Microwave based faecal sludge treatment
Portable microwave based treatment system for on-site faecal sludge treatment for the humanitarian and development WASH sector

Microwave heating

Heating of a material by microwave (i.e. dissipation of microwave energy to heat) is a result two main mechanisms, namely rotation of dipolar species and polarization (migration) of ionic species (Haque, 1999). Dipole rotation, which is the primary heat-induction mechanism of microwave dielectric heating, results from the interaction of the molecular dipoles with electromagnetic field. Dipolar molecules such as water have a random orientation. Whenever an electric field is applied, the molecules orient themselves according to the polarity of the field. However, in a microwave field, the polarity alternates very rapidly, e.g., at the 2,450 MHz microwave frequency, the polarity changes 2.45 billion cycles per second. This results in phase difference which causes molecular rotation as the field is always changing before the dipole re-orients to align itself. Such molecular rotation leads to friction with the surrounding medium, and heat is generated. The ionic polarization occurs when an electrical field is applied to solutions containing ions. The ions of positive and negative charges move at an accelerated pace towards oppositely charged regions of the electrical field. This causes collisions between the ions and disruption of hydrogen bonds within water, both of which result in the generation of heat (Venkatesh and Raghavan, 2004).