How much bacteria can be removed by the filter?
For the Gem505 filter version, microbial removal efficiency evaluation by the Tribhuvan University (laboratory study) and the Kathmandu University (28-days, 5 filters field study) of Nepal showed 85% to over 99% removal of total coliforms. Results of biosand filters installed in other countries showed that physical straining can remove 60-70% of bacteria (because bacteria are often attached to particles). The development of the biological layer (i.e. biofilm) in the fine sand layer will improve the bacteria removal efficiency up to 90 – 99%. Depending on the influent water quality, temperature and other environmental factors, the biological layer can be developed in as little as a few days to as long as a few months.
