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京都大学 / 新制・課程博士 / 博士(工学) / 甲第23184号 / 工博第4828号 / 新制||工||1754(附属図書館) / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 高岡 昌輝, 教授 田中 宏明, 准教授 大下 和徹 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Nitrogen pollution in the environment creates challenging problems globally and locally and can be effectively controlled by a significant reduction in nitrogen release into the natural water system. In addition, nutrients in high-strength wastewater can be recovered as valuable resources such as different types of ammonium solutions for industrial and agricultural utilizations. Selective ammonia separation from high-strength wastewater can be achieved by bipolar membrane electrodialysis (BMED), a relatively new ion exchange technology. A series of 8 bench-scale BMED experiments with bipolar membranes and cation exchange membranes were performed under various voltage applications. Ammonia in the wastewater was rapidly separated and recovered as a high purity ammonium hydroxide solution. BMED operation for 30 minutes at 5.0 V per cell pair was found to be ideal for high purity ammonium hydroxide production and low electrical energy consumption. Additionally, effective organic fouling control and low energy consumption were achieved. The experiments showed a decrease in the feed pH making it ideal for applications in solid-state anaerobic digestion with leachate recirculation. The application of leachate recirculation in solid-state anaerobic digestion (SSAD) has proven effective for mobilizing nutrients and diluting toxic byproducts to enhance biogas production. The leachate after recirculation contains accumulated ammonia and an increased pH and requires water and chemicals for dilution and pH adjustment prior to recirculation. The data from the experiments were used to construct a numerical model for a hypothetical lab-scale and pilot-scale bipolar membrane electrodialysis and solid-state anaerobic digestion with leachate recirculation (BMED-SSAD) system. A final ammonia concentration of less than 2000 mg-N/L in the reactor was found to be achievable by lab-scale (6 mA/cm2) and pilot-scale (12 mA/cm2) BMED-SSAD and low electric energy consumption. The results suggest that BMED is an attractive solution for ammonia separation from high-strength wastewater. / Thesis / Master of Applied Science (MASc)

Two different sludge pretreatments were investigated in an attempt to improve the management and performance of processes for the co-digestion of biosolids with fats, oils, and grease (FOG). The mechanisms of long chain fatty acids (LCFA) degradation in thermal hydrolysis pretreatment and the influence of pH on LCFA degradation in two-phase co-digestion systems were studied. LCFA thermal hydrolysis was investigated at different temperatures (90-250 °C) and reaction times (30 minutes and 8 hours). Approximately 1% of saturated fatty acids were degraded to shorter chain fatty acids at 140 and 160 °C (8-hr thermal hydrolysis). Only 1% or less of unsaturated fatty acids were degraded from 90 to 160 °C (8-hr thermal hydrolysis). Little degradation (< 1%) of both saturated and unsaturated LCFAs was observed at a 30-min reaction time. Both groups of LCFAs were stable up to 250 °C (30-min hydrolysis). The use of chemical-thermal treatments was also investigated. Only unsaturated LCFAs, C18:1 and C18:2, were degraded when thermally hydrolyzed with hydrogen peroxide coupled with activated carbon or copper sulfate. Semi-continuous, acid-phase digesters (APDs) under different pH conditions were studied in order to understand the effects of pH on FOG degradation. Increases in soluble chemical oxygen demand (SCOD) were observed in all APDs. However, the APDs with pH adjustment appeared to perform better than the controls in terms of solubilizing organic compounds. Approximately 38% and 29% of total COD (TCOD) was solubilized, and maximum volatile fatty acid (VFA) concentrations of 10,700 and 7,500 mg/L TCOD were achieved at pH 6 and 7, respectively; It is useful to note that the feed sludge had a VFA concentration of 2,700 mg/L COD. Higher pH (6.0-7.0) showed less accumulation of LCFA materials and more soluble LCFAs in the APDs. This indicates that the lower pH in the APDs was most likely the cause of precipitation and accumulation of LCFAs due to saturation of unsaturated LCFAs. / Master of Science

The increased demand for advanced sludge stabilization in wastewater treatment facilities over the past decade has led to the implementation of various pretreatment techniques prior to anaerobic digestion. In an attempt to reduce sludge volumes and improve sludge conditioning properties, the use of thermal hydrolysis process before anaerobic digestion has been adopted with an increase in solids destruction, COD removal, and methane gas. In this study, the evaluation of thermal hydrolysis process as a viable pretreatment strategy to anaerobic digestion has been conducted in order to assess its capacity for solids solubilization. Solubilization experiments were conducted at temperatures ranging from 130 to 170℃ and reaction times between 10 and 60 min. Anaerobic biogas production by thermally pre-treated sludge was carried out through a mesophilic anaerobic digester. The results showed that solids solubilization increased with increases in temperature and time, while temperatures above 160℃ for 30 min strongly affected the sludge characteristics. Ammonia production via deamination by thermal hydrolysis was less significant than protein solubilization at a temperature of 170℃. Both protein and carbohydrate solubilization were more dependent on temperature than reaction time. The enhancement of the biogas production was achieved with increases in temperature as pretreatment of 170℃ yielded 20% more biogas than at 130℃. However, it seems the enhancement was linked to the initial biodegradability of the sludge. / Master of Science

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We analyze a simplified mathematical model of the complete degradation of monochlorophenol. The model takes form of a system of six ordinary differential equations, the dynamics of which can be reduced to the dynamics of a three-dimensional system on the invariant set. We extend the previous analysis by considering multiple substrate inflow. We also focus on the bifurcations occurring in the system and their biological meaning. / Thesis / Master of Science (MSc)