JP4145406B2 - Method for preventing phosphorus from being eluted in sludge and phosphorus elution preventing agent for sludge - Google Patents
Method for preventing phosphorus from being eluted in sludge and phosphorus elution preventing agent for sludge Download PDFInfo
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Description
【0001】
【発明の属する技術分野】
本発明は、廃水処理で発生する汚泥を濃縮し、脱水あるいは搬送する廃水処理システムにおける汚泥中のリンの溶出防止方法および汚泥処理に使用される汚泥中のリンの溶出防止剤に関し、詳しくは、汚泥に固定化されたリンの溶出を防止し、汚泥の濃縮および脱水で発生する分離水中のリン濃度を低減させる汚泥中のリンの溶出防止方法および汚泥中のリンの溶出防止剤に関する。
【0002】
【従来の技術】
従来より、し尿や下水などの都市廃水、工場等からの有機性産業廃水などは、その中に含まれる種々の懸濁物質(SS)を取り除く処理が施されてから、河川などに放流されている。
上記都市廃水や有機性産業廃水の処理システムにおいては、例えば図2に示すように、まず、処理しようとする廃水原水が最初沈殿池に導入され、ここで比較的大きな懸濁物質が沈殿分離される。次に、曝気槽にて、活性汚泥により廃水中の水溶性有機成分等を分解する生物処理がなされる。その後、最終沈殿池にて汚泥が沈殿分離された後、処理水は河川などに放流され、一方、沈殿した汚泥は曝気槽に返送される。
【0003】
また、一般的に最終沈殿池からの汚泥の一部は、余剰汚泥として、最初沈殿池からの初沈汚泥とともに汚泥濃縮槽にて濃縮される。ここでの分離水は返流水として最初沈殿池に返送される。濃縮された汚泥は汚泥貯留槽に送られて貯留される。
汚泥貯留槽に貯留した汚泥は、適宜、脱水処理され、または脱水設備のない施設においては他の処理施設へと搬送されて処理される。脱水処理によって分離された分離水もまた、返流水として最初沈殿池へと返送されるのが一般的である。
【0004】
このような廃水処理システムにおいては、汚泥の濃縮処理や脱水処理の汚泥処理過程で汚泥から溶出する高濃度のリンが、返流水と一緒に最初沈殿池に返送されという問題があった。リンを高濃度で含む返流水は、最終沈殿池から河川等への放流される処理水のリン濃度へも影響を与えるため、汚泥処理過程からの返流水中に含まれるリンの低減が望まれていた。
【0005】
このような問題を解決する方法としては、鉄系、アルミニウム系等の無機凝集剤を利用した脱リン方法が提案されている。例えば、無機凝集剤が添加された汚泥を濃縮し、この濃縮汚泥にアニオン系高分子凝集剤とカチオン系高分子凝集剤を添加して凝集フロックを生成させ、脱水する方法(特開昭61−234999号公報)、無機凝集剤を添加した汚泥を濃縮し、この濃縮汚泥にさらに無機凝集剤を添加した後、アニオン系高分子凝集剤とカチオン系高分子凝集剤を添加して凝集フロックを生成させ、脱水する方法(特開昭63−91200号公報)、最初沈殿池および最終沈殿池からの汚泥それぞれに無機凝集剤を添加した後、アニオン系高分子凝集剤とカチオン系高分子凝集剤を添加して凝集フロックを生成させ、脱水する方法(特開昭63−91199号公報)等が提案されている。
【0006】
【発明が解決しようとする課題】
しかしながら、鉄系、アルミニウム系等の無機凝集剤を使用してリンを汚泥中に固定化したとしても、経時によりリンが再溶出してしまい、脱リン効果が長時間持続しないという問題があった。すなわち、ほとんどの処理場では、汚泥の濃縮に固形分の自然沈降を利用した重力濃縮槽を使用しているため、汚泥の濃縮に時間がかかり、無機凝集剤を添加してリンを固定化しても、汚泥の濃縮している間にリンが分離水中へ再溶出してしまうという問題があった。
【0007】
そこで、本発明は、汚泥中に固定化されたリンの溶出を防止し、薬剤注入装置以外に新たな設備を必要とせずに、汚泥の濃縮処理や脱水処理によって分離された分離水中のリン濃度を低減させるための新たな汚泥中のリンの溶出防止方法、および汚泥中にリンを固定化し、かつリンの再溶出を防止する汚泥中のリンの溶出防止剤を開発する目的でなされたものである。
【0008】
【課題を解決するための手段】
すなわち、本発明の汚泥中のリンの溶出防止方法は、廃水処理で発生する汚泥を濃縮した後、脱水あるいは搬送する廃水処理システムにおける汚泥中のリンの溶出防止方法において、脱水あるいは搬送する前の汚泥に、無機凝集剤と殺菌剤とを添加することを特徴とする。
また、前記無機凝集剤は、鉄系凝集剤およびアルミニウム系凝集剤からなる群より選ばれる1種以上の無機凝集剤であることが望ましい。
また、前記殺菌剤が次亜塩素酸ソーダであることが望ましい。
また、本発明の汚泥中のリンの溶出防止剤は、無機凝集剤と殺菌剤とを含有することを特徴とする。
【0009】
【発明の実施の形態】
以下、本発明を図1に示す一例を参照して説明する。
この例では、まず、処理しようとする廃水原水は最初沈殿池に導入される。この最初沈殿池では、比較的大きな懸濁物質が沈殿分離される。そして、廃水は曝気槽で活性汚泥によって生物処理され、廃水中の水溶性有機成分等が分解される。なお、ここでは曝気槽の代わりに嫌気・好気循環式硝化脱窒槽のような種々の生物処理法を適用してもよい。次いで、最終沈殿池に導かれて活性汚泥のフロックが分離沈殿される。そして、最終沈殿池での処理水は放流され、最終沈殿池で沈降した汚泥の一部は余剰汚泥として、最初沈殿池からの初沈汚泥とともに汚泥濃縮槽に供給される。
【0010】
汚泥濃縮槽に供給された汚泥には、無機凝集剤と殺菌剤が添加される。そして、この汚泥は、汚泥濃縮槽で重力沈降によって濃縮される。汚泥濃縮槽で分離された分離水は返流水として最初沈殿池に返送され、汚泥濃縮槽で濃縮された濃縮汚泥は汚泥貯留槽に貯留される。汚泥貯留槽に貯留した汚泥は、適宜、脱水処理され、または脱水設備のない施設においては他の処理施設へと搬送されて処理される。脱水処理によって分離された分離水もまた、返流水として最初沈殿池へと返送される。
【0011】
本発明においては、前記汚泥濃縮槽等にて、通常の汚泥処理で添加される鉄系やアルミニウム系等の無機凝集剤に加えて、新たにリンの溶出防止効果を有する、殺菌剤を添加して、前記無機凝集剤と殺菌剤とを併用することに特徴がある。
【0012】
本発明に係る無機凝集剤としては、例えば、鉄系凝集剤、アルミニウム系凝集剤、カルシウム系凝集剤等が挙げられるが、これらに限定されるものではない。中でも、汚泥の凝集能力に優れることから、鉄系凝集剤およびアルミニウム系凝集剤が好適に用いられる。鉄系凝集剤としては、例えば、ポリ硫酸第二鉄、硫酸第二鉄、塩化第二鉄等の3価の鉄塩が挙げられる。アルミニウム系凝集剤としては、ポリ塩化アルミニウム、塩化アルミニウム、硫酸アルミニウム、硫酸アルミニウムカリウム、硫酸アルミニウムアンモニウム、アルミン酸ナトリウム等のアルミニウム塩が挙げられる。中でも、汚泥の凝集能力に優れることから、硫酸第二鉄、硫酸アルミニウムが好適に用いられる。これら無機凝集剤は、単独で用いてもよく、2種類以上を併用してもよい。
【0013】
前記無機凝集剤の添加量は、汚泥の凝集が観察され、汚泥中の溶解性リン濃度が1mg/L以下になる程度が好ましく、通常、汚泥中の懸濁物質(SS)100重量部に対して1〜200重量部となる量が好ましいが、これに限定されるものではない。1重量部未満では、溶解性リンの除去が不十分となる。また、200重量部を超えると、後の濃縮汚泥の脱水処理に悪影響を与えるので好ましくない。
【0014】
本発明に係る殺菌剤としては、例えば、塩素系化合物、イソチアゾロン系化合物、ピリジン系化合物およびハロゲンカルボニル系化合物等が用いられるが、これらに限定されるものではない。塩素系化合物としては、例えば、次亜塩素酸、亜塩素酸、トリクロロイソシアヌル酸、およびこれらの塩等が挙げられ、さらに具体的に、次亜塩素酸、次亜塩素酸ソーダ、次亜塩素酸カリウム、亜塩素酸、亜塩素酸ソーダ、トリクロロイソシアヌル酸、トリクロロイソシアヌル酸ソーダ、トリクロロイソシアヌル酸カリウム等が挙げられる。イソチアゾロン系化合物としては、例えば、1,2−ベンゾイソチアゾロン−3−オン、1,2−ベンゾイソチアゾロン−3−オン、5−クロロ−2−メチル−4−イソチアゾロン−3−オン等が挙げられる。ピリジン系化合物としては、例えば、ソジウム−2−ピリジンチオール−1−オキサイド、2−メルカプトピリジン−N−オキサイド等が挙げられる。ハロゲンカルボニル系化合物としては、例えば、ビスブロモアセトキシエタン、トリクロロ酢酸、ビス(1,4−ブロモアセトキシ)−2−ブテン等が挙げられる。中でも、リンの溶出防止効果に優れることから、次亜塩素酸、、次亜塩素酸ソーダ、次亜塩素酸カリウム、亜塩素酸、亜塩素酸ソーダ、トリクロロイソシアヌル酸、トリクロロイソシアヌル酸ソーダ、トリクロロイソシアヌル酸カリウム、1,2−ベンゾイソチアゾロン−3−オン、ビスブロモアセトキシエタンが好適に用いられる。これら殺菌剤は、単独で用いてもよく、2種類以上を併用してもよい。
【0015】
前記殺菌剤の添加量は、特に限定はされないが、汚泥中の懸濁物質(SS)100重量部に対して0.1〜100重量部となる量が好ましい。0.1重量部未満では、リンの再溶出防止効果が不十分となる。また、100重量部を超えて添加しても、リンの再溶出防止効果の大きな向上が望めず、経済的でないため好ましくない。
【0016】
前記無機凝集剤および殺菌剤の添加方法は、これらが脱水あるいは搬送する前の汚泥に添加されていれば、特に限定されず、例えば、両方を汚泥濃縮槽または汚泥貯留槽に加える方法、一方を汚泥濃縮槽にもう一方を汚泥貯留槽に加える方法等が挙げられる。汚泥に無機凝集剤および殺菌剤が十分撹拌混合され、汚泥濃縮槽から出る分離水中のリン濃度を下げることができることから、汚泥濃縮槽に添加する方法が好ましい。
また、添加順序も、特に限定されず、まず無機凝集剤を添加し、次いで殺菌剤を添加してもよく、まず殺菌剤を添加して、次いで無機凝集剤を添加してもよく、無機凝集剤と殺菌剤を同時に添加してもよい。また、前記無機凝集剤と殺菌剤とをあらかじめ混合し、この混合物を汚泥中のリンの溶出防止剤として汚泥に添加してもよい。
【0017】
本発明における汚泥の濃縮方法としては、例示された重力沈降による重力濃縮法以外に、遠心濃縮法、膜濃縮法等の公知の方法を適用できるが、これらに限定されるものではない。
このようにして得られた濃縮汚泥は高分子凝集剤を添加して脱水する。濃縮汚泥の脱水方法としては、ベルトプレス脱水法、遠心脱水法、スクリュープレス脱水法、フィルタープレス脱水法等の公知の方法を適用できるが、これらに限定されるものではない。濃縮汚泥に高分子凝集剤を添加することによって、脱水ケーキ含水率の低下、濾液量の増加等の効果が得られる。
【0018】
前記高分子凝集剤としては、カチオン系やアニオン系、両性系の公知の高分子凝集剤を用いることができる。これらは、単独で用いてもよく、2種類以上を併用してもよい。
カチオン系高分子凝集剤としては、例えば、ポリアミン、ポリエチレンイミン等の縮合系高分子凝集剤、ポリアクリルアミドのマンニッヒ変性物ないしホフマン分解物、ポリアミジン系高分子凝集剤、およびジメチルアミノエチル(メタ)アクリレート、ジエチルアミノエチル(メタ)アクリレート、ジメチルアミノプロピル(メタ)アクリルアミド、ジエチルアミノプロピル(メタ)アクリルアミドもしくはこれらの中和塩や四級塩からなる重合体もしくは共重合体、あるいはこれらのカチオン性モノマーに対して(メタ)アクリルアミド、N,N−ジメチル(メタ)アクリルアミド、N,N−ジエチル(メタ)アクリルアミド等を共重合させたもの等が挙げられる。
アニオン系高分子凝集剤としては、例えば、アクリルアミドと、(メタ)アクリル酸、2−アクリルアミド−2−メチルプロパンスルホン酸、ビニルスルホン酸またはこれらの塩との共重合物、ポリアクリルアミドの部分加水分解物等が挙げられる。
【0019】
両性系の高分子凝集剤とは、分子内にアニオン性基としてカルボキシル基またはその塩を有し、カチオン性基として第三級アミン、その中和塩、四級塩等を有する高分子凝集剤であり、これらのイオン性成分の他にノニオン成分が含まれているものであってもよい。この両性系の高分子凝集剤は通常、前記のカチオン性基、アニオン性基や更にノニオン性基を有するモノマー単位を共重合することによって得られるものである。構成単位となるアニオン性モノマー単位としては、アクリル酸、メタクリル酸、もしくはこれらのアルカリ金属塩等を挙げることができる。カチオン性モノマー単位としては、ジメチルアミノエチル(メタ)アクリレート、ジエチルアミノエチル(メタ)アクリレート、ジメチルアミノプロピル(メタ)アクリルアミド、ジエチルアミノプロピル(メタ)アクリルアミドもしくはこれらの中和塩や四級塩等を挙げることができる。ノニオン性のモノマー単位としては、(メタ)アクリルアミド、N,N−ジメチル(メタ)アクリルアミド、N,N−ジエチル(メタ)アクリルアミド等を挙げることができる。
【0020】
本発明の汚泥中のリンの溶出防止方法においては、脱水あるいは搬送する前の汚泥に前記無機凝集剤と殺菌剤とを添加しているので、汚泥中にリンを固定化し、かつ固定化されたリンの溶出を防止し、汚泥の濃縮処理や脱水処理によって分離される分離水中のリン濃度を低減させることができる。
また、本発明の汚泥中のリンの溶出防止剤は、前記無機凝集剤と殺菌剤とを含有しているので、これが添加された汚泥中にリンを固定化し、かつ固定化されたリンの溶出を防止し、汚泥の濃縮処理や脱水処理によって分離される分離水中のリン濃度を低減させることができる。
【0021】
本発明において、汚泥中に固定化されたリンの溶出が防止される理由としては、次のようなことが考えられる。
すなわち、無機凝集剤によるリンの固定化は、例えば、鉄系凝集剤を用いた場合、鉄イオンとリン酸イオンとの反応による難溶性金属リン酸塩の生成(下記(式1))、および下記(式2)のようにして生成する水酸化鉄へのリン酸イオンの吸着によって行われているものと考えられている。
Fe3+ + PO4 3- → FePO4 ↓ (式1)
Fe3+ + 3OH- → Fe(OH)3 ↓ (式2)
【0022】
通常、汚泥濃縮槽内等の嫌気性雰囲気では、難溶性である3価の鉄イオンが易溶性である2価の鉄イオンに還元されてしまい、経時により鉄イオンが液相に溶出し、吸着していたリンを放出するため、固定化されていたリンは、分離水中に再溶出してしまう。しかしながら、次亜塩素酸ソーダ等の殺菌剤が存在することによって、汚泥中の微生物が減少し、汚泥の嫌気化が抑制され、鉄イオンが還元されにくい環境となっているため、リンの再溶出を防止しているものと考えられる。
【0023】
【実施例】
[実施例1]
濃縮前の下水汚泥(pH=6.8、SS=1.25重量%、VSS(SSの強熱減量)=54.6%)に、ポリ硫酸第二鉄を、汚泥中のSSに対して13重量%となるように添加し、ついで次亜塩素酸ソーダを、汚泥中のSSに対して8.0重量%となるように添加した。これを重力沈降によって24時間濃縮した後、上澄み液と沈降濃縮汚泥とに分離し、それぞれの溶解性リン濃度を測定した。溶解性リン濃度は、溶解性リンをモリブデンブルー吸光光度法にて測定した。結果を表1に示す。
【0024】
[比較例1]
次亜塩素酸ソーダを添加しなかった以外は、実施例1と同様に行った。結果を表1に示す。
次亜塩素酸ソーダを添加しない場合、上澄み液、沈降濃縮汚泥ともに、溶出性リン濃度の増加が見られた。
【0025】
【表1】
【0026】
[実施例2]
ポリ硫酸第二鉄の代わりに、硫酸アルミニウムを汚泥中のSSに対して20重量%となるように添加した以外は、実施例1と同様に行った。結果を表2に示す。
【0027】
[比較例2]
次亜塩素酸ソーダを添加しなかった以外は、実施例2と同様に行った。結果を表2に示す。
次亜塩素酸ソーダを添加しない場合、上澄み液、沈降濃縮汚泥ともに、溶出性リン濃度の増加が見られた。
【0028】
【表2】
【0029】
【発明の効果】
以上説明したように、本発明の汚泥中のリンの溶出防止方法によれば、脱水あるいは搬送する前の汚泥に前記無機凝集剤と殺菌剤とを添加しているので、汚泥中にリンを固定化し、かつ固定化されたリンの溶出を防止し、汚泥の濃縮処理や脱水処理によって分離される分離水中のリン濃度を低減させることができ、そして、汚泥処理過程から廃水処理過程へ返送される返流水中のリンの量を低減させ、河川等に放流される処理水中のリン濃度を低減させることができる。
また、本発明の汚泥中のリンの溶出防止剤は、前記無機凝集剤と殺菌剤とを含有しているので、これが添加された汚泥中にリンを固定化し、かつ固定化されたリンの溶出を防止し、汚泥の濃縮処理や脱水処理によって分離される分離水中のリン濃度を低減させることができる。
【図面の簡単な説明】
【図1】 廃水処理システムの一例を示す流れ図である。
【図2】 従来例の廃水処理システムを示す流れ図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for preventing elution of phosphorus in sludge in a wastewater treatment system for concentrating and dewatering or transporting sludge generated in wastewater treatment and an antielution agent for phosphorus in sludge used for sludge treatment. The present invention relates to an elution prevention method for phosphorus in sludge and an elution inhibitor for phosphorus in sludge that prevent elution of phosphorus immobilized on sludge and reduce the concentration of phosphorus in separated water generated by concentration and dehydration of sludge.
[0002]
[Prior art]
Conventionally, municipal wastewater such as human waste and sewage, organic industrial wastewater from factories, etc. have been treated to remove various suspended solids (SS) contained therein, and then discharged into rivers and the like. Yes.
In the above-mentioned municipal wastewater or organic industrial wastewater treatment system, for example, as shown in FIG. 2, first, the raw water to be treated is first introduced into the settling basin, where a relatively large suspended substance is precipitated and separated. The Next, biological treatment is performed in the aeration tank to decompose water-soluble organic components and the like in the wastewater with activated sludge. Thereafter, after the sludge is settled and separated in the final sedimentation basin, the treated water is discharged into a river or the like, while the precipitated sludge is returned to the aeration tank.
[0003]
In general, a part of the sludge from the final sedimentation basin is concentrated in the sludge concentration tank as the excess sludge together with the initial sedimentation sludge from the first sedimentation basin. The separated water here is first returned to the settling basin as return water. The concentrated sludge is sent to a sludge storage tank for storage.
The sludge stored in the sludge storage tank is appropriately dewatered, or in a facility without a dewatering facility, transported to another processing facility for processing. The separated water separated by the dehydration process is also generally returned to the first settling basin as return water.
[0004]
In such a wastewater treatment system, there has been a problem that high-concentration phosphorus eluted from sludge during sludge concentration and dewatering treatment is returned to the settling basin together with the return water. Return water containing high concentrations of phosphorus also affects the concentration of treated water discharged from the final sedimentation basin to rivers, etc., so it is desirable to reduce the phosphorus contained in the returned water from the sludge treatment process. It was.
[0005]
As a method for solving such a problem, a dephosphorization method using an inorganic flocculant such as iron or aluminum has been proposed. For example, a method of concentrating sludge to which an inorganic flocculant has been added and adding an anionic polymer flocculant and a cationic polymer flocculant to the concentrated sludge to produce agglomerated flocs and dehydrating them (Japanese Patent Laid-Open No. Sho 61-61). No. 234999), sludge added with inorganic flocculant is concentrated, and after adding inorganic flocculant to this concentrated sludge, anionic polymer flocculant and cationic polymer flocculant are added to produce flocculent flocs After adding an inorganic flocculant to the sludge from the first sedimentation basin and the final sedimentation basin, and then adding an anionic polymer flocculant and a cationic polymer flocculant. There has been proposed a method of adding and producing agglomerated floc and dewatering (Japanese Patent Laid-Open No. 63-91199).
[0006]
[Problems to be solved by the invention]
However, even if phosphorus is fixed in sludge using an inorganic flocculant such as iron-based or aluminum-based, there is a problem that phosphorus re-elutes with time and the dephosphorization effect does not last for a long time. . That is, most treatment plants use gravity concentration tanks that use natural sedimentation of solids to concentrate sludge, so it takes time to concentrate sludge, and add inorganic flocculants to immobilize phosphorus. However, there is a problem that phosphorus is re-eluted into the separated water while the sludge is concentrated.
[0007]
Therefore, the present invention prevents the dissolution of phosphorus immobilized in the sludge, and does not require any new equipment other than the chemical injection device, and the phosphorus concentration in the separated water separated by the sludge concentration treatment or dehydration treatment It was made for the purpose of developing a new method for preventing the dissolution of phosphorus in sludge and reducing the dissolution of phosphorus in sludge by fixing phosphorus in the sludge and preventing re-elution of phosphorus. is there.
[0008]
[Means for Solving the Problems]
That is, the method for preventing phosphorus from eluting in the sludge according to the present invention is the method for preventing phosphorus from eluting in the sludge in the wastewater treatment system in which the sludge generated in the wastewater treatment is concentrated and then dewatered or transported. An inorganic flocculant and a disinfectant are added to the sludge.
The inorganic flocculant is preferably one or more inorganic flocculants selected from the group consisting of iron-based flocculants and aluminum-based flocculants.
The disinfectant is preferably sodium hypochlorite.
Moreover, the elution inhibitor of phosphorus in the sludge of the present invention is characterized by containing an inorganic flocculant and a disinfectant.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to an example shown in FIG.
In this example, the raw wastewater to be treated is first introduced into the settling basin. In this first settling basin, a relatively large suspended substance is precipitated and separated. The wastewater is biologically treated with activated sludge in an aeration tank, and water-soluble organic components and the like in the wastewater are decomposed. Here, various biological treatment methods such as an anaerobic / aerobic circulation type nitrification denitrification tank may be applied instead of the aeration tank. Next, the flocs of activated sludge are separated and settled by being led to the final sedimentation tank. Then, the treated water in the final sedimentation basin is discharged, and a part of the sludge settled in the final sedimentation basin is supplied to the sludge concentration tank together with the initial sedimentation sludge from the first sedimentation basin as surplus sludge.
[0010]
An inorganic flocculant and a disinfectant are added to the sludge supplied to the sludge concentration tank. And this sludge is concentrated by gravity sedimentation in a sludge concentration tank. The separated water separated in the sludge concentration tank is first returned to the settling basin as return water, and the concentrated sludge concentrated in the sludge concentration tank is stored in the sludge storage tank. The sludge stored in the sludge storage tank is appropriately dewatered, or in a facility without a dewatering facility, transported to another processing facility for processing. The separated water separated by the dehydration process is also returned to the first settling basin as return water.
[0011]
In the present invention, in addition to the inorganic flocculant such as iron or aluminum added in the normal sludge treatment in the sludge concentration tank or the like, a fungicide having a new phosphorus elution preventing effect is newly added. Thus, the inorganic flocculant and the bactericide are used in combination.
[0012]
Examples of the inorganic flocculant according to the present invention include, but are not limited to, iron-based flocculants, aluminum-based flocculants, and calcium-based flocculants. Among them, iron-based flocculants and aluminum-based flocculants are preferably used because of their excellent sludge flocculation ability. Examples of iron-based flocculants include trivalent iron salts such as polyferric sulfate, ferric sulfate, and ferric chloride. Examples of the aluminum flocculant include aluminum salts such as polyaluminum chloride, aluminum chloride, aluminum sulfate, aluminum potassium sulfate, aluminum ammonium sulfate, and sodium aluminate. Among these, ferric sulfate and aluminum sulfate are preferably used because of their excellent sludge aggregation ability. These inorganic flocculants may be used alone or in combination of two or more.
[0013]
The amount of the inorganic flocculant added is preferably such that sludge aggregation is observed and the concentration of soluble phosphorus in the sludge is 1 mg / L or less, and is usually 100 parts by weight of suspended matter (SS) in the sludge. The amount of 1 to 200 parts by weight is preferable, but is not limited thereto. If it is less than 1 part by weight, removal of soluble phosphorus will be insufficient. Moreover, when it exceeds 200 weight part, since it has a bad influence on the dehydration process of concentrated sludge after that, it is unpreferable.
[0014]
Examples of the bactericides according to the present invention include chlorine compounds, isothiazolone compounds, pyridine compounds, halogen carbonyl compounds, and the like, but are not limited thereto. Examples of the chlorine compound include hypochlorous acid, chlorous acid, trichloroisocyanuric acid, and salts thereof, and more specifically, hypochlorous acid, sodium hypochlorite, hypochlorous acid, and the like. Examples include potassium, chlorous acid, sodium chlorite, trichloroisocyanuric acid, sodium trichloroisocyanurate, potassium trichloroisocyanurate and the like. Examples of the isothiazolone compounds include 1,2-benzisothiazolone-3-one, 1,2-benzisothiazolone-3-one, and 5-chloro-2-methyl-4-isothiazolone-3-one. Examples of pyridine compounds include sodium-2-pyridinethiol-1-oxide, 2-mercaptopyridine-N-oxide, and the like. Examples of the halogencarbonyl compound include bisbromoacetoxyethane, trichloroacetic acid, bis (1,4-bromoacetoxy) -2-butene, and the like. Among them, it has excellent phosphorus elution prevention effect, so hypochlorous acid, sodium hypochlorite, potassium hypochlorite, chlorous acid, sodium chlorite, trichloroisocyanuric acid, sodium trichloroisocyanurate, trichloroisocyanuric Potassium acid, 1,2-benzisothiazolone-3-one, and bisbromoacetoxyethane are preferably used. These bactericides may be used alone or in combination of two or more.
[0015]
Although the addition amount of the said bactericidal agent is not particularly limited, an amount of 0.1 to 100 parts by weight is preferable with respect to 100 parts by weight of suspended matter (SS) in sludge. If the amount is less than 0.1 part by weight, the effect of preventing re-elution of phosphorus is insufficient. Moreover, even if it adds exceeding 100 weight part, since the big improvement of the re-elution prevention effect of phosphorus cannot be expected and it is not economical, it is unpreferable.
[0016]
The method for adding the inorganic flocculant and the disinfectant is not particularly limited as long as they are added to the sludge before being dehydrated or transported. For example, the method of adding both to the sludge concentration tank or the sludge storage tank, A method of adding the other to the sludge concentration tank and the like is included. Since the inorganic flocculant and the disinfectant are sufficiently stirred and mixed in the sludge, and the phosphorus concentration in the separated water discharged from the sludge concentration tank can be lowered, the method of adding to the sludge concentration tank is preferable.
Also, the order of addition is not particularly limited. First, an inorganic flocculant may be added, then a bactericidal agent may be added, first a bactericidal agent may be added, and then an inorganic flocculant may be added. An agent and a disinfectant may be added simultaneously. Further, the inorganic flocculant and the disinfectant may be mixed in advance, and this mixture may be added to the sludge as an elution inhibitor of phosphorus in the sludge.
[0017]
As a method for concentrating sludge in the present invention, known methods such as centrifugal concentration method and membrane concentration method can be applied in addition to the exemplified gravity concentration method by gravity sedimentation, but the method is not limited thereto.
The concentrated sludge thus obtained is dehydrated by adding a polymer flocculant. As a method for dewatering the concentrated sludge, known methods such as a belt press dewatering method, a centrifugal dewatering method, a screw press dewatering method, and a filter press dewatering method can be applied, but the method is not limited thereto. By adding a polymer flocculant to the concentrated sludge, effects such as a decrease in the moisture content of the dehydrated cake and an increase in the amount of filtrate can be obtained.
[0018]
As the polymer flocculant, known polymer flocculants of cationic, anionic and amphoteric types can be used. These may be used alone or in combination of two or more.
Examples of the cationic polymer flocculant include condensation polymer flocculants such as polyamines and polyethyleneimines, Mannich modified products or Hoffman degradation products of polyacrylamide, polyamidine polymer flocculants, and dimethylaminoethyl (meth) acrylate. , Diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide, diethylaminopropyl (meth) acrylamide or a polymer or copolymer of these neutralized salts or quaternary salts, or a cationic monomer thereof Examples include those obtained by copolymerizing (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide and the like.
Examples of the anionic polymer flocculants include copolymers of acrylamide and (meth) acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid or salts thereof, and partial hydrolysis of polyacrylamide. Thing etc. are mentioned.
[0019]
The amphoteric polymer flocculant is a polymer flocculant having a carboxyl group or a salt thereof as an anionic group in the molecule and a tertiary amine, a neutralized salt thereof, a quaternary salt or the like as a cationic group. In addition to these ionic components, nonionic components may be included. This amphoteric polymer flocculant is usually obtained by copolymerizing the monomer units having the cationic group, the anionic group, and further the nonionic group. Examples of the anionic monomer unit serving as a structural unit include acrylic acid, methacrylic acid, and alkali metal salts thereof. Examples of the cationic monomer unit include dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide, diethylaminopropyl (meth) acrylamide or neutralized salts or quaternary salts thereof. Can do. Nonionic monomer units include (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide and the like.
[0020]
In the method for preventing elution of phosphorus in the sludge of the present invention, the inorganic flocculant and the disinfectant are added to the sludge before dehydration or transportation, so that phosphorus is fixed and fixed in the sludge. Phosphorus elution can be prevented, and the concentration of phosphorus in the separated water separated by sludge concentration treatment or dehydration treatment can be reduced.
Moreover, since the dissolution inhibitor of phosphorus in the sludge of the present invention contains the inorganic flocculant and the bactericidal agent, the phosphorus is fixed in the sludge to which it is added, and the immobilized phosphorus is eluted. Can be prevented, and the phosphorus concentration in the separated water separated by the sludge concentration treatment or dehydration treatment can be reduced.
[0021]
In the present invention, the reason why the phosphorus immobilized in the sludge is prevented from elution is as follows.
That is, for example, in the case of using an iron-based flocculant, the immobilization of phosphorus with an inorganic flocculant produces a hardly soluble metal phosphate by the reaction between iron ions and phosphate ions (the following (formula 1)), and It is considered that this is carried out by adsorption of phosphate ions to iron hydroxide produced as shown below (Formula 2).
Fe 3+ + PO 4 3- → FePO 4 ↓ (Formula 1)
Fe 3+ + 3OH - → Fe ( OH) 3 ↓ ( Formula 2)
[0022]
Normally, in an anaerobic atmosphere such as in a sludge concentrating tank, trivalent iron ions, which are poorly soluble, are reduced to divalent iron ions, which are easily soluble, and the iron ions elute into the liquid phase over time and are adsorbed. Since the released phosphorus is released, the immobilized phosphorus is re-eluted in the separated water. However, the presence of bactericides such as sodium hypochlorite reduces the microorganisms in the sludge, suppresses the anaerobization of the sludge, and makes it difficult for iron ions to be reduced. It is thought that it is preventing.
[0023]
【Example】
[Example 1]
Prior to concentration, sewage sludge (pH = 6.8, SS = 1.25 wt%, VSS (SS ignition loss) = 54.6%), ferric polysulfate was added to SS in the sludge. It added so that it might become 13 weight%, Then, sodium hypochlorite was added so that it might become 8.0 weight% with respect to SS in sludge. This was concentrated by gravity settling for 24 hours, and then separated into a supernatant and a settling sludge, and the respective soluble phosphorus concentrations were measured. The soluble phosphorus concentration was measured by molybdenum blue absorptiometry. The results are shown in Table 1.
[0024]
[Comparative Example 1]
The same procedure as in Example 1 was performed except that sodium hypochlorite was not added. The results are shown in Table 1.
When sodium hypochlorite was not added, the elution phosphorus concentration was increased in both the supernatant and the sedimented sludge.
[0025]
[Table 1]
[0026]
[Example 2]
It carried out similarly to Example 1 except having added aluminum sulfate so that it might become 20 weight% with respect to SS in sludge instead of poly ferric sulfate. The results are shown in Table 2.
[0027]
[Comparative Example 2]
The same procedure as in Example 2 was performed except that sodium hypochlorite was not added. The results are shown in Table 2.
When sodium hypochlorite was not added, the elution phosphorus concentration was increased in both the supernatant and the sedimented sludge.
[0028]
[Table 2]
[0029]
【The invention's effect】
As described above, according to the method for preventing phosphorus from eluting in the sludge according to the present invention, the inorganic flocculant and the disinfectant are added to the sludge before dewatering or transporting, so that phosphorus is fixed in the sludge. And can prevent the elution of immobilized phosphorus, reduce the concentration of phosphorus in the separated water separated by sludge concentration treatment and dewatering treatment, and return it from the sludge treatment process to the wastewater treatment process The amount of phosphorus in the return water can be reduced, and the phosphorus concentration in the treated water discharged into rivers and the like can be reduced.
Moreover, since the dissolution inhibitor of phosphorus in the sludge of the present invention contains the inorganic flocculant and the bactericidal agent, the phosphorus is fixed in the sludge to which it is added, and the immobilized phosphorus is eluted. Can be prevented, and the phosphorus concentration in the separated water separated by the sludge concentration treatment or dehydration treatment can be reduced.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an example of a wastewater treatment system.
FIG. 2 is a flowchart showing a conventional wastewater treatment system.
Claims (4)
脱水あるいは搬送する前の汚泥に、無機凝集剤と殺菌剤とを添加することを特徴とする汚泥中のリンの溶出防止方法。In the method for preventing the dissolution of phosphorus in sludge in a wastewater treatment system that dewaters or conveys after sludge generated in wastewater treatment is concentrated,
A method for preventing the dissolution of phosphorus in sludge, comprising adding an inorganic flocculant and a disinfectant to the sludge before dehydration or transportation.
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