曝氣增氧系統(tǒng)頻繁應(yīng)用于污水處理、水產(chǎn)養(yǎng)殖、水生態(tài)治理等場(chǎng)景中。那么曝氣增氧系統(tǒng)都有什么設(shè)備組成呢？今天，我們一起來(lái)探討一下！

       一、曝氣原理

　　1.曝氣及其作用

　　曝氣是采用相應(yīng)的設(shè)備和技術(shù)措施，使空氣中的氧轉(zhuǎn)移到混合液中而被微生物利用的過(guò)程。曝氣的主要作用除供氧外，還起攪拌混合作用，使曝氣池內(nèi)的活性污泥保持懸浮狀態(tài)，與污水充分接觸混合，從而提高傳質(zhì)效率，保證曝氣池的處理效果。

　　2.氧轉(zhuǎn)移原理

　　空氣中的氧通過(guò)曝氣傳遞到混合液中，氧由氣相向液相中轉(zhuǎn)移，**被微生物所利用。這種轉(zhuǎn)移通常以雙膜理論為理論基礎(chǔ)。雙膜理論認(rèn)為，在氣-水界面上存在著氣膜和液膜，當(dāng)氣液兩相做相對(duì)運(yùn)動(dòng)時(shí)，氣膜和液膜間屬層流狀態(tài)，而在其外的兩相體系中均為紊流，氧的轉(zhuǎn)移是通過(guò)氣、液膜間進(jìn)行的分子擴(kuò)散和在膜外進(jìn)行的對(duì)流擴(kuò)散完成的。對(duì)于難溶于水的氧來(lái)說(shuō)，分子擴(kuò)散的阻力大于對(duì)流擴(kuò)散，傳遞的阻力主要集中在液膜上。因此，采用曝氣攪拌是快速變換氣-水界面克服液膜阻力的*有效方法。

　　二、曝氣裝置

　　曝氣裝置，又名空氣擴(kuò)散裝置，是活性污泥系統(tǒng)的重要設(shè)備，按曝氣方式可將其分為鼓風(fēng)曝氣和機(jī)械曝氣兩大類。

　　衡量曝氣裝置的主要技術(shù)性能指標(biāo)有動(dòng)力效率(EP)，氧的利用效率(EA)和氧的轉(zhuǎn)移效率(EL)。動(dòng)力效率是每消耗1kW電能轉(zhuǎn)移到混合液中的氧量(kg/kWh);氧的利用效率是通過(guò)鼓風(fēng)曝氣轉(zhuǎn)移到混合液中的氧量，占總供氧量的百分比(%);氧的轉(zhuǎn)移效率也稱充氧能力，是通過(guò)機(jī)械曝氣裝置，在單位時(shí)間內(nèi)轉(zhuǎn)移到混合液中的氧量(kg/ h)。

　　1.鼓風(fēng)曝氣裝置

　　鼓風(fēng)曝氣系統(tǒng)由鼓風(fēng)機(jī)、曝氣裝置和空氣輸送管道組成。鼓風(fēng)機(jī)將空氣通過(guò)一系列管道輸送到安裝于曝氣池底部的曝氣裝置，經(jīng)過(guò)曝氣裝置，將空氣中的氧轉(zhuǎn)移到混合液中去。

　　鼓風(fēng)曝氣系統(tǒng)的曝氣裝置主要分為微氣泡、中氣泡、水力剪切、水力沖擊等類型。

　　(1)微氣泡曝氣器

　　也稱多孔性空氣擴(kuò)散裝置，采用多孔材料如陶粒、粗瓷等摻以適當(dāng)?shù)娜绶尤?shù)脂一類的粘合劑，在高溫下燒結(jié)成為擴(kuò)散板、擴(kuò)散管和擴(kuò)散罩的形式。

　　這一類擴(kuò)散裝置的特點(diǎn)是產(chǎn)生微小氣泡，氣、液接觸面積大，氧利用率高;缺點(diǎn)是氣壓損失大，易堵塞，送入的空氣應(yīng)預(yù)先通過(guò)過(guò)濾處理。

　　1)固定式平板型微孔曝氣器

　　平板型微孔曝氣器主要組成包括擴(kuò)散板、布?xì)獾妆P、通氣螺栓、配氣管、三通短管、橡膠密封圈、壓蓋和連接池底的配件等。

　　常見(jiàn)的平板型微孔曝氣器有鈦板微孔曝氣器、微孔陶板、青剛玉和綠剛玉為骨料燒結(jié)成的曝氣板。其主要技術(shù)參數(shù)：平均孔徑100～200μm;服務(wù)面積0.3～0.75m2/個(gè);動(dòng)力效率4～6kgO2/kWh;氧利用率20%～25%。

　　2)固定式鐘罩型微孔曝氣器

　　有微孔陶瓷鐘罩型盤、青剛玉骨料燒結(jié)成的鐘罩型盤。技術(shù)參數(shù)與平板型微孔曝氣器基本相同。

　　3)膜片式微孔曝氣器

　　該曝氣器的底部為聚丙烯制作的底座，底座上覆蓋著合成橡膠制成的微孔膜片，膜片被金屬絲箍固定在底座上。在膜片上開(kāi)有按同心圓形式布置的孔眼。鼓風(fēng)時(shí)，空氣通過(guò)底座上的通氣孔進(jìn)入膜片和底座之間，使膜片微微鼓起，孔眼張開(kāi)，空氣從孔眼逸出，達(dá)到布?xì)鈹U(kuò)散的目的。供氣停止，壓力消失，在膜片的彈性作用下，孔眼自動(dòng)閉合，由于水壓的作用膜片壓實(shí)在底座之上。曝氣池內(nèi)的混合液不能倒流，因此，不會(huì)堵塞膜片孔眼。這種曝氣器可擴(kuò)散出直徑為1.5～3.0mm的氣泡，即使空氣中含有少量塵埃，也可以通過(guò)孔眼，不會(huì)堵塞，也不需設(shè)除塵設(shè)備。

　　(2)中氣泡曝氣器

　　這種裝置產(chǎn)生的氣泡直徑2～6mm，在過(guò)去主要是穿孔管。穿孔管由鋼管或塑料管制成，直徑25～50mm，在管壁兩側(cè)下部開(kāi)直徑3～5mm的孔眼，間距50～100mm。穿孔管不易堵塞，構(gòu)造簡(jiǎn)單，阻力小;但氧的利用率低，動(dòng)力效率低。因此，目前在活性污泥曝氣池中較少采用。

　　網(wǎng)狀膜曝氣器是近年來(lái)開(kāi)發(fā)出的具有代表性的中氣泡曝氣器。其特點(diǎn)是不易堵塞，布?xì)饩鶆?，?gòu)造簡(jiǎn)單，便于維護(hù)管理，氧的利用率較高。

　　該曝氣器由主體、螺蓋、網(wǎng)狀膜、分配器和密封圈所組成;空氣由曝氣器底部進(jìn)入，經(jīng)分配器**次切割并均勻分配到氣室，然后通過(guò)網(wǎng)狀膜進(jìn)行二次切割，形成微小氣泡擴(kuò)散到混合液中。

　　每個(gè)網(wǎng)狀膜曝氣器的服務(wù)面積為0.5 m2，動(dòng)力效率2.7～3.7kgO2/kWh，氧利用率12%～15%。

　　(3)水力剪切式空氣曝氣器

　　1)倒傘式曝氣器

　　倒傘式曝氣器由傘形塑料殼體、橡膠板、塑料螺桿和壓蓋等組成?？諝鈴纳喜窟M(jìn)氣管進(jìn)入，由傘形殼體和橡膠板間的縫隙向周邊噴出，在水力剪切的作用下，空氣泡被剪切成小氣泡。停止供氣，借助橡膠板的回彈力，使縫隙自行封口，防止混合液倒灌。

　　該曝氣器的服務(wù)面積為6×2m2;動(dòng)力效率1.75～2.88kgO2/kWh，氧利用率6.5%～8.5%。

　　2)固定螺旋曝氣器

　　該曝氣器由直徑300或400mm、高1500mm的圓形外殼和固定在殼體內(nèi)部的螺旋葉片組成，每個(gè)螺旋葉片扭曲180o，兩個(gè)相鄰葉片的螺旋方向相反?？諝庥刹?xì)夤軓牡撞康牟細(xì)饪走M(jìn)入裝置內(nèi)，向上流動(dòng)，由于殼體內(nèi)外混合液的密度差，產(chǎn)生**作用，使混合液在殼體內(nèi)外不斷循環(huán)流動(dòng)?？諝馀菰谏仙^(guò)程中，被螺旋葉片反復(fù)切割，形成小氣泡。

　　該曝氣器有固定單螺旋、固定雙螺旋和固定三螺旋三種形式。

　　(4)水力沖擊式曝氣器

　　該種曝氣器以射流式空氣擴(kuò)散裝置為主，利用水泵打入的泥、水混合液的高速水流的動(dòng)能，吸入大量空氣，泥、水、氣混合液在喉管中強(qiáng)烈混合攪動(dòng)，將氣泡粉碎為霧狀，使氧迅速轉(zhuǎn)移至混合液中，氧的轉(zhuǎn)移率可高達(dá)20%，但動(dòng)力效率不高。近年來(lái)，由于泵的防水性能的改進(jìn)，已實(shí)現(xiàn)動(dòng)力裝置和擴(kuò)散裝置的一體化。

　　2.機(jī)械曝氣裝置

　　機(jī)械曝氣裝置安裝在曝氣池水面上、下，在動(dòng)力的驅(qū)動(dòng)下進(jìn)行轉(zhuǎn)動(dòng)，通過(guò)下述3方面的作用使空氣中的氧轉(zhuǎn)移到污水中去：曝氣裝置轉(zhuǎn)動(dòng)時(shí)，表面的混合液不斷地從曝氣裝置周邊拋向四周，形成水躍，液面劇烈攪動(dòng)，卷入空氣;曝氣裝置轉(zhuǎn)動(dòng)，具有**液體的作用，使池內(nèi)混合液連續(xù)上下循環(huán)流動(dòng)，氣液接觸界面不斷更新，不斷地使空氣中的氧向液體內(nèi)轉(zhuǎn)移;曝氣裝置轉(zhuǎn)動(dòng)，在其后側(cè)形成負(fù)壓區(qū)，吸入空氣。

　　按轉(zhuǎn)動(dòng)軸的安裝方向，機(jī)械曝氣裝置可分為豎軸式和臥軸式兩類。

　　(1)豎軸式曝氣裝置

　　又稱豎軸葉輪曝氣機(jī)，常用的曝氣葉輪有泵型葉輪、倒傘型葉輪、平板型葉輪等，見(jiàn)圖6-8。

　　曝氣葉輪的充氧能力和**能力與葉輪直徑、葉輪旋轉(zhuǎn)速度和浸液深度等因素有關(guān)。葉輪直徑一定，葉輪旋轉(zhuǎn)的線速度大，充氧能力也強(qiáng)，但線速度過(guò)大時(shí)，會(huì)打碎活性污泥顆粒，影響沉淀效率。一般葉輪周邊線速度以2～5m/s為宜。葉輪浸液深度適當(dāng)時(shí)，充氧效率高，浸液深度過(guò)大，沒(méi)有水躍產(chǎn)生，葉輪只起攪拌作用，充氧量極小，甚至沒(méi)有空氣吸入，浸液深度過(guò)小，則提水和輸水作用減小，池內(nèi)水流緩慢，甚至存在死區(qū)，造成表面水充氧好，而底層充氧不足。因此，常將葉輪旋轉(zhuǎn)的線速度和浸液深度設(shè)計(jì)成可調(diào)的，以便運(yùn)行中隨時(shí)調(diào)整。一般豎軸葉輪曝氣機(jī)的氧轉(zhuǎn)移率為15%～25%，動(dòng)力效率為2.5～3.5kgO2/kWh。

　　(2)臥軸式曝氣裝置

　　臥軸式曝氣裝置主要是轉(zhuǎn)刷曝氣器。由水平轉(zhuǎn)軸和固定在軸上的葉片所組成，轉(zhuǎn)軸帶動(dòng)葉片轉(zhuǎn)動(dòng)，攪動(dòng)水面濺成水花，空氣中的氧通過(guò)氣液界面轉(zhuǎn)移到水中。

　　轉(zhuǎn)刷曝氣器主要用于氧化溝，它具有負(fù)荷調(diào)節(jié)方便、維護(hù)管理容易、動(dòng)力效率高等優(yōu)點(diǎn)。

　　三、曝氣池池型

　　活性污泥法處理污水的主要構(gòu)筑物是曝氣池。按混合液在曝氣池中的流態(tài)可分為推流式、完全混合式和循環(huán)混合式三種池型;按平面幾何形狀可分為長(zhǎng)方形、廊道形、圓形、方形和環(huán)形跑道形四種;按所采用的曝氣方法可分為鼓風(fēng)曝氣池、機(jī)械曝氣池和兩種方法聯(lián)合使用的機(jī)械-鼓風(fēng)曝氣池;按曝氣池和二次沉淀池的關(guān)系可分為曝氣-沉淀合建式和分建式兩種。

　　1.推流式曝氣池

　　推流式曝氣池多為長(zhǎng)方廊道形，常采用鼓風(fēng)曝氣。傳統(tǒng)的作法是將空氣擴(kuò)散裝置安裝在曝氣池廊道底部的一側(cè)，這樣布置可使水流在池中呈螺旋狀流動(dòng)，提高氣泡和混合液的接觸時(shí)間。如果曝氣池的寬度較大，則應(yīng)考慮將空氣擴(kuò)散裝置安裝在曝氣池廊道底部的兩側(cè)。也可按一定的形式，如互相垂直的正交形式或呈梅花形交錯(cuò)式均衡地布置在整個(gè)曝氣池池底。

　　曝氣池的數(shù)目隨污水處理廠的規(guī)模而定，一般在結(jié)構(gòu)上分成若干單元，每個(gè)單元包括一座或幾座曝氣池，每座曝氣池常由1個(gè)或2～5個(gè)廊道組成。當(dāng)廊道數(shù)為單數(shù)時(shí)，污水的進(jìn)、出口在曝氣池的兩端;而廊道數(shù)為雙數(shù)時(shí)，則位于廊道的同一端。

　　曝氣池廊道的長(zhǎng)度可達(dá)100m，一般以50～70m為宜。為了防止短流，廊道的長(zhǎng)度和寬度之比應(yīng)大于5，甚至大于10。曝氣池的寬深比常在1.5～2之間。池深與造價(jià)和動(dòng)力費(fèi)用密切相關(guān)。池深大，有利于氧的利用，但造價(jià)和動(dòng)力費(fèi)用將有所提高。反之，造價(jià)和動(dòng)力費(fèi)用降低，但氧的利用率也將降低。

　　此外，還應(yīng)考慮土建結(jié)構(gòu)和曝氣池的功能要求、允許占用的土地面積，能夠購(gòu)置到的鼓風(fēng)機(jī)所具有的壓力等因素。目前我國(guó)對(duì)推流式曝氣池采用的深度多為3～5m。

　　為了使混合液在曝氣池內(nèi)的旋轉(zhuǎn)流動(dòng)能夠減少阻力，并避免形成死區(qū)，將廊道橫剖面池壁兩墻的墻頂和墻腳作成45°斜面。為了節(jié)約空氣管道，相鄰廊道的空氣擴(kuò)散裝置常沿公共隔墻布置。

　　曝氣池的進(jìn)水口和進(jìn)泥口均設(shè)于水面以下，采用淹沒(méi)出流方式，以免形成短流，并設(shè)閘門以調(diào)節(jié)流量;出水一般采用溢流堰的方式，處理水流過(guò)堰頂，溢流入排水渠道。

　　在曝氣池底部設(shè)直徑為80～100mm放空管，用于維修或池子清洗時(shí)放空?？紤]到在活性污泥培養(yǎng)、馴化周期排放上清液的要求，根據(jù)具體情況，在距池底一定距離處設(shè)2～3根排水管，直徑也是80～100mm。

　　2.完全混合曝氣池

　　完全混合曝氣池常采用表面機(jī)械曝氣裝置供氧，其表面多呈圓形、方形或多邊形。使用較多的是合建式完全混合曝氣沉淀池，簡(jiǎn)稱曝氣沉淀池，由曝氣區(qū)、導(dǎo)流區(qū)和沉淀區(qū)3部分組成。

　　1)曝氣區(qū)

　　曝氣裝置設(shè)于池頂部中央，并深入水下某一深度。污水從池底部進(jìn)入，并立即與池內(nèi)原有混合液完全混合，并與從沉淀區(qū)回流縫回流的活性污泥充分混合、接觸。經(jīng)過(guò)曝氣反應(yīng)后的污水從位于頂部四周的回流窗流出并導(dǎo)入導(dǎo)流區(qū)。回流窗設(shè)有活門，可以通過(guò)調(diào)節(jié)窗孔大小，控制回流污泥量。

　　2)導(dǎo)流區(qū)

　　位于曝氣區(qū)和沉淀區(qū)之間，寬度一般在0.6m左右，高約1.5m。內(nèi)設(shè)豎向擋流板，起緩沖水流作用，并在此釋放混合液中挾帶的氣泡，使水流平穩(wěn)進(jìn)入沉淀區(qū)，為固液分離創(chuàng)造良好條件。

　　3)沉淀區(qū)

　　位于導(dǎo)流區(qū)和曝氣區(qū)的外側(cè)，其作用是泥水分離，上部為澄清區(qū)，下部為污泥區(qū)。澄清區(qū)的深度不宜小于1.5m，污泥區(qū)的容積應(yīng)不小于2h的存泥量。澄清的處理水沿設(shè)于池四周的出流堰進(jìn)入排水槽，出流堰常采用鋸齒狀的三角堰。

　　污泥通過(guò)回流縫回流曝氣區(qū)，回流縫一般寬0.15～0.20m，在回流縫上側(cè)設(shè)池裙，以避免死角。在污泥區(qū)的一定深度設(shè)排泥管，以排出剩余污泥。

　　在生產(chǎn)實(shí)踐中還有與沉淀池分建的完全混合曝氣池。污水和回流污泥沿曝氣池池長(zhǎng)均勻引入，并均勻地排出混合液，進(jìn)入二次沉淀池。

      簡(jiǎn)單來(lái)說(shuō)，常見(jiàn)的污水處理、水產(chǎn)養(yǎng)殖、水生態(tài)治理場(chǎng)景中的曝氣增氧系統(tǒng)分別由鼓風(fēng)機(jī)、曝氣盤、管道、閥門等設(shè)備組成！

　　Aeration system is frequently used in sewage treatment, aquaculture, water ecological treatment and other scenarios. What are the components of the aeration and oxygenation system? Today, let's discuss it together!

　　1、 Aeration principle

　　1. aeration and its function

　　Aeration is a process in which the oxygen in the air is transferred to the mixed liquid and utilized by microorganisms by using corresponding equipment and technical measures. The main function of aeration is not only to supply oxygen, but also to stir and mix, so as to keep the activated sludge in the aeration tank suspended and fully contact and mix with the sewage, so as to improve the mass transfer efficiency and ensure the treatment effect of the aeration tank.

　　2. oxygen transfer principle

　　The oxygen in the air is transferred to the mixed liquid through aeration. The oxygen is transferred from the gas phase to the liquid phase and finally used by microorganisms. This kind of transfer is usually based on the double membrane theory. According to the double film theory, there are gas film and liquid film on the gas-water interface. When the gas-liquid two phases move relative to each other, the gas film and liquid film are in a laminar state, while the outer two-phase system is turbulent. The transfer of oxygen is completed through the molecular diffusion between the gas and liquid films and the convective diffusion outside the film. For water-insoluble oxygen, the resistance of molecular diffusion is greater than that of convective diffusion, and the transfer resistance is mainly concentrated on the liquid membrane. Therefore, aeration agitation is the most effective method to quickly change the air-water interface to overcome the liquid film resistance.

　　The aeration and oxygenation system is composed of a fan, an aeration device and an air delivery pipe

　　2、 Aerator

　　Aeration device, also known as air diffusion device, is an important equipment of activated sludge system. According to aeration mode, it can be divided into blast aeration and mechanical aeration.

　　The main technical performance indicators of the aerator are power efficiency (EP), oxygen utilization efficiency (EA) and oxygen transfer efficiency (EL). Power efficiency is the amount of oxygen (kg/kwh) transferred to the mixture for every 1kW of electric energy consumed; The utilization efficiency of oxygen is the percentage (%) of the oxygen transferred to the mixed liquid through blast aeration; The oxygen transfer efficiency, also known as the oxygen charging capacity, is the amount of oxygen (kg/ h) transferred to the mixed liquid in unit time through the mechanical aeration device.

　　1. blast aeration device

　　The blast aeration system consists of a blower, an aeration device and an air transmission pipeline. The blower transmits the air to the aeration device installed at the bottom of the aeration tank through a series of pipes, and the oxygen in the air is transferred to the mixed liquid through the aeration device.

　　The aeration devices of the blast aeration system are mainly divided into micro bubble, medium bubble, hydraulic shear, hydraulic impact and other types.

　　(1) Microbubble aerator

　　It is also called porous air diffusion device. Porous materials such as ceramsite and coarse porcelain are mixed with appropriate adhesives such as phenolic resin, and sintered into the form of diffusion plate, diffusion tube and diffusion cover at high temperature.

　　This kind of diffusion device is characterized by producing tiny bubbles, large gas-liquid contact area and high oxygen utilization rate; The disadvantage is that the air pressure loss is large and it is easy to be blocked. The incoming air should be filtered in advance.

　　1) Fixed plate type microporous aerator

　　The plate type microporous aerator is mainly composed of a diffuser, an air distribution chassis, a vent bolt, a gas distribution pipe, a tee short pipe, a rubber sealing ring, a gland and accessories connecting the bottom of the tank.

　　Common plate type microporous aerators include titanium plate microporous aerators, microporous ceramic plates, and aerated plates made of green corundum and green corundum. Its main technical parameters: average aperture 100 ~ 200 μ m; Service area: 0.3 ~ 0.75m2/ unit; Power efficiency 4 ～ 6kgo2/kwh; The oxygen utilization rate is 20% ~ 25%.

　　2) Fixed bell jar type microporous aerator

　　There are microporous ceramic bell shaped disc and green corundum aggregate sintered bell shaped disc. The technical parameters are basically the same as those of the plate type microporous aerator.

　　3) Diaphragm microporous aerator

　　The bottom of the aerator is a base made of polypropylene, which is covered with a microporous membrane made of synthetic rubber, and the membrane is fixed on the base by a metal wire hoop. The diaphragm is provided with holes arranged in the form of concentric circles. During air blowing, the air enters between the diaphragm and the base through the vent hole on the base, so that the diaphragm is slightly inflated, the eyelet is opened, and the air escapes from the eyelet to achieve the purpose of air distribution and diffusion. The air supply stops and the pressure disappears. Under the elastic action of the diaphragm, the eyelet closes automatically. Due to the action of water pressure, the diaphragm is compacted on the base. The mixed liquid in the aeration tank cannot flow back, so it will not block the diaphragm holes. The aerator can diffuse bubbles with a diameter of 1.5 ~ 3.0mm. Even if there is a small amount of dust in the air, it can pass through the eyelet without blocking, and no dust removal equipment is required.

　　(2) Medium bubble aerator

　　The diameter of bubbles produced by this device is 2 ~ 6mm. In the past, they were mainly perforated tubes. The perforated pipe is made of steel pipe or plastic pipe with a diameter of 25 ~ 50mm. Holes with a diameter of 3 ~ 5mm are opened at the lower part of both sides of the pipe wall with a spacing of 50 ~ 100mm. The perforated pipe is not easy to be blocked, with simple structure and small resistance; However, the utilization rate of oxygen is low and the power efficiency is low. Therefore, it is seldom used in the activated sludge aeration tank at present.

　　Reticulated membrane aerator is a representative medium bubble aerator developed in recent years. The utility model is characterized by not easy blockage, uniform gas distribution, simple structure, easy maintenance and management, and high oxygen utilization rate.

　　The aerator is composed of a main body, a screw cap, a mesh membrane, a distributor and a sealing ring; The air enters from the bottom of the aerator, is cut by the distributor for the first time and evenly distributed to the air chamber, and then is cut through the mesh membrane for the second time to form tiny bubbles and diffuse into the mixed liquid.

　　The service area of each reticular membrane aerator is 0.5 m2, the dynamic efficiency is 2.7 ~ 3.7kgo2/kwh, and the oxygen utilization rate is 12% ~ 15%.

　　(3) Hydraulic shear air aerator

　　1) Inverted umbrella aerator

　　The inverted umbrella aerator is composed of an umbrella shaped plastic shell, a rubber plate, a plastic screw and a gland. The air enters from the upper air inlet pipe and is ejected from the gap between the umbrella shell and the rubber plate to the periphery. Under the action of hydraulic shear, the air bubble is sheared into small bubbles. Stop the gas supply and seal the gap by itself with the help of the resilience of the rubber plate to prevent the backflow of the mixed liquid.

　　The service area of the aerator is 6 × 2m2; The power efficiency is 1.75 ~ 2.88kgo2/kwh, and the oxygen utilization rate is 6.5% ~ 8.5%.

　　2) Fixed spiral aerator

　　The aerator is composed of a circular shell with a diameter of 300 or 400mm and a height of 1500mm and spiral blades fixed inside the shell. Each spiral blade is twisted 180 o, and the spiral directions of two adjacent blades are opposite. The air enters the device from the air distribution hole at the bottom through the air distribution pipe and flows upward. Due to the density difference of the mixed liquid inside and outside the shell, the lifting effect is generated, making the mixed liquid circulate continuously inside and outside the shell. During the rising process, the air bubble is repeatedly cut by the spiral blade to form small bubbles.

　　The aerator has three forms: fixed single screw, fixed double screw and fixed triple screw.

　　(4) Hydraulic impact aerator

　　This kind of aerator is mainly a jet type air diffusion device. It uses the kinetic energy of the high-speed water flow of the mud water mixture pumped by the water pump to suck in a large amount of air. The mud water air mixture is strongly mixed and stirred in the throat, crushing the bubbles into mist, so that oxygen can be quickly transferred to the mixture. The oxygen transfer rate can be as high as 20%, but the power efficiency is not high. In recent years, due to the improvement of the waterproof performance of the pump, the integration of the power device and the diffusion device has been realized.

　　2. mechanical aeration device

　　The mechanical aeration device is installed above and below the water surface of the aeration tank and rotates under the driving of power to transfer the oxygen in the air to the sewage through the following three aspects: when the aeration device rotates, the mixed liquid on the surface is constantly thrown from the periphery of the aeration device to form a hydraulic jump, and the liquid level is violently agitated and drawn into the air; The rotation of the aeration device has the function of lifting the liquid, making the mixed liquid in the pool circulate up and down continuously, and the gas-liquid contact interface is constantly updated, constantly transferring the oxygen in the air to the liquid; The aeration device rotates to form a negative pressure zone at its rear side to inhale air.

　　According to the installation direction of rotating shaft, mechanical aerators can be divided into vertical shaft type and horizontal shaft type.

　　(1) Vertical shaft aerator

　　Also known as vertical shaft impeller aerator, commonly used aeration impellers include pump impeller, inverted umbrella impeller, flat plate impeller, etc., as shown in Figure 6-8.

　　The oxygen charging capacity and lifting capacity of aeration impeller are related to impeller diameter, impeller rotation speed and immersion depth. With a certain impeller diameter, the impeller rotates at a large linear speed and has a strong oxygenation capacity. However, if the linear speed is too large, the activated sludge particles will be broken and the sedimentation efficiency will be affected. Generally, the peripheral linear speed of the impeller should be 2 ~ 5m/s. When the immersion depth of the impeller is appropriate, the oxygen charging efficiency is high. If the immersion depth is too large, there is no hydraulic jump. The impeller only plays the role of stirring, and the oxygen charging is very small, or even no air is sucked in. If the immersion depth is too small, the water lifting and water transmission will be reduced. The water flow in the pool is slow, even there is a dead zone, resulting in good oxygen charging of the surface water and insufficient oxygen charging of the bottom layer. Therefore, the linear speed of impeller rotation and immersion depth are often designed to be adjustable so that they can be adjusted at any time during operation. Generally, the oxygen transfer rate of vertical shaft impeller aerator is 15% ~ 25%, and the power efficiency is 2.5 ~ 3.5kgo2/kwh.

　　(2) Horizontal shaft aerator

　　Horizontal axis aerator is mainly rotary brush aerator. It is composed of a horizontal rotating shaft and blades fixed on the shaft. The rotating shaft drives the blades to rotate, stirs the water surface and splashes, and the oxygen in the air is transferred to the water through the gas-liquid interface.

　　Rotary brush aerator is mainly used in oxidation ditch. It has the advantages of convenient load adjustment, easy maintenance and management, and high power efficiency.

　　3、 Aeration tank type

　　The main structure of sewage treatment by activated sludge process is aeration tank. According to the flow pattern of the mixed liquid in the aeration tank, it can be divided into three types: push flow type, complete mixing type and circulating mixing type; According to the plane geometry, it can be divided into rectangle, corridor, circle, square and circular runway; According to the adopted aeration methods, it can be divided into blast aeration tank, mechanical aeration tank and mechanical blast aeration tank combined with the two methods; According to the relationship between aeration tank and secondary sedimentation tank, it can be divided into Aeration Sedimentation combined construction and separate construction.

　　1. push flow aeration tank

　　The push flow aeration tank is usually in the shape of rectangular Gallery, and blast aeration is often used. The traditional method is to install the air diffusion device on one side of the bottom of the aeration tank gallery. This arrangement can make the water flow in the tank spiral and improve the contact time between bubbles and mixed liquid. If the width of the aeration tank is large, the air diffusion device should be installed on both sides of the bottom of the aeration tank gallery. It can also be evenly arranged at the bottom of the whole aeration tank in a certain form, such as mutually perpendicular orthogonal form or quincunx staggered form.

　　The number of aeration tanks depends on the scale of the sewage treatment plant. Generally, the structure is divided into several units. Each unit includes one or several aeration tanks. Each aeration tank is usually composed of one or two to five galleries. When the number of galleries is singular, the sewage inlet and outlet are at both ends of the aeration tank; When the number of corridors is even, it is located at the same end of the corridor.

　　The length of aeration tank gallery can reach 100m, generally 50 ~ 70m. In order to prevent short flow, the ratio of length to width of the gallery should be greater than 5, or even greater than 10. The width depth ratio of the aeration tank is usually between 1.5 and 2. The pool depth is closely related to the cost and power cost. The deep pool is conducive to the utilization of oxygen, but the cost and power cost will be increased. On the contrary, the cost and power cost will be reduced, but the utilization rate of oxygen will also be reduced.

　　In addition, the functional requirements of the civil structure and aeration tank, the allowable occupied land area, the pressure of the blower that can be purchased and other factors shall be considered. At present, the depth of push flow aeration tank is mostly 3 ~ 5m in China.

　　In order to reduce the resistance and avoid the formation of dead zone for the rotating flow of mixed liquid in the aeration tank, the top and foot of the two walls of the tank wall in the cross section of the gallery are made into a 45 ° slope. In order to save air ducts, air diffusers in adjacent corridors are often arranged along public partitions.

　　The water inlet and sludge inlet of the aeration tank are set below the water surface, and the submerged outflow method is adopted to avoid short flow, and a gate is set to regulate the flow; Generally, the overflow weir is used for the outlet water. The treated water flows through the weir crest and overflows into the drainage channel.

　　A vent pipe with a diameter of 80 ~ 100mm is set at the bottom of the aeration tank for venting during maintenance or tank cleaning. Considering the requirements for discharging supernatant during the cultivation and acclimation cycle of activated sludge, according to the specific conditions, 2 ~ 3 drainage pipes with a diameter of 80 ~ 100mm are set at a certain distance from the bottom of the tank.

　　2. fully mixed aeration tank

　　Fully mixed aeration tanks often use surface mechanical aeration devices for oxygen supply, and their surfaces are mostly circular, square or polygonal. The combined fully mixed aeration sedimentation tank, called aeration sedimentation tank for short, is widely used. It consists of aeration area, diversion area and sedimentation area.

　　1) Aeration zone

　　The aeration device is set in the center of the tank top and goes deep into a certain depth underwater. The sewage enters from the bottom of the tank, and is immediately fully mixed with the original mixed liquid in the tank, and fully mixed and contacted with the activated sludge returned from the reflux joint of the sedimentation area. The sewage after aeration reaction flows out of the reflux window around the top and is led into the diversion area. The return window is equipped with a valve, which can control the amount of returned sludge by adjusting the size of the window hole.

　　2) Diversion area

　　It is located between the aeration area and the sedimentation area, with a width of about 0.6m and a height of about 1.5m. A vertical baffle is set inside to buffer the water flow, release the bubbles carried in the mixed liquid, make the water flow smoothly into the sedimentation zone, and create good conditions for solid-liquid separation.

　　3) Sedimentation zone

　　It is located outside the diversion area and aeration area. Its function is to separate mud and water. The upper part is the clarification area and the lower part is the sludge area. The depth of the clarification area should not be less than 1.5m, and the volume of the sludge area should not be less than 2h of sludge storage. The clarified treated water enters the drainage channel along the outlet weir around the pool, and the outlet weir often adopts a serrated triangular weir.

　　The sludge flows back to the aeration area through the return joint, which is generally 0.15 ~ 0.20m wide. A tank skirt is set on the side of the return joint to avoid dead corners. A sludge discharge pipe shall be set at a certain depth in the sludge area to discharge the excess sludge.

　　In production practice, there is also a fully mixed aeration tank separately built with the sedimentation tank. Sewage and return sludge are evenly introduced along the length of the aeration tank, and the mixed liquid is evenly discharged into the secondary sedimentation tank.

　　Simply put, the aeration and oxygenation system in common sewage treatment, aquaculture and water ecological treatment scenarios is composed of blowers, aeration discs, pipelines, valves and other equipment!