Bank Filtration Systems Research Articles

Spatiotemporal variations of redox conditions and microbial responses in a typical river bank filtration system with high Fe2+ and Mn2+ contents

The redox conditions strongly affect redox kinetics, hydrochemical composition and microbial reactions under river bank filtration (RBF). For investigating the redox conditions, zonation factors, and microbial responses in a typical RBF with high Fe2+ and Mn2+ contents, three wells were established 20 m apart perpendicular to the south bank of the Songhua River with a constant flow rate of 400 m3/h. Redox zonation was identified from the redox sequences, redox products, reactions identified and seasonality. High-throughput sequencing, principal coordinates analysis, and redundancy analysis were used to identify the microbial responses to redox zonation. The results indicated that the RBF was stabilized after 21 d of water extraction with a 51%, 36% and 21% decrease of Fe2+, Mn2+ and NH4+ contents, respectively. Feature redox indices varied with strong regularity in the horizontal and vertical filtration directions, and the filtration area could be divided into O2/NO3−, Fe/Mn, and SO42− reduction zones. Seasonality resulted in markedly fluctuation of Fe2+ and Mn2+ contents in groundwater. Pseudomonas, Flavobacterium, and Limnobacter were the dominant bacteria in the O2/NO3−, Fe/Mn, and SO42− reduction zones, respectively. DO explained 21.1% of microbial variability in the fluctuation zone, while Mn2+ and Fe2+ explained 27.7%, and 26.2%, respectively, of microbial variability in the saturated zone.

Assessing biological stability in a\xa0porous groundwater aquifer of a\xa0riverbank filtration system: combining traditional cultivation-based and emerging cultivation-independent in situ and predictive methods

Riverbank filtration systems are important drinking water resources. Aquifers of riverbank filtration systems are subjected to considerable dynamics concerning the quantity and quality of the infiltrating water. The microbiological quality is mainly jeopardized by faecal contamination of the main river. Besides, water quality can be impacted by growth of natural water-borne bacteria due to the input of nutrients resulting in the proliferation of opportunistic pathogens, impairment of odour and taste or bio-corrosion. The occurrence of such phenomena indicates a biological instability. For highly dynamic riverbank filtration systems, it is thus of high relevance to assess the biological stability of the groundwater resource.In the present study, we applied a holistic, two-tiered concept of in situ and predictive methods to assess the biostability of the aquifer in a bank filtration system of the Danube River. We applied traditional cultivation-based and selected cultivation-independent methods—including cultivation on yeast extract and R2A agar, determination of total cell counts via fluorescence microscopy and flow cytometry, leucine incorporation and 16S rRNA gene amplicon sequencing—at critical control points along the infiltration path from the river to the abstraction well.The concentration of organic nutrients and the hydrological variability were the main controlling factors driving the biological stability of the groundwater body. Wells situated at greater distance displayed significantly lower dissolved organic carbon concentrations and a dampened hydrological influence in comparison to the well situated next to the river. Apparent discrepancies between the methods used indicated a different indicator function of the cultivation-based and cultivation-independent approaches. For complex systems, we thus recommend this new holistic concept for assessing biostability by combining in situ as well as predictive parameters and using cultivation-based and cultivation-independent methods.

The fate of heavy metals during bank filtration: Effect of dissolved organic matter

The effectiveness of bank filtration (BF) is highly dependent on the source water quality (e.g., organic matter composition, pH, and concentration of heavy metals (HMs)). In this study, the impact of dissolved organic matter (DOM) on the removal of selected metals (Cu, Zn, Pb, Se, and Ni) during BF was investigated. Column studies were conducted at 30 °C with feed water sources of different organic matter composition. Excitation–emission matrix fluorescence coupled with parallel factor analysis (PARAFAC–EEM) was used to characterise the organic composition of the feed waters. Moreover, another series of column studies was conducted to assess the impact of natural organic matter type (humic, protein) and concentration on the HMs removals. The experimental results revealed a high Pb(II) removal efficiency during filtration, which depends only slightly on the organic matter content of the feed water. In comparison, the removals of Cu, Zn and Ni ranged between 65 and 95 %; and relied significantly on the organic concentration and composition in the raw waters. Humic compounds (terrestrial or microbial) demonstrated adequate ability to reduce the removal efficiencies of these HMs during the infiltration. Conversely, biodegradable matter was found to be effective in enhancing the sorption of HMs onto the sand grains. The Se-removal was enhanced when the feed water contained a higher concentration of biodegradable matter. In general, it can be concluded that the organic composition of the source water affects profoundly the removal of HMs during the BF, and should be considered in the design of BF systems.

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.

Analysis of the Performance of Bank Filtration for Water Supply in Arid Climates: Case Study in Egypt

Bank filtration (BF) is acknowledged as a sustainable and effective technique to provide drinking water of adequate quality; it has been known for a long time in Europe. However, this technique is site-specific and therefore its application in developing countries with different hydrologic and environment conditions remains limited. In this research, a 3-discipline study was performed to evaluate the feasibility of the application of this technique in Aswan City (Egypt). Firstly, a hydrological model was developed to identify key environmental factors that influence the effectiveness of BF, and to formulate plans for the design and management of the BF system. Secondly, water samples were collected for one year (January 2017 to December 2017) from the water sources and monitoring wells to characterize the bank-filtrate quality. Lastly, an economic study was conducted to compare the capital and operating costs of BF and the existing treatment techniques. The results demonstrated that there is high potential for application of BF under such hydrological and environmental conditions. However, there are some aspects that could restrict the BF efficacy and must therefore be considered during the design process. These include the following: (i) Over-pumping practices can reduce travel time, and thus decrease the efficiency of treatment; (ii) Locating the wells near the surface water systems (<50 m) decreases the travel time to the limit (<10 days), and thus could restrict the treatment capacity. In such case, a low pumping rate must be applied; (iii) the consequences of lowering the surface water level can be regulated through the continuous operation of the wells. Furthermore, laboratory analysis indicated that BF is capable of producing high quality drinking water. However, an increase in organic matter (i.e., humics) concentration was observed in the pumped water, which increases the risk of trihalomethanes being produced if post-chlorination is implemented. The economic study ultimately demonstrated that BF is an economic and sustainable technique for implementation in Aswan City to address the demand for potable water.

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.

Impact of river reconstruction on groundwater flow during bank filtration assessed by transient three-dimensional modelling of flow and heat transport

Bank filtration (BF) is an established indirect water-treatment technology. The quality of water gained via BF depends on the subsurface capture zone, the mixing ratio (river water versus ambient groundwater), spatial and temporal distribution of subsurface travel times, and subsurface temperature patterns. Surface-water infiltration into the adjacent aquifer is determined by the local hydraulic gradient and riverbed permeability, which could be altered by natural clogging, scouring and artificial decolmation processes. The seasonal behaviour of a BF system in Germany, and its development during and about 6 months after decolmation (canal reconstruction), was observed with a long-term monitoring programme. To quantify the spatial and temporal variation in the BF system, a transient flow and heat transport model was implemented and two model scenarios, ‘with’ and ‘without’ canal reconstruction, were generated. Overall, the simulated water heads and temperatures matched those observed. Increased hydraulic connection between the canal and aquifer caused by the canal reconstruction led to an increase of ~23% in the already high share of BF water abstracted by the nearby waterworks. Subsurface travel-time distribution substantially shifted towards shorter travel times. Flow paths with travel times <200 days increased by ~10% and those with <300 days by 15%. Generally, the periodic temperature signal, and the summer and winter temperature extrema, increased and penetrated deeper into the aquifer. The joint hydrological and thermal effects caused by the canal reconstruction might increase the potential of biodegradable compounds to further penetrate into the aquifer, also by potentially affecting the redox zonation in the aquifer.

The migration of pesticide residues in groundwater at a bank filtration site (Krajkowo well field, Poland)

River bank filtration systems are widely used for water supply purposes. Using these systems, the movement of water over short distances between the river bottom and extraction wells can decrease the concentrations of some contaminants. Such systems are especially important for the removal of specific micro-pollutants that seasonally appear in river water. In this article, pesticides migration at the Krajkowo well field is analysed based on different water extraction schemes. The water is extracted by two groups of wells (one located 60–80 m from the Warta River, and the second located more than 400 m from the river) and by a horizontal well with radial drains located 5 m below the river bottom. Based on this scheme, the rate of pesticide residues removal was analysed in wells located at different distances from the river channel. The results of the three sampling campaigns conducted in summer and autumn 2017 and winter 2018 indicate the presence of pesticide compounds in the Warta River (max. total concentration of 0.171 μg/l). The pesticides were also present in the horizontal well (max. total concentration of 0.137 μg/l). Much smaller concentrations (max. 0.064 μg/l) were observed in vertical wells located 60–80 m from the river. Additionally, in the well located 250 m from the river, only two pesticide constituents were detected (at concentrations just above the detection limit), and in a well located 680 m from the river, the concentrations of pesticide residues were below the detection limit (excluding isoproturon, which was slightly above the detection limit). This research illustrates the effectiveness of pesticides removal by river bank filtration.

Use of bank filtration systems in the sub-tropical region of the lower Brahmaputra valley

Abstract River bank filtration (RBF) is a natural method of obtaining surface water from a river or lake via the sub-surface for domestic use. It has been intensively used worldwide to augment water supply systems for sustainability and can be operated under various conditions. Its energy requirements are comparatively lower than those of conventional water treatment systems. Field investigations were carried out at various locations in Kokrajhar district of Assam, India to assess groundwater quality and aquifer characteristics. The results suggest that major water quality parameters were within the Indian drinking water standards. The iron concentration exceeded the permissible maximum in more than 50% of samples from hand pumps, its concentration ranging between 0.33 and 3.50 mg/L. The pH was mostly in the range 5.4 to 7.4, suggesting that the water is slightly acidic. Aquifer and riverbed material collected along the banks of the Gaurang River were sieved, and classified as coarse silt to fine gravel, with gravel and sand predominant. The hydraulic conductivity, determined from the grain size distributions, were between 5 × 10−3 and 1.4 × 10−2 m/s, suggesting good aquifer permeability. The maximum safe well yield was estimated at 2,000 to 7,500 L/min, and the mean travel time at less than a week during the monsoon and more than 3 years under non-monsoon conditions. The aim of this paper is to demonstrate the RBF method for treating river water naturally under wet climatic conditions. The lower Brahmaputra basin is a unique physiographic setting with a powerful monsoon regime and a fragile geological base. The approach was to prepare a comparative study of water quality and aquifer characteristics with the present site and few active RBF sites.

Operational Strategies and Adaptation of RBF Well Construction to Cope with Climate Change Effects at Budapest, Hungary

The objective of this paper is to give an overview on the Hungarian experience of river bank filtration (RBF) systems. The study addresses the conflict, which arises between the stochastic character of river water quantity and quality, and the required standard of drinking-water supply. Trends in water levels, flow, and water quality are discussed, along with technical measures and operational rules that were developed for implementation of RBF systems. This paper also provides an overview of the average lifespan of the wells and operational strategies. The emerging reconstruction and reconditioning needs are highlighted, and existing alternatives are presented. Large-scale infrastructural elements, such as the Danube-based RBF systems, have to be adapted to a changing environment. The increasing frequency of floods and droughts stresses the need to implement climate-adapted RBF systems and related operational strategies. Operational strategies which were developed by the Budapest Waterworks to deal with extreme hydrological scenarios are presented.

Water Crisis: Bank Filtration and Aquifer Storage Recharge Systems as Possible Alternatives

AbstractRiverbank filtration (RBF) is a simple yet effective treatment technology that uses the natural soil and aquifer media to remove various pollutants from river water during induced infiltrat...

Cyanobacteria breakthrough: Effects of Limnothrix redekei contamination in an artificial bank filtration on a regional water supply

Mitigation of cyanobacterial or “blue-green algal” blooms is a challenging task for water managers across Australia. In the present study, a regional drinking water source (located in Central Queensland) was studied to identify the potential risks posed by cyanobacteria. Data were collected from the drinking water source (a lagoon) as well as the drinking water supply infrastructure, at monthly intervals between September 2012 and December 2014. In March 2013 there was an extreme rainfall event where floodwaters infiltrated the water supply without passing through bank filtration. The floodwaters also compromised the bank filtration via erosion. The pump well and bank filtration system were subsequently upgraded/maintained in May 2013. Results showed that following the extreme event and infrastructure upgrade, two distinct Limnothrix redekei blooms microscopically identified, were detected in the drinking water supply chain. Further investigations indicated that the species was also present in the pump well infrastructure, a dark environment, growing on the surface of the newly installed pump well cement pipe. After observing the occurrence and habitat niche of this species during the present study, a suggestion was made to minimise cyanobacterial contamination and proliferation within the water supply chain infrastructure. The preliminary proposal is to use clean sand on the sub-surface layer of the bank filtration, complemented with biologically active sand as a surface cap. Furthermore, the culturing techniques reported in this study can potentially be used to optimize assessment for Limnothrix redekei populations surrounding water extraction points.

Estimating Travel Time in Bank Filtration Systems from a Numerical Model Based on DTS Measurements.

An approach is presented to determine the seasonal variations in travel time in a bank filtration system using a passive heat tracer test. The temperature in the aquifer varies seasonally because of temperature variations of the infiltrating surface water and at the soil surface. Temperature was measured with distributed temperature sensing along fiber optic cables that were inserted vertically into the aquifer with direct push equipment. The approach was applied to a bank filtration system consisting of a sequence of alternating, elongated recharge basins and rows of recovery wells. A SEAWAT model was developed to simulate coupled flow and heat transport. The model of a two-dimensional vertical cross section is able to simulate the temperature of the water at the well and the measured vertical temperature profiles reasonably well. MODPATH was used to compute flowpaths and the travel time distribution. At the study site, temporal variation of the pumping discharge was the dominant factor influencing the travel time distribution. For an equivalent system with a constant pumping rate, variations in the travel time distribution are caused by variations in the temperature-dependent viscosity. As a result, travel times increase in the winter, when a larger fraction of the water travels through the warmer, lower part of the aquifer, and decrease in the summer, when the upper part of the aquifer is warmer.

Impacts of Accumulated Particulate Organic Matter on Oxygen Consumption and Organic Micro-Pollutant Elimination in Bank Filtration and Soil Aquifer Treatment

Bank filtration (BF) and soil aquifer treatment (SAT) are efficient natural technologies in potable water reuse systems. The removal of many organic micro-pollutants (OMPs) depends on redox-conditions in the subsoil, especially on the availability of molecular oxygen. Due to microbial transformation of particulate and dissolved organic constituents, oxygen can be consumed within short flow distances and induce anoxic and anaerobic conditions. The effect of accumulated particulate organic carbon (POC) on the fate of OMPs in BF and SAT systems is not fully understood. Long-term column experiments with natural sediment cores from the bank of Lake Tegel and from a SAT basin were conducted to investigate the impact of accumulated POC on dissolved organic carbon (DOC) release, on oxygen consumption, on mobilization of iron and manganese, and on the elimination of the organic indicator OMPs. The cores were fed with aerated tap water spiked with OMPs to exclude external POC inputs. Complete oxygen consumption within the first infiltration decimeter in lake sediments caused mobilization of iron, manganese, and DOC. Redox-sensitive OMPs like diclofenac, sulfamethoxazole, formylaminoantipyrine, and gabapentin were eliminated by more than 50% in all sediment cores, but slightly higher residual concentrations were measured in effluents from lake sediments, indicating a negative impact of a high oxygen consumption on OMP removal.

Evaluation of bank filtration as a pretreatment method for the provision of hygienically safe drinking water in Norway: results from monitoring at two full-scale sites

Two case studies were carried out in central Norway in order to assess the performance of bank filtration systems in cold-climate fluvial aquifers relying on recharge from humic-rich surface waters with moderate microbial contamination. Three municipal wells and two surface-water sources at operative bank filtration systems were monitored for naturally occurring bacteriophages, fecal indicators, natural organic matter (NOM) and physico-chemical water quality parameters during a 4-month period. Aquifer passage effectively reduced the microorganism and NOM concentrations at both study sites. Bacteriophages were detected in 13 of 16 (81%) surface-water samples and in 4 of 24 (17%) well-water samples, and underwent 3 ± 0.3 log10 reduction after 50–80-m filtration and 20–30 days of subsurface passage. NOM reductions (color: 74–97%; dissolved organic carbon: 54–80%; very hydrophobic acids: 70%) were similar to those achieved by conventional water-treatment processes and no further treatment was needed. Both groundwater dilution and sediment filtration contributed to the hygienic water quality improvements, but sediment filtration appeared to be the most important process with regard to microbial and NOM reductions. A strengths-weaknesses-opportunities-threats analysis showed that bank filtration technology has a high potential as a pretreatment method for the provision of hygienically safe drinking water in Norway.

Advancing Sequential Managed Aquifer Recharge Technology (SMART) Using Different Intermediate Oxidation Processes

Managed aquifer recharge (MAR) systems are an efficient barrier for many contaminants. The biotransformation of trace organic chemicals (TOrCs) strongly depends on the redox conditions as well as on the dissolved organic carbon availability. Oxic and oligotrophic conditions are favored for enhanced TOrCs removal which is obtained by combining two filtration systems with an intermediate aeration step. In this study, four parallel laboratory-scale soil column experiments using different intermittent aeration techniques were selected to further optimize TOrCs transformation during MAR: no aeration, aeration with air, pure oxygen and ozone. Rapid oxygen consumption, nitrate reduction and dissolution of manganese confirmed anoxic conditions within the first filtration step, mimicking traditional bank filtration. Aeration with air led to suboxic conditions, whereas oxidation by pure oxygen and ozone led to fully oxic conditions throughout the second system. The sequential system resulted in an equal or better transformation of most TOrCs compared to the single step bank filtration system. Despite the fast oxygen consumption, acesulfame, iopromide, iomeprol and valsartan were degraded within the first infiltration step. The compounds benzotriazole, diclofenac, 4-Formylaminoantipyrine, gabapentin, metoprolol, valsartan acid and venlafaxine revealed a significantly enhanced removal in the systems with intermittent oxidation compared to the conventional treatment without aeration. Further improvement of benzotriazole and gabapentin removal by using pure oxygen confirmed potential oxygen limitation in the second column after aeration with air. Ozonation resulted in an enhanced removal of persistent compounds (i.e., carbamazepine, candesartan, olmesartan) and further increased the attenuation of gabapentin, methylbenzotriazole, benzotriazole, and venlafaxine. Diatrizoic acid revealed little degradation in an ozone–MAR hybrid system.

Seasonality of temperatures and redox zonations during bank filtration – A modeling approach

Bank filtration (BF) is a common technique for supplying drinking water, using the ability of the infiltration zone and aquifer passage to attenuate or degrade undesired substances that infiltrate from surface waters to groundwater abstraction wells. Temporal and spatial changes of temperatures and redox conditions are often the controlling factors for the fate and behavior of micropollutants during subsurface passage and consequently for the extracted raw water quality. A 2-dimensional cross-sectional heat transport and multi-species reactive transport model was set up to simulate the seasonally varying temperatures and redox conditions on the infiltration path at a bank filtration site in Berlin, Germany. The calibrated model was able to capture the observed variations in O2 and NO3− when considering temperature dependence of the redox reaction kinetics. The observed Mn2+- and Fe2+-concentrations were not well replicated by the model, presumably due to mineral reactions that were not accounted for in the simulations. SO42− was found to behave conservative, i.e., the observed concentration could be well simulated without any reactions. The simulations reveal the transience of BF systems with regard to temperatures and redox conditions, which has important implications for the BF quality and should therefore be accounted for.

Optimal Well Location in a River Bank Filtration System: Sensitivity to Aquifer Characteristics and Decay Rate

AbstractAn optimization model is developed to locate pumping wells in a river bank filtration system to minimize the overall cost of pumping and treatment. The model combines the numerical solution of water flow and solute transport from the river to the pumping wells with a genetic-algorithm-based optimization technique. The water quality parameters considered in the study are the concentration of (1) suspended solids, (2) endosulfan, which is a widely used pesticide in agriculture, and (3) E. coli. It was observed that the fitness function increases at a faster rate near the river before attaining the optimum. However, the rate of decrease in the fitness function is gradual after the optimum. It is concluded that the genetic-algorithm-based optimization technique is an efficient and robust in the estimation of optimum well distance. Sensitivity analysis of the optimal distance and total cost due to variation in aquifer characteristics and decay rate is also presented.

Malaysia's largest river bank filtration and ultrafiltration systems for municipal drinking water production

This paper presents a case study of Wakaf Bunut water treatment plant (the ‘plant’) in Kelantan, Malaysia. The plant was successfully commissioned in February 2013 and started operating in March 2013. It is capable of supplying up to 14 million liters a day of potable water to Tok Bali. Feasibility studies were carried out on the combination of river bank filtration (RBF) and ultrafiltration (UF) to reduce operating costs while maintaining filtrate quality. The plant is the largest municipal drinking water treatment plant in Malaysia using combined RBF and UF technologies. Actual operating data from the plant were collected and are discussed in this paper.

Stable pumping rates for horizontal wells in bank filtration systems

We consider common bank filtration systems and develop an explicit analytic solution representing steady, two-dimensional, groundwater flow to a horizontal well near a river in an unconfined aquifer. For the boundary-value problem investigated, we find that a unique solution exists for all negative well discharges. For positive discharges, a maximum value exists which corresponds to the formation of a cusp on the free surface. For positive discharges less than the maximum, the solution is not unique, consisting of two alternate configurations of the free surface. One solution includes a stable free surface on a single-valued physical plane, while the alternate solution includes a looped free surface lying on two sheets of a Riemann surface. Imposing a stability condition on the free surface results in a unique solution to the problem. We use the solution to investigate the behavior of the free surface under varying well discharges to identify stable pumping rates and predict well yield. In particular, we examine the well yield and the stability of the free surface when the head in the horizontal well is maintained at the top of the well screen. This condition is shown to produce a stable free surface for a wide range of well radii; the stability is independent of the hydraulic conductivity of the aquifer, the location of the well, or the presence of a skin resistance at the well.