穩定型態交聯聚乙烯醇乘載活性污泥移除水中化學需氧量

Abstract

聚乙烯醇 (PVA) 與海藻酸鈉於pH 10 四羥基硼酸鈉水溶液交聯之水凝膠經過重複乾燥潤濕循環下皆能保持形狀穩定，而其經由硫酸根二次交聯之水凝膠於型態穩定上則沒什麼太大差異。本研究皆露出B(OH)4-核心 (B4) 為鹼性條件下硼酸聚乙烯醇交聯水凝膠 (PVA-Bb) 之主要骨幹，與酸性環境下硼酸聚乙烯醇水凝膠 (PVA-Ba) B(OH)3核心 (B3) 有所不同。而在PVA-Bb等規結構裡，其B4核心與PVA的二醇數量比為1 : 2.25，而經由親核試劑硫酸根的攻擊後之穩定二次交聯水凝膠PVA-Sb，其硫酸核心 (S4) 取代B4核心之比例可達到82.2%。 接著就利用型態穩定之PVA-Sa、PVA-Bb和PVA-Sb水凝膠固定普魯士藍作為有效率之重金屬銫吸附劑，而銫於此三種水凝膠結構中之通透性，PVA-Sa最高，而PVA-Bb和PVA-Sb為接近沒什麼差別。 再者聚乙烯醇水凝膠也可被用作微生物之無毒固定基材且成本便宜，且具有乾燥儲存的特性，包覆微生物之PVA水凝膠可用於廢水處理，降解廢水中無機和有機汙染物。本研究第一次利用乾溼循環下高型態穩定之PVA水凝膠包裹活性污泥，經由連續三天之COD測試中，可見到PVA活性污泥水凝膠具有高度生物活性和穩定性，而可見實際應用化之可能性。本研究四種主要型態之PVA水凝膠中，PVA-Sa與汙泥的結合具有最好的實用性，PVA-Sa裡的B3-S4核心具有足夠的結構彈性和強度抵抗乾燥與潤濕所要承受之強大伸縮應力，而此核心同時也能充分對抗頑強的生物攻擊性，相反地，不管是PVA-Ba還是鹼性PVA水凝膠，皆無充分具有上述之條件，所以是包覆微生物首選之水凝膠型態為PVA-Sa。理想之PVA-Sa微生物製劑不僅具有乾燥儲存的能力，且能低成本的大量生產，而乾燥儲存特性讓其具備異地生產異地使用之好處。 最後本研究四種主要PVA交聯水凝膠經過性質相反之酸鹼度環境調整，皆會出現結構和型態之變化，因為硼酸和四硼為路易士酸鹼對，因為pH值不同而有不同形態。本研究利用傅立葉紅外光譜、拉曼光譜、熱重分析法、硼硫取代實驗和核磁共振圖譜做結構分析，乾溼循環測試則可得出水凝膠大小變化和其潤濕能力，進而得知PVA水凝膠於pH值轉移後的結構核心與其穩定性。經由鹼性pH轉移，原本酸性PVA水凝膠[B3]核心會轉換成[B4]核心，反之亦然，然而其轉換並非完全，仍會保有少許原本核心結構未被轉換。另外酸性轉移會破壞鹼性PVA水凝膠之型態穩定性和潤濕能力，相反地，鹼性轉移不影響酸性水凝膠之穩定性甚至提升了潤濕能力。最後從結果推測[B3][B4]或[B4]核心傾向增加結構穩定性，而[B4]和[S4]轉換為[B4][B4]或[B4][S4]雙核心時，則會降低結構穩定性，另外本研究亦會提出四種轉移水凝膠之可能化學結構、核心轉換和反應機制。

The poly(vinyl alcohol) (PVA) and alginate hydrogels crosslinked at pH 10 with sodium tetrahydroxyborate (PVA-Bb) hydrogels are shape-stable under repeated dry-rewet cycles while the PVA-Ba hydrogel counterparts are not. Further crosslinking with sulfate ions to substitute the involved borate complex (PVA-Sb) only moderately enhanced the hydrogel stability. This study reveals that the B(OH)4- (hydrogen would be dehydrated) cores constitute the skeleton of the PVA-Bb matrix under alkaline condition, which is different from the B(OH)3 cores that are noted principally constituting the hydrogel matrix under acidic condition. The nucleophiles, SO42- can substitute up to 82.2% of incorporated borate cores in PVA-Bb matrix with isotactic segments at d : B = 2.25 : 1 to form shape-stable PVA hydrogels (PVA-Sb). The shape-stable PVA-Sa, PVA-Bb and PVA-Sb Prussian blue (PB) immobilized hydrogels are effective adsorbent of Cs ions from waters. The Cs permeability for PVA-Bb and PVA-Sb are close, and PVA-Sa has highest permeability for Cs ions. Next, the poly(vinyl alcohol) (PVA) hydrogels can be used as a non-toxic and inexpensive immobilization matrix for microbial cells with capability of degrading organic or inorganic pollutants in wastewaters. This study for the first time produced the PVA hydrogels with immobilized cells by two-stage crosslinking which have high shape-stability at dry-rewet cycles and, when recovered after sequentially three 24-hr cultivations, reveal high bioactivity in wastewater treatment. The [B(OH)3][SO42-] cores inside the PVA-boric acid-sulfate hydrogels (PVA-Sa) are proposed to support the immobilized cells with sufficient structure flexibility and strength to maintain hydrogel structural integrity and of sufficient recalcitrance to biological attack. Conversely, neither the PVA-boric acid hydrogels nor the PVA-borate hydrogels can be applied as organic pollutant degraders with dry storage capability. The PVA-boric acid-sulfate hydrogels are proposed as ideal matrix that can be produced and stored in dry, massive quantity and then applied latter at the same or different sites. Finally, the PVA-Ba, PVA-Bb and their second crosslinking type hydrogels all have structure and formation change by pH value shift applying. Because boric acid and borate are Lewis acid-base controlled by pH value, former pH 5 and latter pH 10. The PVA hydrogels yielded at different pH values can be applied to environment with opposite pH. This study investigated the linkage core and the shape stability changes when the PVA hydrogels were subjected to pH shock. The sizes, weights and chemical composition changes for the yielded hydrogels, the FTIR, Raman and NMR spectroscopy, and the TGA analysis of pH shocked hydrogel samples were recorded. With alkaline pH shock, the [B3] cores in PVA hydrogels are converted to [B4], while at acidic pH shock, the [B4] cores in the hydrogels are transformed to [B3] cores, but all in an incomplete conversion. The acidic pH shock would deteriorate the shape stability and moisture swelling capability of borate hydrogels ; conversely, the basic pH shock would not affect shape stability of boric acid hydrogels but even enhanced swelling capability of the boric acid hydrogels. The [B3][B4] or [B4] cores in the mix tend to enhance water stability of the hydrogels, the conversion of [B4] and [S4] to [B4][B4] or [B4][S4] dimers would destabilize the shape stability of the hydrogels. The findings proposed a way to manipulate the structure stability of PVA hydrogels by designing the compositions and configurations of the linkage cores.