Natural and sustainable filtration of polluted water of River Yamuna for municipal use

River Yamuna in Delhi is facing severe degradation due to insufficiently treated wastewater entering into it from industries and local communities. Despite the efforts being made to restore the river water quality through the Yamuna Action Plan phase I and II (YAP), river water quality has not been improved. The objective of the present study was to assess the changes in water quality during natural and sustainable bank filtration of contaminated river water. To meet the objective, water samples from the Yamuna River and eight Ranney wells (RWs) were analysed in the non-monsoon and monsoon seasons. The proportion of the bank filtrate drawn by the RWs was determined by monitoring δ 18 O and δ 2 H, the stable isotopes of the water samples. An attempt was made to establish the hydraulic connectivity between the river and RWs using δ 18 O data. Despite turbidity of > 1500 NTU in river water, particularly during the monsoon, the goal of achieving a prescribed limit of turbidity (< 5 NTU) through riverbank filtration (RBF) is attainable. RBF was very useful for removal of organics. Even in case of source waters affected by wastewaters (non-monsoon average DOC > 15 mg/L), attenuation of DOC < 2 mg/L in RWs is possible. The same trend of removal was followed by ultraviolet absorption at 254 nm (UV-254) and specific UV absorbance (SUVA). E.coli and total coliform were reduced by > 4-log (base 10). However, in the case of source waters rich in organics, production of coliform-free filtrate does not seem to be a realistic target. Post-treatment of filtrate is a must. The study concludes that even in the case of polluted raw water sources, the value of RBF as an effective natural pre-treatment step cannot be undermined. Graphical abstract