Activated sludge immobilization using the PVA-alginate-borate method

The PVA-alginate-borate method was used successfully to immobilize activate d sludge. The optimum polyvinyl alcohol (PVA) concentration in the immobili zed sludge was determined to be 10-12.5%. A minimal alginate of 1% in the b eads was needed to prevent bead agglomeration. If the pH of the saturated b oric acid was adjusted to 7.0 prior to allowing droplets of the mixture of PVA, alginate and sludge to enter the solution, a high level of sludge acti vity could be maintained in the beads formed. During the continuous operati on of a fluidized bed reactor, with hydraulic retention time (HRT) in the r ange of 24-3 h (BOD loading from 0.176 to 0.766 kg/d/m(3)) and an aeration rate at 1.0 L/min, more than 90% of BOD5, NH4+-N and TKN were removed. The immobilized sludge exhibited satisfactory mechanical stability without appa rent breakage.