Bank filtration (BF) is a drinking water pre-treatment step, where river water is induced to percolate in subsurface passage through a river bed and mix with ambient (or natural) groundwater, before being extracted through a pumping well adjacent to the river bed. It can be applied as first step within a multi-barrier approach in an overall treatment chain where groundwater quantity is insufficient or of poor quality (e.g. geogenic pollution).
The contents of this factsheet are results of the Indo-European Project NaWaTech- “Natural Water Systems and Treatment Technologies to cope with Water Shortages in Urbanised Areas in India”, co-financed by the EC and the DST – India.
Design and construction principles
During subsurface passage in biologically active soil layers (with aerobic, anaerobic and anoxic milieus), water quality of surface water can be improved before being mixed with groundwater and extracted for use. BF systems involve several physical, chemical and biochemical processes and are particularly known for the efficient reduction/removal (or even elimination) of suspended solids, organic pollutants, microorganisms, heavy metals, nitrogen, toxic algae as well as organic trace compounds (e.g.: pharmaceutical products), salinity or taste- and odour causing compounds (RAKESH et al. 2010; SPRENGER et al. 2006; HUELSHOFF et al. 2009b).
Relying on natural processes, design and treatment capacity (and efficiency) of BF systems strongly depends on local circumstances such as quality and quantity of available river- and ground water, hydraulic residence times of the water in the soil, the porosity of the soil, the hydraulic potential of the aquifer, temperature, pH values and oxygen concentrations as well as underlying redox processes (SCHMIDT et al. 2003; ZIEGLER 2001). Depending on the bank filtrate quality, disinfection or even supplementary treatment steps are necessary to achieve drinking water quality. Besides its polishing function, BF also provides huge fresh water storage capacity for buffering extreme climatic conditions and shock loads (HUELSHOFF et al. 2009a&b; SHARMA & AMY 2009; SCHMIDT et al. 2003), but also represents an artificial groundwater recharge technique preventing the overuse of aquifers, saltwater intrusion and land subsidence (NRMMC 2009).
Operation and maintenance
Basic requirements for the operation of a BF system are the availability of surface water as primary water source and a detailed consideration of the groundwater level in the surroundings of the abstraction well. Water abstraction should not result in adverse effects on the aquifer or the river downstream of the site. Depending on the BF site’s characteristics and purpose of the output water, operation of a BF system is easy and only little maintenance is needed (HUELSHOFF et al. 2009a; HISCOCK & GRISCHEK 2002). Compared to high-end technologies, requirements for skilled labour and energy & chemical use are very low (RAY et al. 2002; ZIEGLER 2001). However, more requirements may arise in relation to design, operation and maintenance of the water abstraction well. One challenge in relation to well operation is the prevention/handling of colmation of the infiltration path.
Costs for establishing riverbank filtration systems depend on many factors, including aquifer characteristics, type of well-screen installation, facility design, and distance to the population served. However, costs can be classified as moderate. Using natural treatment processes, BF system can be considered as cost-effective system, which ideally can reduce costs for subsequent treatment steps (SCHMIDT et al. 2003). Additional costs can arise in dependency of raw-water quality and continuative treatment steps for diverging intended purpose (e.g. drinking water use).
Investment costs are costs for the abstraction well (construction, pump, main, control system etc.) as a minimum, as well as costs for groundwater monitoring of BF processes and water quality. Operational costs are primarily costs for pumping electricity for abstraction well operation. For abstraction (and treatment) facilities skilled personal is required.
Experiences in Europe and other cities of the world
For many decades Bank Filtration has been used in Europe and the United States for drinking water supply in communities located on river banks, applying both large-scale schemes involving high-tech extraction methods (providing water for central water supply entities) as well as low-tech household-based schemes. In Germany, more than 300 water works use BF producing about 16% of the German drinking water. Along the Danube River large-scale BF-systems exist in all major cities like Vienna (Austria), Bratislava und Gabicikova (Slovakia), Budapest (Hungary) and Belgrad (Serbia). About 50% of the public drinking water supplies in Slovakia and about 45% in Hungary are provided through BF (HISCOCK & GRISCHEK 2002). Production capacities are varying significantly not only depending on the productivity of the aquifer, but also on the type and number of extraction wells used. In Vienna, for example, up to 2.000 L/s are extracted with BF from the Danube using a total of 13 radial collector wells and 11 vertical filter wells.
In Central Europe, increasing chemical pollution, high concentrations of ammonia, organic compounds and micro-pollutants in the river water called for the introduction of supplementary pre- and post-treatment steps to build up a multi-barrier system (e.g. granular activated carbon filters, often combined with isolation and filtration) (SCHMIDT et al. 2003). SANDHU et al. (2011) emphasised on the necessity to be aware of the severe differences in the geological, hydrogeochemical, hydrological and river morphological characteristics of river systems, when transferring experiences from Europe to India. Thus, design and operation of BF systems should not only use adapted well designs, but also take into account prevalent cultural and operational constraints.
Experiences in India
SANDHU et al. (2011) investigated the potential of riverbank filtration for drinking water supply in India based on experiences with operating large-scale riverbed filtration schemes in the cities of Ahmedabad, Delhi, Haridwar, Mathura, Medinipur and Kharagpur, Nainital, Patna and Srinagar. Large diameter caisson wells, vertical filter wells, radial collector wells and small-scale radial collector wells are used for water abstraction with production capacities ranging from 29 m3/day to up to 110.000 m3/day. Reported travel times of the bank filtrate range from min. 2 to max. 100 days. BF proved to be advantageous as pre-treatment in situations with high concentrations of organic compounds. Also the removal of pathogenic microorganisms, colour and dissolved organic carbon, UV absorbance, turbidity, total and faecal coliform counts during monsoon season could be observed. All investigated examples proved to sustain their treatment efficiency. They conclude that BF has a great potential for improving both quality and quantity of many water supplies throughout the country.
In cities where BF is already applied, the BF process is accepted as purification treatment step in combination with – compared to other supply systems – much more limited post-treatment chlorination or ozonation (SANDHU et al. 2011; SINGH et al. 2010). SANDHU et al. (2011) identified a number of feasibility issues such as sufficient flow in rivers, protection of landside groundwater from contamination, high arsenic concentrations at shallow depths, insufficient scouring of riverbed and removal of the clogging layer due to heavily regulated surface flows and discontinuous well operation due to lack of continuous electricity supply or electricity saving measures.
Facing increasing quantities of insufficiently treated wastewater being discharged into rivers, the authors propose to preferably locate BF systems upstream of big cities to minimise the risk of landside groundwater contamination. Moreover, attention should be paid to private production wells and unmonitored pumping resulting in decline of the groundwater level (e.g. as been observed in Delhi). LORENZEN et al. (2010) propose to accompany planning and operation of BF sites by ﬁeld studies on a local scale to optimise the systems in accordance with local conditions (e.g.: observing content of undesired substances, obtain the desired shares from each source and attenuate contaminant concentrations).
Hydrogeological investigations are pointed out to be essential, not only to assess hydraulic parameters but also to evaluate the risk of contamination by different substances and to understand the contributing processes. Water levels and quality in surface water should be monitored throughout the first year at least, to identify temporal and spatial variations in the interaction zone of surface water and groundwater. Temperature logging is proposed as relatively easy and cheap method that may reveal valuable information on the ﬂow regime.
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|The research leading to these results has received funding from the European Union Seventh Framework Programme ([FP7/2007-2013]) under Grant Agreement N°  and the Department of Science and Technology of the Government of India DS.O DST/IMRCD/NaWaTech/ 2012/(G).
Analysis of the Vulnerability of Bank Filtration Systems to Climate Change by Comparing Their Effectiveness Under Varying Environmental Conditions
This technical paper explains the vulnerability of bank filtration systems to climate change like the effect of changing temperature or raw water quality and quantity. It also features a case study from Berlin, Germany, where 60% of the water abstracted from wells is due to bank filtration schemes.HUELSHOFF, I. GRESKOWIAK, J. GRUETSMACHER, G. (2009): Analysis of the Vulnerability of Bank Filtration Systems to Climate Change by Comparing Their Effectiveness Under Varying Environmental Conditions. Unknown: Techneau URL [Accessed: 04.03.2019] PDF
Relevance and Opportunities of Bank Filtration to Provide Safe Water for Developing and Newly-industrialised Countries
This report gives an overview of the opportunities that BF provides for developing and newly-industrialised countries. The information should support these countries in evaluating whether BF constitutes an attractive supplement or even alternative to their water supply system.HUELSHOFF, I. GRESKOWIAK, J. WIESE, B. GRUETSMACHER, G. (2009): Relevance and Opportunities of Bank Filtration to Provide Safe Water for Developing and Newly-industrialised Countries. Unknown: Techneau URL [Accessed: 04.03.2019] PDF
In the densely populated semi-arid territory around Delhi, the water demand is rising continuously, while the surface- and groundwater resources are threatened by contamination and over exploitation. This is a typical scenario in many newly industrialising and developing countries, where new approaches for a responsible resources management have to be found. Bank ﬁltration holds a great potential, thus being a low tech method and beneﬁting from the storage and contaminant attenuation capacity of the natural soil/rock. For this study, three ﬁeld sites have been constructed to investigate bank ﬁltration in different environments in and around the megacity with a main focus on inorganic contaminants. Hydraulic heads, temperature gradients and hydrochemistry of surface water and ground water were analysed in three different seasons. Depending on site-speciﬁc conditions, distinct hydrogeological conditions were observed and both positive and negative effects on water quality were identiﬁed. Most concerning issues are the impact of anthropogenic ammonia, the mixing with ambient saline groundwater and the mobilisation of arsenic during the reductive dissolution of manganese- and iron-(hydr)oxides. Positive aspects are the dilution of contaminants during the mixing of waters from different sources, the sorption of arsenic, denitriﬁcation, and the precipitation of ﬂuoride under favourable conditions.LORENZEN, G. ; SPRENGER, C. ; TAUTE, T. ; PEKDEGER, A. ; MITTAL, A. ; MASSMANN, G. (2010): Assessment of the Potential for Bank Filtration in a Water-stressed Megacity (Delhi, India). In: Environmental Earth Sciences: Volume 61 , 1419-1434. URL [Accessed: 18.03.2015]
This publication is one of the three modules that comprise the second phase of the Australian Guidelines for Water Recycling, which address health and environmental risks associated with water recycling. The guidelines as a whole, including this module, are designed to provide an authoritative reference that can be used to support beneficial and sustainable recycling of waters generated from sewage, grey water and stormwater, which represent an underused resource. The guidelines describe and support a broad range of recycling options, without advocating particular choices. It is up to communities as a whole to make decisions on uses of recycled water at individual locations. The intent of these guidelines is simply to provide the scientific basis for implementing those decisions in a safe and sustainable manner.NRMMC Biotext (2009): Australian Guidelines for Water Recycling: Managing Health and Environmental Risks (Phase 2). Managed Aquifer Recharge. (= National Water Quality Management Strategy Document , 24 ). Canberra: Natural Resource Management Ministerial Council, Environment Protection and Heritage Council, National Health and Medical Research Council URL [Accessed: 18.03.2015]
What is Riverbank Filtration? The purpose of this book is to show that riverbank filtration (RBF) is a low-cost and efficient alternative water treatment for drinking-water applications. There are two immediate benefits to the increased use of RBF: Minimized need for adding chemicals like disinfectants and coagulants to surface water to control pathogens. Decreased costs to the community without increased risk to human health.RAY, C. ; MELIN, G. ; LINSKY, R.B. (2002): Riverbank Filtration. Improving Source-Water Quality. (= Water Science and Technology ). Dordrecht: Kluwer Academic Publishers
Riverbank filtration (RBF) has been used for many decades in Europe and the United States to provide drinking water to communities located on riverbanks. In India, the development of RBF has the potential to provide drinking water to many cities located on the Ganga Plains currently using surface water as a source for their public water supply. Water diversion for irrigation and discharge of wastewater to rivers with extremely low flows has aggravated the water supply situation for many Indian cities using surface water. A number of Indian cities, with source waters of significantly varying quality, are already using RBF. In most of these cities no significant additional treatment is provided to the filtrate for their water supply. The objective of this article is to examine selected operating bank filtration sites in India (that have been investigated since 2005) and to elucidate additional potential RBF sites based on water problems and hydrogeologic suitability. A summary of selected operational RBF systems in Ahmedabad, Delhi, Haridwar, Mathura, Medinipur and Kharagpur, Nainital, Patna and Srinagar and their ability to produce potable water is provided. Analysis of the suitability of RBF for Allahabad, Bhubaneswar, Guwahati, and Vijayawada, based on hydrogeology and land use, is also provided.SANDHU, C. ; GRISCHEK, T. ; KUMAR, P. ; RAY, C. (2011): Potential for Riverbank Filtration in India. In: Clean Technologies Environmental Policy: Volume 13 , 295-316.
Based on the results of two feasibility studies conducted in Malawi and Kenya, this paper explains the potentials and constraints of promoting the bank filtration technology for water treatment in developing countries.SHARMA, S.K. AMY, G. (2009): Bank Filtration – A Sustainable Water Treatment Technology for Developing Countries. (= 24th WEDC International Conference, Addis Ababa, Ethiopia ). Delft: UNESCO-IHE URL [Accessed: 24.08.2011]
The impact of riverbank filtration (RBF) on the treatment of water from the River Yamuna at Mathura, which has disagreeable visual properties, has been investigated. The dissolved organic carbon (DOC) and colour of the river water were 4.0–6.8 mg/L and 40–65 colour units (CU), respectively. Pre-chlorination is in practice to improve raw water quality. Chlorine doses as high as 60 mg/L ahead of the water treatment units reduced colour by about 78%. Removal of DOC and UV-absorbance was less than 18%. In comparison to direct pumping of the river water, collection of water through RBF resulted in the reduction of DOC, colour, UV-absorbance and fecal coliforms by around 50%. However, riverbank filtrate did not conform to the drinking water quality standards. Therefore, riverbank-filtered water along with the Yamuna water were ozonated for different durations. To reduce DOC to the desired level, the dose of ozone required for the riverbank filtrate was found to be considerably less than the ozone required for the river water. RBF as compared to direct pumping of Yamuna water appears to be effective in improving the quality of the raw water.SINGH, P. ; KUMAR, P. ; MEHROTRA, I. ; GRISCHEK, T. (2010): Impact of Riverbank Filtration on Treatment of Polluted River Water. In: Journal of Environmental Management: Volume 91 , 1055-1062.
Occurrence and Fate of Microbial Pathogens and Organic Compounds at Riverbank Filtration Sites in Delhi, India
This report provides an overview of pathogen and organic trace compound content in water samples from three riverbank filtration (RBF) sites in Delhi, India. Based on the microbial results given in this report and the literature reviewed, it is concluded that RBF effectively reduces (indicator) bacteria and viruses even when the surface water is heavily polluted with pathogens.SPRENGER, C. LORENSEN, G. PAKDEGER, A. (2006): Occurrence and Fate of Microbial Pathogens and Organic Compounds at Riverbank Filtration Sites in Delhi, India. Unknown: Techneau URL [Accessed: 04.03.2019] PDF
About 75 % of Berlin's drinking water is bank filtrate or artificially recharged groundwater. At the same time, Berlin's treated wastewater is being discharged partially upstream of bank filtration sites.ZIEGLER, D.H. (2001): Untersuchungen zur nachhaltigen Wirkung der Uferfiltration im Wasserkreislauf Berlin. Dissertation. Berlin: Fakultät III - Prozesswirtschaften der Technischen Universität Berlin
Compendium of Natural Water Systems and Treatment Technologies to cope with Water Shortages in Urbanised Areas in India
The Compendium of NaWaTech Technologies presents appropriate water and wastewater technologies that could enable the sustainable water management in Indian cities. It is intended as a reference for water professionals in charge of planning, designing and implementing sustainable water systems in the Indian urban scenario, based on a decentralised approach.BARRETO DILLON, L. ; DOYLE, L. ; LANGERGRABER, G. ; SATISH, S. ; POPHALI, G. (2013): Compendium of Natural Water Systems and Treatment Technologies to cope with Water Shortages in Urbanised Areas in India. Berlin: EPUBLI GMBH URL [Accessed: 11.12.2015]