抄録
Aiming the recovery of ferromagnetic powder, the excess activated sludge supplemented with magnetite (magnetic sludge) was solubilized with the thermochemical treatment using alkaline solution, the ultrasonic treatment, and was decomposed with the aerobic digestion treatment. The incineration of sludge was not carried out. There is no problem for the reuse of magnetic powder including small amount of organic materials. We expected to remove more than 85% of activated sludge from the magnetic sludge. As the results, both the thermochemical treatment and the ultrasonic treatment were found to be effective for the sludge solubilization. However, in the case of thermochemical treatment, we obtain alkaline suspension of sludge as a byproduct after the recovery of magnetic powder. In another case, the ultrasonic treatment takes less than 10 minutes to recover the magnetic powder. This method is not available for the treatment in large quantity. On the other hand, the aerobic digestion treatment was the most effective with only the aeration. By adding magnetic sludge into the aeration tank at regular intervals, the MLVSS decreased under aeration and the magnetic powder was accumulated. We made the aerobic digestion treatment to an end, when the ratio of magnetic powder against sludge reached to more than 4 times in the aeration tank. The magnetic powder was separated easily as the digested magnetic sludge by magnetic attraction.
