Like ultrasonication, microwave (MW) irradiation is considered a popular alternative to conventional heating technology. In industry, a shorter frequency either close to 900 MHz or at 2450 MHz is often adopted. Damage to sludge cells with MW irradiation may occur in two ways: thermal effect that is generated through the rotation of dipoles under oscillating electromagnetic fields; and athermal effect that is induced by the changing dipole orientation of polar molecules, giving rise to the possible breakage of hydrogen bonds and the unfolding and denaturing of complex biological molecules. MW irradiation is recognized as an efficient technology due to its considerable advantages, e.g., low cost, flexible control and high hemical oxygen demand. Recently, it has been suggested that MW pre-treatment should be combined with further methods to improve the disintegration of the sludge and sanitization from pathogens.