JP2004075763A - Polyvinyl alcohol hydrous gel and its manufacturing method - Google Patents
Polyvinyl alcohol hydrous gel and its manufacturing method Download PDFInfo
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- JP2004075763A JP2004075763A JP2002235528A JP2002235528A JP2004075763A JP 2004075763 A JP2004075763 A JP 2004075763A JP 2002235528 A JP2002235528 A JP 2002235528A JP 2002235528 A JP2002235528 A JP 2002235528A JP 2004075763 A JP2004075763 A JP 2004075763A
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
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Abstract
Description
【0001】
【発明の属する技術分野】
本発明は、排水処理などに用いられる微生物固定化担体に適したポリビニルアルコ−ル系含水ゲルおよびその製造方法に関する。
【0002】
【従来の技術】
高分子含水ゲルは、生体触媒の担体、保水剤、保冷剤、眼・皮膚・関節などの生体ゲルの代替、薬物の徐放材、アクチュエ−タ−の基材として、その研究が盛んに進められている。これらの含水ゲルの原料となる高分子素材としては、寒天、アルギン酸塩、カラギ−ナン、ポリアクリルアミド、ポリビニルアルコ−ル、光硬化性樹脂などが知られている。これらの高分子素材を原料とする含水ゲルは、これに微生物菌体を固定させ、排水処理などの分野で用いられている。排水処理などに用いられる担体の特性としては、含水率が高いこと、酸素や基質の透過性に優れていること、生体との親和性が高いことなどが必要とされ、これらの要求特性を満たすポリビニルアルコ−ル(以下、PVAと略記することがある)からなる含水ゲルは、排水処理用担体、バイオリアクタ−用担体などとして重用されている。
【0003】
従来、PVA系含水ゲルの製造法として、PVAおよびアルギン酸ナトリウムの水溶液を塩化カルシウム水溶液に接触させて球状化した後、凍結解凍を行う方法(特開昭64−43188号公報)、PVA水溶液を飽和ホウ酸水溶液に接触させてゲル化する方法(「下水道協会誌」、1986年、第23巻、41頁;「用水と廃水」、第30巻、36頁(1986年))、PVA水溶液を鋳型に注入した後、凍結により部分的に脱水を行う方法(特開昭58−36630号公報)などが知られている。しかし、排水処理に用いられる、従来知られているPVA系含水ゲルからなる担体は、担体の強度を保つために、ゲルを製造する際に、水溶液中における主成分のPVAは5〜20重量%の濃度であり、そのため得られる含水ゲルの比重は、水に近いとはいえ、1.025〜1.05程度と軽いと言えるものではなかった。
【0004】
PVA系含水ゲル担体の比重が大きいと、これを曝気槽に入れて排水処理を行う際に、水深が5m以内と浅い標準曝気槽において担体の流動性が問題になることはほとんどなかったが、都市下水処理場などで採用されている水深約10mの深槽曝気方式による排水処理においては、担体が槽の底部に滞留し担体の利用効率が低下するという問題があった。
【0005】
【発明が解決しようとする課題】
そこで本発明は、反応槽中において流動性に優れており、深度が深い反応槽中にあっても、槽の底部に滞留することがなくて、取扱性に優れた担体となりうるPVA系含水ゲルを提供することを目的とする。
【0006】
【課題を解決するための手段】
本発明によれば、上記課題は、PVAおよび水よりなるゲルであり、含水率が91%以上98%以下であり、比重が1.00以上1.02以下であるPVA系含水ゲルにより解決されることが見出された。このようなPVA系含水ゲルは、PVA(a)1〜4重量%、およびカチオンとの接触によりゲル化する能力のある水溶性多糖類(b)0.1〜0.9重量%を含む水溶液をカチオン含有水溶液と接触させた後、不溶化処理を行うことにより製造することができる。そして、上記PVA系含水ゲルは、排水処理などに用いられる微生物固定化担体として有効に用いることができる。
【0007】
【発明の実施の形態】
本発明のPVA系含水ゲルは、含水率が91%以上98%以下であり、比重が1.00以上1.02以下であることが重要である。PVA系含水ゲルの含水率が91%未満であったり、あるいは比重が1.02を越える場合、深槽曝気槽において担体が槽の底部に滞留し担体の効率が低下するため好ましくない。PVA系含水ゲルの含水率が98%を超える場合、含水ゲルの強度が小さく、槽内を流動中に担体が破壊されることがあり好ましくない。また、PVA系含水ゲルの比重が1.00未満の場合、担体が槽の上部に浮上して槽内を流動しなくなることがあり好ましくない。
【0008】
本発明のPVA系含水ゲルは、PVA(a)1〜4重量%、およびカチオンとの接触によりゲル化する能力のある水溶性多糖類(b)0.1〜0.9重量%を含む水溶液をカチオン含有水溶液と接触させた後、不溶化処理を行うことにより製造することができる。PVA(a)としては、含水ゲルの機械的強度の点から平均重合度が2000以上であることが好ましく、2400以上がより好ましい。平均重合度について厳密な意味での上限は存在しないが、平均重合度が大き過ぎると、PVAの製造時に、PVAを含有する水溶液の流動性が低下し、生産性が悪くなる傾向があるので、平均重合度は8000以下が好ましい。PVAのケン化度について特に制限はないが、PVAを含有する水溶液の粘度や製造した含水ゲルの機械的強度の点から、通常75モル%以上であり、98.5モル%以上が好ましく、99.85モル%以上がより好ましい。
【0009】
カチオンとの接触によりゲル化する能力のある水溶性多糖類(b)とは、水溶性であり、少なくとも1種のカチオンを含有する水溶液に接触させることにより水に不溶性又は難溶性のゲルに変化する能力のある物質である。このような水溶性多糖類(b)の例としては、アルギン酸のアルカリ金属塩、カラギ−ナン、マンナン、キトサン等が挙げられるが、とりわけアルギン酸ナトリウムが好ましい。
【0010】
PVA(a)および水溶性多糖類(b)を含む水溶液の調製方法は、水中にPVA(a)および水溶性多糖類(b)が溶解され、水中に安定に分散される方法であれば特に制限はなく、その代表的な方法としては、PVA(a)を水に溶解し、次いで水溶性多糖類(b)の水溶液を添加した後、攪拌、混合する方法を挙げることができる。その際、PVA(a)および水溶性多糖類(b)をそれぞれ1〜4重量%および0.1〜0.9重量%の範囲の量で用いることが、本発明のPVA系含水ゲルを製造する上で重要である。PVAの濃度が4重量%を超えると、本発明において規定したよりも比重の大きいPVA系含水ゲルが得られ、深槽曝気槽において担体が槽の底部に滞留し担体の効率が低下するため好ましくない。また、PVAの濃度が1重量%より小さいと、製造されたPVA系含水ゲルは強度が小さく、槽内を流動中に担体が破壊されることがあり、好ましくない。水溶性多糖類の濃度が0.1より小さいと、製造したPVA系含水ゲルの強度が小さく好ましくない。0.9重量%より大きいと、製造したPVA系含水ゲルの比重が大きくなり過ぎるので、好ましくない。
【0011】
PVA(a)および水溶性多糖類(b)を含む水溶液には、本発明の効果を損なわない範囲であれば、上記(a)および(b)以外の成分が含まれていてもよく、その含まれていてもよい成分としては、例えば含水ゲル成形物の強度を上げるための補強材等が挙げられる。
【0012】
本発明の方法においては、PVA(a)および水溶性多糖類(b)を含む水溶液をカチオン含有水溶液と接触させることにより、水溶性多糖類(b)がゲル化する。カチオンの例としては、水溶性多糖類(b)がアルギン酸ナトリウムの場合、カルシウムイオン、マグネシウムイオン、ストロンチウムイオン、バリウムイオンなどのアルカリ土類金属イオン、アルミニウムイオン、ニッケルイオン、セリウムイオンなどの多価金属イオンから選択するのが好ましく、水溶性多糖類(b)がカラギーナン、マンナンまたはキトサンの場合、上記したカチオン以外にナトリウムイオン、カリウムイオンなどのアルカリ金属イオン、アンモニウムイオンなども使用することができる。
【0013】
上記したカチオン含有水溶液におけるカチオンの濃度は水溶性多糖類(b)の種類等によっても異なるが、一般には0.01〜5モル/Lの範囲内である。また、水溶性多糖類としてマンナンまたはキトサンが用いられる場合には、水溶液のpHが8以上、好ましくは10以上に調整されているのがよく、その目的のために、例えば水酸化カルシウム、炭酸ナトリウム等が水に溶解して使用される。
【0014】
PVA(a)および水溶性多糖類(b)を含む水溶液をカチオン含有水溶液と接触させることにより形成されるゲルの形状は、ゲル担体の流動性の点から、球状であることが好ましい。球状のゲルを得る方法としては、PVA(a)および水溶性多糖類(b)を含む水溶液を注射針のような細い管の先端からカチオン含有水溶液中に滴下する、同水溶液を遠心力を利用して球状に飛散させカチオン含有水溶液中に滴下する、同水溶液をスプレーノズルの先端から霧化して球状としカチオン含有水溶液中に滴下する、などの種々の方法を採用することができる。カチオン含有水溶液中に滴下させる液滴の大きさは、目的とする担体の粒径に応じて自由に変えることができるが、通常は直径約0.1mm〜約5mm、好ましくは約0.5mm〜約3mmである。
【0015】
カチオン含有水溶液中で形成されたゲルは、不溶化処理が施こされ、これによりゲルの強度を向上させることができる。不溶化処理の方法としては、ほう酸等による処理を行うこともできるが、PVA系含水ゲルからのPVAの溶出や該ゲルの劣化を回避するため、アセタ−ル化等による化学架橋が好ましい。
【0016】
PVAのアセタール化により不溶化処理を行う場合、カチオン含有水溶液中で形成された含水ゲルを一旦取り出し、アセタ−ル化液に浸漬させる。アセタ−ル化液としては、アルデヒド化合物および酸を含む水溶液が用いられる。使用しうるアルデヒド化合物としては、グリオキザ−ル、ホルムアルデヒド、ベンズアルデヒド、スクシンアルデヒド、マロンジアルデヒド、グルタルアルデヒド、アジピンアルデヒド、テレフタルアルデヒド、ノナンジア−ルなどが挙げられる。また、使用しうる酸としては、硫酸、塩酸、リン酸、硝酸、酢酸、シュウ酸などの酸や、硫酸水素ナトリウム、硫酸水素アンモニウムなどの酸性塩が挙げられる。アルデヒド化合物および酸の存在下において含水ゲルが過膨潤したり、溶解する可能性があることから、アセタ−ル化液にはその抑制剤として、PVAの離液作用のある硫酸ナトリウムなどを添加してもよい。PVAのアセタ−ル化度は、10〜60モル%が好ましく、20〜55モル%がより好ましい。アセタ−ル化度が10モル%より低いと、十分な耐水性が得られなくなることがあり、一方、アセタ−ル化度が60モル%より高いとPVAが過剰に疎水化される結果、微生物の棲息性が低下する傾向が見られる。アセタ−ル化により不溶化処理を行った後の含水ゲルをアセタ−ル化液と分離し、水による洗浄および中和などの処理を施し、含水状態のゲルを得る。含水状態のゲルは一旦乾燥させてもよく、この場合、再び水に浸漬させると含水状態のゲルに復元する。
【0017】
本発明のPVA系含水ゲルは、空隙率が高く微生物の棲息性に優れるため、生物反応槽中において微生物および酵素などの生体触媒を担持する微生物固定化担体として好適に使用される。微生物を担持する方法については特に限定はなく、不溶化処理を施した後の含水ゲルに微生物を後付着させてもよいし、PVA(a)および水溶性多糖類(b)を含む水溶液に微生物を混合して包括固定させてもよい。ただし、微生物の包括固定を行う場合、不溶化処理で用いるアセタール化液等によって微生物が死滅することがないように微生物の種類を選択し、不溶化条件を調整する必要がある。
【0018】
PVA系含水ゲルからなる担体に固定化させることのできる微生物の種類に特に限定はなく、細菌、放線菌、カビ、酵母などのいずれでもよく、純粋培養で得られたものでも混合培養で得られたものでも、活性汚泥のようなものでもよい。微生物としては、たとえば、ムコ−ル(Muccor)属、フザリウム(Fusarium)属、クラドツリックス(Cladothrix)属、スフェロチルス(Sphaerotilus)属、ズ−グレア(Zooglea)属、レプトミツス(Leptomitus)属、アスペルギルス(Aspergillus)属、リゾプス(Rhizopus)属、シュ−ドモナス(Pseudomonas)属、アセトバクタ−(Acetobacter)属、ストレプトマイセス(Streptomyces)属、エシエリシア(Escherichia)属、サッカロマイセス(Saccharomyces)属、キャンディダ(Candida)属に属する微生物が挙げられ、イオウ細菌、メタン菌、酪酸菌、乳酸菌、枯草菌、変形菌、不全菌、硝酸菌、亜硝酸菌、脱窒菌なども例示される。
【0019】
【実施例】
以下、実施例により本発明を具体的に説明するが、本発明はこれらの実施例により限定されるものではない。PVA系含水ゲルの含水率、比重およびアセタール化度は以下の方法にしたがって求めた。また、PVA系含水ゲルからなる担体の流動性は以下の方法にしたがって評価した。
【0020】
(含水率)
PVA系含水ゲルを25℃の水に24時問浸漬し、表面付着水を除去した後、含水ゲルの重量を測定し、その値をwet重量(W1)とする。次に、wet重量を測定した含水ゲルを105℃で4時間乾燥してその重量を測定し、その値をdry重量(W2)とする。含水ゲルのwet重量(W1)およびdry重量(W2)から、下式にしたがって含水率を算出した。
含水率(%)=(W1−W2)/W1×100
【0021】
(比重)
温度25℃の環境中で容量50mLの試験管中に硫酸ナトリウムと水により特定の比重に調製した比重調製液50mLを作製した。PVA系含水ゲル10個を表面付着水を除去した後、試験管内の比重調製液中に投入した。PVA系含水ゲルの投入より10秒後に、浮いているゲル、沈んでいるゲル、中間に留まっているゲルの個数を数え、中間に留まっているPVA系含水ゲルの個数が全体の過半数を超えた場合、そのときの比重調製液の比重を含水ゲルの比重とした。
【0022】
(アセタ−ル化度)
PVA系含水ゲルを105℃で2時間乾燥させた試料0.2gを精秤し、25%硫酸溶液を装填した蒸留装置に投入した。次いで蒸気を送りながら加熱し、遊離するアルデヒドを水と共に留出させ、2%亜硫酸水素ナトリウム(NaHSO3と略記することがある)水溶液に吸収させた。余剰のNaHSO3水溶液をヨウ素により逆滴定して遊離アルデヒド量を求め、ゲル中の水酸基量の割合(モル比)からアセタール化度を算出した。
【0023】
(流動性)
容積1Lのガラス製メスシリンダ−にPVA系含水ゲルからなる担体100g(wet重量換算)を入れ、水を入れて1Lとした。内径4mmのシリコンチュ−ブの先端をメスシリンダ−の底部へ挿入し、1L/分で空気を送りこみ、底部で滞留しているゲルの有無により流動性を評価した。
【0024】
実施例1
PVA((株)クラレ製 平均重合度2400、ケン化度99.8モル%)4重量%、アルギン酸ナトリウム(紀文フードケミファ社製「ダックアルギン」NSPL)0.5重量%の水溶液を調製した。この混合水溶液を先端に内径3mmノズルを取り付けた内径4mmのシリコンチュ−ブを装着したロ−ラ−ポンプにより5mL/分の速度で送液し、スタ−ラ−で撹拌した濃度0.05モル/Lの塩化カルシウム水溶液に滴下した。滴下した液滴は塩化カルシウム水溶液中で球状化して沈降した。この球状成形物を塩化カルシウム水溶液と分離して水洗した後、ホルムアルデヒド30g/L、硫酸200g/L、硫酸ナトリウム100g/Lの40℃の水溶液に60分浸漬した後水洗した。その結果、直径約4.5mmの球状の含水ゲルが得られた。この含水ゲルの含水率は93重量%、比重は1.015、アセタ−ル化度は46モル%であり、流動性評価では、すべての担体が流動し、底部への滞留はなく、流動性は非常に良好であった。
【0025】
実施例2
PVA((株)クラレ製 平均重合度4000、ケン化度99.8モル%)3重量%、アルギン酸ナトリウム(紀文フードケミファ社製「ダックアルギン」NSPL)0.5重量%の水溶液を調製した。この水溶液を先端に内径3mmのノズルを取り付けた内径4mmのシリコンチュ−ブを装着したロ−ラ−ポンプにより5mL/分の速度で送液し、スタ−ラ−で撹拌した濃度0.05モル/Lの塩化カルシウム水溶液に滴下した。滴下した液滴は塩化カルシウム水溶液中で球状化して沈降した。この球状成形物を塩化カルシウム水溶液と分離して水洗した後、ホルムアルデヒド30g/L、硫酸200g/L、硫酸ナトリウム100g/Lの40℃の水溶液に60分浸漬した後水洗した。その結果、直径約4.5mmの球状の含水ゲルが得られた。この含水ゲルの含水率は94重量%、比重は1.01、アセタ−ル化度は42モル%であった。流動性を評価したところ、すべての担体が流動し、底部への滞留はなく、流動性は非常に良好であった。
【0026】
比較例1
PVA((株)クラレ製 平均重合度1700、ケン化度99.8モル%)10重量%、アルギン酸ナトリウム(紀文フードケミファ社製「ダックアルギン」NSPL)1重量%の水溶液を調製した。この混合水溶液を先端に内径2mmのノズルを取り付けた内径3.2mmのシリコンチュ−プを装着したロ−ラ−ポンプにより5mL/分の速度で送液し、スタ−ラ−で撹搾した濃度0.1モル/Lの塩化カルシウム水溶液に滴下した。滴下した液滴は塩化カルシウム水溶液中で球状化して沈降した。この球状成形物を塩化カルシウム水溶液と分離して水洗し、これをトレ−に入れ、−20℃の冷凍庫で24時間凍結し、室温で解凍した。その結果、直径約5mmの球状の含水ゲルが得られた。含水率は90重量%、比重は1.035であった。流動性を評価したところ、底部に約半分の担体が滞留し、流動性は不十分であった。
【0027】
比較例2
PVA((株)クラレ製 平均重合度1700、ケン化度99.8モル%)8重量%、アルギン酸ナトリウム(紀文フードケミファ社製「ダックアルギン」NSPL)1重量%の水溶液を調製した。この混合水溶液を先端に内径3mmのノズルを取り付けた内径4mmのシリコンチュ−ブを装着したロ−ラ−ポンプにより5mL/分の速度で送液し、スタ−ラ−で撹枠した濃度0.1モル/Lの塩化カルシウム水溶液に滴下した。滴下した液滴は、塩化カルシウム水溶液中で球状化して沈降した。この球状成形物を塩化カルシウム水溶液と分離して水洗した後、ホルムアルデヒド20g/L、硫酸200g/Lの40℃の水溶液に90分浸漬した後水洗した。その結果、直径約5mmの球状の含水ゲルが得られた。この含水ゲルの含水率は88重量%、比重は1.04、アセタ−ル化度は58モル%であった。流動性を評価したところ、底部に約半分の担体が滞留し、流動性は不十分であった。
【0028】
【発明の効果】
本発明のPVA系含水ゲルは、微生物の棲息性に優れていることから、生物反応槽中において微生物および酵素などの生体触媒を担持する微生物固定化担体として有効に使用することができる。本発明のPVA系含水ゲルに微生物を固定化させた担体は、生物反応槽中で攪拌されても崩壊しない強度を有する上に、反応槽中において流動性に優れており、深度が深い反応槽中にあっても、槽の底部に滞留することがなくて、取扱性に優れている。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polyvinyl alcohol-based hydrogel suitable for a microorganism-immobilized carrier used for wastewater treatment and the like, and a method for producing the same.
[0002]
[Prior art]
Polymer hydrogel has been actively studied as a carrier for biocatalyst, water-retaining agent, cold-retaining agent, substitute for biogels for eyes, skin, joints, etc., as a sustained-release material for drugs, and as a base material for actuators. Have been. Agar, alginate, carrageenan, polyacrylamide, polyvinyl alcohol, photocurable resin, and the like are known as a polymer material serving as a raw material of these hydrogels. Hydrous gels using these polymer materials as raw materials are used in fields such as wastewater treatment, in which microbial cells are fixed. Carriers used for wastewater treatment, etc., must have high water content, have excellent oxygen and substrate permeability, and have high affinity with living organisms. BACKGROUND ART A hydrogel made of polyvinyl alcohol (hereinafter may be abbreviated as PVA) is frequently used as a carrier for wastewater treatment, a carrier for a bioreactor, and the like.
[0003]
Conventionally, as a method for producing a PVA-based hydrogel, an aqueous solution of PVA and sodium alginate is brought into contact with an aqueous calcium chloride solution to form a spheroid, followed by freezing and thawing (JP-A-64-43188). A method of gelling by contacting with an aqueous boric acid solution ("Sewer Association of Japan", 1986, Vol. 23, p. 41; "Water and wastewater", Vol. 30, p. 36 (1986)). And then partially dehydrating by freezing (JP-A-58-36630). However, in order to maintain the strength of the carrier, the carrier composed of a conventionally known PVA-based hydrogel used for wastewater treatment is required to contain 5-20% by weight of PVA as a main component in an aqueous solution when producing the gel. The specific gravity of the resulting hydrogel was close to that of water, but was not as light as about 1.025 to 1.05.
[0004]
When the specific gravity of the PVA-based hydrogel carrier is large, when it is put into an aeration tank for drainage treatment, the fluidity of the carrier rarely becomes a problem in a standard aeration tank having a shallow depth of 5 m or less, In wastewater treatment by a deep tank aeration method with a water depth of about 10 m employed in an urban sewage treatment plant or the like, there has been a problem that the carrier stays at the bottom of the tank and the utilization efficiency of the carrier is reduced.
[0005]
[Problems to be solved by the invention]
Therefore, the present invention provides a PVA-based hydrogel that is excellent in fluidity in a reaction tank, does not stay at the bottom of the tank even in a deep reaction tank, and can be a carrier excellent in handleability. The purpose is to provide.
[0006]
[Means for Solving the Problems]
According to the present invention, the above problems are solved by a gel comprising PVA and water, which has a water content of 91% or more and 98% or less and a specific gravity of 1.00 or more and 1.02 or less. Was found. Such a PVA-based hydrogel is an aqueous solution containing 1 to 4% by weight of PVA (a) and 0.1 to 0.9% by weight of a water-soluble polysaccharide (b) capable of gelling by contact with a cation. After contacting with a cation-containing aqueous solution, and then performing an insolubilization treatment. The PVA-based hydrogel can be effectively used as a microorganism-immobilized carrier used for wastewater treatment and the like.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
It is important that the PVA-based hydrogel of the present invention has a water content of 91% to 98% and a specific gravity of 1.00 to 1.02. If the water content of the PVA-based hydrogel is less than 91% or the specific gravity exceeds 1.02, the carrier stays at the bottom of the deep aeration tank and the efficiency of the carrier decreases, which is not preferable. When the water content of the PVA-based hydrogel exceeds 98%, the strength of the hydrogel is low, and the carrier may be broken during the flow in the tank, which is not preferable. When the specific gravity of the PVA-based hydrogel is less than 1.00, the carrier may float on the upper portion of the tank and may not flow in the tank, which is not preferable.
[0008]
The PVA-based hydrogel of the present invention is an aqueous solution containing 1 to 4% by weight of PVA (a) and 0.1 to 0.9% by weight of a water-soluble polysaccharide (b) capable of gelling by contact with a cation. After contacting with a cation-containing aqueous solution, and then performing an insolubilization treatment. The average degree of polymerization of PVA (a) is preferably 2000 or more, more preferably 2400 or more, from the viewpoint of the mechanical strength of the hydrogel. There is no upper limit in a strict sense for the average degree of polymerization, but if the average degree of polymerization is too large, during the production of PVA, the fluidity of the aqueous solution containing PVA decreases, and the productivity tends to deteriorate, The average degree of polymerization is preferably 8000 or less. The degree of saponification of PVA is not particularly limited, but is usually at least 75 mol%, preferably at least 98.5 mol%, and more preferably at least 99 mol%, in view of the viscosity of the aqueous solution containing PVA and the mechanical strength of the produced hydrogel. .85 mol% or more is more preferable.
[0009]
The water-soluble polysaccharide (b) capable of gelling upon contact with a cation is a water-soluble gel that is converted into a water-insoluble or hardly-soluble gel by contact with an aqueous solution containing at least one cation. Is a substance capable of Examples of such water-soluble polysaccharides (b) include alkali metal salts of alginic acid, carrageenan, mannan, chitosan and the like, with sodium alginate being particularly preferred.
[0010]
A method for preparing an aqueous solution containing PVA (a) and a water-soluble polysaccharide (b) is particularly suitable as long as PVA (a) and a water-soluble polysaccharide (b) are dissolved in water and are stably dispersed in water. There is no limitation, and as a representative method, a method of dissolving PVA (a) in water, adding an aqueous solution of water-soluble polysaccharide (b), stirring and mixing can be exemplified. In this case, the PVA (a) and the water-soluble polysaccharide (b) are used in amounts of 1 to 4% by weight and 0.1 to 0.9% by weight, respectively, to produce the PVA-based hydrogel of the present invention. It is important in doing. When the concentration of PVA exceeds 4% by weight, a PVA-based hydrogel having a higher specific gravity than that specified in the present invention is obtained, and the carrier stays at the bottom of the deep aeration tank and the efficiency of the carrier is reduced. Absent. On the other hand, if the concentration of PVA is less than 1% by weight, the produced PVA-based hydrogel has low strength, and the carrier may be broken while flowing in the tank, which is not preferable. If the concentration of the water-soluble polysaccharide is smaller than 0.1, the strength of the produced PVA-based hydrogel is low, which is not preferable. If it is more than 0.9% by weight, the specific gravity of the produced PVA-based hydrogel becomes too large, which is not preferable.
[0011]
The aqueous solution containing PVA (a) and the water-soluble polysaccharide (b) may contain components other than the above (a) and (b) as long as the effects of the present invention are not impaired. Examples of the component that may be included include, for example, a reinforcing material for increasing the strength of the hydrogel molded article.
[0012]
In the method of the present invention, the aqueous polysaccharide (b) is gelled by bringing an aqueous solution containing PVA (a) and the water-soluble polysaccharide (b) into contact with an aqueous solution containing cations. Examples of the cation include, when the water-soluble polysaccharide (b) is sodium alginate, alkaline earth metal ions such as calcium ion, magnesium ion, strontium ion, and barium ion; aluminum ions, nickel ions, and cerium ions; It is preferable to select from metal ions. When the water-soluble polysaccharide (b) is carrageenan, mannan or chitosan, an alkali metal ion such as sodium ion and potassium ion, an ammonium ion and the like can be used in addition to the above cations. .
[0013]
The concentration of the cation in the cation-containing aqueous solution varies depending on the type of the water-soluble polysaccharide (b) and the like, but is generally in the range of 0.01 to 5 mol / L. When mannan or chitosan is used as the water-soluble polysaccharide, the pH of the aqueous solution may be adjusted to 8 or more, preferably 10 or more. For that purpose, for example, calcium hydroxide, sodium carbonate Is used by dissolving in water.
[0014]
The gel formed by contacting the aqueous solution containing PVA (a) and the water-soluble polysaccharide (b) with the cation-containing aqueous solution is preferably spherical in view of the fluidity of the gel carrier. As a method of obtaining a spherical gel, an aqueous solution containing PVA (a) and a water-soluble polysaccharide (b) is dropped into a cation-containing aqueous solution from the tip of a thin tube such as an injection needle, and the aqueous solution is centrifuged. Various methods can be adopted, such as scattering into a cation-containing aqueous solution by dropping into a cation-containing aqueous solution, or atomizing the aqueous solution from the tip of a spray nozzle into a spherical shape and dropping into the cation-containing aqueous solution. The size of the droplet to be dropped into the cation-containing aqueous solution can be freely changed according to the particle size of the target carrier, but usually the diameter is about 0.1 mm to about 5 mm, preferably about 0.5 mm to It is about 3 mm.
[0015]
The gel formed in the cation-containing aqueous solution is subjected to an insolubilization treatment, whereby the strength of the gel can be improved. As a method of the insolubilization treatment, treatment with boric acid or the like may be performed, but in order to avoid elution of PVA from the PVA-based hydrous gel and deterioration of the gel, chemical cross-linking by acetalization or the like is preferable.
[0016]
When the insolubilization treatment is performed by acetalization of PVA, the hydrogel formed in the cation-containing aqueous solution is once taken out and immersed in an acetalization solution. As the acetalization liquid, an aqueous solution containing an aldehyde compound and an acid is used. Examples of aldehyde compounds that can be used include glyoxal, formaldehyde, benzaldehyde, succinaldehyde, malondialdehyde, glutaraldehyde, adipine aldehyde, terephthalaldehyde, nonandial, and the like. Examples of the acid that can be used include acids such as sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, acetic acid, and oxalic acid, and acid salts such as sodium hydrogen sulfate and ammonium hydrogen sulfate. Since the hydrogel may be excessively swollen or dissolved in the presence of the aldehyde compound and the acid, sodium acetate having a syneresis effect of PVA or the like is added to the acetalized solution as an inhibitor thereof. You may. The degree of acetalization of PVA is preferably from 10 to 60 mol%, more preferably from 20 to 55 mol%. If the degree of acetalization is lower than 10 mol%, sufficient water resistance may not be obtained. On the other hand, if the degree of acetalization is higher than 60 mol%, PVA is excessively hydrophobized. There is a tendency for the habitability of the to decline. The hydrogel after the insolubilization treatment by acetalization is separated from the acetalization solution and subjected to treatment such as washing with water and neutralization to obtain a hydrous gel. The hydrous gel may be dried once, and in this case, it is restored to a hydrous gel when immersed again in water.
[0017]
The PVA-based hydrated gel of the present invention has a high porosity and is excellent in habitability of microorganisms, and therefore is suitably used as a microorganism-immobilized carrier for carrying a biocatalyst such as microorganisms and enzymes in a biological reaction tank. The method for supporting the microorganisms is not particularly limited, and the microorganisms may be post-adhered to the hydrogel after the insolubilization treatment, or the microorganisms may be added to the aqueous solution containing PVA (a) and the water-soluble polysaccharide (b). You may mix and fix comprehensively. However, when the microorganisms are comprehensively fixed, it is necessary to select the type of microorganisms and adjust the insolubilization conditions so that the microorganisms are not killed by the acetalization solution used in the insolubilization treatment.
[0018]
There is no particular limitation on the type of microorganisms that can be immobilized on the carrier composed of the PVA-based hydrogel, and may be any of bacteria, actinomycetes, molds, yeasts, etc., and those obtained by pure culture or those obtained by mixed culture. Or activated sludge. Examples of the microorganisms include the genus Mucor, the genus Fusarium, the genus Cladothrix, the genus Sphaerotilus, the genus Zooglaa, the genus Leptomitus, and Aspergillus. Aspergillus genus, Rhizopus genus, Pseudomonas genus, Acetobacter genus, Streptomyces genus, Escherichia genus, Saccharidica, Saccharomyces saccharodis Microorganisms belonging to the genus include sulfur bacteria, methane bacteria, butyric bacteria, lactic acid bacteria, Bacillus subtilis, deformed bacteria Failure bacteria, nitrate bacteria, nitrite bacteria and denitrifying bacteria are also exemplified.
[0019]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The water content, specific gravity and degree of acetalization of the PVA-based hydrogel were determined according to the following methods. In addition, the fluidity of the PVA-based hydrogel carrier was evaluated according to the following method.
[0020]
(Water content)
After immersing the PVA-based hydrogel in water at 25 ° C. for 24 hours to remove water adhering to the surface, the weight of the hydrogel is measured, and the value is defined as the wet weight (W1). Next, the wet gel whose wet weight has been measured is dried at 105 ° C. for 4 hours, and its weight is measured. The value is defined as dry weight (W2). The water content was calculated from the wet weight (W1) and the dry weight (W2) of the hydrogel according to the following equation.
Water content (%) = (W1−W2) / W1 × 100
[0021]
(specific gravity)
In a test tube having a capacity of 50 mL in an environment at a temperature of 25 ° C., 50 mL of a specific gravity prepared solution prepared with sodium sulfate and water to a specific gravity was prepared. After removing the water adhering to the surface, 10 PVA-based hydrogels were charged into a specific gravity adjusting solution in a test tube. Ten seconds after the introduction of the PVA-based hydrogel, the number of floating gels, sinking gels, and gels remaining in the middle were counted, and the number of PVA-based hydrogels remaining in the middle exceeded the majority of the total. In this case, the specific gravity of the specific gravity solution at that time was defined as the specific gravity of the hydrogel.
[0022]
(Degree of acetalization)
0.2 g of a sample obtained by drying the PVA-based hydrogel at 105 ° C. for 2 hours was precisely weighed and placed in a distillation apparatus charged with a 25% sulfuric acid solution. Then, the mixture was heated while sending steam, and the liberated aldehyde was distilled off together with water and absorbed into a 2% aqueous sodium bisulfite (sometimes abbreviated as NaHSO 3 ) aqueous solution. The excess NaHSO 3 aqueous solution was back titrated with iodine to determine the amount of free aldehyde, and the degree of acetalization was calculated from the ratio (molar ratio) of the amount of hydroxyl groups in the gel.
[0023]
(Liquidity)
A glass graduated cylinder having a volume of 1 L was charged with 100 g of PVA-based hydrogel-containing carrier (wet weight conversion), and water was added to make 1 L. The tip of a silicon tube having an inner diameter of 4 mm was inserted into the bottom of the graduated cylinder, air was fed at 1 L / min, and the fluidity was evaluated based on the presence or absence of gel remaining at the bottom.
[0024]
Example 1
An aqueous solution containing 4% by weight of PVA (Kuraray Co., Ltd., average polymerization degree 2400, degree of saponification 99.8 mol%) and 0.5% by weight of sodium alginate ("Duck Algin" NSPL manufactured by Kibun Food Chemifa Co.) was prepared. The mixed aqueous solution was fed at a rate of 5 mL / min by a roller pump equipped with a silicon tube having an inner diameter of 4 mm and a nozzle having an inner diameter of 3 mm and agitated with a stirrer. / L of an aqueous calcium chloride solution. The dropped droplets became spherical and settled in the aqueous calcium chloride solution. This spherical molded product was separated from an aqueous calcium chloride solution, washed with water, immersed in an aqueous solution of formaldehyde 30 g / L, sulfuric acid 200 g / L, and sodium sulfate 100 g / L at 40 ° C. for 60 minutes, and then washed with water. As a result, a spherical hydrogel having a diameter of about 4.5 mm was obtained. The water content of this hydrogel was 93% by weight, the specific gravity was 1.015, and the degree of acetalization was 46 mol%. In the evaluation of fluidity, all the carriers flowed, there was no stagnation at the bottom, and the fluidity was low. Was very good.
[0025]
Example 2
An aqueous solution of PVA (Kuraray Co., Ltd., average degree of polymerization 4000, saponification degree 99.8 mol%) 3% by weight, and sodium alginate (Kibun Food Chemifa “Duck Algin” NSPL) 0.5% by weight was prepared. This aqueous solution was fed at a rate of 5 mL / min by a roller pump equipped with a silicon tube having an inner diameter of 4 mm and a nozzle having an inner diameter of 3 mm, and stirred at a concentration of 0.05 mol with a stirrer. / L of an aqueous calcium chloride solution. The dropped droplets became spherical and settled in the aqueous calcium chloride solution. This spherical molded product was separated from an aqueous calcium chloride solution, washed with water, immersed in an aqueous solution of formaldehyde 30 g / L, sulfuric acid 200 g / L, and sodium sulfate 100 g / L at 40 ° C. for 60 minutes, and then washed with water. As a result, a spherical hydrogel having a diameter of about 4.5 mm was obtained. The water content of this hydrogel was 94% by weight, the specific gravity was 1.01, and the degree of acetalization was 42 mol%. When the flowability was evaluated, all the carriers flowed, there was no stagnation at the bottom, and the flowability was very good.
[0026]
Comparative Example 1
An aqueous solution of 10% by weight of PVA (Kuraray Co., Ltd., average polymerization degree 1700, degree of saponification 99.8 mol%) and 1% by weight of sodium alginate ("Duck Algin" NSPL manufactured by Kibun Food Chemifa) was prepared. This mixed aqueous solution was fed at a rate of 5 mL / min by a roller pump equipped with a 3.2 mm inner diameter silicon tube equipped with a 2 mm inner diameter nozzle at the tip, and was stirred with a stirrer. The solution was dropped into a 0.1 mol / L calcium chloride aqueous solution. The dropped droplets became spherical and settled in the aqueous calcium chloride solution. This spherical molded product was separated from the aqueous calcium chloride solution, washed with water, placed in a tray, frozen in a freezer at -20 ° C for 24 hours, and thawed at room temperature. As a result, a spherical hydrogel having a diameter of about 5 mm was obtained. The water content was 90% by weight, and the specific gravity was 1.035. When the fluidity was evaluated, about half of the carrier stayed at the bottom and the fluidity was insufficient.
[0027]
Comparative Example 2
An aqueous solution of 8% by weight of PVA (Kuraray Co., Ltd., average polymerization degree: 1700, saponification degree: 99.8 mol%) and 1% by weight of sodium alginate ("Duck Algin" NSPL by Kibun Food Chemifa) was prepared. The mixed aqueous solution was fed at a rate of 5 mL / min by a roller pump equipped with a silicon tube having an inner diameter of 4 mm and a nozzle having an inner diameter of 3 mm attached to the tip, and the concentration of the aqueous solution was stirred by a stirrer. The solution was dropped into a 1 mol / L calcium chloride aqueous solution. The dropped droplets became spherical and settled in an aqueous solution of calcium chloride. This spherical molded product was separated from an aqueous calcium chloride solution, washed with water, immersed in an aqueous solution of formaldehyde 20 g / L and sulfuric acid 200 g / L at 40 ° C. for 90 minutes, and then washed with water. As a result, a spherical hydrogel having a diameter of about 5 mm was obtained. The water-containing gel had a water content of 88% by weight, a specific gravity of 1.04, and a degree of acetalization of 58% by mole. When the fluidity was evaluated, about half of the carrier stayed at the bottom and the fluidity was insufficient.
[0028]
【The invention's effect】
Since the PVA-based hydrogel of the present invention is excellent in the habitability of microorganisms, it can be effectively used as a microorganism-immobilized carrier for carrying a biocatalyst such as microorganisms and enzymes in a biological reaction tank. The carrier in which microorganisms are immobilized on the PVA-based hydrogel of the present invention has a strength that does not disintegrate even when stirred in a biological reaction tank, has excellent fluidity in the reaction tank, and has a deep reaction tank. Even if it is inside, it does not stay at the bottom of the tank, and is excellent in handleability.
Claims (5)
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Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
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JP2004075762A (en) * | 2002-08-13 | 2004-03-11 | Kuraray Co Ltd | Method for producing polyvinyl alcohol-based hydrogel |
JP2010116439A (en) * | 2008-11-11 | 2010-05-27 | Kuraray Co Ltd | Polyvinyl alcohol-based gel-molded article and method for producing the same |
JP2012076000A (en) * | 2010-09-30 | 2012-04-19 | Kuraray Co Ltd | One tank type anaerobic wastewater treatment apparatus |
WO2013099968A1 (en) * | 2011-12-28 | 2013-07-04 | 株式会社クラレ | Porous water-containing gel molded article, method for producing same, and use of same |
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2002
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Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
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JP2004075762A (en) * | 2002-08-13 | 2004-03-11 | Kuraray Co Ltd | Method for producing polyvinyl alcohol-based hydrogel |
JP2010116439A (en) * | 2008-11-11 | 2010-05-27 | Kuraray Co Ltd | Polyvinyl alcohol-based gel-molded article and method for producing the same |
JP2012076000A (en) * | 2010-09-30 | 2012-04-19 | Kuraray Co Ltd | One tank type anaerobic wastewater treatment apparatus |
WO2013099968A1 (en) * | 2011-12-28 | 2013-07-04 | 株式会社クラレ | Porous water-containing gel molded article, method for producing same, and use of same |
US9868840B2 (en) | 2011-12-28 | 2018-01-16 | Kuraray Co., Ltd. | Shaped article made of porous hydrogel, manufacturing process therefor and use thereof |
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