Riverbank Filtration Site Research Articles

Surface water and groundwater interaction at long-term exploited riverbank filtration site based on groundwater flow modelling (Mosina-Krajkowo, Poland)

Study regionPoland, Warta River catchment. Study focusThe study aimed to explain the reasons for spatial variability in chloride concentrations at the Mosina-Krajkowo riverbank filtration (RBF) site located along the river. This variability is attributed to RBF’s different intensity along the river sections, related, among others, to clogging development. The RBF effectiveness was studied using groundwater flow modelling by: examining the water balance in zones established on hydrogeological setting and chloride concentrations; travel time of the bankfiltrate investigation; RBF parametrisation (i.e. infiltration per unit area and specific infiltration per unit of riverbank). New Hydrological Insights for the RegionThe study identifies zones of the most favourable RBF conditions and establishes the variability causes. The overall share bankfiltrate was found at 75.8 %. Its spatial variation ranged widely from 41.1–89.3%, confirming the usefulness of the RBF performance sectional analysis in managing this type of site. The highest proportion of surface water (>80 %) occurred along the straight river section, where the riverbed was built by fine and medium sands (preventing penetration of organic suspension into the aquifer). In contrast, the lowest values (<42 %) occurred in the meander zone (with the most favourable RBF conditions at the beginning of site operation), where deep erosion reached coarse-grained sediments in the river bottom, followed by the development of clogging processes and a decrease in the RBF efficiency with time.

Feature-based molecular networking for identification of organic micropollutants including metabolites by non-target analysis applied to riverbank filtration

Due to growing concern about organic micropollutants and their transformation products (TP) in surface and drinking water, reliable identification of unknowns is required. Here, we demonstrate how non-target liquid chromatography (LC)-high-resolution tandem mass spectrometry (MS/MS) and the feature-based molecular networking (FBMN) workflow provide insight into water samples from four riverbank filtration sites with different redox conditions. First, FBMN prioritized and connected drinking water relevant and seasonally dependent compounds based on a modification-aware MS/MS cosine similarity. Within the resulting molecular networks, forty-three compounds were annotated. Here, carbamazepine, sartans, and their respective TP were investigated exemplarily. With chromatographic information and spectral similarity, four additional TP (dealkylated valsartan, dealkylated irbesartan, two oxygenated irbesartan isomers) and olmesartan were identified and partly verified with an authentic standard. In this study, sartans and TP were investigated and grouped regarding their removal behavior under different redox conditions and seasons for the first time. Antihypertensives were grouped into compounds being well removed during riverbank filtration, those primarily removed under anoxic conditions, and rather persistent compounds. Observed seasonal variations were mainly limited to varying river water concentrations. FBMN is a powerful tool for identifying previously unknown or unexpected compounds and their TP in water samples by non-target analysis.Graphical abstract

Laboratory and field study on changes in water quality and increase in dissolved iron during riverbank filtration.

Changes in the water quality by the riverbank filtration (RBF) process were investigated in the field-scale demonstration sites. The overall water quality was improved by RBF, but Fe2+ concentration significantly increased in the riverbank-filtered water more than in the river water. This result would be caused by the interaction between the iron minerals and the river water in the aquifer and the influx of the hinterland groundwater into RBF wells. Dissolution properties of iron from the aquifer soils cored at the sites were evaluated through incubation experiment considering various values of redox potential (Eh), dissolved oxygen (DO), and hydrogen-ion concentration exponent (pH). These results presented that at the incubator with the final Eh of 470 mV, DO of 3.4, and pH of 4.53, the iron from the aquifer soil was most dissolved, and the pyrite and siderite contents in the aquifer soil decreased significantly from 11.5 to 6.22% and from 50.8 to 24.5%, respectively. Based on changes of ion concentrations (such as Fe2+, Fe3+, SO42- and NO3-) and iron species in the incubators, it was believed that pyrite and siderite minerals in the aquifer soils cause an increase in the Fe2+ concentration with the absence of DO and an increase in the Fe2+ and Fe3+ concentrations with the presence of DO. The dissolution rates of iron minerals into Fe2+ and Fe3+ were dependent on Eh, pH, and DO and were more sensitive to Eh and pH than DO. The results of this study can provide information on RBF site selection and its operation.

Uncertainty Analysis and Identification of Key Parameters Controlling Bacteria Transport Within a Riverbank Filtration Scenario

AbstractManaged aquifer recharge through bank filtration is an important method to produce sustainable drinking water. Yet, water quality related to transport of pathogens (bacteria and viruses) into groundwater systems from surface waters can be a matter of concern, especially in urbanized regions. Based on a 1‐year monitoring campaign, a reactive transport model was developed for bacteria transport at a riverbank filtration site located in Germany. The model allows simulating advective‐dispersive transport and relies on the colloid filtration theory to mimic attachment and detachment of bacteria to and from the sediment in addition to inactivation, straining and blocking of bacteria. Due to the complexity of the investigated processes, the reactive transport model is characterized by a high level of parametrization, encompassing parameters driving flow as well as solute and colloid transport. A global sensitivity analysis has been applied to identify the most relevant model parameters with respect to piezometric pressure heads, groundwater temperature, and concentrations of chloride, oxygen, coliforms, and Escherichia coli. The model has been calibrated within a stochastic framework, to provide model parameter estimates and to quantify their uncertainty. Our results suggest that bacteria transport models are highly sensitive to inactivation coefficients, straining coefficients, and bacteria size. Permeability of the colmation layer at the riverbank is a key factor for bacteria transport through its influence on residence times. Seasonal variability of boundary conditions, especially anoxic aquifer conditions in the summer and high groundwater flow velocities during flooding periods, resulted in a reduction of inactivation and increased bacteria concentrations at observation wells.

Assessment of river water infiltration conditions based on both chloride mass-balance and hydrogeological setting: the Krajkowo riverbank filtration site (Poland)

Abstract In the present work measurements of chloride concentrations were used to assess the variability of infiltration conditions and contributions of surface water and local groundwater to the discharge of wells at Krajkowo riverbank filtration site (western Poland). Tests were performed on samples from 26 wells located in a well gallery close to the River Warta. Due to higher chloride concentrations in river water in comparison with local groundwater, significant differences in concentrations in samples from individual wells were noted. In particular, lower chloride concentrations in 11 wells were recorded, which can be linked to the local occurrence of low-permeability deposits in the superficial zone; a locally higher degree of riverbed sediment clogging in the highly convex meandering zone, where strong erosion of the riverbed occurred, which in turn led to increased clogging; the occurrence of a more intensive groundwater inflow into the river valley due to water infiltration from a smaller river entering the River Warta valley, as well as unfavourable conditions for the infiltration of surface water to the lower part of the aquifer with a greater thickness. Differences in chloride concentrations observed were also used to quantify approximately river water contribution to the well production. The average contribution of the River Warta to the recharge of the entire well gallery was estimated at 59.8%.

Identification of iron and sulfate release processes during riverbank filtration using chemical mass balance modeling.

Various hydrogeochemical processes can modify the quality of river water during riverbank filtration (RBF). Identifying the subsurface processes responsible for the bank-filtered water quality is challenging, but essential for predicting water quality changes and determining the necessity of post-treatment. However, no systematic approach for this has been proposed yet. In this study, the subsurface hydrogeochemical processes that caused the high concentrations of total iron (Fe) and sulfate (SO42-) in the bank-filtered water were investigated at a pilot-scale RBF site in South Korea. For this purpose, water quality variations were monitored in both the extraction well and the adjacent river over five months. The volumetric mixing ratio between the river water and the native groundwater in the RBF well was calculated to understand the effect of mixing on the quality of water from the well and to assess the potential contribution of subsurface reactions to water quality changes. To identify the subsurface processes responsible for the evolution of Fe and SO42- during RBF, an inverse modeling based on the chemical mass balance was conducted using the water quality data and the calculated volumetric mixing ratio. The modeling results suggest that pyrite oxidation by abundant O2 present in an unsaturated zone could be a primary process explaining the evolution of total Fe and SO42- during RBF at the study site. The presence of pyrite in the aquifer was indirectly supported by iron sulfate hydroxide (Fe(SO4)(OH)) detected in oxidized aquifer sediments.

Numerical Investigation for Riverbank Filtration Sustainability Considering Climatic Changes in Arid and Semi-Arid Regions; Case Study of RBF Site at Embaba, Nile Delta, Egypt

Changes in riverine hydrography and reduced aquifer recharge due to projected climate changes in arid and semi-arid regions are the main issues of water supply, especially in the Nile Delta, Egypt. Continuous degradation results from reduced Nile water flow, poor management of groundwater extraction, and human activities throughout the Nile’s course and drainage channels. Contamination of this water with heavy metals and dissolved organic solids reduces the quality of this water, which increases the price of treatment. River Bank Filtration (RBF) is a water treatment technology used for improving the quality of drinking water taken from polluted rivers where abstraction wells are installed on the banks. This study was applied to the RBF site at Embaba, Nile Delta, Egypt using the numerical code MT3D. The study was simulated and calibrated for the current situation and number of scenarios to investigate the effect of climatic changes on RBF sustainability. Four scenarios were simulated to identify and estimate the RBF portion and the total water travel time from the river to the wells. The first scenario involves a reduction in river stages, the second a decrease in aquifer recharge, the third a combination of the first two scenarios, and the fourth scenario combines scenarios 1, 2, and 3. The results indicate that the RBF portion decreased from 67.42% in the base case to 35.46% and 64.99% with a reduction in river stage by 75% from the base case and a decrease in aquifer recharge from 182.50 (base case) to 50 mm per year, respectively. Moreover, the RBF portion increased to reach 87.75% with a reduction in the General Head Boundary of 75% from the base case, while the combination of the three scenarios decreased the RBF portion to 67.24%. Finally, the water supply systems in arid and semi-arid regions should be extended by installing and operating RBF facilities to manage the negative effects of climatic change through reduction in river stages and aquifer recharge, and increasing abstraction due to overpopulation.

Importance of the Induced Recharge Term in Riverbank Filtration: Hydrodynamics, Hydrochemical, and Numerical Modelling Investigations

While ensuring adequate drinking water supply is increasingly being a worldwide challenging need, managed aquifer recharge (MAR) schemes may provide reliable solutions in order to guarantee safe and continuous supply of water. This is particularly true in riverbank filtration (RBF) schemes. Several studies aimed at addressing the treatment capabilities of such schemes, but induced aquifer recharge hydrodynamics from surface water bodies caused by pumping wells is seldom analysed and quantified. In this study, after presenting a detailed description of the Serchio River RBF site, we used a multidisciplinary approach entailing hydrodynamics, hydrochemical, and numerical modelling methods in order to evaluate the change in recharge from the Serchio river to the aquifer due to the building of the RBF infrastructures along the Serchio river (Lucca, Italy). In this way, we estimated the increase in aquifer recharge and the ratio of bank filtrate to ambient groundwater abstracted at such RBF scheme. Results highlight that in present conditions the main source of the RBF pumping wells is the Serchio River water and that the groundwater at the Sant’Alessio plain is mainly characterized by mixing between precipitation occurring in the higher part of the plain and the River water. Based on chemical mixing, a precautionary amount of abstracted Serchio River water is estimated to be on average 13.6 Mm3/year, which is 85% of the total amount of water abstracted in a year (~16 Mm3). RBF is a worldwide recognized MAR technique for supplying good quality and reliable amount of water. As in several cases and countries the induced recharge component is not duly acknowledged, the authors suggest including the term “induced” in the definition of this type of MAR technique (to become then IRBF). Thus, clear reference may be made to the fact that the bank filtration is not completely due to natural recharge, as in many cases of surface water/groundwater interactions, but it may be partly/almost all human-made.

Response of the redox species and indigenous microbial community to seasonal groundwater fluctuation from a typical riverbank filtration site in Northeast China

The effects of the seasonal groundwater level fluctuations on the redox species in groundwater and the microbial communities in aquifer media were investigated at a typical riverbank filtration (RBF) site in northeast China. A total of 50 groundwater samples were collected to illustrate the variations of oxidation-reduction potential (ORP), dissolved oxygen (DO) and redox species such as iron (Fe2+), manganese (Mn2+), ammonium (NH4+), and nitrate (NO3−) during a whole hydrological year. This study observed that the groundwater dynamics fluctuate seasonally with the amplitude of up to 1.0 m, which is mainly related to the hydrological processes of the Songhua river. The groundwater was oxic with an average DO value of 3.6 mg/L and 3.2 mg/L in the two seasons. The ORP measurements showed that the groundwater was mostly under reducing conditions, with the seasonal variations of ORP being concurrent with the water level fluctuation. As electron acceptors, the average values of Fe2+ and Mn2+ were 6.3 mg/L and 6.8 mg/L, and 1.2 mg/L and 1.4 mg/L in wet and dry seasons, respectively. The O2 entrapment induced by the seasonal groundwater level fluctuation facilitates the interaction among O2, Fe2+ and Mn2+ for biotransformation. Moreover, the reductive dissolution of iron and manganese oxides might be major mechanisms for Fe2+ and Mn2+ release under reductive conditions. The average content of NH4+ was 1.5 mg/L and 1.2 mg/L in two seasons, respectively, and NO3− was lower than 0.1 mg/L. The seasonal variation of NH4+ and NO3− in groundwater is mainly related to the periodic application of nitrogen fertilizer in agriculture. The spatiotemporal of microbial communities was significantly different between the two seasons, and Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, Firmicutes, Nitrospirae, Gemmatimonadetes, Bacteroidetes, and Verrucomicrobia were the nine main phyla. pH, DO, EC, NO2−, and Fe2+ were the major factors correlating the microbial community in the wet season, while pH, NO2−, NH4+, TH, COD, and SO42− were the critical parameters in the dry season according to RDA results. These results may be valuable to gain insight into the temporal variation of the redox species due to groundwater seasonal fluctuation and to identify the correlation between the groundwater and microbial communities in the redox-dynamic zone.

Response of redox zonation to recharge in a riverbank filtration system: a case study of the Second Songhua river, NE China

Abstract Bank filtration induced by groundwater pumping results in redox zonation along the groundwater flow path. Besides the river water, recharge from other sources can change local redox conditions; therefore, redox zonation is likely to be complex within the riverbank filtration (RBF) system. In this study, hydrodynamics, hydrogeochemistry, and environmental stable isotopes were combined together to identify the redox conditions at an RBF site. The recharge characteristics and redox processes were revealed by monitoring the variations of water level, δ2H and δ18O, and redox indexes along shallow and deep flow paths. The results show that local groundwater is recharged from river, regional groundwater, and precipitation. The responses of redox zonation are sensitive to different sources. In the river water recharge zone near shore, O2, , Mn(IV), Fe(III), and are reduced in sequence, the ranges of each reaction are wider in deep groundwater because of the high-velocity deep flow. In the precipitation vertical recharge zone, precipitation intermittently drives O2, , and organic carbon to migrate through vadose zone, thereby decreasing the groundwater reducibility. In the regional groundwater lateral recharge zone in the depression cone, the reductive regional groundwater is continuously recharging local groundwater, leading to the cyclic reduction of Mn(IV) and Fe(III).

Groundwater pollution containing ammonium, iron and manganese in a riverbank filtration system: Effects of dynamic geochemical conditions and microbial responses.

Bench-scale experiments were conducted to investigate the effect of hydraulic loadings and influent concentration on the migration and biotransformation behavior of three groundwater pollutants: ammonium (NH4 +), iron (Fe2+) and manganese (Mn2+). Columns packed with aquifer media collected from a river bank filtration (RBF) site in Harbin City, NE China were introduced synthetic groundwater (SGW) or real groundwater (RGW) were at two different constant flow rates and initial contaminant concentrations to determine the impact of system conditions on the fate of the target pollutants biotransformation. The results showed that the biotransformation rate of Fe2+ Mn2+, and NH4 + decreased by 8%, 39% and 15% under high flow rate (50 L d-1) compared to low flow rate (25 L d-1), which was consistent with the residence-time effect. While the biotransformation rate of Fe2+ Mn2+, and NH4 + decreased by 7%, 14% and 9% under high influent concentration compared to original groundwater. The 16S rRNA analysis of the aquifer media at different depths after experiments completion demonstrated that the relative abundance of major functional microbes iron oxidizing bacteria (IOB) and manganese oxidizing bacteria (MnOB) under higher flow rate and higher influent concentration decreased 13%, 14% and 25%, 24%, respectively, whereas the ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) exhibited minimal change, compared to the lower flow rate. Above all results indicated that both high flow rate and high concentration inhibit the biotransformation of NH4 +, Fe2+ and Mn2+. The biotransformation of Fe2+ and Mn2+ occurs primarily in the 0-40 cm and 20-60 cm depth intervals, respectively, whereas the NH4 + biotransformation appears to occur relatively uniformly throughout the whole 110cm column. The biotransformation kinetics of NH4 + in RGW and SGW, Mn2+ in RGW at different depths accords with the first order kinetics model, while Fe2+ in RGW and SGW, Mn2+ in SGW presented more complicated biotransformation process. The results should improve understanding of the transport and fate of common groundwater pollutants in riverbank filtration and other groundwater recharge environments.

Effect of riverbed sediment flushing and clogging on river-water infiltration rate: a case study in the Second Songhua River, Northeast China

Infiltration from natural rivers or streams is the most important source of aquifer recharge at riverbank filtration (RBF) sites. Due to the influence of river hydrological processes and changes in suspended solids in rivers, riverbed sediments often undergo significant flushing and clogging processes, which lead to obvious spatial and temporal changes in riverbed sediment permeability. Moreover, the lithology, structure, and thickness of natural riverbed sediments change with time, influencing the bank infiltration rate into groundwater. At present, how riverbed-sediment flushing and clogging influences the sediment hydraulic conductivity is not fully understood, which results in high uncertainty about the amount of water involved in RBF. An RBF site in the middle reach of the Second Songhua River, northeastern China, was studied, and continuous time series data of riverbed-sediment hydraulic conductivity were obtained for the first time. By identifying the hydrological conditions, using field monitoring, laboratory experiments and field tests, the mechanisms of change associated with sediment lithology, infiltration rate, and hydraulic conductivity during flushing and clogging processes were revealed.

Spatiotemporal evolution of iron and sulfate concentrations during riverbank filtration: Field observations and reactive transport modeling

Riverbank filtration is a commonly-used technology that improves water quality by passing river water through aquifers. In this study, a riverbank filtration site in Busan, South Korea, was investigated to understand the spatiotemporal evolution of high iron and sulfate concentrations observed in the riverbank-filtered water. Discrepancies between the nonreactive transport results and field measurements suggest that iron-sulfate-related geochemical reactions play a major role in the spatiotemporal evolution of the hydrochemical properties. Pyrite oxidation was hypothesized to be the main process driving the release of iron and sulfate. To test this hypothesis, a reactive transport model was developed, that implemented pyrite oxidation as a kinetic process and subsequent ferrous iron oxidation and ferric iron precipitation as equilibrium processes. The model accurately captured the temporal evolution of sulfate; however, iron concentrations were underestimated. Sensitivity tests revealed that adjusting reaction constants significantly improved the prediction of iron concentrations. The results of this study suggest that pyrite oxidation can affect the hydrochemistry of riverbank-filtered water and highlight the potential limitations of using theoretical reaction constants in field modeling applications.

Geohydraulic conditions and post-treatment at riverbank filtration sites in Eastern Europe

Managed aquifer recharge is gaining in importance worldwide. As there is not much information on bank filtration (BF) sites in Eastern Europe, a survey of geohydraulic conditions and post-treatment schemes carried out. Such information will make it possible to assess hydraulic conditions in the region and the commonly required post-treatment. Data were collected from publications, archival documentations, maps as well as through direct communication with administrators of relevant water companies. As a result, a summary of the data from 71 BF or BF/artificial recharge (AR) well fields in the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania, Russia, Serbia, Slovakia and Slovenia was prepared. Data on the source of water, location, capacity, aquifer thickness and hydraulic conductivity, and treatment methods were collected. Thirteen of the studied 71 RBF well fields are combined with AR. The most common type of BF in Eastern Europe is riverbank filtration (RBF) with wells located along a river. 56% of the analyzed sites are located along larger rivers such as the Danube, Drava, Nemunas, Neris, Odra, Volga, Warta and the Wisła. The smallest BF site has a discharge capacity of only 38 m3/day, the largest BF site 210,000 m3/day, while the smallest and the largest combined BF/AR site has a discharge capacity of 5,500 m3/day and 150,000 m3/day, respectively. The average values of aquifer thickness and hydraulic conductivity are 21 m and 2.7*10-3 m/s, respectively, at BF sites and 16 m and 5.7*10-4 m/s, respectively, at BF/AR sites. The most common post-treatment steps include aeration-filtration – disinfection, UV, ozone and activated carbon being used at many sites as well. The collected data can prove helpful in designing and modernizing BF sites, comparing and establishing direct contacts with water companies facing similar conditions. The outcome of this study is the built-up BF database for Eastern Europe, which can supplement the Global Inventory of Managed Aquifer Recharge Schemes (IGRAC 2017)

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.

Use of soil conservation service curve number and filtration coefficient approach for simulating Escherichia coli removal during river bank filtration

Water quality of River Tel and bank filtrate at Belgaon, India were studied for a period of 12 months to assess the effectiveness of river bank filtration (RBF). Escherichia coli(E. coli) were found to be successfully removed from surface water during river bank filtration. As limited work has been done regarding the use of two models i.e. Soil conservation service curve number (SCS-CN) approach and filtration coefficient (FC) approach for water quality modelling and monitoring, these models have been utilized to correlate the influent (source water) and effluent (filtrate water) concentration at Belgaon. The model indicates that filtration coefficient is linearly related to the natural logarithm of the influent concentration. CN is also found well correlated with the influent concentration variations. Both SCS-CN approach and filtration coefficient approach was also found well correlated with variations in the river water quality at other established RBF sites i.e. River Upper Krishna, Southern India and River Yamuna, Palla & Nizamuddin, Delhi. From the study it can be concluded that it is possible to simulate the observed filtrate effluent for E. coli quality using both SCS-CN and filtration coefficient approach.

Solute transport modelling to manage groundwater pollution from surface water resources

This article provides an analytical solute transport model to investigate the potential of groundwater contamination by polluted surface water in a two dimensional domain. The clogging of streambed which makes the aquifer partially penetrated by the stream, is considered in the model. The impacts of pumping process, hydraulic conductivity and clogging layer on the quality of water produced from nearby drinking water wells are evaluated. It is found that results are consistent with numerical simulation conducted by MODFLOW software. Moreover, the model is applied using data of contamination occurrence in Malaysia, where high contaminants concentrations are found close to streams. Results show that the pumping activities (rate and time period) are crucial factors when evaluating the risk of groundwater contamination from surface water. Additionally, this study illustrates that the increase in either hydraulic conductivity or leakance coefficient parameters due to the clogging layer will enlarge the area of contamination. The model is able to determine the suitable pumping rate and location of the well so that the contamination plume never reaches the extraction well, which is useful in constructing riverbank filtration sites.

New Methods for Microbiological Monitoring at Riverbank Filtration Sites

Water suppliers aim to achieve microbiological stability throughout their supply system by regular monitoring of water quality. Monitoring temporal biomass dynamics at high frequency is time consuming due to the labor-intensive nature and limitations of conventional, cultivation-based detection methods. The goal of this study was to assess the value of new rapid monitoring methods for quantifying and characterizing dynamic fluctuations in bacterial biomass. Using flow cytometry and two precise enzymatic detection methods, bacterial biomass-related parameters were monitored at three riverbank filtration sites. Additionally, the treatment capacity of an ultrafiltration pilot plant was researched using online flow-cytometry. The results provide insights into microbiological quality of treated water and emphasize the value of rapid, easy and sensitive alternatives to traditional bacterial monitoring techniques.

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.

The spatial variations of correlation between microbial diversity and groundwater quality derived from a riverbank filtration site, northeast China

To identify the relationship between microbial communities and groundwater quality parameters, especially typical groundwater contaminants including ammonium (NH4+), iron (Fe2+), and manganese (Mn2+), groundwater samples and aquifer media were collected from a riverbank filtration (RBF) site in Harbin city, northeast China. The structures of the microbial communities of aquifer media at different depths were illustrated through 16S rRNA sequencing using the Illumina MiSeq platform, and the correlation between microbial communities and water quality parameters was quantitatively demonstrated by redundancy analysis (RDA). The results revealed that the diversity of microbial communities decreased along the groundwater flow path at the south bank of Songhua river. The richness and diversity in the unsaturated zone (0–5 m) were significantly higher than those in the saturated zone (5–50 m) because of physiochemical properties of aquifer media and the redox environment in the RBF system. Core taxa, which were significantly related to the biotransformation behavior of iron, manganese, and ammonium, were Pseudomonas, Acinetobacter, Ochrobactrum, Sphingobium, and Sphingomonas. RDA results indicated that the critical physiochemical parameters that significantly influenced the composition of microbial communities were different in the saturated and unsaturated zones, and the total organic carbon (TOC), electrical conductivity (EC), nitrate (NO3−), and manganese (Mn2+) levels were the four principal factors affecting the function and composition of microbial communities in the whole RBF system. Proteobacteria, Sphingomonadales, and Sphingobium were the dominant bacteria at the phylum, order, and genus levels with 39.8%, 59.2%, and 65.3% contribution to the overall groundwater quality, respectively. The results obtained from this study should improve the understanding of the relationship between the structure of microbial communities (especially, bacteria related to the biotransformation of NH4+, Fe2+, and Mn2+) and physiochemical parameters.