River bank filtration in tropical metropoles: integrated evaluation of physical, geochemical and biochemical interactions in Recife, NE Brazil.

The increasing need of sustainable technologies to produce domestic water in metropoles of developing countries faces socioenvironmental problems such as contamination, distribution network failures and water depletions due to overexploitation and climate changes. In this paper, a long-term (9 years) multiparameter evaluation of river bank filtration (RBF) was carried out in an urban and tropical environment in NE Brazil. RBF constitutes a promising way to mitigate adverse effects of unsustainable resource management, as it is adaptable to local needs and may limit non-renewable resource uses. Interannual monitoring of stream water and pumped groundwater allowed deciphering an efficient bacteriological (total disappearance of total and thermotolerant coliforms), physicochemical (general increase of COD/BOD ratio from 5 to 8 reaching 10 to more than 30, lowering of turbidity from 10–300 to 0 NTU) and drug attenuation (from 22 to 193 µg L⁻¹ to 9 µg L⁻¹ in the pumped groundwater for diclofenac and total disappearance of paracetamol most of the time). This suggests that RBF is relevant for local water supply: While socioenvironmental context implies great pressures over the resource, hydrological and hydrogeological conditions favor biodegradation performance, promoted by high temperatures (near 25 °C), and natural self-regulation. However, from a chemical point of view, low turbidity was associated with nitrate increase (reaching temporarily more than 40 mg L⁻¹) in the RBF well. This indicates that the great physicochemical/biochemical filtration potential may in turn favor a great biogeochemical reactivity involving redox processes of concern for domestic purposes in urban and tropical context and that adapted pumping schedule is necessary. [ABSTRACT FROM AUTHOR]