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Biofiltration processes are often part of advanced wastewater treatment (aWWT) technologies for the removal of organic micropollutants (OMP) from conventional wastewater treatment plant (WWTP) effluents. Although biological effects are not always the main focus of these technologies (e.g. filtration through granular activated carbon), they have been shown to contribute significantly to total OMP removal. While OMP biodegradation kinetics in conventional biological wastewater treatment are well researched, no systematic comparison to biomass from aWWT is available. This biomass faces different growth conditions and higher OMP concentrations relative to the background organic matter. Adaptation to these conditions could be possible and could lead to faster OMP biodegradation kinetics, which would show in a larger pseudo first-order biodegradation kinetic constant kbiol. In this work, kbiol values for biomass obtained from aWWT biofilters were determined by evaluating OMP removals measured in lab-scale biofilters using a mechanistic model of the experimental setup. A comparison to kbiol values from literature for conventional wastewater treatment (with nutrient removal) revealed similar OMP biodegradation kinetics without any advantages of biomass from aWWT. A conceptual evaluation of influencing factors on OMP removal in biofilters showed that operational parameters (such as the biomass concentration or the empty bed contact time) and the affinity of OMPs to adsorb on biomass have a significant additional effect on biological OMP removal. Therefore, kbiol values alone are not sufficient to estimate biological OMP removal in biofilters and further information about the system is required.

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Granular activated carbon (GAC) filtration is a commonly used method for advanced wastewater treatment. Filters can be operated continuously or discontinuously, with continuous operation not requiring feed flow interruption for backwashing and circulation (B/C). This study investigated the influence of B/C on the effluent quality of continuous filters. Two continuous GAC filters were operated for 1.5 years, with analysis of dissolved substances and particulate matter in the influent and effluent. The results indicated that various B/C modes had no impact on the removal of dissolved organic carbon and organic micropollutants (OMP), achieving an OMP removal of over 70% after 5,600 treated bed volumes (m3 treated wastewater per m3 GAC). However, it was evident that continuous B/C over 2-4 h resulted in increased turbidity, total suspended solids over 30 mg/L and total phosphorus concentrations of 1.3 mg/L in the filter effluent. Additionally, the study demonstrated that longer and more intensive B/C processes resulted in GAC size degradation with AC concentrations of up to 6.9 mg/L in the filter effluent, along with a change in GAC particle size. Furthermore, the importance of pre-filtration in reducing particulate matter in the filter influent and decreasing hydraulic head loss could be demonstrated.

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The use of powdered activated carbon (PAC) is a common process in advanced wastewater treatment to remove micropollutants. Retention and separation of PAC is essential as PAC loaded with micropollutants should not be released into the environment. Determining the activated carbon (AC) residual in the effluent poses a challenge, as there is currently no on-line measurement method. In this study, the correlation between turbidity, measured by scattered light, and absorption at wavelength of 550 nm (Absorption550 nm), measured by transmitted light, was investigated in relation to the AC residue. Linear correlations for turbidity (R2 = 0.95) and Absorption550 nm (R2 = 1.00) to AC concentrations were observed in both laboratory and full-scale experiments in a pilot plant where superfine PAC was added prior to Pile Cloth Media Filtration (PCMF). Decreasing the particle size (d50) while maintaining the same AC concentration leads to increased turbidity: Therefore, a fourfold reduction in d50 results in a 2- to 3-fold increase in turbidity, whereas a 30-fold reduction in d50 leads to a 6-to 8-fold increase. Furthermore, the original wastewater turbidity led to a parallel shift in the linear correlation between turbidity and AC. Coagulant doses of up to 400 mg Me3+/g AC resulted in a 50% reduction in turbidity. However, higher concentrations from 400 to 1,000 mg Me3+/g AC resulted in increased turbidity with only a 30% reduction compared to the initial turbidity. The study also highlights the significance of AC particle size in optical measurements, impacting result accuracy.

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Microplastics (MPs) are ubiquitous in the environment and have been found in every environmental compartment. Wastewater and wastewater treatment plants (WWTPs) have been identified as possible point sources contributing to the emission of microplastic particles (MPP) into the aquatic environment. So far, MPP in wastewater effluents have mainly been analyzed by spectroscopic methods resulting in concentrations as number per volume. In this study, we present mass concentrations in the secondary effluents of four German municipal WWTPs, removal efficiencies of seven post-treatment systems and the resulting load emissions. Differential Scanning Calorimetry (DSC) was used for the analysis of semi-crystalline MPs. The concentrations of secondary effluents ranged from 0.1 to 19.6 µg L-1. Removal efficiencies > 94% were found for a microfiltration membrane (MF), two cloth types of a pile cloth media filter (PCMF), a micro strainer, a discontinuous downflow granulated activated carbon filter (GAC) and a powdered activated carbon (PAC) stage with clarifier and rapid sand filtration. A rapid sand filter (RSF) at WWTP B showed a removal efficiency of 82.38%. Only a continuous upflow GAC filter at WWTP C proved to be unsuitable for MP removal with an average removal efficiency of 1.9%.

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Along with the rise of biological active granular activated carbon (bGAC) filtration as advanced treatment technology for wastewater treatment plant (WWTP) effluents, the mathematical representation of such systems is gaining increasing importance. This work introduces a model that describes the performance of bGAC-filters for Dissolved Organic Carbon (DOC) removal from a WWTP effluent. The DOC removal within bGAC-filters is accomplished by two mechanisms: adsorptive removal and biological transformation. An appropriate representation of the adsorptive removal requires the DOC to be divided into fictive fractions according to its adsorbability. Likewise, a further DOC classification according to its biodegradability is necessary. Modeling a bGAC-filter then becomes a multi-component adsorption problem, with the simultaneous occurrence of DOC degradation within a biofilm. For dealing with this modeling task, this work integrated the Ideal Adsorbed Solution (IAS) theory into a traditional biofilm model compatible with the Activated Sludge Model (ASM) Framework. For the description of the adsorption dynamics, a Freundlich isotherm for the equilibrium and a pseudo first order model for the kinetics were selected. The biofilm consisted of heterotrophic bacteria able to oxidize DOC using oxygen as electron acceptor. The correctness of the model was evaluated using experimental data from a pilot plant. The predicted DOC breakthrough curve satisfactorily fitted the experimental measurements for empty bed contact times (EBCT) of 6, 12, 24 and 33 min. Moreover, the model predicted the relationship between EBCT, DOC removal and bGAC-filter lifespan. The developed model is the first that combines multi-component adsorption and biofilm kinetics in a wastewater treatment context.

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At the core of Wilson et al.'s paper stands the question of intentional change. We propose to extend this notion by introducing concepts from the domains of innovation and knowledge creation. By going beyond their "acceptance and commitment therapy" approach we present a comprehensive framework for a theory of change culminating in the change strategy of "learning from the future as it emerges."

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