LÅNGSAMFILTRERING / Slow Filtration
Production of drinking water by slow filtration is an old method getting new aspect nowadays. Filtration mechanism is on principle the same as in other granular filters. Dispersed matter is destabilized by biochemical activity of microorganisms. Separated organics retained in the filter for several months/years are degradated by aerobic digestion instead of being removed by backwash. The resulting products accompany the water further on, if desirable or not may be questioned. Humic substances and aluminium, attracting attention today, are little attacked by microorganisms and pass to a large extent through the filter. To reach the desired quality of drinking water by slow filtration requires a raw surface water suitable as drinking water. Even chemically purified water ought to be classified as ”suitable” before polishing by slow filtration.