River Bank Filtration

Concept

Bank filtration (BF) is the abstraction of water from aquifers that are hydraulically connected to a surface water body, which is in most cases a riverine system. BF involves wells being established directly by the river used for water purification. By pumping from the wells, the groundwater table is lowered and the surface water infiltrates into the aquifer. As the surface water infiltrates into the aquifer, various physical, chemical and biological processes take place (Figure 1). Depending on the geological conditions, the distance between the wells and the river bank and the level of the river, water infiltration can last a few days or several months.

Vertical BF well in Düsseldorf Figure 1: Concept of riverbank filtration (Source: Hiscock & Grischek, 2002)

The attenuation of particles, organic and inorganic compounds through BF is site specific. Depending on the water quality targets, additional treatment may be necessary. In most cases, BF acts as a pre-treatment step in drinking-water production, while in some cases it can serve as the final treatment step just before disinfection (Tufenkji et al., 2002, Grischek & Ray, 2009).

Types

BF wells can be either horizontal (or radial collector wells - RCW) or vertical, depending on the site conditions and the choice of the competent utility (Figure 2).

Schematic of horizontal and vertical BF wells Figure 2: Water extraction along (horizontal wells) and beneath (vertical wells) a riverbed (Source: Ray et al., 2002)

The construction of RCW is more expensive compared to vertical wells, but RCW have greater production capacity.

The formation of a clogging layer within the riverbed is important for managing BF sites. Clogging is referred to as the reduction of riverbed permeability and is the result of the infiltration and accumulation of both organic and inorganic suspended solids, precipitation of carbonates, iron- and manganese- (hydr)oxides and biological processes. The recoverable amount of bank filtrate strongly depends on the infiltration resistance of the riverbed and the technically viable drawdown of the adjacent pumping wells. An infiltration rate of about 0.2 m3/(m2/d) is considered sustainable, based on long term experience from RBF sites in Europe with high organic load (DOC 5 – 10 mg/L) (Grischek & Bartak, 2016).

Function

Reduction of pollutant levels in BF is attained by physical filtering, sorption, microbial degradation, ion exchange and precipitation. In addition, dispersion of surface water pollutants in aquifers and further dilution of these pollutants with groundwater (where the respective concentrations are expected to be low) help reduce the pollutant concentrations of the pumped water.

Higher temperatures enhance biodegradation and promote the removal of oxygen, nitrate and Mn/Fe-hydr(oxides); many removal processes are redox dependent. The subsurface retention time is important for pollutant removal. Longer retention times result in higher pollutant removal rates. Aerobic redox conditions promote higher DOC degradation kinetics (Gruenheid et al., 2005). The interaction of the physical, hydro-geochemical and microbiological processes involved in BF is complex and water quality changes during BF, such as Fe/Mn dissolution, are difficult to predict (Grischek & Paufler, 2017).

BF can effectively remove various pollutants from surface water (Table 1), e.g.:
  • Organic micropollutants (around 80%);
  • Suspended solids ( -1 NTU);
  • Cell-bound toxins (e.g. microcystins) (reduction of >99% within the first meters);
  • DOC (24-50%), most efficient removal achieved in the oxic infiltration zone (adsorption+degradation);
  • NO3- (under anoxic conditions);
  • Heavy metals (Pb: up to 75%, Cd: 29-99%, Cu: 77-90%, Zn: 75-82%), through ion exchange and precipitation;
  • Pathogens (up to ≥ 5-log10) (see Table 1).

Table 1: Removal of Pathogens during BF

(Source: Huelshoff et al., 2009)

Pathogen

Removal efficiency
(measured / estimated)

Reference

Total Coliforms

≥ 5-log10

  • Schijven et al., (2002)
  • Weiss et al., (2005)
  • Dash et al., (2008)

Fecal coliforms

4-log10

  • Medema et al., (2000)
  • Dash et al., (2008)

Viruses

≥ 3-log10

WHO, (2002)

Protozoa

4-log10

WHO, (2002)
References & Sources for Further Reading
  • Dash, R. R., Mehrotra, I., Kumar, P., & Grischek, T. (2008). Lake bank filtration at Nainital, India: water-quality evaluation. Hydrogeol. J. 16(6), 1089–1099.
  • Grischek, T., & Bartak, R. (2016). Riverbed clogging and sustainability of riverbank filtration. J. Water, 8, 604, 1-12.
  • Grischek, T., & Paufler, S. (2017). Prediction of iron release during riverbank filtration. J. Water, 9, 317, 1-13.
  • Grischek, T., & Ray, C. (2009). Bank filtration as a managed surface-groundwater interaction. J. Water, 5(2), 125-139.
  • Gruenheid, S., Amy, G., & Jekel, M. (2005). Removal of bulk dissolved organic carbon (DOC) and trace organic compounds by bank filtration and artificial recharge. Water Resources, 39(14), 3219-3228.
  • Hiscock, K. M., & Grischek, T. (2002). Attenuation of groundwater pollution by bank filtration. J. Hydrol., 266(3-4), 139-144.
  • Medema, R. H., Kops, G. J., Bos, J. L., & Burgering, B. M. (2000). AFX-like Forkhead transcription factors mediate cell-cycle regulation by Ras and PKB through p27kip1. Nature, 404(6779), 782-787. doi: 10.1038/35008115.
  • Ray, C., Melin, G., & Linsky, R. B. (2002). Riverbank filtration-Improving source-water quality. Netherlands: Springer.
  • Sandhu, C., & Grischek, T. (2012). Riverbank filtration in India – using ecosystem services to safeguard human health. Wat. Sci. Technol., 12(6), 783-790.
  • Schijven, J. F., Hassanizadeh, S. M., & de Bruin, R. H. A. M. (2002). Two-site kinetic modeling of bacteriophages transport through columns of saturated dune sand. Journal of Contaminant Hydrology, 57(3), 259-279. doi: https://doi.org/10.1016/S0169-7722(01)00215-7.
  • Tufenkji, N., Ryan, J. N., & Elimelech, M. (2002). The promise of bank filtration: A simple technology may inexpensively clean up poor-quality raw surface water. Environ. Sci. Technol., 36(21), 422A-428A.
  • Weiss, W. J., Bouwer, E. J., Aboytes, R., LeChevallier, M. W., O’Melia, C. R., Le, B. T., & Schwab, K. J. (2005). Riverbank filtration for control of microorganisms: Results from field monitoring. Water Res, 39(10), 1990-2001. doi: https://doi.org/10.1016/j.watres.2005.03.018.
  • WHO, World Health Organization. (2002). Reducing risks, promoting healthy life. Geneva: WHO.

If you want to learn more about Bank Filtration click here ...

Style Switcher
Theme Colors
Theme Skins

Layout Styles