JP3981759B2 - Sewage sludge treatment method - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、下水汚泥の高度利用と有用成分の回収を可能とし、下水汚泥乾燥物のリサイクル性を高め得る下水汚泥処理方法に関するものである。
【０００２】
【従来の技術】
現在、我が国において、下水汚泥の発生量は固形分として、年間約２００万ｔに達すると言われており、その約８割が有効利用されずに埋立てにより廃棄処理されている。下水汚泥の残りの約２割はコンポスト（堆肥）化等によって利用されているが、充分なリサイクルがなされているとは言えない状況である。
【０００３】
このように、従来から下水汚泥は、コンポスト（堆肥）化等による有効利用が行なわれてきたが、最近、この下水汚泥の脱水ケーキを乾燥し、炭化し、賦活して、活性炭を製造し、例えば都市ごみの焼却炉からの排ガス中に含まれるダイオキシン等の有害物質の吸着除去剤として利用する方法が提案されている。また、これ以外にも、活性炭を下水処理場での脱臭用に利用する方法も提案されている。
【０００４】
【発明が解決しようとする課題】
しかしながら、従来より下水汚泥の有効利用が進展しない原因の一つとして、下水汚泥の脱水ケーキの固形分中に灰分が２５〜３０％含まれていて、この灰分が、下水汚泥の有効利用の妨げとなっていることが挙げられる。
【０００５】
例えば、下水汚泥の脱水ケーキの乾燥物を活性炭化した場合、活性炭として得られる収率は約３５％程度であり、このうちの２５〜３０％が灰分であるため、有効活性炭部分は、その差である５〜１０％しかないことになる。
【０００６】
すなわち、下水汚泥の脱水ケーキ乾燥物から活性炭として得られる製品のうち、約８割は不活性な灰分であり、従って、木質部の比表面積が、通常の活性炭と同様に１０００（ｍ２／ｇ）程度あったと仮定しても、全体としての有効比表面積は２００（ｍ２／ｇ）程度となってしまうのである。
【０００７】
一方、下水汚泥の脱水ケーキ乾燥物からの活性炭の製造のためには、約８５０℃の温度まで昇温して炭化し、賦活しなければならないが、下水汚泥乾燥物の２割の部分を有効利用するために、残りの８割の灰分までも同時に昇温するエネルギーが必要となり、民間ベースでは、なかなか経済性が成り立ち難いという問題があった。
【０００８】
しかし、下水汚泥の脱水ケーキの乾燥物を活性炭化した後、例えば都市ごみの焼却炉からの排ガス中に含まれるダイオキシン類を除去するといった利用法は、現在行なわれている下水処理場から下水汚泥を直接廃棄する状況に比べると、経済性さえ許せば、廃棄物を一度、有効利用してから廃棄することになるので、リサイクル性からは好ましい方向と言える。
【０００９】
このように、下水汚泥廃棄物から製造した活性炭をダイオキシン類等の有害物除去のために使用すること自体は好ましいことであるが、活性炭の場合、吸着容量が存在するので、ある程度使用した後に、必ず再生するか、廃棄する必要が出てくる。特に、ダイオキシン類およびその他有害物を吸着した活性炭はそのまま廃棄することができないので、処理する必要がある。焼却施設の場合、廃活性炭を焼却炉に投入し、活性炭と一緒にダイオキシン類等の有害物を燃焼分解すれば、廃活性炭の処理方法としては問題が無いように見える。
【００１０】
しかしながら、通常の活性炭であれば、灰分が少ないので、上記の焼却処理を行なっても問題は無いが、下水汚泥の脱水ケーキ乾燥物を原料として製造した活性炭の場合は、灰分の量が多いので、これを焼却処理すれば、焼却灰の量を増すことになる。
【００１１】
結局、下水汚泥の脱水ケーキ乾燥物を活性炭化するだけの従来の処理方法では、下水処理場から発生する下水汚泥のうち、固形分の約１／３を占める灰分は、下水処理場からごみ焼却場に移動して、そこで廃棄されるだけであるという問題がある。
【００１２】
本発明者らは、上記の点に鑑み鋭意研究を重ねた結果、下水汚泥乾燥物のリサイクル性を高めるために、下水汚泥乾燥物の灰分から有用成分をさらに回収し得ることを見い出し、本発明を完成するに至った。
【００１３】
本発明の目的は、上記の従来技術の問題を解決し、下水汚泥の高度利用と有用成分の回収を可能とし、下水汚泥乾燥物のリサイクル性を高め得る下水汚泥処理方法を提供しようとすることにある。
【００１４】
【課題を解決するための手段】
上記の目的を達成するために、本発明の請求項１の発明による下水汚泥処理方法は、下水汚泥を脱水し、脱水ケーキを乾燥して得られた下水汚泥の脱水ケーキの乾燥物を、炭化工程、賦活工程を経て無酸素で活性炭化し、得られた活性炭を燃焼排ガス中の有害物の吸着除去用途、脱臭等の気体処理用途、または水処理用途に使用し、使用後の有害物含有廃活性炭を焼却処理することによって、廃活性炭に吸着されている有害物を燃焼分解し、これによって生成した焼却灰を硫酸等の鉱酸で処理し、処理液を濾過した後、濾液より燐酸分を回収するとともに、ほとんどが土壌成分である濾過残渣を回収することを特徴としている。
【００１５】
つぎに、請求項２の発明による下水汚泥処理方法は、上記請求項１において、廃活性炭の焼却灰を硫酸等の鉱酸で処理し、処理液を濾過して得られた濾液を濃縮することによって燐酸分を回収し、この燐酸分を、硫安、燐安等の化学肥料の原料として使用することを特徴としている。
【００１６】
また、請求項３の発明による下水汚泥処理方法は、上記請求項１において、廃活性炭の焼却灰を硫酸等の鉱酸で処理し、処理液を濾過して得られたほとんどが土壌成分である濾過残渣を洗浄して鉱酸等の付着成分を除去した後、脱水し、得られた浄化濾過残査を、セメント原料あるいは路盤材等の土木用資材原料として使用することを特徴としている。
【００１７】
【発明の実施の形態】
つぎに、この発明の実施の形態を説明する。
【００１８】
まず、下水汚泥の高度利用と有用成分の回収を可能とし、下水汚泥のリサイクル性を高めるために、下水汚泥の脱水ケーキ乾燥物の性状と、これを炭化し、賦活して、活性炭化したものについて検討した。下水汚泥の脱水ケーキ乾燥物より得られた活性炭の性状を表１に示した。
【００１９】
【表１】
つぎに、活性炭中の灰分の分析値と、外国産の燐鉱石の成分分析値を比較し、得られた結果を表２に示した。
【００２１】
【表２】
この表２の結果から、明らかなように下水汚泥を焼成して発生する灰分組成は、燐鉱石に匹敵する燐分を含有しており、いわば、低品位燐鉱石という見方ができる。
【００２３】
本発明は、下水汚泥乾燥物の各成分を、つぎのように高度に有効利用することを骨子としている。
【００２４】
１）下水汚泥の有機性揮発分；炭化あるいは賦活時に発生するガスを燃焼させ、乾燥と活性炭製造時の熱エネルギーとして回収利用する。
【００２５】
２）下水汚泥の非揮発性木質分；活性炭として有効利用した後、焼却し、吸着された有害物分解のためのエネルギーの一部に利用する。
【００２６】
３）焼却残査、すなわち灰分は燐酸製造のための原鉱石とみなし、燐酸分を回収し、硫安、燐安等の化学肥料の原料とする。
【００２７】
上記の点から、本発明による下水汚泥処理方法は、下水汚泥を脱水し、脱水ケーキを乾燥して得られた下水汚泥の脱水ケーキの乾燥物を、炭化工程、賦活工程を経て無酸素で活性炭化し、得られた活性炭を燃焼排ガス中の有害物の吸着除去用途、脱臭等の気体処理用途、または水処理用途に使用し、使用後の有害物含有廃活性炭を焼却処理することによって、廃活性炭に吸着されている有害物を燃焼分解し、これによって生成した焼却灰を硫酸等の鉱酸で処理し、処理液を濾過した後、濾液より燐酸分を回収するとともに、ほとんどが土壌成分である濾過残渣を回収するものである。
【００２８】
つぎに、本発明の方法は、廃活性炭の焼却灰を硫酸等の鉱酸で処理し、処理液を濾過して得られた濾液を濃縮することによって燐酸分を回収し、この燐酸分を、硫安、燐安等の化学肥料の原料として使用するものである。
【００２９】
また、本発明の方法は、鉱酸処理後の濾過残渣が、ほとんどが土壌成分である点に鑑み、これをセメント原料あるいは路盤材等の土木用資材原料として使用するものである。
【００３０】
（実験例）
つぎに、下水汚泥の灰分に実際に含有される燐分が回収可能であることを確認するために、下記のような確認試験を行なった。
【００３１】
実験方法；
▲１▼ 下水汚泥の脱水ケーキ乾燥物１００ｇを電気炉に入れ、空気雰囲気で９００℃で焼成した。その結果、２９ｇの焼成灰を得た。
【００３２】
▲２▼ この焼成灰１０ｇを採取し、１０．５％Ｈ２ＳＯ４水溶液５６ｇ中に入れ、攪拌しながら８０℃で３時間反応させた。
【００３３】
▲３▼ ３時間経過後、真空濾過し、濾液３５．３ｇを得た。
【００３４】
▲４▼ 濾液のＰ２Ｏ５分析値は１４．８％であり、Ｐ２Ｏ５の回収率は７４％であった。
【００３５】
上記の実験によって、下水汚泥の脱水ケーキ乾燥物の灰分から、容易に燐酸が得られることが確認された。
【００３６】
【実施例】
つぎに、本発明の実施例を、図面を参照して説明する。
【００３７】
図１は、本発明の下水汚泥処理方法のフローシートを示すものである。
【００３８】
同図において、区画(A) は下水処理場を表わす。この区画(A) の下水処理場において生じた下水汚泥の脱水ケーキ(1) を、ついで乾燥機(2) に入れ、水分が数％になるまで乾燥する。つぎに、下水汚泥の脱水ケーキの乾燥物を炭化炉(3) に送り、不活性ガス雰囲気中で６５０℃に加熱し、炭化する。
【００３９】
炭化物を、つぎの賦活炉(4) に送り、８５０℃に加熱すると共に、水蒸気供給管(5) から吹き込んだ水蒸気によって賦活し、この活性炭を冷却後、下水汚泥活性炭の製品を得、この活性炭製品を流送管(6) より取り出す。
【００４０】
この実施例では、この下水汚泥活性炭製品をごみ焼却炉のダイオキシン除去用に使用する場合を示しており、図１の区画(B) は都市ごみ焼却場を意味する。
【００４１】
上記の賦活炉(4) より流送管(6) によって取り出した下水汚泥活性炭製品を、都市ごみ焼却場(B) に輸送する。図面では、ごみ焼却システムのフローは省略しているが、ごみの焼却によって発生した排ガスを、ボイラで熱回収した後、脱塵、脱塩する。そしてさらに、排ガス中のガス状ダイオキシン濃度を充分に低減するために、排ガスを活性炭塔または活性炭バグフィルターに導入する。
【００４２】
図１には、活性炭バグフィルター(9) を示しており、脱塵、脱塩後の排ガスを導入管(7) から活性炭バグフィルター(9) に導入するが、導入管(7) の煙道で循環活性炭粉末を供給管(8) から吹き込む。排ガス中のダイオキシン類はこの活性炭粉末に吸着されて除去される。この活性炭粉末をバグフィルター(9) で捕集し、清浄なガスを排出管(10)から誘引送風機を経て、煙突から大気中に放出する。
【００４３】
バグフィルター(9) の濾布に付着したダイオキシン類を吸着した活性炭を、一定時間ごとに払い落とし、バグフィルター(9) の下端部から排出する。このダイオキシン類吸着廃活性炭は、通常、ダイオキシン類の飽和吸着量に達していないので、排出管(11)により一定量ずつ抜き出し、その一部を循環活性炭として供給管(8) を介して排ガス導入管(7) の煙道に再循環し、残部のダイオキシン類吸着廃活性炭を流送管(12)から抜き出す。一方、抜出し活性炭に相当する量の下水汚泥活性炭製品を、流送管(6) によって上記供給管(8) 中に循環活性炭として補充する。
【００４４】
バグフィルター(9) より抜き出した廃活性炭の残部は、流送管(12)から専用焼却炉(13)に送り、焼却処理する。この専用焼却炉(13)では廃活性炭の焼却によって、吸着されていた有害成分、この例ではダイオキシン類も高温で分解・燃焼し、ここで発生した排ガスを、さらに２次燃焼炉(14)で完全分解して、清浄ガスを排出管(15)から大気中に放出する。
【００４５】
専用焼却炉(13)内で生じた廃活性炭の燃焼残査である焼却灰を、流送管(16)から蒸解槽(17)に送る。この蒸解槽(17)には、硫酸供給管(18)によって所定濃度の硫酸を供給して、焼却灰と硫酸の混合物を８０℃の温度で３時間攪拌しながら、加熱し、焼却灰から、例えばつぎの反応によって燐酸を抽出する。
【００４６】
２Ｃａ３ＰＯ４＋３Ｈ２ＳＯ４＝２Ｈ３ＰＯ４＋６ＣａＳＯ４
蒸解槽(17)から抜き出したスラリーを、濾過機(19)で濾過し、得られた燐酸を含む濾液を流送管(20)から濃縮釜(21)に送って濃縮し、得られた燐酸製品を排出管(22)から取り出す。スラリーの濾過残査は、ほとんどが土壌成分であるので、これを流送管(23)によって取り出し、洗浄槽(24)に送る。洗浄槽(24)においては濾過残査を洗浄して鉱酸等の付着成分を除去し、さらに、脱水機(25)を経た後、浄化濾過残査を回収管(26)によって回収し、セメント原料あるいは路盤材等の土木用資材原料として再利用する。
【００４７】
【発明の効果】
本発明の請求項１記載の発明による下水汚泥処理方法は、上述のように、下水汚泥を脱水し、脱水ケーキを乾燥して得られた下水汚泥の脱水ケーキの乾燥物を、炭化工程、賦活工程を経て無酸素で活性炭化し、得られた活性炭を燃焼排ガス中の有害物の吸着除去用途、脱臭等の気体処理用途、または水処理用途に使用し、使用後の有害物含有廃活性炭を焼却処理することによって、廃活性炭に吸着されている有害物を燃焼分解し、これによって生成した焼却灰を硫酸等の鉱酸で処理し、処理液を濾過した後、濾液より燐酸分を回収するとともに、ほとんどが土壌成分である濾過残渣を回収するものである。
【００４８】
つぎに、請求項２の発明による下水汚泥処理方法は、廃活性炭の焼却灰を硫酸等の鉱酸で処理し、処理液を濾過して得られた濾液を濃縮することによって燐酸分を回収し、この燐酸分を、硫安、燐安等の化学肥料の原料として使用するものである。
【００４９】
また、請求項３の発明による下水汚泥処理方法は、廃活性炭の焼却灰を硫酸等の鉱酸で処理し、処理液を濾過して得られたほとんどが土壌成分である濾過残渣を洗浄して鉱酸等の付着成分を除去した後、脱水し、得られた浄化濾過残査を、セメント原料あるいは路盤材等の土木用資材原料として使用するものである。
【００５０】
本発明の上記の方法によれば、つぎの効果を生じる。
【００５１】
１．下水汚泥の有効利用
現在、国内で多量に発生しており、ほとんど有効利用されないまま廃棄されている下水汚泥中に大量に含まれている燐分を、資源として回収し、リサイクルすることによって、現在、国内に輸入されている化学肥料原料を節約することができる。
【００５２】
２．下水汚泥を直接焼却し、この灰分から燐酸を生産することも可能であるが、下水汚泥の脱水ケーキを乾燥し、炭化し、賦活して、活性炭を製造し、この活性炭を、例えば焼却炉の排ガス中に含まれるダイオキシンの吸着除去剤、あるいは下水処理場での脱臭剤として一度有効利用した後、廃活性炭を焼却して、ダイオキシン類等の可燃性吸着有害物質を燃焼分解で無害化し、残査を燐酸原料とする方が、資源としてより有効に利用できる。
【００５３】
３．現在、下水汚泥は一部コンポスト（堆肥）化され、肥料として利用されているが、これに比べると、下水汚泥から回収された燐酸を原料とする燐系化学肥料の場合、つぎのような利点がある。
【００５４】
▲１▼ 肥料として使用の時期が制限されない。
【００５５】
▲２▼ 工場で多量に生産できるので、品質が安定する。
【００５６】
▲３▼ 下水汚泥から回収された燐酸を原料とする燐系化学肥料に不足している植物栄養分を後から添加して、補充することができるので、複合系肥料が簡単に生産可能である。
【図面の簡単な説明】
【図１】本発明の下水汚泥処理方法の実施例を示すフローシートである。
【符号の説明】
(A) ：下水処理場
(B) ：都市ごみ焼却場
(1) ：下水汚泥の脱水ケーキ
(2) ：乾燥機
(3) ：炭化炉
(4) ：賦活炉
(5) ：水蒸気供給管
(6) ：下水汚泥活性炭製品流送管
(7) ：都市ごみ焼却排ガス導入管
(8) ：循環活性炭粉末供給管
(9) ：活性炭バグフィルター
(10)：清浄ガス排出管
(11)：ダイオキシン類吸着廃活性炭排出管
(12)：廃活性炭流送管
(13)：専用焼却炉
(14)：２次燃焼炉
(15)：清浄ガス排出管
(16)：焼却灰流送管
(17)：蒸解槽
(18)：硫酸供給管
(19)：濾過機
(20)：燐酸含有濾液流送管
(21)：濃縮釜
(22)：燐酸製品排出管
(23)：濾過残査流送管
(24)：洗浄槽
(25)：脱水機
(26)：濾過残査回収管[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating sewage sludge that enables advanced utilization of sewage sludge and recovery of useful components, and can improve the recyclability of dried sewage sludge.
[0002]
[Prior art]
At present, the amount of sewage sludge generated in Japan is said to reach about 2 million tons per year as solids, and about 80% of it is disposed of by landfill without being effectively used. About 20% of the remaining sewage sludge is used for composting, but it cannot be said that it is fully recycled.
[0003]
Thus, sewage sludge has been used effectively by composting (composting), but recently, dehydrated cake of this sewage sludge is dried, carbonized and activated to produce activated carbon, For example, a method has been proposed in which it is used as an adsorbent / removal agent for harmful substances such as dioxins contained in exhaust gas from municipal waste incinerators. In addition to this, a method of using activated carbon for deodorization at a sewage treatment plant has been proposed.
[0004]
[Problems to be solved by the invention]
However, as one of the reasons why the effective use of sewage sludge has not progressed conventionally, the solid content of the dewatered cake of sewage sludge contains 25-30% of ash, which prevents the effective use of sewage sludge. It is mentioned that.
[0005]
For example, when activated carbonization is performed on the dried product of the dewatered cake of sewage sludge, the yield obtained as activated carbon is about 35%, of which 25-30% is ash. This is only 5 to 10%.
[0006]
That is, about 80% of the product obtained as activated carbon from the dehydrated cake dried product of sewage sludge is inert ash, and therefore the specific surface area of the wood part is 1000 (m 2 / g) as in the case of normal activated carbon. Even if it is assumed that there is a degree, the effective specific surface area as a whole is about 200 (m 2 / g).
[0007]
On the other hand, in order to produce activated carbon from dehydrated cake dried sewage sludge, it must be heated to about 850 ° C and carbonized and activated, but 20% of the dried sewage sludge is effective. In order to use the energy, the remaining 80% of the ash content needs to be heated at the same time, and it has been difficult to achieve economic efficiency on a private basis.
[0008]
However, after activated carbonization of the dried dehydrated cake of sewage sludge, for example, dioxins contained in the exhaust gas from incinerators of municipal waste are removed. Compared to the situation of direct disposal, if economic efficiency is allowed, the waste will be discarded after it has been effectively used once.
[0009]
Thus, it is preferable to use activated carbon produced from sewage sludge waste for removing harmful substances such as dioxins, but in the case of activated carbon, there is an adsorption capacity. It must be regenerated or discarded. In particular, activated carbon adsorbed with dioxins and other harmful substances cannot be discarded as it is, and therefore must be treated. In the case of incineration facilities, if waste activated carbon is put into an incinerator and toxic substances such as dioxins are burned and decomposed together with the activated carbon, there appears to be no problem as a method for treating the waste activated carbon.
[0010]
However, normal activated carbon has less ash, so there is no problem even if the above incineration is performed. However, in the case of activated carbon produced from dried sewage sludge dehydrated cake, the amount of ash is large. If this is incinerated, the amount of incinerated ash will be increased.
[0011]
After all, in the conventional treatment method that only activated carbonizes the dehydrated cake dry matter of sewage sludge, the ash that accounts for about 1/3 of the solids out of the sewage sludge is incinerated from the sewage treatment plant. There is a problem that it only moves to the place and is discarded there.
[0012]
As a result of intensive studies in view of the above points, the present inventors have found that useful components can be further recovered from the ash content of the sewage sludge dry matter in order to enhance the recyclability of the sewage sludge dry matter, and the present invention. It came to complete.
[0013]
An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a sewage sludge treatment method capable of enhancing the recyclability of sewage sludge dry matter, enabling the advanced utilization of sewage sludge and recovery of useful components. It is in.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, a sewage sludge treatment method according to the invention of claim 1 of the present invention is a method of carbonizing a dehydrated cake of sewage sludge obtained by dehydrating sewage sludge and drying the dehydrated cake. Activated carbon without oxygen through the process and activation process, and the resulting activated carbon is used for adsorption removal of harmful substances in combustion exhaust gas, gas treatment applications such as deodorization, or water treatment applications, and waste containing hazardous substances after use By incinerating the activated carbon, the harmful substances adsorbed on the waste activated carbon are burned and decomposed, the incinerated ash produced thereby is treated with a mineral acid such as sulfuric acid, the treatment liquid is filtered, and the phosphoric acid content is removed from the filtrate. While collecting, it is characterized by collecting filtration residue which is mostly soil components.
[0015]
Next, the sewage sludge treatment method according to the invention of claim 2 is the method of claim 1, wherein the incinerated ash of the waste activated carbon is treated with a mineral acid such as sulfuric acid, and the filtrate obtained by filtering the treatment liquid is concentrated. The phosphoric acid content is recovered by the above-mentioned method, and this phosphoric acid content is used as a raw material for chemical fertilizers such as ammonium sulfate and phosphorous acid.
[0016]
Further, the sewage sludge treatment method according to the invention of claim 3 is the above-mentioned claim 1, wherein the waste activated carbon incineration ash is treated with a mineral acid such as sulfuric acid, and the treatment liquid is almost all obtained as a soil component. The filter residue is washed to remove adhering components such as mineral acid, and then dehydrated, and the resulting purified filter residue is used as a raw material for civil engineering such as cement raw material or roadbed material.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described.
[0018]
First, in order to enable advanced use of sewage sludge and recovery of useful components, and to improve the recyclability of sewage sludge, the nature of the dehydrated cake dried product of sewage sludge and the carbonized, activated, activated carbonized one Was examined. Table 1 shows the properties of the activated carbon obtained from the dried sewage sludge cake.
[0019]
[Table 1]
Next, the analysis value of the ash content in the activated carbon and the component analysis value of the foreign phosphate ore were compared, and the results obtained are shown in Table 2.
[0021]
[Table 2]
As is apparent from the results in Table 2, the ash composition generated by firing sewage sludge contains a phosphorus content comparable to that of phosphate ore, which can be regarded as a low-grade phosphate ore.
[0023]
The gist of the present invention is to use each component of the dried sewage sludge in a highly effective manner as follows.
[0024]
1) Organic volatile matter in sewage sludge: gas generated during carbonization or activation is burned and recovered and used as thermal energy during drying and activated carbon production.
[0025]
2) Non-volatile woody content of sewage sludge; after being effectively used as activated carbon, it is incinerated and used as a part of energy for decomposition of adsorbed harmful substances.
[0026]
3) Incineration residue, that is, ash is regarded as raw ore for the production of phosphoric acid, and the phosphoric acid is recovered and used as a raw material for chemical fertilizers such as ammonium sulfate and phosphorous.
[0027]
In view of the above, the method for treating sewage sludge according to the present invention is a method of dehydrating sewage sludge and drying a dehydrated cake to obtain a dried product of a dehydrated cake of sewage sludge, which is activated carbon without oxygen through a carbonization step and an activation step. Activated activated carbon is used for adsorption removal of harmful substances in combustion exhaust gas, gas treatment applications such as deodorization, or water treatment applications, and waste activated carbon containing hazardous substances after use is incinerated. Toxic substances adsorbed on the product are burned and decomposed, and the incinerated ash produced thereby is treated with a mineral acid such as sulfuric acid. After the treatment liquid is filtered, the phosphoric acid content is recovered from the filtrate and most of it is a soil component. The filtration residue is recovered.
[0028]
Next, the method of the present invention treats the incinerated ash of waste activated carbon with a mineral acid such as sulfuric acid, and collects the phosphoric acid content by concentrating the filtrate obtained by filtering the treatment liquid. It is used as a raw material for chemical fertilizers such as ammonium sulfate and phosphorus.
[0029]
Moreover, the method of this invention uses this as a raw material for civil engineering, such as a cement raw material or a roadbed material, in view of the fact that the filtration residue after the mineral acid treatment is mostly a soil component.
[0030]
(Experimental example)
Next, in order to confirm that the phosphorus content actually contained in the sewage sludge ash was recoverable, the following confirmation test was performed.
[0031]
experimental method;
(1) 100 g of dried sewage sludge cake was placed in an electric furnace and fired at 900 ° C. in an air atmosphere. As a result, 29 g of calcined ash was obtained.
[0032]
(2) 10 g of this calcined ash was sampled and placed in 56 g of 10.5% H 2 SO 4 aqueous solution, and reacted at 80 ° C. for 3 hours with stirring.
[0033]
(3) After 3 hours, the solution was vacuum filtered to obtain 35.3 g of a filtrate.
[0034]
(4) The analysis value of P 2 O 5 of the filtrate was 14.8%, and the recovery rate of P 2 O 5 was 74%.
[0035]
From the above experiments, it was confirmed that phosphoric acid can be easily obtained from the ash content of the dried dehydrated cake of sewage sludge.
[0036]
【Example】
Next, embodiments of the present invention will be described with reference to the drawings.
[0037]
FIG. 1 shows a flow sheet of the sewage sludge treatment method of the present invention.
[0038]
In the figure, section (A) represents a sewage treatment plant. The dewatered cake (1) of sewage sludge generated in the sewage treatment plant in this section (A) is then placed in a dryer (2) and dried until the water content reaches several percent. Next, the dried product of the dewatered cake of sewage sludge is sent to the carbonization furnace (3), heated to 650 ° C. in an inert gas atmosphere, and carbonized.
[0039]
The carbide is sent to the next activation furnace (4), heated to 850 ° C. and activated by the steam blown from the steam supply pipe (5). After cooling the activated carbon, a product of sewage sludge activated carbon is obtained. Remove the product from the flow pipe (6).
[0040]
In this embodiment, the case where this sewage sludge activated carbon product is used for dioxin removal in a waste incinerator is shown, and the section (B) in FIG. 1 means a municipal waste incineration plant.
[0041]
The sewage sludge activated carbon product taken out from the activation furnace (4) by the flow pipe (6) is transported to the municipal waste incineration plant (B). In the drawing, the flow of the waste incineration system is omitted, but the exhaust gas generated by the waste incineration is recovered by heat in a boiler, and then dedusted and desalted. Further, in order to sufficiently reduce the concentration of gaseous dioxin in the exhaust gas, the exhaust gas is introduced into the activated carbon tower or the activated carbon bag filter.
[0042]
Fig. 1 shows an activated carbon bag filter (9), and the exhaust gas after dedusting and desalting is introduced into the activated carbon bag filter (9) from the introduction pipe (7). The flue in the introduction pipe (7) Then, circulating activated carbon powder is blown from the supply pipe (8). Dioxins in the exhaust gas are adsorbed and removed by the activated carbon powder. This activated carbon powder is collected by the bag filter (9), and clean gas is discharged from the chimney through the induction fan through the exhaust pipe (10) into the atmosphere.
[0043]
The activated carbon adsorbing dioxins adhering to the filter cloth of the bag filter (9) is removed at regular intervals and discharged from the lower end of the bag filter (9). Since the dioxin adsorption waste activated carbon does not normally reach the saturated adsorption amount of dioxins, it is extracted by a certain amount by the discharge pipe (11), and a part of it is introduced into the exhaust gas through the supply pipe (8) as circulating activated carbon. Recirculate to the flue of the pipe (7), and extract the remaining dioxin adsorption waste activated carbon from the flow pipe (12). On the other hand, the sewage sludge activated carbon product corresponding to the extracted activated carbon is replenished as circulating activated carbon into the supply pipe (8) through the flow pipe (6).
[0044]
The remainder of the waste activated carbon extracted from the bag filter (9) is sent from the flow pipe (12) to the dedicated incinerator (13) for incineration. In this dedicated incinerator (13), the harmful components adsorbed by incineration of the waste activated carbon, in this case dioxins, are also decomposed and burned at high temperature, and the exhaust gas generated here is further decomposed in the secondary combustion furnace (14). The gas is completely decomposed and the clean gas is discharged from the discharge pipe (15) into the atmosphere.
[0045]
Incineration ash, which is a combustion residue of waste activated carbon generated in the dedicated incinerator (13), is sent from the flow pipe (16) to the digester (17). This digester tank (17) is supplied with a predetermined concentration of sulfuric acid through a sulfuric acid supply pipe (18), and the mixture of incineration ash and sulfuric acid is heated at a temperature of 80 ° C. with stirring for 3 hours. For example, phosphoric acid is extracted by the following reaction.
[0046]
2Ca 3 PO 4 + 3H 2 SO 4 = 2H 3 PO 4 + 6CaSO 4
The slurry extracted from the digester (17) is filtered by a filter (19), and the filtrate containing the obtained phosphoric acid is sent from the flow pipe (20) to the concentrating kettle (21) and concentrated, and the resulting phosphoric acid is obtained. Remove the product from the discharge pipe (22). Since most of the filtration residue of the slurry is a soil component, it is taken out by the flow pipe (23) and sent to the washing tank (24). In the washing tank (24), the filtration residue is washed to remove adhering components such as mineral acid, and after passing through the dehydrator (25), the purification filtration residue is recovered by the recovery pipe (26), Reuse as raw materials or raw materials for civil engineering such as roadbed materials.
[0047]
【The invention's effect】
In the sewage sludge treatment method according to the first aspect of the present invention, as described above, the dehydrated cake of sewage sludge obtained by dehydrating sewage sludge and drying the dehydrated cake is subjected to a carbonization step, activation The activated carbon is converted to oxygen-free activated carbon through the process, and the resulting activated carbon is used for adsorption removal of harmful substances in combustion exhaust gas, gas treatment applications such as deodorization, or water treatment applications, and incinerate waste activated carbon containing hazardous substances after use. By treating, the harmful substances adsorbed on the waste activated carbon are burned and decomposed, the incinerated ash produced thereby is treated with a mineral acid such as sulfuric acid, the treatment liquid is filtered and the phosphoric acid content is recovered from the filtrate. The filter residue, which is mostly a soil component, is recovered.
[0048]
Next, the sewage sludge treatment method according to the invention of claim 2 recovers phosphoric acid content by treating the incinerated ash of waste activated carbon with a mineral acid such as sulfuric acid and concentrating the filtrate obtained by filtering the treatment liquid. The phosphoric acid content is used as a raw material for chemical fertilizers such as ammonium sulfate and phosphorous acid.
[0049]
Further, in the sewage sludge treatment method according to the invention of claim 3, the incinerated ash of the waste activated carbon is treated with a mineral acid such as sulfuric acid, and the filtration residue, which is mostly a soil component, is obtained by filtering the treatment liquid. After removing adhering components such as mineral acid, dehydration is performed, and the resulting purified filtration residue is used as a raw material for civil engineering such as cement raw material or roadbed material.
[0050]
According to the above method of the present invention, the following effects are produced.
[0051]
1. Effective utilization of sewage sludge Currently, a large amount of phosphorus contained in sewage sludge that has been generated in Japan and discarded almost without being effectively used is recovered and recycled as a resource. Can save chemical fertilizer raw material imported into the country.
[0052]
2. It is possible to incinerate sewage sludge directly to produce phosphoric acid from this ash, but the dehydrated cake of sewage sludge is dried, carbonized and activated to produce activated carbon, which is then used in an incinerator, for example. After effective use once as an adsorbent removal agent for dioxins contained in exhaust gas or as a deodorizer at sewage treatment plants, incinerated waste activated carbon detoxifies flammable adsorptive substances such as dioxins by combustion decomposition, It is more effective as a resource to use the inspection as a phosphoric acid raw material.
[0053]
3. At present, sewage sludge is partially composted (composted) and used as fertilizer. Compared with this, the following advantages are obtained in the case of phosphorus-based chemical fertilizers using phosphoric acid recovered from sewage sludge as a raw material. There is.
[0054]
(1) The time of use as a fertilizer is not restricted.
[0055]
(2) The quality is stable because it can be produced in large quantities at the factory.
[0056]
(3) Since plant nutrients lacking in phosphorus-based chemical fertilizers using phosphoric acid recovered from sewage sludge can be added later and supplemented, composite fertilizers can be produced easily.
[Brief description of the drawings]
FIG. 1 is a flow sheet showing an embodiment of the sewage sludge treatment method of the present invention.
[Explanation of symbols]
(A): Sewage treatment plant
(B): Municipal waste incineration plant
(1): Dewatered cake of sewage sludge
(2): Dryer
(3): Carbonization furnace
(4): Activation furnace
(5): Steam supply pipe
(6): Sewage sludge activated carbon product flow pipe
(7): Municipal waste incineration exhaust gas introduction pipe
(8): Circulating activated carbon powder supply pipe
(9): Activated carbon bag filter
(10): Clean gas discharge pipe
(11): Dioxin adsorption waste activated carbon discharge pipe
(12): Waste activated carbon flow pipe
(13): Exclusive incinerator
(14): Secondary combustion furnace
(15): Clean gas discharge pipe
(16): Incineration ash pipe
(17): Cooking tank
(18): Sulfuric acid supply pipe
(19): Filter
(20): Phosphate-containing filtrate flow tube
(21): Concentration kettle
(22): Phosphate product discharge pipe
(23): Filtration residual flow pipe
(24): Cleaning tank
(25): Dehydrator
(26): Filtration residue collection tube
Claims (3)
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| JP2002060614A JP3981759B2 (en) | 2002-03-06 | 2002-03-06 | Sewage sludge treatment method |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2002060614A JP3981759B2 (en) | 2002-03-06 | 2002-03-06 | Sewage sludge treatment method |
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| JP3981759B2 true JP3981759B2 (en) | 2007-09-26 |
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| CN109534881A (en) * | 2018-12-28 | 2019-03-29 | 扬州大学 | It is a kind of to utilize the device and method for preparing slow release fertilizer in fuel ash with waste liquid |
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| CN109534881A (en) * | 2018-12-28 | 2019-03-29 | 扬州大学 | It is a kind of to utilize the device and method for preparing slow release fertilizer in fuel ash with waste liquid |
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