Abstract: Activated sludge sewage treatment process comprising aerating a mixed liquor comprising phosphate-containing influent sewage material to cause the microorganisms present to take up phosphate, separating phosphate-enriched sludge from the mixed liquor, and settling the separated sludge in a phosphate stripping zone to form supernatant liquor and settled sludge. At least part of the settled sludge is maintained under anaerobic conditions to cause release of soluble phosphate and the resulting sludge containing released phosphate is contacted with a lower soluble phosphate content medium to effect phosphate enrichment of the supernatant liquor in the stripping zone, with at least a portion of the anaerobic sludge being recirculated to the aeration zone.