1484928 Purifying waste-water DRAVO CORP 24 Oct 1974 [26 June 1974] 46136/74 Heading C1C The purification of waste-water containing BOD ammonia nitrogen and inorganic nitrogen by treatment in a biological aeration zone to reduce BOD and oxidize the nitrogen compounds to nitrate, followed by denitrifying the nitrate-containing water in a denitrification zone, is improved by recycling a portion of the nitrate-containing waste-water and mixing it with incoming raw waste-water under facultative conditions in a zone containing facultative microorganisms wherein denitrification of the recycled waste water and reduction of the BOD of the raw waste-water are effected simultaneously. Plant for carrying out the process is described.
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