1、<p>　　1180單詞，6600英文字符，1975漢字</p><p>　　Controlling sludge settleability in the oxidation ditch process</p><p>　　K.J. Hartley</p><p><b>　　ABSTRACT</b></p><

2、p>　　This paper describes an investigation aimed at developing an operating technique for controlling sludge settleability in the oxidation ditch form of the nitrification denitrification activated sludge process. It w

3、as hypothesized that specific sludge volume index (SSVI) is lowest at an optimum process anoxic fraction and increases at higher and lower fractions. Using effluent ammonia:nitrate ratio as a surrogate for anoxic fractio

4、n, it was found that a simple empirical model based on a three soli</p><p><b>　　Keywords</b></p><p>　　Settleability ；Sludge volume index；SVI；Control；Nitrogen；Oxidation ditch</p>

5、;<p>　　Introduction</p><p>　　The oxidation ditch process has the capability to reliably meet low total nitrogen standards because of its special operating characteristics. Nitrogen removal can be cont

6、inuously optimized in operation by varying the anoxic and aerobic mass fractions to meet short- and long-term changes in wastewater characteristics (Hartley, 1997; Mines and Woods, 1994). It has also been observed that s

7、ludge settleability in oxidation ditches varies with the operating mass fractions (Vivian and Hartley, 1989).</p><p>　　Sludge settleability is one of the most important design and operating characteristics o

8、f the activated sludge process. It affects both the sizing of tankage and the process capacity actually achieved. Yet, nearly 100 years after the activated sludge process was invented (Ardern and Lockett, 1914), positive

9、 control of this parameter remains elusive. Four slightly different tests are in use for measurement of settleability, sludge volume index (SVI, employing simple cylinder settling, Mohlman, 19</p><p>　　A ran

10、ge of factors affects settleability in activated sludge processes, including feed quality, solids retention time (SRT), mixing characteristics, oxygen regime, pH and nutrient availability (Jenkins et al., 2004). For N an

11、d N&P removal processes, the Water Research Group at the University of Cape Town has conducted a comprehensive settleability study, which they published in a lengthy series of papers and summarised in Ekama et al. (1

12、996), Casey et al. (1999) and Tsai et al. (2003). Their stu</p><p>　　Tsai et al. (2003) observed that M. parvicella growth could be stimulated or inhibited by varying the concentration of ammonia (the organi

13、sm’s required nitrogen source) to high or low values, respectively. They therefore postulated that deterioration of settleability at low aerobic fraction can be due to increasing ammonia concentration (decreasing nitrifi

14、cation efficiency).</p><p>　　The oxidation ditch</p><p>　　Fig. 1 illustrates the general oxidation ditch reactor format. Mixed liquor is impelled around a circuit by one or more mechanical aerat

15、ors, or by mixers in the case of diffused air aeration. This provides a typical mixed liquor: feed flow ratio of 100–200. The dissolved oxygen (DO) concentration jumps up at the aerator and declines downstream. The DO co

16、ncentration at the aerator equals the oxygen transfer rate divided by the circulating flow rate. The anoxic fraction is controlled by varying th</p><p>　　Fig. 2 shows the process-operating characteristic. Th

17、ere is an anoxic fraction-operating window that gives lowest total nitrogen (TN) in the effluent. This window shifts as operating conditions (feed and process operating characteristics) change. Lowest TN occurs where eff

18、luent ammonia and nitrate are about equal. The process can therefore be optimised in operation to maintain lowest (or any other) TN concentration. Because the mixed liquor recycle ratio is so high, the ammonia and nitrat

19、e conce</p><p>　　According to the UCT model, sludge settleability in an oxidation ditch should be best when TN is lowest, deteriorating at a lower anoxic fraction where the oxidised nitrogen concentration ex

20、iting the anoxic zone is elevated, and also at a higher anoxic fraction where the ammonia concentration increases. Actual SVIs in operating ditches are variable. For example, von Munch and Komarowski (2001) report an uns

21、tirred SVI value of 105 mL/g for the Thorneside plant and an sSVI value of 155 for the Gib</p><p>　　This paper analyses the operating data from three Australian oxidation ditch plants to demonstrate that (a)

22、 the settleability characteristic does behave as expected, (b) the UCT model appears to require modification to explain the observations and (c) operating settleability can be readily controlled in the oxidation ditch pr

23、ocess. The three plants are Bucasia (located in Mackay), Coolum and West Byron (Byron Bay), all treating domestic sewage. Physical and operating data are summarised in Table</p><p>　　控制氧化溝工藝中的污泥沉降</p>

24、<p>　　K.J. Hartley</p><p><b>　　摘 要</b></p><p>　　本文介紹了一個針對控制硝化反硝化氧化溝活性污泥法中的污泥沉降這項新操作技術的開發(fā)的調查。據(jù)推測，具體的污泥容積指數(shù)（ SSVI ），最低的是在工藝缺氧分數(shù)最佳的部分，在較高和較低的部分污泥容積指數(shù)則會增加。采用出水氨氮：硝酸的比例替代缺氧分數(shù)，會發(fā)現(xiàn)，一

25、個簡單的基于三個固體的經(jīng)驗模型停留時間的移動氮比，能夠完全復制SSVI長期變化的具有兩個獨立氧化溝的全規(guī)模工廠。從第二個氧化溝工廠的操作數(shù)據(jù)可以得出，不管前發(fā)酵槽是處于上線還是離線的狀態(tài)，SSVI都會隨RBCOD變化，RBCOD越高，SSVI越低。得出的結論是，最好的沉降發(fā)生在出水氨氮和硝酸鹽大約相等的地方，出水總氮最低處。最好的操作規(guī)則是使用溶解氧控制，保持出水氨氮和硝酸鹽氮的濃度大約相等。特意用這種方式操作第三個氧化溝廠，實現(xiàn)了，1

26、5個月的中位運行值為：SSVI為60mg/L，流出氨、硝酸鹽和TN分別為0.2、0.3和2.0mgN/ L。</p><p><b>　　關鍵詞</b></p><p>　　沉降；污泥容積指數(shù)；SVI ；控制 ；氮 ；氧化溝</p><p><b>　　1 介紹</b></p><p>　　氧化溝工

27、藝由于其特殊的操作特性的能力，基本能夠滿足低總氮標準。氮的去除可以通過改變缺氧和好氧質量分數(shù)不斷優(yōu)化操作，以滿足廢水水量變化大的特點（Hartley, 1997; Mines and Woods, 1994）。還能觀察到，在氧化溝中污泥沉降會隨著操作質量分數(shù)的變化而變化而變化(Vivian and Hartley, 1989)。</p><p>　　污泥沉降是活性污泥工藝中最重要的設計和運行特征之一。它會影響到池

28、容的大小和實際處理能力。然而，活性污泥工藝被發(fā)明了近100年后(Ardern and Lockett, 1914)，對參數(shù)的準確控制無法得到求證。四個略有不同的測試了沉降比、污泥容積指數(shù)、攪拌的SVI、稀釋SVI和SSVI3.5、或者僅是SSVI。這些參數(shù)的值與污泥的沉降性有密切的關系，它們互相之間的聯(lián)系也可通過出版的統(tǒng)計數(shù)據(jù)看出。</p><p>　　一系列影響活性污泥法中污泥沉降的因素，包括填料質量，固體停留

29、時間（SRT ） ，混合特性，氧氣狀態(tài)， pH值和養(yǎng)分的有效性。對于氮和氮磷的清除過程中，開普敦大學的水研究小組已經(jīng)進行了全面的沉降研究，他們Ekama等（1996）、卡西等人（1999）和Tsai等人（2003）發(fā)表了一系列論文和總結。他們的研究包括間歇曝氣格式模仿氧化溝工藝。他們發(fā)現(xiàn)，在長污泥齡脫氮除磷工藝中低的污泥負荷組合絲狀菌會導致幾乎所有的膨脹問題，并且這個問題無法通過厭氧、缺氧和好氧選擇器來控制。不管處理工藝有沒有生物除磷，

30、它都是通過控制氮的狀態(tài)來控制污泥沉降。根據(jù)他們開發(fā)的模型，在二級處理A/O處理系統(tǒng)中主要利用緩慢生物降解COD，如果反硝化作用在缺氧區(qū)反應不完全并且出現(xiàn)了亞硝酸鹽，那就說明在好氧區(qū)的細胞中還積累著NO且存在抑制反硝化的絮凝劑。絲狀微生物，在缺氧區(qū)沒有競爭力，因為他們只能反硝化硝酸鹽為亞硝酸鹽，它們能在好氧區(qū)增殖不受抑制。當COD被生物降解時，細胞內的NO不會累積，所以，RBCOD的一個顯著功能就是減輕了絮狀物成型的競爭壓力。</p

31、><p>　　Tsai等（2003）觀察到，M. parvicella生長可能通過改變氨的濃度（生物體的需要氮源），氨濃度高受到刺激增長快，氨濃度低時受到抑制增長慢。因此，他們推測，在氧分低的階段沉降出現(xiàn)惡化很可能是因為氨濃度的增加（降低硝化效率）。</p><p><b>　　氧化溝</b></p><p>　　圖1說明了一般氧化溝反應器的形式。

32、混合液在一個環(huán)形槽里被一個或多個機械曝氣機推動，或空氣曝氣的情況下通過攪拌機進行曝氣。這里提供了一個典型的混合液體：100-200進料流量比。溶解氧（DO）的濃度在曝氣區(qū)增加，在工藝下游減少。 DO濃度在曝氣等于氧氣傳輸速率通過循環(huán)流量分配。缺氧部分通過改變曝氣量來控制，來穩(wěn)定設置在好氧區(qū)下游端點設定的溶解氧設定點位。</p><p>　　圖2顯示了操作過程中的特性。有一個缺氧分數(shù)操作窗口，可以在污水中給出最低的

33、總氮。這個窗口隨操作條件的變化而移動（進料和工藝操作特性）。在出水氨氮和硝酸鹽大約相等的地方會出現(xiàn)最低總氮。該過程可以在操作上進行優(yōu)化，以保持最低（或任何其他）總氮濃度。在整個回流里，因為該混合液回流比是如此之高，氨和硝酸鹽的濃度幾乎恒定，并且等于流出物的濃度。</p><p>　　根據(jù)UCT模型，氧化溝中當TN最低的時候污泥沉降應是最好的，在較低的缺氧分數(shù)段會惡化，這個情況出現(xiàn)在缺氧區(qū)末端氧化了的氮的濃度升高的

34、階段，并且在氨濃度增加的時候，會出現(xiàn)更高的缺氧餾分。實際上溝渠的運行期SVIs是可變的。例如，馮·蒙克和Komarowski（2001）報告的105毫升/克的Thorneside的未攪拌的SVI值及155吉布森島工廠的SSVI值吉布森島工廠（無論是在澳大利亞布里斯班）的未攪拌的SVI值。Bundamba廠區(qū)，在相同的區(qū)域中的未攪拌的SVI在90-400mg/L變化（Vivian和哈特利，1989）。</p>&l

35、t;p>　　佛羅里達州的兩個工廠，戴爾馬布里和Falkenburg，報告了分別在不攪拌的SVIs濃度為140和180mg/L的情況下進行操作的結果（哈特利，1995;礦業(yè)和伍茲，1994）。</p><p>　　本文從三個澳大利亞氧化溝廠的操作數(shù)據(jù)證明以下幾點：</p><p>　　（一）沉降特性并不像預期的那樣；（二）UCT模式似乎需要修改來解釋觀察到的情況；（三）在氧化溝工藝中對