Riverbank Filtration Research Articles

Effects of flood inundation on biogeochemical processes in groundwater during riverbank filtration

Well fields along rivers withdrawing groundwater through riverbank filtration (RBF) are popular for urban water supply, due to their good performance in assurance for both water quantity and quality. However, RBF sites are susceptible to flood inundation, which has been found to cause increase of N, Fe, and Mn contents in groundwater and threatens water safety, but the geochemical processes have not been fully understood. To bridge this gap, in situ monitoring of hydrodynamics, hydrochemistry, and stable isotopes for river water and groundwater were employed in a RBF site, NE China, to investigate into the geochemical processes in groundwater in RBF sites under long-term inundation. The results indicated that during long-term inundation, recharge from river water increased significantly, and a large amount of O2, NO3− and organic carbon (OC) from oxidizing river water could recharge far-shore groundwater vertically, whereas less NH4+ were input from regional groundwater, leading to a high content of NO3− and low content of the NH4+ in the groundwater. Meanwhile, limited NH4+ would be produced through dissimilatory nitrate reduction to ammonium (DNRA) and mineralization of organic nitrogen (MON). Moreover, along the infiltration path, aerobic respiration and denitrification (DNF) occurred rapidly. CO2 generated from OC oxidization in the two processes enhanced the dissolution of carbonate minerals, which could be used to trace the oxidizing-reducing (O-R) interface between river water and groundwater. As indicated, the inundation can cause the O-R interface which usually distributed near shore to extend to the entire well field during inundation. In this situation, the redox condition of groundwater used to be suitable for SO42− reduction in non-inundation period decreases to the level favoring the reduction of Mn(IV)/Fe(III) oxides during inundation, and the process of Fe2+ precipitation by reacting with HS− is weaken as the inhabitation of SO42− reduction, leading to a significant increase in Fe2+, Mn2+, and As contents, putting well field groundwater at risk of contamination.

Performance Evaluation of RBF Wells with Special Reference to Water Quality Parameters in Hard Rock Region of Tungabhadra Catchment

Tungabhadra River is the chief source for drinking water and agriculture developments in Davangere and adjoining districts of Karnataka. It is reported that the water of Tungabhadra is getting polluted by the direct / indirect effluent discharges due to which people living on the river bank are facing the problem of drinking water. River Bank Filtration (RBF) wells which will naturally treat the polluted surface and ground water have been drilled in perpendicular to the river at a distance of 30m, 50m and 80m to understand the extent of treatment of RBF wells to provide clean and safe drinking water. The present study deals with the problems of water quality in a selected village (Somlapura) located in a hard rock terrain of river Tungabhadra, Karnataka, India. As a part of the investigation, water samples were collected from River Bank Filtration wells and adjoining river and aquifers were analyzed using standard methods. Outcomes of water quality presents that the concentrations of turbidity and total coliform were lesser in the RBF well water samples when compared to Tungabhadra River water samples. The water from RBF wells contained fresh water, which is highly mineralized and free from bacterial contamination relative to the water from river. However, groundwater of the adjoining aquifers showed wide variations in various physio-chemical parameters. From the analysis, unsafe levels of total coliforms (included E.coli and F. Coli) were detected in Tungabhadra River i.e., It varied between 1680 and 3179 MPN/100 ml. It is observed that the average removal efficiency of coliform bacteria from RBF well 1 & 2 was 99.84% and 99.82% respectively.

Effects of Ammonium and COD on Fe and Mn Release from RBF Sediment Based on Column Experiment

Riverbank filtration (RBF) is an important part of the surface water–groundwater cycle, and it intercepts and retains many pollutants in rivers. However, RBF affects the biogeochemical process which enables aquifer sediments to release iron (Fe) and manganese (Mn). In this study, column experiments were performed to investigate the effects of ammonium ions and organic matter on Fe and Mn release from anaerobic RBF sediments. In addition, high-throughput sequencing technology was used to characterize the microbial community. The results showed that the ammonium ions (NH4+) and organic matter (COD) in groundwater promote the release of Fe and Mn from aquifer sediments. The trends of Fe and Mn release were similar during the leaching process. The maximum concentrations of Fe and Mn were 0.32 and 40 μg/L, respectively. The structural diversity and abundance of the microbial communities in the groundwater were closely related to the Fe/Mn content. Actinobacteriota, Proteobacteria, Acidobacteriota, Bacteroidota, and Chloroflexi were the dominant phyla, while Rhodococcus, Ochrobactrum, and Pseudarthrobacter were the dominant genera. These functional microbes are actively involved in the biogeochemical cycling of Fe, Mn, and N. In summary, contaminants and the microbial-community structure have dual effects on the release of Fe and Mn from RBF aquifers.

Laboratory and field studies on the effect of geoenvironmental factors on the removal of linear alkylbenzene sulfonate during riverbank filtration

Laboratory and field studies on the effect of geoenvironmental factors on the removal of linear alkylbenzene sulfonate during riverbank filtration

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.

Real-Time Groundwater Dynamics Verification in the Embankment’s Substrate during the Transition of a Flood Wave

The scope of the presented research included real-time verification of groundwater dynamics in the zone of the filled erosion channel (crevasses) and in the non-transformed zone of the floodplain area during the transition of a flood wave in the river channel. The technical goal was to provide data for the calibration and verification of mathematical model of groundwater flow. For this purpose, automatic recorders of groundwater level and electrical conductivity were installed in the zones selected earlier with the use of DEM. The measurements were carried out in 3 series during the passage of the flood wave. The obtained results indicate that in the zone of the untransformed terrace, the ascension of the water level between embankments causes the immediate propagation of pressure in the aquifer, while the filtration process itself is considerably limited, whereas the filled crevasse troughs constitute paths of privileged filtration, in particular in the proximal part of the floodplain. The appearance of water with elevated conductivity in the area of the crevasse proves the cyclicality of changes in flow directions, depending on the water level between embankments. The proposed methodology can be a valuable tool in the process of the geotechnical assessment of the construction substrate in the area of flood terraces in the lowland river. The zones with increased water conductivity parameters located near the river channel are also a reasonable place for the construction of coastal water intakes of the Riverbank filtration (RBF) type.

Multivariate Statistical Analysis of the Spatial Variability of Hydrochemical Evolution during Riverbank Infiltration

Riverbank filtration (RBF) is increasingly being used as a relatively cheap and sustainable means to improve the quality of surface water. Due to the obvious differences in physical, chemical, and biological characteristics between river water and groundwater, there are strong and complex physical, chemical, and biogeochemical effects in the process of bank filtration. In this paper, multivariate statistical analysis was used to identify the spatial variation of hydrogeochemical groundwater in the process of bank filtration. Firstly, the evolution process of groundwater hydrochemistry during the filtration process was identified through factor analysis. According to the results, the evolution of groundwater hydrochemistry in this area is attributable to four main types of reactions: (1) Leaching; (2) Regional groundwater influence; (3) Aerobic respiration and denitrification; and (4) Mn (IV)/Fe (III)/SO42− reduction. According to the similarity of the geochemistry, the flow path could be divided into four different hydrochemical zones through cluster analysis, revealing the evolution law of groundwater hydrochemistry and its main influencing factors during riverbank infiltration. Large hydraulic gradient in The Zone Strongly Influenced by River Water (The first group) resulted in a weak effect of leaching on groundwater chemistry. Reoxygenation and microorganism respiration occurred in The Zone Moderately Influenced by River Water (The second group), The Zone Weakly Influenced by River Water (The third group), and The Zone Strongly Influenced by Regional Groundwater (The fourth group), resulting in fluctuations in Eh and pH values of groundwater. As a result, sulfate reduction and Mn (IV) and Fe (III) reduction alternated along the flow path. The Zone Strongly Influenced by Regional Groundwater (The fourth group) groundwater chemistry was mainly affected by regional groundwater.

Effect of Hydraulic Conductivity on Three Dimensional Contaminant Transport in Riverbank Filtration System

Riverbank filtration system is a technique used for surface water treatment that is based on biological activities to attenuate the contamination in water through its movement from the river to the adjacent pumping well. Hydraulic conductivity is a critical parameter that affects the efficiency of riverbank filtration systems. In this study, an analytical model, using Green’s function approach, is developed to investigate the effect of hydraulic conductivity on contaminant transport and RBF system efficiency. The model is applied at the RBF site in Malaysia. The outcomes show that increasing the hydraulic conductivity values results in lowering the quality of the pumped water produced from the well, in which the contamination area around the well increase. Additionally, the distance from well to the river that should be considered when establishing a new RBF site is significantly affected by the hydraulic conductivity value.

Numerical assessment of riverbank filtration using gravel back filter to improve water quality in arid regions

The main challenge of water resource management in high-stress regions, especially in developing countries, is in adopting non-traditional methods to obtain safe drinking water in desired quantities. In Egypt, the riverbank filtration (RBF) system is one of the most common solutions to solve rivers’ water quality issues. Several sites have been investigated, and the system has demonstrated tremendous potential. The drinking water plant in Embaba, Giza, Egypt, is considered in this study to improve the quality of the abstracted water through the vertical well system. The numerical code of MODFLOW and MT3D is used to simulate the impact of using the emplacement of the gravel-pack filter (GPF). Three different scenarios were investigated: the first consists of vertical GPF; the second is horizontal GPF for different geometries, depths, widths or thicknesses, lengths, and permeability of the filter material; and, the third is drilling a pipe filter through the riverbed for different pipe numbers, depths, and the material’s hydraulic conductivity. The results revealed that the riverbank filtration sharing (RBFS) rate was increased by increasing the filter width or thickness at the riverside, the filter pipe numbers, the length of the horizontal filter, and the permeability of filter material. At the same time, the thickness of the river bed decreased by increasing the filter width at the groundwater side. Also, the RBFS was increased by increasing the filter width or the thickness in the two directions and the pipe length. However, it returned to decrease again due to groundwater sharing. Thus, the RBF design should carefully consider the gravel-pack, pipe filter geometry, and permeability impact rate of RBFS.

Benefits and Costs of Managed Aquifer Recharge: Further Evidence

Managed Aquifer Recharge (MAR) provides an integrated solution that allows aquifer storage to complement surface water storage. Cost–benefit analysis provides a systematic method for comparing alternative water infrastructure options. When market valuations of water infrastructure are unavailable, levelised cost is a widely accepted method of comparing MAR with alternative solutions. Benefits of MAR can be estimated by the cost of the cheapest alternative source of supply or the value of production using MAR. This article presents quantitative analysis of levelised costs and benefit cost ratios of 21 MAR schemes from 15 countries, and qualitative assessment of additional social and environmental benefits. MAR schemes recharging aquifers with natural water using infiltration basins or riverbank filtration are relatively cheap with high BCRs. Schemes using recycled water and/or requiring wells with substantial drilling infrastructure and or water treatment are more expensive, while offering positive BCRs. Most MAR schemes have positive or neutral effects on aquifer storage and condition, water quality, and environmental flows. Energy requirements are competitive with alternatives. This paper demonstrates strong returns to investment in the reported MAR schemes. MAR provides valuable social benefits and contributes to sustaining groundwater resources where extraction is managed.

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.

Microbial response to biogeochemical profile in a perpendicular riverbank filtration site.

Due to extensive water exchanges and abundant active biochemical compositions, active and complex hydrogeochemical processes often exist in riverbank filtration (RBF). The distribution of microbes is considered to be profoundly affected by these processes and is considered to impact the hydrogeochemical processes and the migration and transformation of water pollutants in turn and then impact the water quality. The distribution of microbes and their response to the physiochemical properties along a vertical RBF profile perpendicular to the Songhua River in Northeast China was explored by using 16S rRNA and redundancy analysis (RDA). The results showed that various microbes were found in the vertical riparian filter (RBF) curve, including Actinobacteria, Proteobacteria, Acidobacteria, Chloroflexi, and Firmicutes. With increasing depth (vertical) and distance from the river (lateral), the microbial community and diversity in the RBF sediment profile decreased. Nitrospirota, Pseudomonas, Gammaproteobacteria, Ochrobactrum, Acinetobacter and Desulfobacterota of the RBF core taxa were also significantly correlated with the biotransformation behavior of typical groundwater pollutants (ammonia, Fe, Mn and S). The amount of As in the RBF is too low to sustain microbial survival. Some microbes in RBF can also degrade natural organic pollutants. This study not only revealed the spatial distribution of geological microbes under the impact of hydrological processes but also lays a foundation for the further study of the hydrobiogeochemical processes of active biochemical compositions in groundwater and water quality evolution, which is of positive significance to ensure the quality safety of the drinking water supplied by RBFs.

Influence of DOM and microbes on Fe biogeochemistry at a riverbank filtration site

Riverbank filtration (RBF) constitutes an important part of the water cycle, which involves active natural filtration leading to pollution of river water being intercepted and retained. The RBF has the function of water purification, but retention of exogenous pollutants in the RBF system complicates biogeochemical processes due to the presence of primary active components. In this study, we verified the essential role of microbial mediation during the interactions between primary Fe minerals in the RBF system and dissolved organic matter (DOM) in river water based on lab-scale experiments. The results demonstrated that DOM from infiltration of river water increased the amount of iron (Fe) released from the sediment in RBF, leading to an increase in Fe concentration in groundwater by higher than one order of magnitude. In particular, the existence of Fe bacteria even made this effect more thorough and more complex. Abiotic reduction was shown to play a more significant role in increasing Fe release than microbe-mediated reduction. Increasing the amount of Fe released could change the distribution of Fe minerals at the sediment surface, thereby affecting the structure of the microbial community in the RBF system and decreasing the DOM concentration in the groundwater. Moreover, As and Mn were found to behave in a similar manner as Fe due to their close biochemical properties when interacting with primary minerals in sediment. This study not only provides mechanistic insight into the higher Fe concentrations encountered in the groundwater of nearby rivers but also has important practical implications for developing nature-based technologies for water pollution control and environmental remediation.

Quantifying the effect of the nitrogen biogeochemical processes on the distribution of ammonium in the riverbank filtration system

Ammonium (NH4+) enrichment of riverbank filtration (RBF) systems is gaining popularity. However, most previous research has concentrated on NO3− removal efficiencies, while the mechanisms of NH4+ enrichment remain unknown. A nitrogen biogeochemical process model was developed for the quantitative analysis of NH4+ enrichment in the Kaladian well field in northwest Songyuan City, NE China. Data from laboratory experiments and in-situ monitoring were used to determine initial values and calibrate the thermodynamic/kinetic parameters representing nitrogen (N) biogeochemical reactions. (1) The NO3− from river was subjected to denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) within 10–14 m of the shore, whereas the NH4+ in groundwater was caused by DNRA, organic nitrogen mineralization (MIN), and mixing with laterally recharged high NH4+ groundwater. (2) DNF and DNRA were regulated by hydrodynamic processes, with the ranges of these processes being more significant in the wet season due to a higher hydraulic gradient. MIN occurred widely throughout the water flow path, with temperature primarily controlling the rates of the three reactions. (3) DNRA activity was relatively higher in the wet season when the water temperature was higher within 10–14 m of the shore. In the wet season, DNRA contributed 25%–30% to NO3− reduction, which was higher than in the dry season (5%–10%). DNRA contributed at least 40% and 15% to NH4+ enrichment in the wet and dry seasons, respectively. (4). Organic N in media gradually released NH4+ into groundwater via MIN and desorption across the entire flow path, with contributions to NH4+ enrichment reaching 75% and 85%, respectively, in the wet and dry seasons.

Physical, Chemical, and Mineralogical Controls on Retardation of Anatoxin-a Migration by Sorption to Natural Soils with Implications for Groundwater Protection

Increasing prevalence of cyanotoxins in surface water bodies worldwide threatens groundwater quality when contaminated water recharges an aquifer through natural or artificial means. The subsurface fate of anatoxin-a (ATX) is not well studied. Laboratory batch experiments were performed to expand the current knowledge of ATX sorption affinities to geologic media, with a focus on natural soil (Vertisol, Ultisol, Alfisol, and Inceptisol) and physical, chemical, and mineralogical characteristics. For a range of aqueous ATX concentrations (0.3–14 μg/L), linear, Freundlich, and Langmuir isotherms fit observed data well (r2 = 0.92–1.00, RMSE = 0.4–6.3 μg/kg). Distribution coefficient (Kd) and retardation factor (Rf) values were computed for the linear isotherm, giving Kd of 22.3–77.1 L/kg and Rf of 62–256. Average percent removals were 85.0–92.2%. The strongest predictors of Kd were kaolinite and smectite group mineral abundances and for Rf were smectite group and silt and clay abundances. Results indicate that loamy, silty, or clayey soils—particularly Vertisols—tend to substantially slow migration of ATX through natural soil systems. Where implemented as a functionalized amendment in an engineered pollution control media, such soils may enhance natural ATX attenuation processes, thereby supporting the protection of in situ and extracted groundwater during irrigation, natural and managed aquifer recharge, or riverbank filtration.

Methodology for evaluation of potential sites for large-scale riverbank filtration

Despite being a simple and inexpensive pretreatment technology, the cost-effectiveness of riverbank filtration (RBF) depends on complex hydrogeological and hydrogeochemical variables. One of the most important issues for decision makers regarding RBF is optimal site selection. Therefore, a methodology for multicriteria site evaluation for large-scale RBF schemes is offered. The methodology is primarily designed as a prescreening method, applied over a wide area, but can also serve as a guide for evaluating individual RBF sites. To facilitate further discussion about improvements on the methodology, the reasoning behind each relevant factor and its weight in the evaluation is presented. The methodology is divided into three sequential steps through which a site can be assessed. The first step is to establish the existence of connectivity between the river and aquifer. This is termed the essential criterion, and is a binary determination of site suitability. If the site is determined to be suitable, it is then assessed via a set of quantity criteria, which measure the aquifer capacity and amount of bank filtrate that can be effectively abstracted. Lastly, water quality criteria are assessed by means of surface-water and groundwater quality. The quantity and quality criteria form a result expressed as the site suitability index (SSI), which ranges from 0 to 1, where higher scores represent increased suitability. Finally, the methodology is applied to evaluate existing sites of large-scale RBF application as a demonstration of its applicability. The success of these existing sites is compared to the calculated SSI value and discussed.

A study on adsorption of anionic surfactant from water during riverbank filtration

Riverbank filtration (RBF) is a low-cost and environmentally friendly alternative to advanced treatment technologies for pre-treatment or removal of various synthetic organic micro-pollutants from surface water. Through laboratory-scale batch tests employing aquifer soil with varying fine content and particle size, the removal of Linear Alkylbenzene Sulfonate (LAS) from river water during riverbank filtration (RBF) was investigated to determine its adsorption behavior. In addition to it, the effect of adsorbent dosage (3–60 g/L), adsorbate conc. (2–60 mg/L), contact time (10–240 min), agitation speed (80–200 rpm), and pH (2 to 10) on the adsorption for nine types of aquifer soil were studied in batch experiments. The optimal conditions for maximum rate of LAS adsorption on aquifer soil were found to be as initial LAS conc. of 15 mg/L, pH at 7, contact time of 150 min, agitation speed at 160 rpm and adsorbent dosage of 15 g/L respectively. The removal efficiency of LAS was obtained as 88.9% for aquifer soil with 15% fine content and 86.3% for fine sand at an adsorbent dose of 15 g/L, initial LAS conc. of 15 mg/l, neutral pH, agitation speed of 160 rpm, and contact time of 150 mins. Equilibrium data were fitted to Langmuir and Freundlich isotherms, and Langmuir isotherm (R2 = 0.99) was revealed to be the best fit of these models. From multiple linear regression, the LAS removal by soil samples was found to be strongly associated with all five geo-environmental factors (R2 = 0.91). So during the design of the RBF system, suitable contact time or travel time should be maintained in addition to the selection of proper aquifer site conditions for the RBF.

The Impact of Clogging Issues at a Riverbank Filtration Site in the Lalin River, NE, China: A Laboratory Column Study

Although riverbank filtration (RBF) has been widely applied in China, the managers do not pay enough attention to the inevitable clogging issues during continuous RBF operation. The RBF site, which is located near the Lalin River, northeastern China, was selected as the study area, and the laboratory column experiments were used to simulate the RBF process and further investigate the physical and chemical clogging. The removal of turbidity (59.4–95.1%), COD (21.9–71.7%), NH4+ (10.9–39.4%), Fe (18.5–64.8%), and Mn (19.8–71.7%) demonstrated the water quality improvement by RBF. Whereas, the significant decrease in permeability (39.6–88.2%) also indicated that the clogging issues could not be ignored during RBF. Among them, the physical clogging-dominated area, chemical clogging-dominated area, and the transition zone were located at 0–12.5%, 37.5–100%, and 12.5–37.5% of the infiltration pathway, respectively. Moreover, the concentration of suspended particle materials, mean size of riverbed sediments, and aquifer media are the major impact factors for physical clogging; the precipitation of soluble constituents and redox reaction and other hydrochemical processes were the major impact factors for chemical clogging. The conclusion of this study can contribute to managers alleviating the clogging issues and improving the effectiveness of the sustainable operation in the local RBF system.

Effects of carbon load on nitrate reduction during riverbank filtration: Field monitoring and batch experiment

Riverbank filtration (RBF) is a well-established technique worldwide, and is critical for the maintenance of groundwater quality and production of clean drinking water. Evaluation of the decay of exogenous nitrate (NO3−) in river water and the enrichment of ammonium (NH4+) in groundwater during RBF is important; these two processes are mainly influenced by denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) controlled by the groundwater carbon load. In this study, the effects of carbon load (organic carbon [OC]: NO3−) on the competing nitrate reduction (DNRA and DNF) were assessed during RBF using field monitoring and a laboratory batch experiment. Results show the groundwater OC: NO3− ratio did not directly affect the reaction rate of DNRA and DNF, however, it could control the competitive partitioning between the two. In the near-shore zone, the groundwater OC: NO3− ratio shows significant seasonal variations along the filtration path owing to the changing conditions of redox, OC-rich, and NO3−-limited. A greater proportion of NO3− would be available for DNRA in the wet season with higher OC: NO3− ratio (> 10), resulting in a significantly NH4+-N enrichment rate (from 1.43 × 10−3 to 9.54 × 10−4 mmol L−1 d−1) in the near-shore zone where the zone of Mn (IV) oxide reduction. However, the activity of DNRA was suppressed with lower OC: NO3− ratio (< 10) in the dry season, resulting in a stable NH4+-N enrichment rate (from 3.12 × 10−4 to 1.30 × 10−4 mmol L−1 d−1). Benefiting from seasonal variation of OC-rich and NO3−-limited conditions, DNRA bacteria outcompeted denitrifiers, which eventually led to seasonal differences in NO3− reduction in the near-shore zone. Overall, under the effect of DNRA induced by continuous high carbon load in RBF systems, nitrogen input is not permanently removed but rather retained in groundwater during RBF.

Tracing sources and transformations of ammonium during river bank filtration by means of column experiments

Ammonium is an undesirable substance in the abstracted water of riverbank filtration (RBF) schemes, due mainly to the complications it causes during post-treatment (e. g. during chlorination). During RBF, ammonium can be formed in the riverbed by mineralization of organic nitrogen. Column experiments with riverbed sediments and river water from the Elbe were performed to evaluate the controls on ammonium concentrations during riverbed infiltration. Concentrations of ammonium went from <0.1 mgN/l in the feed water up to 1 mgN/l in the columns effluent. Higher temperatures and lower infiltration rates led to increased ammonium concentrations in the effluent. This shows higher susceptibility to ammonium increases of RBF settings in warmer climates and points to potential threats of climate change to water quality at RBF sites. In the later phases of the experiments, after the columns have been flushed their pore volumes several times, ammonium concentrations continually decreased. This behavior was attributed to the partial consumption of easily degradable organic material in the sediments, leading to lesser reducing conditions and lower mineralization rates. Based on operation with varied nitrate concentrations (0–11 mgN/l) and 15N isotopic measurements, dissimilatory nitrate reduction to ammonium (DNRA) was not shown to be relevant in the formation of ammonium. Anaerobic ammonium oxidation (anammox), however, was hypothesized to be an important sink of ammonium inside the columns, which indicates that rivers with high nitrate concentrations, such as the Elbe, may have a buffer of protection against ammonium formation during RBF.