A magnetically patterned hard disk is made by sputtering the magnetic layers, sputtering the carbon layer, applying a nonfunctional lubricant, buffwiping the disk to remove sputtering debris and asperities, removing the nonfunctional lubricant using a standard degreasing process, applying and patterning a resist, and thereafter subjecting the exposed disk to inert ion irradiation. The devices and methods of the invention are useful for enhanced secondary wastewater treatment, including BOD and TSS removal. Therefore, it is possible to appropriately control of applying the current to the electrically heated catalyst based on the insulation property of the carrier retention unit, and hence it becomes possible to appropriately prevent an electrical leak of the electrically heated catalyst.