Database of relevant pollutants in urban areas and their attenuation at RBF sites. Deliverable 1.1

Zusammenfassung

Until around 2004, the term riverbank filtration (RBF) or simply bank filtration (BF, a unified term for river and lake bank / bed filtration) was not commonly used in context to drinking water supply in India. The abundant recharge of traditional dug wells (used for drinking and irrigation) located near surface water bodies (mainly rivers but also some lakes) by very low-turbidity water via natural bank filtration during and after the monsoon has been recognised in India for a very long time. Induced bank filtration has been suggested in the 1970s to address the growing agricultural irrigation demand in the alluvial plains along the Ganga River by inducing recharge from surface water bodies during and after the monsoon (Chaturvedi and Srivastava 1979). Documented evidence till date suggests that induced bank filtration has been used in India for at least 56 years, although even older BF systems may exist. In Nainital, bank filtrate has been abstracted from Nainital Lake since 1956 (Kimothi et al. 2012). BF supplements existing surface and groundwater abstraction for drinking water supply in the cities of Ahmedabad (by the Sabarmati River), Delhi and Mathura (Yamuna) and Nainital (Nainital Lake); on the other hand in Haridwar and Patna (Ganga), and Medinipur and Kharagpur (Kangsabati), BF is used as an alternative to surface water abstraction and to supplement groundwater abstraction (Sandhu et al. 2012). Considering the continuously growing demand for drinking water in sufficient quantities, the emphasis at many BF sites has traditionally been on maximising the volumes of raw water abstracted. Furthermore, the results of a fact-finding study (Ray and Ojha 2005) on the use of BF for drinking water production in India on one hand confirmed that a number of river-side communities have been already using BF for a long time, but that on the other hand only scarce information on the hydrogeological conditions and water quality of these BF sites existed. Holistic investigations on water quality aspects and sustainability (qualitative and quantitative) of these existing BF sites began only after 2004. Water quality investigations conducted at the BF sites of Srinagar by the Alaknanda river (Ronghang et al. 2011), Haridwar and Nainital (Dash et al. 2008, 2010; Sandhu et al. 2011a), Delhi (Sprenger et al. 2008; Lorenzen et al. 2010) and Mathura (Singh et al. 2010; Kumar et al. 2012) and Patna (Sandhu et al. 2011b) showed that the main advantage of using BF in comparison to direct surface water abstraction lies in the removal of pathogens and turbidity. The surface water concentration of trace organic contaminants and their removal at the investigated sites has not been widely investigated, but has shown to be high at sites in Delhi and Mathura (Sprenger et al. 2008; Singh et al. 2010). For conventional treatment, high concentrations of organic contaminants requires high (40–60 mg/L) doses of chlorine prior to flocculation thus creating a greater risk for formation of carcinogenic disinfection by-products, as reported in Mathura (Singh et al. 2010; Kumar et al. 2012). In such situations BF is advantageous as a pre-treatment in order to reduce the necessary doses of chlorine prior to flocculation. Additional advantages of BF may also be seen during the monsoon season principally in the removal of turbidity and pathogens, as well as in the removal of color and dissolved organic carbon (DOC), UV absorbance, turbidity, total and thermotolerant coliform counts, endocrine disruptor compounds and organochlorine pesticides (Dash et al. 2008, 2010; Sandhu et al. 2011a; Thakur et al. 2009a, 2009b; Sprenger et al. 2011; Mutiyar et al. 2011). BF, however, does not present an absolute barrier to other substances of concern (e.g. ammonium) and some inorganic trace elements may even be mobilized. This has been observed in Delhi which has poor surface water quality (Sprenger et al. 2008), at which extensive post-treatment is applied to remove high levels of ammonium. The objective of this deliverable is to provide an overview of known BF schemes in urban areas of India where the abstraction of bank filtrate is intentional. The main water quality issues of concern are highlighted. Related published and unpublished data, as well as new data collected since the commencement of the Saph Pani project in October 2011, is presented for the BF schemes in Haridwar, Nainital, Srinagar (by the Alaknanda river in Uttarakhand), Delhi Mathura and Satpuli (by the Eastern Nayar river in Uttarakhand).

Publikation
Kompetenzzentrum Wasser Berlin gGmbH
Sprenger, C.
Sprenger, C.
Researcher