Bank filtration: Application in rural areas. Case studies in Santa Catarina, Brazil.

Abstract

Bank filtration consists of abstraction of water from pumping wells located at the banks of alluvial aquifers or unconsolidated soils hydraulically connected to rivers, lakes and reservoirs. In this study bank filtration was applied in an aquaculture lake and in the river Itajai do Sul, both located in Ituporanga-SC, Brazil. In both sites, production wells were installed and hydrogeological and water quality tests were performed. The microbiological analysis indicated average removal of total coliforms of 1.77 log and 2.04 log in bank-filtered water produced from the lake and the river respectively. The average E. coli reductions were 2.15 log in the lake site and 2.97 log in the river. The lake water turbidity increased from 15.4±10 to 87±47 NTU which is probably due to an intermittent operation of the well and the local soil properties. Furthermore, the bottom of the lake presented a clogging layer that limited the production of water coming from the lake. The concentration of carbofuran pesticide was less in the bank filtrated water than in the Itajai do Sul River water. The pesticide was reduced by approximately 60%: from 0.339±0.087 µg/L in the river water to 0.130±0.050 µg/L in the well. This concentration complies with the stricter regulation of the European Union (0.1 µg/L). The removal of the carabofuran may involve principally chemical and biological degradation that may produce by products that should also be monitored. The bank filtrate river water presented improvement in some other parameters like turbidity. However, both sites presented iron released from the subsoil. This problem can be solved by a subsequent aeration and precipitation step treatment. The study demonstrates the possibilities of bank filtration as an alternative for the removal of pesticides in surface water as well as the importance of the hydraulic connectivity between the water body and the abstraction well.