Radiolabeled LAS Anaerobic Biodegradation Study
To follow up on the reports of LAS anaerobic biodegradation at the CESIO 2000 conference (Angelidaki et al., Prats et al., Sanz et al.), the Council for LAB/LAS Environmental Research (CLER) and the European Council on Studies on LAB/LAS (ECOSOL) conducted an anaerobic biodegradation study in two parts using radiolabeled (carbon-14 in the benzene ring) LAS.
- The first part of this study measured the production of radiolabeled CO2 and/or methane gas, which could only be produced by complete biodegradation (mineralization) of the LAS. In agreement with the results of Steber (2001) and other researchers, no mineralization of LAS was observed.
- The second part of the study was a die-away experiment that determined initial (primary) anaerobic biodegradation of LAS. This was measured both by following the levels of intact LAS throughout the 139-day course of the study and by analysis for any metabolites of LAS biodegradation by thin-layer chromatography (TLC) and high performance liquid chromatography (HPLC). Surprisingly in view of the previous reports of LAS anaerobic biodegradation, no primary biodegradation of LAS was observed under the conditions of this study.
- The die-away and mineralization experiments were both batch tests using anaerobic digester sludge as the source of biodegradation microorganisms. Many of the studies demonstrating anaerobic biodegradation of LAS were also batch tests with anaerobic digester sludge. However, there were a number of differences between the die-away experiment and the batch tests reporting LAS anaerobic biodegradation:
- The batch tests showing LAS anaerobic biodegradation used modifications of the ECETOC-28 test method in which specific analytical methods such as HPLC, or sometimes nonspecific methods such as methylene blue active substance, were used to measure LAS biodegradation. The die-away experiment used a modification of the Federle and Itrach (1997) method for measuring the kinetics of primary and complete biodegradation in which the experiment was conducted under anoxic conditions. There are a number of differences in experimental protocol between the ECETOC-28 method and the die-away test, including source and concentration of sludge, test medium, etc., that may explain the different results between the ECETOC tests and the die-away experiment.
- Of the 12 anaerobic digester sludges from activate sludge treatment plants in Spain and Germany tested in the ECETOC-28 test [two by the University of Alicante (Sanz et al., 2000), one by the Fraunhofer Institute (Fraunhofer, 2001), five by Petresa (Ferrer et al., 2002a,b), and four by CSIC-Barcelona (Garcia et al., 2002)], 10 sludges showed LAS anaerobic biodegradation ranging from 18 to 93%, one sludge showed LAS anaerobic biodegradation only in the presence of added LAS (32 mg/L) and one sludge showed no LAS anaerobic biodegradation in the presence or absence of added LAS. Consequently, the source of the digester sludge may be an important factor in determining whether or not LAS anaerobic biodegradation is observed.
- Other factors that may be important in anaerobic biodegradation studies include the level of LAS in the test and the LAS/sludge ratio. High levels of added LAS may be inhibitory to anaerobic processes needed for biodegradation of LAS (Sanz et al., 2000)
- LAS anaerobic biodegradation has also been reported in flow-through systems such as continuous stirred tank reactors and upflow anaerobic sludge blanket reactors (Angelidaki et al., 2000; Mogensen, 2001; Mogensen & Ahring, 2002, Angelidaki et al., unpublished). These results demonstrate that LAS anaerobic biodegradation can be observed under experimental conditions different from the ECETOC-28 test.
- Further research sponsored by ECOSOL and CLER is being conducted at Denmark Technical University to better understand the conditions under which LAS anaerobic biodegradation can be observed, the intermediates and mechanism of the biodegradation and the microorganisms responsible.
- Further information on the radiolabeled LAS mineralization and die-away experiments may be obtained by contacting CLER (TEL: 202-737-0171, Fax: 202-737-8406, www.cler.com) and ECOSOL (TEL: 32-2-676-72-46, Fax: 32-2-676-73-01, http://www.ecosol.com/.
Angelidaki, I., Haagensen, F., and Ahring, B.K., 2000, “Anaerobic Transformation of LAS in Continuous Stirred Tank Reactors Treating Sewage Sludge,” Proceedings, CESIO 5th World Surfactants Congress, May 29 – June 2, 2000, Firenze, Italy, FEDERCHIMICA Assobase – P.I.T.I.O., Milano, pp. 1551-7.
Federle, T.W., and Itrich, N.R., 1997, “Comprehensive Approach for Assessing the Kinetics of Primary and Ultimate Biodegradation of Chemicals in Activated Sludge: Application to Linear Alkylbenzene Sulfonate,” Environmental Science & Technology, vol. 31, pp. 1178-84.
Ferrer, J., López, I., Moreno, A., and Berna, J.L., 2002a, “Anaerobic Biodegradation of LAS, Effect of Inoculum Source on Biodegradation Rate and Assessment of Individual Homologues Removal,” Society of Environmental Toxicology and Chemistry (SETAC) 12th Annual Meeting in Europe, Vienna, May 2002.
Ferrer, J., López, I., Moreno, A., and Berna, J.L., 2002b, “Influence of Inoculum Source and Bioavailability on the Rate of Anaerobic Biodegradation of LAS Homologues,” 10th World Congress on Anaerobic Digestion, Mexico City, October 2002.
Fraunhofer UMSICHT, 2001, “Chapter 15, Biodegradability Tests under Anaerobic Conditions,” in Anerobic Biodegradation of Detergent Surfactants, 2nd Interim Report to the European Commission, pp. 137-185.
García, M.T., Campos, E., Dalmau, and Ferrer, J., 2002, “Anaerobic Biodegradation of LAS: Effect of the Bacterial Inoculum,” 32 Annual Meeting, Comité Español de la Detergencia Tensioactivios y Afines (CED), Barcelona, April 2002.
Mogensen, A.S., 2001, “Anaerobic Biodegradation of Linear Alkylbenzene Sulfonate and Other Organic Contaminants from Sewage Sludge,” Ph.D. Thesis, BioCentrum-DTU, Technical University of Denmark, Lyngby.
Mogensen, A.S., and Ahring, B.K., 2002, “Formation of Metabolites during Biodegradation of Linear Alkylbenzene Sulfonate in an Upflow Anaerobic Sludge Bed Reactor under Thermophilic Conditions,” Biotechnology and Bioengineering, vol. 77, pp. 483-8.
Prats, D., Rodriguez, M., Llamas, J.M., De La Muela, M.A., Ferrer, J., Moreno, A. and Berna, J.L., 2000, “The Use of Specific Analytical Methods to Assess the Anaerobic Biodegradation of LAS,” Proceedings, CESIO 5th World Surfactants Congress, May 29 – June 2, 2000, Firenze, Italy, FEDERCHIMICA Assobase – P.I.T.I.O., Milano, pp. 1655-8.
Steber, J., 2001, Biodegradability of Ring-labeled LAS in a Digester Simulation System: Summary of Studies Conducted at Henkel (Report No. 1984/2257), unpublished.
Sanz, J.L., Rodriquez, N., Ferrer, J., Moreno, A., and Berna, J.L., 2000, “Evaluation of the Inhibition Potential of LAS (Linear Alkylbenzene Sulfonate) to the Methanogenic Process,” Proceedings, CESIO 5th World Surfactants Congress, May 29 – June 2, 2000, Firenze, Italy, FEDERCHIMICA Assobase – P.I.T.I.O., Milano, pp. 1603-8.