Environ. Sci. Techno/. 1995, 29, 856-863
Introduction
NICHOLAS J. FENDINGER,* WILLIAM M . B E G L E Y , D . C . M C A V O Y , AND W . S . E C K H O F F The Procter and Gamble Company, The Ivorydale Technical Center, 5299 Spring Grove Avenue, Cincinnati, Ohio 4521 7
Alkyl ethoxylate alcohols (AE) are used in a wide variety of household cleaning products. In order to monitor environmental levels of AE and to determine AE removal during wastewater treatment, an analytical procedure that provides total AE concentration resolved by alkyl chain length for various environmental matrices (influent, effluent, and river water) was developed. The method utilizes a reverse-phase column to extract and concentrate AE from surface waters and wastewaters and utilizes strong anionic and cationic exchange columns to remove potential interferences. AE were reacted with hydrogen bromide to form corresponding alkyl bromide derivatives that were analyzed by capillary gas chromatography with mass selective detection. Recovery of AE from influent, treatment plant effluent, and river water was quantitative (65-102%) over a range of concentrations for all matrices. AE removal was 99% at two activated sludge treatment plants and 92% a t t w o trickling filter plants. Total AE in low dilution (effluent to river water) surface waters downstream from wastewater treatment plants were less than 0.037 m g l L.
856 1 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29. NO. 4, 1995
Alkyl ethoxylates (AE) are nonionic surfactants currently used in a wide variety of household and commercial cleaning applications. AE surfactants consist of an aliphatic hydrocarbon chain connected to a block of one or more ethoxylate groups (Figure 1). Commercially available AE consist of material mixtures with alkyl chain lengths of 1218 carbons; however, in the United States, most AE have alkyl chain lengths of 12- 15 carbons. Alkyl ethoxylatesare typically identified by the range of alkyl chain lengths present in the mixture and the molar average number of ethoxylate groups across all alkyl chain lengths. Consumer products that contain AE surfactants are typically disposed of “down-the-drain’’after use and enter municipally owned wastewater treatment plants. Once introduced into wastewater treatment systems, AE undergo both aerobic and anaerobic biodegradation (1-3) and are expected to be highly removed (4-6). Given the widespread use of AE, a number of methods have been developed to measure their concentrations in environmental matrices and to investigate AE behavior in laboratory test systems. The simplest of these methods are nonspecific techniques that concentratem from water samples along with other nonionic surfactants by either solvent extraction or sublation. Extracted AE are then reacted to form a complex that can be measured either spectrophotometrically or by titration. Common complexing reagents include cobalt isothiocyanate ( 7 ) , potassium picrate (8),and iodobismuthate (9). The nonspecific methods of analysis are subject to a number of positive and negative interferences and do not distinguish AE from other types of nonionic surfactants. Specific methods of analysis include high-pressure liquid chromatography (HPLC) with derivatizationand W detection (10,11),gas chromatography (GC)with flame ionization detection (512,131,and supercriticalfluid chromatography (SFC) with flame ionization detection (14). AE homologs can be resolved by HPLC either as a function of alkyl chain length or ethoxylate chain length depending on the chromatographic conditions used. For example, Schmitt et al. (10) used reverse-phase chromatographic conditions to separate AE by alkyl chain length and normal-phase chromatographic conditions to separate AE by ethoxylate chain length. Because AE do not contain a chromophoric group, HPLC analyses usually include derivatization by phenyl isocyanate (10, 11)combined with W detection to obtain adequate sensitivity needed for environmental analysis. Gas chromatographic methods also require derivatization to either simplify the analysis or produce a more volatile analyte that is better suited to GC analysis. The most commonly used derivatizationmethod is to cleave ethylene oxide groups by reaction with hydrobromic acid to form alkyl bromides that are analyzed by GC equippedwith either flame or electron capture detection (5, 12, 13). Because the cleavage reaction products formed are independent of ethoxylate chain length, the number of components analyzed is reduced. While AE can be resolved using specialized high-temperature GC conditions (14),the alkyl bromide derivatives are more volatile and better suited to
0013-936X/95/0929-0856$09.00/0
0 1995 American Chemical
Society
RO - (CHZ- CH2O)n- H R represents alkyl chainlength of 12 to 15 carbons
Water Sample f C-1 Reverse Phase Column
c
Discard water
1
n represents ethoxylated chainlength of 1 to 20 FIGURE 1. Chemical structure of alkyl ethoxylate nonionic surfactants.
GC analysis and do not discriminate against high molecular weight components. Chromatographic resolution of individual homologs in AE mixtures can be accomplished using supercritical fluid chromatography (SFC). Silver and Kalinoski (14)compared the analysis of AE by SFC and high-temperature GC. SFC analyses used a density-programmedcarbon dioxide mobile phase to obtain homolog resolution of C12-C14 while high temperature GC separations were obtained with a hightemperature polyimide-coated fused silica capillary column. High-temperature GC was found to have the advantage of resolving C12-C18 alcohol ethoxylate oligomers but discriminated against high molecular weight components where SFC provided better chromatographic performance. Although SFC and high-temperature GC provide superior chromatographicresolution to either HPLC or GC combined with derivatization, analysis of low AE concentrations in environmental samples is complicated by the number of components present and limited by the low mass contribution of each individual component. In this study, we developed an analytical technique to measure AE resolved by alkyl chain length for various environmentalmatrices (innuent, effluent, and river water). This technique utilizes hydrogen bromide derivatization combined with GC/mass selective detection. The method described simplifies AE analysis and is more specific than previous techniques. The utility of this method was demonstrated by spike and recovery in the various environmental matrices. AE removal by activated sludge and trickling filter wastewatertreatment, diurnal concentration changes that result from the varied use of AE-containing products, and concentration measurements in low dilution receiving streams are also presented.
Experimental Section A flow chart of the AE analysis procedure is shown in Figure 2. Details of the analytical procedure are provided in the following sections. Reagents andMaterials. Reverse-phase (RP)C-1, strong anionic exchange (SAX), and strong cationic exchange ( S a columns (500 mg) were obtained from Varian Sample Preparation Products (Harbor City, CAI. Extractions were carried out on a Supelco (Belfonte, PA) vacuum manifold. Derivatization reactions were carried out with a Pierce Reacti-Therm unit. High-puritywater used in this study was produced with the Waters (Milford,MA) Milli-Q system. HPLC-grade ethyl acetate, methylene chloride, and methanol were obtained from Fisher Scientific (West Haven, CT). Hydrogen bromide (30%wt solution in acetic acid) used for AE derivatization was obtained from Aldrich Chemical (Milwaukee,WI). Akyl bromide standards (1-bromolinear alkanes, c12,13,14,15)were obtained from Sigma Chemical Co. (St. Louis, MO) and had reported purities of greater than 96%. Commercially available AE surfactants obtained from Shell Development (Houston, TX) were used in spike and
Elute with 15 ml 1 :1 Ethy1acetate:MethanoI through Stacked SCX and SAX Columns t Evaporate to Dryness
c
Derivatize with HBr t
Extract alkyl bromides with MeCh 1
Evaporate to 0.5 mL f Analyze by GC/MSD FIGURE 2. Alkyl ethoxylate analysis scheme.
recovery experiments, in derivatization efficiency experiments, and as calibration standards. Neodol25-9 has an average ethoxylate chain length of 9 and the following alkyl distribution: C12, 28%; C13, 29%; C14, 24%; and CIS,20%. This material was chosen for matrix spike and recovery experiments because it contains the range of materials currently used in commerce. A second Shell material, Neodol45-2.25 was used to test the robustness of derivatization technique. The Neodol 45-2.25 material has an average ethoxylate chain length of 2.25 and the following alkyl distribution: c13, maximum 3%;c14, 51%; C15, 48%; and C16,maximum 1%. Radiolabeled (14C) C&3 and C13E9 were custom synthesized by Shell Development (Houston, rx)and were used to optimize extraction conditions. Radiochemical purities of these materials exceeded 90%. Sample Collection. Samples were collected in polycarbonate or glass bottles. Polycarbonatebottles (250 mL) were rinsed three times with tap water and three times with high-purity water. Each bottle was also rinsed with a small amount of the matrix to be added. Glass containers were preconditioned with a suitable sample matrix prior to sample addition to prevent sorption of AE on container walls. Sample preservation was accomplished by the addition of 8%of the sample volume of a 37%formaldehyde solution. Grab samples of untreated wastewater prior to entering the treatment plant (influent), treated plant effluent at the dischargepipe (effluent),and river water were collected on two occasionsat the Sycamore, OH, activated sludge wastewater treatment plant for purposes of method validation and preservation. Validation experiments consisted of AE spike and recovery using Neodol25-9 in influent, effluent, and river water at two concentrations for each matrix. Additional sampling was also conducted at treatment plants located in Kenton, OH (activated sludge); Grinnel, IA (tricklingfilter);and Oskaloosa, IA (activated sludge and trickling filter plants) to (a) further demonstrate the utility of the method with additional spike and recovery experiments with samples collected from different locations and (b) obtain more detailed information on AE removal during wastewatertreatment. The treatment plants were selected for sampling based on treatment type (trickling filter and activated sludge), low industrial contributions to total VOL. 29, NO. 4, 1995 I ENVIRONMENTAL SCIENCE &TECHNOLOGY 1857
wastewater flow, and low surface water dilution. This additional sampling, conducted during late summer and fall, consisted of the collection of 24-h, 3-day flow-weighted composite samples of influent, effluent from the primary clarifier (1" effluent), and effluent. Grab samples were collected in the receiving water upstream and downstream from the treatment plant discharge. Flow-weighted composite samples were manually prepared by combining samples collected hourly with an ISCO autosampler. In addition, hourly collected samples of influent and effluent at the Oskaloosa trickling plant were combined into two h composites over a 24-h period to investigate AE diurnal concentration variations. Sample Extraction and Derivathtion. RP extraction columns were fittedwith a 75-mLsample reservoir equipped with a glass fiber filter. The extraction columns and filter were preconditioned prior to sample extraction by eluting each column with 5 mL of methanol followed by 10 mL of high-purity water. Samples were passed through the extraction column at a flow that did not exceed 5 mLlmin. Sample volumes used for analysis of the various matrices studied were as follows: 50 mL influent and 1" effluent; 200 mL for effluent and river water. Following sample elution, the RP extraction column was dried slightly by drawing air through the column. SCX and SAXcolumns used to remove potential cationic and anionic interferences were prepared by elution with 5 mL of methanol. The RP extraction column was stacked on top of the SAX column, which was placed on top of the SCX column. A 1:l ethyl acetatelmethanol solution (15 mL) was used to first rinse the sample containers to remove sorbed AE and was then poured onto the glass fiber prefilter and eluted through the stacked columns. AE and potential anionic and cationic interferences were eluted from the C1 extraction column and passed directly through the SAX and SCX extract cleanup columns. The SAX and SCX columns retained anionic and cationic materials while nonionic AE were unretained. A n additional 5-mL methanol rinse was used to complete the sample elution. Sample extracts were concentrated to 2-3 mL at 40 "C under a stream of nitrogen. The sample was then transferred to a 5 mL vial and evaporated to dryness under a stream of nitrogen at 40 "C. Conversion of AE to alkyl bromide derivatives was accomplished by adding 500 ,uL of hydrogen bromide (33%solution in glacial acetic acid) to each dried extract. The reaction vessels were capped tightly and heated to 100 "C for 4 h. The samples were allowed to cool to room temperature, and 2 mL of highpurity water was added to each sample. Alkyl bromide derivatization products were then extracted from the derivatization mixture with three 500-pLmethylene chloride extractions. Methylene chloride extracts were then evaporated to approximately500,uLinataredvialpriorto analysis by GC/MSD. Exact volume of each extract was determined by weight. Instrumental Analysis. Alkyl bromide AE derivatives were analyzed with a Hewlett Packard (HP, Palo Alto, CA) Model 5890 gas chromatograph equipped with a HP Model 5971A mass selective detector (MSD) and Restek (Bellfonte, PA) Rtx-1 (dimethylpolysiloxane)60 m x 0.25 mm, 0.25pm film thickness bonded-phase capillary column. Chromatographic conditions were as follows: injection, splitless; carrier, He; injector temperature, 280 "C; initial oven temperature, 50 "C for 2 min and then ramped at 10 "Clmin300 "C and held for 8 min; detector temperature, 280 "C. 858
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 4, 1995
A
B
J
J
D
io00
i
FIGURE 3. GCMS chromatograms of alkyl bromides formed from alkyl ethoxylate surfactants. Shown are chromatograms for the Neodol45-225 standard (A), treatment plant affluent (B), treatment plant influent (C), and river water (D). Alkyl bromides with alkyl chains of 12 (I); 13 (2); 14 (3); and 15 (4) are identified in each chromatogram.
The MSD was operated in the single ion monitoring mode. Electron impact (EI) ionization was used. Because the E1 spectra for alkyl bromides are similar, the ions monitored for all chain lengths were 135and 137. The ions reflect the isotopic ratio of 79Brand 81Br (approximately 50/50) and have the formula C4HBBr-.Quantification was accomplished with the 135 ion; the 137 ion was used as a qualifier ion and should be present at the approximately the same abundance as the 135 ion. The minimum alkyl bromide detectable quantity with a 1-pL injection was approximately 500 pg for each alkyl chain length with a signal to noise ratio of 35. Chromatograms for all matrices were generally free from other peaks and were similar as illustrated in Figure 3.
14C activity in methods development experiments was measured by liquid scintillation spectrometry with a Beclanan LS 7800 liquid scintillation spectrometer. Samples were corrected for background and quench. Quantitation.. Alkyl bromides were analyzed by injecting 1pL of the methylene chloride extract. The instrument was calibrated with either commercially available alkyl bromides or standards prepared by derivatizing the Neodol 25-9. Calibration by either technique provided similar results. In most cases, standards prepared by both techniques were runwith samples. This technique allowed the derivatization efficiency to be monitored. AE concentrations with this method are determined by measurement of alkyl bromide derivatization products. Because the derivatization is independent of ethoxylate chain length, peaks measured are resolved by alkyl chain length and are a summation of all ethoxylate chain lengths for each alkyl chain length present in the original sample. Therefore, in order to calculate the weight ofAE present in the original sample, an ethoxylate distribution for each alkyl chain length in the original mixture must be assumed. This is illustrated in the example calculation for C12 AE where weight of C,,EO in sample = weight of C,,Br measured x (MW C,,EO,/MW C,,Br) C12EOn represents the average ethoxylate distribution for materials with a C12 alkyl chain length in the starting material. The calculations forthis workassumed an average ethoxylate distribution of 9.0 for all alkyl chain lengths and is based on estimated consumer product use of AE surfactants. A previous researcher (5)assumed an average ethoxylate distribution of seven based on a widely used AE surfactant (Neodol45-7).
Results and Discussion Method Evaluation. The efficiency of the method to extract and measure AE surfactants is dependent on the efficiency of the reverse-phase extraction, extract cleanup steps, and derivatization efficiency. The efficiency of the extraction and extract cleanup steps was evaluated using 14C-labeled C13E3 and C13E9 AE. The radiolabeled AE materials allowed the rapid optimization of the reverse-phase AE extraction without having to conduct the derivatization and GC analysis. Results with the labeled AE materials demonstrated that AE were quantitatively extracted with the C1 reverse-phase column and quantitatively eluted with a 1:l mixture of ethyl acetate and methanol; they were not retained by either the SAX or SCX columns. Recoveries of the labeled material exceeded 90% for the combination of the extract and cleanup steps. Derivatization of AE to form alkyl bromides must be quantitative and be independent of ethoxylate chain length for reliable measurement of AE in environmental samples. Quantitative derivatization of the AE was demonstrated throughout the study by comparison of slopes obtained from calibration curves determined from pure alkyl bromide materials and from analysis of alkyl bromide materials obtained from derivatization of Neodol25-9. To determine if derivatization efficiencyvaried as a function of ethoxylate chain length, a calibration curve for the CI4chain length prepared from Neodol 25-9 and 45-2.25 was compared. The Neodol25-9 has an average ethoxylate distribution of
Peak Area
150,000
100,000
50,000
0
* 0
0.05
0.1
0.15
0.2
Amount Injected(micr0-moles)
FIGURE 4. Molar response of the CI, AE alkyl homolog following derivatization of two different ethoxylate chain lengths.
nine while the Neodol45-2.25 has an average ethoxylate distribution of 2.25. Shown in Figure 4 is the instrument response as a function of C14 AE molar concentrations in Neodol25-9 and 45-2.25. The similar response obtained for the differentAE materials demonstrates that derivatization was independent of AE ethoxylate chain length. The efficiency of the entire method for analysis of AE from various matrices was evaluated by analysis of samples amendedwith Neodol25-9. Neodol25-9contained all alkyl chain lengths of interest (c12,13,14,15). Percent recovery of the Neodol25-9 was calculated by dividing the amount of AE in the background-corrected sample by the spike level. AE recovery from high-qualitywater, influent, effluent, and river water collected from the Sycamore, OH, wastewater treatment plant was quantitative throughout the range of concentrations investigated (Table 1). Utilizing sample volumes of 50 (influent)to 200 mL (effluent and river water), a final extract volume of 1 mL, and a 1-pL injection volume, the observed minimum detectable concentration for each alkyl chain length AE homolog was approximately 0.001 mglL for effluent and river water and 0.01 mg/L for influent. The utility of the method under various water chemistries and waste loads found at different plants was demonstrated by spike and recovery experiments on flow-weighted, 24h, 3-day composite samples collected at one trickling filter plant and two activated sludge plants in the midwestern United States. Results from these spike and recovery experiments are summarized in Table 2. Quantitative recovery of AE was demonstrated for all the matrices at all the locations. Recovery of AE from effluent samples was consistently high (average 132%),indicating a tendency to overestimateAE effluent concentrations. Further analysis of mass spectra and chromatograms did not show the presence of materials that would cause an interference in the effluent sample. However, the presence of neutral organics that react to form alkyl bromides such as esters of long-chain alcohols could be a source of positive interference that could not be distinguished from AE. The presence oflong-chain alcohols in treatment plant effluent is unlikely given the high potential for biodegradation of these materials. Total AE recovery from all matrices and concentrations from the three different treatment plants averaged 103 f 21%. Given the potential variability in wastewater matrices, the method could be further improved by use of an internal standard for quantification. Further evaluation is also needed if the method is to be used specifically for quantitation of alkyl branched AE to determine MS fragmentation patterns. VOL. 29, NO. 4,1995
ENVIRONMENTAL SCIENCE
TECHNOLOGY
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TABLE 1
Percent Recovery of Alkyl Etkgxylate Surfactants from Hig4-Put-i~Water, Influent, Effluent, and River Water Collected at Sycamore, OH, Wastewater Treatment Plant with Standard Deviation YO recovery sample/AE amendment, (mg/LI high-purity water 0.05 mg/L ( n = 2a) 0.50 mg/L ( n = 2) influent 2.0 mg/L ( n = 5) 4.0 mg/L ( n = 6) effluent 0.1 mg/L ( n = 6) 0.2 mg/L ( n = 6) river water 0.05 mg/L ( n = 3) 0.2 mg/L ( n = 6) a
97b 72b
103b 936
c15
total
60b 86b
996 95b
99fl5C 87flc
6 5 f 18
83 f 19 75 f 24
73 f 34 55 f 13
77 f 19 6 5 f 18
7 8 f 16 6 5 f 18
70 f 41 79 f 24
100 f 16 98 f 9
112f9 1 0 2 f 11
109 f 13 100 f 10
9 8 f 12 94 f 9
87 f 39 75 f 6
97 f 2 102 f 8
103 f 21 121 f 17
103 f 26 105 f 13
9 8 f 18 102 f 17
80 f 13
Indicates number of samples analyzed. Indicates average recovery from two determinations. Indicates range from two determinations.
TABLE 2
Percent Recovery of Alkyl Etheqhte Surfactants from Water Collected at Wastewater Treatment Facilitiesa % recovery*
treatment plant/matrix Kenton, OH (AS) influent 1" effluent effluent up river Down River Grinnel, IA (TF) influent 1" effluent effluent up river down river Oskaloosa, IA (AS) influent 1" effluent effluent up river down river
CIZ
CIS
CM
CI5
total
NDC 88 133 93 110
ND 103 134 93 104
ND
ND 97 143 85 96
ND
89 135 92 103
74 78 145 115 97
75 80 148 127 92
85 79 138 108 89
87 86 144 142 109
81 143 122 97
70 75 130 124 101
74
66 84 102 80 94
78 80 141 130 127
72 79 122 110 99
80 115 108 74
95 136 91 103
80
a Spike levels were 2 mg/L influent and 1" effluent and 0.2 mg/L effluent and riverwater. *Recoveries are based on analysis of a single sample of each matrix at each treatment plant. ND, not determined.
Sample Preservation. Percent recovery of AE from samples of influent spiked with 4 mg/L, effluent spiked with 0.2 mg/L, and river water spiked with 0.2 mg/L and analyzed at time 0, 1, and 9 months averaged 103 k 18%. There was no trend of decreased recovery as a function time, nor did recoveries fall outside the range expected from precision of the method. These results demonstrated that samples of influent, effluent, and river stored in polycarbonate bottles and preserved with 8%formalinwere stable for periods up to 9 months. AE Environmental Levels. Alkyl homolog and total AE concentrations plotted as a function of time for influent and effluent collected at the Oskaloosa, IA, trickling filter treatment plant are shown in Figure 5A-C. The most abundant AE alkyl homologs in the influent are C ~ and Z (214. The concentrations of Clz and C14and the concentrations of C13 and C15 closely follow each other over the 24-h period sampled. This is not unexpected because much of 860
Clk
c13
c12
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29. NO. 4, 1995
the C ~and Z C14 AE are both derived from natural oils while C13 and CISare derived from petrochemically derived oils. The concentration relationship between alkyl homologs observed in influent was not present in effluent from the Oskaloosa, IA, trickling filter plant. The C14AE homolog is present in the highest concentration and varies between approximately 0.05 and 0.07 ppm while concentrations of other AE alkyl homologs do not exceed 0.05 ppm and do not vary as a function of time. Total influent AE concentrations are highest (3.5 ppm) during morning (8-11A.M.) and evening hours (7-1 1 P.M.) when the use of surfactant-containing products by consumers is expected to be the greatest. The variation of surfactant concentration as a function of time is very similar to that previously observed for alkyl sulfate (AS) anionic surfactants (17). Effluent AE concentrations are independent of influent concentrations and remain relatively constant at approximately 0.15 ppm. The relatively consistent effluentAE concentrations and the lack of correlation between influent and effluent can be explained by the association of AE with suspended solids and the uniform concentration of suspended solids (about 10 mg/L) in the effluent from the treatment plant. Thus, the amount ofAE present in the effluent is probably controlled by the suspended solids concentration. Determination of an AE sludge partition coefficient (Kd) and measurement of AE partitioned on solids in effluents will be needed to confirm this hypothesis. Average influent and effluent concentrations calculated from this data are 1.81 and 0.13 mg/L, respectively. This corresponds to an AE removal of 93% during wastewater treatment. To obtain better estimates of AE removal during wastewater treatment 24-h, 3-day composite samples collected from two trickling filter and two activated sludge treatment plants were analyzed. These were the same samples analyzed for background levels of AE and were used to evaluate recovery of AE from treatment plant matrices. Results from these analyses are summarized in Table 3. TotalAE influent concentrations ranged from 0.68 mg/L at Grinnel, IA, to as high as 3.67 mg/L at Oshaloosa, IA (activated sludge). The lower influent concentration measured at Grinnel compared to the other plants can be attributed to significant rainfall immediately preceding and during the sample collection. This rainfall probably resulted in water infiltration into the wastewater distribution system
Concentration ( ppm) 1.5
I*
I
C-12 C-13 C-14C-15 +-+-I\,
-
11:30am
7:30
3:30
1:30pm
5:30
11:30 3:30 7:30 9:30 1 :30am 5:30 9:30
0.5 0.4 0.3
0.2 0.1
0 3:30 7:30 11:30 3:30 7:30 1 1 :30am 1:30pm 5:30 9:30 1 :30am 5:30 9:30 4
3
2
1
0 3:30 7:30 11:30 3:30 7:30 1:30am 1:30pm 5:30 9:30 1:30am 5:30 9:30
Time of Day FIGURE 5. AE homolog concentrations as a function of time in influent (A) and effluent (B) collected at the publicly owned wastewater treatment facility in Oskaloosa, IA. Total AE concentrations in influent and effluent plotted as a function of time are shown in panel C.
and dilution of the surfactant present. Influent C12and C14 alkyl homologs were present in the highest concentration as was observed in the diurnal sampling conducted at Oskaloosa IA. AE influent and effluent concentrations are comparable to levels found by Wee (5) using a similar analytical
technique. In the study conducted by Wee (9,influent and effluent C14and C15AE levels collected in morning and afternoon grab samples from a single plant ranged from 0.19-0.47 mglL and from 0.008-0.12 mglL, respectively. The concentrations measured in these grab samples fall within the range of concentrations measured in this study. VOL. 29, NO. 4, 1995 / ENVIRONMENTAL SCIENCE &TECHNOLOGY
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TABLE 3
AE Concentrations Maastired in Influent, 1" Eluelent, Effluent. River Water above Outfall, and River Water bebw Outfall at Two Activated Sludge and Two Trickling Filter Wastewater Treatment Plants concentration (m@) sampling location
CIZ
c13
Kenton, OH (ASa) 1.13 0.43 infIue nt 1.19 0.35 1" effluent 0.003 0.001 effluent 0.001 0 up river down river 0.006 0.002 Grinnel, IA (TFb) influent 0.19 0.069 0.17 0.48 1" effluent 0.010 0.003 effluent 0.005 0 up river 0.003 0.007 down river Oskaloosa, IA (ASa) influent 1.22 0.60 1" effluent 0.97 0.37 effluent 0.009 0.013 up river 0.002 0.013 0.008 0.010 down river Oskaloosa, IA (TFb) influent 0.82 0.34 0.82 0.31 1" effluent 0.028 0.010 effluent 0.002 0 up river 0.009 0.003 down river
c14
CIS
total
0.94 0.88 0.004 0.002 0.005
0.71 0.40 0.003 0.014 0.005
3.21 2.82 0.011 0.017 0.018
0.22 0.14 0.022 0.01 1 0.009
0.20 0.16 0.015 0.004 0.011
0.68 0.95 0.050 0.020 0.030
1.25 0.88 0.048 0.010 0.020
0.61 0.44 0.0 0 0.0
3.67 2.67 0.071 0.026 0.037
0.86 0.81 0.033 0 0.005
0.65 0.56 0.043 0 0.017
2.67 2.50 0.114 0.002 0.034
a AS indicates activated sludge type plant. TF indicates trickling filter type plant.
Total AE concentrations also agree well with predicted concentrations (2-3 mg/L) that are based on AE use and per capita water consumption (15, 16). Removal of AE by primary treatment was less than 12% at the plants sampled. Effluent from the primary clarifier at Grinnel was higher than concentrations measured in the influent and was probably caused by the rain event that occurred during the sampling at this location. Total AE removal ({ 1 - effluent AE concentration/influent AE concentration} x 100) ranged from 92% for the trickling filter plant at Grinnell, IA, to as high as 299% for the activated sludge plant at Kenton, OH. Average AE removal for the two trickling filter plants and the two activated sludge plants was 94% and 99%, respectively. The AE removals for trickling plants in this study were similar to those measured for alkyl sulfate surfactants at two trickling filter plants that ranged from 90-94% ( 1 7 ) and greater than removals measured for linear alkyl benzenesulfonate (77%;18, 19). The AE removals measured in this study confirm quantitatively the high removal predicted by laboratory biodegradation testing and bench-scale activated sludge treatment experiments. For example,Tobin et al. (13)found complete degradation (99%)of Dobanol25-9 in shake flask experiments and in a bench-scale activated sludge plant. Kravitz et al. (6)also demonstratedthe potential for high AE removal in BOD tests and simulated activated sludge treatment. It was not determined in this study whether removal was accomplished primarily by sorption or biodegradation. There was no preferential removal of- homologs with longer alkyl chains from the wastewater as was observed 862 1 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 4, 1995
in previous studies investigating AS and linear alkyl benzenesulfonate (LAS) behavior during wastewater treatment (17-19). Preferential removal of AS and LAS homologs with longer alkyl chain lengths is attributed to increased sorption that is correlated with increased hydrophobicity of longer alkyl chain lengths (20). In the case ofAE, the hydrophobic portion of the molecule can change as a function of alkyl chain length along with changes in the hydrophilic portion of the molecule because of various ethoxylate chain lengths. The more complex relationship between hydrophobic and hydrophillic properties of AE molecules probably masks the effect of increased sorption and removal of the longer AE alkyl chain lengths. Streamwater concentrations ofAE collected immediately below the outfall of the wastewater treatment plants reflect both the level ofAE removal at each location and the stream dilution of effluent. Stream dilution was measured as a dilution factor equal to the stream flow plus effluent flow divided by effluent flow. Highest streamwater concentrations were found downstream from the Oskaloosa,IA, plants where the highest AE effluent concentrations and the lowest dilution factor (1.8)were measured. Lowest AE streamwater concentrations were found downstream from the Kenton, OH, activated sludge plant where high total AE removal (99%) and a dilution factor 4.3 were observed.
Conclusions A method was developed to determine AE concentrations in influent, effluent, and river water. This method was shown to quantitatively measure AE in influent, effluent and river water with recoveries that ranged from 78-102%. AE surfactants were shown to be highly removed during both trickling filter and activated sludge treatment. As a result of the near complete removal of these surfactants during wastewater treatment, AE concentrations in the receiving streams directly below wastewater treatment outfallswith low surfacewater dilutions had concentrations that were less than 0.037 mg/L. Even lower AE concentrations can be expected in streams where greater dilution of the effluent occurs and further downstream of the effluent where there may be additional removal of AE by biodegradation or settling on particles.
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Received for review March 17, 1994. Revised manuscript received October 24, 1994. Accepted January 19, 1995.* ES940172U @
Abstract published in AdvanceACSAbstracts, February 15,1995.
VOL. 29, NO. 4, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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