Influence of the schmutzdecke microbial community and varying operational conditions on the performance of biosand filters for domestic drinking water treatment

Abstract

Household water treatment technologies offer an interim solution for people who remain without access to a safe drinking water source. Biosand filters (BSFs) are among the most sustainable point-of-use (POU) water treatment techniques in terms of treatment efficiency and user satisfaction. However, the lack of knowledge pertaining to the impact of operating conditions on filter performance and the microbial community structure of the schmutzdecke is potentially limiting the optimisation of BSFs. This thesis provides insight into the impact of varying operating conditions including filter media characteristics, resting water depth and ambient temperature on the performance of BSFs. In addition it provides the first insight into changes in the schmutzdecke bacterial community structure during the maturation of BSFs. This thesis has shown that deviations from the recommended sand grain sizes was not detrimental to filter performance, indicating that there is potential to ease the current recommendation for a maximum grain size of ≤ 0.7 mm. It was also found that variations in the resting water depths of between 2 and 11 cm did not negatively impact the removal of microbial indicator organisms or the metabolic activity and functional diversity of the schmutzdecke. However, operating temperature was found to impact the performance of BSFs, with filters operated at a lower temperature (10 ± 1 ˚C) having a higher E. coli removal when compared with filters operated at 26 ± 1˚C. This suggests that householders may experience variations in filter performance due to seasonal temperature changes. A further interesting observation in this thesis was that the rate of bacterial family colonization and succession differed in three, full-scale BSFs. However as the filters aged the same bacterial families eventually dominated the schmutzdecke in all three filters. It was also found that bacterial family dominance in the feed water was not a driver for the subsequent dominance of the family (Planctomycetaceae and Acidobacteria) in the schmutzdecke. The findings of this thesis, along with further studies on the effect of operating conditions on filter performance and schmutzdecke development, will enable the design and operation of BSFs to be optimised.