Assessing the Chemical-Free Oxidation of Trace Organic Chemicals by VUV/UV as an Alternative to Conventional UV/H2O2

Low-pressure mercury lamps with high-purity quartz can emit both vacuum-UV (VUV, 185 nm) and UV (254 nm) and are commercially available and promising for eliminating recalcitrant organic pollutants. The feasibility of VUV/UV as a chemical-free oxidation process was verified and quantitatively assessed by the concept of H2O2 equivalence (EQH2O2), at which UV/H2O2 showed the same performance as VUV/UV for the degradation of trace organic contaminants (TOrCs). Although VUV showed superior H2O activation and oxidation performance, its performance highly varied as a function of light path length (Lp) in water, while that of UV/H2O2 proportionally decreased with decreasing H2O2 dose regardless of Lp. On increasing Lp from 1.0 to 3.0 cm, the EQH2O2 of VUV/UV decreased from 0.81 to 0.22 mM H2O2. Chloride and nitrate hardly influenced UV/H2O2, but they dramatically inhibited VUV/UV. The competitive absorbance of VUV by chloride and nitrate was verified as the main reason. The inhibitory effect was partially compensated by •OH formation from the propagation reactions of chloride or nitrate VUV photolysis, which was verified by kinetic modeling in Kintecus. In water with an Lp of 2.0 cm, the EQH2O2 of VUV/UV decreased from 0.43 to 0.17 mM (60.8% decrease) on increasing the chloride concentration from 0 to 15 mM and to 0.20 mM (53.5% decrease) at 4 mM nitrate. The results of this study provide a comprehensive understanding of VUV/UV oxidation in comparison to UV/H2O2, which underscores the suitability and efficiency of chemical-free oxidation with VUV/UV.

Photochemical fate of quaternary ammonium compounds (QACs) and degradation pathways predication through computational analysis

Quaternary ammonium compounds (QACs) are commonly used in many products, such as disinfectants, detergents and personal care products. However, their widespread use has led to their ubiquitous presence in the environment, posing a potential risk to human and environmental health. Several methods, including direct and indirect photodegradation, have been explored to remove QACs such as benzylalkyldimethyl ammonium compounds (BACs) and alkyltrimethyl ammonium compounds (ATMACs) from the environment. Hence, in this research, a systematic review of the literature was conducted using PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) method to understand the fate of these QACs during direct and indirect photodegradation in UV/H2O2, UV/PS, UV/PS/Cu2+, UV/chlorine, VUV/UV/chlorine, O3/UV and UV/O3/TiO2 systems which produce highly reactive radicals that rapidly react with the QACs, leading to their degradation. As a result of photodegradation, several transformation products (TPs) of QACs are formed, which can pose a greater risk to the environment and human health than the parent QACs. Only limited research in this area has been conducted with fewer QACs. Hence, quantum mechanical calculations such as density functional theory (DFT)-based computational calculations using Gaussian09 software package were used here to explain better the photo-resistant nature of a specific type of QACs, such as BACs C12-18 and ATMACs C12, C14, C18, and their transformation pathways, providing insights into active sites participating in the phototransformation. Recognizing that different advanced oxidation processes (AOPs) come with pros and cons in the elimination of QACs, this review also highlighted the importance of implementing each AOP concerning the formation of toxic transformation products and electrical energy per order (EEO), especially when QACs coexist with other emerging contaminants (ECs).

Interlaboratory comparison using inactivated SARS-CoV-2 variants as a feasible tool for quality control in COVID-19 wastewater monitoring

Wastewater-based SARS-CoV-2 epidemiology (WBE) has proven as an excellent tool to monitor pandemic dynamics supporting individual testing strategies. WBE can also be used as an early warning system for monitoring the emergence of novel pathogens or viral variants. However, for a timely transmission of results, sophisticated sample logistics and analytics performed in decentralized laboratories close to the sampling sites are required. Since multiple decentralized laboratories commonly use custom in-house workflows for sample purification and PCR-analysis, comparative quality control of the analytical procedures is essential to report reliable and comparable results. In this study, we performed an interlaboratory comparison at laboratories specialized for PCR and high-throughput-sequencing (HTS)-based WBE analysis. Frozen reserve samples from low COVID-19 incidence periods were spiked with different inactivated authentic SARS-CoV-2 variants in graduated concentrations and ratios. Samples were sent to the participating laboratories for analysis using laboratory specific methods and the reported viral genome copy numbers and the detection of viral variants were compared with the expected values. All PCR-laboratories reported SARS-CoV-2 genome copy equivalents (GCE) for all spiked samples with a mean intra- and inter-laboratory variability of 19 % and 104 %, respectively, largely reproducing the spike-in scheme. PCR-based genotyping was, in dependence of the underlying PCR-assay performance, able to predict the relative amount of variant specific substitutions even in samples with low spike-in amount. The identification of variants by HTS, however, required >100 copies/ml wastewater and had limited predictive value when analyzing at a genome coverage below 60 %. This interlaboratory test demonstrates that despite highly heterogeneous isolation and analysis procedures, overall SARS-CoV-2 GCE and mutations were determined accurately. Hence, decentralized SARS-CoV-2 wastewater monitoring is feasible to generate comparable analysis results. However, since not all assays detected the correct variant, prior evaluation of PCR and sequencing workflows as well as sustained quality control such as interlaboratory comparisons are mandatory for correct variant detection.

OrbiFragsNets. A tool for automatic annotation of orbitrap MS2 spectra using networks grade as selection criteria

We introduce OrbiFragsNets, a tool for automatic annotation of MS2 spectra generated by Orbitrap instruments, as well as the concepts of chemical consistency and fragments networks. OrbiFragsNets takes advantage of the specific confidence interval for each peak in every MS2 spectrum, which is an unclear idea across the high-resolution mass spectrometry literature. The spectrum annotations are expressed as fragments networks, a set of networks with the possible combinations of annotations for the fragments. The model behind OrbiFragsNets is briefly described here and explained in detail in the constantly updated manual available in the GitHub repository. This new approach in MS2 spectrum de novo automatic annotation proved to perform as good as well established tools such as RMassBank and SIRIUS.•A new approach on automatic annotation of Orbitrap MS2 spectra is introduced.•Possible spectrum annotation are described as independent consistent networks, with annotations for each fragment as nodes, and annotations for the mass difference between fragments as edges.•Annotation process is described as the selection of the most connected fragments network.

Ozonation of Gabapentin in Water─Investigating Reaction Kinetics and Transformation Mechanisms of a Primary Amine Using Isotopically Labeled Ozone

Aliphatic amines are abundant micropollutants in wastewater treatment plant effluents. In order to mitigate such micropollutants, ozonation is one of the most commonly employed advanced treatment processes. Current research regarding ozone efficiency is heavily focusing on reaction mechanisms of different contaminant groups, including structures with amine moieties as reactive sites. This study analyzes pH-dependent reaction kinetics and pathways of gabapentin (GBP), an aliphatic primary amine with an additional carboxylic acid group. The transformation pathway was elucidated applying a novel approach using isotopically labeled ozone (18O) and quantum chemistry calculations. While the direct reaction of GBP with ozone is highly pH-dependent and slow at pH 7 (13.7 M-1 s-1), the rate constant of the deprotonated species (1.76 × 105 M-1 s-1) is comparable to those of other amine compounds. Pathway analysis based on LC-MS/MS measurements revealed that ozonation of GBP leads to the formation of a carboxylic acid group and simultaneous nitrate formation, which was also observed in the case of the aliphatic amino acid glycine. Nitrate was formed with a yield of approximately 100%. Experiments with 18O-labeled ozone demonstrated that the intermediate aldehyde does most likely not include any oxygen originating from ozone. Furthermore, quantum chemistry calculations did not provide an explanation for the C-N scission during GBP ozonation without ozone involvement, although this reaction was slightly more favorable than for respective glycine and ethylamine reactions. Overall, this study contributes to a deeper understanding of reaction mechanisms of aliphatic primary amines during wastewater ozonation.

Exploring the effects of intermittent aeration on the performance of nitrifying membrane-aerated biofilm reactors

Membrane-aerated biofilm reactors (MABRs) are an emerging technology for nutrient removal; however, a trade-off remains between their removal rate and oxygen transfer efficiency. This study compares nitrifying flow-through MABRs operated under continuous and intermittent aeration modes at mainstream wastewater ammonia levels. The intermittently-aerated MABRs maintained maximal nitrification rates, including under conditions allowing the oxygen partial pressure on the gas side of the membrane to considerably drop during the no-aeration period. Nitrous oxide emissions of all reactors were comparable and amounted to approximately 20 % of the converted ammonia. Intermittent aeration increased the transformation rate constant of atenolol, yet did not affect the removal of sulfamethoxazole. Seven additional trace organic chemicals were not biodegraded by any of the reactors. The ammonia-oxidizing bacteria in the intermittently-aerated MABRs were dominated by Nitrosospira, previously shown to be abundant at low oxygen concentrations and provide reactor stability under changing conditions. Our findings indicate that intermittently-aerated flow-through MABRs can achieve high nitrification rates and oxygen transfer efficiencies, highlighting the possible implications of air supply discontinuity on nitrous oxide emissions and trace organic chemical biotransformation.

A new workflow for assigning removal credits to assess overall performance of managed aquifer recharge (MAR)

Pathogen removal in managed aquifer recharge (MAR) systems is dependent upon numerous operational, physicochemical water quality, and biological parameters. Due to the site-specific conditions affecting these parameters, guidelines for specifying pathogen removal have historically taken rather precautionary and conservative approaches in order to protect groundwater quality and public health. A literature review of regulated pathogens in MAR applications was conducted and compared to up-and-coming indicators and surrogates for pathogen assessment, all of which can be gathered into a toolbox from which regulators and operators alike can select appropriate pathogens for monitoring and optimization of MAR practices. Combined with improved knowledge of pathogen fate and transport obtained through lab- and pilot-scale studies and supported by modeling, this foundation can be used to select appropriate, site-specific pathogens for regarding a more efficient pathogen retention, ultimately protecting public health and reducing costs. This paper outlines a new 10 step-wise workflow for moving towards determining robust removal credits for pathogens based on risk management principles. This approach is tailored to local conditions while reducing overly conservative regulatory restrictions or insufficient safety contingencies. The workflow is intended to help enable the full potential of MAR as more planned water reuse systems are implemented in the coming years.

Advanced oxidation processes for removal of monocyclic aromatic hydrocarbon from water: Effects of O3/H2O2 and UV/H2O2 treatment on product formation and biological post-treatment

Several oxidative treatment technologies, such as ozonation or Fenton reaction, have been studied and applied to remove monocyclic hydroaromatic carbon from water. Despite decades of application, little seems to be known about formation of transformation products while employing different ozone- or ^∙OH-based treatment methods and their fate in biodegradation. In this study, we demonstrate that O₃/H₂O₂ treatment of benzene, toluene, ethylbenzene (BTE), and benzoic acid (BA) leads to less hydroxylated aromatic transformation products compared to UV/H₂O₂ as reference system - this at a similar ^∙OH exposure and parent compound removal efficiency. Aerobic biodegradation tests after oxidation of 0.15 mM BA (12.6 mg C L^-1 theoretical DOC) revealed that a less biodegradable DOC fraction > 4 mg C L^-1 was formed in both oxidative treatments compared to the BA control. No advantage of ozonation over UV/H₂O₂ treatment was observed in terms of mineralization capabilities, however, we detected less transformation products after oxidation and biodegradation using high-resolution mass spectrometry. Biodegradation of BA that was not oxidized was more complete with minimal organic residual. Overall, the study provides new insights into the oxidation of monocyclic aromatics and raises questions regarding the biodegradability of oxidation products, which is relevant for several treatment applications.

The Minus Approach Can Redefine the Standard of Practice of Drinking Water Treatment

Chlorine-based disinfection for drinking water treatment (DWT) was one of the 20th century's great public health achievements, as it substantially reduced the risk of acute microbial waterborne disease. However, today's chlorinated drinking water is not unambiguously safe; trace levels of regulated and unregulated disinfection byproducts (DBPs), and other known, unknown, and emerging contaminants (KUECs), present chronic risks that make them essential removal targets. Because conventional chemical-based DWT processes do little to remove DBPs or KUECs, alternative approaches are needed to minimize risks by removing DBP precursors and KUECs that are ubiquitous in water supplies. We present the "Minus Approach" as a toolbox of practices and technologies to mitigate KUECs and DBPs without compromising microbiological safety. The Minus Approach reduces problem-causing chemical addition treatment (i.e., the conventional "Plus Approach") by producing biologically stable water containing pathogens at levels having negligible human health risk and substantially lower concentrations of KUECs and DBPs. Aside from ozonation, the Minus Approach avoids primary chemical-based coagulants, disinfectants, and advanced oxidation processes. The Minus Approach focuses on bank filtration, biofiltration, adsorption, and membranes to biologically and physically remove DBP precursors, KUECs, and pathogens; consequently, water purveyors can use ultraviolet light at key locations in conjunction with smaller dosages of secondary chemical disinfectants to minimize microbial regrowth in distribution systems. We describe how the Minus Approach contrasts with the conventional Plus Approach, integrates with artificial intelligence, and can ultimately improve the sustainability performance of water treatment. Finally, we consider barriers to adoption of the Minus Approach.

Roles of radical species in vacuum-UV/UV/peroxydisulfate advanced oxidation processes and contributions of the species to contaminant degradation at different water depths

Vacuum-UV (VUV) (wavelength 185 nm)/ UV (wavelength 254 nm) are applied to improve performances of UV-based advanced oxidation processes. However, the improvements were strongly affected by water depth because of poor VUV transmittance in water. In this study, VUV/UV and peroxydisulfate (PDS) were used to degrade carbamazepine. More SO₄^•- oxidation occurred in VUV/UV/PDS than VUV/UV with similar ^•OH oxidation occurring. The additional SO₄^•- oxidation could be caused by VUV/PDS in superficial water or UV/PDS in deeper water. The synergistic factor for VUV/UV/PDS processes relative to VUV/UV and UV/PDS processes was 1.32. VUV/UV/PDS performances were affected by competition for photon absorption by dissolved organic matter (32-58 % inhibition), radical quenching by CO₃^2-/HCO₃^- and NO₃^-, and conversion of ^•OH and SO₄^•- into reactive chlorine species by Cl^-. Radical probe experiments and steady-state kinetic modeling simulations indicated that 34 %, 25 %, and 40 % of carbamazepine degradation occurring in 2-cm-deep bulk solution was due to ^•OH oxidation through VUV/H₂O, SO₄^•- oxidation through VUV/PDS, and SO₄^•- oxidation through UV/PDS, respectively. Contribution of VUV-driven processes decreased with increasing water depth and became equivalent to contribution of 3.5-cm-deep UV-driven processes, which indicated the importance of optimizing water depth in VUV/UV-advanced oxidation process reactors.

Digest, stain and bleach: Three steps to achieving rapid microplastic fluorescence analysis in wastewater samples

Efforts associated with common analytical techniques for microplastics including spectroscopic and thermo-analytical techniques are limiting the ability to perform large-scale monitoring of microplastics in the aquatic environment, because the analytical equipment required is costly and the analysis itself time consuming. Thus, there is a need to develop low cost, rapid alternative monitoring approaches. One possible alternative is the use of selective fluorescence staining of microplastic particles directly applied to environmental samples. However, to the best of our knowledge this has not yet been successfully implemented for wastewater samples. In this study, sludge samples are used as surrogates for wastewater alongside six different polymers to develop a combined sample preparation and staining protocol that could selectively stain microplastics without significant interference from the natural constituents of the sludge. Results confirmed that using Fenton's reagent to remove the organic matter before staining the sample with Nile red (NR) and subsequently bleaching it by sodium hypochlorite resulted in the best workflow to selectively stain microplastics and then analyze them in wastewater samples using fluorescence microscopy.

An actinometric method to characterize performance of reflecting UVC reactors used for water treatment

The applicability of chemical actinometry to characterize the fluence in UV reactors with reflections, non-parallel light, and variable water transmittance is limited due to the unknown effective path length or hydraulic shortcuts within the reactor. In this study, the effects of reflection and transmittance on actinometry were examined and a new, optimized and easy method for determining fluence was developed. KI/KIO₃ and uridine actinometry experiments were carried out under controlled conditions using a collimated beam apparatus and a completely mixed batch reactor with or without diffuse reflection and compared to biodosimetry results. Whereas optically opaque actinometers such as KI/KIO₃ are not directly capable of predicting the fluence of reflecting reactors, the results of uridine actinometry are influenced by reflection and transmission. To precisely predict the fluence rate in UV reactors with uridine, knowledge about the effective optical path length of the light is needed. Here, an existing method to mathematically calculate the optical path length was adopted and optimized for uridine actinometry. Results for average fluence were validated by biodosimetry using MS2 phages under different degrees of reflection and transmission. It could be shown that by modifying the bottom of the reactor with diffusely reflecting polytetrafluoroethylene foil, the fluence rate was increased by a factor of approximately 2.6 and the path length by factor of 2.4. When only half of the bottom was covered with reflective foil, fluence rate increased by a factor of 1.8 and path length by 1.8. Although this new approach cannot replace biodosimetry, to predict the fluence distribution received by microorganisms, it can provide means to characterize more complex reactor designs, validate results of advanced reactor modeling, and quantify fluence for non-parallel irradiation and reflective light, especially for the application of high fluence (e.g., advanced oxidation processes), where biodosimetry may be too sensitive. Further, comparing the fluence obtained with actinometry to the results of biodosimetry might qualitatively indicate hydraulic short cuts or unideal fluence distributions for flow-through reactors.

Wastewater-Based Epidemiology for SARS-CoV-2 Biomarkers: Evaluation of Normalization Methods in Small and Large Communities in Southern Germany

In the context of the COVID-19 pandemic, wastewater-based epidemiology (WBE) emerged as a useful tool to account for the prevalence of SARS-CoV-2 infections on a population scale. In this study, we analyzed wastewater samples from three large (>300,000 people served) and four small (<25,000 people served) communities throughout southern Germany from August to December 2021, capturing the fourth infection wave in Germany dominated by the Delta variant (B.1.617.2). As dilution can skew the SARS-CoV-2 biomarker concentrations in wastewater, normalization to wastewater parameters can improve the relationship between SARS-CoV-2 biomarker data and clinical prevalence data. In this study, we investigated the suitability and performance of various normalization parameters. Influent flow data showed strong relationships to precipitation data; accordingly, flow-normalization reacted distinctly to precipitation events. Normalization by surrogate viruses CrAssphage and pepper mild mottle virus showed varying performance for different sampling sites. The best normalization performance was achieved with a mixed fecal indicator calculated from both surrogate viruses. Analyzing the temporal and spatial variation of normalization parameters proved to be useful to explain normalization performance. Overall, our findings indicate that the performance of surrogate viruses, flow, and hydro-chemical data is site-specific. We recommend testing the suitability of normalization parameters individually for specific sewage systems.

Treatment of micropollutants in wastewater: Balancing effectiveness, costs and implications

In this contribution, we analyse scenarios of advanced wastewater treatment for the removal of micropollutants. By this we refer to current mainstream, broad spectrum processes including ozonation and sorption onto activated carbon. We argue that advanced treatment requires properly implemented tertiary (nutrient removal) treatment in order to be effective. We review the critical aspects of the main advanced treatment options, their advantages and disadvantages. We propose a quantification of the costs of implementing advanced treatment, as well as upgrading plants from secondary to tertiary treatment when needed, and we illustrate what drives the costs of advanced treatment for a set of standard configurations. We propose a cost function to represent the total costs (investment, operation and maintenance) of advanced treatment. We quantify the implications of advanced treatment in terms of greenhouse gas emissions. Based on the indicators of total toxic discharge, toxicity at the discharge points and toxicity across the stream network discussed in Pistocchi et al. (2022), we compare costs and effectiveness of different scenarios of advanced treatment. In principle the total toxic load and toxicity at the points of discharge could be reduced by about 75 % if advanced treatment processes were implemented virtually at all wastewater treatment plants, but this would entail costs of about 4 billion euro/year for the European Union as a whole. We consider a "compromise" scenario where advanced treatment is required at plants of 100 thousand population equivalents (PE) or larger, or at plants between 10 and 100 thousand PE if the dilution ratio at the discharge point is 10 or less. Under this scenario, the length of the stream network exposed to high toxicity would not increase significantly compared to the previous scenario, and the other indicators would not deteriorate significantly, while the costs would remain at about 1.5 billion Euro/year. Arguably, costs could be further reduced, without a worsening of water quality, if we replace a local risk assessment to generic criteria of plant capacity and dilution in order to determine if a WWTP requires advanced treatment.

European scale assessment of the potential of ozonation and activated carbon treatment to reduce micropollutant emissions with wastewater

Micropollutants (MPs) in wastewater pose a growing concern for their potential adverse effects on the receiving aquatic environment, and some countries have started requiring that wastewater treatment plants remove them to a certain extent. Broad spectrum advanced treatment processes, such as ozonation, activated carbon or their combination, are expected to yield a significant reduction in the toxicity of effluents. Here we quantify the reduction of effluent toxicity potentially achieved by implementing these advanced treatment solutions in a selection of European wastewater treatment plants. To this end, we refer to a list of "total pollution proxy substances" (TPPS) composed of 1337 chemicals commonly found in wastewater effluents according to a compilation of datasets of measured concentrations. We consider these substances as an approximation of the "chemical universe" impinging on the European wastewater system. We evaluate the fate of the TPPS in conventional and advanced treatment plants using a compilation of experimental physicochemical properties that describe their sorption, volatilization and biodegradation during activated sludge treatment, as well as known removal efficiency in ozonation and activated carbon treatment, while filling the gaps through in silico prediction models. We estimate that the discharge of micropollutants with wastewater effluents in the European Union has a cumulative MP toxicity to the environment equal to the discharge of untreated wastewater of ca. 160 million population equivalents (PE), i.e. about 30 % of the generated wastewater in the EU. If all plants above a capacity of 100,000 PE were equipped with advanced treatment, we show that this load would be reduced to about 95 million PE. In addition, implementing advanced treatment in wastewater plants above 10,000 PE discharging to water bodies with an average dilution ratio smaller than 10 would yield a widespread improvement in terms of exposure of freshwater ecosystems to micropollutants, almost halving the part of the stream network exposed to the highest toxic risks. Our analysis provides background for a cost-effectiveness appraisal of advanced treatment "at the end of the pipe", which could lead to optimized interventions. This should not be regarded as a stand-alone solution, but as a complement to policies for the control of emissions at the source for the most problematic MPs.

Converting recycled membranes into photocatalytic membranes using greener TiO2-GRAPHENE oxide nanomaterials

Despite the widespread use of membrane separation processes for water treatment, operation costs and fouling still restrict their application. Costs can be overcome by recycled membranes whereas fouling can be mitigated by membrane modification. In this work, the performance of recycled reverse osmosis membranes modified by greener titanium dioxide (TiO₂) and graphene oxide (GO) in different modification routes were investigated and compared. The use of recycled membranes as a support acted more than a strategy for costs reduction, but also as an alternative for solid waste reduction. Low adhesion of nanoparticulate materials to the membrane surfaces were verified in depositions by self-assembly, whereas filtration and modification with dopamine generated membranes with well adhered and homogeneous layers. Considering the stability, permeability, and rejection efficiency of dyes as model substrates, the membranes modified with the aid of dopamine-TiO₂-GO were the most promising. The nanomaterials increased the membrane hydrophilicity and formed a hydrated layer that repels the organic contaminants and reduces fouling. Besides membrane rejection, adsorption (contribution: ∼10%) and photocatalysis (contribution: ∼20%) were additional mechanisms for pollutants removal by the modified membranes. The photocatalytic membrane modified with dopamine-TiO₂-GO was furthermore evaluated for the removal of six different pharmaceutical active compounds (PhACs), noticing gains in terms of removal efficiency (up to 95.7%) and fouling mitigation for the modified membrane compared to the original membranes. The photocatalytic activity still contributed to a simultaneous degradation of PhACs avoiding the generation of a concentrated stream for further disposal.

Removal of antibiotic microbial resistance by micro- and ultrafiltration of secondary wastewater effluents at pilot scale

Low-pressure membrane filtration was investigated at pilot scale with regard to its removal of antimicrobial resistance genes (ARGs) in conventional secondary treated wastewater plant effluents. While operating microfiltration (MF) and ultrafiltration (UF) membranes, key operational parameters for antimicrobial resistance (AMR) studies and key factors influencing AMR removal efficiencies of low-pressure membrane filtration processes were examined. The main factor for AMR removal was the pore size of the membrane. The formation of the fouling layer on capillary membranes had only a small additive effect on intra- and extrachromosomal ARG removal and a significant additive effect on mobile ARG removal. Using feeds with different ARGs abundances revealed that higher ARG abundance in the feed resulted in higher ARG abundance in the filtrate. Live-Dead cell counting in UF filtrate showed intact bacteria breaking through the UF membrane. Strong correlations between 16S rRNA genes (as surrogate for bacteria quantification) and the sul1 gene in UF filtrate indicated ARBs likely breaking through UF membranes.

Enhanced methane production kinetics by graphene oxide in fed-batch tests

The study aims to prove that the addition of graphene oxide (GO) improves anaerobic digestion (AD) kinetic performance. Classical batch tests were modified to a fed-batch strategy at four GO levels while using two substrates (glucose and microcrystalline cellulose (MCC)). First-order and modified Gompertz models were respectively applied to evaluate the kinetic performance. The results showed significantly (p < 0.05) improved kinetic from the third refeeding step for both substrates. 20 mg GO per g of volatile solids (VS) led to an increase of up to 210% for the first-order rate constant (k) and up to 120% for maximum biochemical methane potential (BMP) rate (R_MAX) compared to control for glucose and MCC, respectively. The findings of this work suggest the implementation of GO in continuously operated systems to accelerate the AD process.

Microplastic sampling from wastewater treatment plant effluents: Best-practices and synergies between thermoanalytical and spectroscopic analysis

Wastewater treatment plants (WWTPs) may represent point sources for microplastic discharge into the environment. Quantification of microplastic in effluents of WWTPs has been targeted by several studies although standardized methods are missing to enable a comparability of results. This study discusses theoretical and practical perspectives on best practices for microplastic sampling campaigns of WWTPs. One focus of the study was the potential for synergies between thermoanalytical and spectroscopic analysis to gain more representative sampling using the complementary information provided by the different analytical techniques. Samples were obtained before and after sand filtration from two WWTPs in Germany using cascade filtration with size classes of 5,000 - 100 µm, 100 - 50 µm, and 50 - 10 µm. For spectroscopic methods samples were treated by a Fenton process to remove natural organic matter, whereas TED-GC-MS required only sample extraction from the filter cascade. µFTIR spectroscopy was used for the 100 µm and 50 µm basket filters and µRaman spectroscopy was applied to analyze particles on the smallest basket filter (10 µm). TED-GC-MS was used for all size classes as it is size independent. All techniques showed a similar trend, where PE was consistently the most prominent polymer in WWTP effluents. Based on this insight, PE was chosen as surrogate polymer to investigate whether it can describe the total polymer removal efficiency of tertiary sand filters. The results revealed no significant difference (ANOVA) between retention efficiencies of tertiary sand filtration obtained using only PE and by analyzing all possible polymers with µFTIR and µRaman spectroscopy. Findings from this study provide valuable insights on advantages and limitations of cascade filtration, the benefit of complementary analyses, a suitable design for future experimental approaches, and recommendations for future investigations.

SARS-CoV-2 wastewater surveillance in Germany: Long-term RT-digital droplet PCR monitoring, suitability of primer/probe combinations and biomarker stability

In recent months, wastewater-based epidemiology (WBE) has been shown to be an important tool for early detection of SARS-CoV-2 circulation in the population. In this study, a detection methodology for SARS-CoV-2 RNA (wildtype and variants of concern) in wastewater was developed based on the detection of different target genes (E and ORF1ab) by polyethylene glycol (PEG) precipitation and digital droplet PCR. This methodology was used to determine the SARS-CoV-2 concentration and the proportion of N501Y mutation in raw sewage of the wastewater treatment plant of the city of Karlsruhe in south-western Germany over a period of 1 year (June 2020 to July 2021). Comparison of SARS-CoV-2 concentrations with reported COVID-19 cases in the catchment area showed a significant correlation. As the clinical SARS-CoV-2 official case report chain takes time, viral RNA titre trends appeared more than 12 days earlier than clinical data, demonstrating the potential of wastewater-based epidemiology as an early warning system. Parallel PCR analysis using seven primer and probe systems revealed similar gene copy numbers with E, ORF, RdRP2 and NSP9 assays. RdPP1 and NSP3 generally resulted in lower copy numbers, and in particular for N1 there was low correlation with the other assays. The occurrence of the N501Y mutation in the wastewater of Karlsruhe was consistent with the occurrence of the alpha-variant (B.1.1.7) in the corresponding individual clinical tests. In batch experiments SARS-CoV-2 RNA was stable for several days under anaerobic conditions, but the copy numbers decreased rapidly in the presence of dissolved oxygen. Overall, this study shows that wastewater-based epidemiology is a sensitive and robust approach to detect trends in the spread of SARS-CoV-2 at an early stage, contributing to successful pandemic management.

SARS-CoV-2 wastewater surveillance in Germany: Long-term RT-digital droplet PCR monitoring, suitability of primer/probe combinations and biomarker stability

In recent months, wastewater-based epidemiology (WBE) has been shown to be an important tool for early detection of SARS-CoV-2 circulation in the population. In this study, a detection methodology for SARS-CoV-2 RNA (wildtype and variants of concern) in wastewater was developed based on the detection of different target genes (E and ORF1ab) by polyethylene glycol (PEG) precipitation and digital droplet PCR. This methodology was used to determine the SARS-CoV-2 concentration and the proportion of N501Y mutation in raw sewage of the wastewater treatment plant of the city of Karlsruhe in south-western Germany over a period of 1 year (June 2020 to July 2021). Comparison of SARS-CoV-2 concentrations with reported COVID-19 cases in the catchment area showed a significant correlation. As the clinical SARS-CoV-2 official case report chain takes time, viral RNA titre trends appeared more than 12 days earlier than clinical data, demonstrating the potential of wastewater-based epidemiology as an early warning system. Parallel PCR analysis using seven primer and probe systems revealed similar gene copy numbers with E, ORF, RdRP2 and NSP9 assays. RdPP1 and NSP3 generally resulted in lower copy numbers, and in particular for N1 there was low correlation with the other assays. The occurrence of the N501Y mutation in the wastewater of Karlsruhe was consistent with the occurrence of the alpha-variant (B.1.1.7) in the corresponding individual clinical tests. In batch experiments SARS-CoV-2 RNA was stable for several days under anaerobic conditions, but the copy numbers decreased rapidly in the presence of dissolved oxygen. Overall, this study shows that wastewater-based epidemiology is a sensitive and robust approach to detect trends in the spread of SARS-CoV-2 at an early stage, contributing to successful pandemic management.

[Innovative SARS-CoV-2 crisis management in the public health sector: Corona dashboard and wastewater surveillance using the example of Berchtesgadener Land, Germany]

Hintergrund

Eine infektiologische Krisensituation wie die SARS-CoV-2-Pandemie stellte die Verwaltungsstrukturen des öffentlichen Gesundheitsdienstes vor erhebliche Herausforderungen, die abhängig von der personellen und digitalen Ausstattung in einer unterschiedlichen Effizienz des Ausbruchsmanagements resultierten. Die Einbindung von innovativen Instrumenten der Pandemiebekämpfung, wie Clusternachverfolgung, Risikogruppentestungen oder wie z. B. die von der EU-Kommission empfohlene Einbindung des Abwassermonitorings, wurde dadurch maßgeblich erschwert.

Ziel

In dieser Fallstudie im Berchtesgadener Land stellen wir die Einbindung eines flächendeckenden georeferenzierten Abwassermonitorings vor, das seit Nov. 2020 95 % der gesamten Bevölkerung erfasst.

Methoden

Für eine flächendeckende Erfassung erfolgte die Probennahme an 2 Tagen pro Woche an 9 kommunalen Kläranlagen und zusätzlich direkt aus der Kanalisation an 3 Standorten. Die Abwasserproben wurden direkt mittels Zentrifugation zur Feststoffabtrennung aufbereitet und über eine digitale Droplet Polymerase-Kettenreaktion (PCR) 4 spezifische Gene von SARS-CoV‑2 erfasst und quantifiziert.

Ergebnisse

Die Einbindung des georeferenzierten Abwassermonitorings war erfolgreich. Die Abwasserbefunde werden für jede Gemeinde mit den Inzidenzen pro 100.000 Einwohnern dargestellt. Änderungen im Infektionsgeschehen sind 10 Tage vor den offiziellen Fallzahlen mit einer Sensitivität von ca. 20 pro 100.000 Einwohner erkennbar.

Diskussion

Die Integration dieser innovativen Ansätze in eine umfassende Lageführung mittels eines digitalen Dashboards und der Etablierung eines Frühwarnsystems anhand eines quantitativen Abwassermonitorings resultierte im Landkreis Berchtesgadener Land in einem sehr effizienten, proaktiven Krisenmanagement. Dieses kann als Blaupause für andere Kommunen in Deutschland dienen.

Quantitative microbial risk assessment of a non-membrane based indirect potable water reuse system using Bayesian networks

Risk-based approaches are used to define performance standards for water and wastewater treatment to meet health-based targets and to ensure safe and reliable water quality for desired end use. In this study, a screening level QMRA for a non-membrane based indirect potable reuse (IPR) system utilizing the sequential managed aquifer recharge technology (SMART) concept was conducted. Ambient removals of norovirus, Campylobacter and Cryptosporidium in advanced water treatment (AWT) steps were combined in a probabilistic QMRA utilizing Bayesian networks constructed in Netica. Results revealed that all pathogens complied with disease burden at the 95th percentile, and according to the assumptions taken about pathogen removal, Cryptosporidium was the pathogen with the greatest risk. Through systematic sensitivity analysis, targeted scenario analysis, and backwards inferencing, critical control points for each pathogen were determined, demonstrating the usefulness of Bayesian networks as a diagnostic tool in quantifying risk of water reuse treatment scenarios.

Methodological Advances to Study Contaminant Biotransformation: New Prospects for Understanding and Reducing Environmental Persistence?

Complex microbial communities in environmental systems play a key role in the detoxification of chemical contaminants by transforming them into less active metabolites or by complete mineralization. Biotransformation, i.e., transformation by microbes, is well understood for a number of priority pollutants, but a similar level of understanding is lacking for many emerging contaminants encountered at low concentrations and in complex mixtures across natural and engineered systems. Any advanced approaches aiming to reduce environmental exposure to such contaminants (e.g., novel engineered biological water treatment systems, design of readily degradable chemicals, or improved regulatory assessment strategies to determine contaminant persistence a priori) will depend on understanding the causal links among contaminant removal, the key driving agents of biotransformation at low concentrations (i.e., relevant microbes and their metabolic activities), and how their presence and activity depend on environmental conditions. In this Perspective, we present the current understanding and recent methodological advances that can help to identify such links, even in complex environmental microbiomes and for contaminants present at low concentrations in complex chemical mixtures. We discuss the ensuing insights into contaminant biotransformation across varying environments and conditions and ask how much closer we have come to designing improved approaches to reducing environmental exposure to contaminants.

Varying attenuation of trace organic chemicals in natural treatment systems - A review of key influential factors

The removal of trace organic chemicals (TOrCs) from treated wastewater and impacted surface water through managed aquifer recharge (MAR) has been extensively studied under a variety of water quality and operating conditions and at various experimental scales. The primary mechanism thought to dictate removal over the long term is biodegradation by microorganisms present in the system. This review of removal percentages observed in biologically active filtration systems reported in the peer-reviewed literature may serve as the basis to identify future indicators for persistence, as well as variable and efficient removal in MAR systems. A noticeable variation in reported removal percentages (standard deviation above 30%) was observed for 24 of the 49 most commonly studied TOrCs. Such variations suggest a rather inconsistent capacity of biologically active filter systems to remove these TOrCs. Therefore, operational parameters such as the change in dissolved organic carbon (ΔDOC) during treatment, hydraulic retention time (HRT), filter material, and redox conditions were correlated to the associated TOrC removal percentages to determine whether a data-based relationship could be elucidated. Interestingly, 11 out of the 24 compounds demonstrated increased removal with increasing ΔDOC concentrations. Furthermore, 10 compounds exhibited a positive correlation with HRT. Based on the evaluated data, a minimum HRT of 0.5-1 day is recommended for removal of most compounds.

Inferring trophic conditions in managed aquifer recharge systems from metagenomic data

Humans are increasingly dependent on engineered landscapes to minimize negative health impacts of water consumption. Managed aquifer recharge (MAR) systems, such as river and lake bank filtration, surface spreading or direct injection into the aquifer have been used for decades for water treatment and storage. Microbial and sorptive processes in these systems are effective for the attenuation of many emerging contaminants including trace organic chemicals such as pharmaceuticals and personal care products. Recent studies showed a superior efficiency of trace organic chemical biotransformation by incumbent communities of microorganisms under oxic and carbon-limited (oligotrophic) conditions. This study sought to identify features of bacterial genomes that are predictive of trophic strategy in this water management context. Samples from a pilot scale managed aquifer recharge system with regions of high and low carbon concentration, were used to generate a culture collection from which oligotrophic and copiotrophic bacteria were categorized. Genomic markers linked to either trophic strategy were used to develop a Bayesian network model that can infer prevailing carbon conditions in MAR systems from metagenomic data.

Organic Contaminants and Interactions with Micro- and Nano-Plastics in the Aqueous Environment: Review of Analytical Methods

Micro- and nanoplastic particles are increasingly seen not only as contaminants themselves, but also as potential vectors for trace organic chemicals (TOrCs) that might sorb onto these particles. An analysis of the sorbed TOrCs can either be performed directly from the particle or TOrCs can be extracted from the particle with a solvent. Another possibility is to analyze the remaining concentration in the aqueous phase by a differential approach. In this review, the focus is on analytical methods that are suitable for identifying and quantifying sorbed TOrCs on micro- and nano-plastics. Specific gas chromatography (GC), liquid chromatography (LC) and ultraviolet-visible spectroscopy (UV-VIS) methods are considered. The respective advantages of each method are explained in detail. In addition, influencing factors for sorption in the first place are being discussed including particle size and shape (especially micro and nanoparticles) and the type of polymer, as well as methods for determining sorption kinetics. Since the particles are not present in the environment in a virgin state, the influence of aging on sorption is also considered.

Differentiating between adsorption and biodegradation mechanisms while removing trace organic chemicals (TOrCs) in biological activated carbon (BAC) filters

Efficient adsorption of certain trace organic chemicals (TOrCs) present in secondary treated municipal wastewater treatment plant (WWTP) effluents onto granular activated carbon (GAC) has already been demonstrated at lab- and full-scale. Due to high organic matter concentrations in WWTP effluents, GAC filters eventually develop a biofilm and turn into biological activated carbon filters (BAC), where removal of organic compounds is governed by biodegradation as well as by adsorption. However, determining TOrC breakthrough by conducting a long-term BAC column experiment to discern between the removal mechanisms is not possible due to competition for adsorption sites, fluctuating water quality, and other variables. Therefore, a rapid small scale column test (RSSCT) was conducted to determine the contribution of adsorption for select chemicals at 10,000 bed volumes treated (BVT). These results were then used in the pore surface diffusion model (PSDM) to model adsorption behavior at 40,000 BVTs. Pseudo-Freundlich K values obtained from the PSDM model were compared with K values obtained from an integral mass balance calculation. This comparison revealed that the modeling was most accurate for moderately to poorly adsorptive compounds. In comparing RSSCT results to long-term BAC columns, the modeling approach best predicted BAC removal of well adsorbing compounds, such as atenolol, trimethoprim, metoprolol, citalopram, and benzotriazole. However, differences in predicted vs observed BAC removal for the removals of venlafaxine, tramadol and carbamazepine revealed that BAC adsorption capacity was not yet exhausted for these compounds. Therefore, a comparison was not possible. The approach would be improved by operation at longer EBCT and improved calculation of compound fouling indices.

Effects of ultrasonic reactor design on sewage sludge disintegration

The impact of ultrasound (US) reactor design on cavitation intensity distribution and disintegration efficiency was studied for sewage sludge pre-treatment, using a US flatbed reactor of variable reaction chamber height (RCH, 20-100 mm). Mapping of cavitation intensity and treatment effects was conducted using (i) hydrophone measurements, (ii) aluminum foil tests, and (iii) soluble chemical oxygen demand (COD) analyses. The overall disintegration efficiency was evaluated based on average COD solubilization. The impact of flow on treatment (in)homogeneity was additionally examined using computational fluid dynamics (CFD). Results of all measurement techniques suggest that small RCHs (20 mm, for instance) enable uniform and intense treatments, while large RCHs, which are subjected to strong sound wave attenuation, entail inhomogeneous treatments where large fractions of substrate are no longer exposed to notable cavitation activity. For instance, COD solubilization (relative to alkaline hydrolysis) measured in the channel center dropped from 6.4% to zero as RCH widened from 20 mm to 100 mm. Flow-through sonication further aggravates treatment inhomogeneity due to the high flow rates in the low-cavitation channel centers. Overall disintegration efficiency declined with increasing RCH, showing a drop in average COD solubilization by 73% from RCH = 20 mm to RCH = 100 mm. The drop correlated with average cavitation noise levels (R² = 0.82), indicating that hydrophone measurements may be a suitable tool for US reactor design optimization. Overall, results suggest that reactor geometry has a critical impact on both treatment (in)homogeneity and treatment efficiency and that equal specific energy inputs do not imply equal US treatments.

Microbial genetic potential for xenobiotic metabolism increases with depth during biofiltration

Water infiltration into the subsurface can result in pronounced biogeochemical depth gradients. In this study, we assess metabolic potential and properties of the subsurface microbiome during water infiltration by analyzing sediments from spatially-segmented columns. Past work in these laboratory set-ups demonstrated that removal efficiencies of trace organic pollutants were enhanced by limited availability of biodegradable dissolved organic carbon (BDOC) associated with higher humic ratios and deeper sediment regions. Distinct differences were observed in the microbial community when contrasting shallow versus deeper profile sediments. Metagenomic analyses revealed that shallow sediments contained an enriched potential for bacterial growth and division processes. In contrast, deeper sediments harbored a significant increase in genes associated with the metabolism of secondary metabolites and the biotransformation of xenobiotic water pollutants. Metatranscripts further supported this trend, with increased potential for metabolic attributes associated with the biotransformation of xenobiotics and antibiotic resistance within deeper sediments. Furthermore, increasing ratios of humics in feed solutions correlated to enhanced expression of genes associated with xenobiotic biodegradation. These results provide genetic support for the interplay of dissolved organic carbon limitation and enhanced trace organic biotransformation by the subsurface microbiome.

Characterizing a novel in-situ oxygen delivery device for establishing controlled redox zonation within a high infiltration rate sequential biofilter

By applying favorable oxic and oligotrophic conditions through subsequent aeration and an additional infiltration step, the sequential managed aquifer recharge technology (SMART) was proven to better remove trace organic chemicals (TOrCs) than conventional MAR systems. To minimize the physical footprint, pumping costs and hydraulic retention times, as well as to overcome limitations of site-specific heterogeneities of such systems, the SMART concept was further upgraded by two main engineered technologies. This SMARTplus bioreactor is comprised of an infiltration trench and highly homogenous porous media to provide high infiltration rates and plug-flow conditions. Additionally, an in-situ oxygen delivery device, in particular a self-designed PDMS gas-liquid membrane contactor, was designed to establish favorable subsurface oxic conditions. This novel SMARTplus technology was investigated at pilot scale and is designed for advanced water treatment either in the context of water reuse or treatment of impaired surface water. To determine the design specifications and to construct a pilot-scale membrane contactor, the mass transfer coefficients of the PDMS membrane were investigated at lab-scale for varying Reynold numbers (0.2-2). With the help of the customized membrane contactor, homogenous, bubble-free and passive oxygen delivery could be successfully demonstrated at pilot-scale under laminar flow conditions and short contact times. Oxygen concentrations downstream of the membrane contactors met the design specifications (>1 mg/L) as long as the required feed water quality was provided. However, high NH₄⁺ concentrations in the secondary effluent resulted in higher and unsteady oxygen demand than the target oxygen transfer rates could meet and suboxic conditions prevailed. Although a 20-50% enhancement in the removal of certain compounds (4-FAA, antipyrine, sulfamethoxazole, and citalopram) was achieved, demonstration of the full potential of enhanced TOrC removal by SMARTplus was hindered due to unsteady feed water quality.

Developing a novel biofiltration treatment system by coupling high-rate infiltration trench technology with a plug-flow porous-media bioreactor

The sequence of two infiltration steps combined with an intermediate aeration named 'sequential managed aquifer recharge technology (SMART)' proved to be a promising approach to replenish groundwater using treated wastewater effluents or impaired surface waters due to efficient inactivation of pathogens and improved removal of many trace organic chemicals. To minimize the physical footprint of such systems and overcome limitations through site-specific heterogeneity at conventional MAR sites, an engineered approach was taken to further advance the SMART concept. This study investigated the establishment of plug-flow conditions in a pilot scale subsurface bioreactor by providing highly controlled hydraulic conditions. Such a system, with a substantially reduced physical footprint in comparison to conventional MAR systems, could be applied independent of local hydrogeological conditions. The desired redox conditions in the bioreactor are achieved by in-situ oxygen delivery, to maintain the homogenous flow conditions and eliminate typical pumping costs. For the time being, this study investigated hydraulic conditions and the initial performance regarding the removal of chemical constituents during baseline operation of the SMARTplus bioreactor. The fit of the observed and simulated breakthrough curves from the pulse injection tracer test indicated successful establishment of plug-flow conditions throughout the bioreactor. The performance data obtained during baseline operation confirmed similar trace organic chemical biotransformation as previously observed in lab- and field-scale MAR systems during travel times of <13 h.

Assessment of sonotrode and tube reactors for ultrasonic pre-treatment of two different sewage sludge types

The effectiveness of tube and sonotrode reactors for the sonication of sewage sludge under identical conditions was compared for the first time. Despite the considerable structural differences, sonication with each ultrasonic reactor led to an accelerated degradation rate and an increased methane production within the first five days for the majority of the sewage sludge samples tested. On closer examination, however, it becomes clear that the investigated sonication systems are not equally suitable for the substrates considered. While the use of a sonotrode proved to be particularly advantageous for the treatment of waste activated sludge (+25% methane yield at 300 kJ/kg_TS), the use of a 2-inch tube reactor achieved the highest enhancement for low-intensity sonication in digested sludge (+22% methane yield at 300 kJ/kg_TS). With increasing energy input, more chemical oxygen demand was solubilized, but this did not result in an increase in methane yield for all samples. Sonication of waste activated sludge led to a significant reduction in viscosity of up to 50%, and a reduction of up to 60% was observed after sonication of digested sludge with low energy inputs. The study, therefore, demonstrates that the choice of the most suitable sonication system essentially depends on the properties of the sludge to be sonicated.

Elucidation of removal processes in sequential biofiltration (SBF) and soil aquifer treatment (SAT) by analysis of a broad range of trace organic chemicals (TOrCs) and their transformation products (TPs)

Many chemicals with different physico-chemical properties are present in municipal wastewater. In this study, the removal of a broad range of trace organic chemicals (TOrCs) was determined in two biological treatment processes differing in hydraulic retention time: sequential biofiltration (SBF) and soil-aquifer treatment (SAT), operated in Germany and Spain. Occurrence and the degree of removal of more than 150 TOrCs with different physico-chemical properties were analysed, including precursors as well as human metabolites and environmental transformation products (TPs). Ninety TOrCs were detected in the feed water of the SBF system, 40% of these showed removal efficiencies of higher than 30% during biological treatment. In SAT, 70 TOrCs were detected in the feed water, 60% of these could be reduced by more than 30% after approximately 3 days of subsurface treatment. For uncharged and negatively charged TOrCs biological degradation was mainly responsible for the removal, while positively charged TOrCs were most likely also removed by ionic interactions. The detections of TPs confirmed that biodegradation was a major removal process in both systems. The analysis of positively and negatively charged, neutral and zwitterionic TOrCs and the simultaneous analysis of precursors and their biologically formed TPs enabled a detailed understanding of underlying mechanisms of their removal in the two systems. On this basis, criteria for site-specific indicator selection were proposed.

Antibiotic microbial resistance (AMR) removal efficiencies by conventional and advanced wastewater treatment processes: A review

The World Health Organization (WHO) has identified the spread of antibiotic resistance as one of the major risks to global public health. An important transfer route into the aquatic environment is the urban water cycle. In this paper the occurrence and transport of antibiotic microbial resistance in the urban water cycle are critically reviewed. The presence of antibiotic resistance in low impacted surface water is being discussed to determine background antibiotic resistance levels, which might serve as a reference for treatment targets in the absence of health-based threshold levels. Different biological, physical and disinfection/oxidation processes employed in wastewater treatment and their efficacy regarding their removal of antibiotic resistant bacteria and antibiotic resistance geness (ARGs) were evaluated. A more efficient removal of antibiotic microbial resistance abundances from wastewater effluents can be achieved by advanced treatment processes, including membrane filtration, ozonation, UV-irradiation or chlorination, to levels typically observed in urban surface water or low impacted surface water.

Role of reduced empty bed contact times and pre-treatment by coagulation with Fe(III) salts on the removal of trace organic compounds during sequential biofiltration

Sequential biofiltration (SBF) has been demonstrated to be a promising approach to achieve enhanced biological removal of various trace organic compounds (TOrCs) from wastewater treatment plant (WWTP) effluents by establishing oxic and carbon-limited conditions. This study investigated options to further advance the feasibility of SBF systems by reducing empty bed contact times (EBCTs). Additional experiments were conducted to investigate the pre-treatment of WWTP effluent by coagulation as an option to further decrease the organic carbon availability during SBF. Results indicated that an EBCT reduction in the first filter stage from 90 to 45 and 30 min adversely affected process performance regarding the removal of organic bulk parameters and several TOrCs over short-term. However, after an extended adaptation period of ten weeks comparable performance was observed in two SBF systems with first stage filters operated at EBCTs of 90 and 45 min. The pre-treatment of secondary effluent by coagulation, flocculation and sedimentation was not found to enhance the performance of an SBF system despite substantial removal of organic bulk parameters during the pre-treatment. However, despite the vast removal of total phosphorous during coagulation, nutrient limitation was not found to adversely affect the biological performance of the subsequent SBF system.

Load change capability of an anaerobic thermophilic trickle bed reactor for dynamic H2/CO2 biomethanation

Increasing shares of energy production originating from fluctuating renewable sources require measures that are able to balance power production for a stable electricity grid. H₂/CO₂ biomethanation is a suitable approach to convert fluctuating excess renewable energy into the storable substitute natural gas. This study investigated the rapid load change capability of an anaerobic thermophilic trickle bed reactor while maintaining a high methane content. The return to full load (62.1 m³_H2/m³_{trickle bed}/d) after a 30-min operational off-cycle was possible almost immediately, while 24-h interruptions required a 60-min stepwise load increase. To accelerate this delayed microbial conversion activity, non-steady state substrate gas conversion can be controlled via substrate and product gas flow rates, allowing to reactivate the entire microbial community and produce high quality product gas. Reactor design might be further improved to avoid short-circuiting and use the entire trickle bed gas phase as high quality gas buffer during initial load increases.

Spatial distribution of zinc in the topsoil of four vegetated infiltration swales treating zinc roof runoff

Since stormwater runoff from zinc roofs is polluted with high concentrations of zinc (Zn), runoff treatment is recommended in order to avoid harmful influences to the ecosystem. For the retention of Zn, vegetated infiltration swales with a topsoil layer are often used as decentralized Sustainable Urban Drainage Systems (SUDS). The aim of this study was to assess the risks of groundwater contamination due to infiltration of stormwater runoff of a Zn roof using infiltration swales. The spatial horizontal and vertical distribution of Zn content in four 15 year old vegetated infiltration swales at a zinc roof was analyzed and evaluated. High Zn contents (up to 27.9 g/kg dry mass) have been measured only for spatially limited areas at the inflow zones of each infiltration swale. Zn content decreased significantly with increasing distance from inflow and with increasing topsoil depth. Because the topsoil is still contaminated in deeper layers and because the soil's sorption potential is locally exceeded, the risk of groundwater contamination was expected to be high. Possible optimization of the hydraulic functioning and regular maintenance of the swales is recommended as well as a regular topsoil exchange of highly polluted areas.

Impact of ultrasound-induced cavitation on the fluid dynamics of water and sewage sludge in ultrasonic flatbed reactors

The fluid dynamics of water, thickened waste activated sludge (WAS, total solids concentration 4.4%) and digested sludge (DS, total solids concentration 2.5%) within a lab-scale ultrasonic flatbed reactor were experimentally investigated. For a visual observation of the opaque sludge flow, sewage sludges were approximated by transparent xanthan solutions with identical flow behavior. The visualization of the flow was realized by use of an ultrasonic reactor with a transparent panel and dye streams injected into the flow. Without ultrasonic treatment, xanthan solutions showed distinct laminar flow behavior (generalized Reynolds numbers < 1), at a flow rate of 100 L/h. In water, dye streams remained coherent as well, but with slightly unsteady features (Reynolds number ∼ 350). Activation of the ultrasound reactor caused strong fluid dynamic disturbance in the water flow and dye streams were dissolved instantly, thus indicating turbulent mixing. For the xanthan solutions, however, mixing was considerably less pronounced. The dye streams in the DS substitute (0.5% xanthan solution) remained overall in laminar shape, but exhibited an eruption-like branching and an increase in diameter with advancing treatment duration. For the solution resembling WAS (2.0% xanthan solution), only weak dye stream disruption was observed, thus indicating that WAS flow in flatbed reactors is nearly laminar during ultrasonic treatment.

Dynamics of Wastewater Effluent Contributions in Streams and Impacts on Drinking Water Supply via Riverbank Filtration in Germany-A National Reconnaissance

The discharge of wastewater effluents to a stream that is subsequently used for drinking water abstraction has been previously referred to as de facto water reuse. Where the abstraction of surface water for drinking water production occurs via induced bank filtration or aquifer recharge, additional site-specific factors should be considered to assess the impact of wastewater effluents on bank-filtered water. This study represents the first national reconnaissance to quantify wastewater effluent contributions in streams across Germany and consequences for indirect drinking water abstraction from these streams. An automated assessment using ArcGIS was conducted for river basins considering minimum and mean average discharge conditions of streams as well as discharge from more than 7500 wastewater facilities. In urban areas, where the natural base discharge is low, wastewater effluent contributions greater than 30-50% were determined under mean minimum discharge conditions, which commonly prevail from May to September. A conceptual model was proposed to estimate critical bank filtrate shares resulting in exceedances of monitoring trigger levels for health-relevant chemicals as a universal qualitative assessment regarding the relevance of de facto reuse conditions in surface waters used for drinking water abstraction. This approach was validated using chemical monitoring data for three case study locations.

Variable non-linear removal of viruses during transport through a saturated soil column

Reduction of viral surrogates (bacteriophage MS2 and murine norovirus-1 [MNV-1]) and viruses naturally present in wastewater (enteroviruses, adenoviruses, Aichi viruses, reovirus, pepper mild mottle virus) was studied in a long-term experiment simulating soil-aquifer treatment of a non-disinfected secondary treated wastewater effluent blend using a 4.4 m deep saturated soil column (95% sand, 4% silt, 1% clay) with a hydraulic residence time of 15.4 days under predominantly anoxic redox conditions. Water samples were collected over a four-week period from the column inflow and outflow as well as from seven intermediate sampling ports at different depths. Removal of MS2 was 3.5 log₁₀ over 4.4 m and removal of MNV-1 was 3 log₁₀ over 0.3 m. Notably, MNV-1 was removed to below detection limit within 0.3 m of soil passage. In secondary treated wastewater effluent, MNV-1 RNA and MS2 RNA degraded at a first-order rate of 0.59 day^-1 and 0.12 day^-1, respectively. In 15.4 days, the time to pass the soil column, the RNA-degradation of MS2 would amount to 0.8 log_10, and in one day that of MNV-1 0.3 log₁₀ implying that attachment of MNV-1 and MS2 to the sandy soil took place. Among the indigenous viruses, genome copies reductions were observed for Aichi virus (4.9 log₁₀) and for pepper mild mottle virus (4.4 log₁₀). This study demonstrated that under saturated flow and predominantly anoxic redox conditions MS2 removal was non-linear and could be described well by a power-law relation. Pepper mild mottle virus was removed less than all of the other viruses studied, which substantiates field studies at managed aquifer recharge sites, suggesting it may be a conservative model/tracer for enteric virus transport through soil.

Capturing the oxic transformation of iopromide - A useful tool for an improved characterization of predominant redox conditions and the removal of trace organic compounds in biofiltration systems?

The biological degradation of many trace organic compounds has been reported to be strongly redox dependent. The traditional characterization of redox conditions using the succession of inorganic electron acceptors such as dissolved oxygen and nitrate falls short in accurately describing the critical transition state between oxic and suboxic conditions. Novel monitoring strategies using intrinsic redox tracers might be suitable to close that gap. This study investigated the potential use of the successive biological transformation of the iodinated contrast medium iopromide as an intrinsic tracer of prevailing redox conditions in biofiltration systems. Iopromide degradation in biofiltration systems was monitored by quantifying twelve known biological transformation products formed under oxic conditions. A novel dimensionless parameter (T_IOP) was introduced as a measure for the successive transformation of iopromide. A strong correlation between the consumption of dissolved oxygen and iopromide transformation emphasized the importance of general microbial activity on iopromide degradation. However, results disproved a direct correlation between oxic (>1 mg/L O₂) and suboxic (<1 mg/L O₂) conditions and the degree of iopromide transformation. Results indicated that besides redox conditions also the availability of biodegradable organic substrate affects the degree of iopromide transformation. Similar behavior was found for the compounds gabapentin and benzotriazole, while the oxic degradation of metoprolol remained stable under varying substrate conditions.

Biotransformation of trace organic chemicals in the presence of highly refractory dissolved organic carbon

Previous studies demonstrated that the transformation of trace organic chemicals (TOrCs) in managed aquifer recharge (MAR) systems is favored under carbon-limited and oxic redox conditions especially, if the dissolved organic carbon (DOC) serving as primary substrate has a refractory character. Since co-metabolism is suggested to be the dominant removal mechanism, it is hypothesized that TOrCs transformation is controlled by the concentration of the refractory carbon under oxic redox conditions. A laboratory-scale soil column experiment mimicking MAR was established to investigate the influence of two different concentrations of highly refractory carbon sources on TOrCs transformation, namely drinking water (DW) and drinking water augmented with humic acid (DW + HA). Oxic redox conditions and carbon-limitation were present in both systems (ΔDOC_DW+HA ≈ 0.6-0.7 mg/L; ΔDOC_DW ≈ 0.1 mg/L). Of the 12 TOrCs investigated seven exhibited moderate to efficient transformation in both systems with only one compound (diclofenac) showing significantly enhanced (co-metabolic) biotransformation by adding humic acids as primary growth substrate. It is postulated that transformation of some TOrCs is characterized by metabolic degradation under starving conditions (ΔDOC ≤ 0.1 mg/L). By comparing the transformation efficiency of selected TOrCs with previous studies operated under carbon-limited and oxic conditions, an inconsistent behavior of some compounds was observed. These results demonstrate that key factors triggering the transformation of TOrCs are still poorly understood and thus, further investigations regarding the biodegradation pathways of TOrCs, upregulation of key enzymes by the microbial community but also more detailed analysis of the composition of the biodegradable DOC are needed.