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RBF

NASI UK

River bank Filtration

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River Bank filtration as an alternative to direct surface water abstraction

Process of bank filtration: Riverbank filtration (RBF) or simply bank filtration (BF) is an established technique to enhance aquifer recharge from the surface water by constructing the abstraction wells in the vicinity of natural surface water bodies (mainly rivers and sometimes also lakes)..

The process of bank filtration is initiated by the lowering of the groundwater, which causes surface water to flow through the permeable river bed and bank or lake bed into the aquifer as a result of the difference in water levels, provided that no artificial or natural barriers to this subterranean flow exist (viz., brick or concrete line river, canal or lake bed, or a low hydraulic conductivity layer like clay).This flow may be the direct result of an influent river under natural conditions or be induced by groundwater abstraction wells (tube wells). These wells extracting bank filtrate can be vertical (e.g. typically called "tube wells'' in India)or horizontal(Collector well). Ground-and surface water levels, geologic data pertaining to the aquifer and river bed and hydro geological modelling help in describing flow conditions during bank filtration. Before implementing RBF technology, it is necessary to conduct a detailed hydro geological pre-investigation. Purification during bank filtration strongly depends on environmental conditions, well design, and location at bank, well operation, travel time, runoff regime, surface and ground water qualities. The porous media serves as a natural filter and also biochemically attenuates potential contaminants present in the surface water. The formation of a layer within the riverbed that has reduced hydraulic conductivity due to clogging from the input of fine sediment particles, microorganisms and colloids, precipitation of iron and manganese oxy-hydroxides and calcium carbonates as well as formation of gas bubbles is a significant factor affecting the volume of bank filtrate derived. Intensive biodegradation and sorption of contaminants also occur in this layer. The permeability of such clogged portions of the river bed varies with fluctuating surface flows, thereby influencing the volume of bank filtrate and cannot be considered constant.
Quantitative management of bank filtration systems requires information on :

  • Surface water hydrology and river bed stability.
  • Groundwater catchment and surface water infiltration zones.
  • Mixing proportions of surface and ground water in the abstracted raw water.
  • Flow paths and flow velocities of the bank filtrate
  • Surface water quality.

Water quality improvements of bank filtration

An improvement in physical, chemical and biological water quality parameters through the underground passage from the surface water body to the abstraction well demonstrates the efficiency of RBF. Compared with surface water abstraction, bank filtration with its effective natural attenuation processes has the following advantages:
  • Removal of particles and turbidity, bacteria, viruses and parasites
  • Attenuation of biodegradable organic compounds, especially dissolved organic carbon and trace organics(e.g. pesticides, hydrocarbons, algae toxins, pharmaceuticals).
  • Equilibration of temperature changes and of concentrations of dissolved constituents in the bank filtrate
  • Partial attenuation of absorbable compounds.
  • Even under sub-optimal retention time and flow-path lengths, bank filtration is likely to mitigate the adverse impacts on public health.

Application of bank filtration

In Europe, bank filtration has been a common practise for more than 130 years and for instance today it provides almost 70% of the drinking water supply for the city of Berlin itself. Until now bank filtration has been successfully implemented in the countries like Austria, India, Germany, Netherlands, United Kingdom, United States, Serbia Etc. However,due to an increased understanding of the various advantages of bank filtration, RBF is now becoming increasingly popular in the United States ,Brazil, Russia, India, Srilanka, Egypt and countries in South East Asia such as Thailand. Meanwhile in growing economies like Brazil, Columbia, India and other countries in South and South East Asia, North Africa, RBF can be a low-cost option for increasing the security of safe drinking water as its potential has not yet been fully explored.
In many regions of India, various factors have lead to unsustainable management of water resources. As a consequence, conventional surface water abstraction treatment now requires high levels of technology and high investment. In Uttarakhand the variation in surface water quality is large. The implementation of RBF will ensure affordable access to safe drinking water. The immediate benefits would be a reduction of medical cost: For instance, various other advantages from the use of RBF can be well appreciated from the literature, some of which are listed as follows:
  • Reduced carbon foot print if a renewable energy system is integrated with the RBF wells.
  • RBF can help to reduce the use of chemicals and accumulation of Disinfection by-products in drinking water.
  • Removal of pathogens like bacteria, viruses and protozoa.
  • Ensured riverbank storage for water which his less vulnerable to draught or high flood events.
  • Lower maintenance compared to the conventional treatment methods due to RBF at least serving as a pre-treatment step in the drinking water treatment system.

Objectives and Deliverables

Objectives
The objectives of this project, as stated in the project proposal ,are
  • The development of RBF in hill-regions of Uttarakhand, for the eventual wider replication in hill region across India, as a low-cost domestic water(pre-) treatment technology to remove turbidity and microbial pathogens(bacteria, viruses and protozoa)in source water for drinking.
  • To formulate concepts for quick identification and selection of sites suitable for using RBF for drinking water supply in specified locations of Uttarakhand State.
  • To identify prospects and limitations for the application of RBF under hilly conditions in India for wider replication throughout the country.
  • To start pilot-scale RBF systems for drinking water supply at five locations in Uttarakhand to conduct hydro geological and water quality investigations for obtaining data to meet above objectives.
  • To couple the objectives to a project "Development of tools and services for safe drinking water supply via bank filtration during extreme floods and monsoon"submitted by partners of the Cooperation Center for Riverbank Filtration under the first call for proposals of the newly created Indo-German Science and Technology Center(IGSTC).

Deliverables

The deliverables of this project, as stated in the project proposal, are:
  • To demonstrate the application and awareness of RBF Technology to pump water from the river bank instead of direct abstraction of surface water for domestic use
  • After completion of the project, to prepare a manual on application of RBF technology in hill-regions
  • To prepare information material and publications
  • To create permanent infrastructural establishments for the supply of bank filtrate for drinking water at five sites in Uttarakhand.
  • To create national and international linkages with universities, institutes and companies for collaborative research and to utilize the low cost RBF technique for potable water.

RBF Project in R&D Achievements

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