Laterite as a disinfectant.

A groundwater programme monitoring flow and quality of a potable water spring in a slum district in Kampala, Uganda revealed that although latrines acted as the principal means of organic waste disposal for the 1000 plus people living in the spring’s catchment, levels of faecal indicator bacteria (TVC 45 Deg C) in spring discharge remained at or below detection during the dry season, despite the presence of high levels of chloride (45mg/l-56mg/l) and nitrate (23mg/l – 30mg/l NO3-N), indicating sewage impacts. A programme of column and batch testing of laterite underlying the area provided a means of investigating the soil’s attenuation capacity under more controlled conditions. <br/>X-ray diffraction analyses revealed the laterite to be dominated by quartz and kaolinite with minor (<5% by volume) quantities of haematite. Batch studies revealed that over 99% of bacteriophage adsorbed to haematite in less than 5 minutes. By contrast batch tests on haematite-free soil samples from the Blue Hills in Australia showed that although they had comparable dominant mineralogy and iron coverage on their surfaces (determined from Energy dispersive X-ray fluorescence) they had negligible ability to adsorb H40/1. <br/>Based on the results of the batch studies using natural soils, a programme of batch studies, undertaken using pure haematite showed the mineral to have an extremely high capacity to adsorb bacteriophage, and suggested that it was responsible for the levels of attenuation observed. <br/>The results of column studies were in keeping with the findings of batch experiments. Injection of 20 pore volumes of 300 pfu/mL of the bacteriophage H40/1 into a 20mm diameter glass column packed with sand sized (Ø>500µm) laterite revealed that the column could irreversibly remove over 2.5 log10 bacteriophage over its 10cm length. <br/>Importance: <br/>Mineralogical and batch test data provide convincing evidence to show that laterite can potentially act as an inexpensive means of removing micro organisms from water. The material, particularly in nodular form, displays considerable potential to act as an alternative filter material to conventional quartz filter sands. <br/>