Purifying river water to give bathing quality water

摘要

Method for processing surface water by biofiltration, especially for processing river water of water Classes II-IV to give at least bathing quality water, in which the water is passed through a pre-purification tank in which coarse mechanical impurities settle out, is new. The novelty is that the water is passed, in relatively flat tanks having a high surface area, through a gravel filter layer of grain size 1-14 (preferably 2-8) mm, on which a biological coating is growing up to a depth of 3 cm (preferably up to 5 cm), at a filtration speed of 0.005-0.5 (preferably 0.1-0.3) m/hr. The contents of the water are biologically degraded by a microorganism population in the region of the coated gravel filter layer. The microorganisms are linked in an ecosystem by nutritional chains, such that the amount of excess sludge is markedly decreased by bacterial consumption and clogging of the gravel filter is inhibited.