Triclosan in a sewage treatment process—balances and monitoring data
Introduction
2,4,4′-Trichloro, 2′-hydroxy-phenylether (triclosan) (structural formula in Fig. 1) is currently used in a multitude of consumer products such as a bactericide in toothpaste, detergents, plastic cutting boards, as well as sports clothing such as underwear, socks and shoes [1]. It has been detected in sewage plants in various countries such as the USA [2], [3] Sweden [4] and Switzerland [5]. Additionally, it has been detected in surface waters of the USA [6] as well as Switzerland [5]. Hale and Smith [7] found this bactericide in biota (fish) samples in Chesapeake Bay.
Concern has been rising in the last few years, as this bactericide was not only detected in wildlife near sewage plants, but also in human milk [1]. Additionally, it has been found that this compound has adverse effects on a diversity of organisms at relevant concentrations [8]. Thus some effort was taken to measure elimination of triclosan from wastewater with the 14C labelled compound in controlled laboratory experiments [9]. However, the concentrations in these experiments were some orders of magnitude higher than in real life.
In sewage plants triclosan may be methylated by metabolic processes, but the concentrations of triclosan in wastewater are much higher than of the methylated product, e.g., the concentrations in wastewater are ∼1 μg l−1 while those for the methylated derivative are about 0.1 μg l−1. The reported concentrations of triclosan in sludge are around 10 μg g−1 in the USA [3].
Systematic data on balances of triclosan in a sewage plant and a comparison of diverse sludges, as disposed from the sewage treatment plants (STPs) are missing, though. This study aims at filling this gap with a 5 days balance on a real-life sewage plant. Additionally, the sludge of 20 sewage plants has been analysed to get some comparison in plant-to-plant variability.
Section snippets
Materials and methods
Samples for the balancing experiment were taken at a sewage plant processing 200,000 m3 wastewater per day which is located in the vicinity of the city of Dortmund, Germany. This plant processes the wastewater of about 350,000 inhabitants of this city as well as some industry, mainly a brewery. About half of the wastewater that is processed is domestic. The plant is an activated sludge plant with secondary treatment step. It includes primary settlement basins, activated sludge treatment basins,
Results and discussion
Triclosan was identified by its mass spectrum in sewage water. Its presence was verified by comparing mass spectral data and retention times with an original standard. In Fig. 2 the mass spectrum of triclosan obtained from a inflow-water sample from a STP is shown, while in Fig. 3 selected ion chromatograms of a sludge sample extract is shown in comparison to a standard solution of triclosan.
Balancing experiment
During the balancing experiment the inflow concentrations ranged around 1200 ng l−1 (Table 2), while the concentrations in the effluent were about 50 ng l−1. A removal rate calculated from these data is about 96% a “breakthrough” about 4%, respectively. These data are similar to those published recently for a small swiss STP [13]. On the other hand, the concentrations of the sludge were about 1200 ng g−1. The concentrations in the sludge as well as the water samples exhibited very little variation,
Sewage sludge monitoring
Sewage sludge samples of 20 sewage plants of different sizes and operating principles (samples from various points in the respective plants, disinfected sludge (calcium carbonate) and non-disinfected sludge; after anaerobic stabilisation and without anaerobic stabilisation) were taken randomly from a larger set of samples and analysed to check whether or not the concentrations found in the sewage plant used for balancing was representative for such large sewage plants or not. The concentrations
Conclusions
This study shows that concentrations of triclosan in the wastewater inflow of the plant under observation were 1.1–1.3 μg l−1. The removal was higher than 90%, while about 30% was sorbed to the sludge. Another fraction of triclosan could be released from the sludge by treatment with sodium hydroxide; obviously triclosan may form bound residues under the conditions of this plant. The major amount of this compound, though is not found, may be transformed to hitherto unknown metabolites (not the
Acknowledgments
The author is indebted to G. Hardes, C. Stolle and K. Fänger who provided excellent technical work in the laboratory. The crew of the sewage plant was extremely helpful during the sampling intervals. The federal countries’ environmental protection agency (LUA-NRW) partially supported the experiments with Contract No. 11.2-1781 MZ 72/01 and direct contract 36138.
References (13)
- et al.
Triclosan a commonly used bactericide found in human milk and in the aquatic environment in Sweden
Chemosphere
(2002) Organic pollutants in the effluents of large wastewater treatment plants in Sweden
Water Res
(1996)- et al.
Triazine herbicide concentrations in the German Wadden Sea
Chemosphere
(1996) - et al.
Organic compounds in an industrial wastewater. Their transport into sediments
Environ Sci Technol
(1980) - et al.
Measurement of triclosan in wastewater treatment systems
Environ Toxicol Chem
(2002) - et al.
Occurrence and environmental behavior of the bactericide triclosan and its methyl derivative in surface waters and in wastewater
Environ Sci Technol
(2002)
Cited by (253)
Simultaneous removal of triclosan and nitrate by a stable denitrifying microbial consortium
2023, Journal of Environmental Chemical EngineeringUnstructured kinetic models with time-averaged growth approach in the biodegradation of triclosan by activated sludge culture
2023, Alexandria Engineering JournalRecent advancements on the migration and transformation of hydrophobic pharmaceutically active compounds in anaerobic digestion process
2022, Chemical Engineering Journal