| Summary: | 碩士 === 國立雲林科技大學 === 環境與安全工程系碩士班 === 91 === The enhanced biological phosphorus removal (EBPR) activated sludge process has been developed for long time to removal the phosphorus in wastewater. However, it was also observed that the EBPR process was destroyed under some non-identified condition. The competition of carbon source between glycogen accumulating organism (GAO) and phosphate accumulating organism (PAO) is considered as an important reason. No clearly conclusion of the presence of GAO was obtained yet, but two factors, influent phosphate concentration and the operation conditions (pH, temperature, sludge retention time etc.) of EBPR process, were generally considered to influence the presence of GAO. Thus, this study cultured the GAO-enriched sludge by using low phosphorus loading anaerobic selector (anaerobic-aerobic activated sludge) to investigate the metabolisms of GAO and PAO under different carbon sources (acetate and glucose) and operation conditions (pH and temperature), and denitrification characteristics of GAO and PAO by using acetate and glucose as carbon source. Besides, the microscopic examination with sludge staining and 16S rDNA based molecular biotechnology were also used to identify the microbial diversity of the sludge.
The daily performance showed that under the low phosphorus loading condition, the phosphorus content of activated sludge was only 1 %, which was obviously lower than that of 3 to 10% of normal EBPR process. Additionally, by using microscopic examination of Neisser- and PHA-staining, the GAO-like tetracocci was found to be predominant, and it was also observed that the sludge accumulated high PHA with low poly-phosphorus storage. Both of wastewater quality and microscopic examination showed that the sludge should be identified as “GAO enriched sludge”.
The batch experiments which were changed the different carbon sources (acetate and glucose) and operation conditions (pH and temperature) were performed at this study. When the pH was controlled between 5.5 to 8.5, the phosphate release was positive relation with pH, no matter the carbon source was acetate or glucose. Besides, the optimal phosphate removal performance was achieved at pH was 7.0. When pH was 7.0, the phosphate removal rates were 100% and 80% while using acetate and glucose as carbon source, respectively. Furthermore, the pH of 6.0 was observed to be an optimal pH for GAO growth.
When the temperature was controlled between 10 to 35℃, it was observed that the higher the temperature, the faster the reaction rate, no matter the carbon source was acetate or glucose. It was also observe that at 25℃, the sludge consumed the lowest carbohydrate at anaerobic phase while accumulated the highest carbohydrate at aerobic phase. This was considered to be the optimal temperature for GAO growth. It was also calculated that for the GAO-enriched sludge, the temperature coefficient (θ) of anaerobic COD uptake between 10 to 35℃ were 1.043 and 1.051 for acetate and glucose as carbon source, respectively. By using acetate as carbon source, the θ of anaerobic phosphate release were 1.048 and 1.054 when the temperature were between 10 to 20℃ and 20 to 35℃ respectively, while the θ of aerobic phosphate uptake were 1.128 and 1.071 respectively at the above temperature range. In addition, the θ of anaerobic phosphate release and aerobic phosphate uptake using glucose as carbon source were 1.026 and 1.041 when the temperature were between 10℃∼35℃.
Additionally, the denitrification experiments were also performed to identify whether the GAO can denitrification or not. By calculating the aerobic- and anoxic- phosphate uptake rate, it reveled that the denitrifying PAO were quite low, which were only 23 and 20% of total PAO when using acetate and glucose as carbon sources. Besides, by considering the interferences of extra cellular carbon and phosphate, the experiments results showed that all the specific denitrification rates were similar. It revealed that the GAO contributed the most denitrification performance. This implied that the GAO can denitrify by using intracellular polymer under anoxic condition. After kinetic analysis, the specific denitrification rate of GAO were 0.2 mgNO3-N/gMLSS*hr and 0.1 mgNO3-N/gMLSS*hr when using acetate and glucose as carbon source.
Finally, by using 16S rDNA based molecular biotechnology analysis, the microbial diversity of low phosphorus loading anaerobic-aerobic activated sludge can be divided into three phylum, i.e., Proteobacteria(47.5%), Bacteroidetes (39.5%) and Planctomycetes (3%). It was also found that lots of microorganisms were found to be relationship with GAO, included the 12.5% of Haliscomenobacter sp. which was identified as GAO and 27% of microorganisms which was considered play a negative role in EBPR process.
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