Activated sludge immobilization using the PVA-alginate-borate method

The PVA-alginate-borate method was used successfully to immobilize activated sludge. The optimum polyvinyl alcohol (PVA) concentration in the immobilized sludge was determined to be 10-12.5%. A minimal alginate of 1% in the beads was needed to prevent bead agglomeration. If the pH of the saturated boric 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 activity could be maintained in the beads formed. During the continuous operation of a fluidized bed reactor, with hydraulic retention time (HRT) in the range 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 apparent breakage.