The reduction of excessive discharge of phosphate into water bodies is a dominant theme to combat the critical eutrophication issue and requires the development of high-performance materials for effective phosphate treatment. In this study, rice straw was used as a raw material for the synthesis of biochar functionalized with layered double hydroxides (BC-LDHs) as efficacious phosphate adsorbents, and their successful synthesis was corroborated via characterization analysis. Experimental investigations, including pH, coexisting anion, reaction time, and initial phosphate concentration effects were systematically performed with selected BC-LDHs 6 and pure LDHs. An optimum pH of 3.0 was observed in both samples. Kinetic and isotherm studies indicated that phosphate adsorption on these samples was controlled by the pseudo-second-order model and the Freundlich model. Comparative kinetic tests also demonstrated that BC-LDHs 6 and pure LDHs reached the equilibrium within 24 h and 3 h, respectively. Nonetheless, the maximum adsorption capacity of the composite was 192 mg/g, which was higher than that of pure LDHs (166 mg/g). The coexistence of various anions negligibly affected the removal efficiency of the composite; however, fluoride was the most competitive anion for adsorption on pure LDHs. The adsorption mechanisms of the composite involved electrostatic interaction, inner-sphere complexation, pore diffusion, precipitation, and reconstruction. Furthermore, phosphate adsorbed on both materials could be easily recovered by 0.1 M NaOH solution owing to the displacement reaction between phosphate and hydroxyl ions. Additional evidence from reusability experiments exhibited that the composite could maintain its good adsorption performance even after three adsorption-desorption cycles. The transformation of BC-LDHs 6 after its usage in phosphate treatment (P-BC-LDHs 6) into a fertilizer was further explored by using seed germination and early growth assays of lettuce through a comparison with phosphate-loaded LDHs (P-LDHs). Lettuce seeds germinated in all P-BC-LDH 6 treatments showed undesirable growth characteristics compared with the controls, while total germination failure was observed under high concentrations of P-LDHs. In the latter experiments, the optimal application rates for plant growth were 2.5% for P-BC-LDHs 6 and 1.0% for P-LDHs. The considerably greater biomass development and length of lettuce were visible in samples delivered from P-BC-LDHs 6 compared to those from P-LDHs. The results obtained suggest that BC-LDHs 6 is a promising adsorbent for phosphate treatment and post-adsorption BC-LDHs 6 has the application potential to serve as a fertilizer for horticultural crop production.

Phosphorus is an indispensable nutrient to sustain the daily life of all living things on Earth. However, the over-enrichment of the aquatic ecosystem with phosphorus leads to eutrophication, which is still a global environmental problem. More stringent regulations have been put in place for the limit of phosphorus discharge to address this problem and resulted in the removal of phosphorus removal becomes exceptionally crucial. Furthermore, phosphorus deposits are a non-renewable resource and forecasted to deplete until 2170, given the current usage and global population growth. Thus, the removal of phosphorus coupled with the recovery and reuse of phosphorus offer the best strategies to meet the future phosphorus demand. Accordingly, adsorption represents a fascinating separation technique for phosphate from water because of the possibility of phosphorus recovery. Moreover, this approach has many advantages, such as efficient, easy operating conditions, low sludge production, and the possibility of regenerating the adsorbent. Numerous attractive low-cost adsorbents have been studied for phosphate removal, one of which is layered double hydroxides (LDH). Unfortunately, a high phosphate adsorption capacity of LDH can generally be achieved by calcination, which increases the preparation cost of LDH. In this study, LDH is functionalized with amorphous zirconium (hydr)oxide to obtain enhanced adsorption capacity and eliminate the high-temperature requirement during the synthesis process. Although different treatment techniques have been developed to eliminate phosphorus contamination, including for wastewater treatment, treated water often fails to meet quality regulations. Amorphous zirconium (hydr)oxide/MgFe layered double hydroxides composites (am-Zr/MgFe-LDH) with different molar ratios (Zr/Fe = 1.5 2) were prepared in two-stage synthesis by the combination of coprecipitation and hydrothermal methods. The synthesis of the composite could eliminate the requirement of high-temperature calcination in the LDH for phosphate adsorption. Moreover, the phosphate adsorption ability of the composite was higher than that of the individual LDH and amorphous zirconium (hydr)oxide. The presence of amorphous zirconium (hydr)oxide increased the phosphate adsorption ability of composite at low pH. The adsorption capacity was increased by decreasing the pH and increasing the temperature (from 290 to 324 K). The bicarbonate (HCO3 ) was the most competitive anion for phosphate adsorption. The pseudo-secondorder model provided the best description of the kinetic adsorption data. Furthermore, the adsorbed phosphate was easily desorbed by 1 N and reused 2 N of NaOH solutions. The results suggest that the am-Zr/MgFe-LDH composite is a promising material for phosphate removal and recovery from wastewater. A Fixed-bed column has been considered an industrially feasible technique for phosphate removal from water. Besides the adsorption capacity, the effectiveness of an adsorbent is also determined by its reusability efficiency. In this study, phosphate removal by a synthesized am-Zr/MgFe-LDH in a fixed-bed column system was examined. The results showed that the increased bed height and phosphate concentration, and reduced flow rate, pH, and adsorbent particle size were found to increase the column adsorption capacity. The optimum adsorption capacity of 25.15 mg-P g^{-1} was obtained at pH 4. The coexistence of seawater ions had a positive effect on the phosphate adsorption capacity of the composite. Nearly complete phosphate desorption, with a desorption efficiency of 91.7%, could be effectively achieved by 0.1 N NaOH for an hour. Moreover, the initial adsorption capacity was maintained at approximately 83% even after eight adsorption-desorption cycles, indicating that the composite is economically feasible. The am-Zr/MgFe-LDH, with its high adsorption capacity and superior reusability, has the potential to be utilized as an adsorbent for phosphorus removal in practical wastewater treatment. The possible adsorption mechanisms of phosphate by am-Zr/MgFe-LDH were investigated via X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and pH at the point of zero charge (pHPZC) analyses. It was suggested that the high phosphate adsorption capacity of the composite involves three main adsorption mechanisms, which are the electrostatic attraction, inner-sphere complexation, and anion exchange, where the amorphous zirconium (hydr)oxide on the surface of the layered double hydroxides likely increased the number of active binding sites and surface area for adsorption. This study provides insights into the design of am-Zr/MgFe- LDH for phosphorus removal and recovery in a practical system.

クロマトグラフィーは、バイオ医薬品の分離精製工程の重要な単位操作である。抗体タンパク質をはじめとしてバイオ医薬品の需要は増加しており、生産プロセスの能力向上は喫緊の課題である。また、プロセスの形態も従来の柔軟性の低い古典的なプロセスから様々な操作方法に迅速に対応可能なプロセスに近代化することが求められている。このため、本学位論文では従来の経験に基づいた回分式操作法に代わる連続式のマルチカラム型クロマトグラフィープロセスに着目し、実験的検討と数値計算を併用したプロセス開発手法の確立を目指した。また、プロセスの能力の指標として、単位時間当たりの抗体精製量とカラムの有効使用率や消費溶媒量を用い、操作条件の最適化を行った。 クロマトグラフィーの解析には機構モデルを用いた。機構モデルは吸着と物質移動過程を表現するものであり、クロマトグラフィーにおける移動現象を解析する上で統計的モデルよりも優れている。まず、バイオ医薬品としてタンパク質を使用し、いくつかの実験データを基に機構モデルを用いてモデルパラメータの決定を行った。得られたパラメーターを用い溶出挙動を精度よくシミュレーション可能であることを示した(第2章)。次に核酸を使用し、本手法の応用可能性について検討した(第3章)。次世代型のグラフト型クロマト担体における拡散の移動現象を細孔内拡散モデルにより記述し、リガンド構造の違いとモデルパラメータの関係を明らかにした。 さらにモノクローナル抗体のキャプチャープロセスへのマルチカラム型クロマトグラフィーシステム(continuous periodic counter-current (PCC))の導入を検討するために、機構モデルによる解析とシミュレーションを行った(第4章)。4カラムを有するPCCシステムを使用し比較対象として連続型回分式クロマトシステムを用いた。様々な操作条件でのプロセスの生産効率とカラム有効利用率、消費溶媒量をシミュレーションによりもとめプロセスの比較を行った。PCCを用いたキャプチャーステップの重要なパラメーターはカラム切り替えを行う破過点(BT%)である。破過点の決定にはカラム吸着容量とタンパク質の物質移動特性に加えて、サンプルの押し出し・平衡化・洗浄などのカラムにタンパク質を供給する以外の操作に関する情報も必要となる。これらの情報を統合して最適なBT%を取得するための計算式を機構モデルに基づくシミュレーション結果から確立した。確立した計算式で最適化した操作条件でPCCを操作した場合、回分式操作と比較して溶媒使用量を20％削減できることが分かった。またPCCのプロセス設計を迅速に行うための、さまざまな流速やカラム条件に適用できる動的吸着量(Dynamic binding capacity, DBC)と生産効率の回帰関係式を作成した。 最後に、精製効率を向上する手法としてキャプチャーステップにおけるタンパク質の新しい供給方法の開発を行った(第5章)。本手法では全吸着容量とサンプル供給量を時間の関数とした。DBCのカラム滞留時間依存性に基づき、流量を初期流量から後期流量まで直線的に減少させた。実際のプロセスで可能となるカラム滞留時間の範囲内で、初期流量および後期流量と流量の変化時間を網羅的に変化させてDBCの計算を行い、最適な操作条件の探索を行った。また4カラムのPCCへの応用も検討し、一定流量で操作した場合よりも流量変化法でPCCを操作した方が13%の担体コストの削減と1.4倍の生産効率の向上を達成できることを明らかにした。 第6章では、モデル化とシミュレーションの解析、連続プロセスの現状と今後について考察をまとめた。タンパク質医薬品製造プロセスでは、さらなる高速・効率化・低コスト化したプラットフォームを開発するべく、連続化に適したたんいそうさを連結・統合した連続精製プロセスの設計および構築が行われようとしている。この中で本研究で開発した機構モデルに基づく解析とシミュレーションを組み合わせたプロセスの開発手法は重要な役割を果たすと考えられる。