| Summary: | 碩士 === 雲林科技大學 === 環境與安全工程系碩士班 === 96 === Polyhydroxyalkanoates (PHAs) are synthesized biopolymers that have typical properties similar to those of thermoplastics (such as PE and PP). PHAs can be complete biodegraded in environment. But the industrial processes of PHAs production are based on the use of pure cultures, and their production costs are high. Therefore, interests in the use of mixed cultures for the production of polyhydroxyalkanoates has increased in the recent years. The anaerobic-aerobic mixed cultures process can select PHAs producting bacteria; however, this system is so complicated that it contains a great deal of non-PHAs producting bacteria. In this study, the acetate-fed A/O activated sludge system was constructed, which can reduce complicated fermention requirement in anaerobic period, and promote the proportion of PHAs producting bacteria. Then, sludge from the aerobic zone of the system was harvested to proceed aerobic batch experiments for PHAs production. Although this experimental result has demonstrated maximum PHAs content, the main structure of PHAs is still based on PHB. When feeding propionate to the same sludge to proceed batch experiments, proportion of PHV was raised, but PHAs content was low. Thus, this research attempted to use propionate to acclimate activated sludge, hoping to elevate PHAs content and PHV proportion at the same time.
The experimental results indicated that the PHAs production capability for activated sludge system with an short SRT(5 days) was better than that of the sludge with an long SRT(15 days), when using acetate-fed activated sludge and using acetate as carbon source for batch experiment of PHAs production. No matter the carbon source was acetate or propionate, the maximium PHAs content were obtained when the carbon source was COD = 4000 mg/L. The PHAs content, production rate and conversion ratio obtained with acetate were higher than the ones obtained with propionate. Furthermore, use of acetate as carbon source led to the production of PHB, and use of propionate as carbon source led to the production of PHB, PHV, 3H2MV and among them mostly PHV. This results showed that use of propionate as carbon source can improve PHV content, but that still have low PHAs content (8%).
Acetate fed to the A/O activated sludge system was changed to propionate in order to improve PHAs content and PHV proportion at the same time. This sludge in adapted period were utilized to perform batch experiment of PHAs production. Experimental results showed that PHAs producting bacteria need a long adaption time (about 30 days) to improve PHAs content and PHV proportion at the same time. When using propionate-fed activated sludge and using propionate as carbon source to proceed batch experiment for PHAs production, experimental results showed that the highest amount of PHAs content 12%, production rate 8.3 mg C/g SS/h and conversion ratio 0.20 C-mole/C-mole. These production properties were lower than the ones obtained with activated sludge fed with acetate (PHAs content (41%), production rate (32.58 mg C/g SS/h) and conversion ratio (0.61 C-mole/C-mole)).
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