Fremgangsmåte for rensing av avvann

摘要

Wastewater containing impurities refractory to secondary treatment is first introducted into an aerobic biological treatment stage operating with an oxygen-enriched stream and subsequently into a precipitation stage where the biologically treated wastewater is combined with Ca(OH)2 to precipitate Ca(OH)2CaCO3 sludge which adsorbs or occludes impurities. The clear liquid, separated from the resultant sludge, is passed to a second precipitation stage where it reacts with a CO2 and oxygen-containing waste gas at least in part from the aerobic biological treatment stage, thereby forming additional CaCO3. Waste gas withdrawn from the second precipitation stage, being enriched in oxygen is recycled to the aerobic biological treatment stage.