| Summary: | 碩士 === 國立雲林科技大學 === 環境與安全工程系碩士班 === 93 === Anaerobic/oxic (A/O) activated sludge system has found extensive application in sludge bulking control and phosphorus removal. Nevertheless, high sulfate influent concentration was experimentally proved to be one of the main reasons accounted for filamentous bulking due to the anaerobic sulfate reduction and the following oxic sulfur oxidation in an A/O process. The objective of this research was therefore to investigate the effect of coagulant addition on sludge settling properties and supernatant water quality of the bulking sludge from A/O process. Besides, emphasis is placed on conducting phosphate release/uptake batch test that would give an appropriate appraisal of optimum coagulant dosage.
Long-term operation results of the A/O pilot plant indicated that sulfate hindered the phosphate removal and filamentous bulking seriously interfered sludge settling. Sulfate reducing bacteria (SRB) compete with phosphate-accumulating microorganism (PAO) for influent substrate; this phenomenon decreases the phosphate removal efficiency. Besides, SRB and filamentous sulfur bacteria (FSB) construct a sulfur cycle in the A/O process, serious bulking therefore occurred. The filamentous bacteria in the A/O pilot plant were identified to be Thiothrix according to Eikelboom’s classification techniques, which was in accordance with the high influent sulfate concentration of this study (65mg/L sulfate). Besides, all three coagulant (FeCl3, Al2(SO4)3, PC-325) improved the settling properties of the bulking sludge. Soluble phosphate was further eliminated when FeCl3 or Al2(SO4)3 was adopted; nevertheless, no phosphate reduction was observed when using PC-325 as coagulant. The optimum dosage of FeCl3 was much higher than that of Al2(SO4)3.
Cultivating GAO-enriched sludge in an A/O activated sludge system usually may include PAOs. Past researches tended to utilize the metabolic behavior of GAO-enriched sludge to represent that of GAOs. This study hence tried a series of batch tests to isolate the possible contribution of PAOs from GAOs by using their metabolic differences. Experimental results showed that although only relatively low PAOs fraction were not selected out of the A/O system by sludge wasting, the poly-phosphate granules clearly observed inside activated sludge bacteria verified the existence of PAOs. The kinetic coefficients of GAO-enriched sludge for anaerobic acetate uptake rate were calculated from regression analysis to be qmax = 1.0784 mg/g MLSS*hr and Ks = 70.486 mg/L. However, the kinetic coefficients of GAO were qmax = 0.9437 mg/g MLSS*hr and Ks = 95.54 mg/L. GAO-enriched sludge obviously demonstrated high substrate uptake behavior than GAO. These results imply that applying the kinetic behavior of GAO-enriched sludge to represent that of GAOs requires carefully examining the effect of PAOs.
Phosphate accumulating organisms has been experimentally proved to be capable of denitrifying by using their intracellular carbon as sole electron donor. Such PAOs are usually termed as DNPAO, i.e. denitrifying PAOs. If GAOs were also equipped with similar function, competition between PAOs and GAOs on nitrate in an anoxic state will affect the population community of a biological nutrient removal system, such as anaerobic-anoxic-oxic activated sludge process. Still, little information is available on the denitrification potential of GAOs. This study therefore evaluates the denitrification capability of GAOs in a continuous-flow A/O activated sludge system fed with P-limiting (P/COD = 1.4/300) substrate by using a series of batch tests with acetate and glucose as carbon sources. Experimental results indicated that denitrification behavior of GAO apparently followed Monod equation no matter acetate or glucose was fed as substrate. The maximum specific denitrification rates (qmax) and half-saturation constants (Ks) for acetate and glucose were determined to be 2.316 mg/g MLSS*hr, 5.589 mg/L (acetate) and 2.626 mg/g MLSS*hr, 6.85 mg/L (glucose), respectively. Feeding GAO with glucose obviously demonstrated higher denitrification capability than acetate.
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