What does “log credit” mean in reference to pathogen removal in a slow sand filter?
“Log credit” means: The log10 (the log relative to base 10) of the number of organisms per unit volume before filtering minus the log10 of the number of organisms per unit volume after filtering. For example 1000 beaver fever cysts before filtering per 100 ml of water as compared to 1 beaver fever cyst per 100 ml of water after filtering is the log10 of 1000 minus the log10 of 1 or 3 – 0 or 3. A very good filter. The corresponding percentage would be 999/1000 or 99.9 percent removal. back to top 15.
