Drinking water treatment using indigenous wood filters combined with granular activated carbon

A gravity-driven wood filtration system, incorporating granular activated carbon (GAC) as an appropriate point of-use technology for the rural poor, has been designed, tested and optimized. Four systems were assessed in respect of metal, bacteria and particle removal when exposed to polluted river water with and without GAC. These were evaluated using fresh, wet preserved and dry preserved Southern African indigenous wood species. Initially, all filter systems with the following indigenous wood species Combretum erythrophyllum in System 1, Tarchonanthus camphoratus in System 2, Leonotis leonurus in System 3 and Salix mucronata in System 4 did not incorporate GAC. The systems recorded 83.3, 85.4, 94.3 and 57.3% Escherichia coli removals, respectively, for fresh filters. Incorporation of GAC in Systems 1 and 4 showed high potential for significant E. coli removals (>99.9%) . Particulate removals were: 97% TSS (total suspended solids) and 96% turbidity removals by System 1; and 100% TSS and 100% turbidity removals by System 4. Metal removals by the combined systems were noteworthy and in the following order: Fe > Pb > Ni > Al > Zn > Cu > As > Cr > Cd > Mn (with average removals for the first five >90% and the last five >50%). Each combined system consistently met turbidity guidelines (≤5 NTU) and produced water with pleasant aesthetic aspects.