JP2004081959A - Dehydration method for organic sludge utilizing sludge incineration ash - Google Patents
Dehydration method for organic sludge utilizing sludge incineration ash Download PDFInfo
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Abstract
Description
【０００１】
【技術分野】
本発明は排水処理技術の分野、詳しくは排水処理において発生する汚泥の処理技術に関する。
【０００２】
【背景技術および課題】
下水道処理施設やし尿処理施設において日常的に発生する汚泥は高割合の有機分を含み、そのため凝集剤（脱水剤）を添加して脱水性を向上させない限り効率良く脱水し、減容化することはできない。この目的のため無機凝集剤および有機高分子凝集剤が単独または組合せて使用される。
【０００３】
一般に使用される無機凝集剤は、硫酸バンド、ポリ塩化アルミニウム、塩化第二鉄、ポリ硫酸第二鉄など水溶性アルミニウム塩および水溶性鉄（ＩＩＩ ）塩である。これらは有機高分子凝集剤に比較して安価であるが、多量に添加する必要があり、脱水した汚泥ケーキをさらに減容化するため焼却した場合焼却灰の発生が増加する。
【０００４】
焼却灰を焼き固めてレンガとするなどその有効利用も試みられているが、そのような用途に利用できる量には限りがあり、もっと多量に有効利用できる用途の開拓が求められている。
【０００５】
【課題の解決方法】
そこで本発明者らは汚泥の焼却灰を元の汚泥の脱水性を向上させるための脱水剤として利用することを考えた。汚泥の焼却灰は酸化物の形でカルシウム、アルミニウム、鉄などの金属を含んでおり、そのままの形で汚泥の脱水性を向上させることはできないが、これを強酸へ投入し、一部が該強酸の塩の形で溶けている酸性スラリーの形で添加することにより、無機凝集剤の少なくとも一部に代って汚泥の脱水に利用できることがわかった。しかしながら有機性汚泥の焼却灰には多量のリン酸化物が含まれているので、その酸性スラリーはリン酸の形で可溶化されたリンを含むことになる。そのため焼却灰の酸性スラリーを単独で汚泥に添加するとリン酸が汚泥の脱水により生ずる濾液に含まれて下水処理系を循環し、下水処理系への負荷を増加させることになる。
【０００６】
本発明は、焼却灰の酸性スラリーの添加後または添加と同時に鉄系またはアルミニウム系の無機凝集剤を添加し、リン酸を固定化する。固定化されたリンは脱水ケーキに含まれて回収され、下水処理系へ再循環されない。
【０００７】
有機高分子凝集剤の添加は焼却灰酸性スラリーおよび無機凝集剤を添加した後に行う。これにより汚泥の脱水性が満足なレベルに向上し、汚泥を含水率の低い脱水ケーキへ脱水することができる。
【０００８】
このように本発明によれば、焼却灰をリサイクルすることにより新規に添加される無機凝集剤の量を減らし、従って無機凝集剤による焼却灰発生の増加を抑制することができる。
【０００９】
【好ましい実施態様】
有機性汚泥の焼却灰は、酸化物の形でアルミニウム、鉄、カルシウムなどの金属を含んでいる。焼却灰をスラリー化するために使用する酸は、これら酸化物のうち少なくともアルミニウムおよび鉄を可溶化できる無機の強酸であれば良い。しかしながら経済性などの面から塩酸および硫酸が好ましく、特にカルシウムを可溶化し凝集に役立たせることができることから塩酸が好ましい。酸の量はスラリーのｐＨを２以下とする量であり、塩酸の場合塩化水素として一般に焼却灰の２０〜１００重量％である。スラリーは焼却灰を酸水溶液へ投入し、酸と十分な時間反応させた後に用いるのが好ましい。
【００１０】
焼却灰スラリーの添加量は可溶化された金属の含有量および汚泥の性質、蒸発残分（ＴＳ）などによって変動するが、一般に汚泥ＴＳに対して焼却灰として２〜２０重量％が適当である。この量は汚泥１Ｌあたり焼却灰５００〜５，０００ｍｇに相当するであろう。
【００１１】
無機凝集剤は慣用のものであり、硫酸バンド、ポリ塩化アルミニウム、塩化第二鉄、ポリ硫酸第二鉄などから選ばれる。無機凝集剤の添加量は焼却灰スラリーを添加しない場合と比較して少なくてすむけれども、しかし前に説明したように、焼却灰スラリーに含まれるリン酸を固定化するのに十分な量でなければならない。この量は一般にスラリー中の焼却灰の１〜３０重量％である。無機凝集剤は汚泥へ焼却灰スラリーを添加した後に添加するか、または焼却灰スラリーと混合して同時に添加することができる。焼却灰と反応させる酸水溶液へ添加しても有効である。
【００１２】
汚泥へ最後に添加される有機高分子凝集剤は水処理技術の分野で良く知られたものから選ぶことができる。中でも有機性汚泥の脱水に特に効果があることが知られている（メタ）アクリレート系カチオン高分子凝集剤または（メタ）アクリレート系両性高分子凝集剤が好ましい。その添加量は汚泥のＴＳに対して１重量％以下、好ましくは０．５重量％以下で十分である。
【００１３】
好ましい有機高分子凝集剤の例は以下のものを含む。
（メタ）アクリレート系カチオン高分子凝集剤：
ジメチルアミノエチル（メタ）アクリレート塩化メチル４級塩重合体；
ジメチルアミノエチル（メタ）アクリレート塩化メチル４級塩と（メタ）アクリルアミドの共重合体；
ジメチルアミノエチル（メタ）アクリレート酸付加塩と（メタ）アクリルアミドとの共重合体
（メタ）アクリレート系両性高分子凝集剤：
ジメチルアミノエチル（メタ）アクリレート塩化メチル４級塩と（メタ）アクリルアミドと（メタ）アクリル酸の共重合体
これらは単独で、または混合して用いることができる。
【００１４】
【実施例】
以下の実施例および比較例により本発明を例証する。これらにおいて「％」は特記しない限り重量基準による。
【００１５】
実施例１〜３および比較例１〜３
【材料】
１．汚泥
Ａ下水処理場汚泥を用いた。汚泥の性質は次のとおり。
蒸発残分（ＴＳ）＝２．５０％
浮遊物質（ＳＳ）＝２．３１％
灰分＝２０．０％ＴＳ
焼却灰成分の分析値＝ＳｉＯ２ ４２．９％；Ａｌ２ Ｏ３ １７．９％；Ｆｅ２ Ｏ３ ５．３％；ＣａＯ ４．７％；ＭｇＯ １．５％；Ｋ２ Ｏ ２．０％；Ｐ２ Ｏ５ ２１．５％；その他 ４．２％
２．焼却灰スラリー
上の焼却灰３０ｇを３５％塩酸２０ｇと水２０ｇの溶液へ投入し、十分に攪拌した後１２時間放置して用いた。
３．無機凝集剤：
４０％塩化第二鉄水溶液を用いた。
４．有機高分子凝集剤：
（１）アクリレート系カチオン高分子凝集剤
ジメチルアミノエチルアクリレート塩化メチル４級化塩（ＤＡＣ）８０モルと、アクリルアミド（ＡＡｍ）２０モルとの共重合体を用いた。固有粘度＝５０ｄｌ／ｇ
（２）アクリレート系両性高分子凝集剤
ＤＡＣ６０モルと、ＡＡｍ１０モルと、アクリル酸（ＡＡｃ）２０モルとの共重合体を用いた。固有粘度＝６０ｄｌ／ｇ
【００１６】
【汚泥調質方法】
汚泥２００ｍｌを３００ｍｌビーカーに取り、焼却灰スラリー、４０％塩化第二鉄水溶液および高分子凝集剤を表１に示すように添加した。
【００１７】
【表１】
高分子凝集剤は０．２％水溶液として添加し、攪拌機で１０００ｒｐｍ×３０秒攪拌した。高分子凝集剤の添加率は結果と共に表２に示されている。
１．凝集性の評価
調質した汚泥をナイロン製濾布（６０メッシュ）を敷いたヌッチェ（径７０ｍｍ）に注ぎ、３０秒後の濾液を測定する。
２．脱水性および分離液の評価
調質した汚泥を遠心機中の６０メッシュ濾布袋の中に静かに入れ、試料が安定した状態になったのを確認した後、徐々に遠心機の回転数を上げ、４，０００ｒｐｍに達した時点より６０秒間遠心分離し、濾布に付着した脱水ケーキの含水率を測定する。また分離した濾液についてＳＳおよびリン濃度を測定する。
３．結果を表２に示す。
【００１９】
【表２】
【考察】
焼却灰スラリー単独と高分子凝集剤を添加した比較例３と比べると、焼却灰スラリーを無機凝集剤と組合せ、さらに高分子凝集剤を添加した実施例では、濾液中のリン濃度が有意に低くなることがわかる。さらに焼却灰スラリーと無機凝集剤をあらかじめ混合して添加した場合、分離濾液中のリン濃度の低下のみならず、分離水中のＳＳも有意に減少する。焼却灰スラリーと無機凝集剤を添加し、高分子凝集剤として両性高分子凝集剤を添加した実施例３は、試験した項目のすべてにおいて最良の結果を示した。
【００２１】
実施例４〜６および比較例４〜５
【材料】
１．汚泥
Ｂ下水処理場汚泥を用いた。汚泥の性質は次のとおり。
蒸発残分（ＴＳ）＝３．７５％
浮遊物質（ＳＳ）＝３．５０％
灰分＝２５．０％ＴＳ
焼却灰成分の分析値＝ＳｉＯ２ ３９．１％；Ａｌ２ Ｏ３ １８．７％；Ｆｅ２ Ｏ３ ７．３％；ＣａＯ ８．２％；ＭｇＯ ２．２％；Ｋ２ Ｏ ２．３％；Ｐ２ Ｏ５ １８．５％；その他 ３．２％
２．焼却灰スラリー
上の焼却灰３０ｇを３５％塩酸２０ｇと水２０ｇの溶液へ投入し、十分に攪拌した後１２時間放置して用いた。
３．無機凝集剤：
４０％塩化第二鉄水溶液を用いた。
４．有機高分子凝集剤：
（１）メタクリレート系カチオン高分子凝集剤
ジメチルアミノエチルメタクリレート塩化メチル４級化塩（ＤＭＣ）の重合体を用いた。固有粘度＝１０ｄｌ／ｇ
（２）メタクリレート系両性高分子凝集剤
ジメチルアミノエチルメタクリレート塩酸塩６０モルと、ＡＡｍ１０モルと、アクリル酸（ＡＡｃ）１５モルとの共重合体を用いた。固有粘度＝２０ｄｌ／ｇ
【００２２】
【汚泥調質方法】
汚泥２００ｍｌをビーカーに取り、焼却灰スラリー、４０％塩化第二鉄水溶液および高分子凝集剤を表３に示すように添加した。
【００２３】
【表３】
高分子凝集剤は０．２％水溶液として添加し、攪拌機で２００ｒｐｍ×３０秒攪拌した。高分子凝集剤の添加率は結果と共に表４に示されている。
１．凝集性の評価
調質した汚泥をナイロン製濾布（９６メッシュ）を敷いたヌッチェ（径７０ｍｍ）に注ぎ、３０秒後の濾液を測定する。別に調質した汚泥のフロック径を目視で評価する。
２．脱水性および分離液の評価
上の１で得た濾過ケーキを２０ｃｍ四方の濾布ではさみ、０．１ＭＰａ×１分の圧力でプレス脱水し、脱水後のケーキ含水率と、１および２の操作で分離した濾液のＳＳとリン濃度を測定する。結果を表４に示す。
【００２５】
【表４】
【考察】
実施例１〜３および比較例１〜３についての考察は実施例４〜６および比較例４〜５にも同様に当てはまる。[0001]
【Technical field】
The present invention relates to the field of wastewater treatment technology, and more particularly, to a technology for treating sludge generated in wastewater treatment.
[0002]
[Background technology and issues]
Sludge generated daily in sewage treatment facilities and human waste treatment facilities contains a high proportion of organic matter. Therefore, unless a coagulant (a dehydrating agent) is added to improve the dewatering properties, dewatering is efficiently performed to reduce the volume. Can not. For this purpose, inorganic coagulants and organic polymer coagulants are used alone or in combination.
[0003]
Commonly used inorganic flocculants are water-soluble aluminum salts and water-soluble iron (III) salts such as sulfate bands, polyaluminum chloride, ferric chloride, and ferric polysulfate. These are inexpensive as compared with the organic polymer flocculant, but need to be added in a large amount, and when dewatered sludge cake is incinerated to further reduce the volume, generation of incinerated ash increases.
[0004]
Attempts have been made to use bricks by baking incinerated ash for effective use. However, the amount that can be used for such purposes is limited, and there is a need to develop applications that can be used more effectively.
[0005]
[Solution of the problem]
Then, the present inventors considered using sludge incineration ash as a dehydrating agent for improving the dewatering property of the original sludge. Sludge incineration ash contains metals such as calcium, aluminum, and iron in the form of oxides, and cannot improve the dewatering properties of sludge as it is. It has been found that by adding in the form of an acidic slurry dissolved in the form of a salt of a strong acid, it can be used for dewatering sludge instead of at least a part of the inorganic coagulant. However, since the incinerated ash of organic sludge contains a large amount of phosphorus oxides, the acidic slurry contains phosphorus solubilized in the form of phosphoric acid. Therefore, when an acidic slurry of incinerated ash is added to sludge alone, phosphoric acid is contained in the filtrate generated by dewatering sludge and circulates through the sewage treatment system, increasing the load on the sewage treatment system.
[0006]
In the present invention, an iron-based or aluminum-based inorganic coagulant is added after or simultaneously with the addition of the acidic slurry of incinerated ash to fix phosphoric acid. The immobilized phosphorus is recovered in the dewatered cake and is not recycled to the sewage treatment system.
[0007]
The addition of the organic polymer flocculant is performed after the acidic ash slurry and the inorganic flocculant are added. Thereby, the dewatering property of the sludge is improved to a satisfactory level, and the sludge can be dewatered into a dewatered cake having a low water content.
[0008]
As described above, according to the present invention, the amount of the newly added inorganic coagulant can be reduced by recycling the incinerated ash, and therefore, the increase in incinerated ash generation due to the inorganic coagulant can be suppressed.
[0009]
[Preferred embodiment]
Organic sludge incineration ash contains metals such as aluminum, iron and calcium in the form of oxides. The acid used for slurrying the incinerated ash may be an inorganic strong acid capable of solubilizing at least aluminum and iron among these oxides. However, hydrochloric acid and sulfuric acid are preferred from the viewpoint of economy and the like, and hydrochloric acid is particularly preferred because it can solubilize calcium and contribute to aggregation. The amount of the acid is an amount for adjusting the pH of the slurry to 2 or less. In the case of hydrochloric acid, it is generally 20 to 100% by weight of incinerated ash as hydrogen chloride. The slurry is preferably used after incinerated ash is charged into an acid aqueous solution and reacted with the acid for a sufficient time.
[0010]
The amount of the incinerated ash slurry varies depending on the content of the solubilized metal, the properties of the sludge, the evaporation residue (TS), and the like. Generally, 2 to 20% by weight of the incinerated ash is appropriate for the sludge TS. . This amount would correspond to 500-5,000 mg of incinerated ash per liter of sludge.
[0011]
The inorganic coagulant is a conventional one and is selected from a sulfate band, polyaluminum chloride, ferric chloride, ferric polysulfate and the like. The amount of addition of the inorganic coagulant is small compared to the case where no incineration ash slurry is added, but as described above, it must be sufficient to fix the phosphoric acid contained in the incineration ash slurry. Must. This amount is generally between 1 and 30% by weight of the incineration ash in the slurry. The inorganic coagulant can be added after adding the incinerated ash slurry to the sludge, or can be added simultaneously with the incinerated ash slurry. It is also effective to add it to an acid aqueous solution to be reacted with incineration ash.
[0012]
The organic polymeric flocculant finally added to the sludge can be selected from those well known in the field of water treatment technology. Among them, a (meth) acrylate-based cationic polymer flocculant or a (meth) acrylate-based amphoteric polymer flocculant, which is known to be particularly effective in dehydrating organic sludge, is preferable. The amount of addition is 1% by weight or less, preferably 0.5% by weight or less, based on the sludge TS.
[0013]
Examples of preferred organic polymeric flocculants include:
(Meth) acrylate-based cationic polymer flocculant:
Dimethylaminoethyl (meth) acrylate methyl chloride quaternary salt polymer;
Copolymer of dimethylaminoethyl (meth) acrylate methyl chloride quaternary salt and (meth) acrylamide;
Copolymer of dimethylaminoethyl (meth) acrylate acid addition salt and (meth) acrylamide (meth) acrylate-based amphoteric polymer flocculant:
Copolymer of dimethylaminoethyl (meth) acrylate methyl chloride quaternary salt, (meth) acrylamide and (meth) acrylic acid These can be used alone or as a mixture.
[0014]
【Example】
The following examples and comparative examples illustrate the invention. In these, “%” is based on weight unless otherwise specified.
[0015]
Examples 1-3 and Comparative Examples 1-3
【material】
1. Sludge A Sewage treatment plant sludge was used. The properties of sludge are as follows.
Evaporation residue (TS) = 2.50%
Suspended solids (SS) = 2.31%
Ash content = 20.0% TS
Analytical value of incineration ash component = SiO 2 42.9%; Al 2 O 3 17.9%; Fe 2 O 3 5.3%; CaO 4.7%; MgO 1.5%; K 2 O 2.0 %; P 2 O 5 21.5%; others 4.2%
2. 30 g of the incinerated ash on the incinerated ash slurry was put into a solution of 20 g of 35% hydrochloric acid and 20 g of water, and the mixture was sufficiently stirred and left for 12 hours before use.
3. Inorganic flocculant:
A 40% ferric chloride aqueous solution was used.
4. Organic polymer flocculant:
(1) Acrylate-based cationic polymer flocculant A copolymer of dimethylaminoethyl acrylate methyl chloride quaternized salt (DAC) 80 mol and acrylamide (AAm) 20 mol was used. Intrinsic viscosity = 50 dl / g
(2) A copolymer of 60 moles of acrylate amphoteric polymer coagulant DAC, 10 moles of AAm, and 20 moles of acrylic acid (AAc) was used. Intrinsic viscosity = 60 dl / g
[0016]
[Sludge conditioning method]
200 ml of the sludge was placed in a 300 ml beaker, and an incinerated ash slurry, a 40% aqueous ferric chloride solution and a polymer flocculant were added as shown in Table 1.
[0017]
[Table 1]
The polymer flocculant was added as a 0.2% aqueous solution, and stirred with a stirrer at 1000 rpm for 30 seconds. The addition rate of the polymer flocculant is shown in Table 2 together with the results.
1. Evaluation of coagulation property The treated sludge is poured into a Nutsche (diameter 70 mm) lined with a nylon filter cloth (60 mesh), and the filtrate after 30 seconds is measured.
2. Evaluation of dehydration and separation liquid The conditioned sludge was gently put into a 60-mesh filter cloth bag in a centrifuge, and after confirming that the sample was in a stable state, the rotation speed of the centrifuge was gradually increased. , 4,000 rpm, and centrifuged for 60 seconds to measure the water content of the dehydrated cake attached to the filter cloth. The SS and the phosphorus concentration of the separated filtrate are measured.
3. Table 2 shows the results.
[0019]
[Table 2]
[Discussion]
In comparison with Comparative Example 3 in which the incinerated ash slurry alone and the polymer flocculant were added, in the example in which the incinerated ash slurry was combined with the inorganic flocculant and further the polymer flocculant was added, the phosphorus concentration in the filtrate was significantly lower. It turns out that it becomes. Furthermore, when the incinerated ash slurry and the inorganic coagulant are mixed and added in advance, not only the phosphorus concentration in the separated filtrate is reduced, but also the SS in the separated water is significantly reduced. Example 3 in which the incineration ash slurry and the inorganic flocculant were added, and the amphoteric polymer flocculant was added as the polymer flocculant, showed the best results in all the items tested.
[0021]
Examples 4 to 6 and Comparative Examples 4 to 5
【material】
1. Sludge B Sewage treatment plant sludge was used. The properties of sludge are as follows.
Evaporation residue (TS) = 3.75%
Suspended solids (SS) = 3.50%
Ash content = 25.0% TS
Analytical value of incinerated ash component = SiO 2 39.1%; Al 2 O 3 18.7%; Fe 2 O 3 7.3%; CaO 8.2%; MgO 2.2%; K 2 O 2.3 %; P 2 O 5 18.5%; others 3.2%
2. 30 g of the incinerated ash on the incinerated ash slurry was put into a solution of 20 g of 35% hydrochloric acid and 20 g of water, and the mixture was sufficiently stirred and left for 12 hours before use.
3. Inorganic flocculant:
A 40% ferric chloride aqueous solution was used.
4. Organic polymer flocculant:
(1) Methacrylate-based cationic polymer flocculant A polymer of dimethylaminoethyl methacrylate methyl chloride quaternary salt (DMC) was used. Intrinsic viscosity = 10 dl / g
(2) Methacrylate-based amphoteric polymer flocculant A copolymer of 60 mol of dimethylaminoethyl methacrylate hydrochloride, 10 mol of AAm, and 15 mol of acrylic acid (AAc) was used. Intrinsic viscosity = 20 dl / g
[0022]
[Sludge conditioning method]
200 ml of the sludge was placed in a beaker, and an incinerated ash slurry, a 40% aqueous ferric chloride solution and a polymer flocculant were added as shown in Table 3.
[0023]
[Table 3]
The polymer flocculant was added as a 0.2% aqueous solution, and stirred with a stirrer at 200 rpm × 30 seconds. The addition rate of the polymer flocculant is shown in Table 4 together with the results.
1. Evaluation of coagulation property The treated sludge is poured into a Nutsche (diameter 70 mm) lined with a nylon filter cloth (96 mesh), and the filtrate after 30 seconds is measured. The floc diameter of the separately treated sludge is visually evaluated.
2. Dehydration property and evaluation of separation liquid The filter cake obtained in 1 above was sandwiched between filter cloths of 20 cm square, and dewatered by press at a pressure of 0.1 MPa x 1 minute. The SS and the phosphorus concentration of the filtrate separated in the above are measured. Table 4 shows the results.
[0025]
[Table 4]
[Discussion]
The considerations of Examples 1 to 3 and Comparative Examples 1 to 3 apply to Examples 4 to 6 and Comparative Examples 4 to 5 as well.
Claims (5)
（ｂ）次いで有機高分子凝集剤を添加するステップ、及び
（ｃ）得られる有機質汚泥を脱水するステップ、
を含む有機性汚泥の脱水方法。(A) adding, to the organic sludge, a slurry obtained by adding the incinerated ash of the organic sludge to an acid aqueous solution having a pH of 2 or less and an inorganic flocculant;
(B) then adding an organic polymer flocculant, and (c) dehydrating the resulting organic sludge,
For dehydrating organic sludge.
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