Removing phosphate from waste water - by activated sludge treatment after pre-incubation of water with recycle sludge in presence of iron oxide precipitant

摘要

Pptn. of chemical pollutants, esp. phosphates, in waste water comprises purifying the water in a clarifying plant at least in one activated sludge stage, and the activated sludge (AS) is withdrawn from this stage and returned as recycle sludge (RS). A portion of this is removed as excess sludge (to maintain a constant level of AS) and an iron oxide contg. pptg. agent is added to RS. The new features are that all the RS is added to the waste water in a separate step, before the AS stage, without introducing any additional O2, and the RS/waste water mixt. is allowed to stand for at least 30 min before passing to the AS stage. USE/ADVANTAGE - By carrying out the pptn in a separate stage (rather thanin the AS stage), this method provides a significantly higher level of pptn. and thus more effective elimination of phosphate, even in non-acidic waters. The new treatment step can be incorporated into existing plants with only small modifications.