Reference : The impact of macro-substrate on micropollutant degradation in activated sludge systems
Dissertations and theses : Doctoral thesis
Engineering, computing & technology : Civil engineering
The impact of macro-substrate on micropollutant degradation in activated sludge systems
Christen, Anne mailto [University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Engineering Research Unit >]
University of Luxembourg, ​Luxemburg, ​​Luxembourg
Docteur de l'Université du Luxembourg en Sciences de l'Ingénieur
Hansen, Joachim mailto
Wilmes, Paul mailto
Köhler, Christian
Abbt-Braun, Gudrun
Knerr, Henning
[en] micropollutants ; macro-substrate ; xenobiotic degradation
[en] Wastewater treatment plants are designed as a first barrier to reduce xenobiotic emission into rivers. However, they are not sufficient enough to fully prevent environmental harm of emerging substances in the water body. Therefore, advanced treatment processes are currently being investigated but their implementation is cost-intensive. The optimisation of the activated sludge treatment to enhance biological micropollutant removal could reduce operating costs and material. Although the impact of operational parameters, such as sludge retention time and hydraulic retention time on the xenobiotic removal have been investigated, the influence of the macro-substrate composition and load on micropollutant elimination causes a high degree of uncertainty.
This study focuses on the latter by analysing 15 municipal wastewater treatment plants, where variations in load and composition of the macro-substrate were expected. Assuming that macro-substrate shapes the biomass and triggers their activity, the impact of macro-substrate composition and load on xenobiotic degradation by microorganisms was analysed. It was hypothesised that on the one hand, a high dissolved organic carbon concentration might lead to enhanced xenobiotic degradation for certain substances due to a high microbial activity. The latter is assumed to be caused by a high labile dissolved organic carbon portion and the tendency for a shorter sludge retention time. On the other hand, a low dissolved organic carbon concentration, probably containing a predominant recalcitrant substrate portion, tends to a longer sludge retention time. Consequently, slow-growing and specialised microorganisms may develop, able to degrade certain xenobiotics. As a second question, the contribution of the autotrophic biomass to xenobiotic degradation was tested by inhibiting the autotrophic microorganisms during the degradation test. To additionally test the hypothesis, the impact of a readily biodegradable substrate (acetate) on the xenobiotic degradation was tested and the sensitivity of the fluorescence signal of tryptophan was used to analyse the impact of tryptophan on xenobiotic degradation. Degradation tests focusing on the removal of macro-substrate and micropollutants within 18 hours incubation in the OxiTop® system were performed. The OxiTop® system is known as fast and easy method for organic matter analysis in the wastewater. To assess the macro-substrate composition prior to and after the degradation test, three characterisation methods were applied. Firstly, to determine the labile and the rather recalcitrant portion in the dissolved organic carbon, absorbance was measured at 280 nm and further analysed. This was verified by the characterisation of both portions based on the oxygen consumption measurements. Secondly, to analyse the organic matter concerning its fluorescent properties, excitation-emission scans were run and analysed using the parallel factor analysis approach. Lastly, the chromophoric and fluorescent organic matter was separated via size-exclusion chromatography to investigate the macro-substrate composition. Micropollutant elimination efficiency was followed by measuring initial and final concentrations of the targeted substances using liquid chromatography tandem-mass spectrometry and calculating pseudo-first-order degradation rates. To distinguish between the contribution of the heterotrophic biomass and the total biomass on xenobiotic degradation, allylthiourea was added to inhibit the autotrophic biomass. No significant composition changes of the chromophoric macro-substrate were observed. A higher initial dissolved organic carbon concentration led to higher chromophoric and fluorescent properties. The same was found for the degraded dissolved organic carbon amount and the loss of signal within the chromophoric and fluorescent portions. Variations in the macro-substrate load or rather concentration were tracked. Derived from the oxygen consumption measurements, a prominent labile and non-chromophoric portion was present at higher dissolved organic carbon levels, impacting the microbial activity. However, a characterisation of the non-chromophoric macro-substrate composition was not done within the study. Regarding the micropollutant removal, varying elimination rates were observed. For 4 out of 17 substances, distinct degradation dynamics were found, suggesting a possible impact of the present macro-substrate load. However, no overall impact of the macro- substrate on xenobiotic removal was observed. Atenolol, bezafibrate and propranolol showed a negative correlation with the initial dissolved organic carbon concentration, meaning higher degradation rates at a lower substrate load. This might indicate the presence of specialised microorganisms and a higher microbial diversity. Furthermore, inhibition studies using allylthiourea suggest a contribution of the autotrophic biomass to xenobiotic degradation. Sulfamethoxazole showed a positive trend with the initial dissolved organic carbon concentration, possibly indicating co-metabolic degradation of sulfamethoxazole by the autotrophic and heterotrophic biomass. Thus, it seemed that the removal efficiencies of sulfamethoxazole benefited from higher substrate loads. With respect to the short term experiments with acetate, higher degradation efficiencies were observed for several substances in the presence of acetate. Ketoprofen and bezafibrate showed in all tested wastewaters enhanced removal efficiencies. The tryptophan test indicated the presence of tryptophan in wastewater, but no clear contribution to the xenobiotic degradation was seen. The presented findings substantially contribute to the understanding of the influencing parameters on xenobiotic degradation in activated sludge systems. By using the OxiTop® application for xenobiotic degradation tests, an easy and fast method was established. Absorbance and fluorescence measurements proved to be a sufficient method for characterisation and biodegradability estimation of organic matter, which could be further applied as online measurements on wastewater treatment plants. Thus, the current study will serve as a base for future work investigating the influencing parameters on the xenobiotic degradation pathways and focusing on the optimisation of the biological and advanced treatment process to overcome current limitations.

There is no file associated with this reference.

Bookmark and Share SFX Query

All documents in ORBilu are protected by a user license.