Development of xylem-based water filters

Abstract

Diarrheal diseases caused due to microbial contamination are one of the leading causes of fatalities amongst children. Despite the availability of numerous commercial products for water filtration and treatment, there continues to be a need for technological solutions that can make safe drinking water affordable and accessible. Due to their low cost, high filtration rate per unit weight and the ability to be manufactured locally with little infrastructure, xylem-based filtration devices have potential to address the challenge of microbial contamination of water in resource-limited settings. Previous studies by Boutilier et al. have demonstrated the ability of sapwood xylem from conifers to achieve up to 99.9% rejection of bacteria from water. However, it has been reported that drying of xylem after extraction leads to a drop in permeability by a factor of over 100. This poses a huge challenge in the context of transportation and storage of these filters. Maintaining the filters in a wet state would require special packaging and also reduce their shelf-life. Further, previous tests with the xylem filters at laboratory scale have involved the use of gas-pressure to drive the flow. In practical applications, the use of pumps would drive up the cost of the device negating the primary advantage of these filters. To keep operational costs as minimal as possible, it is critical to operate xylem filters offline. This thesis aims to address the challenge of dry storage and offline, gravity-based operation of xylem filters. Moreover, the use of xylem for water filtration has not been explored before and little is known about its performance characteristics. This thesis also seeks to advance the understanding of xylem as a filter material through the study of attributes such as degradation of xylem when soaked in water, filter lifetime, its variation with water quality and variation of flow rate with time. Methods to engineer the xylem filters to improve their rejection capability have also been discussed. In parallel to technology development, efforts were also made to identify avenues for implementation of these filters in India. The insights gathered from field visits to India and discussions with key stakeholders have also been presented..