JP3886069B2

JP3886069B2 - Treatment of return water for sewage sludge intensive treatment

Info

Publication number: JP3886069B2
Application number: JP14294497A
Authority: JP
Inventors: 豊米山; 康弘本間; 輝明北村; 廣野口; 英俊石井
Original assignee: Ebara Corp; Tokyo Metropolitan Government
Current assignee: Ebara Corp; Tokyo Metropolitan Government
Priority date: 1997-05-19
Filing date: 1997-05-19
Publication date: 2007-02-28
Anticipated expiration: 2017-05-19
Also published as: JPH10314505A

Description

【０００１】
【発明の属する技術分野】
本発明は、有機性排水の処理法に係り、特に下水返流水、し尿、工場排水等のＳＳ、溶解性有機物、りん、窒素を多く含む排水に無機凝集剤を添加して凝集処理した後に、生物処理する下水汚泥の集約処理の返流水の処理法に関する。
【０００２】
【従来の技術】
近年、河川等の水域の富栄養化が問題となり、下水、し尿、工場排水等の有機性排水処理においては有機物以外の窒素、りんの処理が要求されている。このため、図６に示すように生物処理において、嫌気タンク１０、無酸素タンク１１、好気タンク３を設けて窒素、りんの一部を処理し、後段の凝集処理槽１でりんの仕上げ処理を行う方法が知られている。
また、図１に示されるように、ＳＳ濃度、りん濃度の高い排水においては、あらかじめ生物処理３の前で、無機凝集剤１３及び高分子凝集剤１４を添加して凝集処理１することが提唱されている。
【０００３】
後者においての凝集処理は、生物処理のＳＳ等の有機物負荷量の低減を目的としたもので、単に処理目標のＳＳ濃度又はりん濃度単独に対しての無機凝集剤の添加を行っているだけである。このため、排水中のＳＳ濃度、りん濃度が変動した場合、ＳＳ濃度、りん濃度各項目のみで無機凝集剤添加量を調整し処理する方法では、両者の処理目標水質を同時に満足することができなかった。例えは、原水りん濃度が極端に高くなったときには、凝集処理後の残存りん濃度レベルも高くなり、生物処理後にりんが残存するため、もう一度凝集剤を添加して凝集処理する必要があった。
【０００４】
【発明が解決しようとする課題】
本発明は、上記の従来技術の問題点を解決して、ＳＳ、溶解性有機物、窒素、りん等の原水中の濃度変動に対しても効率的に除去することができる下水汚泥の集約処理の返流水の処理法を提供することを課題とする。
【０００５】
【課題を解決するための手段】
上記課題を解決するために、本発明では、ＳＳ、溶解性有機物、りん、窒素を含む下水汚泥の集約処理の返流水を、無機凝集剤及び高分子凝集剤で凝集処理した後に、その処理水を生物処理する処理法において、前記凝集処理は、前記返流水に硫酸バンド、高分子凝集剤の順で添加した処理水が、目標値ＳＳ濃度となる単位返流水ＳＳ量当たりの硫酸バンド添加量（係数ａ）を図３から求め、かつ前記処理水が、目標値りん濃度となる単位返流水りん量当たりの硫酸バンド添加量（係数ｂ）を図４から求め、前記係数ａに返流水のＳＳ濃度を乗じて硫酸バンド添加量（Ａ）を算出すると共に、前記係数ｂに測定した返流水のりん濃度を乗じて硫酸バンド添加量（Ｂ）を算出し、該添加量（Ａ）と添加量（Ｂ）のうち、多い方の添加量で硫酸バンドを添加し、次いで高分子凝集剤を添加して行うことを特徴とする下水汚泥の集約処理の返流水の処理法としたものである。
前記処理法において、凝集処理を、前記返流水のＳＳ濃度とりん濃度の測定を自動測定で行い、その測定値をもとに硫酸バンド注入量を自動的に調節して行うことができる。
【０００６】
【発明の実施の形態】
本発明では、凝集処理に用いる無機凝集剤の添加量を、有機性排水のＳＳ濃度とりん濃度に対する必要量の両者から判断し、その必要添加量の多い方を無機凝集剤添加量としているため、りん濃度が高くなったときでも、処理水りん濃度レベルは高くならない。また、原水ＳＳ濃度が高くなったときでも、処理水ＳＳ濃度レベルは高くならない。
また、有機性排水中のＳＳ及びりん濃度の測定を、自動分析にて計測する自動測定で行い、その測定値に基づく信号をもとに無機凝集剤注入ポンプ量を調整する自動制御で行うため、安定した凝集処理水質が得られる。
本発明で使用できる無機凝集剤としては、硫酸バンド、ＰＡＣ等のアルミニウム塩、あるいは塩化第二鉄、ポリ鉄等の鉄塩の何れでも良い。また、高分子凝集剤としてはアニオン系高分子凝集剤、ノニオン系高分子凝集剤のどちらを使用しても良い。
【０００７】
本発明の有機性排水の処理法は、例えば図１に示した処理工程により行う。
図１において、有機性排水である原水５は、ＳＳ濃度とりん濃度が測定されて凝集処理槽１に導入され、必要量が多い方の濃度に基づいて無機凝集剤１３が添加され、次いで高分子凝集剤１４が添加されて、沈殿池２に流入される。沈殿池２では、固形分が排泥７として分離され、上澄液６は生物処理槽である曝気槽３に導入され、沈殿池４からの返送汚泥と共に処理され、処理水は沈殿池４に流入して、固液分離され、沈殿物は返送汚泥８として曝気槽３に循環され、上澄液は処理水９として放流される。
【０００８】
【実施例】
以下、本発明を実施例により具体的に説明する。
実施例１
図２に、本発明の処理法を用いた下水汚泥の集約処理の全体工程図を示し、本発明の処理法はこの集約処理の返水処理に用いている。
図２において、下水処理場Ａ、Ｂ、Ｃ、２１から排出される混合生汚泥２３を集めて、一括して濃縮工程２４、脱水工程２５、焼却工程２６で処理する。その際、濃縮工程２４からの分離水２７と脱水工程２５からのろ液２８を、一緒にして本発明の有機性排水の原水５とする。次いで、原水５は本発明の処理法によって処理される。
【０００９】
即ち、原水５は、その水質が自動制御機１５によって自動測定され、凝集処理槽１に導入される。凝集処理槽１には、自動測定されたＳＳ濃度とりん濃度に基づいて、無機凝集剤１３の注入量が注入ポンプ１６を自動的に制御することにより調節される。次いで、高分子凝集剤１４を添加して、沈殿池２に流入し、排泥７を分離して上澄液６を脱窒槽１１に導入する。脱窒槽１１には、返送汚泥８と硝化槽３からの循環液１２が導入されて脱窒処理された後、硝化槽３に流入し、曝気処理される。硝化槽３では、一部が循環液１２として脱窒槽に循環され、他の一部が抜き出されて沈殿池４で汚泥が沈降分離されて、返送汚泥８として脱窒槽に循環される。上澄水は処理水９として放流される。
【００１０】
図２に従って、汚泥濃縮工程、脱水処理工程より排出される返流水を処理した。返流水中には高濃度のＳＳ、ＢＯＤ、窒素及びりんを含んでおり、表１に代表的水質を示す。
【表１】

【００１１】
この返流水に、無機凝集剤を添加し、苛性ソーダにて所定のｐＨに調整を行った後に、高分子凝集剤を添加して、凝集沈殿処理することで排水中のＳＳ、りんは除去される。ここでの目標水質はＳＳ＜１００ｍｇ／リットル、ＰＯ₄−Ｐ＜５ｍｇ／リットルである。
図３には、硫酸バンド添加量と処理水ＳＳ濃度との関係を示す。また、図４に硫酸バンド添加量と処理水りん濃度との関係を示す。処理水ＳＳ＜１００ｍｇ／リットルを満足させるための硫酸バンド添加量は、０．０５ｍｇＡｌ₂Ｏ₃／ｍｇ原水ＳＳ程度である。一方、処理水りん（ここではＰＯ₄−Ｐ）＜５ｍｇ／リットルに必要な硫酸バンド添加量は、１．８ｍｇＡｌ₂Ｏ₃／原水ｍｇＰＯ₄−Ｐ程度である。
この関係を用いて凝集沈殿処理を行った結果を図５に示す。図５において、本発明による処理水を（ａ）、原水りん濃度のみで薬注量を決めた処理水（従来法）を（ｂ）、原水ＳＳ濃度のみで薬注量を決めた処理水（従来法）を（ｃ）、原水を（ｄ）として表わしている。
【００１２】
原水ＳＳ濃度１０００ｍｇ／リットル、ＰＯ₄−Ｐ６０ｍｇ／リットルの時、原水ＳＳ濃度のみ測定して無機凝集剤の添加量を設定している従来法（ｃ）は処理水ＳＳ＜１００ｍｇ／リットルは満足しているが、処理水ＰＯ₄−Ｐは３０ｍｇ／リットル残存している。また、原水１５００ｍｇ／リットル、ＰＯ₄−Ｐ３０ｍｇ／リットルの時、原水ＰＯ₄−Ｐのみ測定して無機凝集剤の添加量を設定している従来法（ｂ）は処理水＜５ｍｇ／リットルは満足しているが、処理水ＳＳ濃度は２００ｍｇ／リットルとなっている。
一方、原水ＳＳ濃度、原水ＰＯ₄−Ｐ濃度より両者の必要添加量の多い方の無機凝集剤添加量とした本発明（ａ）では処理水＜１００ｍｇ／リットル、ＰＯ₄−Ｐ５ｍｇ／リットルの水質が安定して得られた。
【００１３】
本発明では、原水ＳＳ濃度、原水りん濃度を自動分析器にて計測し、その信号を演算機にかけ、無機凝集剤添加量の多い方を選択し、無機凝集剤添加ポンプのストローク調整を行う自動制御も可能である。制御方法はＰＩ、ＰＩＤ等種々の制御方式を選択できる。
また、原水りん濃度が流入ＳＳ濃度の影響で測定困難な場合は、りんを含まない水で希釈して測定を行うか、あるいは処理水りんを測定しフィードバック制御を行い、無機凝集剤の添加量を調整する。りん濃度の測定には全りん計（Ｔ−Ｐ法）、オルトりん酸濃度計（ＰＯ₄−Ｐ法）どちらでも良いが、分析時間が早く、出力信号の多くとれるＰＯ₄−Ｐ法の方が望ましい。
ここで示した実施例は下水返流水の場合であるが、本発明はその他屎尿、工場排水にも適用可能である。
【００１４】
【発明の効果】
本発明によれば、有機性排水の凝集処理において、凝集処理する流入水のＳＳ濃度とりん濃度に対して必要な無機凝集剤の添加量を計算し、両者の多い方の添加量を選んで、無機凝集剤を添加することにより、次の効果を奏することができた。
（１）凝集処理後のＳＳ、りん目標水質を絶えず安定して得られた。
（２）無機凝集剤の添加量が常に適正値を示すため、経済性の面でもコスト低減が可能となった。
【図面の簡単な説明】
【図１】本発明の処理方法を示す処理工程図。
【図２】本発明の処理方法を用いた下水汚泥の集約処理の全体工程図。
【図３】硫酸バンド添加量と処理水ＳＳ濃度との関係を示すグラフ。
【図４】硫酸バンド添加量と処理水りん濃度との関係を示すグラフ。
【図５】実施例１の結果を示すグラフ。
【図６】公知の生物学的窒素りん処理法を示す工程図。
【符号の説明】
１：凝集槽、２：沈殿池、３：曝気槽（硝化槽）、４：沈殿池、５：有機性排水の原水、６：凝集処理水、７：排泥、８：返送汚泥、８′：余剰汚泥、９：処理水、１０：嫌気槽、１１：無酸素槽、１２：循環流、１３：無機凝集剤、１４：高分子凝集剤、１５：測定制御機、１６：注入ポンプ、１７：流入下水、１８：放流水、１９：注煙排水、２１：下水処理場、２３：混合生汚泥、２４：濃縮工程、２５：脱水工程、２６：焼却工程、２７：濃縮工程分離水、２８：脱水工程ろ液、イ：集約処理の汚泥処理プラント、（ａ）：本発明による処理水、（ｂ）：原水りん濃度のみで薬注量を決めた場合の処理水、（ｃ）：原水ＳＳ濃度のみで薬注量を決めた場合の処理水、（ｄ）：原水、（ａ′）：本発明による硫酸ばん土添加量、（ｂ′）：原水りん濃度のみで決めた場合の硫酸ばん土添加量、（ｃ′）：原水ＳＳ濃度のみで決めた場合の硫酸ばん土添加量[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating organic wastewater, in particular, after adding an inorganic flocculant to SS, such as sewage return water, human waste, and factory wastewater, and wastewater containing a large amount of soluble organic matter, phosphorus, and nitrogen, relating to the processing method of the return flow water of aggregation processing of sewage sludge biological treatment.
[0002]
[Prior art]
In recent years, eutrophication of water areas such as rivers has become a problem, and in the treatment of organic wastewater such as sewage, human waste, and factory wastewater, treatment of nitrogen and phosphorus other than organic matter is required. Therefore, as shown in FIG. 6, in biological treatment, anaerobic tank 10, oxygen-free tank 11, and aerobic tank 3 are provided to treat a part of nitrogen and phosphorus, and a finishing treatment of phosphorus is performed in a subsequent agglomeration treatment tank 1. The method of doing is known.
In addition, as shown in FIG. 1, in wastewater with high SS concentration and high phosphorus concentration, it is proposed that the aggregation treatment 1 is performed by adding the inorganic flocculant 13 and the polymer flocculant 14 in advance before the biological treatment 3. Has been.
[0003]
The latter agglomeration treatment is intended to reduce the amount of organic substances such as SS in biological treatment, and simply adding an inorganic flocculant to the target SS concentration or phosphorus concentration alone. is there. For this reason, when the SS concentration and phosphorus concentration in the wastewater fluctuate, the method of adjusting and treating the inorganic flocculant addition amount only with the SS concentration and phosphorus concentration items can simultaneously satisfy both treatment target water qualities. There wasn't. For example, when the raw water phosphorus concentration becomes extremely high, the residual phosphorus concentration level after the flocculation treatment also becomes high, and phosphorus remains after the biological treatment. Therefore, it is necessary to add the flocculating agent once again and perform the flocculation treatment.
[0004]
[Problems to be solved by the invention]
The present invention solves the above-mentioned problems of the prior art, and is an integrated process for sewage sludge that can be efficiently removed even with respect to concentration fluctuations in raw water such as SS, soluble organic matter, nitrogen, and phosphorus . and to provide a treatment for return flow water.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention, SS, soluble organic substances, phosphorus, the return flow water aggregation processing of sewage sludge containing nitrogen, after coagulation treatment with an inorganic flocculant and a polymer flocculant, the process in disposal law water you biological treatment, the aggregation treatment, the return sulfate in running water, the treated water was added in the order of polymer flocculant, the target value SS concentration to become units return water flow SS amount sulfate per The addition amount (coefficient a) is obtained from FIG. 3, and the sulfuric acid band addition amount (coefficient b) per unit return water phosphorus amount at which the treated water reaches the target phosphorus concentration is obtained from FIG. The sulfuric acid band addition amount (A) is calculated by multiplying the SS concentration of running water, and the sulfuric acid band addition amount (B) is calculated by multiplying the phosphorus concentration of the return water measured by the coefficient b, and the addition amount (A) And addition amount (B) It was added de, then is obtained by the treatment of return flow water aggregation processing of sewage sludge, which comprises carrying out the addition of polymeric flocculant.
In the processing method, the aggregation treatment, the perform return flow water measurements SS concentration and the phosphorus concentration in the automatic measurement can be performed by adjusting the aluminum sulfate injection amount on the basis of the measured values automatically.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the amount of the inorganic flocculant used for the flocculation treatment is judged from both the necessary amount for the SS concentration and the phosphorus concentration of the organic waste water, and the larger amount of the necessary amount of addition is taken as the inorganic flocculant added amount. Even when the phosphorus concentration increases, the treated water phosphorus concentration level does not increase. Moreover, even when the raw water SS concentration becomes high, the treated water SS concentration level does not become high.
In addition, SS and phosphorus concentrations in organic wastewater are measured by automatic measurement using automatic analysis, and automatic control is performed to adjust the amount of inorganic flocculant injection pump based on the signal based on the measured value. A stable agglomerated water quality can be obtained.
The inorganic flocculant that can be used in the present invention may be any of aluminum salts such as sulfuric acid band and PAC, or iron salts such as ferric chloride and polyiron. As the polymer flocculant, either an anionic polymer flocculant or a nonionic polymer flocculant may be used.
[0007]
The organic wastewater treatment method of the present invention is performed, for example, by the treatment process shown in FIG.
In FIG. 1, raw water 5 that is organic wastewater is measured for SS concentration and phosphorus concentration and introduced into the agglomeration treatment tank 1, and an inorganic flocculant 13 is added based on the concentration of the larger required amount, and then high A molecular flocculant 14 is added and flows into the sedimentation basin 2. In the sedimentation basin 2, the solid content is separated as waste mud 7, and the supernatant 6 is introduced into the aeration tank 3, which is a biological treatment tank, and is treated together with the returned sludge from the sedimentation basin 4. It flows in and is separated into solid and liquid, the precipitate is circulated to the aeration tank 3 as return sludge 8, and the supernatant is discharged as treated water 9.
[0008]
【Example】
Hereinafter, the present invention will be specifically described by way of examples.
Example 1
FIG. 2 shows an overall process diagram of the sewage sludge aggregation process using the treatment method of the present invention, and the treatment method of the present invention is used for the water return process of this aggregation process.
In FIG. 2, the mixed raw sludge 23 discharged from the sewage treatment plants A, B, C, and 21 is collected and collectively processed in the concentration step 24, the dehydration step 25, and the incineration step 26. At that time, the separated water 27 from the concentration step 24 and the filtrate 28 from the dehydration step 25 are combined to obtain the organic waste water 5 of the present invention. Next, the raw water 5 is treated by the treatment method of the present invention.
[0009]
That is, the quality of the raw water 5 is automatically measured by the automatic controller 15 and introduced into the flocculation treatment tank 1. In the flocculation treatment tank 1, the injection amount of the inorganic flocculant 13 is adjusted by automatically controlling the injection pump 16 based on the automatically measured SS concentration and phosphorus concentration. Subsequently, the polymer flocculant 14 is added, it flows into the sedimentation basin 2, the waste mud 7 is separated, and the supernatant 6 is introduced into the denitrification tank 11. In the denitrification tank 11, the return sludge 8 and the circulating liquid 12 from the nitrification tank 3 are introduced and denitrified, and then flows into the nitrification tank 3 and aerated. In the nitrification tank 3, a part is circulated to the denitrification tank as the circulating liquid 12, the other part is extracted, the sludge is settled and separated in the settling tank 4, and is circulated as the return sludge 8 to the denitrification tank. The supernatant water is discharged as treated water 9.
[0010]
According to FIG. 2, the return water discharged | emitted from the sludge concentration process and the dehydration process was processed. The return water contains high concentrations of SS, BOD, nitrogen and phosphorus. Table 1 shows typical water quality.
[Table 1]

[0011]
To this return water, an inorganic flocculant is added, and after adjusting to a predetermined pH with caustic soda, a polymer flocculant is added, and SS and phosphorus in the waste water are removed by agglomeration and precipitation treatment. . The target water quality here is SS <100 mg / liter and PO ₄ −P <5 mg / liter.
FIG. 3 shows the relationship between the added amount of sulfuric acid band and the treated water SS concentration. FIG. 4 shows the relationship between the amount of sulfuric acid band added and the concentration of treated water phosphorus. The amount of sulfuric acid band added to satisfy the treated water SS <100 mg / liter is about 0.05 mg Al ₂ O ₃ / mg raw water SS. On the other hand, the amount of added sulfuric acid band required for treated water phosphorus (here PO ₄ -P) <5 mg / liter is about 1.8 mgAl ₂ O ₃ / mg raw water PO ₄ -P.
FIG. 5 shows the result of the coagulation sedimentation treatment using this relationship. In FIG. 5, the treated water according to the present invention is (a), treated water (conventional method) in which the chemical injection amount is determined only by the raw water phosphorus concentration (b), and treated water (in which the chemical injection amount is determined only by the raw water SS concentration ( The conventional method is represented as (c) and the raw water is represented as (d).
[0012]
When the raw water SS concentration is 1000 mg / liter and PO ₄ -P 60 mg / liter, the conventional method (c) in which only the raw water SS concentration is measured and the addition amount of the inorganic flocculant is set satisfies the treated water SS <100 mg / liter. However, the treated water PO ₄ -P remains at 30 mg / liter. In addition, when the raw water is 1500 mg / liter and PO ₄ -P 30 mg / liter, the conventional method (b) in which only the raw water PO ₄ -P is measured and the amount of the inorganic flocculant is set is satisfied when the treated water <5 mg / liter. However, the treated water SS concentration is 200 mg / liter.
On the other hand, in the present invention (a) in which the amount of inorganic flocculant added is larger than the concentration of raw water SS and raw water PO ₄ -P, the water quality of treated water <100 mg / liter, PO ₄ -P ₅ mg / liter Was obtained stably.
[0013]
In the present invention, the raw water SS concentration and the raw water phosphorus concentration are measured by an automatic analyzer, the signal is applied to a calculator, the one with the larger amount of inorganic flocculant added is selected, and the stroke of the inorganic flocculant addition pump is adjusted automatically. Control is also possible. As a control method, various control methods such as PI and PID can be selected.
If the raw water phosphorus concentration is difficult to measure due to the influence of the inflow SS concentration, it is diluted with water that does not contain phosphorus, or the treated water phosphorus is measured and feedback control is performed, and the amount of inorganic flocculant added Adjust. Total phosphorus meter to measure the phosphorus concentration (T-P method), orthophosphoric acid concentration meter (PO ₄ -P method) either good, fast analysis time, who take more output signals PO ₄ -P method Is desirable.
Although the embodiment shown here is a case of sewage return water, the present invention can also be applied to other types of manure and industrial wastewater.
[0014]
【The invention's effect】
According to the present invention, in the agglomeration treatment of organic waste water, the amount of inorganic flocculant required for the SS concentration and phosphorus concentration of the influent water to be agglomerated is calculated, and the larger addition amount of both is selected. By adding an inorganic flocculant, the following effects could be achieved.
(1) The SS and phosphorus target water quality after the coagulation treatment was constantly obtained stably.
(2) Since the addition amount of the inorganic flocculant always shows an appropriate value, the cost can be reduced also in terms of economy.
[Brief description of the drawings]
FIG. 1 is a process diagram showing a processing method of the present invention.
FIG. 2 is an overall process diagram of sewage sludge aggregation treatment using the treatment method of the present invention.
FIG. 3 is a graph showing the relationship between the amount of sulfuric acid band added and the concentration of treated water SS.
FIG. 4 is a graph showing the relationship between the amount of sulfuric acid band added and the concentration of treated water phosphorus.
5 is a graph showing the results of Example 1. FIG.
FIG. 6 is a process diagram showing a known biological nitrogen phosphorus treatment method.
[Explanation of symbols]
1: coagulation tank, 2: sedimentation tank, 3: aeration tank (nitrification tank), 4: sedimentation tank, 5: raw water of organic waste water, 6: coagulated treated water, 7: waste mud, 8: return sludge, 8 ' : Excess sludge, 9: treated water, 10: anaerobic tank, 11: anoxic tank, 12: circulating flow, 13: inorganic flocculant, 14: polymer flocculant, 15: measurement controller, 16: injection pump, 17 : Inflow sewage, 18: Effluent, 19: Smoke drainage, 21: Sewage treatment plant, 23: Mixed sludge, 24: Concentration process, 25: Dehydration process, 26: Incineration process, 27: Concentration process separation water, 28 : Dewatering step filtrate, b: intensive treatment sludge treatment plant, (a): treated water according to the present invention, (b) treated water when the chemical injection amount is determined only by the raw water phosphorus concentration, (c): raw water Treated water when the chemical injection amount is determined only by the SS concentration, (d): raw water, (a ′): added amount of sulfated clay according to the present invention, (b ′) : Aluminum sulfate addition amount when determined only by the raw phosphorus concentration, (c '): aluminum sulfate addition amount when determined only by the raw water SS concentration

Claims

SS, soluble organic substances, phosphorus, the return flow water aggregation processing of sewage sludge containing nitrogen, after coagulation treatment with an inorganic flocculant and a polymer flocculant, the treated water in the Disposal Law you biological treatment, the aggregated processing said return sulfate in running water, treated water was added in the order of the polymeric flocculant, calculated aluminum sulfate addition amount of the unit return water flow SS amount per a target value SS concentration (coefficient a) 3, In addition, the amount of sulfuric acid band added per unit return water phosphorus amount (coefficient b) at which the treated water becomes the target phosphorus concentration is obtained from FIG. 4, and the sulfuric acid band addition amount ( A) is calculated, and the sulfuric acid band addition amount (B) is calculated by multiplying the coefficient b by the measured phosphorus concentration of the return water, and the larger of the addition amount (A) and the addition amount (B). It was added aluminum sulfate in amount, then adding a polymer coagulant Treatment of return flow water aggregation processing of sewage sludge, characterized in that performed.

In the processing method, the aggregation treatment, was measured in the SS concentration and the phosphorus concentration in the return flow water at the automatic measurement, and characterized by performing the aluminum sulfate injection amount on the basis of the measured values automatically adjust to treatment of return flow water aggregation processing of sewage sludge according to claim 1.