| Summary: | 碩士 === 國立屏東科技大學 === 環境工程與科學系 === 91 === The objective of the study is to investigate effects of the mesophilic (37℃) and the thermophilic (55℃) anaerobic digestions treating kitchen wastes using the two-phase continuously-stirred flow tank reactor (CSTR). Hydrolysis pretreatment under different temperatures was evaluated. Operating conditions of different organic loading rates (OLR) and hydraulic retention time (HRT) were also investigated.
When different temperatures (55 and 70℃) were tested for effect of thermal pre-treatment for 24 hours, results showed that the highest hydrolysis rate under 55 and 70℃ were 28.02% and 34.62 %, respectively. Under both tested temperatures, the majority of hydrolysis reaction occurred at the first 5 hours. For acidification test, without artificial pH control in the system, the total volatile fatty acids (TVFAs) were found to increase with reaction time. It took about 16 hours for the system to reach a stable condition, and the TVFA levels were increased more than 600 mg/L of COD within 10 hours.
In the CSTR experiments, system went through a pre-treatment of hydrolysis and acidification for 6 hours before subsequent methanogenesis. For the mesophilic system, the highest loading was operated under an OLR of 3 kg COD/m3-d and a HRT of 10 days. The highest COD removal efficiency was 90%, with a daily gas production of 3~4 L/day and a methane percentage of 40%. On the other hand, the thermophilic system was operated under an OLR of 5 kg COD/m3-d and a HRT of 5 days, and the highest COD removal efficiency was 94.4%, with a gas production of 3~4 L/day and a methane content about 50%.
Kinetic study of kitchen wastes using chemostats showed that the maximum specific utilization rate (k) of the mesophilic system was 1.28 mg COD/mg VSS Activity-d, while the thermophilic one was 3.54 mg COD/mg VSS Activity-d. This verified the fact that thermophilic one had a must higher substrate utilization rate than the mesophilic one when treating kitchen wastes. Considering factors such as COD removal efficiency, organic loading rate, hydraulic retention time, methane percentage in the gas production, and kinetic parameters, the thermophilic system was found to be superior to the mesophilic one, and should be considered in the application of full-scale anaerobic digestion processes.
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