JP4028189B2

JP4028189B2 - Method and apparatus for removing phosphorus

Info

Publication number: JP4028189B2
Application number: JP2001181839A
Authority: JP
Inventors: 和彰島村; 友紀子三浦; 克之片岡; 俊博田中
Original assignee: Ebara Corp
Current assignee: Ebara Corp
Priority date: 2001-06-15
Filing date: 2001-06-15
Publication date: 2007-12-26
Anticipated expiration: 2021-06-15
Also published as: JP2002370094A

Description

【０００１】
【発明の属する技術分野】
本発明は、被処理水中に含有するリンをリン酸マグネシウムアンモニウム（以下「ＭＡＰ」とも言う）を生成させることにより、除去する方法及び装置に係わり、特に、被処理水中のリンを高効率で回収できる脱リン方法及び装置に関する。
【０００２】
【従来の技術】
下水、し尿、排水などを嫌気、及び好気処理したあとの脱水処理工程、消化工程から出る廃水は、リン及びアンモニアを含有している。それらの廃水にマグネシウムを添加し、ｐＨを調整することによってＭＡＰを生成させ、リンを除去する方法が提案されている。これをＭＡＰ法という。ＭＡＰ法の適用は、廃水中のリン濃度が５０〜５００ｍｇ／リットルの範囲にあることが多い。
ＭＡＰは、液中のマグネシウム、アンモニウム、リン、水酸基が以下のような形態で反応し、生成される。
Mg²⁺+NH_４ ⁺+HPO_４ ^2-+OH ^-+6H_２O → MgNH_４PO_４・6H_２O(MAP)+H_２O
【０００３】
ＭＡＰを生成させるための条件は、リン、アンモニア、マグネシウム、水酸基の各モル濃度を掛け合わせた濃度（イオン積という。［ＨＰＯ_４ ^2-］［ＮＨ_４ ⁺］［Ｍｇ²⁺］［ＯＨ^-］；［］内の単位はｍｏｌ／リットル）が、ＭＡＰの溶解度積以上のときである。このとき、被処理水中のリン濃度に対し、アンモニア濃度、マグネシウム濃度を等モル、或いはそれ以上となるように存在させると、処理水のリン濃度をより低下させることが可能となる。
マグネシウムの添加量は、流入するリンに対しモル比で１．２位になるようにすると効率的で良い。添加するマグネシウムは、塩化マグネシウム、水酸化マグネシウム、酸化マグネシウムが主な物質である。
【０００４】
処理方式は、流動層方式が多い。この方法は、反応槽内にＭＡＰ粒子を高濃度に保ち、被処理水を上向流で通水することにより、ＭＡＰ粒子を流動化させ、その粒子表面上でＭＡＰの生成を行うものである。流動化させるＭＡＰ粒子は、液上昇流速以上の沈降速度を持った粒子とする。粒子の流動が悪い場合には、機械的攪拌や空気攪拌などをする。
この方法のメリットは、ＭＡＰの生成反応と固液分離を一緒に行うことができることにある。
【０００５】
【発明が解決しようとする課題】
しかしながら、上記の処理方法で脱リンを行った場合、次のような問題点があった。
まず、ＭＡＰ粒子の過大成長による装置容積当たりのリン回収量の低下がある。反応槽内のＭＡＰ粒子は、被処理水と薬品の添加によって成長する。粒子が成長すると、反応槽内の単位容積当たりのＭＡＰ反応表面が減少し、回収量が低下する。また、流動が悪くなることによって反応効率が低下する。
本発明者らが得た知見によると（図２参照）、ＭＡＰ平均粒子径１ｍｍの場合、ＭＡＰ充填容積当たりに回収可能なリンは、最大で約７０ｋｇ−Ｐ／ｍ³／ｄ、ＭＡＰ平均粒子径２ｍｍの場合、最大で約５０ｋｇ−Ｐ／ｍ³／ｄ、ＭＡＰ平均粒子径３ｍｍの場合、最大で約２０ｋｇ−Ｐ／ｍ³／ｄと、粒径の増加と共に充填容積当たりのリンの回収量は著しく低下する。
【０００６】
また、ＭＡＰ粒径が極端に小さくなるとＭＡＰ粒子の沈降速度は遅くなり、液流速を高く取ることはできない。これにより、ＭＡＰ粒径の減少と共に最大リン負荷量（ＭＡＰ容積当たりにかけることが可能な最大のリン負荷量）が減少する傾向が見られる。
本発明者らが得た知見によると（図３参照）、ＭＡＰ粒径と最大リン負荷量の関係は、ＭＡＰ粒径１．０ｍｍの場合、約７０ｋｇ−Ｐ／ｍ ^３／ｄ、０．７ｍｍの場合、約５０ｋｇ−Ｐ／ｍ ^３／ｄ、０．５ｍｍの場合、約４０ｋｇ−Ｐ／ｍ ^３／ｄであった。なお、この場合、被処理水のリン濃度は約１００ｍｇ／リットルとした（微細なＭＡＰ粒子の析出を防ぐため、被処理水のリン濃度は約１００ｍｇ／リットル以下とするのが好ましい）。
しかも、ＭＡＰ粒径が小さくなると装置容積当たりのＭＡＰ表面積がきわめて大きくなり、そのため、ＭＡＰ粒子当たりの過飽和度が極端に低下するため、著しくＭＡＰ成長速度が低下する。
【０００７】
さらに、ＭＡＰの成長速度を速くする目的で、リン表面積負荷を高めて運転しようとすると以下のような問題点もあった。
リン表面積負荷が高いと、ＭＡＰ生成が反応槽内のＭＡＰ粒子の表面だけでなく、自ら微細ＭＡＰ結晶を生成してしまう。この微細ＭＡＰ結晶の沈殿速度は、液の上昇流速よりも遅いために、反応槽から流出する。その結果、リン回収率が低下する。
本発明者らが得た知見によると、リン表面積負荷が高いほど回収率が低下する傾向がみられた。特に、２０ｇ−Ｐ／ｍ²／ｄ以上の負荷をかけた場合、回収量は約２０ｇ−Ｐ／ｍ²／ｄで一定となった。
【０００８】
本発明は、このような従来の課題に鑑みてなされたものであり、晶析反応槽において流動層形式で行うＭＡＰ粒子の生成に際して、リンの回収量が最大となるようにするとともに、被処理水の流速を最大にするという目的を両立できる条件を見いだすことにより、上記の従来の技術の問題点を解決し、被処理水中のリンを高効率で回収できる脱リン方法及び装置を提供することを課題とする。
【０００９】
【課題を解決するための手段】
本発明者らは、上記の課題を解決するために鋭意検討を行い、上記した如く、粒径の増加と共に充填容積当たりのリン回収量が著しく低下すること、各粒径に対する最適液上昇流速は粒径の大きさに応じて大きくなること、及びリン表面積負荷が高いほどリン回収率が低下することを見出し、これらの知見に基づいて最大の効率でリンを回収できる条件をＭＡＰ粒子の粒径との関係で検討した結果、本発明を完成するに至った。
【００１０】
すなわち、本発明は、以下の手段を用いることによって、上記の課題を解決することができた。
（１）被処理水中のリンを晶析反応槽内で流動しているリン酸マグネシウムアンモニウム粒子の表面で晶析させて除去する方法において、前記晶析反応槽内を空気曝気しつつ槽内で析出した微細なリン酸マグネシウムアンモニウム結晶を固液分離槽にて回収し、回収した微細なリン酸マグネシウムアンモニウム結晶に被処理水とマグネシウムを添加することによって該結晶を熟成槽で成長させ、成長させたリン酸マグネシウムアンモニウム結晶を前記晶析反応槽に返送し、前記晶析反応槽内の空気曝気を一定時間曝気を止めて被処理水の連続通水を行うことにより槽内の前記粒子のうち粒径の大きなものを沈降させて分級し、分級された粒径の大きなリン酸マグネシウムアンモニウム結晶を前記晶析反応槽より抜き出し、前記晶析反応槽内で平均粒径が０．５〜２ｍｍであるリン酸マグネシウムアンモニウム粒子を流動させるように制御することを特徴とする脱リン方法。
（２）被処理水中のリンを晶析反応槽内で流動しているリン酸マグネシウムアンモニウム粒子の表面で晶析させて除去する方法において、前記晶析反応槽内で析出した微細なリン酸マグネシウムアンモニウム結晶を固液分離槽にて回収し、回収した微細なリン酸マグネシウムアンモニウム結晶に被処理水とマグネシウムを添加することによって該結晶を熟成槽で成長させ、成長させたリン酸マグネシウムアンモニウム結晶を前記晶析反応槽に返送し、前記晶析反応槽内の前記粒子を抜き出し、抜き出した前記粒子を分級機で分級し、分級された粒径の大きなリン酸マグネシウムアンモニウム結晶を前記晶析反応槽より抜き出し、前記晶析反応槽内で平均粒径が０．５〜２ｍｍであるリン酸マグネシウムアンモニウム粒子を流動させるように制御することを特徴とする脱リン方法。
（３）リン酸マグネシウムアンモニウム粒子表面積当たりのリン負荷を２０ｇ−Ｐ／ｍ ^２／ｄ以下とすることを特徴とする請求項１又は請求項２記載の脱リン方法。
【００１１】
（４）内部の水中でリン酸マグネシウムアンモニウム粒子が流動しており、リンを含有する被処理水を導入して前記粒子の表面にリン酸マグネシウムアンモニウムを析出させる晶析反応槽と、前記晶析反応槽内で析出した微細なリン酸マグネシウムアンモニウム結晶を回収する固液分離槽と、前記固液分離槽で回収した微細なリン酸マグネシウムアンモニウム結晶が導入されて、被処理水とマグネシウムを添加することによって前記結晶を成長させる熟成槽からなり、前記晶析反応槽は、リン酸マグネシウムアンモニウム粒子の取出し管と、槽内を空気曝気する曝気手段と、一定時間曝気を止めて被処理水の連続通水を行うことにより槽内の前記粒子のうち粒径の大きなものを沈降させて分級する分級手段を有し、前記熟成槽で成長させたリン酸マグネシウムアンモニウム粒子を前記晶析反応槽に返送する返送管を設けたことを特徴とする脱リン装置。
（５）内部の水中でリン酸マグネシウムアンモニウム粒子が流動しており、リンを含有する被処理水を導入して前記粒子の表面にリン酸マグネシウムアンモニウムを析出させる晶析反応槽と、前記晶析反応槽内で析出した微細なリン酸マグネシウムアンモニウム結晶を回収する固液分離槽と、前記固液分離槽で回収した微細なリン酸マグネシウムアンモニウム結晶が導入されて、被処理水とマグネシウムを添加することによって前記結晶を成長させる熟成槽からなり、前記晶析反応槽は、リン酸マグネシウムアンモニウム粒子の取出し管と、前記晶析反応槽内の前記粒子を抜き出し、抜き出した前記粒子を分級機で分級する分級手段を有し、前記熟成槽で成長させたリン酸マグネシウムアンモニウム粒子を前記晶析反応槽に返送する返送管を設けたことを特徴とする脱リン装置。
【００１２】
本発明者は、その晶析反応槽内でＭＡＰ粒子が平均粒径で１〜２ｍｍのものを流動させることによって、晶析反応槽において流動層形式で行うＭＡＰ粒子の生成に際して、リンの回収量が最大となるようにするとともに、被処理水の流速を最大にするという目的を両立させることができることを見いだした。
本発明において、その晶析反応槽内でＭＡＰ粒子の平均粒径が１〜２ｍｍのものが流動するように制御する手段としては、前記晶析反応槽内のＭＡＰ粒子を分級する手段を備えればよい。そのＭＡＰ粒子を分級する手段としてはいくつかの手段を用いることができる。
例えば、（ａ）槽内に粒径が１ｍｍから２ｍｍのＭＡＰ粒子の流動層を形成させている、槽内を空気曝気する攪拌型流動層晶析反応槽において、分級させる際に、１）曝気を止める、２）曝気を止めた状態で約３０分、被処理水などを連続通水する、３）槽内のＭＡＰ粒子が分級される（この場合一番大きい粒子が下に来る）、４）ＭＡＰ粒子の取り出し管から、分級された粒径の大きなＭＡＰ粒子を抜き出す、といったサイクル操作を行う。また、（ｂ）晶析反応槽内のＭＡＰ粒子を抜き出し、目開き１．５ｍｍの分級機で分級する、などが挙げられる。
【００１３】
この場合、平均粒径が小さいＭＡＰ粒子が減少するので、これを補給する必要があり、その補給手段としては別の反応槽で前記した平均粒径の範囲をもつＭＡＰ粒子を反応で生成させ、それを晶析反応槽に供給するようにしてもよい。そのようにすると、別の反応槽を必要とするので、前記したように流動層式の晶析反応槽では、微細なＭＡＰ粒子が流出する液とともに排出されるので、この微細なＭＡＰ粒子を沈殿槽などで分離し、これにマグネシウム成分などを添加して所定の平均粒径のＭＡＰ粒子に成長させてこれを晶析反応槽に供給するようにしてもよい。
【００１４】
【発明の実施の形態】
図面を参照して本発明の実施の形態を詳細に説明する。
以下においては、晶析反応槽（以下「反応槽」とも略称する）内のリン酸マグネシウムアンモニウム粒子の平均粒径を制御する方法を説明する。
図１は本発明を実施する処理系の一形態を示したものであり、反応槽１、熟成槽２、沈殿槽３からなる。
被処理水（原水）４の供給管５は、晶析反応槽１と熟成槽２にそれぞれ接続されており、また、マグネシウム成分６の供給管とアルカリ成分７の供給管は、反応槽１と熟成槽２にそれぞれ接続されている。反応槽１と沈殿槽３は、流出液供給管８で接続されている。沈殿槽３には処理水９を排出する処理水管１０が、熟成槽２には処理水１１を排出する処理水管が配設されている。
反応槽１、及び熟成槽２にはそれぞれｐＨ計１２を設置し、リアルタイムにｐＨを測定し、アルカリ注入制御を行う。
【００１５】
リン、アンモニアを含有した被処理水４は、被処理水供給管５から反応槽１の底部より上向流で流入させる。
反応槽内１は、予め粒径が０．５〜２ｍｍのＭＡＰ粒子を、適度な液上昇流速（およそ、２０〜６０ｍ／ｈｒ）によって流動させる。マグネシウム成分６の添加とアルカリ成分７の添加は連続的、或いは間欠的に行う。被処理水４中のリンはＭＡＰ粒子の表面で晶析されるが、一部は自らが微細ＭＡＰ粒子となって、反応槽１から流出する。ＭＡＰ粒子の流動層の高さは、ＭＡＰ粒子が成長することによって増加する。増加した流動層高さ分のＭＡＰ粒子は、反応槽１底部より、ＭＡＰ抜き出し管１３を経て定期的に抜き出す。被処理水４の流入を停止した場合には、ＭＡＰ粒子は充填層となっている状態でみられるが、その充填層の増加した分を抜き出すようにすればよい。
【００１６】
沈殿槽３では、反応槽１、熟成槽２よりも、タンク径を大きくして、液上昇流速を小さくしてある。よって、反応槽１から流出した微細ＭＡＰ粒子は、沈殿槽３底部に堆積する。固液分離したあとの上澄液は、槽上部より処理水９として越流させる。
【００１７】
沈殿槽３で堆積した微細ＭＡＰ粒子は、連続的、或いは間欠的に熟成槽２に供給する。熟成槽２では、被処理水４、マグネシウム成分６、アルカリ成分７の供給によって、微細ＭＡＰ粒子を約０．３〜０．５ｍｍ程度になるまで成長させる。熟成槽２においても、固液分離機能を備えた方法とし、固液分離した上澄液は槽上部より処理水１１として越流させる。
【００１８】
さらに、本発明者らは、０．３〜０．５ｍｍに成長させた微細ＭＡＰ粒子を、連続的或いは間欠的に反応槽内に供給するにあたり、微細ＭＡＰ粒子の供給量を変えることで、反応槽内のＭＡＰ粒子平均粒径を制御できることを見いだした。
被処理水４の供給によっても異なるが、反応槽１内でのＭＡＰ粒子の滞留時間を２０〜４０日くらいにすると、０．３〜０．５ｍｍの微細ＭＡＰ粒子は１．５〜２ｍｍほどの粒子となる。微細ＭＡＰ粒子の反応槽１への供給量は、ＭＡＰ粒子の抜出量に対し、１／２０〜１／４０にすると良い。
【００１９】
このようなサイクルを繰り返すことによって、微細ＭＡＰ粒子を処理系から排出することなく、反応槽１内のＭＡＰ粒子径を１〜２ｍｍに制御できる。このとき、ＭＡＰ表面積負荷が２０ｇ−Ｐ／ｍ²／ｄ以下、好ましくは１０ｇ−Ｐ／ｍ²／ｄ以下にすると、回収率が８０％以上となる。
【００２０】
他にＭＡＰ粒子平均径を制御する方法として、反応槽１内部或いは外部にＭＡＰ粒子粉砕ポンプを配置し、連続或いは間欠的に動作させたり、反応槽１内のＭＡＰ粒子を一部或いは全部抜き出し、別途平均径１ｍｍ程度の種晶を添加する方法がある。
いずれの場合も、反応槽１内のＭＡＰ粒子の粒径分布は０．５〜５ｍｍと広くても良いが、平均径を１〜２ｍｍに制御することが重要である。
【００２１】
【実施例】
以下において、本発明を実施例により更に具体的に説明するが、本発明は、この実施例により限定されるものではない。
【００２２】
実施例１
処理フローは図１のものを用いた。
食品廃水を嫌気性処理した実廃水に、水道水、塩化アンモニウム、リン酸一カリウムを添加したものを原水とした。原水の性状を第１表に示す。
原水、及び、処理水の一部は、内径１５０ｍｍφ×高さ４０００ｍｍのカラムを反応槽として、カラム底部より上向流で通水させた。反応槽の操作条件を第２表に示す。反応槽内のＭＡＰ平均粒子径は約１．５ｍｍとなるようにし、また、リン表面積負荷は約１０ｇ−Ｐ／ｍ²／ｄとなるようにした。
反応槽を流出した処理水は、内径３００ｍｍφ×高さ２４００ｍｍの沈殿槽に供給される。沈殿槽で堆積した微細ＭＡＰ粒子は、間欠的に熟成槽に移送させた。
【００２３】
熟成槽では、被処理水、マグネシウム、アルカリ成分の添加によって、微細ＭＡＰ粒子を約３００〜５００μｍになるように成長させた。ＭＡＰの滞留時間は約１０日とした。熟成槽で成長したＭＡＰ粒子は、濃度約５０ｇ／リットルのものを約２．８リットル／ｄで反応槽に供給した。
連続通水実験の結果を第３表に示す。原水Ｔ−Ｐ１２０ｍｇ／リットルに対し、処理水Ｔ−Ｐは１６．６ｍｇ／リットルであり、除去率は８６％であった。
反応槽内の平均ＭＡＰ粒子径は測定開始時１．５ｍｍであった。また、３０日後の反応槽内の平均ＭＡＰ粒子は、１．５５ｍｍであり、平均径はほとんど増加しなかった。ＭＡＰ粒径を１．５ｍｍ、リン表面積負荷を２０ｇ−Ｐ／ｍ²／ｄ以下を保つことにより、回収率８５％以上を長期にわたって維持できた。
【００２４】
【表１】

【００２５】
【表２】

【００２６】
【表３】

【００２７】
比較例１
実施例１と同様に、食品廃水を嫌気性処理した実廃水に、水道水、塩化アンモニウム、リン酸一カリウムを添加したものを原水とした。原水の性状を第４表に示す。処理フローは実施例１と同じであるが、熟成槽への添加量を半分とした。
原水、及び、処理水の一部はカラム底部より上向流で通水させた。反応槽の操作条件を第５表に示す。反応槽内のＭＡＰ平均粒子径を約２．５ｍｍに保ち、また、ＭＡＰ表面積負荷は約２２ｇ−Ｐ／ｍ²／ｄとなるようにした。
連続通水実験の結果を第６表に示す。原水Ｔ−Ｐ１１０ｍｇ／リットルに対し、処理水Ｔ−Ｐは３２ｍｇ／リットルであり、除去率は７１％であった。この回収率の低下は、明らかに、反応槽内の平均粒径を２．５ｍｍと大きくしたこと、ＭＡＰ表面積負荷を２０ｇ−Ｐ／ｍ²／ｄ以上にしたことが原因である。
【００２８】
【表４】

【００２９】
【表５】

【００３０】
【表６】

【００３１】
【発明の効果】
本発明によれば、反応槽内のＭＡＰ粒子の平均粒径を１〜２ｍｍに保ち、なおかつ、リン表面負荷を２０ｇ−Ｐ／ｍ²／ｄ以下とすることによって、長期にわたり、安定してリンの回収が行われた。
【図面の簡単な説明】
【図１】本発明のリンの除去方法の原理を説明する工程系統図である。
【図２】ＭＡＰ平均粒子径とリンの最大回収量の関係を示すグラフである。
【図３】ＭＡＰ粒径と最大リン負荷量の関係を示すグラフである。
【符号の説明】
１晶析反応槽
２熟成槽
３沈殿槽
４被処理水（原水）
５被処理水供給管
６マグネシウム成分
７アルカリ成分
８流出液供給管
９処理水
１０処理水管
１１処理水
１２ｐＨ計
１３ＭＡＰ粒子抜き出し管
１４、１５ＭＡＰ粒子返送管[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for removing phosphorus contained in water to be treated by producing magnesium ammonium phosphate (hereinafter also referred to as “MAP”), and in particular, phosphorus in water to be treated is recovered with high efficiency. The present invention relates to a dephosphorization method and apparatus.
[0002]
[Prior art]
Waste water discharged from the dehydration process and digestion process after anaerobic and aerobic treatment of sewage, human waste, drainage, etc. contains phosphorus and ammonia. A method has been proposed in which magnesium is added to these wastewaters to adjust the pH to generate MAP and remove phosphorus. This is called the MAP method. The application of the MAP method often has a phosphorus concentration in the wastewater in the range of 50 to 500 mg / liter.
MAP is produced by the reaction of magnesium, ammonium, phosphorus and hydroxyl groups in the liquid in the following forms.
^{_{^{Mg 2+ + NH 4 + + HPO}}} 4 2+ OH - + 6H 2 O → MgNH 4 PO 4 · 6H 2 O (MAP) + H 2 O
[0003]
The condition for generating MAP is a concentration obtained by multiplying each molar concentration of phosphorus, ammonia, magnesium, and a hydroxyl group (referred to as an ionic product. [HPO ₄ ²⁻ ] [NH ₄ ⁺ ] [Mg ²⁺ ] [OH ⁻ ]]. The unit in [] is mol / liter) when the solubility product of MAP is equal to or higher. At this time, if the ammonia concentration and the magnesium concentration are present in an equimolar amount or more with respect to the phosphorus concentration in the water to be treated, the phosphorus concentration in the treated water can be further reduced.
The amount of magnesium added may be efficient if the molar ratio of the added phosphorus is 1.2. Magnesium chloride, magnesium hydroxide, and magnesium oxide are the main substances to be added.
[0004]
There are many fluidized bed processing methods. In this method, the MAP particles are kept at a high concentration in the reaction vessel, and the water to be treated is passed in an upward flow to fluidize the MAP particles and generate MAP on the particle surfaces. . The MAP particles to be fluidized are particles having a sedimentation speed equal to or higher than the liquid ascending flow rate. When the flow of particles is poor, mechanical stirring or air stirring is performed.
The merit of this method is that the MAP formation reaction and the solid-liquid separation can be performed together.
[0005]
[Problems to be solved by the invention]
However, when dephosphorization is performed by the above processing method, there are the following problems.
First, there is a decrease in phosphorus recovery per unit volume due to overgrowth of MAP particles. The MAP particles in the reaction vessel grow by adding water to be treated and chemicals. When the particles grow, the MAP reaction surface per unit volume in the reaction vessel decreases, and the recovery amount decreases. In addition, the reaction efficiency decreases due to poor flow.
According to the knowledge obtained by the present inventors (see FIG. 2), when the MAP average particle diameter is 1 mm, the maximum recoverable phosphorus per MAP filling volume is about 70 kg-P / m ³ / d, and the MAP average particle When the diameter is 2 mm, the maximum is about 50 kg-P / m ³ / d, and when the MAP average particle diameter is 3 mm, the maximum is about 20 kg-P / m ³ / d. The amount is significantly reduced.
[0006]
Moreover, when the MAP particle size becomes extremely small, the sedimentation rate of the MAP particles becomes slow and the liquid flow rate cannot be increased. Accordingly, there is a tendency that the maximum phosphorus load (the maximum phosphorus load that can be applied per MAP volume) decreases as the MAP particle size decreases.
According to the knowledge obtained by the present inventors (see FIG. 3), the relationship between the MAP particle size and the maximum phosphorus loading is about 70 kg-P / m ³ / d , 0. In the case of 7 mm, it was about 50 kg-P / m ³ / d , and in the case of 0.5 mm, it was about 40 kg-P / m ³ / d . In this case, the phosphorus concentration of the water to be treated was about 100 mg / liter (in order to prevent the precipitation of fine MAP particles, the phosphorus concentration of the water to be treated is preferably about 100 mg / liter or less).
In addition, when the MAP particle size is reduced, the MAP surface area per unit volume becomes extremely large, so that the degree of supersaturation per MAP particle is extremely reduced, so that the MAP growth rate is significantly reduced.
[0007]
Furthermore, when the operation is attempted with an increased phosphorus surface area load for the purpose of increasing the growth rate of MAP, there are the following problems.
When the phosphorus surface area load is high, MAP generation generates not only the surface of the MAP particles in the reaction vessel but also a fine MAP crystal by itself. Since the precipitation rate of this fine MAP crystal is slower than the rising speed of the liquid, it flows out of the reaction vessel. As a result, the phosphorus recovery rate decreases.
According to the knowledge obtained by the present inventors, the recovery rate tends to decrease as the phosphorus surface area load increases. In particular, when a load of 20 g-P / m ² / d or more was applied, the recovered amount became constant at about 20 g-P / m ² / d.
[0008]
The present invention has been made in view of such a conventional problem, and in the production of MAP particles performed in a fluidized bed format in a crystallization reaction tank, the recovery amount of phosphorus is maximized, and the treatment is performed. To provide a dephosphorization method and apparatus capable of solving the above-mentioned problems of the prior art by finding conditions that can achieve the purpose of maximizing the flow rate of water and recovering phosphorus in treated water with high efficiency. Is an issue.
[0009]
[Means for Solving the Problems]
The inventors of the present invention have intensively studied to solve the above problems, and as described above, the amount of phosphorus recovered per filling volume is significantly reduced as the particle size is increased, and the optimum liquid rising flow rate for each particle size is It was found that the phosphorus recovery rate decreases as the particle size increases and the phosphorus surface area load increases. Based on these findings, the conditions under which phosphorus can be recovered with the maximum efficiency are determined. As a result, the present invention has been completed.
[0010]
That is, the present invention was able to solve the above problems by using the following means.
(1) In the method of crystallizing and removing phosphorus in the water to be treated on the surface of magnesium ammonium phosphate particles flowing in the crystallization reaction tank, the inside of the crystallization reaction tank is aerated while air is aerated. The precipitated fine magnesium ammonium phosphate crystals are collected in a solid-liquid separation tank, and the crystal is grown in an aging tank by adding treated water and magnesium to the collected fine magnesium ammonium phosphate crystals. The magnesium ammonium phosphate crystal is returned to the crystallization reaction tank, and the aeration of air in the crystallization reaction tank is stopped for a certain period of time, and the water to be treated is continuously passed among the particles in the tank. The particles having a large particle size are settled and classified, and the classified magnesium ammonium phosphate crystals having a large particle size are extracted from the crystallization reaction tank, Dephosphorization method Hitoshitsubu diameter and controls so as to flow the magnesium ammonium phosphate particles is 0.5 to 2 mm.
(2) Fine magnesium phosphate precipitated in the crystallization reaction tank in a method for removing phosphorus in the water to be treated by crystallization on the surface of the magnesium ammonium phosphate particles flowing in the crystallization reaction tank. Ammonium crystals are collected in a solid-liquid separation tank, and the crystal is grown in an aging tank by adding treated water and magnesium to the collected fine magnesium ammonium phosphate crystals. Returning to the crystallization reaction tank, extracting the particles in the crystallization reaction tank, classifying the extracted particles with a classifier, and classifying the magnesium ammonium phosphate crystals having a large particle diameter into the crystallization reaction tank The magnesium ammonium phosphate particles having an average particle diameter of 0.5 to 2 mm are allowed to flow in the crystallization reaction tank. Dephosphorization method characterized by.
(3) The phosphorus removal method according to claim 1 or ^{2, wherein} a phosphorus load per surface area of the magnesium ammonium phosphate particles is 20 g-P / m ² / d or less.
[0011]
(4) A crystallization reaction tank in which magnesium ammonium phosphate particles are flowing in the internal water and introducing water to be treated containing phosphorus to deposit magnesium ammonium phosphate on the surface of the particles, and the crystallization A solid-liquid separation tank for collecting fine magnesium ammonium phosphate crystals precipitated in the reaction tank and a fine magnesium ammonium phosphate crystal collected in the solid-liquid separation tank are introduced, and water to be treated and magnesium are added. The crystallization reaction tank comprises a magnesium ammonium phosphate particle take-out tube, an aeration means for aeration of the inside of the tank, and a continuous treatment water by stopping aeration for a certain period of time. It has a classifying means for precipitating and classifying the particles having a large particle size among the particles in the tank by passing water, and has been grown in the aging tank. Dephosphorization apparatus characterized in that a return pipe for returning magnesium ammonium particles in said crystallization reaction tank.
(5) A crystallization reaction tank in which magnesium ammonium phosphate particles are flowing in the internal water and introducing water to be treated containing phosphorus to precipitate magnesium ammonium phosphate on the surface of the particles, and the crystallization A solid-liquid separation tank for collecting fine magnesium ammonium phosphate crystals precipitated in the reaction tank and a fine magnesium ammonium phosphate crystal collected in the solid-liquid separation tank are introduced, and water to be treated and magnesium are added. The crystallization reaction tank is composed of an extraction tube for magnesium ammonium phosphate particles, the particles in the crystallization reaction tank are extracted, and the extracted particles are classified by a classifier. A return pipe for returning the magnesium ammonium phosphate particles grown in the aging tank to the crystallization reaction tank. Dephosphorization and wherein the digit.
[0012]
The present inventor made a recovery of phosphorus when producing MAP particles in a fluidized bed format in the crystallization reaction tank by flowing particles having an average particle diameter of 1 to 2 mm in the crystallization reaction tank. It has been found that the purpose of maximizing the flow rate of the water to be treated can be achieved at the same time.
In the present invention, a means for controlling the MAP particles having an average particle diameter of 1 to 2 mm to flow in the crystallization reaction tank includes a means for classifying the MAP particles in the crystallization reaction tank. That's fine. Several means can be used as a means for classifying the MAP particles.
For example, (a) When classifying in a stirred fluidized bed crystallization reaction tank in which a fluidized bed of MAP particles having a particle diameter of 1 to 2 mm is formed in the tank and the inside of the tank is aerated, 1) aeration 2) Continuously pass the water to be treated for about 30 minutes while aeration is stopped. 3) The MAP particles in the tank are classified (in this case, the largest particles are below). 4 ) A cycle operation is performed in which the classified MAP particles having a large particle diameter are extracted from the MAP particle take-out tube. Moreover, (b) MAP particles in the crystallization reaction tank are extracted and classified with a classifier having an opening of 1.5 mm.
[0013]
In this case, since the MAP particles having a small average particle size are reduced, it is necessary to replenish them, and as a replenishing means, MAP particles having the above average particle size range are generated by reaction in another reaction tank, You may make it supply it to a crystallization reaction tank. In such a case, since a separate reaction tank is required, in the fluidized bed type crystallization reaction tank as described above, the fine MAP particles are discharged together with the liquid flowing out, so that the fine MAP particles are precipitated. It may be separated in a tank or the like, and a magnesium component or the like may be added thereto to grow into MAP particles having a predetermined average particle diameter, and this may be supplied to the crystallization reaction tank.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in detail with reference to the drawings.
Hereinafter, a method for controlling the average particle diameter of the magnesium ammonium phosphate particles in the crystallization reaction tank (hereinafter also abbreviated as “reaction tank”) will be described.
FIG. 1 shows an embodiment of a processing system for carrying out the present invention, which comprises a reaction tank 1, an aging tank 2 and a precipitation tank 3.
The supply pipe 5 for the water to be treated (raw water) 4 is connected to the crystallization reaction tank 1 and the aging tank 2, and the supply pipe for the magnesium component 6 and the supply pipe for the alkali component 7 are connected to the reaction tank 1. Each is connected to the aging tank 2. The reaction tank 1 and the precipitation tank 3 are connected by an effluent supply pipe 8. The settling tank 3 is provided with a treated water pipe 10 for discharging treated water 9, and the aging tank 2 is provided with a treated water pipe for discharging treated water 11.
A pH meter 12 is installed in each of the reaction tank 1 and the aging tank 2, and the pH is measured in real time to perform alkali injection control.
[0015]
The treated water 4 containing phosphorus and ammonia is introduced from the treated water supply pipe 5 in an upward flow from the bottom of the reaction tank 1.
In the reaction tank 1, MAP particles having a particle diameter of 0.5 to 2 mm are caused to flow at an appropriate liquid rising speed (approximately 20 to 60 m / hr) in advance. The addition of the magnesium component 6 and the addition of the alkali component 7 are performed continuously or intermittently. Phosphorus in the water to be treated 4 is crystallized on the surface of the MAP particles, but a part thereof becomes fine MAP particles and flows out of the reaction tank 1. The height of the fluidized bed of MAP particles increases as the MAP particles grow. The increased fluidized bed height MAP particles are periodically extracted from the bottom of the reaction vessel 1 through the MAP extraction tube 13. When the inflow of the water to be treated 4 is stopped, the MAP particles are seen in a packed bed, but the increased amount of the packed bed may be extracted.
[0016]
In the sedimentation tank 3, the tank diameter is made larger than the reaction tank 1 and the aging tank 2, and the liquid ascending flow rate is made smaller. Therefore, the fine MAP particles that have flowed out of the reaction tank 1 are deposited on the bottom of the precipitation tank 3. The supernatant liquid after solid-liquid separation is allowed to overflow as treated water 9 from the upper part of the tank.
[0017]
Fine MAP particles deposited in the settling tank 3 are supplied to the aging tank 2 continuously or intermittently. In the aging tank 2, fine MAP particles are grown to about 0.3 to 0.5 mm by supplying the water to be treated 4, the magnesium component 6, and the alkali component 7. In the aging tank 2 as well, a method having a solid-liquid separation function is used, and the supernatant liquid that has been subjected to solid-liquid separation is allowed to overflow as treated water 11 from the upper part of the tank.
[0018]
Furthermore, the present inventors changed the supply amount of fine MAP particles by changing the supply amount of fine MAP particles when supplying fine MAP particles grown to 0.3 to 0.5 mm continuously or intermittently into the reaction vessel. It was found that the average particle diameter of MAP particles in the tank can be controlled.
Although it depends on the supply of the water 4 to be treated, when the residence time of the MAP particles in the reaction tank 1 is about 20 to 40 days, the fine MAP particles of 0.3 to 0.5 mm are about 1.5 to 2 mm. Become particles. The supply amount of the fine MAP particles to the reaction tank 1 is preferably 1/20 to 1/40 with respect to the extraction amount of the MAP particles.
[0019]
By repeating such a cycle, the MAP particle diameter in the reaction vessel 1 can be controlled to 1 to 2 mm without discharging fine MAP particles from the treatment system. At this time, when the MAP surface area load is 20 g-P / m ² / d or less, preferably 10 g-P / m ² / d or less, the recovery rate is 80% or more.
[0020]
As another method for controlling the average MAP particle diameter, a MAP particle pulverization pump is arranged inside or outside the reaction tank 1 to operate continuously or intermittently, or a part or all of the MAP particles in the reaction tank 1 are extracted. There is another method of adding seed crystals having an average diameter of about 1 mm.
In either case, the particle size distribution of the MAP particles in the reaction vessel 1 may be as wide as 0.5 to 5 mm, but it is important to control the average diameter to 1 to 2 mm.
[0021]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples.
[0022]
Example 1
The processing flow shown in FIG. 1 was used.
Raw water was obtained by adding tap water, ammonium chloride, and monopotassium phosphate to actual wastewater that was anaerobically treated from food wastewater. The properties of raw water are shown in Table 1.
Raw water and a part of the treated water were allowed to flow upward from the bottom of the column using a column having an inner diameter of 150 mmφ × height of 4000 mm as a reaction vessel. The operating conditions of the reaction tank are shown in Table 2. The MAP average particle size in the reaction vessel was set to about 1.5 mm, and the phosphorus surface area load was set to about 10 g-P / m ² / d.
The treated water flowing out of the reaction tank is supplied to a sedimentation tank having an inner diameter of 300 mmφ × height of 2400 mm. Fine MAP particles deposited in the settling tank were intermittently transferred to the aging tank.
[0023]
In the aging tank, fine MAP particles were grown to about 300 to 500 μm by adding water to be treated, magnesium and alkali components. The residence time of MAP was about 10 days. The MAP particles grown in the aging tank were supplied with a concentration of about 50 g / liter to the reaction tank at about 2.8 liter / d.
The results of the continuous water flow experiment are shown in Table 3. The treated water TP was 16.6 mg / liter against the raw water TP 120 mg / liter, and the removal rate was 86%.
The average MAP particle size in the reaction vessel was 1.5 mm at the start of measurement. Moreover, the average MAP particle | grains in the reaction tank 30 days after were 1.55 mm, and the average diameter hardly increased. By maintaining the MAP particle size at 1.5 mm and the phosphorus surface area load at 20 g-P / m ² / d or less, the recovery rate of 85% or more could be maintained over a long period of time.
[0024]
[Table 1]

[0025]
[Table 2]

[0026]
[Table 3]

[0027]
Comparative Example 1
In the same manner as in Example 1, raw water was obtained by adding tap water, ammonium chloride, and monopotassium phosphate to actual wastewater obtained by anaerobically treating food wastewater. Table 4 shows the properties of the raw water. The processing flow is the same as in Example 1, but the amount added to the aging tank was halved.
Raw water and a part of the treated water were passed upward from the bottom of the column. The operating conditions of the reaction vessel are shown in Table 5. The average MAP particle size in the reaction vessel was kept at about 2.5 mm, and the MAP surface area load was about 22 g-P / m ² / d.
Table 6 shows the results of the continuous water flow experiment. The treated water TP was 32 mg / liter against the raw water TP 110 mg / liter, and the removal rate was 71%. This reduction in the recovery rate is clearly caused by the fact that the average particle size in the reaction vessel was increased to 2.5 mm and the MAP surface area load was set to 20 g-P / m ² / d or more.
[0028]
[Table 4]

[0029]
[Table 5]

[0030]
[Table 6]

[0031]
【The invention's effect】
According to the present invention, the average particle diameter of the MAP particles in the reaction vessel is kept at 1 to 2 mm, and the phosphorus surface load is set to 20 g-P / m ² / d or less, so that phosphorus can be stably produced over a long period of time. Was collected.
[Brief description of the drawings]
FIG. 1 is a process flow diagram illustrating the principle of a phosphorus removal method of the present invention.
FIG. 2 is a graph showing the relationship between the MAP average particle size and the maximum amount of phosphorus recovered.
FIG. 3 is a graph showing the relationship between MAP particle size and maximum phosphorus loading.
[Explanation of symbols]
1 Crystallization reaction tank 2 Aging tank 3 Precipitation tank 4 Water to be treated (raw water)
5 treated water supply pipe 6 magnesium component 7 alkaline component 8 effluent supply pipe 9 treated water 10 treated water pipe 11 treated water 12 pH meter 13 MAP

particle extraction pipes

14, 15 MAP particle return pipe

Claims

In the method for removing phosphorus in the water to be treated by crystallization on the surface of magnesium ammonium phosphate particles flowing in the crystallization reaction tank, the fine particles deposited in the tank while aerated in the crystallization reaction tank Phosphoric acid obtained by growing a magnesium ammonium phosphate crystal in a solid-liquid separation tank, growing the crystal in an aging tank by adding treated water and magnesium to the collected fine magnesium ammonium phosphate crystal Magnesium ammonium crystals are returned to the crystallization reaction tank, air aeration in the crystallization reaction tank is stopped for a certain period of time, and continuous treatment of the treated water is carried out to adjust the particle size of the particles in the tank. Large particles are settled and classified, and the classified magnesium ammonium phosphate crystals having a large particle diameter are extracted from the crystallization reaction tank, and the average grains in the crystallization reaction tank are extracted. There dephosphorization method characterized by controlling so as to flow the magnesium ammonium phosphate particles is 0.5 to 2 mm.

In the method of removing phosphorus in the water to be treated by crystallization on the surface of magnesium ammonium phosphate particles flowing in the crystallization reaction tank, fine magnesium ammonium phosphate crystals precipitated in the crystallization reaction tank The crystal is recovered in a solid-liquid separation tank, and the crystal is grown in an aging tank by adding water to be treated and magnesium to the collected fine magnesium ammonium phosphate crystal, and the grown magnesium ammonium phosphate crystal is crystallized. Returning to the reaction tank, extracting the particles in the crystallization reaction tank, classifying the extracted particles with a classifier, and extracting the classified magnesium ammonium phosphate crystals having a large particle diameter from the crystallization reaction tank, Control to flow magnesium ammonium phosphate particles having an average particle diameter of 0.5 to 2 mm in the crystallization reaction tank. Dephosphorization method comprising and.

Phosphorus loading per surface area of magnesium ammonium phosphate particles is 20 g-P / m ^２2 The dephosphorization method according to claim 1 or 2, characterized by being / d or less.

A crystallization reaction tank in which magnesium ammonium phosphate particles are flowing in the internal water, introducing water to be treated containing phosphorus to precipitate magnesium ammonium phosphate on the surface of the particles, and in the crystallization reaction tank The solid-liquid separation tank that collects the fine magnesium ammonium phosphate crystals precipitated in step 1 and the fine magnesium ammonium phosphate crystals collected in the solid-liquid separation tank are introduced, and the treatment water and magnesium are added to The crystallization reaction tank comprises a ripening tank for growing crystals, an extraction pipe for magnesium ammonium phosphate particles, an aeration means for aeration of air inside the tank, and continuous flow of treated water by stopping aeration for a certain period of time. Having a classification means for precipitating and classifying the particles having a large particle size among the particles in the tank, Dephosphorization device, characterized in that the Neshi um ammonium particles provided a return pipe for returning to said crystallization reaction tank.

A crystallization reaction tank in which magnesium ammonium phosphate particles are flowing in the internal water, introducing water to be treated containing phosphorus to precipitate magnesium ammonium phosphate on the surface of the particles, and in the crystallization reaction tank The solid-liquid separation tank that collects the fine magnesium ammonium phosphate crystals precipitated in step 1 and the fine magnesium ammonium phosphate crystals collected in the solid-liquid separation tank are introduced, and the treatment water and magnesium are added to The crystallization reaction tank comprises a ripening tank for growing crystals, the magnesium ammonium phosphate particle take-out pipe, and the classification means for extracting the particles in the crystallization reaction tank and classifying the extracted particles with a classifier. And a return pipe for returning the magnesium ammonium phosphate particles grown in the aging tank to the crystallization reaction tank. Dephosphorization and wherein the door.