(63) Lake, G. R., McCutchan, P., Van Meter, R., Neel, J. C., Anal. Chem., 23,1634 (1951). (64) Phelps, I. K., J . Assoc. Off., Agric. Chem., 3,306 (1920). (65) Shirley,R. L., Becker, W. W., Ind. Eng. Chem., Anal. Ed., 17, 437 (1945). (66) Bradstreet, R. B., Anal. Chem., 29,944 (1957). (67) Jirka, A. M., Carter, M. J., ibid., 47,1397 (1975). (68) Bolleter, W. T., Bushman, C. J., Tidwell, P. W., ibid., 33, 592 (1961). (69) Riley, J. P., Anal. Chim.Acta, 9,575 (1953). (70) Russell, J. A., J . Biol. Chern., 156,457 (1944). (71) Milham, P. J., Short, C. C., J . Assoc. Off. Agric. Chem., 56,882 (1973).
(72) Zinzadze, C., Ind. Eng. Chem., Anal. Ed., 7,230 (1935). (73) Johnson, D. L., Enuiron. Sci. Technol., 5,411 (1971). (74) Johnson, D. L., Pilson, E. Q.,Anal. Chim. Acta, 58, 289 (1972). (75) Fed. Regist., 38,28759 (1973). (76) Wyeth, R. K., Proc. 16th Conf. Great Lakes Res., 345,1973.
Receiued for reuiew January 26, 1976. Accepted May 10, 1976. Mention of trade names or commercial products does not imply endorsement by the Enuironmental Protection Agency or the Central Regional Laboratory.
NOTES
Granular Packed Bed Coalescer: Influence of Packing Wettability on Coalescence James R. Madia Department of Energy and Kinetics, University of California, Los Angeles, Calif. 90024
Steven M. Fruh Exxon Research and Engineering Co., Government Research Laboratory, Linden, N.J. 07036
Clarence A. Miller' Carnegie-Mellon University, Department of Chemical Engineering, Pittsburgh, Pa. 15213
Alan Beerbower Exxon Research and Engineering Co., Products Research Division, Linden, N.J. 07036
Beds of granular material provide one means of removing small oil drops from aqueous effluent streams. For certain applications such as shipboard use, it is important to minimize bed size by using bed materials which can most efficiently remove oil. Experiments are performed which show that oil removal ability increases with increasing oil wettability of bed material. XAD-2, a copolymer of styrene and divinylbenzene, is particularly effective in oil removal. Wettability of the various bed materials is determined with a novel application of gas chromatography.
To protect our harbors from pollution by oil, recent laws have been enacted to limit discharge of oily waste from seagoing vessels. These efforts are being spearheaded worldwide by the Intergovernmental Maritime Consultive Organization. The Water Quality Act of 1972 limits discharge of oily waste into U.S. harbors. To give an idea of the size of the problem, Los Angeles harbor alone would be faced with 350 000 gallday of oily wastes if ships could not clean up the wastes on board or discharge these wastes at sea. One proposal exists that, by 1980, no seagoing vessel may discharge waste into the ocean with an oil concentration large enough to cause a visible sheen. The actual concentration of oil associated with this effect is in the range of 1G20 ppm. The average of many samples of bilge water found on board ships showed about 0.1% oil or 1000 ppm ( I ) . Suspended particles of solids are present in bilge water. Their average concentration is around 0.04% or 400 ppm ( I ) . 1044
Environmental Science & Technology
Several shipboard separators, which were evaluated by the Naval Research and Development Labs a t Annapolis, have recently been installed on some Navy vessels. These separators contain filter cartridges packed with fibrous material in which oil drops are coalesced. The technique has been discussed by several authors (2-4). Although these systems are capable of achieving the desired oil separation, they are very susceptible to plugging by suspended solids. A possible solution to this problem is to use a granular rather than a fibrous bed. A granular bed could be easily backwashed when plugging occurs. Large sand and mixedmedia filters actually have been used for several years at shore installations. However, weight and volume constraints on a ship require more efficient, lightweight systems than the shore units. Minimizing bed size and weight requires using a packing material with optimum oil removal characteristics. The literature contains conflicting statements, however, as to what types of packing materials are best in this respect (3, 5-7). Accordingly, preliminary experiments were carried out to investigate oil removal capability as a function of packing material wettability. The techniques used and the results obtained are summarized below.
Wettability Measurements If the interfacial free energy ysw of a given solid material in contact with water is lower than yso for the same material in contact with oil, the material is said to be water wet. The more yso exceeds y s ~the , more water wet it is. On the other hand, if ysw > yso,the material is said to be oil wet. Because its attractive interaction with oil is stronger than with water,
one might expect such a material to be effective in removing oil drops from aqueous effluents. Measuring the equilibrium contact angle an oil-water interface makes with a solid surface is the usual way of determining the solid’s wettability. According to Young’s equation, the contact angle 0 measured through the water is related to the various interfacial tensions or free energies by ( 8 ) cos 8 =
YSO
- YSW
YOW
Clearly, the contact angle decreases as the material becomes more water wet. If yso exceeds the sum of YSW and yaw, there is no equilibrium contact angle, and water spreads spontaneously on an oil-covered solid surface. For the small bed particles (about 30 mesh) of interest here, contact angle measurements were not feasible; therefore, a novel application of gas chromatography was devised to determine the relative wettability of various solids. The times t w and t H required for pulses of water vapor and hexane vapor to pass through a chromatographic column filled with a granular solid of interest were measured. The more oil wet the material, the greater its interaction with hexane relative to
Table 1. Coalescence Runs Under Experimental Conditions Packing material
Am1 used In bed, g
Coal
61.3
Ottawa sand a
43.0
Polypropylene
32
XAD-2
50
Vol of feed processed,
Emulsion flow rate, i./min
Llnear velocity, cm/mln
Steadystate A P , In. H 2 0
30 (300 ppm
0.4
79
10
15
0.1
79
48
0.4
79
25
0.5
98
40
I.
oil)
(500ppm
oil) 40
(500 ppm
oil) 60
(500ppm
oil)
For this run, a column of identical height but of onafourth the cross-sectional area was used to reduce the volume of feed needed to approach steady state. One-fourth of the volumetric flow rate was used to keep the same flow rate per unit area. Contains 10% water. a
Table II. Properties of Oil Used Surface tension, 77 O F 30.7 dyn/cm Interfacial tension against distilled water, 77 O F 30.3 dyn/cm Interfacial tension against synthetic seawater, 77 O F 20.0 dynlcm Specific gravity, 60 O F 0.84 Flash point 152 O F Kinematic viscosity, 100 O F 2.96 CS 1.17 cS Kinematic viscosity, 210 O F Table 111. Properties and Sources of Packing Materials Packing material
Anthracite coal Ottawa sand
Size, mesh
30-40 30-40
Polypropylene 20-40 XAD-2
polymeric adsorbent
20-50
Source
Other Information
U S .Bureau of Mines Ace Scientific Exxon Chemical co. Rohm & Haas
Glenborn high volatile Kilndried CD-100 injection mold
powder sifted to size Highly cross-linked copolymer of styrene and divinylbenzene
water, and the longer the retention time of hexane relative to that of water. Hence, the ratio (tH/tw)increases monotonically as materials become more oil wet. A Hewlett-Packard 700 gas chromatograph was used for this work. The carrier gas was helium a t a flow rate of 30 cc/ min. The injection port temperature was 170 “C, and the detector temperature was 210 OC. The column was a 6-ft length of %-in. stainless steel tubing filled with the packing material of interest. Young (9) describes the basic technique in some detail.
Oil Removal Measurements A vertical packed column 1in. in diameter and 2 in. long was used for the coalescence runs. Auxiliary equipment included a centrifugal pump, a flow meter, and gauges to measure column pressure drop. Prior to each run, a concentrated emulsion was prepared by adding 25 ml of “Navy distillate” to 500 ml of distilled water and blending a t high speed for 15 min. The concentrate was allowed to settle for 15 min, and 400 ml of the resulting oil-in-water emulsion was siphoned off and diluted in a feed tank containing 16 1. of distilled water. The feed emulsion was then allowed to flow through the packed bed a t conditions shown in Table I. After about half an hour, the inlet, direct outlet, and settled outlet samples (see below) all showed consistent oil concentrations, and the pressure drop across the bed remained constant. Inlet and outlet samples were taken in two ways. First, a direct sample was taken from each sample port, followed by a water-phase sample taken from a separatory funnel in which any coalesced oil was allowed to float out. The ratio of the inlet oil concentration to the oil concentration from the settled outlet sample provides the index of oil removal performance. The Navy distillate oil used in the experiments is very similar to diesel fuel, and its properties are shown in Table 11. Oil concentration was measured by infrared spectroscopy using a Beckman IR-8 infrared spectrometer. The procedures of Simard et al. ( I O ) and Gruenfeld ( 1 1 ) were followed. The drop size distribution was determined with a Model T Coulter counter equipped with a 100-pm aperture tube (12). In this work the Coulter counter was used in the manometer mode, a setting which allows a reproducible volume of sample to go through the orifice for each measurement. The output reading gives the number of particles which were counted in each of 14 drop size categories ranging from 1.59 to 50 pm. Results
Four materials were characterized for wettability by the previously described technique using gas chromatography (Table 111).The ratio of retention times for hexane and water vapors will be referred to as the wettability parameter. The results of this characterization are given in Table IV. The effect of the packing material on oil removal performance is also shown in Table IV. Since it is not possible to characterize the inlet and outlet drop size distributions by a single parameter, it was decided to use the ratio (CI/CO)of the inlet and outlet oil concentrations in the water phase. The infrared and Coulter counter data were consistent, but the latter were considered to be more precise. Therefore, counter data were used for all but the Ottawa sand tests, during which the machine was being repaired. Although the data are limited in this preliminary study, Table IV shows a definite correlation between wettability and oil removal capability. The excellent performance of XAD-2 is particularly noteworthy. Although Table IV indicates that higher wettability by oil leads to more effective coalescence, the reader should be aware that wettability is not the only significant factor affecting the oil removal process. For example, the electrolyte concentration Volume
10, Number 10, October 1976
1045
Table IV. Wettability and Oil Removal Results Packing materlal
Anthracite coal
Ottawa sand Polypropylene Polypropylene
Hexane retentlon tlme, s, f H
Water retentlon t h e , s, fw
Wenablltty parameter, f H / f W
8 8.5 31
32 7.5 11
0.25 1.13 2.82
...
...
...
Re1 * water-phase Inlet oil concn, CI
0.139 X
g
682 PPm 0.413 X g 0.734 X g 0.432 X g
XAD-2
Oil removal
Re1 a water-phase
outlet OH concn, Co
0.125 X
g
136 ppm 0.079 X g g 0.094 X 0.017 X g
ca ablilty, Ei/CO
1.11 5.01 5.17 7.82 24.55
167 17 9.82 a The relative concentration data, with one exception, were obtained by adding up the weights of the drops counted on the Coulter counter. The exception is for Ottawa sand, for which absolute concentrations were obtained with IR measurements.
in the emulsion is also an important factor, though it was maintained approximately constant in the present study. As a result of this work, evidence exists that oil-wet packing materials provide better codlescing media than water-wet materials for the treatment of oil-in-water emulsions. Literature Cited (1) Finger, S. M., presentation to ASME Aerospace Division a t In-
tersociety Conference on Environmental Systems, San Diego, Calif., July 16-19, 1973. (2) Spielman, L. A., Goren, S. L., Ind. Eng. Chem. Fundam., 11,66 (1972). (3) Davies, G. A., Jeffreys, G. V., Ali, F., Afzal, M., Chem. Eng. (London),No. 266,392 (Oct. 1972). (4) Langdon, W. M., Naik, P. P., Wasan, D. T., Enuiron. Sci. Technol., 6,905 (1972).
(5) Treybal, R. E., “Liquid Extraction”, 2nd ed., p 448, McGraw-Hill, New York, N.Y., 1963. (6) Spielman, L. A., Goren, S. L., Ind. Eng. Chem. Fundam., 11,73 (1972). (7) Voyutskii, S. S., Kal’yanova, K. A., Panich, R., Fodiman, N., Dokl. Akad. Nauk SSSR, 91,1155 (1953). (8) Adamson, A. W.; “Physical Chemistry of Surfaces”, 2nd ed., Wiley, New York, N.Y., 1967. (9) Young, C. L., Chromatogr. Rev., 10,129 (1968). (10) Simard, R. G., Hasegawa, I., Bandaruk, W., Headington, C. E., Anal. Chem., 23,1384 (1951). (11) Gruenfeld, M., Environ. Sci. Technol., 7,636 (1973). (12) Lien, T. R., Phillips, C. R., ibid., 8, 558 (1974). Received for review November 24,1975. Accepted April 29,1976. This work was supported jointly by the Ennon Research and Engineering Co.,Linden, N.J., and by the Processing Research Institute at Carnegie-Mellon University. Parts of the work were curried out at both. locations.
Fugitive Dust Emissions from Trucks on Unpaved Roads Rodney 1. J. Dyck’ and James J. Stukel* Department of Civil Engineering, University of Illinois, Urbana, 111. 61801
w An expression for estimating the fugitive dust emissions from trucks operating on unpaved construction site haul roads is given. The expression suggests a linear relationship between vehicle speed, vehicle weight, and silt content of the road. Previous studies have shown that many activities commonly practiced on construction sites significantly degrade the air quality. A consistently cited construction practice that adversely affects the air quality is haul road traffic on unpaved surfaces ( I ) . All previous studies that developed vehicleunpaved road emission factors have examined automobile traffic on unpaved secondary roads ( 2 , 3 ) . This study, however, investigates fugitive dust emissions from construction site haul roads. Thus, heavier vehicles similar to those used on a construction site are employed. Truck movement on access roads to construction sites differ from secondary road automobile traffic in the following ways. Trucks generally travel at slower speeds because of the proximity of the construction site, transport much greater weights, contact the road differently, and possess different aerodynamic wake characteristics. In addition, the intrinsic road characteristics of temporary haul roads may vary from those typical of secondary roads. The objective of this study was to characterize the source ~
Present address, Sargent and Lundy Engineers, Chicago, Ill. 1046
Environmental Science 8 Technology
particulate emission strength of an unpaved haul road as a function of various vehicle, road, and meteorological parameters. This study focuses on such controlling parameters as vehicle speed, vehicle weight, road surface moisture content, road surface particle size distribution, and road surface soil type. Theory
To calculate the source emission strength of the measured atmospheric concentrations, the following infinite line source equation was used ( 3 , 4 ) :
For purposes of describing dust emissions by vehicle transport over the “infinite line source”, the source strength calculation must also take into account the rate of road use. Rearranging the above equation and taking into account the rate of road use give: e=
C sin 4 v‘Ga, Ut 2N
In an attempt to relate the source strength to the road, vehicle, and meteorological parameters, a multiple regression analysis was performed. The variables considered in the analysis included the vehicle speed, V;the vehicle weight, W; the percentage of silt in the road surface, S; surface moisture, M ; the road type, R; and the wind speed, U.
