Basic principle of anaerobic digestion is simply reviewed. It includes anaerobic digestion theory and the main influencing factors. The development history of anaerobic digesters is summarized, and the characters, the running mechanisms, and application of some typically high-load reactors, such as Upflow Anaerobic Sludge Blanket (UASB), anaerobic expanded granular sludge bed and IC anaerobic reactor, are especially introduced. In summing up, the problems and the defects of the high-load anaerobic reactors are put forward. Finally, it is also pointed out that the future study of anaerobic digester should focus on how to raise the reactors' efficiency.
