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Investigation of occurrence and elimination of hazardous compounds in wastewater treatment plants

 

Aim

The behaviour of different organic trace contaminants in selected wastewater treatment plants has been explored with the objective to understand their elimination from the system. In addition, a mass balance pertaining to the water route and the sludge path of the waste water treatment plants was constructed by considering the most important processing steps. The University of Dortmund, the Deutsche Projekt Union GmbH and the Landesumweltamt North Rhine-Westphalia were involved in this project.

 

Approach

The waste water treatment plants located at Duesseldorf-South and Cologne-Stammheim, as well as the semi-technical pilot plant of Neuss, were sampled at weekly intervals (flow charts of the two wastewater treatment plants see Fig. 1).

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Flow chart of the investigated wastewater treatment plant (WWTP) at Duesseldorf-South and Cologne-Stammheim

 

Four groups of contaminants were determined in up to six waste water and sludge samples in each weekly sampling period. The analytes included halogenated and non-halogenated organophosphates which are used as flame retardants and plasticisers, together with synthetic musk fragrances, in particular galaxolide and tonalide.Phthalates which are used as additives and plasticisers, together with the phenolic compounds (bisphenol A, nonylphenol and pentachlorophenol) were also monitored. In the latter case, the residues of these industrial chemicals or their metabolites are of great concern on account of their possible impact on the mammalian system as endocrine disruptors. This also applies to the phthalic acid-based plasticisers which are found in the environment ubiquitously.

 

Analytical methods

In order to achieve the aim of the project sensitive and selective analytical methods, suitable for waste water and sludge samples, were required. Samples were prepared by solid-phase-extraction, liquid-liquid-extraction or accelerated-solvent-extraction. Additionally, some substances had to be derivatized to enable sufficient volatility for sensitive gas chromatographic analysis. The identification and quantification of the groups of substances was performed by gas chromatographic separation and detection by mass spectrometry (GC/MS).

The advantage of the GC/MS is the explicit identification and quantification of the target compounds. By applying selected ion monitoring (SIM), a selective detection of the analytes was possible. However, musk fragrances, organophosphates and phthalates could not be determined simultaneously with alkyl phenols, namely bisphenol A and triclosan. Therefore, two separate measuring procedures had to be used.

 

Results

The results (Fig. 2) show the different elimination behaviour of the groups of substances. The various substances belonging to the individual groups were eliminated to a very different extent.

 

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 Concentrations and eliminations of the groups of compounds examined

 

A critical appraisal of the data on the total elimination in the municipal treatment plants reveals that many of the substances detected could be removed by up to 85% (synthetic musk fragrances) or more than 90% (phthalates and phenolic compounds). The relative elimination of halogenated organophosphates is clearly lower than that for their non-halogenated counterparts . The poor degradability (< 50%) of the halogenated organophosphates makes them interesting as a group of substances for future investigations. The behaviour of the trace substances examined in the Duesseldorf and Cologne WWTPs has been investigated and a balance was made of their occurrence on the basis of the complete sampling of all procedural steps of the water route, the sludge path and the process waters (Fig. 3).

 

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Mass balance of dibutylphthalate in the investigated wastewater treatment plants of Duesseldorf-South and Cologne-Stammheim

 

For example, a very good total elimination of DBP up to more than 95% was achieved in both wastewater treatment plants. The influent concentrations were, in contrast to the loads in the median, in particular DBP somewhat higher in the Duesseldorf WWTP than in the Cologne WWTP. The elimination of DBP could be attributed to adsorption on sludge as well as to biological degradation in the activated sludge tanks. In the Duesseldorf WWTP, the biological degradation contributed up to 70 - 75%, whereas in the Cologne WWTP, an equal contribution to elimination by sorption and biological degradation was observed. The elimination taking place in the filter stages of the wastewater treatment plants investigated amounted to less than 5%.

The effluent concentrations in particular must be investigated for an evaluation of a wastewater treatment plant. This is particularly important because even if the removal efficiency for some contaminants appears to be very high, the residual concentrations might be still eco-toxicologically relevant.
In order to minimize the load of organic trace contaminants in surface waters a treatment technology is essential which can supplement the aeration unit. An example for a supplementary technology is the combination of an oxidation process followed by a biological treatment, to improve the elimination of persistent substances such as TCEP.

 

Funding

Ministry of the Environment and Conservation, Agriculture and Consumer Protection of the State of North Rhine-Westphalia (MUNLV - NRW, Germany)

 

Publications

  1. MUNLV Hrsg. (2007):
    "Untersuchung zum Eintrag und zur Elimination von gefährlichen Stoffen in kommunalen Kläranlagen, Abschlussbericht zum Forschungsvorhaben - Teil 2" Broschüre des MUNLV in press.
  2. Zühlke, S. (2007):
    "Das Verhalten organischer Spurenstoffe während der Abwasserbehandlung", ISSN 1618- 3258 Mitt. Umweltchem. Ökotox., 1/2007, 7-9.



Sub content

Contact

Prof. Dr. Dr. h.c. Michael Spiteller
Tel.: 0231 755-4080
Dr. Sebastian Z├╝hlke
Head of Laboratory
Tel.: 0231 755-4088