Bank filtration in a coastal lake in South Brazil: water quality, natural organic matter (NOM) and redox conditions study

Bank filtration (BF) was evaluated as new treatment or pre-treatment option for drinking water production in Brazil. General water quality parameters, natural organic matter (NOM) and redox conditions were evaluated in Lagoa do Peri, a costal lake in Santa Catarina, South Brazil. Studies in two periods at two bank filtrations well systems, in a 45-m-length column and in a test filter laboratory scale set-up, were performed. The well systems and the column showed the removal of turbidity and colour from around 7 NTU and 65 Pt–Co, respectively, to below the local regulations (1 NTU and 15 Pt–Co units). Both systems demonstrated a good removal of NOM and trihalomethanes (THM) precursors with a preference removal of THM precursors. The NOM and THM precursor removal in the large column and the test filter were effectively modelled. In both cases, an easily degradable organic matter fraction was modelled; in the large column a moderate degradable fraction was identified as well. The first fraction was removed during the first days of travel time of the bank filtrate. A change to reduced redox conditions was observed in the large column experiment. The same happened in the wells system, showing the dissolution of iron, manganese and sulphide in the bank filtrate. This was the principal drawback of BF comparing with the already existing direct filtration (DF) treatment plant. BF performed slightly better in THM precursor removal (52%) than DF (42%). Therefore, BF could be a pre-treatment for the DF treatment system, and the existing facility could be adapted for iron and manganese removal.