A method of inactivating pathogens contaminating water and sludge, such as sewage sludge from wastewater treatment plants by exposing the contaminated material to an intense alternating mechanical field, at sonic and/or ultrasonic frequencies, producing and sustaining cavitation along spiral-shaped like paths between two or more disks, where at least one disk rotates or more than one disk rotates or the disks counter-rotate at high RPM. Alkaline material may be added to enhance the inactivation of pathogens. Heavy metals, which may also be present in the sewage sludge may be extracted from the sludge by adsorption.