To improve a biological wastewater process, magnetic separation was applied to a biological wastewater treatment process. An aerobic biological wastewater treatment process utilizing magnetic activated sludge (MAS) was introduced to simplify process operations, as well as to enable excess sludge production to be controlled. Standard bench-scale experimental equipment and a few mobile pilot plants for the MAS process have been developed in the past few years. After developing a full-scale magnetic separator with a typical MAS suspension separation capacity of 200 m³d^-1, it became possible to design a full-scale plant and estimate the initial cost. It has been estimated that the total cost of the process (i.e., initial setup and operation) will result in savings, being less than that required for the conventional activated sludge process. It is possible that a new field of superconductive magnet applications can be developed if the MAS process is applied for large-scale wastewater treatment processes such as municipal sewage treatment.