The fate of organic micropollutants during long-term/long-distance river bank filtration

Managed aquifer recharge as a potential pathway of contaminants of emerging concern into groundwater systems - A systematic review

Groundwater is an often-overlooked resource, while its declining quantity and quality is of global concern. To protect and ensure stable quantity and quality of groundwater systems used as drinking water supplies, a common method is to artificially recharge these groundwater supplies with surface water, a process called managed aquifer recharge (MAR), that has been used globally for decades. However, surface waters used for MAR often contain elevated concentrations of anthropogenic chemicals of emerging concern (CECs), such as plastics, pesticides, pharmaceuticals and personal care products (PPCPs), or per- and polyfluoroalkyl substances (PFAS). When infiltrating this surface water, MAR can thus act as a shortcut for CECs into groundwater systems and eventually drinking water supplies. Especially PFAS are an example of very persistent contaminants showing atypical transport patterns during MAR and thus posing a risk for ground- and drinking water contamination. This systematic review addresses the transport process of CECs through MAR systems by looking at (1) common CEC concentrations in surface waters, (2) factors affecting CEC transport and possible retention during MAR, such as sorption and other physio-chemical mechanisms of CECs, biological and chemical decomposition, or hydrogeological properties of the MAR system, and (3) key contaminants leaching through the MAR systems as well as possible treatment options to improve the retention of CECs during MAR. Since we are facing increasing needs for high quality drinking water, lower CEC drinking water guidelines as well as an increasing number of identified CECs in surface waters, we conclude with a series of recommendations and future research directions to address these issues. Those include the need for regular monitoring programs specifically addressing CECs and especially not yet regulated, (very) persistent and (very) mobile contaminants, such as PFAS, as well as redesigned MAR systems to ensure stable ground- and drinking water quantity and quality.

Selection of pharmaceuticals of concern in reclaimed water for crop irrigation in the Mediterranean area

The reuse of reclaimed water in agriculture is being fostered in areas suffering from water scarcity. However, water pollutants can compromise food safety and pose a risk for the environment. This study aims to select the pharmaceutical compounds worth monitoring and investigating when reclaimed water is used for tomato and lettuce irrigation. A comprehensive study was first conducted to identify the pharmaceuticals frequently detected in secondary wastewater effluents in Catalonia (Northeast Spain). Priority pharmaceuticals were further selected based on their occurrence in secondary effluents, persistence (removal in conventional treatment), bioaccumulation potential, toxicity for aquatic organisms, and the risks they pose to the terrestrial environment and human health (through the consumption of crops). Out of the 47 preselected priority compounds, six could pose a risk to organisms living in soil irrigated with reclaimed water and seven could be potentially taken up by the crops. Nonetheless, no risk for human consumption was foreseen.

MTBE exposure may increase the risk of insulin resistance in male gas station workers

Insulin resistance is closely related to many metabolic diseases and has become a serious public health problem worldwide. So, it is crucial to find its environmental pathogenic factors. Methyl tert-butyl ether (MTBE), a widely used unleaded gasoline additive, has been proven to affect glycolipid metabolism. However, results from population studies are lacking. For this purpose, the potential relationships between MTBE exposure and the triglyceride glucose (TyG) index, a useful surrogate marker of insulin resistance, were evaluated using a small-scale occupational population. In this study, 201 participants including occupational and non-occupational MTBE exposure workers were recruited from the Occupational Disease Prevention and Control Hospital of Huaibei, and their health examination information and blood samples with informed consent were collected. The internal exposure levels were assessed by detecting blood MTBE using solid-phase-micro-extraction gas chromatography-mass spectrometry. Then the adjusted linear regression model was used to assess the relationship between MTBE exposure and fasting plasma glucose (FPG), or TyG index. Then, receiver-operating-characteristic (ROC) curves were performed to calculate the optimal cut-off points. Multivariable and hierarchical logistic regression models were used to analyze the impact of MTBE exposure on the risk of insulin resistance. Obvious correlations were observed between blood MTBE levels with TyG index (p = 0.016) and FPG (p = 0.001). Further analysis showed that using the mean of the TyG index (8.77) as a cutoff value had a good effect on reflecting the risk of insulin resistance. Multivariable logistic regression analysis also indicated that MTBE exposure was an independent risk factor for a high TyG index (OR = 1.088, p = 0.038), which indicated that MTBE exposure might be a new environmental pathogenic factor leading to insulin resistance, and MTBE exposure might increase the risk of insulin resistance by independently elevating the TyG index in male gas station workers.

The fate of nitrification and urease inhibitors in simulated bank filtration

The application of nitrification and urease inhibitors (NUI) in conjunction with nitrogen (N) fertilizers improves the efficiency of N fertilizers. However, NUI are frequently found in surface waters through leaching or surface runoff. Bank filtration (BF) is considered as a low-cost water treatment system providing high quality water by efficiently removing large amounts of organic micropollutants from surface water. The fate of NUI in managed aquifer recharge systems such as BF is poorly known. The aim of this work was to investigate sorption and degradation of NUI in simulated BF under near-natural conditions. Besides, the effect of NUI on the microbial biomass of slowly growing microorganisms and the role of microbial biomass on NUI removal was investigated. Duplicate sand columns (length 1.7 m) fed with surface water were spiked with a pulse consisting of four nitrification (1,2,4-triazole, dicyanodiamide, 3,4-dimethylpyrazole and 3-methylpyrazole) and two urease inhibitors (n-butyl-thiophosphoric acid triamide and n-(2-nitrophenyl) phosphoric triamide). The average spiking concentration of each NUI was 5 μg/L. Experimental and modeled breakthrough curves of NUI indicated no retardation for any of the inhibitors. Therefore, biodegradation was identified as the main elimination pathway for all substances and was highest in zones of high microbial biomass. Removal of 1,2,4-triazole was 50% and n-butyl-thiophosphoric acid triamide proved to be highly degradable and was completely removed after a hydraulic retention time (HRT) of 24 h. 50% of the mass recovery for nitrification inhibitors except for 3,4-dimethylpyrazole was observed at the effluent (4 days HRT). In addition, a mild effect of NUI on microbial biomass was noted. This study highlights that the degradation of NUI in BF depends on HRT and microbial biomass.

Identification of riverbank filtration sites at watershed scale: A geochemical and isotopic framework

Identifying groundwater wells performing riverbank filtration (RBF) is crucial to ensure safe drinking water through vulnerability assessment plans adapted to these hybrid water sources. Nonetheless, RBF is often unintentional or insufficiently documented and official inventories are scarce. We developed a user-friendly geochemical and isotopic framework for the in-situ identification of RBF facilities. It includes an interpretation abacus for non-specialists. While most studies using tracers are site-specific and/or based on discrete samples, we propose a novel multi-site characterization where time-series of EC, δ²H and δ¹⁸O are directly used as proxies of surface water infiltration at the watershed-scale. The basic statement is that time varying signal of raw water from a groundwater pumping facility reveals a significant induced infiltration of surface water. The framework was applied on nearly 2000 samples from 40 pumping wells and 4 neighboring rivers (<500 m), collected through collaborative sampling on a weekly to monthly basis for 18 months. Despite proximity to surface water, two-third of the complete dataset (19 facilities) were revealed not to benefit from significant contribution of surface water, demonstrating location criteria to be insufficient to identify RBF sites. Permanent RBF was evidenced at 5 facilities, where year-long seasonal variation of tracers in raw groundwater highlighted a continuous high proportion of infiltrated surface water. Unexpectedly, time-series also unveiled a third category: occasional RBF, where induced infiltration occurred only when specific hydrodynamic conditions were met (4 facilities). This study also provided concrete illustrations on how climate change may impact the efficiency of RBF to naturally attenuate microbiological contaminants and how geochemical and isotopic time-series considerably help at anticipating the evolution of contaminant attenuation capacity of RBF sites. Finally, by highlighting the existence of occasional RBF, this study tackles the common oversimplification that groundwater facilities can be binarily and classified either as RBF or groundwater.

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.

Soil self-cleaning capacity: Removal of organic compounds during sub-surface irrigation with sewage effluent

Globally, the reuse of treated sewage effluent for irrigation purposes is increasingly encouraged as a practical solution against the mismatch between the demand for and availability of freshwater resources. The reuse of sewage effluent for sub-surface irrigation (SSI) in agriculture serves the dual purpose of supplying water to crops and diminishing emissions of contaminants of emerging concern (CoECs) into surface water. To investigate such reuse, in a real scale cropland with SSI using sewage effluent, from September 2017 to March 2019 including the extremely dry year 2018, residues were followed of 133 CoECs as related to their physicochemical properties and quantified by liquid chromatography coupled to high-resolution mass spectrometry. Of the 133 target CoECs, 89 were retrieved in the field, most non-detect CoECs have low persistency. During the growing season with sub-surface irrigation, CoECs spread to the shallow groundwater and rhizosphere. Significantly lower concentrations are found between infiltration pipes as compared to directly next to the pipes in shallow groundwater for all persistency-mobility classes. CoECs belonging to the class pm (low persistency and low mobility) or class PM (high persistency and high mobility) class show no change amongst their removal in the rhizosphere and groundwater in a dry versus normal year. CoECs belonging to the class pM (low persistency and high mobility) show high seasonal dynamics in the rhizosphere and shallow groundwater, indicating that these CoECs break down. CoECs of the class Pm (high persistency and low mobility) only significantly build up in the rhizosphere next to infiltration pipes. Climatic conditions with dry summers and precipitation surplus and drainage in winter strongly affect the fate of CoECs. During the dry summer of 2018 infiltrated effluent is hardly diluted, resulting in significantly higher concentrations for the CoECs belonging to the classes pM and Pm. After the extremely dry year of 2018, cumulative concentrations are still significantly higher, while after a normal year during winter precipitation surplus removes CoECs. For all persistency-mobility classes in the shallow groundwater between the pipes, we find significant removal efficiencies. For the rhizosphere between the pipes, we find the same except for Pm. Next to the pipes however we find no significant removal for all classes in both the rhizosphere and shallow groundwater and even significant accumulation for Pm. For this group of persistent moderately hydrophobic CoECs risk characterization ratio's were calculated for the period of time with the highest normalized concentration. None of the single-chemical RCRs are above one and the ΣRCR is also far below one, implying sufficiently safe ambient exposures. Overall the deeper groundwater (7.0-11.8 m below soil surface) has the lowest response to the sub-surface irrigation for all persistency-mobility. When adopting a SSI STP effluent reuse system care must be taken to monitor the CoECs that are (moderately) hydrophobic as these can build up in the SSI system. For the deeper groundwater and for the discharge to the surface water, we find significant removal for the pM and the PM class but not for other classes. In conclusion, relatively high removal efficiencies are shown benefiting the surface waters that would otherwise receive the STP effluent directly.

Role of ammonia-oxidizing microorganisms in the removal of organic micropollutants during simulated riverbank filtration

Biodegradation plays an important role in the removal of organic micropollutants (OMPs) during riverbank filtration (RBF) for drinking water production. The ability of ammonia-oxidizing microorganisms (AOM) to remove OMPs has attracted increasing attention. However, the distribution of AOM in RBF and its role in the degradation of OMPs remains unknown. In this study, the behavior of 128 selected OMPs and the distribution of AOM and their roles in the degradation of OMPs in RBF were explored by column and batch experiments simulating the first meter of the riverbank. The results showed that the selected OMPs were effectively removed (82/128 OMPs, >70% removal) primarily by biodegradation and partly by adsorption. Inefficiently removed OMPs tended to have low molecular weights, low log P, and contain secondary amides, secondary sulfonamides, secondary ketimines, and benzyls. In terms of the microbial communities, the relative abundance of AOM increased from 0.1%-0.2% (inlet_-sand) to 5.3%-5.9% (outlet_-sand), which was dominated by ammonia-oxidizing archaea whose relative abundance increased from 23%-72% (inlet_-sand) to 97% (outlet_-sand). Comammox accounted for 23%-64% in the inlet_-sand and 1% in the outlet_-sand. The abundances of AOM amoA genes kept stable in the inlet_-sand of control columns, while decreased by 78% in the treatment columns, suggesting the inhibition effect of allylthiourea (ATU) on AOM. It is observed that AOM played an important role in the degradation of OMPs, where its inhibition led to the corresponding inhibition of 32 OMPs (5/32 were completely suppressed). In particular, OMPs with low molecular weights and containing primary amides, secondary amides, benzyls, and secondary sulfonamides were more likely to be removed by AOM. This study reveals the vital role of AOM in the removal of OMPs, deepens our understanding of the degradation of OMPs in RBF, and offers valuable insights into the physiochemical properties of OMPs and their AOM co-metabolic potential.

Do NH4+-N and AOB affect atenolol removal during simulated riverbank filtration?

Biodegradation is regarding as the most important organic micro-pollutants (OMPs) removal mechanism during riverbank filtration (RBF), but the OMPs co-metabolism mechanism and the role of NH₄⁺-N during this process are not well understood. Here, we selected atenolol as a typical OMP to explore the effect of NH₄⁺-N concentration on atenolol removal and the role of ammonia oxidizing bacteria (AOB) in atenolol biodegradation. The results showed that RBF is an effective barrier for atenolol mainly by biodegradation and adsorption. The ratio of biodegradation and adsorption to atenolol removal was dependent on atenolol concentration. Specifically, atenolol with low concentration (500 ng/L) is almost completely removed by adsorption, while atenolol with higher concentration (100 μg/L) is removed by biodegradation (51.7%) and adsorption (30.8%). Long-term difference in influent NH₄⁺-N concentrations did not show significant impact on atenolol (500 ng/L) removal, which was mainly dominated by adsorption. Besides, AOB enhanced the removal of atenolol (100 μg/L) as biodegradation played a more crucial role in removing atenolol under this concentration. Both AOB and heterotrophic bacteria can degrade atenolol during RBF, but the degree of AOB's contribution may be related to the concentration of atenolol exposure. The main reactions occurred during atenolol biodegradation possibly includes primary amide hydrolysis, hydroxylation and secondary amine depropylation. About 90% of the bio-transformed atenolol was produced as atenolol acid. AOB could transform atenolol to atenolol acid by inducing primary amide hydrolysis but failed to degrade atenolol acid further under the conditions of this paper. This study provides novel insights regarding the roles played by AOB in OMPs biotransformation during RBF.

Occurrence and distribution of Pharmaceuticals and Personal Care Products (PPCPs) in wastewater related riverbank groundwater

Pharmaceutical and personal care products (PPCPs) are among the most frequently reported groups of emerging contaminants in groundwater worldwide. PPCPs in rivers may infiltrate into groundwater through hydraulic exchange and potentially threaten drinking water safety and human health. In the present study, the occurrence and distribution of nine PPCPs in riverbank groundwater and adjacent rivers (distance up to 113 m) were investigated at four sites with different lithological features and permeabilities of aquifers in a city in North China. Seven of nine PPCPs were detectable in groundwater, ranging from <LOQ (limit of quantification) to 128 ng/L. N,N-diethyl-meta-toluamide (DEET), carbamazepine, and caffeine had the highest detection frequencies (>90%). The concentrations and major compounds in river water varied with the sampling location and water system distribution, resulting in distinct compositions of PPCPs in the groundwater at each site along with different lithology and hydrological conditions. The spatial distribution of PPCPs in riverbank groundwater was affected by the hydraulic connection between the groundwater and river and the lithology of aquifers. Direct hydraulic connection of a fine sand aquifer to the adjacent river caused a decrease in PPCPs with increasing distance. The results also suggested that sandy gravel aquifers had a lower capacity to attenuate PPCPs compared to that of fine sand. Significant correlations between PPCP concentrations and thirteen physicochemical factors of groundwater were discovered, including nitrate, potassium, and manganese. Overall, this study provides important evidence on the role of lithology and hydrological conditions on the composition, distribution, and influential physicochemical factors of PPCPs in riverbank groundwater.

Efficiency of the bank filtration technique for diclofenac removal: A review

Bank filtration (BF) has been employed for more than a century for the production of water with a better quality, and it has been showing satisfactory results in diclofenac attenuation. Considered the most administered analgesic in the world, diclofenac has been frequently detected in water bodies. Besides being persistent in the environment, this compound is not completely removed by the conventional water treatments, drinking water treatment plants (DWTPs) and wastewater treatment plant (WWTPs). BF has a high complexity, whose efficiency depends on the characteristics of the observed pollutant and on the environment where the system in installed, which is why this is a topic that has been constantly studied. Nevertheless, studies present the behavior of diclofenac during the BF process. In this context, this research performed the evaluation of the factors and the biogeochemical processes that influence the efficiency of the BF technique in diclofenac removal. The aerobic conditions, higher temperatures, microbial biomass density, hydrogen potential close to neutrality and sediments with heterogeneous fractions are considered the ideal conditions in the aquifer for diclofenac removal. Nonetheless, there is no consensus on which of these factors has the greatest contribution on the mechanism of attenuation during BF. Studies with columns in laboratory and modeling affirm that the highest degradation rates occur in the first centimeters (5-50 cm) of the passage of water through the porous medium, in the environment known as hyporheic zone, where intense biogeochemical activities occur. Research has shown 100% removal efficiency for diclofenac persistent to compounds not removed during the BF process. However, half of the studies had removal efficiency that ranged between 80 and 100%. Therefore, the performance of more in-depth studies on the degradation and mobility of this compound becomes necessary for a better understanding of the conditions and biogeochemical processes which act in its attenuation.

Dynamics of pathogens and fecal indicators during riverbank filtration in times of high and low river levels

Riverbank filtration is an established and quantitatively important approach to mine high-quality raw water for drinking water production. Bacterial fecal indicators are routinely used to monitor hygienic raw water quality, however, their applicability in viral contamination has been questioned repeatedly. Additionally, there are concerns that the increasing frequency and intensity of meteorological and hydrological events, i.e., heavy precipitation and droughts leading to high and low river levels, may impair riverbank filtration performance. In this study, we explored the removal of adenovirus compared with several commonly used bacterial and viral water quality indicators during different river levels. In a seasonal study, water from the Rhine River, a series of groundwater monitoring wells, and a production well were regularly collected and analyzed for adenovirus, coliphages, E. coli, C. perfringens, coliform bacteria, the total number of prokaryotic cells (TCC), and the number of virus-like particles (TVPC) using molecular and cultivation-based assays. Additionally, basic physico-chemical parameters, including temperature, pH, dissolved organic carbon, and nutrients, were measured. The highest log10 reduction during the >72 m of riverbank filtration from the river channel to the production well was observed for coliforms (>3.7 log10), followed by E. coli (>3.4 log10), somatic coliphages (>3.1 log10), C. perfringens (>2.5 log10), and F+ coliphages (>2.1 log10) at high river levels. Adenovirus decreased by 1.6-3.1 log units in the first monitoring well (>32 m) and was not detected in further distant wells. The highest removal efficiency of adenovirus and most other viral and bacterial fecal indicators was achieved during high river levels, which were characterized by increased numbers of pathogens and indicators. During low river levels, coliforms and C. perfringens were occasionally present in raw water at the production well. Adenovirus, quantified via droplet digital PCR, correlated with E. coli, somatic coliphages, TCC, TVPC, pH, and DOC at high river levels. At low river levels, adenoviruses correlated with coliforms, TVPC, pH, and water travel time. We conclude that although standard fecal indicators are insufficient for assessing hygienic raw water quality, a combination of E. coli, coliforms and somatic coliphages can assess riverbank filtration performance in adenovirus removal. Furthermore, effects of extreme hydrological events should be studied on an event-to-event basis at high spatial and temporal resolutions. Finally, there is an urgent need for a lower limit of detection for pathogenic viruses in natural waters. Preconcentration of viral particles from larger water volumes (>100 L) constitutes a promising strategy.

Impact of Artificial Infiltration on the Removal of Nonsteroidal Anti-Inflammatory Drugs during Treatment of Surface Water

The content of pharmaceuticals in natural waters is steadily increasing. Especially nonsteroidal anti-inflammatory drugs (NSAIDs) are often detected in natural waters due to their widespread use. This group of compounds includes commonly used representatives, such as paracetamol and ketoprofen. The quality of natural waters determines the processes applied for the treatment of drinking water. The methods used in order to remove pharmaceuticals from treated water include adsorption and biologically active filtration. Both processes also occur during artificial infiltration (forced flow of intake surface water through the ground to the collecting wells) at surface water intakes. The processes, which occur in the soil, change the water quality characteristics to a great extent. The goal of the study was to evaluate the removal efficiency of paracetamol and ketoprofen in the process of artificial infiltration used as a pre-treatment of surface water. The studies were conducted at a field experimental installation located at the technical artificial infiltration intake. The experimental installation consisted of three metering wells (piezometers) which were located on the way between the bank of the infiltration pond and the collecting well. The collected water samples allowed to evaluate the change of selected NSAIDs concentrations during the passage of water through the ground. The analysis procedure included solid phase extraction (SPE) and high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Removal of the studied NSAIDs in the infiltration process occurred with variable effectiveness throughout the year. Paracetamol was removed with annual efficiency equal to 42%, although no significant removal of ketoprofen was observed.

Modeling the effects of temperature on the migration and transformation of nitrate during riverbank filtration using HYDRUS-2D

Riverbank filtration is a natural aquifer-based process. The nitrogen dynamics in a riverbank filtration system are affected by many factors, including temperature, water quality, and travel time, which cannot be quantified easily. In this study, a field experiment was conducted to investigate nitrogen transport during riverbank filtration. The HYDRUS-2D software package was used to investigate and quantify the factors that affect the fate of nitrogen. The effects of temperature, water quality, and travel time on nitrate transport were considered. The model was calibrated and validated using field experimental data from the river water and groundwater during riverbank filtration at different periods. The results showed that HYDRUS-2D adequately simulated nitrate transport during riverbank filtration. The denitrification rate constant exhibited a positive exponential relationship with temperature. An empirical formula describing this relationship in riverbank filtration was developed and validated. In addition, the denitrification rate can be quantified within a specified temperature data range under field conditions. Compared with indoor experimental conditions, for the same temperature, there was a 10-fold increase in the denitrification rate constant under field conditions. The results showed that most of the nitrate removal occurred in the riparian zone at high temperatures during riverbank filtration. We concluded that the fate of nitrate in the riparian zone is strongly controlled by groundwater temperature. Travel time also plays an important role in nitrate removal during riverbank filtration.

Transformation of organic micropollutants along hyporheic flow in bedforms of river-simulating flumes

Urban streams receive increasing loads of organic micropollutants from treated wastewaters. A comprehensive understanding of the in-stream fate of micropollutants is thus of high interest for water quality management. Bedforms induce pumping effects considerably contributing to whole stream hyporheic exchange and are hotspots of biogeochemical turnover processes. However, little is known about the transformation of micropollutants in such structures. In the present study, we set up recirculating flumes to examine the transformation of a set of micropollutants along single flowpaths in two triangular bedforms. We sampled porewater from four locations in the bedforms over 78 days and analysed the resulting concentration curves using the results of a hydrodynamic model in combination with a reactive transport model accounting for advection, dispersion, first-order removal and retardation. The four porewater sampling locations were positioned on individual flowpaths with median solute travel times ranging from 11.5 to 43.3 h as shown in a hydrodynamic model previously. Highest stability was estimated for hydrochlorothiazide on all flowpaths. Lowest detectable half-lives were estimated for sotalol (0.7 h) and sitagliptin (0.2 h) along the shortest flowpath. Also, venlafaxine, acesulfame, bezafibrate, irbesartan, valsartan, ibuprofen and naproxen displayed lower half-lives at shorter flowpaths in the first bedform. However, the behavior of many compounds in the second bedform deviated from expectations, where particularly transformation products, e.g. valsartan acid, showed high concentrations. Flowpath-specific behavior as observed for metformin or flume-specific behavior as observed for metoprolol acid, for instance, was attributed to potential small-scale or flume-scale heterogeneity of microbial community compositions, respectively. The results of the study indicate that the shallow hyporheic flow field and the small-scale heterogeneity of the microbial community are major controlling factors for the transformation of relevant micropollutants in river sediments.

Critical review of effluent dissolved organic nitrogen removal by soil/aquifer-based treatment systems

Soil/aquifer-based treatment systems improve wastewater effluent quality by removing trace contaminants in the soil and/or aquifer during groundwater recharge. This paper critically reviews these systems with a focus on removing nitrogen, particularly low levels of dissolved organic nitrogen (DON) present in the wastewater effluent. DON in wastewater effluent is a concern because of its contribution to nitrogen concentration in surface or groundwater and its role as a precursor of nitrogenous disinfection by-products, which are harmful to human health. Biodegradation and sorption are the main DON removal mechanisms in the subsurface environment where most of the removal happens in the vadose zone. Different factors such as temperature, redox conditions, retention time, indigenous microbial community, and soil type affect DON removal in soil/aquifer-based treatment systems. Lack of sufficient current knowledge underlines the need for designing lab/field scale systems for further determination of the relative contribution of biodegradation and sorption, optimal hydraulic loading rate, and the relationship between DON characteristics such as functional groups and physiochemical processes and its removal. Future research needs for DON removal in soil/aquifer-based treatment systems are identified.

Genetic and biochemical changes in liver and kidney of Channa punctatus after treatment with 2-naphthalene sulfonate

2-Naphthalene sulfonate (2NS) is a sulfonated aromatic compound and a momentous intermediate involved in the synthesis of dyes and surfactants. Thus, the present experiment was undertaken to evaluate the variation in biochemical constituents in liver and kidney of fresh water fish, Channa punctatus, after 2NS intoxication. After determination of lethal dose (LD) two sublethal doses, i.e. 0.33 mg/15 g body weight (one-half of LD₅₀) and 0.16 mg/15 g b.w. (one-fourth of LD₅₀) were selected for analyzing oxidative stress, genotoxicity and bioaccumulative potential of 2NS. Highest significant increase in oxidative stress and DNA damage in the exposed groups as compared with control group (P ≤ 0.05) was observed at 96 h. However, decreased values of all the studied parameters after 30 days indicate repair capacity of fish. In order to study the alterations observed in biomolecules including lipids, proteins and nucleic acids, histopathology along with spectroscopic analysis using attenuated total reflection-Fourier transform infrared was also performed for 96 h exposed group. In addition, protein secondary structure analysis was focused in this study, which reveals alterations in α-helix and β-sheet structure after 2NS intoxication. Furthermore, the bioaccumulative potential of 2NS was revealed using high-performance liquid chromatography showing 1.83 and 45.54 μg/ml concentration of 2NS in liver and kidney homogenate, respectively. As the study revealed 2NS as the potential health hazard to aquatic organisms, it entails the augmentation and adoption of pertinent policies regarding the management of such toxic compounds.

Enhanced dissipation of trace level organic contaminants by floating treatment wetlands established with two macrophyte species: A mesocosm study

This study evaluated removal efficiencies of six contaminants of emerging concern (CECs) in floating treatment wetland (FTW) mesocosms established with either Japanese Sweetflag (Acorus gramineus Sol. ex Aiton) or canna lilies (Canna Hybrida L. 'Orange King Humbert'). The CECs included: acetaminophen (APAP), atrazine (ATZ), carbamazepine (CBZ), perfluorooctanoic acid (PFOA), sulfamethoxazole (SMX), and 17β-estradiol (E2). Each treatment was planted with different numbers of plants (i.e., 0, 10, 15, and 20), and the experiments lasted for 17 weeks. Dissipation of CECs was greater in planted treatments than in non-planted controls, and the planting number had little effect on dissipation of CECs. All residues of APAP and E2 dissipated rapidly within 2 weeks in all planted treatments. At the end of the experiment, residues of ATZ and SMX completely dissipated in the canna treatments, but not in the sweetflag treatments (75.8-87.6% and 96.3-97.1%, respectively). During the 17 week study, moderate dissipation of CBZ was observed in treatments including cannas (79.5-82.6%) and sweetflag (69.4-82.3%), while less dissipation was observed for PFOA (9.0-15.0% with sweetflag and 58.4-62.3% with cannas). Principal component analysis indicates that aqueous persistency of CECs and species of plants used influenced the dissipation of CECs in FTWs. Of the two species evaluated, canna was the most promising plant species for FTW systems designed to remove these CECs from surface water.

Naphthalene-2-sulfonate induced toxicity in blood cells of freshwater fish Channa punctatus using comet assay, micronucleus assay and ATIR-FTIR approach

Present inquisition was undertaken to evaluate the genotoxicity of naphthalene-2-sulfonate (2NS), a sulfonated aromatic compound and a momentous intermediate involved in the synthesis of dyes and surfactants, in fresh water fish, Channa punctatus. After LC₅₀ determination, two sublethal concentrations i.e. 2.38 g/15 g b.w. (1/4 of LC₅₀) and 4.77 g/15 g b.w. (1/2 of LC₅₀) were selected for studying acute exposure. For evaluating sub chronic exposure 1/10th (0.238 g/L) and 1/20th (0.119 g/L) of safe application rate (SAR) were reckoned. Blood samples were collected after 24, 48, 72, and 96 h exposure period to study acute effect, and after 30 and 60 days exposure period for sub-chronic effect. Symbolic elevation in time and dose dependent DNA damage was observed by comet assay as well as micronucleus test revealing maximum damage after 60 days of exposure. After cessation of exposure to 2NS, evident recovery was observed after 30 days. Along with comet assay and micronucleus test, spectroscopic evaluation of DNA damage was also noted using Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR). The biomolecular range (800 cm^-1 - 1800cm-¹) in lyophilized red blood cell's extracted from 60 days exposed as well as control group exhibit significant alterations in their nucleic acid indicated through multivariate analysis i.e. Principal Component Analysis (PCA). Further structural analysis of erythrocytes in maximally damaged group using Scanning Electron Microscopy was performed. Thus the study proposed the genotoxic impact of 2NS which is further supported by other toxicity markers like ATR-FTIR and Scanning Electron Microscopy.

Seasonal dynamics modifies fate of oxygen, nitrate, and organic micropollutants during bank filtration - temperature-dependent reactive transport modeling of field data

Bank filtration is considered to improve water quality through microbially mediated degradation of pollutants and is suitable for waterworks to increase their production. In particular, aquifer temperatures and oxygen supply have a great impact on many microbial processes. To investigate the temporal and spatial behavior of selected organic micropollutants during bank filtration in dependence of relevant biogeochemical conditions, we have set up a 2D reactive transport model using MODFLOW and PHT3D under the user interface ORTI3D. The considered 160-m-long transect ranges from the surface water to a groundwater extraction well of the adjacent waterworks. For this purpose, water levels, temperatures, and chemical parameters were regularly measured in the surface water and groundwater observation wells over one and a half years. To simulate the effect of seasonal temperature variations on microbial mediated degradation, we applied an empirical temperature factor, which yields a strong reduction of the degradation rate at groundwater temperatures below 11 °C. Except for acesulfame, the considered organic micropollutants are substantially degraded along their subsurface flow paths with maximum degradation rates in the range of 10^-6 mol L^-1 s^-1. Preferential biodegradation of phenazone, diclofenac, and valsartan was found under oxic conditions, whereas carbamazepine and sulfamethoxazole were degraded under anoxic conditions. This study highlights the influence of seasonal variations in oxygen supply and temperature on the fate of organic micropollutants in surface water infiltrating into an aquifer.

Cyclodextrin-based adsorbents for the removal of pollutants from wastewater: a review

Water is a vital substance that constitutes biological structures and sustains life. However, water pollution is currently among the major environmental challenges and has attracted increasing study attention. How to handle contaminated water now mainly focuses on removing or reducing the pollutants from the wastewater. Cyclodextrin derivatives, possessing external hydrophilic and internal hydrophobic properties, have been recognized as new-generation adsorbents to exert positive effects on water pollution treatment. This article outlines recent contributions of cyclodextrin-based adsorbents on wastewater treatment, highlighting different adsorption mechanisms of cyclodextrin-based adsorbents under different influencing factors. The crosslinked and immobilized cyclodextrin-based adsorbents all displayed outstanding adsorption capacities. Particularly, according to specific pollutants including metal ions, organic chemicals, pesticides, and drugs in wastewater, this article has classified and organized various cyclodextrin-based adsorbents into tables, which could pave an intuitive shortcut for designing and developing efficient cyclodextrin-based adsorbents for targeted wastewater pollutants. Besides, this article specially discusses cost-effectiveness and regeneration performance of current cyclodextrin-based adsorbents. Finally, the challenges and future directions of cyclodextrin-based adsorbents are prospected in this article, which may shed substantial light on practical industrial applications of cyclodextrin-based adsorbents.

Optimizing short time-step monitoring and management strategies using environmental tracers at flood-affected bank filtration sites

Bank filtration is a popular pre-treatment method to produce drinking water as it benefits from the natural capacity of the sediments to attenuate contaminants. Under flood conditions, bank filtration systems are known to be vulnerable to contamination, partly because flow patterns may evolve at short timescales and result in a rapid evolution of the origin and travel times of surface water in the aquifer. However, high frequency monitoring for water quality is not common practice yet, and water quality management decisions for the operation of bank filtration systems are typically based on weekly to monthly assays. The aim of this study is to illustrate how monitoring strategies of environmental tracers at flood-affected sites can be optimized and to demonstrate how tracer-based evidence can help to define adequate pumping strategies. Data acquisition spanned two intense flood events at a two-lake bank filtration site. Based on bacteriological indicators, the bank filtration system was shown to be resilient to the yearly recurring flood events but more vulnerable to contamination during the intense flood events. The origin of the bank filtrate gradually evolved from a mixture between the two lakes towards a contribution of floodwater and one lake only. Automatized measurements of temperature and electrical conductivity at observation wells allowed to detect changes in the groundwater flow patterns at a daily timescale, while the regulatory monthly monitoring for indicator bacteria did not fully capture the potential short timescale variability of the water quality. The recovery to pre-flood conditions was shown to be accelerated for the wells operating at high rates (i.e., ≥1000 m³/day), partly because of floodwater storage in the vicinity of the less active wells. These results establish new perspectives to anticipate water quality changes through selected pumping schemes, which depend on and must be adapted to site-specific water quality issues.

Seasonal performance assessment of four riverbank filtration sites by combined non-target and effect-directed analysis

Targeting the most relevant organic micropollutants (OMP) in routine analysis appears difficult due to formation of transformation products of unknown concentration or toxicity. Performance assessment of water purification processes is still based upon limited target data. Therefore, we broadened the assessment of the removal efficiencies with combined non-target and effect-directed analysis at four riverbank filtration (RBF) sites in Germany. To assess micropollutant elimination, constancy and formation during different seasons, considering local redox conditions, travel distances and total component number in the river, non-target analysis features were grouped into categories. Furthermore, RBF sites were investigated with four endpoints (baseline toxicity, acetylcholinesterase inhibition, antibiotic effects and estrogenic effects) for thin-layer chromatography - effect-directed analysis for the first time. Results showed elimination or reduction of many features and effects, but also constancy and formation of varying proportions. Fall river samples showed precipitation-caused dilution in both tests. Spring samples showed increased effects only in acetylcholinesterase inhibition and estrogenic effects, probably due to phytoestrogens or algae bloom during vegetation period. Sites were ranked considering the total number of features, group proportions, seasonal variations and intensity and number of effects in abstraction wells. Oxic conditions and low initial component numbers in the river (Ruhr sites) resulted in less effects and fewer formations. Longer travel distances were important for a more efficient reduction of effects and features. Combination of non-target and effect-directed analysis proved to be valuable for a more comprehensive assessment of process performance beyond target analysis as also unknown OMP are observed with both methods.

Organic micropollutant removal in full-scale rapid sand filters used for drinking water treatment in The Netherlands and Belgium

Biological treatment processes have the potential to remove organic micropollutants (OMPs) during water treatment. The OMP removal capacity of conventional drinking water treatment processes such as rapid sand filters (RSFs), however, has not been studied in detail. We investigated OMP removal and transformation product (TP) formation in seven full-scale RSFs all treating surface water, using high-resolution mass spectrometry based quantitative suspect and non-target screening (NTS). Additionally, we studied the microbial communities with 16S rRNA gene amplicon sequencing (NGS) in both influent and effluent waters as well as the filter medium, and integrated these data to comprehensively assess the processes that affect OMP removal. In the RSF influent, 9 to 30 of the 127 target OMPs were detected. The removal efficiencies ranged from 0 to 93%. A data-driven workflow was established to monitor TPs, based on the combination of NTS feature intensity profiles between influent and effluent samples and the prediction of biotic TPs. The workflow identified 10 TPs, including molecular structure. Microbial community composition analysis showed similar community composition in the influent and effluent of most RSFs, but different from the filter medium, implying that specific microorganisms proliferate in the RSFs. Some of these are able to perform typical processes in water treatment such as nitrification and iron oxidation. However, there was no clear relationship between OMP removal efficiency and microbial community composition. The innovative combination of quantitative analyses, NTS and NGS allowed to characterize real scale biological water treatments, emphasizing the potential of bio-stimulation applications in drinking water treatment.

Occurrence of pharmaceuticals in the Danube and drinking water wells: Efficiency of riverbank filtration

Surface waters are becoming increasingly contaminated by pharmaceutically active compounds (PhACs), which is a potential risk factor for drinking water quality owing to incomplete riverbank filtration. This study examined the efficiency of riverbank filtration with regard to 111 PhACs in a highly urbanized section of the river Danube. One hundred seven samples from the Danube were compared to 90 water samples from relevant drinking water abstraction wells (DWAW) during five sampling periods. The presence of 52 PhACs was detected in the Danube, the quantification of 19 agents in this section of the river was without any precedent, and 10 PhACs were present in >80% of the samples. The most frequent PhACs showed higher concentrations in winter than in summer. In the DWAWs, 32 PhACs were quantified. For the majority of PhACs, the bank filtration efficiency was >95%, and not influenced by concentrations measured in the river. For carbamazepine lidocaine, tramadol, and lamotrigine, low (<50%) filtration efficiency was observed; however, no correlations were observed between the concentrations detected in the Danube and in the wells. These frequently occurring PhACs in surface waters have a relatively even distribution, and their sporadic appearance in wells is a function of both space and time, which may be caused by the constantly changing environment and micro-biological parameters, the dynamic operating schedule of abstraction wells, and the resulting sudden changes in flow rates. Due to the changes in the efficiency of riverbank filtration in space and time, predicting the occurrence and concentrations of these four PhACs poses a further challenge to ensuring a safe drinking water supply.

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.

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.

Potential use of floating treatment wetlands established with Canna flaccida for removing organic contaminants from surface water

Surface water bodies worldwide may be contaminated with various organic contaminants. In many cases, the actual toxicity thresholds to nontarget organisms are unknown, thus presenting unknown risks. This study evaluated the potential use of floating treatment wetlands (FTWs) planted with Canna flaccida (common name: Canna) for removing two pharmaceuticals (acetaminophen and carbamazepine) and one herbicide (atrazine) from contaminated water. Triplicate FTWs with varying plant densities were established in 378 L mesocosms. After dosing the mesocosms with the contaminants, water samples were collected over a 12-week period for analysis. The planted FTWs showed differing abilities for removing acetaminophen, atrazine, and carbamazepine. Plant densities on the FTWs did not affect dissipation of acetaminophen or atrazine, but did carbamazepine. All acetaminophen residues were removed from the water within 2 weeks, while all atrazine residues were removed within 12 weeks. Approximately, 79-92% of these residues removed were associated with the FTWs. In contrast, all of the carbamazepine was not removed after 12 weeks, at which time only 29-36.7% of the total removed was associated with the FTWs. Overall results suggest that FTWs established with C. flaccida are promising for removing trace concentrations of acetaminophen, atrazine, and carbamazepine from surface water.

Responsible Water Reuse Needs an Interdisciplinary Approach to Balance Risks and Benefits

Freshwater is a precious resource, and shortages can lead to water stress, impacting agriculture, industry, and other sectors. Wastewater reuse is increasingly considered as an opportunity to meet the freshwater demand. Legislative frameworks are under development to support the responsible reuse of wastewater, i.e., to balance benefits and risks. In an evaluation of the proposed European regulation for water reuse, we concluded that the proposed regulation is not practically feasible, as the water provider alone is responsible for the risk assessment and management, even beyond their span of control. The required knowledge and resources are extensive. Therefore, without clear guidance for implementation, the regulation would hinder implementation of reuse programs. As a consequence, the current practice of uncontrolled, unintentional, and indirect reuse continues, including related risks and inefficiency. Therefore, we provide an outline of the interdisciplinary approach required to design and achieve safe, responsible water reuse. Responsible water reuse requires knowledge of water demand and availability, quality and health, technology, and governance for the various types of application. Through this paper we want to provide a starting point for an interdisciplinary agenda to compile and generate knowledge (databases), approaches, guidelines, case examples, codes of practice, and legislation to help bring responsible water reuse into practice.

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.

1,4-Dioxane contamination of German drinking water obtained by managed aquifer recharge systems: Distribution and main influencing factors

1,4-Dioxane, a cyclic ether that has been classified as a class 2B carcinogen by the US-EPA, is a substance of growing environmental concern because of its abundant occurrence in surface waters worldwide. Its high polarity and low biodegradability hamper its retardation in aquifer systems. Previous investigations in Germany have shown that 1,4-dioxane is already widely distributed in rivers and can be found in groundwater at contamination sites. Therefore, the present study shall provide an overview of the Germany-wide distribution of 1,4-dioxane in finished drinking water (FDW) obtained by managed aquifer recharge (MAR) systems. Thus, we investigated the 1,4-Dioxane levels in FDW obtained by MAR, such as river bank filtration (RBF) or artificial groundwater recharge (AGR), in regions that are supplied by surface water bodies (mainly rivers) with already known 1,4-dioxane contaminations. In total, 125 FDW samples and 33 samples of corresponding surface waters were analyzed for 1,4-dioxane content using solid phase extraction followed by gas chromatography-mass spectrometry (SIM-mode) using a slight modification to US-EPA method 522. About 80% of the investigated FDW samples contained 1,4-dioxane at levels exceeding the limit of quantification (0.034 μg/L); the maximum value was 2.05 μg/L. However, a maximum concentration of 3 μg/L was obtained in the surface water samples. Three main factors were associated with elevated levels of 1,4-dioxane in the FDW: A significant 1,4-dioxane contamination of the associated surface water, the application of RBF instead of AGR, and the proportion of available unpolluted groundwater and/or reservoir water blended in the individual waterworks. The results show that 1,4-dioxane should be critically monitored during FDW production by means of MAR not only in Germany. The findings are also of relevance to neighboring countries depending on the same river systems and for research in the field of small mobile substances in drinking water production in general.

Model-Based Analysis of Reactive Transport Processes Governing Fluoride and Phosphate Release and Attenuation during Managed Aquifer Recharge

In water-scarce areas, the reclamation of wastewater through advanced water treatment and subsequent reinjection into depleted aquifers is an increasingly attractive water management option. However, such injection can trigger a range of water-sediment interactions which need to be well understood and quantified to ensure sustainable operations. In this study, reactive transport modeling was used to analyze and quantify the interacting hydrogeochemical processes controlling the mobilization of fluoride and phosphate during injection of highly treated recycled water into a siliciclastic aquifer. The reactive transport model explained the field-observed fluoride and phosphate transport behavior as a result of the incongruent dissolution of carbonate-rich fluorapatite where (i) a rapid proton exchange reaction primarily released fluoride and calcium, and (ii) equilibrium with a mineral-water interface layer of hydrated dibasic calcium phosphate released phosphate. The modeling results illustrated that net exchange of calcium on cation exchange sites in the sediments postbreakthrough of the injectant was responsible for incongruent mineral dissolution and the associated fluoride and phosphate release. Accordingly, amending calcium chloride into the injectant could potentially reduce fluoride and phosphate mobilization at the study site. Insights from this study are broadly applicable to understanding and preventing geogenic fluoride mobilization from fluoride-bearing apatite minerals in many other aquifers worldwide.

Groundwater–Surface Water Interactions: Recent Advances and Interdisciplinary Challenges

The interactions of groundwater with surface waters such as streams, lakes, wetlands, or oceans are relevant for a wide range of reasons—for example, drinking water resources may rely on hydrologic fluxes between groundwater and surface water. However, nutrients and pollutants can also be transported across the interface and experience transformation, enrichment, or retention along the flow paths and cause impacts on the interconnected receptor systems. To maintain drinking water resources and ecosystem health, a mechanistic understanding of the underlying processes controlling the spatial patterns and temporal dynamics of groundwater–surface water interactions is crucial. This Special Issue provides an overview of current research advances and innovative approaches in the broad field of groundwater–surface water interactions. The 20 research articles and 1 communication of this Special Issue cover a wide range of thematic scopes, scales, and experimental and modelling methods across different disciplines (hydrology, aquatic ecology, biogeochemistry, environmental pollution) collaborating in research on groundwater–surface water interactions. The collection of research papers in this Special Issue also allows the identification of current knowledge gaps and reveals the challenges in establishing standardized measurement, observation, and assessment approaches. With regards to its relevance for environmental and water management and protection, the impact of groundwater–surface water interactions is still not fully understood and is often underestimated, which is not only due to a lack of awareness but also a lack of knowledge and experience regarding appropriate measurement and analysis approaches. This lack of knowledge exchange from research into management practice suggests that more efforts are needed to disseminate scientific results and methods to practitioners and policy makers.

Column Experiments on Sorption Coefficients and Biodegradation Rates of Selected Pharmaceuticals in Three Aquifer Sediments

The presence of pharmaceuticals in the environment, and in groundwater, has been recognized as a great environmental concern. Biodegradation and sorption are the main processes leading to the removal of contamination from the water phase. The aim of this study was to determine the transport processes of selected pharmaceuticals (antipyrine, atenolol, carbamazepine, caffeine, diclofenac, ketoprofen, sulfamethoxazole) in selected sediments (coarse sand, medium sand, sandy loam) in laboratory experiments. Moreover, the impact of flow velocities on the sorption and degradation rates of the selected compounds was studied. Column experiments were performed at three flow velocities, under abiotic and biotic conditions, applying conservative (bromide) and reactive tracers (pharmaceuticals). From the breakthrough curves, retardation factors and degradation rates were determined and the influence of variable flow conditions on transport parameters was evaluated. Low observed concentrations and recoveries of atenolol indicated a strong influence of sorption on its transport. Diclofenac, caffeine, and carbamazepine were also affected by sorption but to a lesser extent. Sulfamethoxazole, ketoprofen, and antipyrine were recovered nearly completely, indicating an almost conservative transport behavior. Biodegradation was small for all the compounds, as the results from biotic and abiotic column experiments were similar. Transport of the tested pharmaceuticals was not influenced by different flow velocities, as similar modelled degradation rates and retardation factors were found for all tested flow velocities.

Anthropic and Meteorological Controls on the Origin and Quality of Water at a Bank Filtration Site in Canada

At many bank filtration (BF) sites, mixing ratios between the contributing sources of water are typically regarded as values with no temporal variation, even though hydraulic conditions and pumping regimes can be transient. This study illustrates how anthropic and meteorological forcings influence the origin of the water of a BF system that interacts with two lakes (named A and B). The development of a time-varying binary mixing model based on electrical conductivity (EC) allowed the estimation of mixing ratios over a year. A sensitivity analysis quantified the importance of considering the temporal variability of the end-members for reliable results. The model revealed that the contribution from Lake A may vary from 0% to 100%. At the wells that were operated continuously at >1000 m3/day, the contribution from Lake A stabilized between 54% and 78%. On the other hand, intermittent and occasional pumping regimes caused the mixing ratios to be controlled by indirect anthropic and/or meteorological forcing. The flow conditions have implications for the quality of the bank filtrate, as highlighted via the spatiotemporal variability of total Fe and Mn concentrations. We therefore propose guidelines for rapid decision-making regarding the origin and quality of the pumped drinking water.

Polymerization of micropollutants in natural aquatic environments: A review

Micropollutants with high ecotoxicological risks are frequently detected in aquatic environments, which has aroused great concern in recent years. Humification is one of the most important natural detoxification processes of aquatic micropollutants, and the core reactions of this process are polymerization and coupling. During humification, micropollutants are incorporated into the macrostructures of humic substances and precipitated from aqueous systems into sediments. However, the similarities and differences among the polymerization/coupling pathways of micropollutants in different oxidative systems have not been systematically summarized in a review. This article reviews the current knowledge on the weak oxidation-induced spontaneous polymerization/coupling transformation of micropollutants. First, four typical weak oxidative conditions for the initiation of micropollutant polymerization reactions in aquatic environments are compared: enzymatic catalysis, biomimetic catalysis, metal oxide oxidation, and photo-initiated oxidation. Second, three major subsequent spontaneous transformation pathways of micropollutants are elucidated: radical polymerization, nucleophilic addition/substitution and cyclization. Different solution conditions are also summarized. Furthermore, the importance of toxicity evolution during the weak oxidation-induced coupling/polymerization of micropollutants is particularly emphasized. This review provides a new perspective for the transformation mechanism and pathways of micropollutants from aquatic systems into sediments and the atmosphere and offers theoretical support for developing micropollutant control technologies.

Migration of Pharmaceuticals from the Warta River to the Aquifer at a Riverbank Filtration Site in Krajkowo (Poland)

Studies on the presence of pharmaceuticals in water were carried out on the riverbank filtration site, Krajkowo–Poznań (Poland). A preliminary investigation conducted in 3 sampling points showed the presence of pharmaceuticals in both surface water and bank filtrate. Based on the above, an extended analysis was made in July, August and October 2018 and included surface water and wells located at a different distance (5–250 m) and travel time (1–150 days) from source water (Warta River). Firstly, 75 compounds (antibiotics, anti-inflammatory and analgesic drugs, psychotropic drugs, x-ray agents and β-blockers) were tested and 25 of them were detected in the river or bank filtrate. The highest concentrations were observed in source water and then were reduced along the flow path. The sampling points located close to the river (<38 m) are characterized by low removal. Higher removal is visible in wells located 64–82 m away from the river, while 250 m from the river most compounds are completely attenuated. Carbamazepine, gabapentin, tramadol, oxypurinol, fluconazole, and lamotrigine are the most common compounds. Some of the tested parameters occur only in the river water, e.g., iopromide, diclofenac, iohexol, clindamycin, fexofenadine and valsartan. The research shows that at the site, a significant attenuation of pharmaceuticals can be achieved at travel times of 40–50 days and distances of 60–80 m, although higher values are ensured when the well is located more than 250 m away.

Temperature-dependent redox zonation, nitrate removal and attenuation of organic micropollutants during bank filtration

River bank filtration (RBF) is considered to efficiently remove nitrate and trace organic micropollutants (OMP) from polluted surface waters. This is essential for maintaining good groundwater quality and providing high quality drinking water. Predicting the fate of OMP during RBF is difficult as the biogeochemical factors controlling the removal efficiency are not fully understood. To determine in-situ removal efficiency and degradation rates of nitrate and OMP indicator substances we conducted a field study in a RBF system during a period of one and a half years incorporating temporally and spatially varying redox conditions and temperature changes typically occurring in temperate climates. RBF was analyzed by means of mixing ratios between infiltrated river water and groundwater as well as average residence times of surface water towards the individual groundwater observation wells. These results were used to calculate temperature dependent first order degradation rates of redox sensitive species and several OMP. Five out of ten investigated OMP were completely removed along RBF pathways. We demonstrate that degradation rates of several OMP during bank filtration were controlled by redox conditions and temperature whereby temperature itself also had a significant influence on the extent of the most reactive oxic zone. The seasonal variations in temperature alone could explain a considerable percentage of the variance in dissolved oxygen (34%), nitrate (81%) as well as the OMPs diclofenac (44%) and sulfamethoxazole (76%). Estimated in-situ degradation rates roughly varied within one order of magnitude for temperature changes between 5 °C and 20 °C. This study highlights that temporal variability in temperature and redox zonation is a significant factor for migration and degradation of nitrate and several OMPs.

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.

Nontarget Screening Reveals Time Trends of Polar Micropollutants in a Riverbank Filtration System

The historic emissions of polar micropollutants in a natural drinking water source were investigated by nontarget screening with high-resolution mass spectrometry and open cheminformatics tools. The study area consisted of a riverbank filtration transect fed by the river Lek, a branch of the lower Rhine, and exhibiting up to 60-year travel time. More than 18,000 profiles were detected. Hierarchical clustering revealed that 43% of the 15 most populated clusters were characterized by intensity trends with maxima in the 1990s, reflecting intensified human activities, wastewater treatment plant upgrades and regulation in the Rhine riparian countries. Tentative structure annotation was performed using automated in silico fragmentation. Candidate structures retrieved from ChemSpider were scored based on the fit of the in silico fragments to the experimental tandem mass spectra, similarity to openly accessible accurate mass spectra, associated metadata, and presence in a suspect list. Sixty-seven unique structures (72 over both ionization modes) were tentatively identified, 25 of which were confirmed and included contaminants so far unknown to occur in bank filtrate or in natural waters at all, such as tetramethylsulfamide. This study demonstrates that many classes of hydrophilic organics enter riverbank filtration systems, persisting and migrating for decades if biogeochemical conditions are stable.

Green conversion of crop residues into porous carbons and their application to efficiently remove polycyclic aromatic hydrocarbons from water: Sorption kinetics, isotherms and mechanism

In this study, rape straw- and corn cob-derived porous carbons (PCs) were fabricated by hydrothermal treatment (250 °C, 4 h) and subsequent activation (850 °C, 1 h) using a non-corrosive agent, potassium bicarbonate. The PCs exhibited a very large specific surface area (1069-1281 cm² g^-1), high pore volume (0.55-0.72 cm³ g^-1), wide pore size distribution (from micropores to macropores), high hydrophobicity, and partly graphitized structure. These properties contributed to highly efficient performance for the sorption of polycyclic aromatic hydrocarbons (PAHs), with maximum sorption capacities of 592.97, 480.27, and 692.27 mg g^-1 towards naphthalene, acenaphthene, and phenanthrene, respectively. A three-step sorption process with pore filling, hydrophobic effects, and π-π stacking interactions on the heterogeneous surface is a possible mechanism for the sorption of PAHs onto PCs. This study presents an environmentally friendly strategy for the reuse of crop residues in the field of organic micropollutant-contaminated water treatment.

Degradation of benzophenone-4 in a UV/chlorine disinfection process: Mechanism and toxicity evaluation

This study investigated the degradation of benzophenone-4 (BP-4) in a UV/chlorine disinfection process, with chlorination and UV disinfection as comparisons. With a degradation efficiency of 80% after 10 s, the UV/chlorine process significantly enhanced the degradation of BP-4. However, a rebound of 36% of the initial concentration was observed in the UV/chlorine process ([free active chlorine (FAC)]₀:[BP-4]₀ = 1:1, pH = 7). The same tendency appeared under the addition of alkalinity, Cl^-, and humic acid (HA). This work interpreted this interesting kinetic tendency from the perspective of mechanism. In fact, the transformation between the chlorinated product P1 and BP-4 was reversible under certain conditions. The inhomogeneous charge distribution of the CCl bond in P1 led to the photolytic dechlorination of P1. This transformation caused an increase in BP-4 concentration. In addition, the increase in the UV light power promoted the photodecomposition of P1 under the experimental condition. In addition, this study evaluated the change in absorbable organic halogens (AOX) and three kinds of toxicity changes in the BP-4 solution after chlorination and the UV/chlorine process, including the acute toxicity of luminescent bacteria, endocrine disrupting effect and cytotoxicity. The UV/chlorine process exhibited lower ecotoxicity than chlorination in water treatment.

Are dominant microbial sub-surface communities affected by water quality and soil characteristics?

Subsurface microorganisms must deal with quite extreme environmental conditions. The lack of light, oxygen, and potentially nutrients are the main environmental stresses faced by subsurface microbial communities. Likewise, environmental disruptions providing an unbalanced positive input of nutrients force microorganisms to adapt to varying conditions, visible in the changes in microbial community diversity. In order to test microbial community adaptation to environmental changes, we performed a study in a surface Managed Aquifer Recharge facility, consisting of a settlement basin (two-day residence time) and an infiltration pond. Data on groundwater hydrochemistry, soil texture, and microbial characterization was compiled from surface water, groundwater, and soil samples at two distinct recharge operation conditions. Multivariate statistics by means of Principal Component Analysis (PCA) was the technique used to map the relevant dimensionality reduced combinations of input variables that properly describe the system behavior. The methodology selected allows including variables of different nature and displaying very different range values. Strong differences in the microbial assemblage under recharge conditions were found, coupled to hydrochemistry and grain-size distribution variables. Also, some microbial groups displayed correlations with either carbon or nitrogen cycles, especially showing abundant populations of denitrifying bacteria in groundwater. A significant correlation was found between Methylotenera mobilis and the concentrations of NO₃ and SO₄, and also between Vogesella indigofera and the presence of DOC in the infiltrating water. Also, microbial communities present at the bottom of the pond correlated with representative descriptors of soil grain size distribution.

Adsorptive removal of bisphenol A, chloroxylenol, and carbamazepine from water using a novel β-cyclodextrin polymer

The emerging organic micro-pollutants, such as bisphenol A (BPA), chloroxylenol (PCMX) and carbamazepine (CBZ), have raised concerns owing to their adverse impact on human health and ecological security. In this study, a novel cyclodextrin polymer (β-CDP) has been successfully prepared by nucleophilic substitution of β-cyclodextrin with tetrafluoroterephthalonitrile (TFP). The removal of three emerging organic micro-pollutants (BPA, CBZ and PCMX) by β-CDP under a single or mixture adsorption system was examined, and the adsorption behavior was investigated by adsorption kinetics and isotherm study. The maximum adsorption capacity of β-CDP for BPA, PCMX and CBZ according to Langmuir isotherm in single system was 164.4, 144.1 and 136.4 mg/g, respectively. Compared with single system, the competitive adsorption of each pollutant on β-CDP in mixture system was only slightly inhibited. Changing the pH, raising the presence of fulvic acid (FA) or ionic strength had no significant influence on the adsorption of BPA, PCMX and CBZ onto β-CDP. The removal of these three organic micro-pollutants was related to the value of logK_ow of the contaminants. These results demonstrated remarkable advantages of β-CDP material relevant to organic micro-pollutants removal in wastewater treatment.

Design and Optimization of a Fully-Penetrating Riverbank Filtration Well Scheme at a Fully-Penetrating River Based on Analytical Methods

In order to maintain the sustainable development of pumping wells in riverbank filtration (RBF) and simultaneously minimize the possible negative effects induced, it is vital to design and subsequently optimize the engineering parameters scientifically. An optimizing method named Five-Step Optimizing Method was established by using analytic methods (Mirror-Image Method, Dupuit Equation and the Interference Well Group Method, etc.) systematically in this study considering both the maximum allowable drawdown of the groundwater level and the water demand as the constraint conditions, followed by a case study along the Songhua River of northeast China. It contained three parameters (number of wells, distance between wells, and distance between well and river) for optimizing in the method, in which the well type, depth and radius were beforehand designed and fixed, without the need of optimizing. The interference between wells was found to be a decisive factor that significantly impacts the optimizing effort of all the three parameters. The distance between the well and the river was another decisive factor impacting the recharge from the river and subsequently, the well water yield. There would be more than one optional scheme sometimes in the optimized result, while it’s not yet difficult in practice to single out the optimal one considering both the field setting and the water demand. The established method proved to be applicable in the case study.

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.

Fate of five pharmaceuticals under different infiltration conditions for managed aquifer recharge

Infiltration of treated wastewater (TWW) to recharge depleted aquifers, often referred to as managed aquifer recharge, is a solution to replenish groundwater resources in regions facing water scarcity. We present a mass balance approach to infer the amounts of five pharmaceuticals (carbamazepine, diclofenac, fenoprofen, gemfibrozil, and naproxen) degraded in column experiments based on concentrations of pharmaceuticals in the aqueous and solid (sorbed) phases. Column experiments were conducted under three different conditions: continuous infiltration, wetting and drying cycles, and wetting and drying cycles with elevated concentrations of antibiotics (which may reduce microbially aided degradation of other compounds). A mass balance comparing pharmaceutical mass in the water phase over the 16-month duration of the experiments to mass sorbed to the soil was used to infer the mass of pharmaceuticals degraded. Results show sorption as the main attenuation mechanism for carbamazepine. About half of the mass of diclofenac was degraded with wetting and drying cycles, but no significant degradation was found for continuous infiltration, while 32% of infiltrated mass sorbed. Fenoprofen was degraded in the shallow and aerobic part of the soil, but degradation appeared to cease beyond 27 cm depth. Gemfibrozil attenuated through a combination of degradation and sorption, with slight increases in attenuation with depth from both mechanisms. Naproxen degraded progressively with depth, resulting in attenuation of >90% of the mass. In the column with elevated concentrations of antibiotics, the antibiotics attenuated to about 50% or less of inflow concentrations by 27 cm depth and within this zone, less degradation of the other compounds was observed.