JP2004113945A

JP2004113945A - Water treatment method

Info

Publication number: JP2004113945A
Application number: JP2002281381A
Authority: JP
Inventors: Keisuke Nakamura; 中村　佳介; Shunsuke Okuda; 奥田　俊輔; Seiichi Hayashi; 林　聖一
Original assignee: Katayama Chemical Inc
Current assignee: Katayama Chemical Inc
Priority date: 2002-09-26
Filing date: 2002-09-26
Publication date: 2004-04-15

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treatment method in which the quantity of water to be taken out of an aqueous system (taken-out quantity (X) of water) is calculated using each of various conditions of the aqueous system and, after the taken-out water is sterilized, it is again returned to the aqueous system to control the number of bacteria in the aqueous system. <P>SOLUTION: In the water treatment method, the taken-out quantity (X) of water is calculated using formula 1 : X=-100× [H × 1n(2 × A-10<SP>(logA+K)</SP>/A) + B]/S (wherein A is the initial number of bacteria, B is a proliferation factor, C is a forced blow amount and S is a sterilization rate) and, after the taken-out water is sterilized, it is again refurned to the aqueous system to control of the number of bacteria in the aqueous system. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、水処理方法に関する。さらに詳しくは、水系から取り出す水の量（取出水量（Ｘ））を算出し、取り出した水に殺菌処理を施した後、再び水系に戻し、水系内の菌数を管理することを特徴とする水処理方法に関する。
【０００２】
【従来の技術】
空調設備やプラント設備において熱交換器で効率よく冷却を行なう為に、循環冷却水系では冷却水を冷却し、これに補給水を補給して熱交換器を冷却する循環冷却を行なう。このため、循環冷却水系では外部からの汚れや菌類が混入するとともに、冷却水の蒸発や飛散により循環冷却水が濃縮されて塩類や有機物の濃度が高くなり、様々な障害が発生する。また、製紙工程水などの多量の工業用水を製造工程水として使用する系においても、節水のために可能な範囲で用水を循環し有効利用を図っていることから、様々な障害が発生する。
【０００３】
スライム障害としては、熱交換器にスライムが付着し熱交換率の低下がおこる。スライム障害の防止策として循環水系に殺菌剤を添加して菌類の増殖を防止する方法や装置内を洗浄剤で洗浄する方法や物理的に洗浄する方法が用いられてきた。また、循環冷却水系のスライム処理として、殺菌剤を高濃度、冷却水系内で使用する方法が行われてきたが、飛散などによって環境を汚染することや、循環冷却水系内の設備や配管材質に対して影響を与えるという問題点があった。
【０００４】
また、スライム処理を実施している冷却水の菌数は絶えず増加や減少を繰り返している。スライム処理の効果は、殺菌剤により減少する菌と増殖を繰り返す菌のバランスに左右される。安価なスライム処理剤であれば、経済的には連続添加が可能であるが、多量のスライム処理剤を添加することになると環境への影響が懸念される。経済性、環境への影響性を考慮した場合には、スライム処理剤の使用は少ないほうが好ましく、例えば、経済的に微生物の増殖を抑制するために、冷却水の一部を分離して殺菌する循環冷却水系のレジオネラ属細菌発生防止法（特公平６−７７７３５号公報）が知られている。
一方、微生物の付着を検出し、スライム処理薬剤の添加を自動化する水系の水処理方法（特開２００１−４５９０号公報）などが知られている。この場合、障害発生を検出して、ただちに対応することが可能であるが、スライム処理薬剤による処理状況の悪化の現象を検出した後に、さらなるスライム処理を開始するという事後対応型の処理となる。
【０００５】
【特許文献１】
特公平６−７７７３５号公報
【特許文献２】
特開２００１−４５９０号公報
【０００６】
【発明が解決しようとする課題】
循環水系の良好な状態を長期に渡り継続させる必要がある設備では、事後対応型ではなく、スライム処理の効果をあらかじめ予測し、最適なスライム処理を継続的に行なうことが要望されていた。
【０００７】
本発明は、水系の各種条件を用いて、水系から取り出す水の量（取出水量（Ｘ））を算出し、取り出した水に殺菌処理を施した後、再び水系に戻し、水系内の菌数を管理することを特徴とする水処理方法を提供することを課題とする。
【０００８】
【課題を解決するための手段】
本発明者は、上記の課題を解決すべく鋭意研究を行った結果、水系の保有水量、初期菌数、増殖係数、強制ブロー量および殺菌率を用いることにより、水系から取り出す水の量（取出水量（Ｘ））を算出し、取り出した水に殺菌処理を施した後、再び水系に戻すことにより、水系内の菌数を管理することを見出し、本発明を完成するに到った。
【０００９】
かくして本発明によれば、取出水量（Ｘ）を式（１）
Ｘ＝−１００×〔Ｈ×ｌｎ［｛２　×Ａ−１０^{（ｌｏｇＡ＋Ｋ）}｝÷Ａ］＋Ｂ〕÷Ｓ　　　（１）
〔Ｈ：水系の保有水量、Ａ：初期菌数、Ｋ：増殖係数、Ｂ：強制ブロー量、Ｓ：殺菌率〕
を用いて算出し、取り出した水に殺菌処理を施した後、再び水系に戻し、水系内の菌数を管理することを特徴とする水処理方法が提供される。
【００１０】
【発明の実施の形態】
本発明は、水系から取り出す水の量（取出水量（Ｘ））を算出し、取り出した水に殺菌処理を施した後、再び水系に戻すことが可能な水系であれば特に限定されず、各種工業用あるいはビル空調用の冷却水系や紙パルプ製造工程水系等で適用することができる。
【００１１】
本発明の殺菌処理は、公知の殺菌処理であれば特に限定されない。例えば、過酸化水素、過酢酸、過炭酸、過硫酸などの過酸化物や、塩素、臭素、ヨウ素などのハロゲン化物もしくは、二酸化塩素、次亜塩素酸ナトリウム、塩素化イソシアヌル酸、ヒダントインなどのハロゲン放出化合物、オゾン、５−クロロ−２−メチル−４−イソチアゾリン−３−オン、２−ブロモ−２−ニトロプロパン−１，３−ジオール、２，２−ジブロモ−２−ニトロエタノール、４級アンモニウム塩、グルタルアルデヒド、マレイミド、トリアジンなどの有機系スライムコントロール剤やそれらの誘導体等の殺菌剤等を利用した化学的殺菌処理、加熱、加圧、紫外線照射、超音波、放射線、高周波等を利用した物理的殺菌処理等が挙げられる。
【００１２】
本発明において、取出水量（Ｘ）は、水系の保有水量、初期菌数、増殖係数、強制ブロー量および殺菌率を用いて、式（１）
Ｘ＝−１００×〔Ｈ×ｌｎ［｛２　×Ａ−１０^{（ｌｏｇＡ＋Ｋ）}｝÷Ａ］＋Ｂ〕÷Ｓ（１）
〔Ｈ：水系の保有水量、Ａ：初期菌数、Ｋ：増殖係数、Ｂ：強制ブロー量、Ｓ：殺菌率〕
から算出できる。
【００１３】
式（１）の増殖係数（Ｋ）は、菌の培養前の菌数（（ａ））、培養後の菌数（（ｂ））および培養時間（ｔ_ｂ）を用いて、式（１−１）
Ｋ＝（ｌｏｇ（ｂ）−ｌｏｇ（ａ））÷ｔ_ｂ　　　（１−１）
から算出できる。
【００１４】
式（１）の強制ブロー量（Ｂ）とは、水系内の濃縮管理のため強制的に謦咳に排出している時間あたりの水量のことをいう。
【００１５】
式（１）の殺菌率（Ｓ）は、初期菌数（Ａ）および殺菌処理後の菌数（Ａ’）を用いて、式（１−２）
Ｓ＝｛（Ａ−Ａ’）÷Ａ｝×１００　　　（１−２）
から算出できる。
【００１６】
上記の理論計算結果より、取出水量（Ｘ）を算出し、取り出した水に殺菌処理を施した後、再び水系に戻すことで、水系内の菌数を管理することが可能となる。
【００１７】
本発明において水系内の菌数を管理するとは、１ｍｌ中の菌数の設定基準値から±１０％の範囲内で菌数が保持されている状態をいう。例えば、１ｍｌ中の菌数の設定基準値を１．０×１０^４個とした場合、水系内の菌数は、０．９×１０^４〜１．１×１０^４個の範囲内で保持されている状態であればよい。
【００１８】
本発明においては、取出水量（Ｘ）を設定し、水系内の菌数を管理した後、さらにｔ時間後の水系内の菌数（Ｗ_ｔ）についても算出することができる。
【００１９】
ｔ時間後の水系内の菌数（Ｗ_ｔ）は、次の菌数▲１▼〜▲３▼までの和（（Ｄ_ｔ）：▲１▼水系内の殺菌処理により減少する菌数、▲２▼強制ブローすることにより減少する菌数および▲３▼自己増殖により増加する菌数）とｔ時間後の水系内において、補給水により増加する菌数（Ｐ_ｔ）を用いて、式（２）
Ｗ_ｔ＝Ｄ_ｔ＋Ｐ_ｔ　　　（２）
から算出できる。
【００２０】
式（２）のＤ_ｔは、ｔ−１時間後の菌数（Ｄ_ｔ−１）、変化率（Ｃ）を用いて、式（２−１）
Ｄ_ｔ＝Ｄ_ｔ−１×（１−Ｃ）　　　（２−１）
（ただしｔ≧１で、ｔ＝１のとき、Ｄ_ｔ−１は初期菌数（Ａ）とする。）
から算出できる。
【００２１】
式（２−１）の水系全体の変化率（Ｃ）は、減少率（Ｇ）と増加率（Ｚ）を用いて、式（２−２）
Ｃ＝Ｇ−Ｚ　　　（２−２）
から算出できる。
【００２２】
式（２−２）の減少率（Ｇ）及び増加率（Ｚ）は、殺菌処理とブローにより減少する菌のｔ−１時間後の菌数（Ａ_ｔ−１）と、ｔ時間後の菌数（Ａ_ｔ）、自己増殖より増加する菌のｔ−１時間後の菌数（Ｕ_ｔ−１）とｔ時間後の菌数（Ｕ_ｔ）を用いて、式（２−３）、式（２−４）
Ｇ＝（Ａ_ｔ−１−Ａ_ｔ）÷Ａ_ｔ−１　　　（２−３）
Ｚ＝（Ｕ_ｔ−Ｕ_ｔ−１）÷Ｕ_ｔ−１　　　（２−４）
からそれぞれ算出できる。
【００２３】
式（２−３）のｔ時間後の菌数（Ａ_ｔ）は、初期菌数（Ａ）、取出水量（Ｘ）、殺菌率（Ｓ）、強制ブロー量（Ｂ）、水系の保有水量（Ｈ）を用いて、式（２−５）
Ａ_ｔ＝Ａ×ｅｘｐ｛（−Ｘ×Ｓ÷１００＋Ｂ）×ｔ÷Ｈ｝　　　（２−５）
から算出できる。
【００２４】
式（２−４）のｔ時間後の菌数（Ｕ_ｔ）は、初期菌数（Ａ）、増殖係数（Ｋ）を用いて、式（２−６）
Ｕ_ｔ＝１０^（ ^ｌｏｇ ^{Ａ＋Ｋ×ｔ）}　　　（２−６）
から算出できる。
【００２５】
式（２）のＰ_ｔは、水系に補給される補給水量（Ｌ）、その補給水量に含有されている菌数（Ｍ）、取出水量（Ｘ）、強制ブロー量（Ｂ）及び、水系の保有水量（Ｈ）を用いて、式（２−７）
Ｐ_ｔ＝Ｌ×Ｍ÷（Ｘ＋Ｂ）×（１−ｅｘｐ^｛ ^{−（Ｘ＋Ｂ）×ｔ÷Ｈ} ^｝）　　　　（２−７）
から算出できる。
【００２６】
本発明における補給水量（Ｌ）とは、運転中に失われる水、（ブロー水、蒸発水）を補い、冷却水系の保有水量を一定に保つために、補給される工業用水の水量のことをいい、蒸発水量（Ｅ）、強制ブロー量（Ｂ）を用いて、式（２−８）
Ｌ＝Ｅ＋Ｂ　　　（２−８）
から算出できる。
【００２７】
本発明における蒸発水量（Ｅ）とは、循環水が冷却塔にて冷却される際に、水蒸気となり大気に放出され減少する水量のことをいい、循環水量（Ｒ）と冷却塔へ戻ってくる水とプラントへ送っている水の温度差（ΔＴ）を用いて、式（２−９）
Ｅ＝Ｒ×ΔＴ÷５７４．５　　　（２−９）
から算出できる。
【００２８】
【実施例】
この発明を試験例により以下に説明するが、これらの試験例によりこの発明が限定されるものではない。
【００２９】
試験例１（水系からの取出水量の算定による殺菌効果確認試験）
某食品製造工場の冷却塔から冷却水を採取し、菌数測定を実施した。冷却水系の条件および水系内の初期菌数は、以下のとおりである。

【００３０】
採取した冷却水を実機の水温と同様の温度に設定した恒温槽中にて２４時間培養し、菌数測定したところ１．３×１０^４個／ｍｌであった。増殖係数（Ｋ）は０．００８であった。殺菌処理は紫外線殺菌を行った。殺菌率は９９％であった。
上記条件から、取出水量（Ｘ）は、循環水量に対し０．３％（０．７ｍ^３／ｈ）以上であれば、菌数を減少させることが可能であることが式（１）より算出できた。取出水量（Ｘ）を、循環水量に対し０．３％とした時の菌数変化の予測を図１に示す。
【００３１】
菌数の目標値を１０^３個／ｍｌ以下と設定し、ｔ時間後の水系内の菌数（Ｗ_ｔ）を算出する式（２）を用いて、水系から取り出す取出水量（Ｘ）を循環水量に対し１．０％（２．３ｍ^３／ｈ）とした時の菌数変化を図２に示す。
【００３２】
計算の結果から、７１時間後に１０^３個／ｍｌに菌数が減少することが予想された。
実際に循環水を２．３ｍ^３／ｈで取り出し、連続的に紫外線殺菌した場合における菌数変化について測定した。測定結果を表１に示す。
【００３３】
【表１】

表１の結果から、７２時間後に菌数１．１×１０^３個／ｍｌとなり、計算の結果に近い時間帯において、１０^３個／ｍｌにまで菌数が減少することが確認された。
【００３４】
試験例　２（水系からの取出水量の算定による殺菌効果確認試験）
某石油化学工場の冷却水を採取し、菌数測定を実施した。なお、冷却水系の条件は以下のとおりであり、この条件から蒸発水量（Ｅ）は、約１７ｍ^３／ｈと算出できる。また、冷却水系の殺菌処理については、図３に示すように、取出水量（Ｘ）について殺菌処理を施すのではなく、補給水量（１７ｍ^３／ｈ）に対し１２％次亜塩素酸ナトリウム水溶液を０．３ｍｇ／Ｌとなるように連続添加で殺菌処理を施したものと取出水量（８．５ｍ^３／ｈ）とを併せた水量（２５．５ｍ^３／ｈ）を合計の補給水量として冷却水系に戻した。測定開始時と８日後の水系内の各水質項目について、測定結果を表２に示す。

【００３５】
【表２】

この冷却水系では、冷却水中の菌数が１０^３以下を管理基準として設定していた。しかし一般細菌数が２０から２２００に増加したことから、８日目以降の冷却水系の殺菌処理については図４に示すように、補給水量（１７ｍ^３／ｈ）に対し、１２％次亜塩素酸ナトリウム水溶液を０．５ｍｇ／Ｌとなるように連続添加を実施し、また取出水量（Ｘ）を２４．７ｍ^３／ｈとし、合計の補給水量を４１．７ｍ^３／ｈとした。測定開示時から１３日後の水質項目の測定結果を表３に示す。
【００３６】
【表３】

ｔ時間後の水系内の菌数（Ｗ_ｔ）を算出する式（２）を用いて算出した結果、１２０時間に数１０個／ｍｌに菌数が減少することが予想された。実際に８日目から１３日目までの５日間の菌数測定を実施した場合においても、１０個／ｍｌ以下まで菌数が減少する結果となり、算出値とほぼ一致した。
【００３７】
【発明の効果】
本発明は、水系からの取出水量（Ｘ）を算出し、取り出した水に殺菌処理を施した後、再び水系に戻すことにより、水系内の菌数を水系内の菌数を管理する水処理方法であって、取出水量（Ｘ）とｔ時間後の水系内の菌数（Ｗ_ｔ）を算出することにより、より効率的な殺菌処理を提供することができる。
【図面の簡単な説明】
【図１】水系から取り出す取出水量（Ｘ）を循環水量に対し０．３％とした時の菌数変化の予測図である。
【図２】水系から取り出す取出水量（Ｘ）を循環水量に対し１．０％（２．３ｍ^３／ｈ）とした時の菌数変化の予測図である。
【図３】冷却水系での殺菌処理を示す図である。
【図４】８日目以降の冷却水系での殺菌処理を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a water treatment method. More specifically, the amount of water taken out from the water system (the amount of water taken out (X)) is calculated, the water taken out is sterilized, then returned to the water system again, and the number of bacteria in the water system is managed. It relates to a water treatment method.
[0002]
[Prior art]
In order to perform efficient cooling with a heat exchanger in an air conditioner or a plant, a circulating cooling water system cools a cooling water and supplies replenishing water thereto to perform a circulating cooling in which the heat exchanger is cooled. For this reason, in the circulating cooling water system, dirt and fungi from the outside are mixed, and the circulating cooling water is concentrated due to evaporation and scattering of the cooling water to increase the concentration of salts and organic substances, thereby causing various troubles. Also, in a system that uses a large amount of industrial water such as papermaking process water as the manufacturing process water, various obstacles occur because the water is circulated and used as efficiently as possible to save water.
[0003]
As a slime obstacle, slime adheres to the heat exchanger, and the heat exchange rate decreases. As a method for preventing slime damage, a method of adding a bactericide to a circulating water system to prevent the growth of fungi, a method of cleaning the inside of the apparatus with a cleaning agent, and a method of physically cleaning the apparatus have been used. In addition, as a slime treatment of the circulating cooling water system, a method of using a high concentration of a bactericide in the cooling water system has been used, but it may contaminate the environment by scattering etc. There was a problem that it had an effect on the situation.
[0004]
In addition, the number of bacteria in the cooling water for which the slime treatment is being performed is constantly increasing and decreasing. The effect of the slime treatment depends on the balance between bacteria that are reduced by the bactericide and bacteria that repeatedly grow. If it is an inexpensive slime treating agent, it can be economically added continuously, but if a large amount of the slime treating agent is added, there is a concern about the effect on the environment. In consideration of the economy and the effect on the environment, it is preferable to use a small amount of the slime treatment agent.For example, in order to economically suppress the growth of microorganisms, part of the cooling water is separated and sterilized. A method for preventing the generation of Legionella bacteria in a circulating cooling water system (Japanese Patent Publication No. Hei 6-77735) is known.
On the other hand, there is known an aqueous water treatment method (JP-A-2001-4590) which detects the adhesion of microorganisms and automates the addition of a slime treatment chemical. In this case, it is possible to respond immediately by detecting the occurrence of a fault, but this is a post-reaction type process in which further slime processing is started after a phenomenon of deterioration of the processing situation due to the slime processing chemical is detected.
[0005]
[Patent Document 1]
Japanese Patent Publication No. 6-77735 [Patent Document 2]
JP 2001-4590 A
[Problems to be solved by the invention]
In a facility that needs to maintain a good state of the circulating water system for a long period of time, it has been demanded that the effect of the slime treatment is predicted in advance and that the optimum slime treatment is continuously performed, instead of a reactive type.
[0007]
The present invention calculates the amount of water taken out from a water system (amount of water taken out (X)) using various conditions of the water system, sterilizes the water taken out, returns it to the water system again, and returns the number of bacteria in the water system. It is an object of the present invention to provide a water treatment method characterized by managing water.
[0008]
[Means for Solving the Problems]
The present inventor has conducted intensive studies in order to solve the above-mentioned problems. As a result, the amount of water to be taken out of the water system (the amount of water taken out) was determined by using the water content of the water system, the initial number of bacteria, the growth coefficient, the forced blow rate, and the sterilization rate. After calculating the amount of water (X), sterilizing the extracted water, and then returning the water to the water system again, it was found that the number of bacteria in the water system was controlled, and the present invention was completed.
[0009]
Thus, according to the present invention, the amount of discharged water (X) is calculated by the equation (1).
X = −100 × [H × ln [｛2 × A-10 ^{(logA + K)} ｝ ÷ A] + B] ÷ S (1)
[H: amount of water in the water system, A: initial number of bacteria, K: growth coefficient, B: forced blow amount, S: sterilization rate]
The water treatment method is characterized in that the water is subjected to a sterilization treatment, and then returned to the water system, and the number of bacteria in the water system is managed.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is not particularly limited as long as it is an aqueous system that can calculate the amount of water to be extracted from the aqueous system (the amount of extracted water (X)), sterilize the extracted water, and then return to the aqueous system again. The present invention can be applied to a cooling water system for industrial or building air conditioning, a water system for paper pulp manufacturing process, and the like.
[0011]
The sterilization treatment of the present invention is not particularly limited as long as it is a known sterilization treatment. For example, peroxides such as hydrogen peroxide, peracetic acid, percarbonate, and persulfuric acid, and halides such as chlorine, bromine, and iodine, or halogens such as chlorine dioxide, sodium hypochlorite, chlorinated isocyanuric acid, and hydantoin Release compound, ozone, 5-chloro-2-methyl-4-isothiazolin-3-one, 2-bromo-2-nitropropane-1,3-diol, 2,2-dibromo-2-nitroethanol, quaternary ammonium Chemical sterilization using organic slime control agents such as salts, glutaraldehyde, maleimide, and triazine and germicides such as their derivatives, heating, pressurization, ultraviolet irradiation, ultrasonic waves, radiation, high frequency, etc. Physical sterilization treatment and the like.
[0012]
In the present invention, the amount of water taken out (X) is calculated by using the water content of the water system, the initial number of bacteria, the growth coefficient, the forced blow amount, and the sterilization rate according to the formula (1).
X = −100 × [H × ln [｛2 × A-10 ^{(logA + K)} ｝ ÷ A] + B] ÷ S (1)
[H: amount of water in the water system, A: initial number of bacteria, K: growth coefficient, B: forced blow amount, S: sterilization rate]
Can be calculated from
[0013]
The growth coefficient (K) in the equation (1) is calculated by using the number of bacteria before culture ((a)), the number of bacteria after culture ((b)), and the culture time (t _b ) using the following equation (1- (b)). 1)
K = (log (b) −log (a)) ÷ t _b (1-1)
Can be calculated from
[0014]
The forced blow amount (B) in the equation (1) refers to the amount of water per hour during which the water is forcibly discharged to control the concentration in the water system.
[0015]
The bactericidal rate (S) of the formula (1) is calculated by using the initial bacterium count (A) and the bacterium count (A ′) after the bactericidal treatment, using the formula (1-2).
S = {(AA ′)} A} × 100 (1-2)
Can be calculated from
[0016]
Based on the above theoretical calculation results, the amount of discharged water (X) is calculated, sterilized, and then returned to the water system, whereby the number of bacteria in the water system can be managed.
[0017]
In the present invention, controlling the number of bacteria in an aqueous system refers to a state in which the number of bacteria is maintained within a range of ± 10% from a set reference value of the number of bacteria in 1 ml. For example, when the setting reference value of the number of bacteria in 1 ml is 1.0 × 10 ⁴ , the number of bacteria in the water system is maintained within a range of 0.9 × 10 ^{4 to} 1.1 × 10 ^4. It should just be in the state where it is.
[0018]
In the present invention, after setting the amount of water taken out (X) and managing the number of bacteria in the water system, the number of bacteria (W _t ) in the water system after t hours can also be calculated.
[0019]
The number of bacteria (W _t ) in the water system after t hours is the sum of the following bacteria numbers (1) to (3) ((D _t ): (1) the number of bacteria reduced by the sterilization treatment in the water system; (2) the number of bacteria decreased by forced blowing and (3) the number of bacteria increased by self-proliferation) and the number of bacteria (P _t ) increased by make-up water in the water system after t hours. )
W _t = D _t + P _t (2)
Can be calculated from
[0020]
_{D t} is the formula (2), t-1 hour after the number of bacteria _{(D t-1),} using the rate of change (C), formula (2-1)
_Dt = _Dt-1 * (1-C) (2-1)
(However, when t ≧ 1 and t = 1, D _t−1 is the initial number of bacteria (A).)
Can be calculated from
[0021]
The rate of change (C) of the entire water system in Equation (2-1) is calculated using Equation (2-2) using the rate of decrease (G) and the rate of increase (Z).
C = G-Z (2-2)
Can be calculated from
[0022]
The decrease rate (G) and the increase rate (Z) in the equation (2-2) are the number of bacteria (A _t-1 ) after t-1 hours of the bacteria that are reduced by the sterilization treatment and the blowing, and the number of bacteria after t hours. Using the number (A _t ), the number of bacteria after t-1 hour (U _t-1 ) and the number of bacteria after t hour (U _t ), the number of bacteria increasing from self-proliferation, formula (2-3), (2-4)
G = (A _t−1 −A _t ) ÷ A _t−1 (2-3)
_{_{Z = (U t -U t-}} 1) ÷ U t-1 (2-4)
, Respectively.
[0023]
The number of bacteria (A _t ) after time t in the equation (2-3) is the initial number of bacteria (A), the amount of water taken out (X), the sterilization rate (S), the amount of forced blow (B), the amount of water in the water system ( H) using the formula (2-5)
_{A t = A × exp {(} - X × S ÷ 100 + B) × t ÷ H} (2-5)
Can be calculated from
[0024]
The number of bacteria (U _t ) after time t in equation (2-4) is calculated using the initial number of bacteria (A) and the growth coefficient (K) using equation (2-6).
U _t = 10 ⁽ ^log ^{A + K × t)} (2-6)
Can be calculated from
[0025]
The P _t of formula (2), supply amount of water supplied to the water system (L), the number of bacteria contained in the the supply amount of water (M), extraction water (X), forced blow amount (B) and, in aqueous Using the retained water (H), equation (2-7)
P _t = L × M ÷ (X + B) × (1-exp ^｛ ^{− (X + B) × t ÷ H} ^｝ ) (2-7)
Can be calculated from
[0026]
The replenishment water amount (L) in the present invention refers to the amount of industrial water that is replenished in order to compensate for water lost during operation, (blow water, evaporative water), and to keep the amount of water retained in the cooling water system constant. Equation (2-8) is obtained by using the amount of evaporated water (E) and the amount of forced blow (B).
L = E + B (2-8)
Can be calculated from
[0027]
The amount of evaporated water (E) in the present invention refers to the amount of water that is released into the atmosphere as steam and decreases when the circulating water is cooled by the cooling tower, and returns to the circulating water amount (R) and the cooling tower. Using the temperature difference (ΔT) between water and water sent to the plant, the equation (2-9) is obtained.
E = R × ΔT ÷ 574.5 (2-9)
Can be calculated from
[0028]
【Example】
The present invention will be described below with reference to test examples, but the present invention is not limited to these test examples.
[0029]
Test Example 1 (Test for confirming the disinfection effect by calculating the amount of water taken out from the water system)
Cooling water was collected from a cooling tower of a certain food manufacturing plant, and the bacterial count was measured. The conditions of the cooling water system and the initial number of bacteria in the water system are as follows.

[0030]
The collected cooling water was cultured for 24 hours in a thermostat set at the same temperature as the actual water temperature, and the number of bacteria was measured to be 1.3 × 10 ⁴ cells / ml. The growth coefficient (K) was 0.008. Sterilization treatment was performed by ultraviolet sterilization. The sterilization rate was 99%.
From the above conditions, it is calculated from equation (1) that if the withdrawn water amount (X) is 0.3% (0.7 m ³ / h) or more with respect to the circulating water amount, the number of bacteria can be reduced. did it. FIG. 1 shows the prediction of the change in the number of bacteria when the amount of water taken out (X) is 0.3% of the amount of circulating water.
[0031]
The target value of the number of bacteria is set at 10 ³ cells / ml or less, and the amount of water (X) taken out from the water system is circulated using the equation (2) for calculating the number of bacteria (W _t ) in the water system after t hours. FIG. 2 shows the change in the number of bacteria when 1.0% (2.3 m ³ / h) with respect to the amount of water.
[0032]
From the calculation results, it was expected that the number of bacteria would be reduced to 10 ³ cells / ml after 71 hours.
Actually, circulating water was taken out at 2.3 m ³ / h, and the change in the number of bacteria in the case of continuous ultraviolet sterilization was measured. Table 1 shows the measurement results.
[0033]
[Table 1]

From the results in Table 1, it was confirmed that the number of bacteria was 1.1 × 10 ³ cells / ml after 72 hours, and that the number of bacteria was reduced to 10 ³ cells / ml in a time zone close to the calculation result.
[0034]
Test Example 2 (Test for confirming the disinfection effect by calculating the amount of water taken out from the water system)
Cooling water from a certain petrochemical factory was collected and the bacterial count was measured. The conditions of the cooling water system are as follows, and from these conditions, the amount of evaporated water (E) can be calculated to be about 17 m ³ / h. As for the sterilization treatment of the cooling water system, as shown in FIG. 3, instead of performing the sterilization treatment on the amount of water taken out (X), a 12% aqueous solution of sodium hypochlorite was added to the supply water amount (17 m ³ / h). The cooling water system is defined as a total water supply amount (25.5 m ³ / h) obtained by adding a water amount (8.5 m ³ / h) which has been subjected to a sterilization treatment by continuous addition to 0.3 mg / L and a discharge water amount (8.5 m ³ / h). Back to. Table 2 shows the measurement results for each water quality item in the water system at the start of the measurement and after 8 days.

[0035]
[Table 2]

In this cooling water system, the number of bacteria in the cooling water was set as control standards of 10 ³ or less. However, since the number of general bacteria increased from 20 to 2200, as shown in FIG. 4, in the sterilization treatment of the cooling water system after the 8th day, 12% hypochlorous acid was added to the makeup water amount (17 m ³ / h). aqueous sodium performed continuously added in an amount of 0.5 mg / L, also extraction water (X) is set to 24.7m ³ / h, the replenishing amount of water total was 41.7m ³ / h. Table 3 shows the measurement results of the water quality items 13 days after the disclosure of the measurement.
[0036]
[Table 3]

As a result of calculation using the formula (2) for calculating the number of bacteria (W _t ) in the water system after t hours, it was expected that the number of bacteria would decrease to several tens / ml in 120 hours. Even when the bacterial count was actually measured for 5 days from the 8th day to the 13th day, the bacterial count was reduced to 10 cells / ml or less, which almost coincided with the calculated value.
[0037]
【The invention's effect】
The present invention calculates the amount of water taken out from a water system (X), sterilizes the water taken out, and then returns the water to the water system again, thereby controlling the number of bacteria in the water system to control the number of bacteria in the water system. By calculating the amount of water taken out (X) and the number of bacteria (W _t ) in the water system after t hours, a more efficient sterilization treatment can be provided.
[Brief description of the drawings]
FIG. 1 is a prediction diagram of a change in the number of bacteria when the amount of water taken out from a water system (X) is set to 0.3% with respect to the amount of circulating water.
FIG. 2 is a prediction diagram of a change in the number of bacteria when the amount of water taken out from a water system (X) is set to 1.0% (2.3 m ³ / h) with respect to the amount of circulating water.
FIG. 3 is a diagram showing a sterilization process in a cooling water system.
FIG. 4 is a view showing a sterilization treatment in a cooling water system after the eighth day.

Claims

The amount of water taken out from the water system (the amount of water taken out (X)) is calculated by the equation (1).
X = −100 × [H × ln [｛2 × A-10 ^{(logA + K)} ｝ ÷ A] + B] ÷ S (1)
[H: amount of water in the water system, A: initial number of bacteria, K: growth coefficient, B: forced blow amount, S: sterilization rate]
A water treatment method comprising: calculating the amount of water used, sterilizing the extracted water, returning the water to an aqueous system, and managing the number of bacteria in the aqueous system.

After sterilizing the taken water, the water is returned to the water system again, the number of bacteria in the water system is managed, the number of bacteria in the water system after t hours is set, and the amount of water taken out based on the set number of bacteria ( X), and the equation (2)
W _t = D _t + P _t (2)
[W _t : the number of bacteria in the water system after t hours, D _t : (the number of bacteria reduced by sterilization treatment in the water system) + (the number of bacteria reduced by forced blowing) + (the number of bacteria increased by self-proliferation) ), P _t : number of bacteria increased by makeup water in the water system after t hours]
The water treatment method according to claim 1, wherein the number of bacteria (W _t ) in the water system after t hours is calculated using: