SYSTEM FOR BIOLOGICAL PURIFICATION OF WATER

A system and a method of purifying water in a biological way by means of a two-step process, at which the water to be purified is supplied into the treatment container or reactor (1) distributed uniformly across the bottom surface. The water supplied into the container (1) is caused to pass through a first biological filter consisting of suspended biological mass (11), in which gas is generated and at the same time the organic impurities in the water are decomposed. The water treated in the first treatment step thereafter is caused to pass through one or several stationary biological filters (13), where additional biological purification takes place at the same time as a sludge rich in bacteria grows on the carrier bodies of the biological filters. The stationary biological filters (13) are cleaned by means of the gas generated in the first treatment step, which gas is collected in the upper portion of the container (1) and recovered while the purified water rising to the upper portion of the container is drained off.