FILTRATION OF BACTERIAL COLIFORMS INCLUDING Escherichia coli IN WATER TREATED BY SLOW SAND FILTRATION By

Slow sand filtration is a method of water purification by means of percolating water through a column of fine granulated sediment and in some cases a layer of biological growth at the sand/water interface called the schmutzdecke. A series of nine slow sand filters (six of which were operational) were each connected to a main flow pipe which was attached to a roughing filter filled with gravel to remove solid waste from the untreated water. Raw untreated water was shunted through the roughing filter and then through each of the six operational slow sand filters for a period of roughly four months. The data indicate that there was a significantly greater amount of total coliforms including Escherichia coli present in the raw untreated reservoir water compared to the treated effluent water filtered by each of the six slow sand filters. However, because there was no observable schmutzdecke growth (studies show that the schmutzdecke aids in the removal of coliforms from untreated water (Weber-Shirk, Chan 2006)) in any of the slow sand filters, the significant removal of coliforms and E. coli from the raw untreated water must therefore be attributed to the kinetic adhesion of the bacterial cells to the sand particulates and the microscopic holes and divots located on sand particles. The three cleaning methods that were applied to the slow sand filters were harrowing, scraping and fabric application; however, there was no significant difference among the cleaning methods pertaining to the amount of coliforms present in their respective filtered water. Furthermore, the data suggest that there is no correlation between the influent flow rate (ml/s) of water into the slow sand filters and the prevalence of total coliforms including E. coli in the treated effluent water.