A Rotational Drum Fermentation System (RDFS) for Dry Methane Fermentation (2) — Effect of hydraulic retention time (HRT) and stirring media in fermentor on acidogenic process —

摘要

A two-phase process can be employed to perform dry methane fermentation using a rotational drum fermentation system (RDFS). In the first phase, the acidogenic process is affected by many factors, such as pH, the organic loading rate, hydraulic retention time (HRT), temperature, and physical characteristics such as the stirring media in the fermentor. In this study, the effects of HRT and the stirring media in the fermentor on acidogenic performance were evaluated via system parameters involving volatile acid (VA) production and volatile solids (VS) degradation under mesophilic conditions. Using fresh soybean meal or okara as substrates, two sequential experiments were conducted with a bench-scale RDFS. The first set of experiments was performed at HRTs of 15, 20, 25, and 30 days. A first order hydrolysis rate constant of 3.7 X 10~(-3) d~(-1) calculated at pH values of 4.3-4.8 was less than the previous results, VS degradation and total VA (as acetic acid) ranged from 6.7 to 10.4%, and 13.3 to 16.0g/L, respectively. Results of the second set of experiments showed that the stirring media accelerated the hydrolysis and acidification processes, with K_h values of 5.3-7.2 X 10~(-3) d~(-1), and the VA spectrum was also influenced. However, some adverseeffects from use of stirring media were also observed in this study. The combined results indicate that pH values have an important effect on the distribution of un-ionized VA and ionized VA. Simultaneously, accumulation of VA, especially un-ionized VA,inhibits the hydrolysis process regardless of the type of stirring media in the fermentor.