JPS60810A - Operating method of gravity settling type concentration tank - Google Patents

Abstract

PURPOSE:To take out the amt. predetermined from a specific relationship of discharge sludge by retaining the supplied sludge in a concentration tank for an arbitrarily set period of time which is longer than the time required for concentrating the sludge to a desired concn. and is shorter than the time for the sludge to putrefy and foam. CONSTITUTION:The flow rate Qin and the concn. Cin of the sludge 5 supplied into a gravity settling tank 6 are measured momentarily with a flowmeter 12 and a densitometer 13, and the values are stored in the storage in an operation control unit 19. The desired value of the effluent amt. Qef of sludge is calculated by an arithmetic unit in the operation control unit 19 on the basis of the equation from the measured value Cef of the densitometer 18, and the flow rate Qin(t-R) and Cin(t-R) of the supply sludge which are stored and measured at the set reference retention time R(e.g. 9hr) earlier than the measuring time (t). A sludge discharging pump 16 is driven so that the effluent amt. of sludge may be consistent with said calculated value.

Description

【発明の詳細な説明】 本発明は活性汚泥処理法にもとづく、下水処理場におけ
る重力沈降式濃縮槽の運転方法に関するものである。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for operating a gravity sedimentation type thickening tank in a sewage treatment plant based on an activated sludge treatment method.

周知のように、活性汚泥処理法にもとづく下水処理場は
、第１図に示すような設備から成シ、汚水１は最初沈澱
＃２２に流入し、その上澄水をエアレーションタンク３
及び最終沈澱池４を経て場外降濃縮し、その濃縮汚泥７
は一定時間毎に一定量消化ｌａ８へ排出し、重力龜縮債
６と消化槽８の上澄ｇ、鉱流入汚水１と共に再び最初沈
権池２に戻すしくみになっている。As is well known, a sewage treatment plant based on the activated sludge treatment method consists of equipment as shown in Figure 1. Sewage 1 first flows into sediment #22, and the supernatant water is sent to aeration tank 3.
The concentrated sludge 7 is then precipitated and concentrated outside the site via the final settling tank 4.
A fixed amount of water is discharged into the digester la8 at fixed intervals, and is returned to the initial settling pond 2 together with the gravity shrinkage bond 6, the supernatant g of the digester tank 8, and the mine inflow sewage 1.

つまル従来の重力濃縮佃の運転方法は、濃縮状態に関係
なく間欠宏量排泥を行なう運転方法を採っている。In other words, the conventional method of operating a gravity thickening tank is to carry out intermittent sludge removal regardless of the state of concentration.

しかし濃縮槽６へ流入する供給汚泥ｉ５は天候。However, the supply sludge i5 flowing into the thickening tank 6 is affected by the weather.

季節その他の要因によって異なるため、このような一定
間隔一定体積の排泥では濃縮１１６の機能を十分に果た
すことができない。Since the amount varies depending on the season and other factors, the function of thickening 116 cannot be sufficiently performed by discharging sludge in a constant volume at regular intervals.

例えば、ｎＩ天が続いたあとの降雨直後には、雨水によ
って下水管路内に堆積していた汚泥が多量に下水処理場
に流入することによって供給汚泥量が増大し、供給汚泥
５中の固形物量が排出汚泥７中のそれを上回る状態が継
続するため、１！縮檜６内の汚泥界面が次第に高くなシ
、ついには濃縮檜越流堰を超えて１通常は、上澄水から
なる溢流水９中に混入し、最初沈：ａ池２．エアレーシ
ョンタンク３、最終沈シ殿池４等から構成されている水
処理系に負担を与える。For example, immediately after rain after a series of rainy days, a large amount of sludge that had accumulated in the sewage pipes due to rainwater flows into the sewage treatment plant, increasing the amount of sludge supplied, and the solids in the sludge 5 are increased. Since the amount continues to exceed that in discharged sludge 7, 1! The sludge interface in the shrunken cypress 6 gradually becomes higher, and finally exceeds the thickened cypress overflow weir and mixes into the overflow water 9, which is usually composed of supernatant water, and first settles: pond a2. This places a burden on the water treatment system, which is comprised of the aeration tank 3, final sedimentation tank 4, etc.

まｆｃ長期／ｌ（１ｍが続く時には、下水処理場に流入
する汚泥量が少なくなって供給汚泥量が減少する。When fc long term/l (1 m continues), the amount of sludge flowing into the sewage treatment plant decreases, and the amount of sludge supplied decreases.

すなわち供給汚泥５中の固形物量が排出汚泥７中のそれ
を下回る状態が継続することになる。That is, the state in which the amount of solids in the supplied sludge 5 is lower than that in the discharged sludge 7 continues.

そうなると、消化１１６へ投入される汚泥の良度が稀薄
になル、不必要な負荷を消化槽８へ与えてしまう。In this case, the quality of the sludge introduced into the digestion tank 116 becomes diluted, and an unnecessary load is applied to the digestion tank 8.

つまシ、排泥濃度が稀薄であれば消化槽８へすみやかに
投入する必要がないのに、投入されることになるので、
投入を行なわなければよシ一層消化槽８での処理が進む
はずのものが平均的な処理速度に低下してしまうことに
なる。If the waste sludge concentration is dilute, there is no need to immediately throw it into the digestion tank 8, but it will be thrown into the digestion tank 8.
If this is not done, the processing speed in the digestion tank 8 will be reduced to an average processing speed.

一般には特に前者の場合が多く、仁の磯縮檀溢流水９中
の固形物の蓋が、外部からの流入水中の固形物量に匹敵
するような状態で運転されている下水処理場が多い。In general, the former is particularly the case, and many sewage treatment plants are operated in such a state that the amount of solids in the overflow water 9 is comparable to the amount of solids in the water flowing in from the outside.

このため、濃縮４１６内の汚泥界面の高さ、または排出
汚泥７の牡度を監視することによって排出汚泥７の童を
制御している例も最近見受けられるが、証流水υ中への
汚泥の流出は、上記理由による碌縮＃ｉ６内汚泥界而の
上昇のはかに、濃縮槽６内での汚泥血貿時間が長すぎて
、沈殿していた汚泥が腐敗し浮上することがあるためこ
れらの方法だけでは最適な運転状態を実現できない。For this reason, there have recently been cases where the height of the discharged sludge 7 is controlled by monitoring the height of the sludge interface in the thickener 416 or the consistency of the discharged sludge 7; The outflow is due to the rise in the sludge level in the sludge #i6 due to the above reasons, and the sludge exchange time in the thickening tank 6 is too long, causing the settled sludge to rot and float to the surface. Optimal operating conditions cannot be achieved using these methods alone.

そこで本発明は１以上述べた、問題点のない濃縮槽の運
転方法を提供しようとするものである。SUMMARY OF THE INVENTION The present invention therefore seeks to provide a method of operating a thickening tank that is free from the problems mentioned above.

即ち１本発明は供給された汚泥を、所望の濃度に濃縮さ
れるのに必要な時間（例えば６時間）以上で１ｇ敗発発
泡至る時間（例えば１２時間ン未満の間の任意の設定時
間、濃縮槽６に滞留させたのち、排出されるよう運転す
る方法である。That is, the present invention provides a method for reducing the amount of sludge that is supplied to a desired concentration within a time required for concentrating the sludge to a desired concentration (e.g., 6 hours) or more for an arbitrary set period of time (e.g., less than 12 hours) for 1 g of foaming to occur (for example, less than 12 hours). This is a method of operation in which the water is retained in the concentration tank 6 and then discharged.

つまル、理想的状態では、供給汚泥中の固形物量と排出
汚泥中の固形物量は滞留時間分だけ隔てたものについて
比べた時は、常に等しくなるＬずである。との知見にも
とづくもので、具体的には。In other words, in an ideal state, the amount of solids in the supplied sludge and the amount of solids in the discharged sludge should always be equal when compared when separated by the residence time. Specifically, it is based on the knowledge that.

次に示す（１）式によって遅出される排出汚泥量Ｑｅｆ
に実際の検出値が等しくなるよう排出汚泥量を制御する
運転方法である。The amount of discharged sludge Qef that is delayed by the following equation (1)
This is an operation method that controls the amount of discharged sludge so that the actual detected value is equal to the actual detected value.

但し Ｑｅｆ（す：今回排出すべき排出汚泥量０ｅｆ（ｔ）：
現在の排出汚泥濃度 Ｑムｎ（を−幻：標準滞留時間几だけ過去の供給汚泥蓋 ０ｊｎ（を−几〕：標準涌留時間几だけ過去の供給汚泥
１１Ｉ腿 しかしながら２以上述べ′ｆｃ（０式にもとづく制御は
、無制限に行なわれるのではなく１種々の不適性状態に
応じて、修正したシ、一時中断して対処する必要がある
。However, Qef(su: Amount of discharged sludge to be discharged this time 0ef(t):
Current discharged sludge concentration Qmun (a - phantom: standard retention time 几 past supplied sludge lid 0jn (a - 几): standard retention time 几 past supplied sludge 11 I thighs However, 2 or more 'fc (0 Control based on formulas is not performed indefinitely, but must be corrected or temporarily interrupted in response to various inappropriate conditions.

そこで１本発明は制御計算機の機能を利用し。Therefore, one aspect of the present invention utilizes the functions of a control computer.

後で述べる３条件が全部満足される場合のみ上記（１）
式にもとづく制御全実行し、そうでない場合はすみやか
に３条件の番号の順に満足するように制御することによ
シ最適制御が行なわれるようにしたものである。(1) above only if all three conditions described later are satisfied.
Optimum control is performed by executing all the controls based on the formula, and if not, controlling so that the three conditions are quickly satisfied in the order of their numbers.

以下本発明の運転方法について図面に示す具体的実施例
に基づ＠説明する・ 第２図は本発明による重力沈降式濃縮槽制御装置のブロ
ックで、１１は重力凝縮４１６への汚泥供給ポンプ、１
２は供給汚泥１１Ｉ腿％　１３は供給汚泥１１Ｉ腿、１
４は界面追従装置つき汚泥界面計、１５は排泥弁、１６
は排泥ボンダ、１７は排出汚泥用流量計、１８は排出汚
泥用濃度計であルいずれも運転制御装置１９によって統
括されている。The operating method of the present invention will be explained below based on the specific embodiment shown in the drawings. Fig. 2 is a block diagram of the gravity settling type thickening tank control device according to the present invention, and 11 is a sludge supply pump to the gravity condensation 416; 1
2 is supply sludge 11I thigh% 13 is supply sludge 11I thigh, 1
4 is a sludge interface meter with an interface tracking device, 15 is a sludge drainage valve, 16
1 is a discharged sludge bonder, 17 is a discharged sludge flow meter, and 18 is a discharged sludge concentration meter, all of which are controlled by an operation control device 19.

次にその計測・制御について説明すると％重力濃縮槽６
への供給汚泥５は流量計１２と醜度計１３によって刻々
の流量Ｑｉｎと濃度Ｏｉｎが測定されてその値が運転制
御装置１９内の記憶部に記憶される。Next, to explain its measurement and control, % gravity concentration tank 6
The flow rate Qin and concentration Oin of the sludge 5 supplied to the sludge 5 are measured every moment by a flow meter 12 and an ugliness meter 13, and the values are stored in a storage section in the operation control device 19.

一方１重力磯縮檀６からの汚泥排出流ｊｔ　Ｑｅｆの目
標値は、濃度計１８による測定値Ｏｅｆと前記記憶部に
記憶されているところのその測定時刻ｔよシも設定標準
面質時間Ｒ（例えば９時間）分だけ過去の供給汚泥の流
量Ｑｌｎ（ｔ−１’Ｌ）および濃度０１０（ｔ−ＲＪを
使い前記（１）式に基づき運転制御装置１９内の演算部
で演算される。そして排出汚泥量が、上記計算値に一致
するように、排泥ポンプ１６を運転制御する。ただし、
運転制御装置１９の演算部には次の（＋）　（１０（ｉ
ｌの項目ｔ−６らかしめ設定しておくものとする。On the other hand, the target value of the sludge discharge flow jt Qef from the 1-gravity rock sanding 6 is determined by the measurement value Oef by the densitometer 18 and the measurement time t stored in the storage unit, as well as the standard surface quality time R. (for example, 9 hours) using the flow rate Qln (t-1'L) and concentration 010 (t-RJ) of the past supplied sludge, and is calculated by the calculation unit in the operation control device 19 based on the above equation (1). Then, the operation of the sludge pump 16 is controlled so that the amount of sludge discharged matches the above calculated value.However,
The calculation section of the operation control device 19 has the following (+) (10(i
It is assumed that item t-6 of item 1 is set for tightening.

（１）　汚泥界面がこれ以上畠くなってはならないとい
う汚泥界面上限値（Ｈｍａｘ）　：濃ｍ槽水深給汚泥の
増１を尋があっても、汚泥量が越流しないよう余裕をと
った値である。(1) Upper limit value (Hmax) of the sludge interface, which prevents the sludge interface from becoming a sludge anymore: Even if the sludge added to the thick tank water depth is increased by 1, a margin is set so that the sludge volume does not overflow. It is a value.

（ｌｉ）　これ以上長く滞留させではならないという最
大滞留時間（Ｉ葡ａｘ）　：これは、前述したように、
腐散発泡を防止するためである。前記設定標準面留時間
几は、尚然几（Ｒｍａｘである。(li) Maximum residence time (Iax): As mentioned above, this is the
This is to prevent spoilage and foaming. The set standard retention time is Rmax.

＜ｍ）これ以上薄くなってほしくないという排泥良度の
下限値（Ｕｍｉｎ　）　：これは前述したように消化槽
に不必要な負荷を与えないためである。<m) Lower limit value of sludge removal quality (Umin) at which the sludge should not be thinned any further: As mentioned above, this is to avoid unnecessary load on the digestion tank.

なお、汚泥界ｔ＝１Ｈの検出は、追従装置付汚泥界面Ｈ
↑１４にて連続的に行なわれるものとする。Note that the detection of the sludge interface t=1H is performed using the sludge interface H with a tracking device.
↑It shall be performed continuously at 14.

さて％（０式による制御が行なわれているにもかかわら
ず、　（ｌＹｊらかの理由で、前記項目中〜０ゆの制限
値に達する場合には１次のような制御が行なわれる。Now, even though control is performed using the %(0 formula), if the limit value of 0 to 0 in the above item is reached due to reasons such as (lYj), the following control is performed.

以下１条件に分けて説明すると次の通シである。The following is a general description of each condition.

（１）　排泥濃度Ｏｅｆが最低期待値０ｍ１ｎ　ｔ−下
回った場合（Ｏｅｆ＜０ｍ１ｎ、Ｒ（几ｍａｘ　、Ｈ＜
Ｈｍａｘのとき〕滞留時間を増やす、つまシ（Ｊｅｆ（
ＯｍＩｎを検出した時刻よシ１時間Δ几だけ排泥全停止
し。(1) When the sludge concentration Oef is lower than the minimum expected value 0m1n t- (Oef<0m1n, R(几max, H<
When Hmax] Increase the residence time.
Sludge removal was completely stopped for 1 hour ∆ from the time when OmIn was detected.

それ以後は（１２式のＲに几＋△Ｒを代入して決定され
る排泥１ｉｔＱｅｆで排泥を再開し様子を見る。After that, restart sludge removal at 1itQef, which is determined by substituting R+ΔR into R in equation 12, and observe the situation.

ｆｘオ、Ｏｅｆ＜ＯｍｔｎのままであればさらにΔＲだ
け滞留時間を増やす。fxO, if Oef<Omtn remains, the residence time is further increased by ΔR.

また、△几を増し続け、Ｒ＝几ｍａｘとなづてもなおＯ
ｅｆ（Ｏｍｉｎならば で排泥する。排泥ｍ度が低すぎるのは無視する。Also, △ continues to increase, and even if R = max, it is still O
If it is ef(Omin), remove the sludge with ef(Omin).Ignore the fact that the degree of sludge removal is too low.

運転を続けるうちにＯｄ　）　Ｏｍ　ｉ　ｎとなれば滞
留時間を減らし標準滞留時間に近づける。As the operation continues, if Od) Omin is reached, the residence time is reduced and brought closer to the standard residence time.

したがって、この時の排泥良度ははｌＹ：ｏｍ　ｉ　ｎ
に等しい状態が続く。滞留時間が標準滞留時間に戻って
Ｏｅｆ＞ｏｍｒｎ″ｔ’あっても、それよ少短かい滞留
時間は設定されない。Therefore, the quality of sludge removal at this time is
continues to be equal to . Even if the residence time returns to the standard residence time and Oef>omrn''t', a shorter residence time is not set.

■　汚゛泥界面Ｈが上限値Ｈｍａｘを上回った場合。■ When the sludge interface H exceeds the upper limit Hmax.

次の２通シの場合がある。In some cases, the following two letters may be sent.

ＣＭ−ａ） 流入固形物量が異常に多くなった時は、それまでは標準
滞留時間による排泥が続いていたはずであるから、Ｏｅ
ｆ＞０ｍ１ｎ したかつてとに角、　Ｑｅｆ　ｆ増し界面を下げること
につとめ、同時にＯｅｆは監視しつづける。CM-a) When the amount of inflowing solids becomes abnormally large, sludge removal must have continued according to the standard residence time, so Oe
Once f>0m1n, Qef increases f and strives to lower the interface, while at the same time Oef continues to be monitored.

槽内汚泥高さが浅くなれば、必ずＯｅｆ（Ｏｍｉｎとな
る。そうなったら標準滞留時間による排泥に戻す。If the sludge height in the tank becomes shallow, it will definitely become Oef (Omin). If that happens, return to sludge removal using the standard residence time.

＜ｎ−ｂ） 前記（１）の制御が行なわれると界面高さはそれまでよ
シも高くなる。その結果Ｈ≧Ｈｍａｘとず、できるだけ
高い汚泥界面高さとＲｍａｘをこえずできるだけ長い滞
留時間を保つことによってできるだけ汚泥の圧＠を図シ
、性状が回復するまで待つ。<n-b) When the control described in (1) above is performed, the interface height becomes higher than before. As a result, H≧Hmax, the sludge pressure is kept as high as possible by keeping the sludge interface height as high as possible and the residence time as long as possible without exceeding Rmax, and wait until the properties are recovered.

以上の運転制御ラフローチャートで示すと第３図の通シ
である。The above operation control rough flowchart is shown in FIG. 3.

以上説明したように１本発明によれば１重力沈降式濃ａ
槽６を前後ノ′ロセスに負担をかけることなく最適な状
態で運転制御することが可能である。As explained above, according to the present invention, gravity sedimentation type
It is possible to control the operation of the tank 6 in an optimal state without putting a burden on the front and rear processes.

また重力濃縮槽の後段設備である消化ｗ８は。In addition, the digestion w8 is the downstream equipment of the gravity concentrator.

汚泥ｔ−ｍ気性消化することにようで、その減量化、安
定化を図る目的の設備であるが、反応が極めて緩慢であ
るため一般に３０日前後の滞留日数となるような大きさ
を持っている。The purpose of this equipment is to reduce and stabilize sludge by pneumatic digestion, but because the reaction is extremely slow, the sludge is generally kept for around 30 days. There is.

したがって上記の重力濃縮槽６が異常排泥時の運転方法
をとることがあってもそれが短期間であれば消化槽８に
位十分な緩衝作用があシ大きな負荷とならない。Therefore, even if the gravity thickening tank 6 is operated in the case of abnormal sludge removal, if it is for a short period of time, the digestion tank 8 will have sufficient buffering action and will not be subjected to a large load.

この３０日前後という消化槽８′のＩＮ留日数は一時的
な＾負荷を考慮した上での平均的な数値であるため１通
常時に上記方法で重力濃縮４ｗ排出汚泥の濃度と量を管
理することは消化槽の負荷を軽減するという効果もある
。This 30 days or so, which is the number of days the digester 8' stays in the digester, is an average value after taking into account the temporary load, so the concentration and amount of the gravity-thickened 4w discharged sludge should be controlled using the above method during normal times. This also has the effect of reducing the load on the digester.

【図面の簡単な説明】[Brief explanation of the drawing]

第１図は、下水処理場の概略図、第２図は本発明による
制御装置の一例を示すブロック図、第３図は、動作を示
す７０−チャートである。 ５・・・供給汚泥　６・・・重力濃縮槽７・・・濃縮汚
泥　１１・・・汚泥供給ボンダ１２・・・供給汚泥用流
菫計１３・・・供給汚泥用線度計１４・・・汚泥界面計
　１５・・・排泥弁１６・・・排泥ボンダ　１７・・・
排出汚泥用流量計１８・・・排出汚泥用濃度Ｉｒｔ１９
・・・運転制御装置“、≦・ｉ、−にFIG. 1 is a schematic diagram of a sewage treatment plant, FIG. 2 is a block diagram showing an example of a control device according to the present invention, and FIG. 3 is a 70-chart showing the operation. 5...Supplied sludge 6...Gravity thickening tank 7...Thickened sludge 11...Sludge supply bonder 12...Flow meter for supplied sludge 13... Linearity meter for supplied sludge 14... Sludge interface meter 15... Sludge valve 16... Sludge bonder 17...
Flow meter 18 for discharged sludge... Concentration for discharged sludge Irt19
...Operation control device ", ≦・i, -

Claims (1)

【特許請求の範囲】 供給汚泥と排出汚泥の各流蓋計及び濃度計と、濃縮槽内
の汚泥界面を測定する界面追従装置付汚泥界面計と、排
泥ポンプとその運転制御装置とを具備し、該運転制御装
置位前記流量針、濃度計及び汚泥界面計の検出値を入力
信号として前記排泥ポンプを下記のように制御すること
ｖｉ−特徴とする重力沈降式濃縮槽運転方法。 （ａ）　次の条件中および（ｌｉ）を満足する場合にの
み。 あらかじめ設定した標準滞留時間ごとに、排出汚泥Ｊｔ
ｆｆｉ次式によって算出される量だけ排泥するよう排泥
ポンプを制御する。 条件（１）　汚泥界面があらかじめ設定した上限以下で
あること。 条件（ＩＤ　排泥濃度があらかじめ設定した下限以上で
あること。 但し。 Ｑｅｆ　（す：今回排出すべき排出汚泥量Ｕｅｆ（ｔ）
’現在の排出汚泥濃度 Ｑｉｎ（ｔ　−Ｒ）　：標準滞留時間Ｒだけ過去の供給
汚泥量 ０ｉｎ（ｔ　−Ｒ）　：標準滞留時間几だけ過去の供給
汚泥濃度 （ｂ）前記（ａ）にもとづく運転中に、前記条件（１）
が満たされなくなったときは、排出汚泥濃度の状態によ
って、次の２通シの制御ｌを行なう。 （ｂ−１，１排出汚泥量度が下限よシ高いときは。 排出汚泥量を増量し、汚泥界面を下げ。 排出汚泥濃度が下限に違すれば１手段（ａ）に復帰する
よう排泥ポンプを制御する。 （ｂ−２，）排出汚泥濃度が下限以下のとき鉱、できる
だけ高い汚泥界面（上限以下）と。 できるだけ長い滞留時間（最大滞留時間以下Ｊｔ−保っ
て性状側Ｏ１金待ち１回復後。 手段（ωに復帰するよう排泥ポンプを制御する。。 ＣＣ）　前記（ａ）にもとづく運転中に％前記条件（１
１）が満たされなくなったときは、（１式中の標準滞留
時間を長い時間に設定し直して排泥ポンプを制御する。[Scope of Claims] Equipped with flow cap meters and concentration meters for supplied sludge and discharged sludge, a sludge interface meter with an interface tracking device for measuring the sludge interface in the thickening tank, and a sludge pump and its operation control device. A method for operating a gravity settling thickening tank, characterized in that the operation control device controls the sludge pump in the following manner using detected values of the flow rate needle, concentration meter, and sludge interface meter as input signals. (a) Only if the following conditions and (li) are satisfied: Discharged sludge Jt every preset standard retention time
ffi The sludge pump is controlled to remove sludge by the amount calculated by the following equation. Condition (1) The sludge interface must be below a preset upper limit. Conditions (ID: The sludge concentration must be higher than the preset lower limit. However, Qef: Amount of discharged sludge that should be discharged this time Uef (t)
'Current discharged sludge concentration Qin (t - R): Past supplied sludge amount for standard residence time R 0 in (t - R): Past supplied sludge concentration for standard residence time (b) Operation based on (a) above Among them, the above condition (1)
When this is no longer satisfied, the following two controls are carried out depending on the state of the discharged sludge concentration. (b-1, 1 When the amount of discharged sludge is higher than the lower limit, increase the amount of discharged sludge and lower the sludge interface. If the concentration of discharged sludge is different from the lower limit, set the sludge pump to return to method 1 (a). (b-2,) When the discharged sludge concentration is below the lower limit, the sludge interface is as high as possible (below the upper limit) and the residence time is as long as possible (below the maximum residence time Jt-Keep the property side O1 gold waiting 1 recovery After. Means (control the sludge pump so as to return to
When 1) is no longer satisfied, the standard residence time in set 1 is reset to a longer time and the sludge pump is controlled.