A predictive multi-linear regression model for organic micropollutants, based on a laboratory-scale column study simulating the river bank filtration process

Etemadi regression in chemometrics: Reliability-based procedures for modeling and forecasting

The creation of predictive models with a high degree of generalizability in chemical analysis and process optimization is of paramount importance. Nonetheless, formulating a prediction model based on collected data from chemical measurements that maximize quantitative generalizability remains a challenging task for chemometrics experts. To tackle this challenge, a range of forecasting models with varying characteristics, structures, and capabilities has been developed, utilizing either accuracy-based or reliability-based modeling strategies. While the majority of models follow the accuracy-based approach, a recently proposed reliability-based approach, known as the Etemadi approach, has shown impressive performance across various scientific fields. The Etemadi models were constructed through a reliability-based parameter estimation process in such a manner that maximizes the models' reliability. However, the foundation of modeling procedures for chemometrics purposes is built upon the assumption that high generalizability in inaccessible/test data is achieved through the accuracy-based training procedure in which errors in available historical/training data are minimized. After conducting a thorough review of the current literature, we have found that none of the forecasting models for chemometrics purposes incorporate reliability into their modeling procedures. Given the dynamic and highly sensitive nature of chemistry experiments and processes, implementing a reliable model that controls performance criteria variation is a promising strategy for achieving stable and robust forecasts. To address this research gap, this paper introduces several key innovations, which can be highlighted as follows: (1) Proposing a general design structure based on a new optimal reliability-based parameter estimation process. (2) Introducing a novel risk-based modeling strategy that minimizes the performance variation of models implemented under different conditions in chemical laboratory experiments, to generate a more generalizable model for diverse applications in chemometrics. (3) Specifying the degree of influence that each reliability and accuracy factor has in enhancing the generalizability and uncertainty modeling of chemometric models. Empirical evidence confirms the effectiveness and superior performance of reliability-based models compared to accuracy-based models in 78.95% of the cases across various fields, including Pharmacology, Biochemistry, Agrochemical, Geochemical, Biological, Pollutants, Physicochemical Properties, and Gases Experiment. Furthermore, the study's findings demonstrate that the reliability-based modeling approach outperforms the accuracy-based strategy in terms of MAE, MSE, ARV, and RMSE by an average of 4.697%, 5.646%, 5.646%, and 4.342%, respectively. It is also statistically proven that reliability has a more significant impact on improving the generalizability of chemometric models than accuracy. This emphasizes the importance of including reliability as a crucial factor in chemometrics modeling, a consideration that has been overlooked in traditional modeling processes. Consequently, reliability-based modeling approaches can be regarded as a viable alternative to conventional accuracy-based modeling methods for chemical modeling purposes.

Effect of dissolved organic carbon on micropollutant biodegradation by aquifer and soil microbial communities

Groundwater, a major source of drinking water worldwide, is often contaminated with micropollutants. Although microbial communities in aquifers and soils have the capability to biodegrade some micropollutants, this process is limited in situ. Biostimulation with dissolved organic carbon (DOC) is known to promote micropollutant biodegradation, but the role of DOC biodegradability is still poorly understood. This study investigated how three DOC types with different biodegradability (humics, dextran and acetate) affect the biodegradation of 15 micropollutants by aquifer and soil microbial communities under aerobic and nitrate reducing conditions. Although originating from different environments, both communities were able to biodegrade the same 4 micropollutants under aerobic conditions - 2,4-D, MCPP, chloridazon (CLZ) and chloridazon-desphenyl. However, DOC addition only affected MCPP biodegradation, promoting MCPP biodegradation regardless of DOC biodegradability. Biodegradation of 2,4-D, MCPP and CLZ under aerobic conditions was observed after a lag phase, whose duration differed per compound. 2,4-D was biodegraded first and fully. Aquifer community was able to degrade about half of the initial MCPP concentration (removal efficiency of 49.3 ± 11.7%). CLZ was fully biodegraded by the aquifer community, but not by the soil community, possibly due to substrate competition with organics originating from the inoculum. Therefore, the natural organic carbon present in the inocula and in environmental systems can influence micropollutant biodegradation. Under nitrate reducing conditions micropollutant biodegradation was not observed nor biostimulated by DOC addition. The results also highlight the importance of sufficient exposure time to trigger in situ micropollutant biodegradation.

Influence of redox condition and inoculum on micropollutant biodegradation by soil and activated sludge communities

Micropollutant biodegradation is selected by the interplay among environmental conditions and microbial community composition. This study investigated how different electron acceptors, and different inocula with varying microbial diversity, pre-exposed to distinct redox conditions and micropollutants, affect micropollutant biodegradation. Four tested inocula comprised of agricultural soil (Soil), sediment from a ditch in an agricultural field (Ditch), activated sludge from a municipal WWTP (Mun AS), and activated sludge from an industrial WWTP (Ind AS). Removal of 16 micropollutants was investigated for each inoculum under aerobic, nitrate reducing, iron reducing, sulfate reducing, and methanogenic conditions. Micropollutant biodegradation was highest under aerobic conditions with removal of 12 micropollutants. Most micropollutants were biodegraded by Soil (n = 11) and Mun AS inocula (n = 10). A positive correlation was observed between inoculum community richness and the number of different micropollutants a microbial community initially degraded. The redox conditions to which a microbial community had been exposed appeared to positively affect micropollutant biodegradation performance more than pre-exposure to micropollutants. Additionally, depletion of the organic carbon present in the inocula resulted in lower micropollutant biodegradation and overall microbial activities, suggesting that i) an additional carbon source is needed to promote micropollutant biodegradation; and ii) overall microbial activity can be a good indirect indicator for micropollutant biodegradation activity. These results could help to develop novel micropollutant removal strategies.

Fates of potentially persistent and mobile organic substances in embedded outdoor columns for artificial groundwater recharge simulation

Persistent and mobile organic micropollutants (OMP) are ubiquitously found in the aquatic environment and have a high propensity to distribute in water resources and are difficult to remediate. Managed aquifer recharge systems such as artificial groundwater recharge, produce high-quality drinking water by removing numerous OMP from the source water. In this study, the fates of selected emerging and potentially persistent and mobile OMP were investigated in outdoor columns for artificial groundwater recharge simulation. Breakthrough curves of OMP were modeled to differentiate between sorption and bio-transformation. The study showed that selected OMP were persistent in the surface water and no photo-degradation was observed, except for diclofenac. The trends of dissolved organic carbon concentrations and UV light absorption at 254 nm wavelength suggest elevated biological activity in the first 0.3 m of the columns. The study revealed that the bio-transformation of cyanoguanidine, valsartan acid and diclofenac correlated with the biological activity in the sand columns. Benzyltrimethylammonium, n-(3-(dimethylamino)-propyl)methacrylamide, 1,3-di-o-tolylguanidine, 1,3-diphenylguanidine and melamine were completely eliminated within the first 0.3 m, likely due to sorption. Less mobile compounds such as carbamazepine and adamantan-1-amine also showed sorption. Sorption was also observed for diclofenac, likely due to decreased pH along the column depth. Retardation factors of several OMP were higher in the first 0.3 m of the columns, likely due to higher organic carbon contents compared to the remaining depth. Six organic substances (for example 2-acrylamido-2-methylpropane sulfonate and dimethylbenzene sulfonate) were persistent and mobile throughout the experiment. Overall, this study reveals the vital role of pH and sand organic carbon for sorption and residence time and biological activity for OMP elimination.

Analysis on the attenuation characteristics of PPCPs in surface water and their influencing factors based on a compilation of literature data

The attenuation characteristics of PPCPs play an important part in predicting their environmental concentrations. However, considerable uncertainty remains in reported laboratory data on the attenuation characteristics of PPCPs. In this analysis, we compile information on laboratory-observed photodegradation half-lives (t1/2), biodegradation t1/2, the organic carbon normalized adsorption constant (KOC) and field-observed overall attenuation t1/2 for PPCPs in water bodies from more than 200 peer-reviewed studies. To mitigate the effects of such uncertainty, we derive representative values (RV) for PPCP degradability from these records to better compare the characteristics of different PPCPs. We further examine the influence of experimental conditions and environmental drivers on the determination of t1/2 using difference analysis and correlation analysis. The results indicate that for laboratory photodegradation tests, different light sources, initial concentration and volume significantly affect t1/2, whereas there is no significant difference between values obtained from tests conducted in pure water and natural water. For biodegradation, laboratory-measured t1/2 values in batch, flume and column studies gradually decrease, marking the controlling role of experimental setup. Redox condition, initial concentration and volume are also recognized as important influencing factors. For adsorption, water-sediment ratio is the primary reaction parameter. As two frequently investigated factors, however, pH and temperature are not significant factors in almost all cases. In field observations, the persistence of carbamazepine, typically used as a tracer, is in doubt. Water depth and latitude are the most correlated drivers of t1/2, indicating the predominant status of photodegradation in the overall attenuation rates. These findings call for caution when selecting experimental parameters and environmental drivers in determining PPCP's attenuation rates and establishing PPCP fate models in the field.

The contribution of deeper layers in slow sand filters to pathogens removal

Slow Sand Filtration is popular in drinking water treatment for the removal of a wide range of contaminants (e.g., particles, organic matter, and microorganisms). The Schmutzdecke in slow sand filters (SSFs) is known to be essential for pathogen removal, however, this layer is also responsible for increased head loss. Since the role of deeper layers in bacteria and virus removal is poorly understood, this research investigated the removal of E.coli WR1 and PhiX 174 at different depths of a full-scale SSF. Filter material from top (0-5 cm), middle (5-20 cm) and deep (20-35 cm) layers of an established filter was used in an innovative experimental set-up to differentiate physical-chemical and biological removal processes. In the analysis, we distinguished between removal by biological activity, biofilm and just sand. In addition, we modelled processes by a one-side kinetic model. The different layers contributed substantially to overall log removal of E.coli WR1 (1.4-1.7 log₁₀) and PhiX 174 (0.4-0.6 log₁₀). For E.coli WR1, biological activity caused major removal, followed by removal within biofilm and sand, whereas, removal of PhiX 174 mainly occurred within sand, followed by biofilm and biological activity. Narrow pore radii in the top layer obtained by micro-computed tomography scanner suggested enhanced retention of bacteria due to constrained transport. The retention rates of E.coli WR1 and PhiX 174 in top layer were four and five times higher than deeper layers, respectively (k_ret 1.09 min^-1 vs 0.26 min^-1 for E.coli WR1 and k_ret 0.32 min^-1 vs of 0.06 min^-1 for PhiX 174). While this higher rate was restricted to the Schmutzdecke alone (top 5 cm), the deeper layers extend to around 1 m in full-scale filters. Therefore, the contribution of deeper layers of established SSFs to the overall log removal of bacteria and viruses is much more substantial than the Schmutzdecke.

Transformation of potentially persistent and mobile organic micropollutants in column experiments

The occurrence of potentially persistent and mobile (PM) organic micropollutants (OMP) in the aquatic environment is recognized as a severe threat to water resources and drinking water suppliers. The current study investigated long-term fate (persistency and bio-transformation) of several emerging contaminants in a simulated bank filtration (BF) for the first time. In parallel, four sand column systems were operated with groundwater and continuously spiked with an average concentration of 1 μg/L for 24 OMP. Each column system consisted of two sand columns connected in series. Presumably, biological activities in the first column were higher than in the second column, as dissolved oxygen utilization, dissolved organic matter (DOM) and UV absorbance at 254 nm (UV₂₅₄) reduction rates were high in the first column. This study revealed that 9 out of 24 OMP were persistent and mobile throughout the study under oxic conditions and within a hydraulic retention time (HRT) of 12 days. However, 2 (out of 9) OMP were persistent but showed sorption behavior. 15 (out of 24) OMP displayed bio-transformation, 4 were eliminated entirely within 4.5 days of HRT. Others showed constant or improved degradation with the adaptation (or operation) time. Improved degradation with adaption was high in the bioactive sand columns. However, 8 OMP showed improved elimination at high HRT, even in low biologically active columns. In addition, no significant effect of the DOM on the eliminations of OMP was found except for 4-hydroxy-1-(2-hydroxyethyl)-2,2,6,6,-tetramethylpiperidine (HHTMP), 2-methyl-2-propene-1-sulfonic acid (MPSA) and sulfamethoxazole (SMX). The eliminations of HHTMP (Pearson's r > 0.80, p < 0.05), MPSA (Pearson's r > 0.70) and SMX (Pearson's r > 0.80) correlated with the removals of humic substances in the sand columns. Overall, adaptation time and HRT play a crucial role in the elimination of emerging OMP through BF, yet at the same time several OMP exhibit persistent behavior.

Primary and ultimate degradation of benzophenone-type UV filters under different environmental conditions and the underlying structure-biodegradability relationships

Ten common benzophenone-based UV filters (BPs), sharing the same basic structure and differing only in their substituents, were investigated with respect to their primary and ultimate biodegradability. This study was carried out in order to gain deeper insights into the relationship between structure and biodegradability. The primary biodegradation of the selected BPs was studied in river water at environmentally relevant concentrations (1 µg/L) while varying specific, crucial environmental conditions (aerobic, suboxic, supplementation of nutrients). For this purpose, both batch and column degradation tests were performed, which allowed a systematic study of the effects. Subsequently, the ultimate biodegradation, i.e. the potential to achieve full mineralization of BPs, was examined according to OECD guideline 301 F. The results indicate that mineralization is limited to derivatives in which both aromatic rings contain substituents. This hypothesis was supported by docking simulations showing systematic differences in the orientation of BPs within the active site of the cytochrome P450 enzyme. These differences in orientation correspond to the substitution pattern of the BPs. This study provides valuable insights for assessing the environmental hazards of this class of trace organic compounds.

Degradation of seven pesticides and two metabolites before and during aquifer storage transfer and recovery operation

Degradation of 7 common pesticides (bentazon, boscalid, chloridazon, fluopyram, flutolanil, imidacloprid, and methoxyfenozide) and 2 metabolites of chloridazon (desphenyl-chloridazon, and methyl-desphenyl-chloridazon) was studied in an anoxic and brackish sandy aquifer before and during Aquifer Storage Transfer and Recovery (ASTR) operation. Fresh tile drainage water was injected and stored for later re-use as irrigation water. We hypothesized that electron acceptors (O₂, NO₃), dissolved organic carbon (∼24.7 mg/L), nutrients (NO₃: ∼14.1 mg/L, NH₄: ∼0.13 mg/L, PO₄: ∼5.2 mg/L), and biodegrading bacteria in tile drainage water could stimulate degradation of the pesticides and metabolites (ranging between 0.013 and 10.8 μg/L) introduced in the aquifer. Pesticide degradation was studied at 6 depths in the aquifer using push-pull tests lasting ±18 days before the onset of ASTR operation. Degradation was too limited to quantify and/or could not be assessed because of the potential occurrence of pesticide retardation. Utilizing push-pull tests to obtain degradation constants should only be considered in future studies for non-retarding pesticides with relative low half-lives (here <20 days). During ASTR operation, pesticide degradation was studied at the same depths during 3 storage periods equally spread over 1.5 years of ASTR operation. Overall, trends of degradation were observed, although with relatively high half-lives of at least 53 days. Microbial adaptation of the aquifer and/or bioaugmentation by the injected biodegrading bacteria did not result in enhanced degradation during consecutive storage periods. Operational monitoring data over longer periods and distances yielded half-lives of at least 141 days. The slow degradation mostly agrees with previous studies. The injected tile drainage water composition did therefore not notably stimulate pesticide degradation. The relatively persistent behavior of the studied pesticides/metabolites implies that ASTR abstracted water will have generally high pesticide concentrations, and non-abstracted water may form a contamination risk for the surrounding native brackish groundwater.

Design and Construction of Repacked Soil Columns for Measuring Solute Transport, Plant Growth and Soil Biota

Researchers face a number of challenges in the construction of soil columns which can affect the outcome of their experiments. The use of intact soil cores closely mimics actual field conditions. However, the excavation of large intact soil cores is a time-consuming, labor-intensive process and may lead to soil compaction that would influence the solute transport behavior of the soil column. Repacked soil columns are used as an option to circumvent these challenges of intact soil cores. However, repacked soil columns also have their limitations and introduce other challenges. Here, we present a step by step procedure for the design of repacked soil columns to achieve a realistic bulk density, prevent preferential flow paths, and ensure hydraulic connectivity between soil layers. This protocol will be beneficial to Soil Scientists, Hydrologists and other Environmental Scientists utilizing repacked soil columns.

A review of the biotransformations of priority pharmaceuticals in biological wastewater treatment processes

Wastewater effluent discharges have been considered as one of the main sources of synthetic chemicals entering into the aquatic environment. Even though they occur at low concentrations, pharmaceutically active compounds (PhACs) can have an impact on ecological toxicity that affects aquatic organisms. Moreover, new regulations in development toward preserving water quality reinforces the increasing need to monitor and abate some PhACs in wastewater treatment plants (WWTPs), where they are typically only partially eliminated. Unlike most previous reviews, we have focussed on how the main biological and chemical molecular factors impact the biotransformations of key PhACs in biological WWTP processes. Biotransformations have been found to be an important contributor towards the removal of PhACs from WWTP effluents. This review paper critically assesses these aspects and the recent advances that have been achieved in wastewater treatment processes for biodegradation of 7 PhACs; namely the non-steroidal anti-inflammatory drug (NSAID) diclofenac (DCF); the macrolide antibiotics azithromycin (AZM), erythromycin (ERY) and clarithromycin (CLR); the two natural estrogens estrone (E1) and 17β-estradiol (E2), and the synthetic estrogen 17α-ethinylesradiol (EE2). These represent the micropollutants of the EU Watch list in Decision 2015/495/EU that are most relevant to WWTPs due to their frequent detection. The metabolic pathways, transformation products and impact of relevant factors to biological WWTP processes is addressed in this review. The biokinetics of PhAC biodegradation in different engineered bioprocesses is also discussed. Promising technologies and operational strategies that are likely to have a high impact on controlling PhAC releases are highlighted and future research needs are also proposed.

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.

Impact of seasonality, redox conditions, travel distances and initial concentrations on micropollutant removal during riverbank filtration at four sites

Riverbank filtration (RBF) is a reliable water purification technique that has proven to be suitable for the removal of organic micropollutants. Its removal efficiency and dependency on a variety of factors such as redox conditions, temperatures, geology, travel times, level of initial micropollutant concentrations and seasonality were investigated during three seasonal sampling campaigns. Two anoxic (silty sand, Ems river) and two oxic (gravel, Ruhr river) RBF sites in Germany with different travel distances (42-633 m) were studied. Micropollutant concentrations were examined using a large-volume direct injection liquid chromatography method coupled to high-resolution mass spectrometry. Seasonal differences in micropollutant concentrations in the rivers were observed for chlorotolurone, diclofenac, terbuthylazine, mecoprop-P, MCPA (2-methyl-4-chlorophenoxyacetic acid) and propyphenazone. Redox dependencies in RBF were only found for sulfamethoxazole, propyphenazone, terbuthylazine and carbamazepine. Data for oxazepam, tramadol, N-desmethyl-tramadol, tilidin-desmethyl, carbamazepine and carbendazim indicate a required minimum travel distance of e.g. 100-200 m for the complete removal. Notably, travel time did not seem to be a substantial factor for their removal. High conductivity aquifers are also well suited for micropollutant removal. Seasonal initial concentration level variations showed no impact on the resulting abstraction well concentrations. Although the calculated removal efficiencies varied, they proved to be improper for seasonal raw water quality comparison. Knowledge of micropollutant behavior in riverbank filtration was broadened and RBF proved to be well suited for effective micropollutant reduction throughout the year, yet for a complete removal long travel distances or further technical purification steps are required.

A model-based analysis of the reactive transport behaviour of 37 trace organic compounds during field-scale bank filtration

Though bank filtration diminishes the loads of many trace organic compounds (TOrCs) present in the source water, still there is a wide uncertainty on the influence of local environmental conditions on biodegradation processes. This research addresses the fate and transport behaviour of 37 trace organic compounds at a bank filtration site in Germany over a relatively long-time span of six years. Using two-dimensional heat and reactive transport modelling in FEFLOW, TOrCs are classified according to their occurrence in bank filtration wells with a residence time of up to 4 months. We identify 12 persistent compounds, 20 reactive compounds and 5 transformation products formed during aquifer passage. Estimates of first-order biodegradation rate constants are given for six reactive compounds. Minimum biodegradation rate constants (i.e. maximum half-lives) are approximated for eight compounds only present in the surface water. For some compounds, a simple first-order degradation model did not yield satisfactory results and the behaviour appears to be more complex. Processes like sorption, redox- and/or temperature-dependent biodegradation and temperature-dependent desorption are suspected but incorporating these into the model was beyond the scope of this paper that provides an overview for many compounds. Results highlight the ability of the sub-surface to improve the water quality during bank filtration, yet at the same time show the persistence of several compounds in the aquifer.

Biodegradation of pharmaceuticals and personal care products in the sequential combination of activated sludge treatment and soil aquifer treatment

Soil aquifer treatment (SAT), applied after activated sludge treatment (AST), has been widely used for wastewater reclamation. AST and SAT show potential for removing micropollutants, including pharmaceuticals and personal care products (PPCPs). However, the role of sequential combination of AST and SAT on the biodegradation of PPCPs was not clear in previous studies. In this study, the removal characteristics of PPCPs in AST and SAT were evaluated to assess the legitimacy of sequential combination of AST and SAT. SAT showed effective removals of antibiotics (> 80%), including fluoroquinolones and macrolides by sorption, but poor removals of amide pharmaceuticals (i.e. carbamazepine and crotamiton) were observed in both AST and SAT. Additionally, biodegradation contributed to the effective removal of carboxylic PPCPs (i.e. ketoprofen and gemfibrozil) in both ASTs and SAT, but effective biodegradation of halogenated acid and polycyclic aromatic compounds (i.e. clofibric acid and naproxen) was observed only in SAT (82.1% and 81.8%, respectively). Furthermore, the microbial substrate metabolic patterns showed that amino acids, amines, and polymers were biodegradable in SAT, which was fit for the biodegradation characteristics of PPCPs in SAT. For microbial communities, Proteobacteria were dominant in AST and SAT, but Acidobacteria and Actinobacteria were more abundant in SAT than AST, which could contribute to the effective removals of halogenated acid in SAT. Considering PPCP biodegradation and substrate metabolism, SAT displays a wider range on the biodegradation than AST. Therefore, we conclude that these two processes can complement each other when used for controlling PPCPs.

Spatiotemporal resolved sampling for the interpretation of micropollutant removal during riverbank filtration

Riverbank filtration (RBF) systems along rivers are widely used as public water supplies. In these systems, many organic micropollutants (OMPs) are attenuated, but some compounds have shown to be rather persistent. Their fate and transport has been studied in RBF sites along lakes and small rivers, but not extensively along large and dynamic rivers. Therefore, the influence of flood events on OMP behavior in these large and dynamic RBF sites was investigated. Monthly samples were taken from surface- and groundwater up to a distance of 900 m from the riverbank of the Danube from March 2014 till May 2016. Two flood events were sampled more extensively nearby the river. Results showed that changes in flow conditions in the river not only caused changes in OMP concentrations, but also in their load. It was seen that the load of benzotriazole, carbamazepine and sulfamethoxazole in the river increased with increasing river discharges. After a relatively long, oxic groundwater passage, several OMPs were reduced. In contrast to previous work, we found that benzotriazole was almost fully removed under oxic conditions. When entering the aquifer, benzotriazole concentrations were significantly reduced and at a distance of 550 m from the river, >97% was degraded. Carbamazepine and sulfamethoxazole showed relatively persistent behavior in the aquifer. The concentrations measured during flood events were in the same range as seasonal sampling. Furthermore concentrations in the groundwater were higher during these events than in the Danube and can reach further into the aquifer. During flood events some highly degradable compounds (i.e. diclofenac) were found up to a distance of 24 m from the river. These results implied that drinking water utilities with RBF wells in oxic, alluvial aquifers located close to highly dynamic rivers need to consider a potential reduction in groundwater quality during and directly after flood events.

Metronidazole removal by means of a combined system coupling an electro-Fenton process and a conventional biological treatment: By-products monitoring and performance enhancement

In order to mineralize Metronidazole (MTZ), a process coupling an electro-Fenton pretreatment and a biological degradation was implemented. A mono-compartment batch reactor containing a carbon-felt cathode and a platinum anode was employed to carry out the electro-Fenton pretreatment of MTZ. A total degradation of MTZ (100 mg L^-1) was observed at 0.07 mA.cm^-2 after only 20 min of electrolysis. Yet, after 1 and 2 h of electrolysis, the mineralization level remained low (16.2% and 32% respectively), guaranteeing a significant residual organic content for further biological treatment. LCMS/MS was used to determine the intermediates by-products and hence to propose a plausible degradation pathway. An increase from 0 to 0.44 and 0.6 for 1 and 2 h of electrolysis was observed for the BOD₅/COD ratio. Thus, from 1 h of electro-Fenton pretreatment, the electrolysis by-products were considered biodegradable. A biological treatment of the electrolysis by-products after 1 and 2 h was then realized. The mineralization yields reached very close values, about 84% for 1 and 2 h of electrolysis after 504 h of biological treatment, namely close to 89% for the overall process, showing the pertinence of the proposed coupled process.

The uncertainty of biodegradation rate constants of emerging organic compounds in soil and groundwater - A compilation of literature values for 82 substances

The present study reports on biodegradation rate constants of emerging organic compounds (EOCs) in soil and groundwater available in the literature. The major aim of this compilation was to provide an assessment of the uncertainty of hydrological models with respect to the fate of EOCs. The literature search identified a total number of 82 EOCs for which 1st-order rate constants could be derived. It was found that for the majority of compounds degradation rate constants vary over more than three orders of magnitude. Correlation to factors that are well known to affect the degradation rate, such as temperature or redox condition was weak. No correlation at all was found with results from available quantitative structure-activity relationship models. This suggests that many unknown site specific or experimentally specific factors influence the degradation behavior of EOCs in the environment. Thus, local and catchment scale predictive models to estimate EOC concentration at receptors, e.g., receiving waters or drinking water wells, need to consider the large uncertainty in 1st-order rate constants. As a consequence, applying rate constants that were derived from one experiment or field site investigation to other experiments or field sites should be done with extreme caution.

Removal of pharmaceuticals from municipal wastewaters at laboratory scale by treatment with activated sludge and biostimulation

Municipal wastewater containing 21 pharmaceutical compounds, as well as activated sludge obtained from the aeration tank of the same wastewater treatment plant were used in lab-scale biodegradation experiments. The concentrations of pharmaceutical compounds were determined by high-performance liquid chromatography coupled to Orbitrap high-resolution mass spectrometry and ranged from 13.2ng/L to 51.8μg/L. Activated sludge was characterized in the terms of phylogenetic and catabolic diversity of microbial community, as well as its morphology. Proteobacteria (24.0%) represented the most abundant phylum, followed by Bacteroidetes (19.8%) and Firmicutes (13.2%). Bioaugmentation of wastewater with activated sludge stimulated the biodegradation process for 14 compounds. The concentration of carbamazepine in non-amended and bioaugmented WW decreased during the first 17h up to 30% and 70%, respectively. Diclofenac and ibuprofen demonstrated comparatively slow removal. The stimulating effect of the added nutrients was observed for the degradation of almost all pharmaceuticals detected in WW. The most pronounced effect of nutrients was found for erythromycin. The results were compared with those obtained for the full-scale WW treatment process.