JP4019212B2 - How to recover phosphorus from sludge - Google Patents

Description

【００２２】
（２）還元反応装置について
還元反応装置は、凝集汚泥に硫化ナトリウムや硫化水素等の硫化物を還元剤として添加して、ｐＨ４〜６、酸化還元電位（以下ＯＲＰと略記する）−２３０ｍＶ以下の条件で汚泥を所定時間還元反応させ、凝集汚泥中のリンを液相に溶出させる装置である。
【００２３】
還元反応装置において、還元剤の添加量は凝集汚泥に含まれている無機凝縮剤由来の金属量に対しモル比で好ましくは１〜３である。
【００２４】
本装置による反応の原理は、下記の反応式の通りである。反応式は鉄系の凝集汚泥に硫化ナトリウムを添加した場合のものであるが、アルミニウム系の凝集汚泥に硫化水素を添加しても同様な反応が進行する。
【００２５】
２ＦｅＰＯ_４ ＋ ３Ｎａ_２ Ｓ → ２ＦｅＳ↓ ＋ ２Ｎａ_３ ＰＯ_４ ＋ Ｓ
【００２６】
生成した硫化物は微細粒子であり沈降分離に長時間を要するので、遠心分離機等で機械的分離した方がより良い。分離濃縮した硫化物汚泥は、硫酸または塩酸を添加することによって、次に示す反応式に従って硫酸第一鉄や塩化第一鉄、および硫化水素を生成する。
【００２７】
ＦｅＳ ＋ Ｈ_２ ＳＯ_４ → ＦｅＳＯ_４ ＋ Ｈ_２ Ｓ↑
ＦｅＳ ＋ ２ＨＣｌ → ＦｅＣｌ_２ ＋ Ｈ_２ Ｓ↑
【００２８】
生成された硫酸第一鉄や塩化第一鉄は、オゾンや過酸化水素水等の酸化剤で酸化処理して硫酸第二鉄や塩化第二鉄に変換し、凝集処理工程の凝集剤として再利用できる。
【００２９】
（３）リン化合物製造装置について
本装置は、水中に溶解しているリン酸イオンをカルシウム系やマグネシウム系等の薬剤と反応させてリン化合物を生成させ、リンを回収するものである。回収リン含有物は肥料等の原料として利用したり、湿式反応装置から排出される脱水汚泥に混合して堆肥成分として利用される。
【００３０】
本技術の原理は、次に示す反応式の通りである。
【００３１】
３Ｃａ（ＯＨ）_２ ＋ ２Ｈ_３ ＰＯ_４ → Ｃａ_３ （ＰＯ_４ ）_２ ＋ ６Ｈ_２ Ｏ
Ｎａ_３ ＰＯ_４ ＋ ＮＨ_４ Ｃｌ ＋ Ｍｇ（ＯＨ）_２ ＋ ６Ｈ_２ ０
→ ＭｇＮＨ_４ ＰＯ_４ ・６Ｈ_２ Ｏ ＋ ＮａＣｌ ＋ ２ＮａＯＨ
【００３２】
本技術ではｐＨ域がリン回収率に大きく影響し、適正なｐＨ域は７．５〜１０であり、より好ましくは８．５〜９である。また、水中にアンモニア性窒素が共存している場合は生物処理の窒素負荷を低減できるマグネシウム系化合物の使用が好ましく、アンモニア性窒素濃度が高くなるに伴いリン回収率は高くなる。従って、汚泥等の湿式反応装置から得られた分離液にはアンモニア性窒素が高濃度で含まれているので、この分離液と還元反応装置から得られた分離液を混合し、この混合液にマグネシウム系薬剤を添加することによるリンを効率的に回収することができる。
【００３３】
【発明の実施の形態】
本発明の詳細な実施の形態を図２、図３および図４に基づいて説明する。
【００３４】
（１）湿式反応装置によるリン溶出工程
湿式反応方法とは、反応温度が１５０〜１８０℃で、圧力がゲージ圧で１Ｍｐａ未満、処理時間が３０〜６０分、酸素供給率が汚泥全酸化に必要な理論酸素量の１〜１０％である条件で、余剰汚泥等の各種汚泥を処理する方法である。
【００３５】
図２において、生物処理系等から排出される余剰汚泥（但し、無機凝集剤が混入した汚泥は除く）等は汚泥貯留槽に蓄えられ、処理液のｐＨ調整やスケール防止の為に槽内ｐＨが設定値（８〜１０の範囲）になるようにｐＨ調整剤が自動的に添加される。ｐＨ調整剤としては一般に水酸化ナトリウムが用いられる。
【００３６】
未処理の汚泥は、供給ポンプにより圧力１Ｍｐａ未満で熱交換器に送られる。
熱交換器で未処理汚泥は湿式反応処理汚泥との熱交換により昇温された後、反応塔へ送られる。本工程は通常は連続的に行われる。
【００３７】
反応塔では、汚泥は、底部からボイラーによる水蒸気の吹き込みによって所定の温度まで温められると同時に、底部からコンプレッサーによる空気または高濃度酸素ガスの吹き込みによって塔内で撹拌されながら所定時間湿式反応され、この結果、可溶化による減量化と脱水性向上等の改質が行われるだけでなく、汚泥中に含まれる窒素やリン等の一部が液側に移行（すなわち溶出）される。
【００３８】
湿式反応法はＣＯＤ（Ｃｒ）除去率を極めて低くしているため、反応熱が少なく設定反応温度が維持できないので、汚泥を水蒸気で加熱する。水蒸気は熱交換効率を考慮すると、反応塔へ直接供給する方が好ましい。また、水蒸気の供給量は反応塔出口に設置された温度センサーによって温度が設定値になるよう自動的に調節される。
【００３９】
酸素源は通常空気を用いるが、全体ガス量を少なくしたい場合や、反応温度１８０℃において酸素供給量を少し増したい場合もあり、このような場合には、ＰＳＡ（Pressure Swing Adosorption）方式等の高濃度酸素ガス製造装置により製造した高濃度酸素ガスを用いてもよい。高濃度酸素ガスの酸素濃度は２２〜７５％であり、好ましくは５０〜６０％である。高濃度酸素ガスを用いる場合には、▲１▼空気に比べガス供給量が少なくなるので、反応圧力が低くても反応に適したガス液比の状態が得られる、▲２▼反応圧力が１Ｍｐａ未満と低いためガス量を少なくして配管内流速を低くする、▲３▼酸素分圧が高いので反応速度を向上させることができる。▲４▼湿式反応装置から排出されるガス量が少なくなる、等の利点が得られる。
【００４０】
湿式反応後の処理汚泥は上記熱交換器を経た後圧力調節弁によって減圧され、処理汚泥貯留槽に送られ、ここで気液分離され、分離された反応排ガスは槽頂から脱臭設備へ送られる。他方、残った反応処理液は槽底から供給ポンプにより脱水機へ供給され、脱水により生じた分離液は図１に示す混合槽に送られる。他方、脱水された汚泥は堆肥化設備へ送られ、堆肥の成分として緑農地等に有効利用される。
【００４１】
また、処理汚泥を脱水することにより、含水率を薬剤注入なしで６５％以下にした脱水汚泥を得ることができ、これをごみ焼却施設の助燃材等として利用することもできる。
【００４２】
（２）還元反応装置によるリン溶出工程
図３において、凝集処理系等から排出される凝集汚泥等は汚泥貯留槽に蓄えれられ、この槽から供給ポンプにより定量的に還元槽へ供給される。本工程は、連続式でも回分（バッチ）式でもよいが、通常は連続式で行われる。
【００４３】
還元槽では、硫化ナトリウムまたは硫化水素等の還元剤が凝集汚泥の流入量に応じて定量添加されている。還元剤の添加量は、凝集汚泥中に含まれている鉄やアルミニウム等の金属［Ｍ］含有量に対し、還元剤が硫化物である場合、［Ｓ］／［Ｍ］モル比で１．０〜３．０倍量、より好ましくは１．２〜２．０倍量である。通常、この添加量で凝集汚泥のＯＲＰ値は−２３０ｍＶ以下となるが、その値にならない場合には、還元剤を余分に添加してＯＲＰ値−２３０ｍＶ以下の還元域条件下にて反応を行うことが好ましい。
【００４４】
還元剤添加に伴い還元槽内のｐＨが変動し反応速度に影響がでてくることもあることから、ｐＨが設定された所定値になるよう自動的に中和剤が還元槽内に直接注入されるようになっている。
【００４５】
還元槽の滞留時間３０〜６０分で、凝集汚泥中のリンの約９０％以上がリン酸態リンとして液側に溶出し、凝集汚泥中の金属は水溶性の硫化物となって還元槽内に懸濁している。なお、本還元反応は数分にて行われるが、還元槽の滞留時間は３０〜６０分と長くしている。これは、反応の安定化と次の固液分離操作への貯留を兼ねるためである。
【００４６】
還元槽内に懸濁している硫化物は、微粒子であるため沈降速度が遅い。従って、高速処理を図るには、高分子凝集剤等を用いて重力沈降式の固液分離を行うか、遠心分離機等を用いて機械式の固液分離を行うことが望ましい。こうして分離された分離液は図１に示す混合槽へ送られ、湿式反応装置からの分離液と合流され撹拌混合される。
【００４７】
一方、分離された濃縮汚泥は図１に示す溶解槽へポンプ等で送られる。溶解槽の濃縮汚泥には希硫酸や希塩酸等の酸が添加され、硫化物は硫酸塩や塩化物に変換される。この時、硫化水素が発生するので、溶解槽から出る排ガスは上記還元槽に吹き込んで循環利用できるようにしておく方が好ましい。
【００４８】
硫酸塩や塩化物の溶液は、オゾンや過酸化水素水等によって酸化処理されて、上記凝集処理工程の無機凝集剤として循環利用される。あるいは、凝集処理工程をフェントン酸化方式とし、その酸化処理を凝集処理と同時に行うようにした方がより好ましい。得られた溶液を添加剤として用いることもできる。
【００４９】
また、汚泥の資源化としてこれを固形燃料助剤として用いることを考えた場合、含水率を薬剤注入なしで６５％以下にした脱水汚泥を得ることもできるが、酸化処理後の溶解液を上記湿式反応装置の処理汚泥貯留槽に移送し、撹拌混合して含水率５０％以下の脱水汚泥を製造することが好ましい。この場合、湿式反応処理によって溶出させたリンのほとんどは反応して脱水汚泥側に移行するため、リンの回収率は低下する。
【００５０】
（３）リン化合物製造装置によるリン回収工程
図４において、図１に示す混合槽から来る分離液は、供給ポンプにより晶析槽の反応部に供給される。本工程は通常は連続式に行われる。
【００５１】
反応部では、マグネシウム系化合物やカルシウム系化合物などの晶析剤が所定量注入され、必要に応じて所定のｐＨになるよう水酸化ナトリウム等の中和剤の添加によりｐＨ調整が行われる。
【００５２】
晶析槽内の分離液をブロワーからの空気により撹拌混合することにより、生成した微細な結晶を槽内で循環流動させて適度な粒度まで成長させる。
【００５３】
成長したリン含有結晶を含む液は、晶析槽の分離部で水と結晶に沈殿分離され、分離水は晶析槽上部から生物処理系へ送られる。一方、結晶は槽下部に堆積され定期的に引き抜かれ、ドラムスクリーン等の簡単な分離装置で固形物と含有水に分離される。晶析剤としてカルシウム系化合物を用いる場合は、分離装置に遠心分離機を用いる方が好ましい。
【００５４】
分離された水は生物処理系へ送られ、結晶固形物はホッパへ送られ、水切りや乾燥が行われる。こうして製造された含水率１０〜２０％の乾燥結晶は極めて有効な肥料などとして緑農地等に利用される。
【００５５】
【実施例】
水酸化ナトリウムを添加してｐＨを８．５に調整したし尿処理汚泥の余剰汚泥を対象に、外熱型オートクレーブ装置（内容量７５０ｍｌ）を用いて、図２のフローに従って各反応温度における湿式反応処理（圧力１ＭＰａ、時間６０分）を行った。その結果を表２に示す。同表より、試料の有機物量があまり減少しないにも拘らず、減量化率（ＳＳ除去率）、可溶化率（ＶＳＳ除去率）ともに反応温度の上昇に伴って高くなる傾向が認められる。また、汚泥中のリン成分溶出率（液側移行率）は２７〜３２％であった。さらに、脱水汚泥の含水率は薬剤注入なしでも６１〜６５％程度（未処理の汚泥では薬剤注入にても含水率７５％程度）であり、剥離性も良い状態であったことから、良好な汚泥の改質が行われていることが認められる。
【００５６】
【表２】

【００５７】
一方、し尿処理汚泥の鉄系凝集汚泥を対象に、容量２リットルの還元槽を用いて、図３のフローに従って還元反応を行った。その結果を表３に示す。なお、還元剤は市販の硫化ナトリウムを溶解し約２０％溶液を調製して用いた。同表より、還元剤添加量が［Ｓ］／［Ｆｅ］モル比で１．３倍以上であれば９３％程度、１．７５倍以上であれば９５％程度の高いリン溶出率が得られることが判る。
【００５８】
【表３】

【００５９】
図４に従って、余剰汚泥等を温度１７０℃で湿式反応処理後の分離液４リットルと、鉄系凝集汚泥をモル比１．７５以上（例えば１．８）で還元反応処理後の分離液１リットルを混合撹拌し、この混合液を供給ポンプによって定量的に容量０．２リットルの晶析槽に供給した。混合液中のリン酸形態のリンの濃度は１４６ｍｇ／リットルであった。同時に晶析槽へ晶析剤として３０％水酸化マグネシウム溶液を［Ｍｇ］／［Ｐ］モル比が１．５以上（例えば１．６）になるよう添加した。晶析槽ではｐＨを９前後になるよう２５％水酸化ナトリウム溶液を添加し、リン酸マグネシウムアンモニウムを製造した。その結果、処理水のリン濃度は６．３ｍｇ／リットルであり、分離液からのリン回収率は95％と極めて高い値であった。
【００６０】
溶解槽で得られた硫化鉄は還元されてほとんどが硫化第一鉄となっていた。これに、希硫酸を添加すると、容易に硫酸第一鉄が製造できた。また、硫化水素も発生した。
【００６１】
【発明の効果】
以上述べたように、本発明方法により、リンを含有する各種汚泥からリンを効率的に回収することができるとともに、汚泥の減量化、改質および無機凝集剤の有効利用も達成することができる。より詳しくは、本発明によれば以下に示す効果が得られる。
【００６２】
▲１▼汚泥中のリン成分を容易に、しかも効率良く回収することができる。
【００６３】
▲２▼回収されたリン化合物は粒状で、含水率が２０％程度のため、ハンドリングが容易である。
【００６４】
▲３▼回収されたリン化合物は、衛生的で、重金属などを含まなく安全であり、高純度と付加価値の高いものであることから、肥料原料等として利用用途が大幅に広がる。
【００６５】
▲４▼リン溶出後の凝集汚泥に強酸を添加することによって、無機凝集剤が容易に製造できることから、これを凝集処理工程へ戻し循環使用できる。したがって、凝集処理系から排出される汚泥量は、皆無に等しい。
【００６６】
▲５▼生物処理系から排出される全汚泥量の５０％程度を減量化できる。
【００６７】
▲６▼生物処理系から排出される汚泥の改質が行えるため、脱水汚泥の含水率を薬剤注入なしでも約６５％にでき、堆肥化等の水分調整に要する熱量を大きく低減できる。また、この脱水汚泥を助燃材として問題なく使用できる。
【図面の簡単な説明】
【図１】本発明の実施例を示すフローシートである。
【図２】湿式反応工程を示すフローシートである。
【図３】還元リン溶出工程を示すフローシートである。
【図４】リン化合物製造工程を示すフローシートである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method capable of efficiently recovering phosphorus from various types of sludge containing phosphorus, and reducing sludge, modifying it, and effectively using an inorganic flocculant.
[0002]
[Prior art]
Biological treatment methods (anaerobic / aerobic method, fostrip method), flocculant addition method, crystallization method (MAP method, apatite method, etc.), adsorption method, etc. are known as phosphorus recovery methods. Some facilities have a proven track record. However, these methods are effective for phosphorus dissolved in waste water, but phosphorus contained in suspended (suspended) substances such as sludge can hardly be recovered. Phosphorus removed from wastewater in water treatment facilities and the like is transferred to sludge in a small amount, and phosphorus recovery cannot be completed without sludge treatment.
[0003]
In patent document 1, in biological dephosphorization of organic sludge by the anaerobic aerobic method which has an anaerobic process and an aerobic process, the sludge returned to the anaerobic process from the precipitation process of the activated sludge following an aerobic process is described. Some or some of the sludge extracted from the aerobic process is solubilized by ozone oxidation, then phosphate ions and metal ions that cause precipitation reaction are added to recover phosphorus, and the solubilized sludge after phosphorus removal is anaerobic There has been proposed a method for removing and recovering organic sludge that is sent to the process. However, in ozone oxidation like patent document 1, there is little phosphorus elution amount from sludge, and since the treated sludge is difficult to reuse and returned to the biological treatment system, there is a problem that inorganic substances gradually accumulate in the treatment system. is there.
[0004]
[Patent Document 1]
JP-A-9-94596.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a method capable of efficiently recovering phosphorus from various types of sludge containing phosphorus and also capable of reducing and modifying the sludge and effectively using an inorganic flocculant.
[0006]
[Means for Solving the Problems]
The present invention elutes phosphorus contained in surplus sludge and the like generated from the biological treatment process by a wet reaction method, and phosphorus contained in coagulated sludge and the like generated from the coagulation treatment process by a reduction reaction method, respectively. The present invention relates to a method for recovering phosphorus in sludge by crystallizing a phosphorus compound from a mixture of the separated liquids.
[0007]
That is, the method for recovering phosphorus from sludge according to the present invention treats excess sludge and the like generated from the biological treatment process using a wet reactor, and treats the aggregated sludge and the like generated from the agglomeration process using a reduction reactor. In this method, phosphorus contained in the sludge is eluted, and a phosphorus compound is crystallized from the obtained eluate , wherein the reaction temperature is 150 to 180 ° C. and the pressure is gauged in a wet reactor. The sludge is treated under the conditions that the pressure is less than 1 Mpa, the treatment time is 30 to 60 minutes, and the oxygen supply rate is 1 to 10% of the theoretical oxygen amount necessary for the total oxidation of the sludge .
[0008]
In a wet reactor, the temperature is preferably 150 to 180 ° C., the pressure is preferably less than 1 Mpa, the treatment time is preferably 30 to 60 minutes, and the sludge is treated under oxygen-deficient conditions to elute phosphorus in the sludge. It is preferable to make it.
[0009]
In the wet reactor, it is preferable to use water vapor to maintain the temperature.
[0010]
In the reduction reaction apparatus, preferred reducing agents are sulfides such as hydrogen sulfide and sodium sulfide.
[0011]
In the reduction reaction apparatus, the amount of the reducing agent added is preferably 1 to 3 in terms of molar ratio to the amount of metal contained in the aggregated sludge.
[0012]
In the phosphorus compound production apparatus, the pH range for crystallization is preferably 7.5 to 10.
[0013]
It is preferable that the amount of dewatered sludge discharged from the wet reactor is about half that of the raw material sludge, and the water content of the dehydrated sludge is 65% or less without chemical injection.
[0014]
The concentrated sludge discharged from the reduction reaction apparatus can be treated with a strong acid, the resulting treatment can be oxidized, and the flocculant can be recovered from the sludge.
[0015]
FIG. 1 shows an embodiment of the present invention, FIG. 2 shows a flow of a wet reaction apparatus, FIG. 3 shows a flow of a reduction reaction apparatus, and FIG. 4 shows a flow of a phosphorus compound production apparatus.
[0016]
The present invention aims to improve the recovery rate (efficiency) by separating the agglomerated sludge from other sludge and eluting phosphorus. Therefore, from the viewpoint of phosphorus recovery rate in the entire facility, the standard denitrification method, high load denitrogenation method and membrane separation high load denitrogenation method are good in biological treatment methods, and septic tank sludge compatible denitrification that performs pre-flocculation treatment. The method is not preferred. This is not limited to the present invention, and the same applies to other phosphorus recovery methods.
[0017]
(1) About wet reactor The wet reactor uses both wet oxidation and heat treatment characteristics, the reaction temperature is 150 to 180 ° C, the pressure is less than 1 Mpa in gauge pressure, and the treatment time is 30 to 30 minutes. It is an apparatus for treating various sludges such as excess sludge under the condition that the oxygen supply rate is 1 to 10% of the theoretical oxygen amount required for sludge total oxidation for 60 minutes. In other words, the wet reactor is designed to control the oxygen supply rate to suppress oxidation and attach importance to solubilization, which can reduce sludge to some extent and at the same time elute some of the phosphorus contained in the sludge. It can also be made.
[0018]
By reducing the supply of oxidizing gas (air, high-concentration oxygen gas, oxygen gas, etc.), the S / A (kg-steam / kg-dry gas) in the reaction system is set to a high value. However, it does not become a dry reaction and is safe. Moreover, the high pressure gas safety method is not applied to the present technology by setting the internal pressure of the present technology to a gauge pressure of less than 1 Mpa.
[0019]
As shown in FIG. 2, the wet reaction apparatus has basically the same configuration as the wet oxidation apparatus, and the processing principle is the same although the processing conditions are different. Table 1 shows a comparison of main processing conditions and processing effects of the present technology and the wet oxidation technology. As can be seen from the table, the present technology is inferior to the comparative technology (wet oxidation method) in terms of sludge reduction, reforming, and phosphorus elution rate, but these can be performed to some extent. Therefore, this technology can reduce and modify sludge and is an effective method for pretreatment of phosphorus recovery from various sludges such as surplus sludge (excluding sludge mixed with flocculant).
[0020]
In the wet reactor, it is preferable to use water vapor to maintain the temperature.
[0021]
[Table 1]

[0022]
(2) About the reduction reaction apparatus The reduction reaction apparatus adds a sulfide such as sodium sulfide or hydrogen sulfide to the coagulated sludge as a reducing agent, and has a pH of 4 to 6 and an oxidation-reduction potential (hereinafter abbreviated as ORP) -230 mV or less. It is an apparatus that causes sludge to undergo a reduction reaction for a predetermined time under conditions, and to elute phosphorus in the coagulated sludge into a liquid phase.
[0023]
In the reduction reaction apparatus, the addition amount of the reducing agent is preferably 1 to 3 in terms of a molar ratio with respect to the amount of metal derived from the inorganic condensing agent contained in the coagulated sludge.
[0024]
The principle of reaction by this apparatus is as shown in the following reaction formula. The reaction formula is that when sodium sulfide is added to iron-based coagulated sludge, but the same reaction proceeds even when hydrogen sulfide is added to aluminum-based coagulated sludge.
[0025]
2FePO ₄ + 3Na ₂ S → 2FeS ↓ + 2Na ₃ PO ₄ + S
[0026]
Since the produced sulfide is fine particles and requires a long time for sedimentation separation, it is better to perform mechanical separation with a centrifugal separator or the like. The separated and concentrated sulfide sludge generates ferrous sulfate, ferrous chloride, and hydrogen sulfide according to the following reaction formula by adding sulfuric acid or hydrochloric acid.
[0027]
FeS + H ₂ SO ₄ → FeSO ₄ + H ₂ S ↑
FeS + 2HCl → FeCl ₂ + H ₂ S ↑
[0028]
The produced ferrous sulfate and ferrous chloride are oxidized with an oxidizing agent such as ozone or hydrogen peroxide solution to convert to ferric sulfate or ferric chloride, and are reused as an aggregating agent in the aggregating process. Available.
[0029]
(3) Phosphorus compound production apparatus This apparatus reacts phosphate ions dissolved in water with a chemical such as calcium or magnesium to produce a phosphorus compound, and collects phosphorus. The recovered phosphorus-containing material is used as a raw material such as fertilizer, or mixed with dehydrated sludge discharged from a wet reactor and used as a compost component.
[0030]
The principle of this technology is as shown in the following reaction formula.
[0031]
3Ca (OH) ₂ + 2H ₃ PO ₄ → Ca ₃ (PO ₄ ) ₂ + 6H ₂ O
Na ₃ PO ₄ + NH ₄ Cl + Mg (OH) ₂ + 6H ₂ 0
_{→ MgNH 4 PO 4 · 6H 2} O + NaCl + 2NaOH
[0032]
In the present technology, the pH range greatly affects the phosphorus recovery rate, and the proper pH range is 7.5 to 10, more preferably 8.5 to 9. Moreover, when ammoniacal nitrogen coexists in water, it is preferable to use a magnesium compound that can reduce the nitrogen load of biological treatment, and the phosphorus recovery rate increases as the ammoniacal nitrogen concentration increases. Therefore, since the separation liquid obtained from the wet reaction apparatus such as sludge contains ammonia nitrogen at a high concentration, the separation liquid and the separation liquid obtained from the reduction reaction apparatus are mixed, and this mixture liquid is mixed. Phosphorus can be efficiently recovered by adding a magnesium-based drug.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
A detailed embodiment of the present invention will be described based on FIG. 2, FIG. 3, and FIG.
[0034]
(1) Phosphorus elution process by wet reactor The wet reaction method is a reaction temperature of 150 to 180 ° C., a pressure of less than 1 Mpa in gauge pressure, a treatment time of 30 to 60 minutes, and an oxygen supply rate required for total sludge oxidation This is a method of treating various sludges such as excess sludge under the condition of 1 to 10% of the theoretical amount of oxygen.
[0035]
In FIG. 2, surplus sludge (excluding sludge mixed with inorganic flocculant) discharged from biological treatment systems, etc. is stored in a sludge storage tank, and the tank pH is used to adjust the pH of the treatment liquid and prevent scales. The pH adjuster is automatically added so that becomes a set value (range of 8 to 10). As a pH adjuster, sodium hydroxide is generally used.
[0036]
Untreated sludge is sent to the heat exchanger by a supply pump at a pressure of less than 1 Mpa.
In the heat exchanger, the untreated sludge is heated by heat exchange with the wet reaction-treated sludge and then sent to the reaction tower. This step is usually performed continuously.
[0037]
In the reaction tower, the sludge is heated to a predetermined temperature from the bottom by blowing steam with a boiler, and at the same time, the sludge is wet-reacted for a predetermined time while being stirred in the tower by blowing air or high-concentration oxygen gas from the bottom. As a result, not only reforming such as weight reduction by solubilization and improvement of dewaterability is performed, but also part of nitrogen, phosphorus, etc. contained in the sludge is transferred (ie, eluted) to the liquid side.
[0038]
Since the wet reaction method has an extremely low COD (Cr) removal rate, the reaction heat is small and the set reaction temperature cannot be maintained, so the sludge is heated with steam. In consideration of heat exchange efficiency, it is preferable to supply steam directly to the reaction tower. In addition, the amount of steam supplied is automatically adjusted so that the temperature becomes a set value by a temperature sensor installed at the outlet of the reaction tower.
[0039]
Usually, air is used as the oxygen source, but there are cases where it is desired to reduce the total gas amount or to increase the oxygen supply amount slightly at a reaction temperature of 180 ° C. In such a case, a PSA (Pressure Swing Adosorption) method, etc. You may use the high concentration oxygen gas manufactured with the high concentration oxygen gas manufacturing apparatus. The oxygen concentration of the high-concentration oxygen gas is 22 to 75%, preferably 50 to 60%. When high-concentration oxygen gas is used, (1) since the gas supply amount is smaller than that of air, a gas-liquid ratio suitable for the reaction can be obtained even when the reaction pressure is low. (2) The reaction pressure is 1 MPa. Since the flow rate in the pipe is lowered by reducing the amount of gas because it is low, the reaction rate can be improved. (4) Advantages such as a reduction in the amount of gas discharged from the wet reactor can be obtained.
[0040]
The treated sludge after the wet reaction is reduced in pressure by the pressure control valve after passing through the heat exchanger, sent to the treated sludge storage tank, where it is gas-liquid separated, and the separated reaction exhaust gas is sent from the tank top to the deodorization equipment. . On the other hand, the remaining reaction processing liquid is supplied from the bottom of the tank to the dehydrator by a supply pump, and the separation liquid generated by the dehydration is sent to the mixing tank shown in FIG. On the other hand, the dewatered sludge is sent to a composting facility and is effectively used as a compost component in green farmland.
[0041]
Further, by dehydrating the treated sludge, dehydrated sludge having a water content of 65% or less can be obtained without injecting chemicals, and this can also be used as a combustion aid for a waste incineration facility.
[0042]
(2) Phosphorus elution process by reduction reaction apparatus In FIG. 3, the coagulated sludge discharged from the coagulation treatment system or the like is stored in a sludge storage tank, and quantitatively supplied from this tank to the reduction tank. This step may be continuous or batch (batch), but is usually performed continuously.
[0043]
In the reducing tank, a reducing agent such as sodium sulfide or hydrogen sulfide is quantitatively added according to the inflow amount of the coagulated sludge. When the reducing agent is a sulfide with respect to the metal [M] content such as iron or aluminum contained in the coagulated sludge, the amount of the reducing agent added is 1. in terms of [S] / [M] molar ratio. The amount is 0 to 3.0 times, more preferably 1.2 to 2.0 times. Normally, the ORP value of the coagulated sludge becomes −230 mV or less with this addition amount. However, when the value does not reach that value, an extra reducing agent is added and the reaction is carried out under the conditions of the reducing zone where the ORP value is −230 mV or less. It is preferable.
[0044]
Since the pH in the reducing tank fluctuates with the addition of the reducing agent and the reaction rate may be affected, the neutralizing agent is automatically injected directly into the reducing tank so that the pH becomes a predetermined value. It has come to be.
[0045]
About 90% or more of the phosphorus in the coagulated sludge elutes to the liquid side as phosphate phosphorus in the reduction tank residence time of 30 to 60 minutes, and the metal in the coagulated sludge becomes water-soluble sulfide in the reduction tank. It is suspended in. In addition, although this reduction reaction is performed in several minutes, the residence time of a reduction tank is extended with 30 to 60 minutes. This is because it serves both as stabilization of the reaction and storage for the next solid-liquid separation operation.
[0046]
Since the sulfide suspended in the reduction tank is a fine particle, the sedimentation speed is slow. Therefore, in order to achieve high-speed processing, it is desirable to perform gravity sedimentation solid-liquid separation using a polymer flocculant or the like, or mechanical solid-liquid separation using a centrifuge or the like. The separated liquid thus separated is sent to the mixing tank shown in FIG. 1, where it is combined with the separated liquid from the wet reactor and stirred and mixed.
[0047]
On the other hand, the separated concentrated sludge is sent to the dissolution tank shown in FIG. Acids such as dilute sulfuric acid and dilute hydrochloric acid are added to the concentrated sludge in the dissolution tank, and the sulfide is converted into sulfate and chloride. At this time, since hydrogen sulfide is generated, it is preferable that the exhaust gas discharged from the dissolution tank is blown into the reduction tank so that it can be circulated.
[0048]
The sulfate or chloride solution is oxidized by ozone, hydrogen peroxide, or the like, and recycled as an inorganic flocculant in the agglomeration process. Alternatively, it is more preferable that the coagulation treatment step is a Fenton oxidation method and the oxidation treatment is performed simultaneously with the coagulation treatment. The obtained solution can also be used as an additive.
[0049]
Moreover, when considering using this as a solid fuel auxiliary agent as a sludge resource, it is possible to obtain dehydrated sludge having a water content of 65% or less without chemical injection. It is preferable to transfer to a treated sludge storage tank of a wet reactor and mix by stirring to produce dehydrated sludge having a water content of 50% or less. In this case, most of the phosphorus eluted by the wet reaction treatment reacts and moves to the dewatered sludge side, so that the phosphorus recovery rate decreases.
[0050]
(3) Phosphorus recovery process by phosphorus compound production apparatus In FIG. 4, the separation liquid coming from the mixing tank shown in FIG. 1 is supplied to the reaction part of the crystallization tank by the supply pump. This step is usually performed continuously.
[0051]
In the reaction part, a predetermined amount of a crystallization agent such as a magnesium-based compound or a calcium-based compound is injected, and pH adjustment is performed by adding a neutralizing agent such as sodium hydroxide as necessary to obtain a predetermined pH.
[0052]
The separated liquid in the crystallization tank is stirred and mixed with the air from the blower, whereby the generated fine crystals are circulated and flown in the tank to grow to an appropriate particle size.
[0053]
The liquid containing the grown phosphorus-containing crystals is precipitated and separated into water and crystals in the separation part of the crystallization tank, and the separated water is sent from the upper part of the crystallization tank to the biological treatment system. On the other hand, the crystals are deposited at the bottom of the tank and are periodically extracted, and separated into solids and contained water by a simple separation device such as a drum screen. When a calcium compound is used as the crystallizing agent, it is preferable to use a centrifuge for the separation device.
[0054]
The separated water is sent to a biological treatment system, and the crystalline solid is sent to a hopper for draining and drying. The dried crystals having a water content of 10 to 20% thus produced are used for green farmland and the like as extremely effective fertilizers.
[0055]
【Example】
2. Wet reaction at each reaction temperature according to the flow of FIG. 2 using an externally heated autoclave device (internal volume 750 ml) for surplus sludge of urine-treated sludge whose pH was adjusted to 8.5 by adding sodium hydroxide The treatment (pressure 1 MPa, time 60 minutes) was performed. The results are shown in Table 2. From the table, it can be seen that both the reduction rate (SS removal rate) and the solubilization rate (VSS removal rate) tend to increase as the reaction temperature increases although the amount of organic matter in the sample does not decrease so much. Moreover, the phosphorus component elution rate (liquid side transfer rate) in sludge was 27 to 32%. Furthermore, the moisture content of the dewatered sludge is about 61 to 65% without chemical injection (the moisture content is about 75% even with chemical injection for untreated sludge), and the releasability was also good. It is recognized that sludge is being reformed.
[0056]
[Table 2]

[0057]
On the other hand, a reduction reaction was performed according to the flow of FIG. 3 using a reduction tank having a capacity of 2 liters for iron-based agglomerated sludge of human waste treatment sludge. The results are shown in Table 3. As the reducing agent, a commercially available sodium sulfide was dissolved to prepare an approximately 20% solution. From the table, a high phosphorus elution rate of about 93% is obtained when the reducing agent addition amount is 1.3 times or more in the [S] / [Fe] molar ratio and about 1.75 times or more. I understand that.
[0058]
[Table 3]

[0059]
According to FIG. 4, 4 liters of the separated liquid after the wet reaction treatment at a temperature of 170 ° C. and 1 liter of the separated liquid after the reduction reaction treatment of iron-based coagulated sludge at a molar ratio of 1.75 or more (for example, 1.8). Were mixed and stirred, and this mixed solution was quantitatively supplied to a crystallization tank having a capacity of 0.2 liter by a supply pump. The concentration of phosphoric acid form phosphorus in the mixture was 146 mg / liter. At the same time, a 30% magnesium hydroxide solution was added to the crystallization tank as a crystallization agent so that the [Mg] / [P] molar ratio was 1.5 or more (for example, 1.6). In the crystallization tank, a 25% sodium hydroxide solution was added so that the pH was around 9, and magnesium ammonium phosphate was produced. As a result, the phosphorus concentration of the treated water was 6.3 mg / liter, and the phosphorus recovery rate from the separated liquid was an extremely high value of 95%.
[0060]
Most of the iron sulfide obtained in the dissolution tank was reduced to ferrous sulfide. When dilute sulfuric acid was added thereto, ferrous sulfate could be easily produced. Hydrogen sulfide was also generated.
[0061]
【The invention's effect】
As described above, according to the method of the present invention, phosphorus can be efficiently recovered from various sludges containing phosphorus, and sludge reduction, reforming, and effective use of inorganic flocculants can be achieved. . More specifically, according to the present invention, the following effects can be obtained.
[0062]
(1) The phosphorus component in the sludge can be recovered easily and efficiently.
[0063]
(2) Since the recovered phosphorus compound is granular and has a water content of about 20%, handling is easy.
[0064]
(3) The recovered phosphorus compounds are sanitary, safe and free of heavy metals, and have high purity and high added value. Therefore, their use is greatly expanded as fertilizer raw materials.
[0065]
(4) By adding a strong acid to the coagulated sludge after elution of phosphorus, an inorganic coagulant can be easily produced, so that it can be recycled and used for the coagulation treatment step. Accordingly, the amount of sludge discharged from the coagulation treatment system is equal to none.
[0066]
(5) About 50% of the total sludge discharged from the biological treatment system can be reduced.
[0067]
(6) Since the sludge discharged from the biological treatment system can be modified, the water content of the dewatered sludge can be reduced to about 65% even without chemical injection, and the amount of heat required for moisture adjustment such as composting can be greatly reduced. Moreover, this dehydrated sludge can be used without any problem as a combustion aid.
[Brief description of the drawings]
FIG. 1 is a flow sheet showing an embodiment of the present invention.
FIG. 2 is a flow sheet showing a wet reaction process.
FIG. 3 is a flow sheet showing a reducing phosphorus elution step.
FIG. 4 is a flow sheet showing a phosphorus compound production process.

Claims (7)

The excess sludge generated from the biological treatment process is treated using a wet reactor, and the sludge generated from the coagulation process is treated using a reduction reactor to elute phosphorus contained in the sludge. A phosphorus recovery method for crystallizing a phosphorus compound from the obtained eluate, wherein the reaction temperature is 150 to 180 ° C. in a wet reactor, the pressure is less than 1 Mpa in gauge pressure, the treatment time is 30 to 60 minutes, A method for recovering phosphorus from sludge, characterized in that the sludge is treated under the condition that the oxygen supply rate is 1 to 10% of the theoretical oxygen amount necessary for total oxidation of sludge . In the wet reactor, phosphorus recovery method from sludge according to claim 1, characterized by using the water vapor to the holding temperature. The method for recovering phosphorus from sludge according to claim 1 or 2 , wherein the reducing agent is a sulfide in the reduction reaction apparatus. In the reduction reactor, the addition amount of the reducing agent, from sludge according to any one of claims 1 to 3, characterized in that 1 to 3 in a molar ratio to the metal amount contained in agglomerated sludge Phosphorus recovery method. The method for recovering phosphorus from sludge according to any one of claims 1 to 4 , wherein a pH range in crystallization is 7.5 to 10 in the phosphorus compound production apparatus. The amount of dewatered sludge discharged from the wet reactor is about half that of the raw material sludge, and the water content of the dewatered sludge is 65% or less without chemical injection, according to any one of claims 1 to 5. A method for recovering phosphorus from the described sludge. From the sludge according to any one of claims 1 to 6 , wherein the concentrated sludge discharged from the reduction reaction apparatus is treated with a strong acid, the resulting treatment is oxidized, and the flocculant is recovered from the sludge. Of phosphorus recovery.

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