Environ. Sci. Technol. 1997, 31, 3397-3404
Biodegradation of Coproducts of Commercial Linear Alkylbenzene Sulfonate ALLEN M. NIELSEN,* LARRY N. BRITTON, CHARLES E. BEALL, TIMOTHY P. MCCORMICK, AND GEOFFREY L. RUSSELL Research and Development Department, CONDEA Vista Company, 12024 Vista Parke Dr., Austin, Texas 78726-4050
Dialkyltetralin sulfonate (DATS) and single methyl-branched isomers of linear alkylbenzene sulfonate (iso-LAS) are coproducts that together can range from 1 to 10% of commercial LAS depending on the manufacturing process. Biodegradation studies using radiolabeled DATS and isoLAS showed mineralization by indigenous microbial populations in laboratory simulations of aquatic and soil environments. Half-lives ranged from 2 to 20 days, which is rapid enough to suggest that accumulation would not occur in these environments. Upon exposure to laboratory activated sludge treatment, most model iso-LAS compounds showed greater than 98% parent compound removal, extensive mineralization (>50%), and 79-90% ultimate biodegradation (mineralization plus conversion to biomass). Activated sludge treatment of DATS and one of the isoLAS isomers (methyl group attached to the benzylic carbon of the alkyl chain) resulted in >98% removal, 3-12% ultimate biodegradation and apparent formation of carboxylated biodegradation intermediates that accounted for 8897% of the original material. These DATS and iso-LAS biodegradation intermediates continued to mineralize in simulated receiving water and soil environments at rates similar to that of sulfophenyl carboxylate (SPC) intermediates of a standard LAS.
Introduction Commercial linear alkylbenzene sulfonate (LAS) is a widely used synthetic surfactant in detergents and household cleaning products. For example, consumption of LAS in Europe, North America, and Japan was approximately 950 000 metric tons in 1994 (1). Numerous studies on the environmental fate and effects of LAS have been published (2). Extensive field monitoring studies in Europe and North America as well as evaluations by several governmental agencies have been completed (3-6). These studies confirm earlier conclusions that LAS is completely biodegradable; environmental concentrations of LAS are low, and the use of LAS at current levels is protective of biological populations in receiving environments (2, 7). LAS is often represented as a linear alkyl chain attached to a sulfonated benzene ring, as illustrated in Figure 1. Commercial LAS, however, is a blend of LAS molecules that vary in terms of alkyl chain length, position of the benzene ring along the alkyl chain, and concentrations of coproducts called dialkyltetralin sulfonates and iso-LAS. * Corresponding author telephone: 512-331-2461; fax: 512-3312387.
S0013-936X(97)00023-0 CCC: $14.00
1997 American Chemical Society
Dialkyltetralin sulfonates (DATS) and LAS with single methyl branching on the alkyl chains (iso-LAS) are minor components in commercial LAS. Concentrations range from 90%. Porous Pot Biodegradation Test System. The porous pot method for assessing biodegradation of the test compounds in a simulated wastewater activated sludge was a modification of ASTM test method E1798-96. The porous pot system consisted of cylindrical glass containers with porous (>65 µ pore size) high-density polyethylene (HDPE) candles inserted into the glass cylinders (Figure 2). The candles held 282 mL of activated sludge, and a glass aeration tube to the bottom of the candle provided mixing and aeration at a 0.5 standard ft3/h flow rate. Sewage feed was pumped into the units from a 10 L carboy container through Teflon tubing by means of Model QG6 laboratory metering pumps (F. M. I., Inc., Oyster Bay, NY). Test chemicals were fed via Teflon tubing with Model 22 syringe pumps manufactured by Harvard Apparatus (South Natick, MA). Effluents from the porous pot units were collected in 2 L vacuum flasks which were manifolded to the laboratory vacuum system. The CO2 trapping system was a series of three 500 mL gas collection bottles, each with 300
mL 2 N KOH. A comparison between the performance of the laboratory scale porous pot biodegradation test system and conventional activated sludge treatment in the U.S. is shown in Table 1. A 21 day acclimation phase was initiated by feeding settled domestic sewage [adjusted to a chemical oxygen demand (COD) of 400 mg/L] and the nonradioactive analogs of the test compounds. The units were operated with the following parameters: nonradioactive chemical feed concentrations: C12 LAS, 5 mg/L; C8 DATS, 500 µg/L; iso-LAS, 250 µg/L; hydraulic retention time (HRT), 0.25 days; sludge retention time (SRT), 10 days (DATS units were 20 days); activated sludge concentration, ∼2000 mg/L volatile suspended solids (VSS). Steady state conditions, which were defined as a period of 7 days, in which COD removal was >90% and HRT daily variation was 95%. Kinetic Analysis. Data for CO2 evolution were analyzed using nonlinear regression models, a technique which has been successfully applied to several chemicals which manifest first order kinetics (21). The half-life and asymptote were calculated using Statgraphics Plus 5.2 software. These were obtained by minimizing the residual sum of squares using a search procedure suggested by Marquardt (22). All CO2 data were corrected for CO2 released in the HgCl2 controls before use in kinetic analysis.
Results and Discussion Mineralization of Model Compounds in Aquatic and Soil Environments. Since commercial LAS is primarily discarded down-the-drain with or without sewage treatment, the initial objective was to evaluate the potential ultimate biodegradation of DATS and iso-LAS in receiving environmental compartments. A typical receiving water (Lake Creek) was the first environmental compartment tested. Long lag times (>10 days) and very slow rates were observed which did not fit first-order kinetics. Therefore, no attempt was made to calculate rate constants for DATS, iso-LAS, and standard LAS in Lake Creek water. This was probably due to the very low level of biodegradable organic compounds (BOD5 < 2 mg/L) which resulted in a low population of bacteria (50%) and ultimate biodegradation (79-90%) but released some (1020%) of their carbon as water soluble intermediates. Activated sludge treatment of DATS and iso-LAS type IIB results in nearly complete removal (>98%) of the test surfactant, some ultimate biodegradation (3-12%) and a concurrent release of apparent carboxylated biodegradation intermediates (88-97%). These intermediates could be characterized as (1) having intact aromatic rings which demonstrate UV fluorescence; (2) having
increased polarity compared to the parent compounds; and (3) eluting on the HPLC-UVF chromatograms in the same region as with SPC biodegradation intermediates of LAS. Confirmatory evidence comes from the recent work of Cavalli et al. (14) and Ko¨lbener et al. (16, 17) and the monitoring work of Trehy et al. (10) in which carboxylated intermediates were found to be the major intermediates remaining after biological treatment of commercial LAS. Since the rate-limiting and last steps in SPC biodegradation are desulfonation, ring cleavage, and further oxidation of the ring-cleavage products (28), it is reasonable to assume that analagous biochemical pathways occur during the complete biological destruction of DATS and iso-LAS. Therefore, the complete biodegradation of these coproducts can be assessed by following the oxidation of the ring-labeled compounds in the porous pot effluents as summarized in Table 5. No kinetics were calculated for the mineralization of porous pot effluents in the creekwater alone. However, significant mineralization, which followed first-order kinetics, occurred if biomass in the form of periphyton-covered rocks, sediments, or sludge amended soils were added. Furthermore, the mineralization rates for the DATS and iso-LAS carboxylated intermediates were similar to those for the LAS SPCs. Table 6 presents the radiochemical mass balances at the temination of the die-away experiments with creekwater plus periphyton and creekwater plus sediments. Total CO2 production was significant for all the intermediates during the 77 or 37 day incubations except for the DATS catabolic intermediates (DATSI) in the water/sediment incubations. In contrast, the total CO2 from DATSI incubations in soil was 35% during the 37 day incubation (data not shown). Therefore, it appears that mineralization of DATSI can vary with the environmental conditions and presumably the microbial populations. The transient nature of these carboxylated biodegradation intermediates was demonstrated by HPLC-UVF/radiochemical detection. Water soluble fractions were analyzed of the porous pot feeds, effluents, effluent/sediment, and effluent/ periphyton die-aways, and the results are displayed in Figures 4, 5, and 6. The typical chromatographic pattern of C12-LAS is shown in Figure 4. The parent compound is almost completely removed during porous pot activated sludge treatment, and about 14% of it is released into the effluent as many water-soluble biodegradation intermediates. During the effluent/sediment die-away, 47% of the remaining radioactivity was mineralized, and only 3.3% remained in solution after 77 days of exposure. Only the results for LAS are shown since the HPLC-UVF/radiochemical patterns for iso-LAS types IA, IB, and IIA were the same as those for LAS. Furthermore, very little (6% or less) of these starting radioactivities remained after the die-away. The biodegradation pattern for iso-LAS type IIB is shown in Figure 5. It is clear that one major and several minor watersoluble SPCs are formed during activated sludge treatment. Cavalli (14) also found that one major and several minor SPCs were formed during activated sludge treatment of another
TABLE 6. Radiochemical Mass Balances for Porous Pot Effluent Die-Awaysa water/periphyton
LAS DATS iso-LAS IA IB IIA IIB
water/sediment
actual recovery (%)
CO2b
solubleb
solidsb
actual recovery (%)
CO2b
solubleb
solidsb
91.4 67.5 90.2 92.6 89.2 88.4
48.1 29.2 59.5 45.3 51.1 60.8
43.1 62.5 11.2 24.9 32.6 31.7
8.8 8.3 29.3 29.8 16.3 7.5
100.3 89 93.7 87.9 94.3 96.7
46.9 11 70.3 57.1 56.4 50.3
23.6 75.8 5.2 17.2 7.1 24.1
29.5 13.1 24.5 25.7 36.5 25.6
a Die-away incubations in creek water plus periphyton or creek water plus sediments were 77 days except for DATS which was 37 days. b Percentage recoveries of CO2, soluble fraction and solids fraction are normalized to 100%. Actual recoveries are given.
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FIGURE 4. HPLC-UVF/radiochemical analysis of C12LAS in porous pot feed (top panel), effluent (middle panel), and effluent/creekwater + sediment die-away (bottom panel). Results (not shown) for the creekwater + periphyton die-away experiment are comparable except that the amounts in each fraction are slightly greater.
FIGURE 6. HPLC-UVF/radiochemical analysis of C8DATS in porous pot feed (top panel), effluent (middle panel) and effluent/creek water + periphyton die-away (bottom panel). Results (not shown) for the creek water + sediment die-away experiment are comparable except that the amounts in each fraction are slightly greater.
FIGURE 5. HPLC-UVF/radiochemical analysis of iso-LAS type IIB in porous pot feed (top panel), effluent (middle panel), and effluent/ creekwater + sediment die-away (bottom panel). Results (not shown) for the creekwater + periphyton die-away experiment are comparable except that the amounts in each fraction are slightly greater. iso-LAS type II isomer of the same homolog. This isomer, however, showed a higher level (∼87%) of ultimate biodegradation than the type IIB during activated sludge treatment.
Even though these SPC intermediates formed by activated sludge treatment of iso-LAS type IIB make up most (88%) of the starting radioactivity, they are not recalcitrant since exposure to biomass on sediments during the 77 day dieaway mineralized all the minor SPCs and over 50% of the major intermediate. A very similar pattern was observed for the DATS biodegradation as illustrated in Figure 6, except that almost all (97%) of the intact DATS were converted to water soluble intermediates (DATSI) in the porous pot treatment. These DATSI were metabolized by the presumably different microbiological populations found in the sediments and periphyton. The end result of the DATSI die-aways in water/ periphyton was removal of 56% of the soluble radioactivity (97% or original radiolabel at beginning minus 41% remaining) during the 37 days. Ko¨lbener and co-workers have concluded from their studies on the biodegradation of commercial LAS in a laboratory “trickling filter” test system using immobilized activated sludge that from 3.2 to 13.6% of the commercial LAS carbon is refractory (16). These researchers have extended their studies and have reported that major components of this refractory portion are carboxylated biodegradation intermediates of DATS and iso-LAS (17). Their conclusion was that many of the coproducts of commercial LAS are recalcitrant. The porous pot results of this paper and field monitoring results of Trehy et al. (10) are consistent with the observations of Ko¨lbener et al. (15-17). It is clear from these studies, as well as other unpublished observations, that the microbial populations of domestic and industrial activated sludge and trickling filter wastewater treatment plants are not capable
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of the complete mineralization of all the DATS and iso-LAS homologs and isomers found in commercial LAS even though nearly complete primary biodegradation of these coproducts occurs. The new information provided in this paper is that these DATS and iso-LAS biodegradation intermediates produced during wastewater treatment could mineralize when exposed to receiving water environments or soils that contain a more diverse population of degraders.
Acknowledgments We thank John Lin (CONDEA Vista Company), James Innis (The Procter and Gamble Company), and Paul Sieving (Wizard Laboratories, Inc.) for synthesis of test compounds; Bruce Leach (formerly of CONDEA Vista Company) for assistance with kinetic calculations; and Paul Filler (CONDEA Vista Company) for technical assistance and John Heinze (Council for LAB/LAS Environmental Research) for helpful discussions.
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(10) Trehy, M. L.; Gledhill, W. E.; Mieure, J. P.; Adamove, J. E.; Nielsen, A. M.; Perkins, H. O.; Eckhoff, W. S. Environ. Toxicol. Chem. 1996, 15 (3), 233-240. (11) Field, J. A.; Barber, L. B., II; Thurman, M. E.; Moore, B. L.; Lawrence, D. L.; Peake, D. A. Environ. Sci. Technol. 1992, 26, 1140-1148. (12) Field, J. A.; Leenheer, J. A.; Thorn, K. A.; Barber, L. B., II; Rostad, C.; Macalady, D. L.; Daniel, S. R. J. Contam. Hydrol. 1992, 55-78. (13) Tabor, C. F.; Barber, L. B., II. Environ. Sci. Technol. 1996, 30, 161-171. (14) Cavalli, L.; Cassani, G.; Lazzarin, M.; Maraschin, C.; Nucci, G.; Berna, J.L.; Bravo, J.; Ferrer, J.; Moreno, A. Toxicol. Environ. Chem. 1996, 54, 167-186. (15) Ko¨lbener, P.; Baumann, U.; Leisinger, T.; Cook, A. M. Environ. Toxicol. Chem. 1995, 14 (4), 561-569. (16) Ko¨lbener, P.; Baumann, U.; Leisinger, T.; Cook, A. M. Environ. Toxicol. Chem. 1995, 14 (4), 571-579. (17) Ko¨lbener, P.; Ritter, A.; Corradini, F.; Baumann, U.; Cook, A. M. Tenside Surfactants, Deterg. 1996, 33 (2), 149-157. (18) Larson, R. J.; Federle, T. W.; Shimp, R. J.; Ventullo, R. M. Tenside, Surfactants, Deterg. 1989, 26 (2), 116-121. (19) Dworkin, M.; Foster, J. J. Bacteriol. 1958, 75, 592-603. (20) Tchobanoglous, G. Wastewater Engineering: Treatment Disposal Reuse; McGraw-Hill Book Co.: New York, 1979; pp 44-45. (21) Larson, R. J.; Payne, A. G. Appl. Environ. Microbiol. 1981, 41 (3), 621-627. (22) Marquardt, D. W. J. Soc. Ind. Appl. Math. 1963, 2, 431-441. (23) Knaebel, D. B.; Federle, T. W.; Vestal, J. R. Environ. Toxicol. Chem. 1990, 9, 981-988. (24) Federle, T. W.; Ventullo, R. M. Appl. Environ. Microbiol. 1990, 56 (2), 333-339. (25) Rapaport, R. A.; Larson, R. J.; McAvoy, D. C.; Nielsen, A. M.; Trehy, M. 3rd CESIO World Congress; 1992, Section E, pp 7887. (26) Berna, J. L.; Moreno, A.; Ferrer, J. J. Chem. Technol. Biotechnol. 1991, 50, 387-398. (27) Sharabi, N. E.; Bartha, R. Appl. Environ. Microbiol. 1993, 59, 1201-1205. (28) Schoberl, P. Tenside, Surfactants, Deterg. 1989, 26 (2), 86-94.
Received for review January 10, 1997. Revised manuscript received August 11, 1997. Accepted September 13, 1997.X ES970023M X
Abstract published in Advance ACS Abstracts, October 15, 1997.
