Person: Dittmann, Daniel
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Veröffentlichung Characterization of activated carbons for water treatment using TGA-FTIR for analysis of oxygen-containing functional groups(2022) Dittmann, Daniel; Zietzschmann, Frederik; Ruhl, Aki Sebastian; Schumann, Pia; Saal, Leon; Braun, UlrikeWater treatment with activated carbon (AC) is an established method for the removal of organic micropollutants and natural organic matter. However, it is not yet possible to predict the removal of individual pollutants. An appropriate material characterization, matching adsorption processes in water, might be the missing piece in the puzzle. To this end, this study examined 25 different commercially available ACs to evaluate their material properties. Frequently reported analyses, including N2 adsorption/desorption, CHNS(O), point of zero charge (PZC) analysis, and X-ray photoelectron spectroscopy (XPS) were conducted on a selected subset of powdered ACs. Inorganic elements examined using X-ray fluorescence (XRF) and X-ray iffraction spectroscopy (XRD) revealed that relative elemental contents were distinctive to the individual AC's raw material and activation procedure. This study also is the first to use thermogravimetric analysis (TGA) coupled to Fourier-transform infrared spectroscopy (FTIR) to conduct quantitative analyses of functional surface oxygen groups (SOGs: carboxylic acid, anhydride, lactone, phenol, carbonyl, and pyrone groups) on such a large number of ACs. The comparably economical TGA provides a surrogate for the PZC, the oxygen and carbon content, as well as mass loss profiles that depict the AC's chemistry. Furthermore, we found that SOG contents determined by TGA-FTIR covered a wide individual range and depended on the raw material of the AC. Surface chemistry might therefore provide an indication of the suitability of a particular AC for a variety of target substances in different target waters. TGA and TGA-FTIR can help practitioners to control AC use in waterworks or wastewater treatment plants.Veröffentlichung Specific adsorption sites and conditions derived by thermal decomposition of activated carbons and adsorbed carbamazepine(2020) Eisentraut, Paul; Dittmann, Daniel; Goedecke, Caroline; Braun, Ulrike; Ruhl, Aki SebastianThe adsorption of organic micropollutants onto activated carbon is a favourable solution for the treatment of drinking water and wastewater. However, these adsorption processes are not sufficiently understood to allow for the appropriate prediction of removal processes. In this study, thermogravimetric analysis, alongside evolved gas analysis, is proposed for the characterisation of micropollutants adsorbed on activated carbon. Varying amounts of carbamazepine were adsorbed onto three different activated carbons, which were subsequently dried, and their thermal decomposition mechanisms examined. The discovery of 55 different pyrolysis products allowed differentiations to be made between specific adsorption sites and conditions. However, the same adsorption mechanisms were found for all samples, which were enhanced by inorganic constituents and oxygen containing surface groups. Furthermore, increasing the loadings led to the evolution of more hydrated decomposition products, whilst parts of the carbamazepine molecules were also integrated into the carbon structure. It was also found that the chemical composition, especially the degree of dehydration of the activated carbon, plays an important role in the adsorption of carbamazepine. Hence, it is thought that the adsorption sites may have a higher adsorption energy for specific adsorbates, when the activated carbon can then potentially increase its degree of graphitisation. © The Author(s) 2020Veröffentlichung Quantification and characterisation of activated carbon in activated sludge by thermogravimetric and evolved gas analyses(2018) Braun, Ulrike; Dittmann, Daniel; Jekel, Martin; Ruhl, Aki SebastianAdvanced 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. © 2018 Elsevier Ltd. All rights reserved.