Auflistung nach Autor:in "Dittmar, Stefan"

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Fast empirical lab method for performance projections of large-scale powdered activated carbon re-circulation plants
(2019) Zietzschmann, Frederik; Dittmar, Stefan; Ruhl, Aki Sebastian
Powdered activated carbon (PAC) for organic micro-pollutant (OMP) removal can be applied effectively on wastewater treatment plant (WWTP) effluents by using recirculation 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 recirculation 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/recirculation 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 aim was 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). © 2018 Elsevier Ltd. All rights reserved.
Optimized and validated settling velocity measurement for small microplastic particles (10-400 My m)
(2023) Dittmar, Stefan; Jekel, Martin; Ruhl, Aki Sebastian
The settling velocity of nonbuoyant microplastics is one of the key parameters to describe their vertical transport in water, yet it has rarely been studied for small microplastics (<500 My m) thus far. Respective measurements are challenging as they are prone to disruptive factors such as thermal convection. With decreasing size, it also becomes more difficult to handle target particles separately. Instead, it is favorable to work with suspensions-especially when characterizing particle populations based on sufficient individual measurements. This study establishes and validates a suitable measuring setup, which mainly consists of a precisely tempered settling column that is monitored via optical imaging with subsequent particle tracking. Comprehensive validation experiments with different spherical particles covering the desired size (10-388 My m) and density range (1.05-2.46 g/cm3) verify exceptionally high measurement accuracy and precision. Different investigation schemes were proposed and successfully tested for polydisperse and monodisperse particle samples, respectively. At elevated particle doses, measured settling velocities increased due to swarm effects and interactions between particles. A novel empirical model was fitted to represent those effects. The model can aid in limiting the particle dosage and thus prevent overestimations of single particle velocities. © 2023 The Authors
Simulating effluent organic matter competition in micropollutant adsorption onto activated carbon using a surrogate competitor
(2018) Dittmar, Stefan; Zietzschmann, Frederik; Mai, Maike; Ruhl, Aki Sebastian
Adsorption onto activated carbon is a promising option for removing organic micropollutants (OMPs) from wastewater treatment plant (WWTP) effluents. The heterogeneity of activated carbons and adsorption competition between OMPs and adsorbable compounds of the effluent organic matter (EfOM) complicate the prediction of OMP removals. Thus, reliable and simple test systems are desirable. For this study, batch experiments with powdered activated carbon (PAC) were carried out to examine methyl orange (MO) as a selected surrogate competitor to simulate EfOM adsorption competition. MO solutions were spiked with carbamazepine (CBZ) as an indicator substance for well-adsorbing OMPs. On the basis of CBZ adsorption isotherms in WWTP effluents, MO concentrations for batch test solutions with identical adsorption competition toward CBZ were calculated. The calculations were performed according to an empirical model of CBZ adsorption in the presence of MO, since predictions employing the ideal adsorbed solution theory (IAST) proved to be inaccurate. Comparative batch tests with five different PACs were conducted with WWTP effluent and respective MO batch test solutions. Except for one PAC, the achieved CBZ removals were very similar in WWTP effluent and the test solution. Additionally, a universal correlation between MO and CBZ removals was found for four PACs. Quelle: https://pubs.acs.org/
System zur Untersuchung der Sedimentation von Mikroplastik (10-300 (micro)m)
(2021) Dittmar, Stefan; Pries, J.; Ruhl, Aki Sebastian
Im Vergleich zu gelösten Stoffen unterliegen partikuläre Substanzen wie Mikroplastik (MP) in aquatischen Systemen anderen Dynamiken. Die wirksamen Transportmechanismen wie Deposition und Resuspendierung sowie Flotation und Sedimentation sind dabei nicht nur von Charakteristiken des betrachteten Gewässers, sondern in höherem Maß auch von Eigenschaften der Partikel selbst abhängig. Da gängige Polymere sowohl geringere (zum Beispiel PE, PP) als auch höhere Dichten (zum Beispiel PS, PET, PVC) als Wasser aufweisen, flotieren einige MP-Partikel, wohingegen andere sedimentieren. Partikeldichte, -größe und -form können potenziell wiederum durch Agglomeration, Fragmentierung sowie biologischen Bewuchs verändert werden. Quelle: https://onlinelibrary.wiley.com/