IWW Water Centre

Chlorine dioxide (ClO2) is increasingly used as an alternative to chlorine in oxidative water treatment to mitigate the formation of halogenated disinfection byproducts. However, ClO2 can generate in situ free available chlorine (FAC) as a secondary oxidant, whose role in microbial inactivation remains poorly understood. This study investigates the impact of in situ-formed FAC during ClO2-based disinfection of Escherichia coli in the presence of natural organic matter (NOM). Bacterial inactivation was quantified using a novel approach based on lag phase extension in the growth curves. Exposure to 100 μM ClO2 extended the E. coli lag phase by approximately 40% relative to untreated controls. In contrast, the presence of 100 μM methionine, a selective FAC scavenger, markedly reduced disinfection efficacy, indicating that in situ FAC formation is a key driver of ClO2-based microbial inactivation. Additionally, disinfection efficiency decreased with increasing pH, consistent with FAC speciation (HOCl/OCl–; pKa = 7.54), as OCl– is less effective than HOCl. Moreover, pH-dependent speciation of NOM (phenol/phenolate; pKa ≈ 10) influences FAC reactivity, with phenolate exhibiting a higher scavenging capacity. These findings highlight the critical role of both FAC formation and NOM composition in determining the efficacy of ClO2-based disinfection.

The quantification of gaseous chemicals such as CO and H2, obtained during the electrochemical reduction of CO2 or water using online gas chromatography (GC), is extremely relevant for the evaluation of an electrolysis system's performance. Herein, the causes that may hinder the proper calculation of Faraday efficiencies, when applying industrially relevant current densities, are demonstrated for both water electrolysis and CO2 electroreduction (eCO2RR). The findings highlight that rigorous calibration and an understanding of GC linearity and detection limits are essential for accurate measurement and quantification. Furthermore, the implementation of product dilution immediately after the electrocatalytic reactor, prior to GC analysis, is introduced as a versatile approach that enables reliable product quantification across different applied current densities and GC systems.

Drinking water treatment, from a microbiological perspective, efficiently removes hygienically relevant microorganisms, making the water safe for human consumption. The water quality is strictly regulated. An aspect that is often overlooked, however, is biological stability. In this study, we assessed the effect of drinking water treatment of surface waters on biological stability. Biological stability was assessed as the difference between the actual cell concentrations naturally contained in the water at the time point of sampling and the maximal cell concentrations in the same sample obtained after a batch growth assay. Whereas raw waters were biologically stable, treatment resulted in a loss of biological stability and also partly in an increase in the maximal cell numbers. Treatment steps reducing biological stability resulted in the conversion of biologically fixed nutrients to dissolved nutrients. The stabilizing effect of biologically active filters was annihilated by disinfection at the end of treatment. The lack of biological stability was especially evident when distributing chlorinated water, where actual cell numbers and, in part, regrowth potentials tended to increase throughout transport with strong seasonal variations. Comparing cold drinking water at house entrances in different buildings across Germany, regrowth tests resulted in an average regrowth factor of 54 with high spatial and temporal variability. Biological instability was further increased in drinking water installations during water heating, which contributed to an additional shift towards dissolved nutrients, giving room to microbiological changes once the water cools down and stagnates. It remains to be determined whether the biological stabilization of drinking water can increase its microbiological resilience towards the growth of hygienically relevant bacteria.

The insecticide imidacloprid (IMI) is an ubiquitous environmental contaminant. This study presents an approach to investigate its degradation through the combined use of compound-specific stable carbon isotope analysis and high-resolution mass spectrometry (HRMS). It demonstrates how isotope ratio and HRMS product analysis can complement each other. The photolysis of imidacloprid by simulated sunlight, UV–C (λ = 254 nm), and alkaline hydrolysis all exhibited distinguishable carbon isotope enrichment factors (εC). The largest fractionation is observed during alkaline hydrolysis at pH 12 and 30 °C (εC = −3.9 ± 0.4‰). HRMS product analysis confirms that only one carbon atom is in a reactive position, allowing an AKIE calculation (εC AKIE = −34.1 ± 3.7‰). Carbon isotope enrichment factors of photolysis were not significantly affected by dissolved oxygen content or pH. Irradiation by UV–C did not result in significant isotope enrichment, whereas experiments with simulated sunlight yielded εC values between −1.1 ± 0.1 and −1.4 ± 0.1‰. It was hypothesized that an increased contribution of indirect photolysis led to isotopic enrichment. Finally, we demonstrate how the developed method can be used to determine the carbon isotope fingerprint of imidacloprid in veterinary flea control products.

It is widely assumed that a taxonomic core community emerges among microbial communities from similar habitats because similar environments select for the same taxa bearing the same traits. Yet, a core community itself is no indicator of selection because it may also arise from dispersal and neutral drift, i.e. by chance. Here, we hypothesize that a core community produced by either selection or chance processes should be distinguishable. While dispersal and drift should produce core communities with similar relative taxon abundances, especially when the proportional core community, i.e. the sum of the relative abundances of the core taxa, is large, selection may produce variable relative abundances. We analyzed the core community of 16S rRNA gene sequences of 193 microbial communities occurring in tiny water droplets enclosed in heavy oil from the Pitch Lake, Trinidad and Tobago. These communities revealed highly variable relative abundances along with a large proportional core community (68.0 ± 19.9%). A dispersal-drift null model predicted a negative relationship of proportional core community and compositional variability along a range of dispersal probabilities and was largely inconsistent with the observed data, suggesting a major role of selection for shaping the water droplet communities in the Pitch Lake.

Sorption of hydrophobic organic contaminants onto thermally altered carbonaceous materials (TACM) constitutes a widely used technology for remediation of polluted waters. This process is typically described by sorption isotherms, with one of the most used models, the Polanyi-Dubinin-Manes (PDM) equation, including water solubility (Sw) as a normalizing factor. In case of pharmaceutical active compounds (PhACs), Sw depends on the pH of the environment due to the ionic/ionizable behavior of these chemicals, a fact frequently ignored in sorption studies of PhACs. In this work, we set the theoretical framework to include the variation of Sw with pH in the definition of the PDM model, and we applied this approach to describe the effect of ambient pH in the competitive sorption of three commonly detected PhACs (carbamazepine, ibuprofen, and sulfamethoxazole) onto three carbonaceous sorbents (biochar, powder activated carbon, and colloidal activated carbon). Changes in the ambient pH and hence in the hydrophobicity of the compounds could explain the strong variations observed in single-solute sorption and also in competitive sorption. Furthermore, Sw was used as a parameter for the linear regression model of sorption coefficients of our experiments, suggesting the incorporation of this variable as an improvement to existing approaches for prediction of PhACs sorption onto TACM.

This paper presents a methodological approach for the evaluation of the thermal behavior of cementitious porous media with/without integrated latent-heat thermal energy storage (LHTES). To achieve this goal, the Lewis-Nielsen model has been calibrated to predict the insulation properties of mineralized foamed concretes. Two pore-related microstructural fitting parameters, A and Φm, are presented according to the available data in the literature. In this regard, new findings are implemented for the classification of pore structure and prediction of the homogenized thermal conductivity of two-phase cementitious foams with or without phase change materials. The calibration and predictive analyses have been extended to a wide range of experimental data, including variation of binder types, porosities, and latent components. The presented analytical approach appears to agree well with experimental results and can be employed in the design of two-phase mineral foam materials. Then, to assess the thermal behavior of the predicted insulating envelopes, a one-dimensional (1D) enthalpy-based model is used which combines Fourier’s law of heat conduction, the first law of thermodynamics, Lewis-Nielsen conductivities, and the mixture theory for LHTES additions. The results demonstrated the importance of volumetric heat capacity for the thermal inertia of building envelopes.

Drinking water enters buildings with a given microbiological community composition. Within premise plumbing systems, the drinking water is subject to very different conditions and temperatures. Whereas part of the water stays cold, another part is heated to provide hot water. In this study, drinking water samples were taken at different locations in four buildings that had central heating circles and that were equipped with ultrafiltration modules. The latter were intended to keep bacterial numbers low. When studying the increase in bacterial concentrations in these water samples using regrowth tests at different incubation temperatures, a temperature-dependence could be observed. Bacteria in cold water samples propagated best when incubated at 22°C, but often poorly at 36°C and not at all at 50°C. Bacteria in hot water samples showed the reverse behavior and grew best when incubated at 50°C, whereas growth at 22°C was poor or associated with a long growth lag. Water samples from distal taps in periphery locations used for retrieving both cold and hot water showed intermediate growth behaviors. Results suggest the existence of different temperature-adapted bacterial populations within domestic drinking water systems. The finding was supported by sequence data revealing distinct differences in the microbiomes between cold and hot water samples. Abundant bacterial groups in hot water included Deinococci, Kryptonia, Ignavibacteria, Nitrospiria, Gemmatimonadetes and different genera of Gammaproteobacteria. Stagnation of hot water at 50°C, 55°C, or 60°C furthermore shaped the microbiome in different ways indicating that small temperature differences can have a substantial impact on the bacterial communities.

Adenine and guanine derivatives are widely applied as antiviral agents. Due to their incomplete removal in conventional wastewater treatment, these substances were detected in the aquatic environment. Ozonation as an additional treatment step is known to degrade the antiviral compounds. However, oxidation mechanisms are still poorly examined. This study focused on the basic structures of the large group of antiviral nucleobase analogues, purine, adenine, and guanine. Their reaction with ozone allows prognoses of the ozonation of structurally related micropollutants. Therefore, these structures and the two antivirals acyclovir and penciclovir are investigated regarding their kinetics and degradation. Both characteristics are the basis for further research regarding the comprehensive understanding of the purines’ ozonation. Results show differences for the basic structures but similarities between guanine derivatives. Overall, the fundamental examinations exhibit a strong pH-dependency. Investigation of kinetics and ozone consumption ratios at pH 7 indicates ozone attack at nitrogen sites for purine (k < 8 × 10–2 M–1 s–1) and adenine (k = 100 M–1 s–1) with a slight shift to a C-C double bond at a higher pH for adenine. In guanine analogues (k = 3 × 104 M–1 s–1), the attack occurs mostly at carbon. Altogether, knowledge transfer to structurally related micropollutants is possible in the absence of additional strong electron-withdrawing or electron-donating substituents.