• excess sludge;
  • ferrite particles;
  • electromagnet


Every year, the ratio of the sewarage treatment to population is increasing in Japan. Expansion in sewer networks is leading to the production of excess sludge which is one of the major problems in wastewater treatment plants. There are several approaches to treat the excess activated sludge. A new approach is to reduce excess sludge production by using magneto-ferrite treatment. The Suzuki Lab of Akita University, Japan, is working on this project. We have succeeded in using magneto-ferrite treatment in the lab scale to reduce sludge production. Ferrite particles and magnets are used in this method. Ferrite particles are nontoxic and safe for biological systems. They can be easily separated from the sludge by using magnets. However, the movement of the ferrite particles in the sludge is controlled by permanent magnets which can be made more effective by changing to electromagnets. In this paper, we describe an approach to use electromagnets instead of permanent magnets. Electromagnets can be controlled easily with an AC power supply. The results of our experiments have shown a good possibility for reduction of excess sludge. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.