A low-cost water-treatment system for potable water supplies in developing countries and after a natural disaster: ability to remove total coliforms and E. coli

Providing potable water in developing countries and following a natural disaster is a challenge. Among the different low-cost water treatments, slow sand filtration (SSF) has been widely used; however, it is not clear whether SSF can also be used with an influent water having high bacterial loads (>10⁵ MPN/100 mL). These high levels of bacteria in the feed water can be naturally present in developing countries or can occur as a result of sewage spills or after a natural disaster. Two SSF units and a point of use device, an in-line UV unit, were tested using feed water with high bacterial loads. The study confirmed that SSF can be effectively used to treat feed water with high bacterial loads. Approximately 60 % of the bacterial removal occurred in the top 5 cm of the SSF unit where a biolayer is found. Bacterial removal efficiency was related not only to the quality of the biolayer (i.e., whether it was completely or partially developed) but also to the SSF unit itself (i.e., age of unit). The ability of the biolayer to remove bacteria appears to be marginally impacted by the water used to develop the biolayer. During the restoration period that followed the addition of 20 % primary effluent to the feed water, higher bacterial removal occurred in the biolayer developed with stream water and 1 % primary effluent than in the biolayer developed with stream water alone. An in-line UV unit consistently removed total coliforms and Escherichia coli up to 10⁵ MPN/100 mL from the effluent of a SSF unit.