Environ. Sci. Technol. 1984, 18,483-490
Emission of Organic Air Pollutants from Shale Oil Wastewaters Steven 6. Hawthorne and Robert E. Slevers"
Department of Chemistry and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309 The emission of organic compounds from shale oil wastewaters was investigated by using headspace and purge and trap sampling followed by analysis by gas chromatography with mass spectral and flame ionization detection. The air above wastewater samples held in closed containers contained relatively small amounts of organic compounds (ng/mL), while 3 orders of magnitude greater quantities were purged from the wastewaters. Six wastewaters exposed to large amounts of air emitted similar distributions of the same compounds, with aromatic nitrogen-containing compounds (primarily alkylpyridine isomers) accounting for 40-78% of the total emitted organics from a single wastewater, ketones for 3-13%, phenols for 2-11%, and nitriles for 2-6%. Vaporized organic compounds accounted for 2-5% of the dissolved organic carbon for the three process retort wastewaters, compared to 23-52% of the three gas-condensate retort wastewaters. Air samples collected in and near a pilot shale oil wastewater treatment facility displayed qualitative agreement with the results of purge and trap analyses.
Introduction Oil shale reserves in western Colorado and Utah contain an estimated 400 billion barrels of oil that are recoverable by using existing technologies, a quantity of oil that would satisfy U.S. consumption for about 70 years ( I ) . The retorting of oil shale to release the product oil produces retort wastewaters that will require control and disposal in an environmentallyacceptable manner. Shale oil wastewaters are generally characterized by a pH of 8-10, high electrical condcutivity, high dissolved organic carbon (DOC), and a strong, unpleasant odor (2). Reports on the organic components of shale oil wastewaters have recently been summarized by Leenheer et al., who also reported an extensive list of organic compounds found in wastewaters from a modified in situ retort (3). Major classes of organic compounds that have been reported include short-chain carboxylic acids, phenols, aromatic amines (mostly alkylpyridine derivatives), nitriles, aliphatic alcohols, and aliphatic ketones. Many of these compounds have a high vapor pressure and limited water solubility, indicating a potential for their emission from a wastewater into the atmosphere. Although the treatment, reuse, and disposal options to be employed for these wastewaters have not yet been finalized, it is likely they will be used for cooling tower water, for dust control spraying, for cooling hot spent shale, and/or for codisposal with spent shale ( 4 ) . Each of these options would allow contaminant species with high vapor pressures and limited water solubilities to be emitted into the atmosphere. Unless shale oil wastewaters are treated to remove volatile contaminants (by a method such as steam stripping with recovery of ammonia and volatile organic compounds) before reuse or disposal, these emissions could result in a source of air pollutants that is difficult to control, particularly if the wastewaters are widely distributed as in proposed codisposal in open fields with retorted spent shale. The objective of this study was to identify and quantitate the organic compounds which are volatilized from shale oil wastewaters at ambient temperature. Two 0013-936X/84/0918-0483$01.50/0
techniques, headspace analysis and purge and trap analysis, which are normally used for the analysis of organic components in water, were applied in this study to investigate the emission of organic compounds from shale oil wastewaters. Static headspace analysis ( 5 , 6 )was used to simulate the volatilization of organic compounds in an equilibrated closed system such as a wastewater stored in a sealed holding tank. Purge and trap analysis (7,8) was used to simulate the organic emissions from wastewaters that are exposed to large amounts of air such as wastewaters that are aerated in open treatment ponds, used for cooling tower makeup, or sprayed for dust control. Qualitative and quantitative analyses of three gas-condensate retort wastewaters (those waters condensed from the offgas stream of a retorting operation) and three processes retort wastewaters (those waters separated from the product oil) are reported. To avoid the loss of volatile components (5),only wastewaters that were freshly collected and stored headspace free at 4 "C were analyzed and reported here. Air samples collected in and near an operating pilot-scale shale oil wastewater treatment plant were also analyzed in order to investigate the extent of the relationship between organic compounds volatilized from shale oil wastewaters in our laboratory studies and those volatilized during wastewater treatment. Comparisons of the organic air pollutants found in these air samples with those found in a typical urban air sample and those found in an undeveloped area of the oil shale region are reported.
Sample Description Gas-condensate and process retort water samples I and I11 were freshly collected on-site in glass bottles sealed with Teflon-lined caps. All bottles were completely filled before sealing. Wastewater samples I were collected from the modified in situ (MIS) retort 1 burn at Rio Blanco Oil Shale Co. (Tract C-a) in July 1981. Wastewater samples I11 were collected during the recycle mode of the MIS retorts 7 and 8 at the Logan Wash site of Occidental Oil Shale Inc. during Dec 1982. Wastewater samples I1 were collected by Tom Spedding from run 20 of the experimental 150-ton retort at Laramie Energy Technology Center during May 1982. A t the sampling site all samples were cooled to 4 "C and upon receipt at our laboratory were divided into aliquots placed in new 2-mL glass vials (headspace free) and sealed with Teflon-lined caps in order to avoid loss of the volatile constituents. All samples were stored at 4 "C until analysis. Dissolved organic carbon measurements (DOC) were performed with a Beckman Model 915-B total organic carbon analyzer. DOC values are reported at the end of Table 11. The pH of the wastewaters ranged from 8.2 to 9.1. Methods Gas Chromatography/Mass Spectrometry. All gas chromatographic separations were performed on a Hewlett-Packard Model 5730A gas chromatograph equipped with a Grob-type injection system. The chromatographic column was a 30 m X 0.35 rnm i.d. (1-pm film thickness) DB-5 manufactured by J & W Scientific, Inc. (Rancho Cordova, CA).
0 1984 American Chemical Society
Environ. Sci. Technol., Vol. 18, No. 6, 1984 483
Species identification was performed with a HewlettPackard Model 5982A gas chromatograph mass spectrometer/data system (GC/MS) that has been modified so that the chromatographic column is connected directly to the ion source. Mass spectra were obtained by scanning mass to charge ratios (rn/z) from 50 to 300 (25-150 for low molecular weight species) at a scan rate of 167.5 amu/s. The electron impact ionizing voltage was 70 eV. Identifications were confirmed whenever possible by comparison of the retention indexes and mass spectra of injected standards with those of the sample species. Quantitation in all headspace and purge and trap analyses was based on gas phase n-hydrocarbon standards (C, to CIJ generated from diffusion devices constructed by fusing an appropriate length of 6 mm 0.d. glass tubing to a 2.0 cm 0.d. X 3.0 cm high reservoir. The length and inner diameter of each 6 mm 0.d. diffusion tube necessary to obtain the desired rate of emission of each alkane standard were estimated by calculation (9, 10). After construction of the devices, the exact rate of emission of each alkane standard (at 30 "C) was gravimetrically determined. Each diffusion device was connected to a glass manifold with a Swagelok union, and the entire apparatus was submerged in a constant temperature water bath at 30 "C. The flow of air through the manifold could be varied to yield different gas-phase standard concentrations, which could be calculated from the emission rate of each diffusion device and the measured air flow rate. Injection into the gas chromatograph of a known volume of the gas-phase standards was accomplished with a 0.5-mL sample loop as described below. Flame ionization detection (FID) was used for quantitative analysis of the chromatographically separated species. The reported quantitative results were corrected for the FID response of each species relative to that of the normal hydrocarbon standards (11). Headspace Analysis. Headspace samples were prepared by pulling 2.5 mL of sample water into a 5-mL glass syringe which had been modified by fusing 3 cm of 6 mm 0.d. X 2 mm i.d. glass tubing to the end of the syringe barrel. The syringe was immediately sealed by capping the glass tube with a. Teflon-lined septum and left to stand for ca. 18 h for sample equilibration. Gas chromatographic analysis of the headspace air was accomplished by puncturing the septum with a stainless steel syringe needle connected to a 0.5-mL sample loop mounted on a gas-tight eight-port valve. The sample loop was flushed with headspace air by depressing the syringe plunger. Sample injection was accomplished by diverting the helium carrier gas flow from the injection port to the eight-port valve, which was then rotated so that the sampling loop was flushed by the carrier gas directly into the gas chromatographic column, which was held at -50 "C to cryogenically trap the sample species. After 5 min the carrier gas flow was returned to normal, and the chromatographic column was heated at approximately 25 "C/min to 0 "C, followed by temperature programming at 8 "C/min to 250 "C. Quantitation was based on FID areas reported by a Hewlett-Packard Model 3390A recording integrator and the normal alkane standards described above. All samples were analyzed in duplicate. GC/MS analysis of headspace samples (after equilibration between equal volumes of water and air) was performed by using a 20-mL glass vial containing 10 mL of wastewater. The air in this vial was flushed by the carrier gas stream directly into the chromatographic column for cryogenic trapping by diverting the carrier gas flow from the injection port to the sample vial. After 10 min the carrier gas flow was returned to 484
Environ. Sci. Technol., Voi. 18, No. 6, 1984
NIC SPECIES EMITTEO A SHALE OIL WASTEWATER
METHOD BLANK
0
lb R E T E N T I O N
210
TIME
3b
( M I N U T E S )
Flgure 1. Gas chromatogram of organic components volatilized during purge and trap (Tenax-GC)analysis of shale oil retort water I1 (upper chromatogram). The numbers on the chromatogram designate species listed in Table 11. The lower chromatogram is a typical method blank generated by performing an identical purge and trap analysis of organic-free water. Purge and trap and gas chromatographic conditions are given under Methods.
normal and the chromatographic analysis was performed as described above. Purge and Trap Analysis. Samples for purge and trap analysis were prepared by placing a 0.1-mL aliquot of the wastewater in a 6 mm 0.d. X 20 mm test tube and immediately capping with a Teflon-lined silicone septum. The water sample was then purged into a trap containing 0.1 g of the Tenax-GC adsorbent (6, 7) with 40 mL/min air for 20 min. Stainless steel gas chromatographic syringe needles were used to introduce the purge air into the water and to allow collection of the air into the Tenax-GC trap. The trap was then back-flushed with pure, dry air (40 mL/min) for 2 min to remove most of the condensed water in order to prevent subsequent plugging of the chromatographic column by trapped frozen water. The sample species were then thermally desorbed from the Tenax-GC trap at 200 "C for 10 min while being flushed directly into the gas chromatographiccolumn with helium. The sample species were cryogenically trapped in the chromatographic column and the gas chromatographic analyses were performed by temperature programming as described for the headspace analyses. A second desorption and analysis of several Tenax-GC traps were performed to ensure that the desorption conditions were adequate for our purge and trap samples. In order to investigate the possible irreversible sorption of polar organic species on the Tenax-GC sorbent, 1 pL of a standard solution in methanol containing approximately 100 ng of each sample species was injected both into the sorbent traps and directly into the gas chromatograph. The traps were flushed with 40 mL/min air for 10 min to remove the methanol and sweep the sample species into the sorbent bed. The traps were then analyzed as described above. Integrated areas of the chromatographic peaks generated from the Tenax-GC trap analyses and the direct injections were compared by using undecane as an internal standard to allow the determination of percent recovery for each sample species. Air Sample Collection and Analysis. Two samples of ambient air were collected in and near the shale oil wastewater treatment facility of Occidental Oil Shale Inc. at the Logan Wash site, CO. The samples were collected in Nov 1982 during the recycle mode of operating retorts 7 and 8. Both air samples were collected into 0.1-g Tenax-GC traps by using a Du Pont Model P4000 air sampling pump calibrated to draw 200 mL/min through the sorbent cartridge. After being returned to the laboratory, the Tenax-GC traps were thermally desorbed (200 "C for 10 min) while being flushed with helium into the chromatographic column for cryogenic trapping and subse-
Table I. Organic Compounds Present in the Air Above Shale Oil Wastewaters in a Closed System (ng/l mL of Air above 1 mL of Water) compounda aromatic N compounds 2,6-dimethylpyridine 2,4-dimethylpyridine 2,4,6-trimethylpyridine C3 alkylpyridine isomer C4 alkylpyridine isomer pyrrole 2- or 3-methylpyrrole C3 alkylpyrrole isomer total aromatic N compounds ketones acetoned butanone 2-pentanone 3-pentanone 2-hexanone cyclopentanone 2-methylcyclopentanone 3-methylcyclopentanone total ketones nitriles acetonitriled propionitrile benzonitrile aromatic S compounds thiophene 2-methylthiophene 3-methylthiophene C2 alkylthiophene isomer C3 alkylthiophene isomer total aromatic S compounds aromatic hydrocarbons benzene toluene ethylbenzene m- and p-xylene o-xylene 1,3,5-trimethylbenzene C3 alkylbenzene isomers C4 alkylbenzene isomers naphthalene total aromatic hydrocarbons alkanes and alkenes heptane octane nonane decane undecane dodecane 1-octene 1-nonene 1-decene 1-undecene 1-dodecene total alkanes and alkenes total identified organics emitted, ng/mL emitted organics identified," %
retention index 886 935 995 759
494 599 687 697 789 792 853 491 587 997 676 778 785
666 772 869 877 900 978 1215 700 800 900 1000 1100 1200 792 892 992 1093 1193
retort water I
gas cond I
6.1 ND 12 ND ND ND ND ND 18
NDb ND ND ND ND ND ND ND
16 9.6 2.7 4.1 ND ND ND ND 32 11 ND ND 4.7 8.2 1.5 2.4 2.2 19 32 18 4.1 19 15
