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- Pulveraktivkohle (3)
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- Belebtschlamm (2)
- Carbamazepin (2)
- Mass spectrometry (2)
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Eingeladener Vortrag
- nein (2)
Motivation:
> Zunehmender Einsatz von Pulveraktivkohle (PAK) zur
Spurenstoffelimination in kommunalen Kläranlagen
> Bisher keine analytische Methode zur Quantifizierung von PAK in
Belebungsbecken, bzw. in Gegenwart von Belebtschlamm
> Anwendung der Thermogravimetrischen Analyse (TGA) zur
Feststoffcharakterisierung auf Umweltfragestellungen
Ergebnisse:
> Quantifizierung von PAK in Belebtschlamm ist möglich und kann
über unterschiedliche zweistufige TGA-Methoden erfolgen
> Zersetzungsgasanalyse zeigt veränderte und verzögerte
Freisetzung aliphatischer Produkte des Belebtschlamms
Advanced wastewater treatment with powdered activated carbon (PAC) leads to a spread of PAC into different purification stages of wastewater treatment plants (WWTP) due to recirculation and filter back-wash. Currently, no methods for quantification of PAC in activated sludge are available. In this study, PAC containing activated sludge from four WWTP were examined by two-step thermogravimetric analysis (TGA) with heating up to 600°C in N2 and subsequently in synthetic air. Direct quantification of PAC according to temperature specific weight losses was possible for one WWTP. Quantification by combining specific mass losses was found to be an alternative direct method, with a detection limit of 1.2% PAC in dry sample mass.
Additionally, evolved gas analysis (EGA) by infrared-spectroscopy (FTIR) during TGA revealed interaction mechanisms between PAC and activated sludge. Aliphatic compounds from activated sludge were identified as major substances influenced by PAC. In derivative thermogravimetry (DTG), a typical double peak at approximately 300°C was found to be related to carbonylic species with increased evolution of acetic acid in aged activated sludge. TGA and EGA are promising tools to understand, control and optimise the application of PAC in advanced wastewater treatment.
Im Vortrag wird der Ansatz zur Aufklärung von Adsorptionsprozessen, die in der Wasserphase stattgefunden haben, mittels Thermogravimetrie und Zersetzungsgasanalyse vorgestellt.
Es wird allgemein gezeigt wie TGA zur Charakterisierung von Aktivkohleoberflächen genutzt werden kann und welche Unterschiede sich in verschiedenen Adsorbat-Systemen zeigen. Im Detail wird die thermische Zersetzung von adsorbiertem Carbamazepin an drei verschiedenen Aktivkohlen präsentiert.
In diesem Beitrag wird gezeigt wie mit Thermogravimetrischen Analysen (TGA) Aktivkohleoberflächen charakterisiert werden können. Außerdem wie TGA mit Zersetzungsgasanalyse zur Untersuchung von Adsorbat-Systemen (Carbamazepin an drei verschiedenen Aktivkohlen) zur Aufklärung von Adsorptionszuständen genutzt werden kann.
Advanced wastewater treatment by the application of activated carbon is used to eliminate organic micropollutants in large scale wastewater treatment plants. However, underlying adsorption processes are unclear. On the one hand, compositions of wastewater differ and are very complex. On the other hand, activated carbons have physicochemical properties which impair investigations on adsorption mechanisms, since they are non-graphitic, non-graphitizable and have a highly disordered microstructure. This leads to their large surface areas and internal pore structure but also implies heteroatoms and functional groups. These are not easily accessible for research but affect the adsorption of organic micropollutants. Thermogravimetric analysis and evolved gas analysis can provide valuable insights into these kinds of systems. First, pyrolysis makes functional surface groups accessible, e.g. through decarboxylation, which facilitates characterisation of activated carbons. Second, adsorbates can be investigated by thermal desorption or decomposition, depending on the sorption conditions of the organic micropollutants. Single component systems as well as multi component systems with competing organic background matter are compared for various activated carbons. Surprising distinctions in the adsorption mechanisms will be presented.
In this study, the thermal decomposition of 1,3,5-tris-(2,3-dibromopropyl)-1,3,5-triazine-2,4,6-trione (TDBPTAZTO) and 2,4,6-tris-(2,4,6-tribromo-phenoxy)-1,3,5-triazine (TTBP-TAZ) were investigated for the first time by thermogravimetric analysis. Both compounds were thermal degraded between 225 and 350 °C (TDBP-TAZTO) as well as 300 and 400 °C (TTBP-TAZ).
As a result, mass loss (%) of 98.5% for TTBP-TAZ and 95.4% for TDBP-TAZTO at 600 °C under N2 were observed. The major pyrolytic degradation products of TTBP-TAZ were formed in a single step and identified by FTIR analysis as 2,4,6-tribromophenol and further bromine-substituted aromatic compounds. In comparison, TDBP-TAZTO was pyrolytic degraded in two steps, whereby on the first step the release of hydrogen Bromide and 1,3,5-triallyl-1,3,5-triazine-2,4,6-trione could be detected. In the second minor step, isocyanic acid could be additionally identified.
Subsequently, the obtained products of the TGA-FTIR measurements were used for a targeted search for mass fragments in mass spectrometry measurements. For TTBP-TAZ, only the degradation product 1,3,5-tribromobenzene could be detected by MS/MS analyzes. No comparable thermal degradation products, except hydrogen bromide, were observed in the MS/MS spectra of TDBP-TAZTO. Therefore, the search of further mass fragments was not possible compared to the findings of the TGA-FTIR measurements.
Powdered activated carbon (PAC) for organic micro-pollutant (OMP) removal can be applied effectively on wastewater treatment plant (WWTP) effluents by using re-circulation schemes, accumulating the PAC in the system. This technique is complex because several factors are unknown: (i) the PAC concentration in the system, (ii) specific and average contact times of PAC particles, and (iii) PAC particle loadings with target compounds/competing water constituents. Thus, performance projections (e.g. in the lab) are very challenging. We sampled large-scale PAC plants with PAC sludge re-circulation on eight different WWTPs. The PAC plant-induced OMP removals were notably different, even when considering PAC concentrations in proportion to background organic sum parameters. The variability is likely caused by differing PAC products, varying water composition, differently effective plant/re-circulation operation, and variable biodegradation. Plant PAC samples and parts of the PAC plant influent samples were used in laboratory tests, applying multiples (0.5, 1, 2, 4) of the respective large-scale “fresh” PAC doses, and several fixed contact times (0.5, 1, 2, 4, 48 h). The aimwas to empirically identify suitable combinations of lab PAC dose (as multiples of the plant PAC dose) and contact time, which represent the PAC plant
performances in removing OMPs (for specific OMPs at single locations, and for averages of different OMPs at all locations). E.g., for five well adsorbing, little biodegradable OMPs, plant performances can be projected by using a lab PAC dose of twice the respective full-scale PAC dose and 4 h lab contact time (standard deviation of 13 %-points).