Concentration of Selected Organic Pollutants: Comparison of

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Concentration of Selected Organic Pollutants: Comparison of Adsorption and Reverse-Osmosis Techniques Murugan Malaiyandi , R. H. Wightman , and C. LaFerriere 1

2

2

Environmental Health Directorate, Health and Welfare Canada, Ottawa, Ontario, Canada, K1A 0L2 Department of Chemistry, Carleton University, Ottawa, Ontario, Canada, K1A 5B6

1

2

Polar organic pollutants such as 2,4-dichlorophenol, 2,4,5 -trichlorophenol, 4-chloroaniline, and 3,3'-dichlorobenzidine and nonpolar organics such as α-hexachlorocyclohexane and bis(2 -ethylhexyl)phthalate in aqueous solutions were concentrated by an adsorption-desorption technique using XAD-2 and XAD-4 resins and carbon-impregnated polyurethane foam. By using concentrations ranging from parts-per-million to parts-per-trillion levels, both resins behaved similarly in their concentration effi ciency; however, the modified polyurethane foam was inadequate for 4-chloroaniline. Also compared was the reverse-osmosis tech nique as a potential method for concentrating the same organic pollutants from aqueous solutions. This study reemphasizes the general ineffectiveness of cellulose acetate membranes for reject ing small organic molecules in low concentrations, whereas polyamide hydrazide and polybenzimidazolone membranes seem to show promise for rejecting such compounds.

T H E C O N C E N T R A T I O N A N D A N A L Y S I S of organic pollutants in envi ronmental aqueous samples have been the focus of many studies (1-6). Included in these studies are (1) the large number of organic com pounds and their functional diversity; (2) the variation in their levels; (3) the variety of methods to concentrate or separate these compounds from an aqueous matrix; and (4) techniques for detection, identification, or analysis. However, it is rather difficult to find many comparative studies involving all these factors. W e have attempted to provide a comparison of concentration and (X^5-2393/87/0214/0163$06.00/0 Published 1987 American Chemical Society

Suffet and Malaiyandi; Organic Pollutants in Water Advances in Chemistry; American Chemical Society: Washington, DC, 1986.


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ORGANIC POLLUTANTS IN WATER

analytical methods that include six common priority organic pollutants representing acidic functionalities [2,4-dichlorophenol ( D C P ) and 2,4,5trichlorophenol ( T C P ) ] ; basic functionalities [4-chloroaniline ( C A ) and 3,3'-dichlorobenzidine ( D C B ) ] ; and neutral functionalities [a-1,2,3,4,5,6hexachlorocyclohexane ( B H C ) and bis(2-ethylhexyl) phthalate ( D E H P ) ] . Concentration procedures involving three of the more commonly used solid adsorbents (7-9) were compared to the reverse-osmosis (RO) technique. The solid adsorbents in this study were X A D - 2 (10) and X A D - 4 (11) macroreticular resins and polyurethane foam impreg nated with 1% activated carbon (12, 13). F o r the R O studies, the membranes employed were cellulose triacetate ( C A c ) , polyamide hydrazide (PA), and polybenzimidazolone (PBI) (14-18). This study also includes results f r o m t w o types of analytical methodology, namely, capillary gas chromatography ( G C ) (2, J9-2J) and reverse-phase highperformance liquid chromatography ( H P L C ) (3, 22). Furthermore, G C analysis of t w o field samples of drinking water and G C - m a s s spectrometric ( G C - M S ) identification of some of the compounds found in these water samples are also reported i n this chapter.

Experimental Materials and Reagents. All glassware was washed with chromic acid and thoroughly rinsed successively with water, glass-distilled acetone, and purified hexane (23). Selected organic compounds for this study were commercially available: DCP, TCP, CA, and DEHP (Aldrich Chemicals); DCB (Supelco); and BHC (Analabs). These compounds were purified, if necessary; checked for purity by IR, UV, GC, HPLC, and *H and C NMR; and shown to be >97% pure. Anhydrous N a S 0 4 (pesticide grade, Canlab) was prerinsed with purified solvents before use. 1 3

2

ADSORBENTS. Macroreticular Amberlite resins XAD-2 and XAD-4 (20-50 mesh; Lots 90721 and 898^, respectively) were obtained from BDH Chemicals Ltd. Polyurethane foam (upholstery grade, Woodbridge Foam Co.) and vegetable charcoal (Darco G-60; Lot 363-53; Matheson Canada Ltd.) were purchased. M E M B R A N E S . Flat sheets of CAc, PA, and PBI membranes were cast at the National Research Council of Canada by using published procedures (24) and were selected to obtain two different porosities as determined by percent NaCl rejection. The membrane sheets (ca. 400 μπι thickness) were cut into circles approximately 7.5 cm in diameter. SOLVENTS. Hexanes (distilled in glass, Caledon Laboratories Ltd.) were purified by treating them with H2SO4 and KMn0 as previously described (23). Acetonitrile and acetone (HPLC grade, Caledon Laboratories Ltd.) were used as received. 4

GLASSWARE. All special borosilicate glassware was fabricated in-house. Kuderna-Danish (K-D) evaporators and the modified Snyder columns were constructed as per the design described previously (25); adsorption glass


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Adsorption and RO Techniques


columns (60-cm X 1.1-cm i.d.) were fitted with coarse glass frits, polytetrafluoroethylene (PTFE) polymer stopcocks (2 mm), and ground glass standard-tapered 24/40 joints; reservoirs for the columns were 1-L separatory funnels with ground glass 24/40 joints and PTFE polymer stopcocks (4 mm); effluent receivers were 1-L Buchner filter flasks fitted with ground glass 24/40 joints. A 4 L reservoir for the RO system was provided with a ground glass joint 40/50 and an outlet on the side near the bottom of the reservoir. Equipment. RO cells (Figure 1) were constructed of 316 stainless steel at the Science Technology Centre, Carleton University, Ottawa, Canada, as per design described by Matsuura et al. (26). The RO system consisted of six cells (assembled as shown in Figure 2), a variable-flow circulating pump and motor with 316 stainless steel valves, Viton diaphragm (BIF no. 1731-12-9820, rated at 13 gal/h at 950 psig), a surge tank with Viton diaphragm (Greer, 1 pt; Dynesco Equipment Sales), miscellaneous valves and gauges, and the 4-L borosilicate

•• D

Stainless steel frit Membrane

Figure 1. Exploded view of RO cell (to scale). The various components of the cell fit together, are compressed by machine bolts, and are sealed with Viton Ο-rings. The membrane (effective diameter = 3.8 cm) is compressed against a porous steel plate ( 1/16 in., porosity = 25 μm ) and flushed with feed solution. A certain amount of water penetrates the membrane and is collected as the permeate water (D). The feed solution enters the cell (A) and washes across the membrane (B) before being forced out of the cell (C).



Figure 2. Schematic representation of RO system. Feed solution travels from reservoir (F) via pump (A) through cells (C) where a portion of the water permeates the cells. Pressure in the system is adjusted by the regulator (E) and monitored by gauge and valve system (D). Damping of pressure fluctuations is achieved by nitrogen pressure and the system (B).

1/2" Teflon Tubing 1/4'


H m 33

>

Ζ

G H > Ζ H

o 33 Ο > Ζ

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167

reservoir. The connecting tubing was made of either 316 stainless steel or PTFE polymer. Instrumentation and Analytical Procedures. G A S C H R O M A T O G R A P H Y . A Vista 6000 (Varian) instrument equipped with a fused silica capillary column (DB-5, J or W Scientific, 14 m X 0.25 mm), a flame ionization detector (FID, 1 Χ 10 amperes full scale [AFS]), and an electron capture detector (ECD, Range 10) were used. The detectors were used as required. A splitless injection configuration with a purge flow of 40 mL/min was used at all times. Typical parameters were as follows: carrier gas, ultra-high-purity (UHP) helium (flow adjusted to give a linear velocity of 25 cm/sec for butane); makeup gas to the detector, nitrogen (zero gas, 803>) based on the National Bureau of Standards [NBS] library computer search.) 8

L I Q U I D C H R O M A T O G R A P H Y . A model M 6000A (Waters) instrument was used with a manually variable UV-vis detector (Schoeffel Instruments Co.) and a U6K injector, both supplied by Technical Marketing Associates. A Hamilton PRP-1, reverse-phase resin, 150-mm X 4.1-mm (10 μπι) mesh column packing was used under the following conditions: mobile phase, acetonitrile/water (4:6 v/v); flow rate, 1 mL/min. The retention times were as follows: 5.35 min for CA (λ = 243 nm), 7.3 min for DCP (λ = 243 nm), and 13.4 min for TCP (λ = 257 nm). The composition of mobile phase was altered to 20^ water in acetonitrile to give a retention time of 3.1 min for DCB (λ = 213 nm) at the flow rate of 2.0 mL/min. Injection volumes of actual samples and working standards and attenuations were varied as necessary. An electronic integrator (SpectraPhysics Minigrator) and a 1-m V strip chart recorder (Fisher Recordall 5000) were routinely employed in this study. PREPARATIONS A N D PURIFICATION. Purified water was prepared by pass ing distilled water through two borosilicate glass columns, each separately containing purified XAD-2 and XAD-4 resin (75 cm X 3 cm) connected in series. The resin-treated water was redistilled in glass from an alkaline KMn0 solution by using a Vigreux column (2 m) and was collected in precleaned amber-colored bottles with PTFE polymer-lined caps. 4



168


STOCK SOLUTIONS. Aqueous stock solutions (1-10 ppm) of the polar organic compounds were prepared by adding known weights of pure com pound (s) to an appropriate volume of purified water in a thoroughly rinsed 12-L round-bottomed flask. The mixture was heated to 50 °C and stirred with a PTFE polymer-coated magnetic stirrer for 24-48 h; it was then cooled, while being stirred, to room temperature for 24-48 h before it was filtered through a precleaned Millipore filter (HA, 0.4 μΐη) (25). The exact concentrations of organic compounds in these solutions were determined on the basis of peak heights of the compounds in samples and in working standards. The stock solu tions of the nonpolar compounds (BHC and DEHP, 50-100 ppb) were prepared by adding aliquots of concentrated solutions of known concentrations of these organic compounds in acetone to the required volume of water. A D S O R B E N T S . The macroreticular resins XAD-2 and XAD-4 were separately suspended in distilled water, and the suspensions were stirred to leave the fine particulates floating. These fines were removed by décantation of the supernatant layer. This operation was repeated until no opalescence was noticeable in the supernatant layer. After filtration through Whatman no. 1 filter paper and washing with methanol, the resins were dried at 70 °C in a convection oven prior to further purification. The average weight per milliliter of the resin was found to be 0.40 ± 0.02 g. Polyurethane foam impregnated with 1% carbon was prepared as previously described (13) with slight modification. A slurry of a known weight of polyurethane foam in dichloromethane was prepared by blending for 2 min in a commercial Waring blender and filtering through Whatman no. 1 filter paper. The solids were resuspended in methanol. After the required amount of carbon was added, the mixture was slurried for another minute and then was filtered through Whatman no. 1 filter paper. The resins and the carbon-impregnated polyurethane foam were separately placed in cellulose thimbles and Soxhlet extracted successively for 24 h with HPLC-grade hexane, dichloromethane, acetone, and methanol. The final methanol extract from each adsorbent was concentrated and analyzed by GC by using the FID. Each adsorbent was slurry-packed in borosilicate columns (11-mm i.d.) fitted with glass frits and PTFE polymer stopcocks. Two columns of each adsorbent were packed to heights of 70 and 100 mm and were thoroughly washed with purified water. ADSORPTION STUDIES. The general procedure for sorbing and desorbing organic compounds in fortified water samples was as follows: Approximately 1000 mL ± 20 mL aqueous solutions of each organic compounds or their mixtures were measured into six 1-L separatory funnel reservoirs. The reservoirs were then placed on top of six individual columns packed with the three solid adsorbents of two differing heights. The solutions were allowed to percolate through the column at flow rates of 1/3 bed volume/min. The adsorbates were stripped from the columns with 100 mL of acetone/hexanes (3:7 v/v) per column. The eluates were dried over prewashed, anhydrous N a 2 S 0 and concentrated to 3-5 mL with the aid of K-D evaporators with the modified Snyder columns. The concentrates were then analyzed by GC or HPLC. The adsorbents were thenrinsedwith acetone (100 mL), followed by seven rinses with 100 mL of water, and equilibrated with purified water in preparation for the subsequent run. To measure the possible "breakthrough", the aqueous effluents from the columns were analyzed directly by HPLC for the presence of polar compounds 4


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at a sensitivity of 0.005 AUFS. The absorbance of earlier fractions was below 0.02 AUFS. If any nonpolar compounds were present in the column effluents, they were extracted with purified hexanes (8 X 25 mL). The combined extracts were then dried over anhydrous N a 2 S 0 and concentrated as described earlier for analysis by GC by using ECD to determine the presence or absence of any nonpolar compounds. 4


LARGE-SCALE D R I N K I N G W A T E R STUDY.

A borosilicate glass column (75-

mm X 23-mm i.d.) containing purified XAD-2 resin was connected by means of a ground glass aqueous ethanol (1 X 4 h each), and finally purified water (3 X 10 h). Three pairs of membranes, each with two different porosities, were installed in the RO cells. The membranes used were PA (92$ and 97$), CAc (85% and 91%), and PBI (89% and 99%). Each cell had an effective membrane diameter of 4.1 cm (area of 13.4 cm ). The operating pressure for all runs was 260 ± 10 psig, and the flow rate was adjusted to 410 ± 10 mL/min. The system and membranes were washed by operating with an ethanol/water mixture (1:9 v/v; twice) for a 6-8-h period to getridof any trace organic impurities in the system. The system was then cleaned twice with purified water and equilibrated with purified water (3 X 10 h). During the run, the temperature of the feed solution increased from 20-22 °C to 26-29 °C. The reservoir was filled with 3-4 L of the stock solution (original), and the entire system wasrinsedthoroughly with approximately 1 L of solution, which was discarded. The volume of the cells, tubing, etc. was estimated to be approximately 200 ± 10 mL, whereas the surge tank retained approximately 100 mL of fluid. Initially the concentration of the stock solution was determined to verify whether any loss had occurred during storage. After the run was started, the system was equilibrated by collecting at least 10 mL of the permeate from the slowest membrane, and the solution left in the reservoir was then called the "feed solution". The actual volume of the feed solution was determined at time 2


170


"zero." Cleanflaskswere connected to the permeate end of each cell, and the run was continued until the volume of the feed solution was reduced to approximately one-third of its volume at "zero time". At the end of the run, the exact volumes of the feed solution and each permeate (100-500 mL) were measured, and aliquots of samples of feed and permeates were analyzed to determine the levels of organic compounds. The concentrations of the feed solution and permeates were denoted by C and C , respectively. The RO system wasflushedthoroughly with 1 L of pure water between runs. A new batch of purified water was added to the reservoir, and the system was run to cleanse the membranes by permeation as described earlier. The cleanliness of the system was checked by analyzing the feed solution and the permeates of each wash for the organics under investigation. From the results, permeation rates for each membrane-solute combination were obtained, and the rejection characteristic of the membrane was calculated according to the following equation: percent rejection = [(C — C )/C ] X 100 where C is the concentration of the chemical in the feed solution after 90 min of equilibration and C is the concentration of the chemical in the permeate. (NOTE: A small or a negative value indicates that the membrane is not effective at preventing the solute from passing through the membrane, whereas a large value indicates that the membrane is effective at preventing the solute from permeating through the membrane.)


e

p

e

p

e

e

p

Results and Discussion Adsorption Studies. Extreme care was taken in purifying the adsorbents. To verify the purity of the adsorbents, the final methanol concentrates of the purified adsorbent washings were analyzed to show only a few small peaks. One of the peaks was identified as D E H P by its retention time from the G C trace by using FID. This finding was confirmed by G C - M S . The flow rates and volumes of water samples percolated through the adsorbents were not allowed to exceed the loading limits of the adsorbents (21). After preliminary studies, an acetone/hexane (3:7 v/v) (3) mixture was chosen for stripping the adsorbents. After concentration, the samples were analyzed by G C with fused silica DB-5 column, which gave excellent resolution and peak shapes of the analytes. At the concentrations of the six organic compounds studied, B H C was analyzed by G C by using E C D . C A and D E H P were preferentially detected by using FID. Analyses were performed in triplicate, and the data obtained were averaged for calculations. The percent recoveries of the six organic compounds from the fortified water samples and for the three adsorbents are shown in Table I. The average recoveries for these organic compounds are considered acceptable (individually and in their mixtures). In separate experiments, the average percent recoveries from a set of two runs for individual columns of each adsorbent are reproducible within ±15% (21). Comparison of the data for 70- and 100-mm columns shows that the average percent recoveries are not consistent and bear no relationship


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Table I. Percent Retention-Recovery of Organic Compounds from Various Adsorbents XAD-2

a

Compound


DP TCP CA DCB BHC

DEHP

ind mix ind mix ind 1 ind 2 mix ind mix ind 1 ind 2 ind 3 mix ind 1 ind 2 mix

XAD-4

0

PolyurethaneCarbon 0

70

100

70

100

70

100

107 122 102 111 88 92 111 96 110 93 96 103 89 21 16 34

95 85 118 79 109 99 79 95 91 74 95 70 89 18 13 30

150 115 82 106 101 88 105 91 113 105 85 84 69 24 15 42

112 105 93 102 — 103 93 80 105 70 71 97 55 18 15 36

170 96 103 90 27 (70) 17 (70) 23 (74) 96 109 67 81 93 92 18 19 36

135 107 106 100 44 (51) 36 (61) 46 (58) 88 106 78 103 92 57 21 15 45

N O T E : ind denotes individual, and mix denotes mixture; values in parentheses are the percent recovery measured in the effluent. °The column packing lengths are 70 and 100 mm.

in regard to the height of the column packings. In the case of X A D - 2 and X A D - 4 resins, the recovery values for D C P , T C P , C A , and D C B vary markedly, depending on whether the compounds were present singly or in a mixture. The reason for this variation is unclear at this time. However, with respect to B H C , both X A D - 2 and X A D - 4 resins behaved similarly within experimental error under the conditions described earlier. T w o anomalies are distinctly observable in the recovery data. The first feature involves C A , w h i c h was not well-retained b y the polyurethane-carbon adsorbent either from its individual solution or when mixed with the other five compounds. The effluent f r o m the column contained more C A than was found sorbed onto the adsorbent. Although it is tempting to attribute this lack of sorption to the amino functionality, basicity cannot be the entire reason because D C B with two amino groups behaved normally. Perhaps water solubility could also be a contributing factor. In any event, this result indicates some ineffectiveness of the polyurethane-carbon mixed adsorbent system and shows the need for further investigations of various parameters affecting the recovery of C A or other similar compounds.



172


Secondly, the recoveries for D E H P are not satisfactory. This result is even more puzzling because extraction with ethyl acetate of a water sample similar to that used for the adsorption studies yielded the same magnitude of recovery. Recent studies (27) have shown that about 10-15$ of D E H P was sorbed on the walls of the silylated containers, and this sorbed D E H P could not be recovered b y rinsing with several solvents. Moreover, about 25-35? of D E H P in aqueous solutions breaks through f r o m the macroreticular resin columns even at concentrations of a few micrograms per liter for a 500-mL sample and 5 - m L adsorbents. Further, D E H P might be h y d r o l y z e d in aqueous media, and the resulting acids were not easily desorbed b y the solvents used for elution. These reasons explain the fact that a reasonably constant l o w recovery of D E H P was obtained from all adsorbents in any given run. Drinking Water Samples. T w o tap water samples f r o m municipal sources in the Lake Ontario region, namely Kingston (site 1) and Trenton (site 2), Ontario, Canada, were extracted, concentrated, and analyzed b y using a column of X A D - 2 followed b y a X A D - 4 macroreticular resin column. The combination of the two resin columns was employed to ensure that any unretained organic compound by the X A D - 2 column due to channeling, etc. w o u l d be trapped b y the X A D - 4 resin. Stripping the resins with acetone/hexane (3:7 v/v), drying, and concentrating in the usual manner produced the concentrates of the field water samples. Capillary G C analyses employing both F I D and E C D indicated the probable presence of three of the organic substances under investigation, namely, T C P , B H C , and D E H P , in concentrations greater than the estimated detection threshold of 20-30 p g (Table II). These three compounds were also identified b y G C - M S . The concentrates f r o m the X A D - 4 columns contained detectable amounts of organic substances having the same retention time as those from the

Table II. Analysis of Selected Compounds in Water Samples from Sites 1 and 2 Compound

Sitel

Site 2

DCP TCP CA DCB BHC DEHP

nd 40 nd nd 12 100

nd 990 nd nd 13 30

N O T E : Values are expressed in parts per trillion; nd means none detected.



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X A D - 2 macroreticular resin columns. This situation implied that the X A D - 2 column was not effective in retaining completely all the solutes present in the water samples. [NOTE: The X A D - 2 resin column contained about 25% more packing, and the rate of percolation was about the same as that normally used for processing 200 L of tap water (21).] In addition, a variety of volatiles that appeared immediately following the solvent peak were also present. Subsequent analysis of these concentrates b y G C - M S indicated the presence of 6-chloro-2,4-diamino1,3,5-triazine (tentative), 2,5-diphenylisoxazole (tentative), tributoxyethyl phosphate (confirmed), bis(2-ethylhexyl) phthalate (confirmed), and dimethylbenzoic acid (confirmed) from site 1. The concentrate from site 2, however, showed the presence of 2,4,5-trichlorophenol (confirmed), B H C (confirmed), 2,5-diphenylisoxazole (tentative), bis(2-ethylhexyl) phthalate (confirmed), trimethylbenzene (confirmed), ethylbenzaldehyde (confirmed), ethylacetophenone (confirmed), hexanoic acid (confirmed), and 4-cyano-3,7,ll-tridecatriene (tentative). Reverse-Osmosis Study. The R O system consisted of six radial f l o w cells with flat sheet membranes (as discs), appropriate pumping, pressure regulators, and surge tank components along with stainless steel or P T F E polymer tubing and borosilicate glass reservoir. E a c h type of membrane, namely C A c , P A , and PBI, was represented b y two different porosities as determined b y standard N a C l rejection. Pure water permeation rates were determined at various times during the study. Accordingly, solutions of the six pollutants, singly and as mixtures, were subjected to a standardized R O run. Permeation was allowed to proceed for 90 min to equilibrate the membranes. This method permitted at least 10 m L of solution to permeate through even the low-flux membrane. Instead of taking the original concentration for the calculation of percent rejection of the solutes, the concentration after equilibration was used. Analysis of aqueous solutions of the polar compounds ( D C P , T C P , C A , and D C B ) at concentrations of 1-10 p p m was easily accomplished b y direct aqueous injection liquid chromatography. The Hamilton P R P - 1 reverse-phase column gave a better resolution of these compounds than the conventional reverse-phase columns. Acetonitrile/water mixtures have been found to be as effective as the buffered mobile phases recommended b y the manufacturer (28). Analyses of the nonpolar compounds ( B H C and D E H P ) at concentrations of 25-100 p p b were achieved b y X A D resin adsorption-desorption, concentration, and G C techniques. Table III presents the percent rejection of the selected six organic compounds, both when they are present individually and when mixed with others in aqueous solutions, and for the three pairs of membranes


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O R G A N I C P O L L U T A N T S IN W A T E R

Table III. Percent Rejections of Various Pollutants (Individually and Mixed) by Membrane Types Membrane Type DCP


TCP

CA

DCB

BHC

DEHP

ind mix 1 mix 2 ind mix 1 mix 2 ind 1 ind 2 mix 1 mix 2 ind mix 1 mix 2 ind 1 ind 2 mix 1 mix 2 ind 1 ind 2 mix

PA (92)°

PA (97)

CAc (91)

CAc (85)

PBI (99)

51 55 69 65 70 80 44 50 60 61 78 74 87 97 92 90 95 73 50 73

39

-32 -7 -35 -13 0 -9 -26 -20 -23 -32 15 24 42 55 37 34 31 50 -41 53

-41

11 49 78 60 81 88 0 8 35 47 100 86 97 100 94 84 98 50

51 62 57 65 75 35 37 41 54 74 83 92 95 95 90 m 34 (-) 91

-2

-31 -11 4 -21 -16 -27 -26 -46 21 10 28 31

33

24 23 80 74 80

PBI (89)

29 85

9 40 62 34 67 82 -7 -4 25 30 100 79 95 98 96 87 95 82 34 91

N O T E : ind denotes individual, and mix denotes mixture; (—) indicates sample lost. Values in parentheses indicate the percent rejection of NaCl.

0

with two different porosities (shown i n parentheses as percent rejection of N a C l ) . T h e data show that the C A c membranes are quite ineffective for concentrating or rejecting organic compounds i n general, and more so with respect to polar organic compounds w h i c h have l o w molecular weights and high solubilities. A m o n g the polar organic compounds studied, D C B was the only c o m p o u n d rejected between 10% and 42% b y the C A c membrane. The P A membranes have distinctly better rejection properties for the individual organic compounds (when present in their respective aqueous solutions) in comparison to the two other membrane types. However, P B I membranes have equally good rejection properties except in the cases of D C B and C A . W i t h respect to C A , the rejection behavior of P B I is analogous to the retention properties of polyurethane-carbon adsorbent (see Table I). T h e striking resemblance in percent rejection of P A and P B I membranes is their behavior toward D C B and B H C , and in these cases, their rejection is more than 75%. Comparatively, the percent rejection of these organic compounds i n their mixtures b y P A and P B I is better than when these compounds were present individually. The only possible synergistic effects might be noticeable between D C P and C A in the case of P B I membranes. Such mutually i m p r o v e d rejections might be ascribed to some ionic species separation after salt formation; however, this analysis is purely speculative and requires further inves-



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tigation. T h e C A c membrane has shown some slight improvement in its rejection behavior of the compounds in their mixtures. Also, the aisomer of B H C used in this study has been rejected b y the C A c membrane to the extent of an average of 46%; this value is similar to the 60% reported previously for the y-isomer (17). Table I V presents the comparative data on the permeation rates of the three types of membranes with two different porosities for various aqueous organic solutions and for pure water as measured over the duration of the study. The data shown here represent the relative chronological order i n w h i c h the samples were tested. In the beginning, even though the percent rejection of N a C l is high for P A and C A c (indicating small-size pores), the rates of permeation of pure water are higher for denser membranes than for membranes having lower percent rejection of N a C l . In the case of the P B I membrane, the reverse of this phenomenon is observed. As usually observed, the pure water permeation rates for the membranes plateau at 65-80$ of the original pure water permeation rate after several months of use probably because of compaction or other fouling mechanisms. Also to be expected is the general trend for individual solution runs to be somewhat slower than pure water runs. Apparently, there is little relation between the permeation rates of aqueous solutions containing trace levels of organic compounds and the rejection behavior of membranes except for the denser of the two P B I membranes. This finding indicates some unique properties of the P B I polymer. What is somewhat puzzling is the extremely slow rates of permeation for the mixture of compounds in the aqueous solution. This finding could be indicative of some aggregation phenomenon among the various components of the mixture due to an increase i n viscosity. Table IV. Water Permeation Rates of Pure Water and Pollutant Solutions through Membranes Membrane

PA(92)

PA(97)

CAc(85)

CAc(91)

PBI(99)

PBl(m)

Pure water (beginning) Pure water (60 days) Pure water (—150 days) D C P (-16 ppm) T C P (-19 ppm) C A (-18 ppm) C A repeat (—21 ppm) D C B (-1 ppm) B H C (-155 ppb) D E H P (-30 ppb) First mixture Second mixture

15.2 13.0 12.9 13.1 12.5 13.2 13.2 13.6 13.3 13.4 11.9 11.2

18.6 16.1 16.1 15.9 15.2 16.3 16.2 17.6 17.4 16.6 14.7 13.2

6.5 5.9 6.2 5.7 5.0 5.8 5.8 6.3 6.0 6.0 4.4 4.2

13.8 12.4 12.8 11.0 10.8 12.3 12.4 13.1 12.6 12.4 9.6 9.0

5.7 5.1 4.4 4.7 4.0 5.1 4.6 5.1 5.6 5.0 2.8 3.0

11.4 10.1 8.8 9.0 7.3 10.0 9.7 10.0 10.6 10.0 5.3 5.5

a

N O T E : Values are expressed in grams per hour. Values in parentheses indicate the percent rejection of NaCl.

a



176


Also, the dense P B I membrane is slow (99%). Although this membrane exhibited, in general, the best rejection characteristics, the very l o w flux observed is a definite drawback of such dense membranes. A comparison of the approximate mass balance calculations for the various compounds and for all the membranes combined is presented in Table V . These numbers indicate only an attempt to account for all the organic material in the various runs (concentration volume values at the beginning of the run, namely, the feed solution only; and at the end of the run, namely, the feed solution plus permeate). Again, for the small, water-soluble molecules ( D C P , T C P , and C A ) , total account ability is quite good, whereas for the large, less soluble molecules ( D C B , B H C , and D E H P ) , significant amounts of the compounds have disap peared during the course of the run. Such discrepancies for C A c membranes have been previously noted (17, 18, 29), and it is tempting to speculate that the membranes themselves are somehow retaining the more hydrophobic compounds. However, one can only begin to study this problem b y ensuring that all components used in the feed system are composed of inert materials such as stainless steel, glass, or P T F E polymers. Another interesting comparison is outlined in Table V I where the Table V .Reservoir Mass Balances Initial Permeate Amount After Total

Compound (mass units) DCP (mg) TCP (mg) CA (mg) CA (repeat, mg) DCB (mg) BHC (ΙΟ" mg) BHC (repeat, 10" DEHP (HT mg) 3

3

3

DCP (mg) TCP (mg) CA (mg) DCB (mg) BHC (ΙΟ" mg) 3

DCP (mg) TCP (mg) CA (mg) DCB (mg) BHC (10 mg) DEHP (10- mg) 3

3

mg)

Individual Runs 8.37 15.89 7.66 6.62 18.42 8.57 9.54 18.43 8.59 10.64 20.56 8.56 1.22 0.28 0.52 77 633 149 20 135 52 33.0 3.9 7.9 Mixture 6.63 16.04 8.54 5.23 16.93 8.98 4.67 10.14 4.48 0.37 1.53 0.70 39 221 94 Repeat Mixture 9.84 4.86 4.12 3.32 10.43 5.08 3.93 8.02 3.73 0.46 2.65 1.07 130 27 70 123 16 7

Percent Recovery Recovery 16.03 15.19 18.13 19.20 0.79 226 72 11.8

100 82 98 93 65 36 53 36

15.17 18.70 9.15 1.07 133

91 110 90 70 60

8.98 8.40 7.66 1.53 97 23

91 81 96 58 75 19


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Table VI. Comparison of Feed Concentrations Compound DCP

ind mix ind mix ind mix ind mix ind mix ind mix

TCP


CA DCB BHC DEHP

Original

After Equilibration

Final

7.7 7.0 9.2 7.3 8.2 2.5 0.68 0.76 0.05 0.06 0.10 0.10

6.7 5.1 8.7 5.1 7.6 2.4 0.45 0.46 0.05 0.07 0.11 0.04

7.8 6.9 9.5 7.2 8.6 3.1 0.47 0.56 0.05 0.08 0.00 0.01

NOTE: Values are expressed in parts per million; ind denotes individual, and mix denotes mixture.

concentrations of the selected organic compounds in the feed solution at various times throughout the run are compared. The w o r d "original" denotes the concentration of the feed solution at the beginning of the run; "equilibration" indicates the concentration of the feed solution after 90 m i n of the R O run with permeation; and " f i n a l " denotes the concentration of the feed solution at the termination of the R O run. Although we are dealing with sometimes offsetting effects of various membranes, one should note the disappearance of most of the D E H P . A similar observation was noted during the adsorption studies. Another indication of the somewhat complex initial few hours of interaction between membrane and the solutes in the feed solution, that is, the earlier part of the R O run, can be found in Table V I I . Here, the rejection characteristics of the membranes after 90 m i n of permeation are compared with a final value obtained for the feed solution at the end of the R O run. In most cases, the membranes have not reached a saturation or complete equilibration value even after 10-20 m L of solution has been allowed to permeate the membranes. Although the mechanics of interaction between the membrane and the solute requires sufficient time, and such equilibrations may not be significant for extended runs for several weeks, these details should be considered in exploratory work on the R O process.

Conclusions X A D - 2 and X A D - 4 macroreticular resin adsorbents were found to be adequate to accumulate the organic pollutants considered in the present study except for bis(2-ethylhexyl) phthalate. Polyurethane-carbon ad-


178



Table VII. Comparison of Membrane Rejections at 90 min and at End of Run Compound

PA(92)

PA(97)

CAc(91)

CAc(85)

PBI(99)

PBl(89)

DCP TCP CA DCB

68/51 76/65 48/44 100/78

64/39 72/57 48/35 100/74

59/32 57/-13 -6/-26 100/15

24/-41 -32/-11 -16/-16 100/21

100/11 98/60 77/0 100/100

100/9 99/34 8/-7 100/100

NOTE: The first value is the rejection at 90 min; the second value is the rejection at the end of the run. Values in parentheses indicate the percent rejection of NaCl.

a

sorbent was observed to be ineffective for concentrating 4-chloroaniline and bis(2-ethylhexyl) phthalate. A m o n g the membranes currently inves tigated i n the R O technique, P A membrane was found to be superior to P B I and C A c material. F o r the concentration of bis(2-ethylhexyl) phthalate, the R O technique proved to be superior to X A D resin adsorption. C A c membrane was noted to be ineffective for rejecting the investigated compounds.

Acknowledgments The authors extend their sincere gratitude to F . M . Benoit a n d R. O ' G r a d y for their G C - M S analysis, and w e wish to thank J . G o d i n , M . Abedini, and K . Diedrich for technical assistance. W e are indebted to S. Sourirajan, T . Matsuura, and A . Baxter for their generous advice on many phases of R O studies; G . L . L e B e l and R. Otson for critically reviewing the manuscript; and Jean Ireland for w o r d processing. This chapter is abstracted from a report presented to Health and Welfare Canada as part of contract number 887-1982/83.

Literature Cited 1. Kool, H. J.; van Kreijl, C. F.; van Kranen, H. J.; De Greef, E. Sci. Total Environ. 1981, 18, 135. 2. Williams, D. T.; Nestmann, E. R.; LeBel, G. L.; Benoit, F. M.; Otson, R. Chemosphere, 1982,11,263. 3. Fishbein, L. Toxicol. Environ. Chem. Rev. 1980, 3, 145. 4. Volkoff, A. W.; Creed, C. J. Liq. Chromatogr. 1981, 4, 1459. 5. Drevenkar, V.; Frose, Z.; Stengl, B.; Tkalcevic, B. Mikrochim. Acta 1985, 1, 143. 6. Laane, R. W. P. M.; Manuels, M. W.; Staal, W. Water Res. 1984, 18, 163. 7. Suffet, I. H.; Brenner, L.; Coyle, J. T.; Cairo, P. R. Environ. Sci. Technol. 1978, 12, 1315. 8. Dressler, M. J. Chromatogr. 1979, 165, 167. 9. Harris, J. C.; Cohen, M. J.; Grosser, Ζ. Α.; Hayes, M. J. EPA Project No. PB-81-106585; U.S. Environmental Protection Agency. U.S. Government Printing Office: Washington, DC, 1981.



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10. Narang, A. S.; Eadon, G. Int. J. Environ. Anal. Chem. 1982, 11, 167. 11. Stuber, Η. Α.; Leenheer, J. A . Anal. Chem. 1983, 55, 111. 12. Suffet, I. H.; McGuire, M. J. Activated Carbon Adsorption of Organics from the Aqueous Phase; Ann Arbor Science: Ann Arbor, MI, 1981; Vols. 1 and 2. 13. Babjack, L. J.; Chau, A. S. Y . J. Assoc. Off. Anal. Chem. 1979, 62, 1174. 14. Sourirajan, S. In Sythetic Membranes; Turbak, A . Ed.; ACS Symposium Series 153; American Chemical Society: Washington, DC, 1981; Vol. 1, pp 11-62. 15. Kopfler, F. C.; Coleman, W. E.; Melton, R. G.; Tardiff, R. C.; Lynch, S. C.; Smith, J. K. Ann. Ν.Y. Acad. Sci. 1977, 298, 203. 16. Deinzer, M.; Melton, R.; Mitchell, D. Water Res. 1975, 9, 799. 17. Malaiyandi, M.; Blais, P.; Sastri, V. S. Sep. Sci. Technol. 1980, 15, 1483. 18. Fang, H. H. P.; Chian, E. S. K. Environ. Sci. Technol. 1976, 10, 364. 19. LeBel, G. L.; Williams, D. T. Bull. Environ. Contam.Toxicol.1980, 24, 397. 20. Hurst, R. E.; Settine, R. L.; Fish, F.; Roberts, E. C. Anal. Chem. 1981, 53, 2175. 21. LeBel, G. L.; Williams, D. T.; Benoit, F. M. J. Assoc. Off. Anal. Chem. 1981, 64, 991. 22. Riggin, R. M.; Howard, C. C. Anal. Chem. 1979, 44, 139. 23. Malaiyandi, M.; Benoit, F. M. J. Environ. Sci. Health 1981, A16, 215. 24. Nguyen, T. D.; Chan, K.; Matsuura, T.; Sourirajan, S. I&EC Prod. Res. Dev. 1984, 23, 501. 25. Malaiyandi, M. J. Assoc. Off. Anal. Chem. 1978, 61, 1459. 26. Matsuura, T.; Taketani, Y.; Sourirajan, S. Proceedings of the 4th Bioenergy Research and Development Seminar, National Research Council of Canada 1982, 529. 27. Malaiyandi, M.; Zhow, S., unpublished results. 28. Lee, D. P. J. Chromatogr. Sci. 1982, 20, 203. 29. Chian, E. S. K.; Bruce, W. N.; Fang, H. H. P. Environ. Sci. Technol. 1975, 9, 52. RECEIVED for review August 14, 1985. ACCEPTED January 7, 1986.


Concentration of Selected Organic Pollutants: Comparison of

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