Effectiveness of bank filtration for water supply in arid climates: a case study in Egypt

In many developing countries, water demand is increasing while surface- and groundwater resources are threatened by pollution and overexploitation. Hence, a more sustainable approach to water resources management and water treatment is required. In this capacity, bank filtration is a natural treatment process that makes use of the storage and contaminant attenuation capacity of natural soil. However, BF is site-specific and a significant knowledge gap exists regarding the design and management of bank filtration systems, particularly in developing countries. This research aimed to address these gaps and contribute to the transfer of bank filtration to developing countries. This study comprised both column and batch laboratory-scale experiments to determine the effect of environmental variables such as temperature, raw water organic composition and redox conditions on the removal of chemical pollutants such as organic matter, micro-pollutants and heavy metals as well as the mobility of iron, manganese and arsenic under anaerobic conditions. Ultimately, the effectiveness of BF in improving the quality of drinking water was assessed in a case study in Egypt. The study showed that more than 80% of biodegradable organic matter was removed during BF at temperatures between 20 and 30 °C. However, post-treatment is required to remove humic compounds that were enriched during infiltration. Moreover, infiltrating water with a high concentration of humic compounds reduced the removal of heavy metals and promoted the release of metals into the infiltrating water, rendering it more feasible to install BF wells in surface water systems with low levels of organic matter. Moderately hydrophobic organic micropollutants were most persistent and required infiltration times in excess of 30 days for complete elimination, even at high temperatures (>20 °C). Finally, design parameters such as the number of infiltration wells, should be configured to minimise the proportion of polluted groundwater in the pumped water. Overall, this study provides insight into the effectiveness of BF in removing chemical pollutants from surface water and proposes guidelines for the successful application of BF in developing countries where arid conditions and high temperatures prevail.