Studies on the Effluent VFA Limits and DO Effects for the Treatment of Low-Strength Wastewater with Anaerobic Fluidized Bed

Studies on the Effluent VFA Limits and DO Effects for the Treatment of Low-Strength Wastewater with Anaerobic Fluidized Bed
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A general concern that anaerobic treatment of dilute wastewaters is limited by the inability of methanogenic and related syntrophic organisms to reduce substrate concentrations adequately was evaluated using a 35 oC GAC-containing laboratory-scale anerobic fluidized bed reactor (AFBR) fed an acetate-propionate equal COD mixture synthetic wastewater. Contrary to general expectations, effluent acetate and propionate concentrations remained near or below their detection limits of 0.4 mg/L with influent COD of 200 mg/L, at 17 min hydraulic retention time and organic loading as high as 18 kg COD/m3-d, or with influent COD values ranging from 45 to 2,010 mg COD/L and organic loadings of 4.2-4.5 kg COD/m3-d. The effluent acetate concentrations in these well-fed systems were at or much below reported threshold limits for starving non-fed cultures, suggesting that a better understanding of threshold values and factors affecting treatment efficiency with anaerobic treatment of dilute wastewaters is needed. The effect of influent DO/COD (dissolved oxygen/chemical oxygen demand) ratio on the performance of the AFBR was also studied. A high influent DO concentration was found to have adverse impacts on organic removal efficiency, methane production, and effluent suspended solids (SS) concentration. These problems resulted with a DO/COD ratio of 0.12, but not at a lower ratio of 0.05. At first organic removal appeared satisfactory at the higher DO/COD ratio at a hydraulic retention time of 0.30 h, but soon a rapid growth of oxygen-consuming zoogloeal-like organisms resulted, eventually causing high effluent SS concentrations. The influent DO also had an inhibitory effect, resulting in a long recovery time for adequate methanogenic activity to return after influent DO removal began. With the growing interest in anaerobic treatment of low COD wastewaters, the increased possibility of similar adverse DO effects occurring needs consideration.
1. Introduction 1 1.1. Introduction 1 1.2. References 4 2. Literature Review 6 2.1 Low Strength Wastewater Treatment with High-Rate Anaerobic Reactors 6 2.2 Anaerobic Fluidized Bed Reactor (AFBR) 11 2.3 References 15 3. Lower Operational Limits to Volatile Fatty Acid Degradation with Dilute Wastewaters in an Anaerobic Fluidized Bed Reactor 19 3.1 Introduction 19 3.2 Materials and Methods 21 3.2.1 Experimental Procedures 21 3.2.2 Chemical Analyses 25 3.2.3 Microbial Characterization 27 3.3 Results and Discussion 27 3.3.1 General Performance 27 3.3.2 Effect of OLR 29 3.3.3 Effect of Influent COD Concentration 32 3.3.4 Microbial Analyses 34 3.3.5 Suspended Solids Mass Balance 35 3.3.6 Discussion 36 3.4 Conclusion 41 3.5 References 41 4. Effects of Influent DO/COD Ratio on the Performance of an Anaerobic Fluidized Bed Reactor Fed Low-strength Synthetic Wastewater 44 4.1 Introduction 44 4.2 Methods 47 4.2.1 Anaerobic Fluidized Bed Reactor (AFBR) 47 4.2.2 Analyses 50 4.3 Results and Discussion 52 4.3.1 Performance of the AFBR under the Influence of DO 52 4.3.2 Performance of the AFBR without the Influence of DO 58 4.3.3 Discussion 58 4.4 Conclusion 60 4.5 References 61 5. Conclusions 64
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College of Engineering(공과대학) > Environmental Engineering (환경공학) > Theses(환경공학 석박사 학위논문)
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