the extracts with a Perkin-Elmer Model 247 Grating Infrared Spectrophotometer.Under the conditions of this procedure, the detection limit of the instrument was determined to be about 5 ppm based on the total mass of the leachate. Under the conditions of rainfall on a landfill, the dilution would be much greater, so that the 5 ppm detection limit is conservative. Table 1 shows the maximum liquid-to-carbon ratios allowable to avoid detection of the organic liquids in the leachate. The results show that a 1:10 ratio by mass is a reasonableinitial choice for immobilization of organic liquids. In general, the hieher the molecular weieht or boiling ., ~. o i noft a liouid of a &+en chemiral category, the greater will he the capacity of the GAC LO adsorb and retain it 13
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Do the Immobilized Liquids Retain Their Odors? We assumed that the most severe tests of the GAC method would be the immobilization of stenches. We chose a selection of mercaptans and sulfides, and exercised extreme care with hwd ventilation and with use of carbon to deodorize our pipets and other equipment. Nevertheless, these compounds are so pervasively odorous that our transfer operations could be smelled in the corridors outside the laboratory. The tests were carried out as follows: 0.5-mL, 0.25-mL, and 0.125-mL batehes of each stench were pipeted into 20g samples of the GAC in small beakers. The mixtures were stirred, wvered with watch glasses, and allowed to stand
Table 2. Odors of Stenches Immobilized by Carbon S Compound
Head gas odor intensities, butanol scale, for three IiquidIGAC ratios 0.025
benzyl mercaptan
[EZ lg;; :%rate)
:$Itrate) thiophenol
12 0
0.0125
0.00625
10 0
8 0
12 3
8 0
IE:
15 0
12 0
8 0
[::
10
:$Jtrate) n-butyl sulfide over GAC lover aq. filtrate) t-buly sulfide :[$Itrate) thiophene
lE: IZ+%$Itrate) r
lgnitability 40 CFR 261.21 characterizes a solid waste as ignitable if
it "is capable, under standard temperature and pressure, 15 8
ethyl sulfide :%rate) allyl sulfide
Characteristics of Hazardous Wastes ignitability cormsivity reactivity toxicity
o
o
8
4
12 0
15 0
8 0
20 0
15 0
8 0
15 0
12
12
0
o
0
overnight. The air in each beaker was then smelled and the perceived odor intensity was ranked by two laboratory chemists who previously had been judged to have normal olfactory sensitivity. The ranking used was the "butanol odor intensity" (10) scale, in which 250 ppm by volume of n-butanol vapor in air is arbitrarily assigned an intensity value of 10. An odor to be measured is smelled and compared with the 250 ppm butanol standard. The "butanol value" of the odor is intensity of the odor expressed as 10 x . ~ntensityof the BuOH std To the average observer, an intensity ranking of 10 for hutanol is perceived as "neither too strong nor too weak (10)" and, as a general category, may therefore he considered to be "moderate." Values below 3 are very slight, and 1is essentially an expression of threshold. The head gases of the stenches were far too intense for anyone to sniff, let alone rank. Table 2 displays the butanol scale intensities of the head gases of the various stenches immobilized on carbon and of their aqueous fdtrates. The practical consequences of these findings may be exemplified as follows: If a plastic bag containing, say, benzyl mercaptan immobilized at a GACImercaotan ratio of about 40:l were t o break open during its ride on a garbagr truck, thr odor would nor hr nnticedovrrtheprt.railing bnrkgmund, nor many nqur"us learhntr or surface runolf
Is the Carbon with its Immobilized Liquid a Hazardous Waste? Because "hazardous" is defined by law, i t will he helpful to review the somewhat complex federal regulations. Title 40 of the Code of Federal Remlations (40 CFR) deals with the protection of the envi&ment, and Parts 260 to 281 deal s~ecificallvwith the rerrulations of the Environmental P r o t e c t i o n ~ ~ e n(EPA) c ~ regarding solid wastes (11).Solid wastes are classified as hazardous if they have any of the four "Characteristics of Hazardous Waste" (40 CFR Subpart C) or if they appear among the "Lists of Hazardous Wastes" (40 CFR Subpart Dl.
of causing f r e through friction, absorption of moisture or spontaneous chemical changes and, when ignited, burns so vigorously and persistently that it creates a hazard." We have assumed that a conservative and rigorous test for activated carbon is its ignition temperature. The ASTM procedure (12)involves a programmed heating in a quartz tube, and ignition is defined as the point at which the carbon tem~eraturesuddenlv rises above the tem~eratureof the air entcrmg the bed. Alternatively, thr determination can be made with thcrmoanalytical methods. We found the i~mitiontemperature IASTM method, of our coal-based activated carbon to be ahout 460 ' C , which IS a ~ ~ r o x i m a t e l v the same as that of asphalt. To estimate the ieduction df ignition temperature by the presence of adsorbed organic matter, we impregnated a sample of the carbon with 10% of its weight of mixed hexanes, and found its ignition temperature to be about 450 T. Apparently, the hexanes were desorhed during the temperature program, and the measured ignition temperature was therefore about the same as that of the carbon substrate. Furthermore, we have found that the carbons with their immobilized liauids are by no means readily ignitable by friction or spontaneous chance. We. therctbre. conclude that thev do not have the E.P.Lcharacteristic i f ignitability, Corrosivity 40 CFR 261.22 characterizes a waste as corrosive if it "has a pH less than or equal to 2 or greater than or equal to 12.5. . ."We have assumed that an appropriate test for activated carbon is the pH of its hot water leachate (13). None of the leachates of the immobilized organic liquids we tested had a pH in this range. Reactivity 40 CFR 261.23 characterizes a waste as reactive if it is unstable, explosive, reacts violently with water, or is a cyanide or sulfide-bearing waste "which, when exposed to pH conditions between 2 and 12.5, can generate toxic gases, vapors or fumes in a quantity sufficient to present a danger to human health or the environment." The immobilized liquids described here do not have any of these properties. Toxicity This attribute is undoubtedly the most critical with regard to the disposal of GAC-immobilized organic liquids. 40 CFR 261.24 characterizes a solid waste as toxic if "the extract of a representative sample of the waste contains any of the contaminants listed in Table 1at the concentration equal to or greater than the respective value given in that Table." The table referred to lists 40 contaminants, from arsenic to vinyl chloride. The "Lists of Hazardous Wastes" (40 CFR Suhpart Dl are described in four tables. 40 CFR 261.31 Hazardous wastes from nonspecific sources. This is a list of 23 "generic" wastes, such as spent solvents, plating bath solutions, and other process residues. The waste numbers are all preceded by the letter "F." Volume 69 Number 11 November 1992
931
40 CFR 261.32 Hazardous wastes from specific sources. This is a list of over 100 industrial wastes from specifically described industrial processes. Their numbers are all preceded by "K." 40 CFR 261.33 Discarded commercial chemical products, residues, etc. These include two tables that, together, list some 700 such products. The first table (the "P" list) includes mostly "Acute Hazardous Wastes," such as arsenic compounds, chlorinated pesticides, and cyanides. The second table ('V" list) includes materials in various other categories of hazardous waste
40 CFR 261.5 Conditionally exempt small quantitygenerators. This category is defined on a monthly basis as one who "generates no more than 100 kg of hazardous waste in that month." A further limitation is that exempt generators of "acute hazardous waste" (from the "P" list) are limited to only one kg per month. We return, then, to the question that headed this section: Is a n organic liquid that has been immobilized on activated carbon a hazardous waste? The answer is, as one might expect, "It depends." According to 40 CFR 261.3,if a waste is hazardous "solely because i t exhibits one or more of the characteristics of hazardous waste identified in subpart C. . ." and is then mixed with a nonhazardous solid waste, the resultant mixture is no longer a hazardous waste if it does not exhibit any of those characteristics. Recall that those characteristics, described above, are ignitability, corrosivity, reactivity, and toxicity. Thus, hexane, for example, can be classified as a hazardous waste because of its characteristic of ignitability, but it does not appear on any of the E. P. A. "Lists of Hazardous Wastes." Since hexane no longer has this characteristic when it is suff~cientlvimmobilized on carbon. the mixture is no longer a hazardous waste. It is noteworthy that several tons of exhausted carbon from one of New York Citv's sewage treatment plants were accepted in the Freih Kills (New York) sanitarv landfill after the carbon was found to have none of the af&nentioned characteristics (14..However, if the liquid does appear on one of the l?. P. A. lists, then the is sibject to the appropriate small quantity restriction. Other Questions Q: Who, then, is a "generator;" a n d how many generators can there be in a giuen institution? A: 40 CFR 260.10 defmes "generator" as "any person, by site, whose a d or process produces hazardous waste. . ."An interpretation of "site" gleaned from lengthy discussions with off~cialsofthe E. P. A. regional office in New York City is that different laboratories in a given building, as well as different buildings in a given institution that are not separated by roads open to the general public, are single sites. If they are so separated, they are different sites.
Q: Is there anv orocedure for a n administrative relarn t l k of the haz&ous wasre're,gulalrons 10 applj to GACrmrnobrilz~dorconrc llourds7 A: Yes, 40 CGR 260.i0 tells how to petition the E. P. A. Administrator to modify or revoke any of the provisions described in these regulations.Changes are expected to be difficult and slow. Q: What about local laws?
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Journal of Chemical Education
A: They may be more restrictive than Federal ones; the information is available from your local agencies. Q: Must the chemist conduct laboratory tests of all GACimmobilized liquids to determine whether they haue the %haracteristics of hazardous wastes? waste A: Accordine to 40 CFR Part 262.11 (Hazardous , determination? the generator [the chemist] may determine whether the waste is hazardous bv "A~~lvin€!knowledee of the hazard characteristic of the waste in tEe light orthe materials or the processes used." ~
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~~~~~~~~
. A "
Q: Can samples of GAC that contain different liquids be mixed ~ r i oto r dis~osal? A: yes. Once the liquid is adsorbed so that its vapor pressure is nil, i t does not migrate to any detectable degree. For example, samples of GAC impregnated with phosphoric acid solution can he mixed with GAC impremated with a solution of KOH, without any significant ieu&alization reaction (15). Q: Then why not pour uarious liquids into a large tub of GAC and discard the carbon as a single batch when it is exhausted? A: Under these conditions some of the liquid will be adsorbed on carbon granules that contain oiher chemicals and there will be opportunity for interactions. Don't do it .. this way
Q: What is the eventual fate ofthese immobilized liquids? A: Who knows? Consider, however, that the 10:l earbodliquid ratio we recommend for initial use is conservative. It does not exhaust the capacity of the carbon for most organic liquids (3).Therefore, we strongly suspect that the carbons will remove more organic matter from the water that percolates through them in a landfill than they release to t h a t water, until some sort of steady state is achieved. Some microorganic actions may oecur (16). In anv event. the processes will be slow and the net release to groundwater, ifany, wlll be inconsequential. It may well he that if your sampleof. sav, valer~cacid imrnobihzed on carbon is recovered a thousand years from now, the analyst will find that it is still there. Acknowledgment H. K. and R. L. were supported by the College Research Scholar Program and V T. by the N. I. H. Minority Biomedical Research Support Program at City College. Literature Cited 1. Saunders, H. J. Chm. & Eng News Feb. 3,1986, p 21. 2. Kaufman, J. A,, Ed., was* Digposal in Amdpmlc Inatitufiom: hwi.
Publishera: Chelsea, MI. 1990. 3. Turk, A. In Air Pollution, 3rd.; Stern, A,. Ed.: Academic Ress: Orlanda, FL,1911; Vol. N,Chapter 8. 4. Carbon Telmehlode Arliuify ofAcfiudrd Carbon, Standard Test Method D 3461, ASTM Philsdelphis. PA, 1989. 5. Chiomfluommrbon Achuity of Aefiuofed Carbon, Standard Test Method D 5020, ASTM: Philedelpbia, PA, 1989. 6. hferm~otlonofIodineNumb~rofArtiiiffdC~~bStandardTeetMethodD4601, ASTM Philadelphia, PA, 1986. I. Emthetick. L. Bmthericki Handboaoh ofReoefiue C h i m l Hc,zards, 4th ed.: Butterulolih-Heinemsnn: Stanaham, MA, 1990. U I Ihborntorlcs, S ~ ~ t i 8. prudrnt Pmdrpsfor D ~ S P D BD~~I C ~ D ~ ~fmm Ress: Washingtan, DC, 1983. 9. Federal Register Ma& 29, 1990, Val. 55,No.61, pp 1186211961. 10. Mmkowih, H. R.: Draunids, A ; Cain, W. S.: Turk, A. Chemiml S e m s & FIouor 1914,l. 235-U7. 11. Pmtectian ofEnuimnmpnf, 40 Code ofFederal Regulations (CFR) Psrtr 260 to 299, Offceofthe FederalRe~ter.NationalArchivea&ReeordsAdminishation: Washington, DC,July 1, 199:. 13. Ignilron Tempemtun ofGmnuiorActiuofedCorbon, StandardTest Method D3468, ASTM Philadelphia, PA, 1988. 13. p H of Aefiuated Carbon, Standard Test Method D 3838, ASTM:Philadel~&hia. PA. . 1986. 14. Turk,A.:Karamitaos, H.;M a h c d , K; Mozaffali, J.: Iaewi, R.: Bomwiee, A.N.A+ & W a l e Mona@msniAssn. 1991,Trans. Seties 1 8 1 , l l b l Z R . 15. Turk,A.:Sakslia. E.: Rago, 0.;Karamibm, H.Anna1sN.Yhod Sei. in press. 16. Clark, R.M.:Lykins,B. W. OmnulorAcZiwrtpdCorbon:hdgn, OperotionondCoat: Le%r Publishers: Chelsea,MI, 1989:Chapter 8. ~
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