Attenuation of bacteria at a riverbank filtration site in rural India

A riverbank filtration (RBF) system was installed in a rural village near the Kali River in southwestern India to evaluate its performance in attenuating total coliform bacteria and Escherichia coli loads in a monsoon-dominated climate in a developing country. A statistical analysis showed that RBF water was of higher microbial quality than other water sources in the study area. Based on the geometric mean of the data from the primary RBF well (MW3), the percent removal compared to the Kali River was 95.1% for total coliforms and 99.2% for E. coli. The maximum percent removals were 99.8% for total coliforms and 99.96% for E. coli. Bacteria concentrations were lower during the dry season than during the monsoon season when contaminants apparently infiltrated into the subsurface. The geometric mean of the annual removal efficiency translates to an approximately 1-log unit removal of E. coli per 26 m (≈75 ft) setback distance from the river. During the 1-year monitoring period, Indian water quality standards for total coliform bacteria were regularly exceeded, whereas E. coli standards were met for 29% of the dry season but only 7% of the monsoon season. The consistent problem of attaining local regulatory limits for bacteria show that, at this study site, (1) RBF needs to be considered a pre-treatment method and, (2) should be combined with conventional disinfection technology. Finally, although the bacteria data confirms that the setback distance of a RBF well from a river is an important factor determining the water quality, local conditions, such as influence of flood-irrigation of nearby rice paddies, presence of freely-roaming cattle and latrines, and outside defecation by residents, must be considered when establishing a RBF system in a monsoon climate in a developing country