外文翻譯---污水處理

1、<p>　　附錄 1 外文參考文獻(xiàn)（譯文）</p><p><b>　　污水處理</b></p><p><b>　　摘 要</b></p><p>　　自然或生活污水處理，是指清除包括家庭排放的和地面徑流在內(nèi)的污水廢水和地面污染物的過(guò)程。它包括物理，化學(xué)和生物過(guò)程，消除物理，化學(xué)和生物污染物。其目的是集中產(chǎn)生廢

2、物流（或經(jīng)處理的污水）以及固體廢物或污泥進(jìn)行處理或再進(jìn)入環(huán)境。這種污物通常是在無(wú)意中受到了許多有毒的有機(jī)和無(wú)機(jī)物的污染。</p><p>　　關(guān)鍵詞：污水處理，生物膜處理法和停止增長(zhǎng)生物處理法，活性污泥法，</p><p><b>　　污水起源 </b></p><p>　　污水是由個(gè)人住宅，機(jī)關(guān)，商業(yè)和工業(yè)機(jī)構(gòu)產(chǎn)生的。原進(jìn)水（污水）包括家庭的

3、廁所，浴室，淋浴，廚房，水槽廢液等等，這些水將通過(guò)污水管排放。在許多地區(qū)，污水也包括工業(yè)和商業(yè)污水。在發(fā)達(dá)國(guó)家，家居分別將污水排放為灰水和黑水已經(jīng)越來(lái)越普遍，因?yàn)榛宜梢杂糜跐补嘀参锘蚧厥沼脕?lái)沖馬桶。大量的污水還包括一些屋頂流下的水以及地表水。因此城市廢水包括住宅，商業(yè)和工業(yè)排放的廢水，且可能包括雨水徑流。具有處理雨水能力的污水處理系統(tǒng)被稱為合流排水系統(tǒng)。這種系統(tǒng)通常是不被普遍采用，因?yàn)樗鼈儚?fù)雜化而且由于其季節(jié)性，降低了污水處理廠的效率

4、。由于流量的經(jīng)常變化，也導(dǎo)致處理量往往大于必需的，因而使處理設(shè)施更昂貴。此外，當(dāng)遭遇暴雨時(shí)，過(guò)量的雨水會(huì)造成污水處理能力不足，因而引發(fā)溢流。因此在設(shè)計(jì)排水管網(wǎng)時(shí)最好采用雨污分流系統(tǒng)。 </p><p>　　由于降雨流經(jīng)屋頂和地面時(shí)，會(huì)帶走包括土壤顆粒和其他沉積物，重金屬，有機(jī)物，動(dòng)物排泄物，污油和油脂等各種污染物質(zhì)。因此有些地方會(huì)有法律要求在雨水排入河道之前要進(jìn)行一些一定水平的處理。例如以下對(duì)雨水進(jìn)行的處理：盆地

5、沉淀處理，濕地過(guò)濾處理，混凝土地窖過(guò)濾處理，和旋渦分離器（去除粗固體）。 </p><p><b>　　過(guò)程概述 </b></p><p>　　污水可以在下列構(gòu)筑物(化糞池，生物過(guò)濾器或好氧處理系統(tǒng)）附近被處理，或收集并通過(guò)排水管網(wǎng)和泵站送至城市污水處理廠（見(jiàn)污水處理和管道和基礎(chǔ)設(shè)施）。污水收集和處理，通常取決于當(dāng)?shù)刂莺吐?lián)邦法規(guī)和標(biāo)準(zhǔn)。來(lái)源于的工業(yè)廢水，往往需要專門(mén)的

6、處理過(guò)程（見(jiàn)工業(yè)廢水處理）。 </p><p>　　常規(guī)污水處理可能涉及三個(gè)階段，一級(jí)處理，二級(jí)處理和三級(jí)處理。一級(jí)處理包括在沉淀池中的短時(shí)停留，這樣比較重的固體就會(huì)沉到池底，而油，油脂，更輕的固體則浮到水面。沉淀的和浮動(dòng)的材料都將被去除，其余的液體可被釋放或繼續(xù)二級(jí)處理。二級(jí)處理可以去除溶解和懸浮的生物物質(zhì)。二級(jí)處理通常由好氧或厭氧微生物進(jìn)行。二級(jí)處理還可能需要一個(gè)分離過(guò)程，以去除殘余的微生物或進(jìn)行三級(jí)處理。三

7、級(jí)處理有時(shí)被界定為與一級(jí)和二級(jí)不同的過(guò)程。受處理的水在排放到河流，海灣，瀉湖或濕地前有時(shí)需要化學(xué)消毒或物理（例如瀉湖和微濾）處理，或者可以用于灌溉高爾夫球場(chǎng)，綠色道路或公園。如果它足夠清潔，也可以用于地下水回灌或農(nóng)業(yè)用途。 </p><p><b>　　預(yù)處理 </b></p><p>　　預(yù)處理可以從原始廢水除去垃圾，樹(shù)枝，樹(shù)葉等比較容易收集的物質(zhì)，以防止其損壞或阻

8、塞水泵和一級(jí)處理的澄清池處理。 </p><p><b>　　篩選 </b></p><p>　　進(jìn)水污水必須消除隨污水流進(jìn)行的大的污染物。在服務(wù)大量人口的現(xiàn)代化處理廠，經(jīng)常用自動(dòng)傾斜格柵來(lái)達(dá)到這個(gè)目的。而小的處理廠可能采用手動(dòng)的格柵。機(jī)械式格柵的清污是典型的以格柵污物積累或流量的積累來(lái)進(jìn)行的。收集到的固體將被進(jìn)行填埋或焚燒處理。</p><p&g

9、t;<b>　　除砂 </b></p><p>　　預(yù)處理可使包括沙子或砂礫在內(nèi)的物質(zhì)通過(guò)控制速度在渠道或廳室內(nèi)旋轉(zhuǎn)流動(dòng)，使砂，砂礫和石塊沉淀。 </p><p><b>　　初級(jí)處理</b></p><p>　　在初級(jí)沉淀階段，污水流經(jīng)一個(gè)大池子，俗稱“初級(jí)澄清池”或“初級(jí)沉淀池”。這些池子需要足夠大以令污泥可以沉淀而油

10、和油脂等漂浮物可以上升到表面，并掠出池子。在初級(jí)沉淀階段的主要目的是提供一個(gè)均勻的液態(tài)環(huán)境使微生物和污泥都能被處理。初級(jí)沉淀池，通常裝配有機(jī)械驅(qū)動(dòng)的刮削泥器，不斷推動(dòng)將污泥收集到底部污泥斗，從那里可以抽取污泥進(jìn)行進(jìn)一步處理。油脂和石油的漂浮物有時(shí)會(huì)回收進(jìn)行皂化。 </p><p><b>　　二級(jí)處理 </b></p><p>　　二級(jí)處理的設(shè)計(jì)是為了降低了污水中那些

11、來(lái)自人類垃圾，食物渣滓，肥皂和洗滌劑產(chǎn)生的生化生物污染。大多數(shù)市政都打算采用好氧生物的方法解決污水處理問(wèn)題。為了達(dá)到這個(gè)目的，生物既需要的氧也需要生活的底物。有多種方式來(lái)達(dá)到這個(gè)目的。在所有這些方法中，細(xì)菌和原生動(dòng)物生物都可以降解消耗水中的水溶性有機(jī)污染物（如糖，脂肪，有機(jī)短鏈碳分子等），將大部分可溶性組分結(jié)合成絮狀。二級(jí)處理系統(tǒng)被分為 </p><p>　　生物膜處理法和停止增長(zhǎng)生物處理法。 </p>

12、;<p>　　生物膜處理法和停止增長(zhǎng)生物處理法系統(tǒng)的處理流程包括生物濾池和生物轉(zhuǎn)盤(pán)，它們提供生物生長(zhǎng)的媒體以使污水流過(guò)時(shí)進(jìn)行處理。 </p><p>　　在停止增長(zhǎng)生物處理法如活性污泥系統(tǒng)中，生物質(zhì)可以與與污水充分混合，而且在處理等量污水時(shí)可以比膜系統(tǒng)采用更小的空間操作。然而，生物膜系統(tǒng)比停止增長(zhǎng)生物處理法更能夠應(yīng)付生物污染物數(shù)量急的劇變化，并能提供更高的有機(jī)物及懸浮固體去除率。 </p>

13、;<p>　　粗過(guò)濾器是為了處理特別強(qiáng)烈的或可變有機(jī)負(fù)荷，一般工業(yè)，允許它們由傳統(tǒng)的二級(jí)處理工藝處理后在進(jìn)行處理。在廢水處理程度要求較高的地方，典型的特征包括高及包含開(kāi)放合成過(guò)濾介質(zhì)的圓形填充過(guò)濾器。它們的目的是允許通過(guò)高負(fù)荷的水力和高速流動(dòng)的空氣。在較大的裝置中，使用鼓風(fēng)機(jī)以使空氣強(qiáng)行通過(guò)裝置。由此產(chǎn)生的廢水通常在常規(guī)處理工藝的正常范圍內(nèi)。 </p><p><b>　　活性污泥法<

14、;/b></p><p><b>　　主條目：活性污泥 </b></p><p>　　一般來(lái)說(shuō)，生物活性污泥法涵蓋的各種機(jī)制和方法，通過(guò)溶解氧，以促進(jìn)生物絮體增長(zhǎng)，以此極大地消除有機(jī)物質(zhì)的。 </p><p>　　這個(gè)過(guò)程中的顆粒物質(zhì)在理想的條件下，可將氨轉(zhuǎn)化為亞硝酸鹽和硝酸鹽，并最終為氮?dú)猓硪?jiàn)反硝化）。 </p><

15、;p><b>　　表面曝氣池 </b></p><p>　　大部分工業(yè)廢水處理的生物氧化過(guò)程對(duì)氧氣（或空氣）和微生物的利用是相同的。表面曝氣池在一到十天的停留時(shí)間內(nèi)，對(duì)生化需氧量的去除可達(dá)到80%至90％。曝氣池的深度為1.5至5.0米之間，使用電機(jī)驅(qū)動(dòng)對(duì)廢水水面進(jìn)行曝氣的。 </p><p>　　在一個(gè)曝氣池系統(tǒng)中，曝氣機(jī)提供兩個(gè)功能：他們轉(zhuǎn)移生物氧化反應(yīng)所需

16、要的空氣至曝氣池，它們提供空氣的分散和反應(yīng)物的接觸的所需（即，氧氣，污水和微生物） 。通常情況下，浮動(dòng)表面曝氣機(jī)的額定供氣量，相當(dāng)于1.8 至2.7公斤氧氣/千瓦?每小時(shí)。然而，在活性污泥系統(tǒng)中，它們并不能保證提供混合達(dá)到預(yù)定值，因此活性污泥系統(tǒng)中的曝氣池也不一定能達(dá)到預(yù)定的水平。</p><p>　　生物氧化過(guò)程對(duì)溫度敏感，并在0 ° C和40 ° C時(shí)，生物反應(yīng)速度隨溫度的上升而上升。大多

17、數(shù)表面曝氣池運(yùn)行溫度為4 ° C至32 ° C。</p><p><b>　　濾池（氧化溝） </b></p><p><b>　　主條目：濾池 </b></p><p>　　在老廠和負(fù)荷變化較大的處理廠中，濾池被用來(lái)解決在焦碳（碳化煤），灰石芯片或?qū)ｉT(mén)制造的各種塑料介質(zhì)上漫流的污水溶液。這種介質(zhì)必須有

18、足夠的表面積以支持生物膜的形成。這種溶液是由中心樞紐發(fā)出，通過(guò)旋臂上的穿孔擴(kuò)散的。擴(kuò)散的溶液穿過(guò)濾池，并在池底通過(guò)管道被收集。這些管道同時(shí)也讓空氣進(jìn)入濾池，以保持其氧氣的充足。分布在介質(zhì)表面的細(xì)菌，原生動(dòng)物和真菌生物將以消化或以其他方式使有機(jī)質(zhì)含量減少。幼蟲(chóng)和蠕蟲(chóng)將使生物膜消耗，以幫助維持生物膜最佳的厚度。因?yàn)樯锬み^(guò)厚將會(huì)導(dǎo)致介質(zhì)堵塞和濾池上表面積水。</p><p><b>　　曝氣生物過(guò)濾器 &l

19、t;/b></p><p>　　曝氣生物濾池（或缺氧）濾池（BAF）或生物濾池，將生物還原碳過(guò)濾和硝化反硝化過(guò)濾結(jié)合在了一起。曝氣生物濾池通常包括一個(gè)由過(guò)濾介質(zhì)填充的反應(yīng)器。這個(gè)濾料是懸浮的或者是由過(guò)濾池底的礫石層支撐的。這個(gè)介質(zhì)的兩個(gè)目的是支持存在于它上面的微生物的高活性和過(guò)濾懸浮固體。在有氧模式下進(jìn)行碳減排和氨的轉(zhuǎn)化，缺氧模式下只進(jìn)行單一的硝酸轉(zhuǎn)化。曝氣生物濾池的運(yùn)作是上流還是下流要取決于設(shè)計(jì)制造商設(shè)計(jì)

20、及說(shuō)明。 </p><p><b>　　膜生物反應(yīng)器 </b></p><p>　　膜生物反應(yīng)器（MBR）將活性污泥法和膜的固液分離結(jié)合到了一起。膜是由低壓微濾或超濾膜組成的，因此不必再進(jìn)行澄清或第三次過(guò)濾。膜通常是沉浸在曝氣池中的，然而，也有一些是單獨(dú)應(yīng)用一個(gè)膜反應(yīng)池的。對(duì)一個(gè)MBR系統(tǒng)的主要好處之一是，它有效地克服了傳統(tǒng)活性污泥工藝中的污泥的沉降差問(wèn)題。與CAS系

21、統(tǒng)相比，該技術(shù)允許反應(yīng)器在具有相當(dāng)高濃度的混合液懸浮固體的情況下操作，而這是由污泥沉淀物決定的。這一反應(yīng)過(guò)程通常是在混合液懸浮固體顆粒濃度為8,000-12,000毫克/升中進(jìn)行的，而CAS的允許操作范圍為2000-3000毫克/升。MBR過(guò)程中生物量濃度的升高，可以非常有效地將可溶性顆粒和負(fù)荷率較高的生物可降解材料去除。因此，增加污泥滯留時(shí)間（SRTs） - 通常超過(guò)15天 – 即可確保即使在極其寒冷的天氣里也能完全硝化。 </

22、p><p>　　建設(shè)和經(jīng)營(yíng)一個(gè)MBR的成本通常高于傳統(tǒng)的廢水處理。膜過(guò)濾器會(huì)被油污堵塞或被水流中的沙粒摩擦刮破，且缺乏洪峰流量通過(guò)時(shí)凈水的靈活性。這項(xiàng)技術(shù)在可靠的預(yù)處理廢水上已日益普遍，并取得了廣泛的接受，而且流入水源也已受到控制，同時(shí)，生命周期成本一直在穩(wěn)步下降。膜生物反應(yīng)器系統(tǒng)的體積小，且可以高質(zhì)量的處理污水，使他們?cè)谥兴赜梅矫娲笫軞g迎。 </p><p>　　膜生物反應(yīng)器在世界各地都有

23、建立。包括北Librty，愛(ài)荷華，格魯吉亞和加拿大。 </p><p><b>　　二次沉淀 </b></p><p>　　在第二階段處理的最后一步是為了使生物絮凝或過(guò)濾材料沉淀和產(chǎn)出含有有機(jī)物質(zhì)及懸浮物含量極低的污水。 </p><p><b>　　生物轉(zhuǎn)盤(pán) </b></p><p>　　主條目：

24、旋轉(zhuǎn)生物接觸池 </p><p>　　旋轉(zhuǎn)生物接觸池（RBCs）是機(jī)械二級(jí)處理系統(tǒng)，在承受激增的有機(jī)負(fù)荷時(shí)有強(qiáng)大的應(yīng)該變能力。旋轉(zhuǎn)生物接觸池于1960年在德國(guó)第一次安裝，至今已發(fā)展完善成為一種可靠的處理工序。轉(zhuǎn)盤(pán)為污水中的細(xì)菌和微生物提供生長(zhǎng)方面的支持，用來(lái)破壞與穩(wěn)定有機(jī)污染物。要取得成功，就要提供微生物生活所需的氧氣和生長(zhǎng)所需的食物。氧氣是轉(zhuǎn)盤(pán)旋轉(zhuǎn)過(guò)程中從大氣中獲得的。當(dāng)微生物成長(zhǎng)時(shí)，它們建立于轉(zhuǎn)盤(pán)介質(zhì)之上，直

25、到它們被污水中轉(zhuǎn)盤(pán)旋轉(zhuǎn)產(chǎn)生的剪切力所甩開(kāi)。從旋轉(zhuǎn)生物接觸池流出的污水，將通過(guò)最后澄清池在那里懸浮的微生物將沉淀為絮狀物。澄清池中的污泥將被分離進(jìn)行進(jìn)一步處理。 </p><p>　　與其功能類似的生物過(guò)濾系統(tǒng)已成為家庭魚(yú)缸受歡迎的過(guò)濾和凈化的一部分。該過(guò)濾系統(tǒng)被設(shè)計(jì)為水先流出池子，之后瀑布般自由流經(jīng)一個(gè)皺褶的纖維網(wǎng)格轉(zhuǎn)輪，之后在穿過(guò)一個(gè)含有介質(zhì)的過(guò)濾器，然后流回魚(yú)缸。紗網(wǎng)轉(zhuǎn)輪將成為一個(gè)以水族箱中懸浮飼料廢物為食的

26、微生物形成的生物膜，同時(shí)轉(zhuǎn)輪也由于旋轉(zhuǎn)而暴露于大氣。這個(gè)系統(tǒng)尤其是善于消除魚(yú)類和其他動(dòng)物通過(guò)排泄而在水中產(chǎn)生的尿素和浪費(fèi)尿素和氨。 </p><p>　　附錄 2 外文參考文獻(xiàn)（原文）</p><p>　　Sewage treatment</p><p>　　Abstract：Sewage treatment, or domestic wastewater trea

27、tment, is the process of removing contaminants from wastewater and household sewage, both runoff (effluents) and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biologi

28、cal contaminants. Its objective is to produce a waste stream (or treated effluent) and a solid waste or sludge suitable for discharge or reuse back into the environment. This material is often inadvertently contaminated

29、with m</p><p>　　Key words: Sewage treatment, fixed-film and suspended-growth, Activated sludge</p><p>　　Origins of sewage</p><p>　　Sewage is created by residences, institutions, and

30、 commercial and industrial establishments. Raw influent (sewage) includes household waste liquid from toilets, baths, showers, kitchens, sinks, and so forth that is disposed of via sewers. In many areas, sewage also incl

31、udes liquid waste from industry and commerce. The separation and draining of household waste into greywater and blackwater is becoming more common in the developed world, with greywater being permitted to be used for wat

32、ering plan</p><p>　　As rainfall runs over the surface of roofs and the ground, it may pick up various contaminants including soil particles and other sediment, heavy metals, organic compounds, animal waste,

33、and oil and grease. Some jurisdictions require stormwater to receive some level of treatment before being discharged directly into waterways. Examples of treatment processes used for stormwater include sedimentation basi

34、ns, wetlands, buried concrete vaults with various kinds of filters, and vortex separators (to</p><p>　　Process overview</p><p>　　Sewage can be treated close to where it is created (in septic tan

35、ks, biofilters or aerobic treatment systems), or collected and transported via a network of pipes and pump stations to a municipal treatment plant (see sewerage and pipes and infrastructure). Sewage collection and treatm

36、ent is typically subject to local, state and federal regulations and standards. Industrial sources of wastewater often require specialized treatment processes (see Industrial wastewater treatment).</p><p>　　

37、Conventional sewage treatment may involve three stages, called primary, secondary and tertiary treatment. Primary treatment consists of temporarily holding the sewage in a quiescent basin where heavy solids can settle to

38、 the bottom while oil, grease and lighter solids float to the surface. The settled and floating materials are removed and the remaining liquid may be discharged or subjected to secondary treatment. Secondary treatment re

39、moves dissolved and suspended biological matter. Secondary t</p><p>　　Pre-treatment</p><p>　　Pre-treatment removes materials that can be easily collected from the raw wastewater before they dama

40、ge or clog the pumps and skimmers of primary treatment clarifiers (trash, tree limbs, leaves, etc).</p><p><b>　　Screening</b></p><p>　　The influent sewage water is strained to remove

41、 all large objects carried in the sewage stream. This is most commonly done with an automated mechanically raked bar screen in modern plants serving large populations, whilst in smaller or less modern plants a manually c

42、leaned screen may be used. The raking action of a mechanical bar screen is typically paced according to the accumulation on the bar screens and/or flow rate. The solids are collected and later disposed in a landfill or i

43、ncinerated.</p><p>　　Grit removal</p><p>　　Pre-treatment may include a sand or grit channel or chamber where the velocity of the incoming wastewater is carefully controlled to allow sand, grit a

44、nd stones to settle.</p><p>　　Primary treatment</p><p>　　In the primary sedimentation stage, sewage flows through large tanks, commonly called "primary clarifiers" or "primary sed

45、imentation tanks". The tanks are large enough that sludge can settle and floating material such as grease and oils can rise to the surface and be skimmed off. The main purpose of the primary sedimentation stage is t

46、o produce both a generally homogeneous liquid capable of being treated biologically and a sludge that can be separately treated or processed. Primary settling tank</p><p>　　Secondary treatment</p><

47、;p>　　Secondary treatment is designed to substantially degrade the biological content of the sewage which are derived from human waste, food waste, soaps and detergent. The majority of municipal plants treat the settle

48、d sewage liquor using aerobic biological processes. For this to be effective, the biota require both oxygen and a substrate on which to live. There are a number of ways in which this is done. In all these methods, the ba

49、cteria and protozoa consume biodegradable soluble organic contaminan</p><p>　　fixed-film and suspended-growth. </p><p>　　Fixed-film OR attached growth system treatment process including tricklin

50、g filter and rotating biological contactors where the biomass grows on media and the sewage passes over its surface.</p><p>　　In suspended-growth systems, such as activated sludge, the biomass is well mixed

51、with the sewage and can be operated in a smaller space than fixed-film systems that treat the same amount of water. However, fixed-film systems are more able to cope with drastic changes in the amount of biological mater

52、ial and can provide higher removal rates for organic material and suspended solids than suspended growth systems.</p><p>　　Roughing filters are intended to treat particularly strong or variable organic loads

53、, typically industrial, to allow them to then be treated by conventional secondary treatment processes. Characteristics include typically tall, circular filters filled with open synthetic filter media to which wastewater

54、 is applied at a relatively high rate. They are designed to allow high hydraulic loading and a high flow-through of air. On larger installations, air is forced through the media using blowers. The</p><p>　　A

55、ctivated sludge</p><p>　　Main article: Activated sludge</p><p>　　In general, activated sludge plants encompass a variety of mechanisms and processes that use dissolved oxygen to promote the grow

56、th of biological floc that substantially removes organic material.</p><p>　　The process traps particulate material and can, under ideal conditions, convert ammonia to nitrite and nitrate and ultimately to ni

57、trogen gas, (see also denitrification).</p><p>　　Surface-aerated basins</p><p>　　Most biological oxidation processes for treating industrial wastewaters have in common the use of oxygen (or air)

58、 and microbial action. Surface-aerated basins achieve 80 to 90% removal of Biochemical Oxygen Demand with retention times of 1 to 10 days. The basins may range in depth from 1.5 to 5.0 metres and use motor-driven aerator

59、s floating on the surface of the wastewater. </p><p>　　In an aerated basin system, the aerators provide two functions: they transfer air into the basins required by the biological oxidation reactions, and th

60、ey provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and microbes). Typically, the floating surface aerators are rated to deliver the amount of air equivalen

61、t to 1.8 to 2.7 kg O2/kW·h. However, they do not provide as good mixing as is normally achieved in activated sludge systems and </p><p>　　Biological oxidation processes are sensitive to temperature

62、 and, between 0 °C and 40 °C, the rate of biological reactions increase with temperature. Most surface aerated vessels operate at between 4 °C and 32 °C.</p><p>　　Filter beds (oxidizing b

63、eds)</p><p>　　Main article: Trickling filter</p><p>　　In older plants and plants receiving more variable loads, trickling filter beds are used where the settled sewage liquor is spread onto the

64、surface of a deep bed made up of coke (carbonized coal), limestone chips or specially fabricated plastic media. Such media must have high surface areas to support the biofilms that form. The liquor is distributed through

65、 perforated rotating arms radiating from a central pivot. The distributed liquor trickles through this bed and is collected in drains at the</p><p>　　Biological aerated filters</p><p>　　Biologic

66、al Aerated (or Anoxic) Filter (BAF) or Biofilters combine filtration with biological carbon reduction, nitrification or denitrification. BAF usually includes a reactor filled with a filter media. The media is either in s

67、uspension or supported by a gravel layer at the foot of the filter. The dual purpose of this media is to support highly active biomass that is attached to it and to filter suspended solids. Carbon reduction and ammonia c

68、onversion occurs in aerobic mode and sometime achiev</p><p>　　Membrane bioreactors</p><p>　　Membrane bioreactors (MBR) combine activated sludge treatment with a membrane liquid-solid separation

69、process. The membrane component uses low pressure microfiltration or ultra filtration membranes and eliminates the need for clarification and tertiary filtration. The membranes are typically immersed in the aeration tank

70、; however, some applications utilize a separate membrane tank. One of the key benefits of an MBR system is that it effectively overcomes the limitations associated with poor sett</p><p>　　The cost of buildin

71、g and operating an MBR is usually higher than conventional wastewater treatment. Membrane filters can be blinded with grease or abraded by suspended grit and lack a clarifier's flexibility to pass peak flows. The tec

72、hnology has become increasingly popular for reliably pretreated waste streams and has gained wider acceptance where infiltration and inflow have been controlled, however, and the life-cycle costs have been steadily decre

73、asing. The small footprint of MBR systems, an</p><p>　　There are MBR plants being built throughout the world, including North Librty, Iowa, Georgia, and Canada.</p><p>　　Secondary sedimentation&

74、lt;/p><p>　　The final step in the secondary treatment stage is to settle out the biological floc or filter material and produce sewage water containing very low levels of organic material and suspended matter.&

75、lt;/p><p>　　Rotating biological contactors</p><p>　　Main article: Rotating biological contactor</p><p>　　Rotating biological contactors (RBCs) are mechanical secondary treatment system

76、s, which are robust and capable of withstanding surges in organic load. RBCs were first installed in Germany in 1960 and have since been developed and refined into a reliable operating unit. The rotating disks support th

77、e growth of bacteria and micro-organisms present in the sewage, which breakdown and stabilise organic pollutants. To be successful, micro-organisms need both oxygen to live and food to grow. Oxygen is </p><p&g

78、t;　　A functionally similar biological filtering system has become popular as part of home aquarium filtration and purification. The aquarium water is drawn up out of the tank and then cascaded over a freely spinning corr

79、ugated fiber-mesh wheel before passing through a media filter and back into the aquarium. The spinning mesh wheel develops a biofilm coating of microorganisms that feed on the suspended wastes in the aquarium water and a