Microplastic analysis in sediments of the Elbe River by electrostatic separation and differential scanning calorimetry.

This study presents the most extensive investigation of microplastic (MP) contents in sediment from the Elbe River. We employed electrostatic separation (ES) and differential scanning calorimetry (DSC) to overcome limitations of sample throughput and time-consuming analysis. In total 43 sediment samples were collected using a Van-Veen grab. Subsequently, coarse materials (d10 > 100 µm) and fine materials (d10 ≤ 100 µm) were enriched using ES and density separation. DSC was utilized for MP identification and quantification, based on the phase-transition signals of eight different polymers. MP presence was detected in 25 samples, with successful quantification in 12 samples. The MP content in coarse material samples from shoreline areas ranged from 0.52 to 1.30 mg/kg, while in fine material samples from harbor basins, it ranged from 5.0 to 44.6 mg/kg. The most prevalent polymers identified were LD-PE, HD-PE, PP, and PCL. These findings confirmed the suitability of DSC for analyzing MP in complex environmental samples. MP hotspots were identified in harbor basins, where natural sedimentation processes and increased anthropogenic activities contribute to MP accumulation. Additionally, industrial sewage potentially contributed to MP content in sediment samples. The highest pollution levels were observed in the middle Elbe, between the confluences of Mulde and Havel. Lowest MP contents were found in the lower Elbe, potentially influenced by tides. Future studies should focus on holistic investigations of selected river sections, encompassing sediment, water, and biota samples, rather than the entire catchment area. This approach would facilitate the generation of spatiotemporal data on MP distribution in freshwater streams. In addition, more research is needed to explore potential interactions between different MP and sediment types during DSC measurements.

Release of arsenic during riverbank filtration under anoxic conditions linked to grain size of riverbed sediments.

Geogenic arsenic contamination of groundwater poses a health threat to millions of people worldwide, particularly in Asia. Riverbank filtration (RBF) is a pre-treatment technique that aims to improve surface water quality through natural processes during water infiltration before abstraction. A study in Hanoi, Vietnam is presented, where the water quality of 48 RBF wells from 5 large well fields located in the Pleistocene aquifer along the Red River was analyzed. >80 % of the wells had arsenic concentrations above the WHO limit of 10 µg/l. The riverbed sediment and riverbed pore-water from 23 sites along a stretch of 30 km of the Red River near the well fields was also analyzed. Muddy riverbeds were found to be a hotspot for arsenic release. Already at a 30 cm depth from the riverbed sediment surface, the pore-water at many sites had high concentrations of arsenic (>100 µg/l). Arsenic concentrations in the pore-water of sites where mud lenses were present in the riverbed were significantly higher compared to sites with sandy riverbeds. At well fields along stretches of the Red River where riverbed was mostly muddy, higher arsenic concentrations were found than at well fields where the riverbed was mostly sandy. This indicates that river muds deposition and river morphology can influence arsenic concentrations in the aquifer in Hanoi and potentially other RBF sites in regions with geogenic arsenic contamination. At the end, recommendations regarding site selection of new potential RBF wells in affected regions is given.

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.

Sources and behavior of ammonium during riverbank filtration.

Ammonium is an undesirable substance in the abstracted water of riverbank filtration (RBF) schemes, due mainly to the complications it causes during post-treatment. Based on the investigation of case studies from 40 sites around the world, an overview of the sources and behavior of ammonium during RBF is given. Typical concentrations of ammonium in the bank filtrate (BF) are between 0.1 and 1.7 mg/l. The most common source of ammonium in BF is the mineralization of organic nitrogen occurring in the riverbed, while the most common sink of ammonium is nitrification in the riverbed. Ammonium surface water concentrations do not directly translate to abstracted concentrations. Transformations in the riverbed play a critical role in determining ammonium concentrations, whereby riverbeds with high amounts of organic material will have more electron donor competitors for oxygen, thus limiting ammonium attenuation via nitrification.

Sampling and processing methods of microplastics in river sediments - A review.

Microplastics (MP) in marine environments attract widespread attention due to their small particle size and potential hazardous impacts on aquatic and terrestrial ecosystems. Compared to marine sediments, knowledge about the occurrence of MP in freshwater sediments, especially in river sediments, is limited. Although MP concentrations in sediments and soils have been reported in a considerable number of studies, no standardized method is available for sampling and sample processing. Thus, a comparison of results is hardly possible. The present study reviews over 47 articles to evaluate reports of MP in river sediments and current sampling and processing techniques by highlighting various techniques, equipment and approaches for implementing quality assurance and quality control procedures. The authors emphasize that MP quantification techniques could lead to overestimation or underestimation depending on how sampling and sample processing is conducted. Standardization and harmonization of these techniques are crucial to underpin monitoring decisions aimed at safeguarding the ecological integrity of freshwater environments.

Economic evaluation of water supply systems operated with solar-driven electro-chlorination in rural regions in Nepal, Egypt and Tanzania.

Reliable data on the economic feasibility of small-scale rural water supply systems are insufficient, which hampers the allocation of funds to construct them, even as the need for their construction increases. To address this gap, three newly constructed water supply systems with water points in Nepal, Egypt, and Tanzania were accompanied by the authors throughout the planning and implementation phases and up to several years of operation. This study presents an analysis of their economic feasibility and suggests important factors for successful water supply system implementation at other rural locations. The initial investment for construction of the new water supply systems ranged from 23,600 € to 44,000 €, and operation and maintenance costs ranged from 547 € to 1921 € per year. The water price and actual multi-year average quantity of tapped water at each site were 7.7 €/m³ & 0.67 m³/d in Nepal, 0.7 €/m³ & 0.88 m³/d in Egypt and 0.9 €/m³ & 8.65 m³/d in Tanzania. Although the new water supply systems enjoyed acceptance among the consumers, the actual average water quantity tapped ranged from just 17 to 30 % of the demand for which the new supply systems were designed. While two of three sites successfully yielded a cash surplus through the sale of water, sufficient for operation, maintenance and basic repairs, no site showed a realistic chance of recovering the initial investment (reaching the break-even point) within the projected lifetime of the technical infrastructure. Reaching the break-even point within 5 years, which would be necessary to attract private investors, would require an unrealistic increase of the water price or the water consumption by factors ranging from 5.2 to 9.0. The economic viability of such systems therefore depends strongly on the quantity of water consumed and the water price, as well as the availability of funding from governments, NGOs or other sponsors not primarily interested in a financial return on their investment.

Disinfection for decentralized wastewater reuse in rural areas through wetlands and solar driven onsite chlorination.

Increasing water scarcity is of growing concern in Europe, especially in Mediterranean countries along coastlines. Wastewater reuse reduces water stress, but often requires the absence of pathogen indicators and the application of chlorine to assure residual disinfection. However, the effluent qualities of typical Wastewater Treatment Plants (WWTP) show immense chlorine demands. This makes the supply, handling and dosing of typical WWTP effluent challenging, especially in rural regions. In the work presented here, a vertical flow constructed wetland (VFCW) was combined with a small-scale solar-driven Onsite Chlorine Generation system (OCG) to further improve effluent qualities for different WWTPs and to produce chlorine stock solution directly at the site. To test different operational conditions the VFCW received WWTP effluent from a) an Activated Sludge and b) a High-Rate Algae Pond system. The VFCW reduced TSS by 92%, COD by 80%, and NH4 by over 99% and the chlorine demand by 85%. The log-unit reduction of the VFCW/OCG system reached ≥5.1 for total coliforms and ≥4.6 for E. Coli. During VFCW passage the already high electrical conductivity further increased to beyond permissible reuse limits due to high evapotranspiration (ET) rates of the planted vegetation Arundo donax. Unique aspects of this setup were that neither chemicals nor external electricity were required to run the system. The elevated chloride concentration of the treated WW (819 ± 132 mg/L) proved sufficient for the production of chlorine stock solution. However, the solar-driven OCG system tested here consumed considerably more electricity compared to other OCGs available on the market. Nevertheless, the system presented here may be considered an efficient disinfection alternative for decentralized WW reuse applications at remote sites with both limited access to grid electricity and strict requirements for pathogen indicators.

Arsenic Removal from Groundwater by Solar Driven Inline-Electrolytic Induced Co-Precipitation and Filtration-A Long Term Field Test Conducted in West Bengal.

Arsenic contamination in drinking water resources is of major concern in the Ganga delta plains of West Bengal in India and Bangladesh. Here, several laboratory and field studies on arsenic removal from drinking water resources were conducted in the past and the application of strong-oxidant-induced co-precipitation of arsenic on iron hydroxides is still considered as the most promising mechanism. This paper suggests an autonomous, solar driven arsenic removal setting and presents the findings of a long term field test conducted in West Bengal. The system applies an inline-electrolytic cell for in situ chlorine production using the natural chloride content of the water and by that substituting the external dosing of strong oxidants. Co-precipitation of As(V) occurs on freshly formed iron hydroxide, which is removed by Manganese Greensand Plus® filtration. The test was conducted for ten months under changing source water conditions considering arsenic (187 ± 45 µg/L), iron (5.5 ± 0.8 mg/L), manganese (1.5 ± 0.4 mg/L), phosphate (2.4 ± 1.3 mg/L) and ammonium (1.4 ± 0.5 mg/L) concentrations. Depending on the system setting removal rates of 94% for arsenic (10 ± 4 µg/L), >99% for iron (0.03 ± 0.03 mg/L), 96% for manganese (0.06 ± 0.05 mg/L), 72% for phosphate (0.7 ± 0.3 mg/L) and 84% for ammonium (0.18 ± 0.12 mg/L) were achieved-without the addition of any chemicals/adsorbents. Loading densities of arsenic on iron hydroxides averaged to 31 µgAs/mgFe. As the test was performed under field conditions and the here proposed removal mechanisms work fully autonomously, it poses a technically feasible treatment alternative, especially for rural areas.

Application of risk-based assessment and management to riverbank filtration sites in India.

This is the first reported study of a riverbank filtration (RBF) scheme to be assessed following the Australian Guidelines for Managed Aquifer Recharge. A comprehensive staged approach to assess the risks from 12 hazards to human health and the environment has been undertaken. Highest risks from untreated ground and Ganga River water were identified with pathogens, turbidity, iron, manganese, total dissolved solids and total hardness. Recovered water meets the guideline values for inorganic chemicals and salinity but exceeds limits for thermotolerant coliforms frequently. A quantitative microbial risk assessment undertaken on the water recovered from the aquifer indicated that the residual risks of 0.00165 disability-adjusted life years (DALYs) posed by the reference bacteria Escherichia coli O157:H7 were below the national diarrhoeal incidence of 0.027 DALYs and meet the health target in this study of 0.005 DALYs per person per year, which corresponds to the World Health Organization (WHO) regional diarrhoeal incidence in South-East Asia. Monsoon season was a major contributor to the calculated burden of disease and final DALYs were strongly dependent on RBF and disinfection pathogen removal capabilities. Finally, a water safety plan was developed with potential risk management procedures to minimize residual risks related to pathogens.

Interaction of Aquifer and River-Canal Network near Well Field.

The article presents semi-analytical mathematical models to asses (1) enhancements of seepage from a canal and (2) induced flow from a partially penetrating river in an unconfined aquifer consequent to groundwater withdrawal in a well field in the vicinity of the river and canal. The nonlinear exponential relation between seepage from a canal reach and hydraulic head in the aquifer beneath the canal reach is used for quantifying seepage from the canal reach. Hantush's (1967) basic solution for water table rise due to recharge from a rectangular spreading basin in absence of pumping well is used for generating unit pulse response function coefficients for water table rise in the aquifer. Duhamel's convolution theory and method of superposition are applied to obtain water table position due to pumping and recharge from different canal reaches. Hunt's (1999) basic solution for river depletion due to constant pumping from a well in the vicinity of a partially penetrating river is used to generate unit pulse response function coefficients. Applying convolution technique and superposition, treating the recharge from canal reaches as recharge through conceptual injection wells, river depletion consequent to variable pumping and recharge is quantified. The integrated model is applied to a case study in Haridwar (India). The well field consists of 22 pumping wells located in the vicinity of a perennial river and a canal network. The river bank filtrate portion consequent to pumping is quantified.

A dual isotope approach to identify denitrification in groundwater at a river-bank infiltration site.

The identification of denitrification in the Torgau sand and gravel aquifer, Germany, was carried out by a dual isotope method of measuring both the delta 15N and delta 18O in NO3-. Samples were prepared by an anion exchange resin method (Silva et al., J. Hydrol. 228 (2000) 22) with a modification to the AgNO3-drying process from a freeze-drying to an oven-drying method. The occurrence of denitrification in the aquifer was confirmed by comparing the reduction of dissolved oxygen, dissolved organic carbon and NO3- concentrations with the dual isotope signatures. High nitrate concentrations were associated with low delta 15N and delta 18O values, and vice versa. The denitrification accords with a Rayleigh equation with calculated enrichment factors of epsilon = -13.62@1000 for delta 15N and epsilon = -9.80@1000 for delta 18O. The slope of the straight-line relationship between the delta 15N and delta 18O data demonstrated that the enrichment of the heavy nitrogen isotope was higher by a factor of 1.3 compared with the heavy oxygen isotope. It is concluded that the identification of this factor is a useful means for confirming denitrification in future groundwater studies.