Biosand filtration of high turbidity water : modified filter design and safe filtrate storage

摘要

Unsafe drinking water is a major cause of water-related diseases that predominantly affect people living in developing countries. The most prevalent water-related disease is diarrhea, estimated to kill 1.8 million children every year and the second largest cause of childhood death. Today there are many technologies available to treat unsafe water; however, most of these are suited for use with low turbidity source water. The treatment of high turbidity water (>50 NTU) is a challenge that was investigated in this research. Biosand filters, based on an intermittent slow sand filtration process, are an established household scale water treatment technology widely used in developing countries to treat low turbidity drinking water. This research investigates modifications to the biosand filter design to promote effective pathogen and turbidity reduction in high turbidity water. During field tests conducted in Ghana, a modified biosand filter with dual sand layers for added filtration achieved the greatest pathogen and turbidity removals. This design was then optimised through laboratory studies at MIT. The dual sand layer biosand filter supports straining and sedimentation of particulate matter from the feed water in a 3-7 cm deep raised upper sand layer prior to biological treatment and further filtration of the water in a 15-16 cm deep lower sand layer. Field testing of the dual sand layer biosand filter showed this filter achieved 59% turbidity reduction, 38% higher than an unmodified control filter; and at least 85% E. coli and 95% total coliform reductions, comparable in performance to unmodified control filters.