JP2011050803A - Phosphorus recovery method - Google Patents
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Abstract
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本発明は、排水処理設備で発生する汚泥を嫌気性消化処理する工程において汚泥から放出される多量のリンを効率よく回収する方法に関する。 The present invention relates to a method for efficiently recovering a large amount of phosphorus released from sludge in an anaerobic digestion process of sludge generated in a wastewater treatment facility.
下水にはリンが含まれている。リンは閉鎖水域では富栄養化の原因物質であるので、閉鎖水域が下水処理水の放流先となっている地域では、下水中からリンを除去する高度処理が導入されている。下水高度処理において発生する汚泥にはリンが多く含まれる。 Sewage contains phosphorus. Phosphorus is a causative substance of eutrophication in the closed water area, so advanced treatment to remove phosphorus from the sewage is introduced in the area where the closed water area is the discharge destination of the sewage treated water. The sludge generated in advanced sewage treatment contains a lot of phosphorus.
下水処理において発生する汚泥は汚泥処理プロセスにおいて減容化して処分を行うが、そのプロセスの中には嫌気性消化処理があり、汚泥中の有機物をメタン発酵により、メタンガスと炭酸ガスに分解するものである。このプロセスにおいては、汚泥が嫌気性になるので汚泥中の微生物の細胞内に含まれるリンが溶解性のリン酸（ＰＯ４-P)として溶液側に放出される。 Sludge generated in sewage treatment is reduced and disposed of in the sludge treatment process, but there is an anaerobic digestion process that decomposes organic matter in sludge into methane gas and carbon dioxide by methane fermentation. It is. In this process, since the sludge becomes anaerobic, phosphorus contained in the cells of microorganisms in the sludge is released to the solution side as soluble phosphoric acid (PO 4 -P).
従来、このリンの回収方法として、汚泥を嫌気性処理する工程でＭｇ源を添加してリン酸マグネシウムアンモニウム（ＭＡＰ）を生成させ、汚泥から分離回収する方法が知られている（特許文献１）。この特許文献１では、ＭＡＰ除去後の消化汚泥の濃縮分離水か消化汚泥の脱水ろ液にもＭｇ源とｐＨ調整剤を添加してさらにＭＡＰを生成し、回収している。そこでは、ｐＨ７．４〜７．９に調整している。 Conventionally, as a method for recovering phosphorus, a method is known in which Mg source is added in a step of anaerobically treating sludge to produce magnesium ammonium phosphate (MAP) and separated and recovered from sludge (Patent Document 1). . In this Patent Document 1, MAP is further generated and recovered by adding a Mg source and a pH adjuster to the concentrated separated water of digested sludge after removal of MAP or the dehydrated filtrate of digested sludge. In this case, the pH is adjusted to 7.4 to 7.9.
また、固形物を含む廃水を嫌気性消化して、消化槽内に自然発生したＭＡＰ結晶粒子を分離し、これを脱水ろ液のリン酸を回収するために設置したＭＡＰ回収装置に種晶として用い、ＭＡＰを後回収する方法も知られている（特許文献２）。 In addition, the waste water containing solid matter is anaerobically digested to separate the MAP crystal particles that are naturally generated in the digestion tank, and this is used as a seed crystal in the MAP recovery unit installed to recover the phosphoric acid in the dehydrated filtrate. A method of using and recovering MAP later is also known (Patent Document 2).
さらに、消化汚泥を反応槽に供給し、この反応層へマグネシウム化合物を添加するとともに反応槽内を曝気することにより、消化汚泥に含まれる溶解性リン酸態リンをリン酸マグネシウムアンモニウム粒子として不溶化させ、次いで、リン酸マグネシウムアンモニウム粒子を含有した消化汚泥を前記反応槽より排出することを特徴とする消化汚泥の処理方法も知られている（特許文献３）。 Furthermore, by supplying digested sludge to the reaction tank, adding magnesium compounds to the reaction layer and aeration of the reaction tank, the dissolved phosphorous phosphorus contained in the digested sludge is insolubilized as magnesium ammonium phosphate particles. Then, a digested sludge treatment method characterized by discharging digested sludge containing magnesium ammonium phosphate particles from the reaction tank is also known (Patent Document 3).
嫌気消化にて消化された汚泥は、高分子凝集剤を添加して脱水機にて脱水処理される。この際に、脱水ろ液にはリン酸（ＰＯ４-Ｐ）が多量に含まれる。脱水工程において、特に脱水機が遠心分離機の場合には、消化汚泥が遠心分離機の中で激しく攪拌されて炭酸ガスが抜け、ろ液側のＰＨが上昇し、後述するＭＡＰの生成の最適ＰＨ域となる。溶解性のリン酸（ＰＯ４-Ｐ）はろ液側に行き、消化汚泥の溶液に含まれるアンモニウムとマグネシウムイオンと反応し、不溶性のリン酸マグネシウムアンモニウム（以下「ＭＡＰ］という）が生成する。
ＰＯ４ ３− + ＮＨ４ + + Ｍｇ２+ + ６Ｈ２Ｏ→ ＭｇＮＨ４ＰＯ４・６Ｈ２Ｏ（ＭＡＰ）
Sludge digested by anaerobic digestion is dehydrated with a dehydrator after adding a polymer flocculant. At this time, the dehydrated filtrate contains a large amount of phosphoric acid (PO 4 -P). In the dehydration process, especially when the dehydrator is a centrifuge, the digested sludge is vigorously stirred in the centrifuge, the carbon dioxide gas is released, the pH on the filtrate side rises, and the optimal MAP generation described later PH range. Soluble phosphoric acid (PO 4 -P) goes to the filtrate side and reacts with ammonium and magnesium ions contained in the digested sludge solution to produce insoluble magnesium ammonium phosphate (hereinafter referred to as “MAP”).
PO 4 3− + NH 4 + + Mg 2 + + 6H 2 O → MgNH 4 PO 4 .6H 2 O (MAP)
ＭＡＰは脱水機や配管にスケールとして固着し、閉塞させるので機械的なトラブルとなっている。 Since MAP is fixed as a scale on a dehydrator or piping and clogged, it is a mechanical problem.
一方、消化工程や脱水工程においてＭＡＰとして固定化されるリン酸は消化汚泥中に含まれるマグネシウムイオン量の律速からわずかであり、ほとんどのリン酸は脱水ろ液側に含まれ、返流水として、下水処理プロセスに戻される。返流水のリン濃度が高いと下水処理において、リン除去が困難となり、放流水のリンの規制値を維持できなくなる問題がある。返流水のリン濃度を下げるために、消化槽、脱水機供給汚泥、返流水のいずれかに３価の鉄イオンやアルミニウムなどの金属塩を注入し、下式のように、リン酸を固定化して除去する方法がとられている。
Ｆｅ３+ + ＰＯ４ ３−→ ＦｅＰＯ４↓
On the other hand, phosphoric acid immobilized as MAP in the digestion process and dehydration process is slight due to the rate limiting of the amount of magnesium ions contained in the digested sludge, and most phosphoric acid is contained in the dehydrated filtrate side, Returned to the sewage treatment process. When the phosphorus concentration of the return water is high, it is difficult to remove phosphorus in the sewage treatment, and there is a problem that it becomes impossible to maintain the regulation value of the phosphorus of the discharged water. In order to lower the phosphorus concentration in the return water, metal salts such as trivalent iron ions and aluminum are injected into any of the digestion tank, dehydrator supply sludge, and return water, and phosphoric acid is immobilized as shown in the following formula. The method of removing is taken.
Fe 3+ + PO 4 3- → FePO 4 ↓
この方法では、固定化されたリン酸は最終的には固形分として場外に搬出され、有効利用されない。脱水ケーキやそれを焼却した焼却灰はセメント原料として有効利用されているが、それに含まれるリンはコンクリートの強度を下げるので、リンを除去することが重要である。また、リンを固定するための鉄塩やアルミニウムなどの薬品費用がかかる。 In this method, the immobilized phosphoric acid is finally carried out of the field as a solid content and is not effectively used. Dehydrated cake and incinerated ash that is incinerated are effectively used as a raw material for cement. However, it is important to remove phosphorus because phosphorus contained in it lowers the strength of concrete. In addition, chemical costs such as iron salt and aluminum for fixing phosphorus are required.
そこで、消化汚泥に含まれるリン酸は、脱水ケーキから分離し、有効利用できる形態にして回収することが望ましい。
以上、下水処理で発生した汚泥に含まれるリン酸の処理には次の問題がある。
a. 嫌気性消化をすると、一部のリン酸はＭＡＰとして固定化され、脱水機や脱水ろ液配管にスケールが固着し、機械的なトラブルとなる。
b. 大半のリン酸は脱水ろ液側に行き、水処理系に返流するので、リン酸の固定化のための鉄塩やアルミニウムイオンの薬品費用がかかる。
c. 下水汚泥に含まれるリンはそのまま有効利用できる形態（例えばＭＡＰ）にて回収することが望ましい。
Therefore, it is desirable that the phosphoric acid contained in the digested sludge is separated from the dehydrated cake and recovered in a form that can be used effectively.
As described above, the treatment of phosphoric acid contained in the sludge generated in the sewage treatment has the following problems.
a. When anaerobic digestion is performed, a part of phosphoric acid is immobilized as MAP, and the scale adheres to the dehydrator or dehydrated filtrate piping, resulting in a mechanical trouble.
b. Most phosphoric acid goes to the dehydrated filtrate and returns to the water treatment system, so there is a chemical cost of iron salts and aluminum ions for fixing phosphoric acid.
c. It is desirable to recover the phosphorus contained in the sewage sludge in a form that can be effectively used as it is (for example, MAP).
前記の先行技術は、いずれも脱水機や脱水ろ液配管にスケールが固着するという問題を多かれ少なかれ有しており、根本的に解決したものはない。
本発明は、上記課題を解決して、脱水機や脱水ろ液配管等にスケールの固着の問題がなく、しかもリンを有効利用できる形態で回収できる、安価なリンの回収方法を提供することを目的としている。
All of the above prior arts have more or less the problem that the scale adheres to the dehydrator or the dehydrated filtrate pipe, and none of them has been fundamentally solved.
The present invention solves the above-mentioned problems and provides an inexpensive method for recovering phosphorus that can be recovered in a form in which phosphorus can be effectively used without the problem of scale fixation in a dehydrator, a dehydrated filtrate pipe, or the like. It is aimed.
本発明は、上記課題を解決するべくなされたものであり、次の知見に基いている。
消化汚泥を脱水する脱水機においてＭＡＰを生成させないためには、ＭＡＰの生成の最適ＰＨである８．０〜８．５よりＰＨを下げればよい。消化工程では有機物をメタンと炭酸ガスに分解するものであり、消化槽は水深が２０ｍ程度と深く水圧がかかるので、消化汚泥中には多くの炭酸ガスが溶解している。本発明者は、消化汚泥が、特に遠心脱水機の場合は消化汚泥が遠心分離される際に激しく攪拌され、消化汚泥中に含まれる炭酸が炭酸ガスとして脱気することにより、消化汚泥ではＰＨが７．０〜７．５であったものが、ＰＨが上昇してＭＡＰ生成の最適ＰＨ域の７．９〜８．３となり、ＭＡＰが多量に生成されることを発見した。そこで、消化汚泥の脱水工程でのＭＡＰ生成を阻害するには、脱水機に供給する消化汚泥または脱水ろ液に酸を注入し、ＰＨを６．０〜７．０に下げればよいと考えた。これにより、溶解性であるリン酸はほぼ全量が脱水ろ液側に行き、脱水ろ液中のリン酸は濃度が５０〜４００ｍｇ／Ｌと高濃度となる。ここで注入する酸としては、消化ガスの生物脱硫にて発生する硫酸を用いると、生物脱硫にて発生する硫酸を廃棄することがなく有効利用できる。脱水ろ液にはＳＳ濃度が少なく純度の高いＭＡＰが生成するので、脱水機ろ液にＭＡＰ反応槽を設置し、マグネシウムイオンとＰＨ調整剤であるアルカリを注入しＰＨを８．０〜８．５に調整すれば、効率よくＭＡＰを生成、回収できる。
The present invention has been made to solve the above problems, and is based on the following knowledge.
In order to prevent MAP from being generated in a dehydrator for dewatering digested sludge, the pH may be lowered from 8.0 to 8.5 which is the optimum PH for generating MAP. In the digestion process, organic substances are decomposed into methane and carbon dioxide, and the digestion tank has a water depth of about 20 m, so that water pressure is applied. Therefore, a large amount of carbon dioxide is dissolved in the digested sludge. The present inventor, in the case of a centrifugal dehydrator, vigorously stirred when the digested sludge is centrifuged, and carbon dioxide contained in the digested sludge is degassed as carbon dioxide gas. Was 7.0 to 7.5, and the pH increased to 7.9 to 8.3, which is the optimum PH range for MAP generation, and it was found that a large amount of MAP was generated. Therefore, in order to inhibit the MAP production in the dewatering process of digested sludge, it was thought that acid could be injected into the digested sludge or dehydrated filtrate to be supplied to the dehydrator, and PH should be lowered to 6.0-7.0. . As a result, almost all of the soluble phosphoric acid goes to the dehydrated filtrate side, and the concentration of phosphoric acid in the dehydrated filtrate is as high as 50 to 400 mg / L. If the sulfuric acid generated by biodesulfurization of digestion gas is used as the acid injected here, the sulfuric acid generated by biodesulfurization can be used effectively without being discarded. Since MAP with low SS concentration and high purity is produced in the dehydrated filtrate, a MAP reaction tank is installed in the dehydrator filtrate, and magnesium ions and an alkali as a pH adjusting agent are injected to adjust the pH to 8.0 to 8. If adjusted to 5, MAP can be generated and recovered efficiently.
本発明は、以上の知見に基いてなされたものであり、消化ガスの生物脱硫装置を備えた汚泥消化設備から排出された消化汚泥を、脱水機に供給し脱水した後、得られた脱水ろ液中のリンをリン酸マグネシウムアンモニウム（ＭＡＰ）として回収するリン回収方法において、前記生物脱硫装置より発生する硫酸を前記脱水機に供給する消化汚泥、前記脱水ろ液のいずれかに添加し、ｐＨを６．０〜７．０となるよう調整することを特徴とするリン回収方法を提供するものである。 The present invention has been made on the basis of the above knowledge, and digested sludge discharged from a sludge digestion facility equipped with a biodesulfurization apparatus for digestion gas is supplied to a dehydrator and dehydrated, and then the obtained dewatering filter is obtained. In the phosphorus recovery method for recovering phosphorus in the liquid as magnesium ammonium phosphate (MAP), sulfuric acid generated from the biological desulfurizer is added to either the digested sludge that supplies the dehydrator or the dehydrated filtrate, and the pH Is adjusted to 6.0 to 7.0 to provide a phosphorus recovery method.
本発明により、汚泥の消化工程で発生するリン酸による、脱水機や脱水ろ液配管へのスケールの固着問題を解消でき、しかも、リン酸固定化のための鉄塩やアルミニウムイオンが不要である。また、５０〜４００ｍｇ／Ｌと高濃度であるリン酸を原料とするので、ＭＡＰ反応槽が小さくでき、建設費用が小さい。脱水ろ液を原料としているのでＭＡＰ生成の阻害要因であるＳＳ濃度が少なく、高純度のＭＡＰが生成できるので、有効利用価値が高い。酸は消化ガスの生物脱硫装置から副産物として出る硫酸を使用するので、コストがかからないし、副生成物が有効利用できる。 According to the present invention, the problem of scale fixing to a dehydrator or a dehydrated filtrate pipe due to phosphoric acid generated in the sludge digestion process can be solved, and iron salts and aluminum ions for phosphoric acid fixation are not required. . Moreover, since phosphoric acid having a high concentration of 50 to 400 mg / L is used as a raw material, the MAP reaction tank can be made small and the construction cost is low. Since the dehydrated filtrate is used as a raw material, the SS concentration, which is an inhibitory factor of MAP production, is low, and high-purity MAP can be produced, so that the effective use value is high. Since the acid uses sulfuric acid that is generated as a by-product from the biodesulfurization apparatus for digestion gas, there is no cost and the by-product can be used effectively.
本発明の方法は、廃水処理設備で発生する汚泥を嫌気性消化処理する工程で汚泥から放出される多量のリンを回収する方法である。この廃水処理設備は、微生物を用いて廃水を浄化する設備であればよく、廃水の種類は特に限定されないが、典型的なものは下水である。 The method of the present invention is a method for recovering a large amount of phosphorus released from sludge in a process of anaerobic digestion of sludge generated in a wastewater treatment facility. The wastewater treatment facility may be any facility that purifies wastewater using microorganisms, and the type of wastewater is not particularly limited, but a typical one is sewage.
廃水処理設備においては、増殖した大量の汚泥が余剰汚泥として排出される。そこで、この余剰汚泥を減容のため、消化槽で嫌気性消化処理が行われる。この嫌気性消化処理は、通常メタン発酵によって行われ、消化ガスが発生する。 In the wastewater treatment facility, a large amount of sludge that has grown is discharged as excess sludge. Therefore, anaerobic digestion is performed in the digestion tank in order to reduce the volume of this excess sludge. This anaerobic digestion process is usually performed by methane fermentation, and digestion gas is generated.
消化ガスの主成分はメタンガスと炭酸ガスであり、例えばメタン６０〜７０重量％、炭酸ガス３０〜４０重量を含み、さらに、１００〜３０００ｐｐｍ程度の硫化水素ガスも含んでいる。 The main components of the digestion gas are methane gas and carbon dioxide gas, including, for example, methane 60 to 70% by weight, carbon dioxide gas 30 to 40%, and also hydrogen sulfide gas of about 100 to 3000 ppm.
この消化ガスは、燃料として用いることができ、例えば発電用のガスエンジン、ガスタービン、温水や蒸気を製造するボイラー、さらには燃料電池などへの使用も可能である。ところが、硫化水素が混入していると、燃焼によって硫黄酸化物が生成し、これが機材を腐食させたり、排ガス中の硫黄酸化物濃度を高くするので、これを除去する必要がある。除去手段としては、酸化鉄等の吸着剤を用いた乾式脱硫法や、アルカリを用いた湿式脱硫法がある。その外、硫黄細菌を用いた生物脱硫法も開発されている。この生物脱硫法は、硫化水素を酸化分解する微生物が付着した充填材層を有する生物脱硫塔を用いた生物脱硫設備を利用するものであり、反応は次のように進行する。
Ｈ２Ｓ + ２Ｏ２ → Ｈ２ＳＯ４
This digested gas can be used as a fuel, and can be used for, for example, a power generation gas engine, a gas turbine, a boiler for producing hot water and steam, and a fuel cell. However, if hydrogen sulfide is mixed in, sulfur oxides are generated by combustion, which corrodes the equipment and increases the concentration of sulfur oxides in the exhaust gas, so it must be removed. As the removing means, there are a dry desulfurization method using an adsorbent such as iron oxide and a wet desulfurization method using an alkali. In addition, biodesulfurization methods using sulfur bacteria have also been developed. This biodesulfurization method uses a biodesulfurization facility using a biodesulfurization tower having a filler layer to which microorganisms that oxidize and decompose hydrogen sulfide are attached, and the reaction proceeds as follows.
H 2 S + 2O 2 → H 2 SO 4
この生物脱硫設備は、硫化水素を酸化して硫酸を生成させる細菌を付着させた充填材を充填した生物脱硫塔に必要な付帯設備を付設してなるものである。この細菌は、硫黄酸化細菌と称されるものであり、公知の菌を利用できるが、下水処理場の活性汚泥処理している曝気槽に生息している。そこで、曝気槽内の液を生物脱硫塔に少量投入すればよい。充填材は、各種合成樹脂、ピート、木炭等多種のものを使用でき、例えば、ポリプロピレン製気液接触充填材を使用できる。付帯設備は、この脱硫塔へ硫化水素を酸化するための酸素（空気でよい）供給ライン、細菌を生育させかつ生成した硫酸を取り出すための給水ライン、脱硫塔を適温に保つためのヒータ等である。生物脱硫塔で硫化水素は１０ｐｐｍ以下まで脱硫されるが、細菌の馴致期間やトラブル発生に対処するため、念のため、追加の湿式あるいは乾式の脱硫装置を付設しておくこともできる。この生物脱硫設備は、特開平２−２６６１５号公報、特開２００３−３０５３２８号公報などに開示されている。 This biological desulfurization facility is provided with ancillary facilities necessary for a biological desulfurization tower packed with a filler to which bacteria that oxidize hydrogen sulfide to generate sulfuric acid are attached. This bacterium is called a sulfur-oxidizing bacterium, and a publicly known bacterium can be used, but it lives in an aeration tank that is treated with activated sludge in a sewage treatment plant. Therefore, a small amount of the liquid in the aeration tank may be introduced into the biological desulfurization tower. Various fillers such as various synthetic resins, peat, and charcoal can be used as the filler. For example, a polypropylene gas-liquid contact filler can be used. Ancillary facilities include an oxygen (air is sufficient) supply line for oxidizing hydrogen sulfide to the desulfurization tower, a water supply line for growing bacteria and taking out the generated sulfuric acid, and a heater for keeping the desulfurization tower at an appropriate temperature. is there. In the biological desulfurization tower, hydrogen sulfide is desulfurized to 10 ppm or less, but an additional wet or dry desulfurization device can be provided as a precaution in order to cope with the acclimatization period and trouble occurrence of bacteria. This biological desulfurization facility is disclosed in JP-A-2-26615, JP-A-2003-305328, and the like.
生物脱硫設備で脱硫した消化ガスは、そのままあるいは炭酸ガスを分離して燃料として用いることができる。
生物脱硫設備では、脱硫によって硫酸も生成し、これは塔内に連続投入されている水によってｐＨ１〜２程度の希硫酸として取り出される。
Digested gas desulfurized in a biological desulfurization facility can be used as fuel as it is or after separation of carbon dioxide.
In the biological desulfurization facility, sulfuric acid is also generated by desulfurization, and this is taken out as dilute sulfuric acid having a pH of about 1 to 2 by water continuously fed into the tower.
消化槽から取り出された消化汚泥は大量の水を含んでいるので脱水を行う。脱水手段は特に限定されないが、ろ材などの混入がなく、効率よく汚泥を分離できるので遠心分離機が好適である。 Digested sludge removed from the digestion tank contains a large amount of water, so it is dehydrated. The dehydrating means is not particularly limited, but a centrifugal separator is preferable because it does not contain a filter medium and can efficiently separate sludge.
分離した消化汚泥は、焼却し、あるいは有効利用される。
一方、消化汚泥を分離した脱水ろ液には、汚泥の嫌気性消化処理の際に発生した多量のリン酸が含まれている。そこで、このリン酸をリン酸マグネシウムアンモニウム（ＭＡＰ）として回収する。脱水ろ液中にはリン酸に加えてアンモニウムも多量に含まれているので、マグネシウム化合物を加えてｐＨ７．４〜９．５程度、好ましくはｐＨ８．０〜８．５程度に調整することによってＭＡＰを生成させることができる。この反応は次のように進行する。
ＰＯ４ ３− + ＮＨ４ + + Ｍｇ２+ + ６Ｈ２Ｏ→ ＭｇＮＨ４ＰＯ４・６Ｈ２Ｏ
The separated digested sludge is incinerated or effectively used.
On the other hand, the dehydrated filtrate from which the digested sludge has been separated contains a large amount of phosphoric acid generated during the anaerobic digestion of the sludge. Therefore, this phosphoric acid is recovered as magnesium ammonium phosphate (MAP). Since the dehydrated filtrate contains a large amount of ammonium in addition to phosphoric acid, the magnesium compound is added to adjust the pH to about 7.4 to 9.5, preferably about pH 8.0 to 8.5. A MAP can be generated. This reaction proceeds as follows.
PO 4 3− + NH 4 + + Mg 2 + + 6H 2 O → MgNH 4 PO 4 .6H 2 O
マグネシウム化合物としては、水酸化マグネシウム、塩化マグネシウム等を使用できるが、それ自身がアルカリ性である点で水酸化マグネシウムが好ましい。マグネシウムの添加量は、リン酸１モルに対し、０．８〜２．５倍モル程度、好ましくは１．０〜１．５倍モル程度とするのがよい。脱水ろ液中には消化汚泥由来のマグネシウムも含まれており、これも上記のマグネシウムの量に加える。アンモニウムの量はリン酸１モルに対し、１〜３倍モル程度、好ましくは１．２〜１．５倍モル程度が適当であり、脱水ろ液中のアンモニウムの量がこれより不足する場合には、アンモニウムを追加する。このアンモニウムは、塩でもよいが、アンモニア水あるいはアンモニアガスを吹き込むのがそれ自身がアルカリ性である点で好ましい。 As the magnesium compound, magnesium hydroxide, magnesium chloride and the like can be used, but magnesium hydroxide is preferred in that it is alkaline. The addition amount of magnesium is about 0.8 to 2.5 times mol, preferably about 1.0 to 1.5 times mol, per mol of phosphoric acid. Magnesium derived from digested sludge is also contained in the dehydrated filtrate, and this is also added to the above amount of magnesium. When the amount of ammonium is about 1 to 3 times mol, preferably about 1.2 to 1.5 times mol per mol of phosphoric acid, and the amount of ammonium in the dehydrated filtrate is insufficient. Add ammonium. This ammonium may be a salt, but it is preferable that ammonia water or ammonia gas is blown in view of alkalinity.
脱水ろ液を上記ｐＨに調整する際には、脱水ろ液のｐＨは７．０〜７．５程度であり、しかも炭酸ガスを相当量含んでいるので、まず、曝気をして炭酸ガスを追い出すのがよい。それだけでｐＨが上記範囲にならない場合には適宜アルカリを加えて上記ｐＨ範囲内にする。このアルカリには水酸化ナトリウム等を用いることができる。 When adjusting the pH of the dehydrated filtrate, the pH of the dehydrated filtrate is about 7.0 to 7.5 and contains a considerable amount of carbon dioxide gas. It is good to kick out. If the pH does not fall within the above range, an alkali is appropriately added to bring the pH within the above range. Sodium hydroxide etc. can be used for this alkali.
ＭＡＰを生成するにあたり、予めＭＡＰ粒子を種晶として加えておくことができ、それによってＭＡＰの粒径を大きくすることができる。
ＭＡＰを生成させる反応層には公知のもの、例えば特開平１−１１９３９２号公報記載のものを利用できる。
In generating MAP, MAP particles can be added as seed crystals in advance, whereby the particle size of MAP can be increased.
As the reaction layer for generating MAP, a known layer, for example, one described in JP-A-1-119392 can be used.
生成したＭＡＰの分離手段としては、沈降、ろ過、遠心分離など如何なる手段によってもよい。
本発明の方法は、このようなリンの回収方法において、前記生物脱硫装置より発生する硫酸を、前記脱水機に供給する消化汚泥、前記脱水ろ液のいずれかに添加し、ｐＨ６．０〜７．０となるように調整するところに特徴がある。これは、汚泥の消化によって発生したリン酸とアンモニウムとマグネシウムがＭＡＰ生成の最適ｐＨであるｐＨ８以上にならないようにして、消化汚泥から脱水ろ液を分離してＭＡＰ反応槽に送り込み、消化槽からＭＡＰ反応槽までの間でＭＡＰが析出するトラブルを阻止しているのである。
The generated MAP may be separated by any means such as sedimentation, filtration, and centrifugation.
In the method for recovering phosphorus according to the present invention, sulfuric acid generated from the biological desulfurization apparatus is added to either the digested sludge supplied to the dehydrator or the dehydrated filtrate, and the pH is 6.0 to 7 It is characterized in that it is adjusted to be .0. This is done by separating the dehydrated filtrate from the digested sludge and feeding it into the MAP reaction tank so that the phosphoric acid, ammonium and magnesium generated by digestion of the sludge do not exceed pH 8 which is the optimum pH for MAP production. This prevents the trouble that MAP precipitates up to the MAP reactor.
本発明の方法は、汚泥を消化して脱水し、脱水ろ液をＭＡＰ反応槽に送る間にＭＡＰ付着によるトラブルを生じないため、汚泥を消化し、脱水ろ液からＭＡＰを生成させる方法に広く適用できる。 Since the method of the present invention digests sludge and dehydrates it, and does not cause trouble due to MAP adhesion while sending the dehydrated filtrate to the MAP reaction tank, it is widely used as a method for digesting sludge and generating MAP from the dehydrated filtrate. Applicable.
Claims (2)
An apparatus for recovering phosphorus in digested sludge discharged from a sludge digestion facility equipped with a digestion gas biological desulfurization apparatus, wherein the digested sludge is dehydrated, and phosphorus in the dehydrated filtrate obtained from the dewatering means And a means for collecting phosphorus as magnesium ammonium phosphate (MAP) and means for adding sulfuric acid generated from the biological desulfurizer to the digested sludge and / or the dehydrated filtrate supplied to the dehydrator. A phosphorus recovery device.
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