ON THE STABILITY OF ACTIVATED-SLUDGE FLOCS WITH IMPLICATIONS TO DEWATERING

It was shown thal Ca2+ can be extracted from activated sludge from a plant with biological nitrogen and phosphorus removal either by an ion exchange process, where H+, Na+, K+ or Mg2+ served as counter ions, or by chelation by EGTA. The extraction of Ca2+ led to an increase in the number of small particles and subsequently an increase in the specific resistance to filtration. It was argued that approx. half of the total Ca2+ pool was associated with the exopolymers and thereby formed an alginate-like gel, which constituted the backbone of the floc structure This notion was further emphasized by the observation that addition of Cu2+ which, along with releasing Ca2+, improved the dewaterability-probably because of the Cu2+ ions ability to maintain the three-dimensional structure of the exopolymers.