Daisuke TANIKAWA
Performance of mesophilic methane fermentation reactor treating garbage without addition of water
Akiyoshi OHASHI
We investigated the performance of mesophilic methane fermentation reactor treating garbage without addition of water. Our study focused on avoiding ammonia inhibition when¡¡nitrogen-rich substrate such as garbage was digested anaerobically without dilution by water. The mesophilic methane fermentation reactor was operated at a temperature of 37 ¡î and fed with garbage as a substrate. This continuous experiment was divided into five periods as phase 1 - phase 5. In phase 1 and phase 5, garbage was fed as a substrate. In contrast, paper was mixed with garbage to reduce nitrogen concentration of substrate in phase 3.Phase2 and phase 4 were recovery periods from ammonia inhibition and VFA inhibition, respectively.
As the results, ammonia was accumulated up to 3500 mgN/kg-w.w. in phase 1. Then, gas production rate was reduced by ammonia inhibition. In contrast, ammonia accumulation was not observed in phase 3. However, propionate accumulation was occurred. In this phase, paper was also accumulated in the reactor. So, it seems that propionate was produced from paper accumulated in the reactor.
Then, we installed ammonia absorption tower that was filled with sulfuric acid to removed ammonia gas in gas phase of the reactor. As a result, ammonia accumulation was avoided in spite of garbage was fed as a substrate. In this phase, methane-producing activity was kept enough level to achieve COD volumetric loading of 10 kgCOD.m-3.d-1. So, it seems that mesophilic anaerobic digestion of garbage without addition of water can achieve the same performance as thermophilic wet anaerobic digestion when ammonia absorption tower avoid ammonia accumulation.
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