| Summary: | 碩士 === 雲林科技大學 === 環境與安全工程系碩士班 === 97 === Polyhydroxyalkanoates(PHAs) has been widely recognized to be produced by mixed culture since the lower production cost and the capability of being produced from renewable resources. However, mixed culture, containing a great deal of non-PHAs producting bacteria, exhibited lower PHAs contents than pure culture. Therefore, this research focuses on regulating operational conditions of the mixed culture so as to increase the PHAs contents in the sludge, by elevating PHAs production bacteria. In the present study, we operated two anaerobic-oxic (A/O) activated sludge system , and fed with acetate (named acetate-A/O sludge) and propionate (named propionate-A/O sludge) , respectively. Then, sludge from the aerobic zone of the system was harvested to perform the aerobic batch experiments for PHAs production by using the sole carbon sources and different mixed carbon sources. These experiments were utilized to compare the capability of PHAs production and the metabolisms of these various sludge systems.
Experimental results indicated that when using the propionate as the sole carbon source, propionate-A/O sludge had the best specific substrate uptake rate(-qs), specific PHAs production rate(-qp), PHAs content and PHAs conversion rate (YP/S). However, when the sole carbon source was changed to acetate or valerate, the acetate-A/O sludge had better production than propionate-A/O sludge . These results demonstrated that no matter the acetate-A/O sludge or propionate-A/O sludge was used the uptake rate for odd-number carbon source (Propionate, Valerate) were extremely limited and the 3HV contents in PHAs were low.
In order to improve the substrate uptake rate of the A/O activated sludge fed with propionate and valerate, we used the complex carbon sources (acetate : valerate = 50:50 (C mmol: C mmol)) to perform the batch experiments for PHAs production. The results indicated that the PHAs productivity of the two A/O sludge were enhances , and it is better than that of using the propionate and valerate as sole carbon source. This means that when using the complex carbon sources (acetate and odd-number carbon source ) not only enhance PHAs contents by acetate, but also synthesis the copolymer structure (P(3HB-co-3HV)) that had batter thermal processing . Furthermore, when used the complex carbon sources (acetate and valerate), the PHAs contents were better than that of the complex carbon sources with acetate and propionate, and the specific PHAs production rate (-qp) and PHAs conversion rate (YP/S) were almost the same as acetate as sole carbon source. When the mixed ratios was HAc:Val=75:25, both A/O sludge were obtained the highest PHAs content, and even higher than HAc:Val = 100:0.
Besides, this research tried to change propionate - A/O sludge to propionate-ADF sludge system. The MLSS in the system was gradually reduced during the transient period, but the PHAs contents was increased from 55 mg PHAs/g MLVSS to 102 mg PHAs/g MLVSS.This result indicated that the PHAs production bacterias were gradually raise in the system. Then sludge from this system was used to perform the aerobic batch experiments for PHAs production , and the carbon sources used the different mixed carbon source ratios(acetate and valerate) . The experimental results showed that the PHAs production capability for the propionate - ADF sludge was better than propionate - A/O sludge, except for the PHAs contents increased to 624 mg PHAs/g MLVSS, and the specific PHAs production rate (0.147 - 0.205 C mmol PHAs/C mmol X.hr) was higher than the propionate - A/O sludge (0.012-0.075 C mmol PHAs/C mmol X.hr) . Otherwise, the batch experiments indicated that when the mixed ratios was HAc:Val=75:25, the highest PHAs contents and synthesis the copolymer structure (P(3HB-co-3HV) were obtained at the same time.
Even if the sludge system had change to full aerobic state, but through the propionate-ADF sludge (C/P=400/15) system’s internal metabolic process,we also found the situation about phosphate release. Thus, we tried to reduce the source of phosphorus (C/P=400/4) , hoping to reduce the amount of PAOs and raised the proportion of non - PHAs production bacteria in the ADF sludge system. But the result showed that reduced the source of phosphorus wasn’t significant effect on PHAs production. Then we tried to increase the amount of carbon source (C/P=800/8) , with a view to enhance the amount of carbon sources and trained the bacteria in this systems adapt to high amount of carbon sources. Finally the batch experimental result showed that enhanced the carbon source concentration was not increased the PHAs contents, but bacteria could shorten the time on uptake the carbon source, and the specific PHAs production rate (-qp) was slight increased.
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