A Review on the Research of Promoting Biogas Fermentation Efficiency by Mixing

Mixed agitation can significantly improve the efficiency of anaerobic fermentation, which is shown by the remarkable improvement of biogas production and pollutant removal rate, so it has become an indispensable auxiliary process in modern biogas engineering. However, the internal mechanism of how agitation improves the fermentation efficiency is not clear, so it is difficult to find the best agitation form under complex conditions. However, in recent years, more research results have been obtained in this field. The effects of various agitation forms have been continuously verified on different feedstock characteristics under different fermentation and operating conditions, and the mechanism has been gradually clarified. The most important achievement is that in the 1990s it was clear that continuous agitation would impact the fermentation system, so batch agitation is the correct way to improve the fermentation efficiency. Since the 21st century, the latest research has focused on setting the operating parameters of batch agitation. Researchers have made greatly progress in all the aspects of medium, mode, power, speed and duration of agitation, and optimized the mixing scheme. Some studies have also revealed that stirring will affect the temperature field, impurity removal, toxicity accumulation and so on, and the optimal design of mixing scheme should take into account the comprehensive effects of all aspects. In this paper, the main worldwide research achievements in this field made in recent years are reviewed, and the internal mechanism that agitation can improve the anaerobic fermentation efficiency of biogas is clarified to a certain extent, and the suitable agitation forms under certain conditions are suggested