外文翻譯--城市污水常溫處理中的新型改良egsb（膨脹顆粒污泥床）反應器的發(fā)展

1、<p><b>　　中文4320字</b></p><p>　　附件1：外文資料翻譯譯文</p><p>　　城市污水常溫處理中的新型改良EGSB（膨脹顆粒污泥床）反應器的發(fā)展</p><p>　　近年來，厭氧處理技術已經成為一項有吸引力的可持續(xù)發(fā)展的污水處理技術，因為它耗能少而且產氣量少。特別的，流式厭氧污泥床(UASB)和常規(guī)膨脹

2、顆粒污泥床(EGSB)在城市污水處理中得到了廣泛應運。通常，EGSB比UASB更能有效去除化學需氧量（COD），更能有效抵抗有機負荷率(OLR)、溫度和pH的變化。然而，由于較高的上升流速和較多的甲烷氣泡，使膨脹顆粒污泥床（EGSB）中的三相分離器中的水的流速很高，這就導致了大量生物質的流失,最終廢水中的COD濃度就升高了。所以，有時候不能滿足城市污水處理廠或生物處理系統(tǒng)排放的標準，并導致生物處理系統(tǒng)崩潰。因此,對與EGSB系統(tǒng)來說，城

3、市污水處理中的關鍵問題是如何控制在高上升流速下的生物量流失。</p><p>　　在本文中,提出一種改進型的EGSB反應器模型，它結合了EGSB 和UASB兩者的優(yōu)勢。在相同環(huán)境下通過比較，試驗性地研究EGSBm和EGSBc兩種反應器。在東區(qū)污水處理廠中有一個初級出水沉降池。在對膨脹顆粒污泥床（EGSBm）中水動力特征分析時，進行了停留時間分布(RTD)的實驗和Polvmerase連鎖反應實驗，并且應用變性梯度凝

4、膠電泳(PCR-DGGE)技術來探索顆粒污泥中微生物的多樣性。</p><p><b>　　1.材料和方法</b></p><p>　　1.1影響生物量和養(yǎng)料的來源</p><p>　　常溫厭氧顆粒污泥取自中國無錫市的一家污水處理廠，該廠主要利用全比例內循環(huán)生物反應器處理酸性廢水。黑色的顆粒污泥有規(guī)則的形狀（φ=0.8 - 2毫米）和良好的沉降

5、性能。污泥中含有懸浮固體（TSS）73.6克/升和揮發(fā)性懸浮固體（VSS）59克/升。在EGSBm和EGSBc兩種反應器中，最初的接種污泥量占有效總量的65%。</p><p>　　污水樣本取自上海東區(qū)城市污水處理廠的一個初級沉淀池中。其中包括60%生活污水和40%的工業(yè)廢水。污水的主要指標如表1。</p><p>　　表1 污水的主要指標</p><p><

6、b>　　1.2反應器的描述</b></p><p>　　工業(yè)生產中EGSBm和EGSBc反應器的原理圖如圖1。兩個反應器都是有機玻璃制成的,容量為300 升,采用連續(xù)流動模式。在EGSBc中,配水系統(tǒng)在反應器的底部，進水和污水一起進入循環(huán)。在EGSBm中,其混合液體通過循環(huán)泵和進水一起進入循環(huán)。EGSBm配水系統(tǒng)包括一個5升的水箱和4根聚氯乙烯管（ PVC ）。水箱置于反應器的頂部,管子延伸到反

7、應器的底部。在東區(qū)污水處理廠這兩種類型反應器都有，它們表現(xiàn)可以相媲美。</p><p>　　圖1 EGSBc和EGSBm反應器的原理圖</p><p>　　在EGSBm反應器中，含顆粒污泥的混合液大約在反應器的中部通過循環(huán)泵進入循環(huán)，同位于反應器頂部的進水很好的混合。由于混合液受重力的影響，沿分布管道進而進入底部的反應堆。在底部的反應區(qū)域內,復合液進一步混合了局部液體，水中有機物在高濃度的

8、顆粒污泥中被有效地分解。廢水向上循環(huán)，達到中間的流動循環(huán)管,很大一部分是被吸進管孔并通過水泵循環(huán)至反應器頂部的水箱中，同時一小部分繼續(xù)向上流動達到進一步分解。然后，向上流動的部分會進入三相分離器，在這里氣體、水、顆粒狀污泥會被分開。在分離后,顆粒污泥經過處理還能循環(huán)利用到上層反應室中去。</p><p><b>　　1.3實驗條件</b></p><p>　　在這兩個

9、試驗性反應器成功開動起來，反應達到了穩(wěn)定的狀態(tài)后,它們還得在常溫下連續(xù)運行165 天。基于穩(wěn)態(tài)條件下，總的反應過程分為十個階段。每個階段具體實驗數據在表2中有詳細說明。</p><p>　　表2 各反應階段的實驗數據</p><p><b>　　R：循環(huán)比例</b></p><p>　　1.4反應器的性能評價</p><p&

10、gt;　　在每個反應階段，通過去除COD，CODfilt和SS的效率來評價EGSBc和EGSBm兩者的總體性能。CODfilt表示經過定性濾紙后污水中的COD濃度。COD和CODfilt的濃度可以經重鉻酸鉀溶液檢測出來，而SS的濃度是通過過濾，干燥，然后稱水樣本檢測出來。</p><p>　　1.5顆粒狀污泥的分析</p><p>　　在第4和第10個運行階段結束后，從EGSBm反應器的四

11、個不同反應區(qū)取顆粒污泥樣本，并在圖1中標明A、B、C、D。A、B、C、D四個反應區(qū)距離反應區(qū)底部分別為2.0,1.5,1.0,0.5米。從顆粒污泥中提取DNA后，16S核糖體RNA基因的特定區(qū)域經過聚合酶鏈反應（PCR）被放大，進而用來克隆和排序。然后，使用變形梯度凝膠電泳（EGGB）分離聚合酶鏈反應（PCR）的產物。</p><p>　　已經分化的菌株再經過培養(yǎng)，使菌株數量達到所需的測量水平。</p>

12、;<p>　　在預選的反應時間中，使用激光粒度儀（LS230，美國貝克曼庫爾特）測得四個不同區(qū)域的顆粒污泥的直徑分布在0.04-2000微米的范圍內。</p><p><b>　　1.6水動力特性</b></p><p>　　有一種利用鋰離子（Li+）的脈沖追蹤儀，可以通過鋰離子反應器中不同區(qū)域內停留的時間來分析水動力特性。在每一次試驗中，通過脈沖注射器

13、向進水中注入10mL濃度為10mg/L鋰離子溶液，運用電感耦合等離子ICP/脂肪醇聚氧乙烯醚硫酸鹽AES外加鉑金埃爾默奧普瑪2100等離子發(fā)射光譜儀對污水中鋰離子的濃度進行周期性檢測。</p><p><b>　　2 結果和討論</b></p><p><b>　　2.1反應器的性能</b></p><p>　　1）上升流

14、速（Vup）的影響。對于EGSBc和EGSBm兩種反應器，上升流速對污水中COD和CODfilt濃度的影響在圖2中有說明。結果表明在EGSBm和EGSBc兩種污水中，當上升流速從5.0米/時(階段3)到10.3米/時（階段5），CODfilt濃度分別從94.1和97.1毫克/升（階段1）下降為59.4和71.4毫克/升（階段5）.兩種反應器污水中COD濃度和CODfilt濃度變化趨勢大致相同。在較高的上升流速下，通過比較兩者污水中COD

15、的濃度，顯而易見，EGSBm比EGSBc具有更好的性能和恢復效果。當上升流速從2米/小時（階段1）到10.3米/小時變化時，兩種反應器中SS的濃度分別從18.5和22.2毫克/升上升為60.1和126.5毫克/升。從中我們看出在相同流速下，EGSBm比EGSBc更容易造成生物量的流失。因此，EGSBm具有較好的恢復能力是因為其高污泥濃度的保持能力。</p><p>　　圖2 上升流速對EGSBc和EGSBm兩種反

16、應器中污水中COD和CODfilt濃度的影響</p><p>　　2)水力停留時間的影響。水力停留時間對EGSBm和EGSBc兩種反應器中污水中COD和CODfilt濃度的影響可以在圖3中看出來。結果顯示，在EGSBm反應器中，當水力停留時間從6降為2小時時，COD和CODfilt濃度分別從119.7毫克/升和94.1毫克/升（階段1）下降為104和82.6毫克/升（階段7）。當水力停留時間降為1小時后，EGSB

17、m和EGSBc兩者中COD和CODfilt濃度都有上升趨勢。但是，EGSBm有更好的基質清除效果，主要是因為它具有改進了的水循環(huán)結構。</p><p>　　在EGSBm和EGSBc兩種反應器中，揮發(fā)性脂肪酸的平均濃度分別從28和31克/升（階段6，水力停留時間4小時）上升為42和65克/升（階段7，水力停留時間2小時）。這就意味著在低水力停留時間內，EGSBm比EGSBc更能有效利用揮發(fā)性脂肪酸來產生甲烷氣體。&

18、lt;/p><p>　　圖3水力停留時間對EGSBm和EGSBc兩種反應器中污水中COD和CODfilt濃度的影響</p><p>　　3）有機負載率的影響。在兩種反應器中，有機負載率對COD和CODfilt濃度的影響如圖4。當有機負載率由7.2（階段8）突然降為1.2千克COD/（立方米*天）（階段9），EGSBm反應器能維持它的處理效率不變，而EGSBc則發(fā)生不同程度的變化。當有機負荷率從

19、1.2（階段9）又調整到7.2千克COD/（立方米*天）時，在階段10的初期兩種反應器中COD和CODfilt濃度都有明顯提高。隨后，EGSBm恢復到最初有機去除效率需用10天時間，而EGSBc反應器在20天后任然沒能達到最初的有機物去除率水平。顯而易見，EGSBm更能有效抵抗有機載荷的變化。</p><p>　　圖4有機負載率對EGSBm和EGSBc兩種反應器中污水中COD和CODfilt濃度的影響</p

20、><p>　　總的來講，當實驗條件發(fā)生變化時，EGSBm反應器中COD，CODfilt和SS濃度比EGSBc中的濃度要低得多。即使SS濃度會隨上升流速的升高而升高，但EGSBm比EGSBc的生物量流失少。而且在上升流速高達10.3米/小時時，EGSBm反應器中污水COD含量幾乎不變。</p><p>　　2.2顆粒污泥的分析</p><p>　　這幅變形梯度凝膠電泳剖面

21、圖顯示的是從EGSBm反應器中提取的75天和165天顆粒污泥樣本中9-12DNA片段。相比之下，我們可以從處理酸性污水的最初的接種污泥中提取第15號DNA片段。這些DNA片段分布在16S核糖核酸RNA的V3區(qū)段內，每個基因片段代表一種微生物種類。</p><p>　　圖5顆粒污泥樣本的變形梯度凝膠電泳（DGGE）剖面圖</p><p>　　比較了不同污泥樣品的變形梯度凝膠電泳（DGGE）剖

22、面圖，結果表明,帶1、2、3、4、9、10的接種污泥也存在于第75 天和第165 天 EGSBm污泥樣品中,而其他的9個頻段內的接種污泥很少見。相反,在EGSBm顆粒污泥的樣品中出現(xiàn)了一些新的頻段。頻段的強度隨不同的運行階段和反應區(qū)域而變化。然而,微生物物種的數量在整個反應階段和反應區(qū)域內并沒發(fā)生明顯變化。由于環(huán)境的變化,譬如循環(huán)比率,水力停留時間（HRT），有機負載率（OLR）和進水質量，微生物會選擇性地形成穩(wěn)定的微生物群落，通過競爭

23、來有效地降解有機污染物。</p><p>　　在EGSBm反應器運行1,45,76和110天，分別檢測A、B、C、D四個區(qū)域內顆粒污泥直徑的變化。記錄數據如圖6。在第1天，接種污泥的直徑均勻地分布在0.8-2毫米的范圍內。在第45和76天，大部分顆粒污泥的直徑分布在0.6-2毫米范圍內，而A和B區(qū)域也有一少部分顆粒污泥的直徑分布在0.01-0.4毫米范圍內。在第110天，顆粒污泥的直徑逐漸地變大。從中我們看到顆粒

24、污泥在EGSBm中最初是分散的,隨著反應條件的變化逐步聚集為厭氧微生物菌落。</p><p>　　圖6不同反應階段顆粒污泥直徑的變化</p><p><b>　　2.3 水動力特性</b></p><p>　　當進水向上流動通過顆粒污泥床時，它將和該區(qū)域內污水混合（或分散到污水中）。因此，對于理想的塞式流動應分散考慮，如下面所表達的停留時間分布

25、（RTD）模型：</p><p>　　在公式中，D/UL表示無量綱的離散量，D表示擴散系數（平方米/小時），U表示上升流速Vup（米/小時），L代表反應器的長度（米）。對于理想的塞式流動反應器，D/UL的值是0。相反，對于理想的連續(xù)攪拌釜式反應器（CSTR），D/UL的值趨近無窮大。通過脈沖示蹤劑（例如，Li+）的方法，示蹤劑濃度會隨著試驗時間在不同的水力停留時間發(fā)生變化，如圖7。依據圖7的結果，經過計算和總結得

26、出了表3中的數據，記錄了在三種不同的上升流速下無關量Vd和D/UL的值。</p><p>　　圖7 EGSBm和EGSBc兩種反應器的水力停留時間（RTD）</p><p>　　表3 EGSBm和EGSBc兩種系統(tǒng)中Vd和D/UL的值</p><p>　　對于EGSBc系統(tǒng)，在上升流速為5米/小時時，D/UL最大可取0.18對應的Vd的最小值取10.13。當上升流速

27、降為2米/小時時，D/UL的值會隨之降低，意味著局部流動增強了。這與先前得出的結論一致，在EGSBc系統(tǒng)中，當上升流速超過5米/小時時，SS的濃度會隨上升流速的升高而升高（如圖2所示）。對于EGSBm系統(tǒng)，D/UL的值會隨Vup的增大而增大（Vd下降）。在上升流速Vup為10.3米/小時，Vd取值為0.87%表明EGSBm系統(tǒng)能保持較好的水動力條件。這和前面在EGSBm污水中COD和CODfilt濃度數據結論一致（見圖2）。當上升流速V

28、up上升時，EGSBm的綜合水動力特性有所提高，同時污泥流失得到控制，所以它對有機污染物的去除效果更明顯。這再次證明了改進型的EGSBm提高了污水處理效率。</p><p><b>　　3總結</b></p><p>　　這項研究表明，在常溫條件下，EGSBm反應器通過混合液循環(huán)能更有效，更穩(wěn)定地處理城市污水，相反，EGSBc則采用污水回收的形式。EGSBm比EGSB

29、c更能有效地處理污水中的COD、CODfilt和SS。在較高的上升流速情況下，EGSBc比EGSBm顆粒污泥流失情況嚴重。</p><p>　　在EGSBm系統(tǒng)中，縱貫整個反應過程，不管污水水質的變化和流體力學特性，厭氧生物都保持一個穩(wěn)定的生物群落，這樣就能保證有效降解有機污染物。在EGSBm反應開始后，一小部分顆粒污泥通過分解，新的顆粒污泥厭氧微生物逐步聚集起來進而適應反應條件。</p><

30、p>　　運用流體停留時間模型對水力特性分析顯示，在EGSBm系統(tǒng)中，D/UL的值會隨上升流速Vup的增加而增加。Vd低至0.87%上升流速Vup是10.3米/小時對應的D/UL值為0.15。然而，在EGSBc系統(tǒng)中，當上升流速Vup是5米/小時時，D/UL的最大值是0.18。在EGSBc系統(tǒng)中，無論Vup是增大還是減小，都會導致D/UL值的減小，主要是因為混合不充分進而增強了局部流動。在EGSBm系統(tǒng)中，良好的水動力條件確保了在較

31、高流速情況下污水處理的效率。</p><p>　　附件2：外文原文（摘自哈爾濱工業(yè)大學學報2009，4（16））</p><p>　　development of a novel modified EGSB reactor for municipal sewage treatment at ambient temperatures</p><p>　　In rece

32、nt years，anaerobic treatment has become an attractive sustainable wastewater treatment technology due to its low energy consumption and biogas production.In particular,the application of the up—flow anaerobic sludge blan

33、ket(UASB)and the conventional expand granular sludge bed(EGSBc )in domestic wastewater treatment has gained much more attention.The EGSBc is generally more efficient in COD reduction,and more resistant to shock organic l

34、oading rates(OLR)as well as the changes of temperatur</p><p>　　In this paper,a modified EGSB reactor was developed by combining the advantages of the UASB and EGSBc reactors.Pilot-scale study was carried out

35、 for both EGSBm and EGSBc reactors under ambient conditions for the purpose of comparison.The effluent of a primary sedimentation tank in the Dongqu municipal sewage treatment plant was used as influent.The hydrodynamic

36、characteristics in EGSBm were analyzed by Retention Time Distribution(RTD)experiments and the Polvmerase Chain Reaction.Denaturing Gradi</p><p>　　1 Materials and Methods </p><p>　　1.1 Sources of

37、 Biomass and Feed Influent </p><p>　　Mesophilic anaerobic granular sludge was obtained from a ful1-scale internal circulation bioreactor treating citric acid production wastewater located in Wuxi City,China.

38、The black granular sludge had a regular form(φ=0.8-2 mm)and good settleability.The sludge contained 73．6 g／L total suspended solids(TSS)and 59．0 g／L volatile suspended solids(VSS)．The initial inoculated sludge volume occ

39、upied 65％ of the effective volume of the EGSBm and EGSBc reactors.</p><p>　　The efluent from a primary sedimentation tank of Dongqu municipal sewage treatment plant located Shanghai was used as influent.The

40、raw sewage consisted of 60％of domestic wastewater and 40％ of industrial wastewater.The major characteristics of the influent were summarized in Tab.1 .</p><p>　　1.2 Reactor Description </p><p>　

41、　The schematic diagram of the pilot-scale EGSBc and EGSBm reactors was shown in Fig.1.Both reactors were made of plexiglass with a total volume of 300 L and adopted a continuous flow mode.In the EGSBc ,the distribution s

42、ystem was placed at the bottom of the reactor，and its effluent was recirculated to mix with the influent.In the EGSBm ,its mixed liquid was recirculated to mix with the influent using a pump.The distribution system of EG

43、SBm consisted of a tank of 5 L and 4 PVC tubes．The tank was p</p><p>　　In the EGSBm ,the mixed liquid containing granular sludge was recirculated approximately at the middle of the reactor to the top tank wh

44、ere it was mixed well with the influent.The composite influent then flowed downward gravitationally along the distribution tubes to come into the bottom of the reactor.In the lower reaction chamber,the composite influent

45、 was further mixed with local liquid and got degraded efficiently since a high concentration of granular sludge was available.As the wastewater </p><p>　　1.3 Experimental Conditions </p><p>　　Af

46、ter the two pilot-scale reactors had been successfully started up and reached a steady state condition,they were continuously run for a total period of 165 d at ambient temperatures.Based on the steady state conditions,t

47、he total operation period was divided into ten operation phases．The specific experimental conditions of each operation phase are detailed in Tab.2. </p><p>　　1.4 Reactor Performance Evaluation </p>&l

48、t;p>　　In each operation phase,the overall performance of EGSBc and EGSBm was evaluated by the removal efficiencies of COD,CODfilt and SS.The CODfiltrepresented the COD concentration of the effluent after passing throu

49、gh a qualitative filter paper.The concentrations of COD and CODfilt were measured by the standard potassium dichromate method,and the concentration of SS was measured by filtering,drying and weighing water samples.</p

50、><p>　　1.5 Granular Sludge Analysis </p><p>　　At the end of the operation phases 4 and 10, granular sludge samples were taken from four different regions in the EGSBm which were denoted as A,B,C an

51、d D in Fig.1.The distances of A,B,C and D from the reactor bottom were 2.0,1.5,1.0 and 0.5 m,respectively.After DNA was extracted from the granular sludge samples,the 16SrRNA genes were amplified for cloning and sequenci

52、ng by polymerase chain reactions (PCR)on specific regions.The PCR product was then differentiated by the use of DGGE. </p><p>　　The differentiated strains were amplified again to make the strain quantity rea

53、ch the needed measurement level.</p><p>　　At pre-selected reaction times,the diameters of the granular sludge collected from the above four regions were analyzed by a laser granularity instrument (Model LS23

54、0,Beckman Coulter of America)with a detection range of 0.04-2000 μm. </p><p>　　1.6 Hydrodynamic Characteristics </p><p>　　A pulse tracer,Li+ was used to analyze the retention time distribution i

55、n the reactor.In each analysis,10 mL of 10 mg/L Li+ was introduced into the influent through pulse injection and its concentration in the effluent was determined periodically by ICP/AES coupled with a PerkinElmer Optima

56、2100 DV plasma emission spectrometer. </p><p>　　2 Results and Discussions </p><p>　　2.1 Reactor Performance </p><p>　　1)Effect of VupThe effect of Vup on the COD and CODfilt concent

57、rations of the EGSBc and EGSBm effluents is shown in Fig.2.Results indicate that the mean concentrations of CODfilt of the EGSBm and EGSBc effluents decreased from 94.1 and 97.1 mg/L(P1)to 59.4 and 71.4 mg/L(P5),respecti

58、vely,when the Vup increased from 5.0 m/h(P3)to 10.3 m/h(P5). Effluent COD concentration of the two reactors had the same trend as CODfilt concentration.The EGSBm exhibited a much better performance and restorability a<

59、;/p><p>　　2)Effect of HRT.The effect of HRT on the COD and CODfilt concentrations of EGSBcand EGSBm effluents is shown in Fig.3.Results indicate that the mean concentrations of COD and CODfilt of the EGSBm effl

60、uent decreased from 119.7 and 94.1 mg/L(P1)to 104 and 82.6 mg/L(P7),respectively,when the HRT significantly decreased from 6to 2h.Similarly,the meanconcentrations of COD and CODfilt of the EGSBc effluent decreased from l

61、22.7 and 97.1 mg/L(P1) to 113.3 and 91.5 mg/L(P7),respectively.As the HRT furthe</p><p>　　The mean concentrations of VFA of both EGSBm and EGSBc effluents increased rapidly from 28 and 31 g/L(P6，HRT 4 h)to 4

62、2 and 65 g/L(P7，HRT 2 h),respectively.This implies that the VFA was used more rapidly for methane generation in EGSBmthan EGSBc at low HRT values. </p><p>　　3）Effect of OLR.The effect of OLR on the COD and C

63、ODfilt concentrations of the EGSBm and EGSBc effluents is shown in Fig.4.When the OLR suddenly decreased from 7.2(P8)to 1.2 kgCOD/(m3·d)(P9), the EGSBm almost maintained its treatment efficiency, while the treatment

64、 efficiency of the EGSBc was improved to some extent.When the OLR was adjusted from 1.2(P9) back to 7.2 kgCOD/(m3·d)(P10),a rapid increase of the COD and CODfilt concentrations of both EGSBm and EGSBc effluents was

65、observed during the </p><p>　　In general,the COD,CODfilt and SS concentrations of the EGSBm effluent was notably lower than those of the ECSBc effluent when the experimental condition(e.g.,Vup , HRT,and OLR)

66、was changed.Although the SS concentrations of both EGSBm and EGSBc effluents increased with the increasing Vup,the EGSBm always washed out much less biomass than the EGSBc .The COD concentration of the EGSBm effluent was

67、 maintained quite stable even at a Vup value as high as 10.3 m/h.</p><p>　　2.2 Granular Sludge Analysis </p><p>　　The DGGE profiles showed that 9-12 DNA snippets were extracted from the 75 d and

68、 165 d granular sludge samples of the EGSBm . In comparison,15 DNA snippets could be extracted in total from the original inoculation sludge treating citric acid production wastewater(as shown in Fig.5).These DNA snippet

69、s distributed in the V3 section of the 16SrDNA gene with each snippet representing one microbial species.</p><p>　　Comparing the DGGE profiles of different sludge samples. the results demonstrate that Bands

70、1,2,3, 4,9,10 of the inoculation sludge were also present in the 75 d and 165 d sludge samples of EGSBm ,while other 9 bands of the inoculation sludge were seen few . In contrast, a few new bands appeared in the granular

71、 sludge samples of the EGSBm .Some band intensities varied with different operation phases and reaction regions. However, the number of microbial species remained similar regardless of ope</p><p>　　The diame

72、ter change of the granular sludge in regions A,B,C and D of the EGSBm was inspected at 1,45,76 and 110 d after the reactor was started up, as shown in Fig.6. At 1 d,the diameters of the seed sludge in all regions distrib

73、uted quite uniformly in the range of 0.8-2 mm. At 45 and 76 d,most granular sludge remained in the diameter range of 0.6-2 mm . while a small portion of granular sludge in Regions A and B disaggregated and distributed in

74、 the diameter range of 0.01—0.4 mm .At 110 d, the d</p><p>　　2.3 Hydrodynamic Characteristics </p><p>　　When the influent flowed upward through the granular sludge bed,it would mix with(or dispe

75、rse into)local wastewater.Therefore,the hydrodynamics of an ideal plug-flow should take dispersion into consideration,as expressed by the following residence time distribution(RTD)model： </p><p>　　where D/UL

76、 is the dimensionless dispersion number, D denotes the coefficient of diffusion(m2 /h),U equals Vup(m/h),and L represents the length of reactor(m). For an ideal plug-flow reactor,the value of D/UL equals zero.On the cont

77、rary,for an ideal continuous stirred tank reactor(CSTR),the value of D/UL approaches infinity.Through the pulse tracer (i.e.,Li+)method, the tracer concentration changes along with the experimental time under different H

78、RT were shown in Fig.7.Based on the results of Fig</p><p>　　For the EGSBc,a maximal D/UL of 0.18 which corresponded to a minimal Vd of 10.13 was observed at the Vup of 5 m/h.As the Vup decreased to 2 m/h, th

79、e D/UL value decreased,implying insuficient hydrodynamic mixing. As the Vup increased to 10.3 m/h,the D/UL value also decreased, implying enhanced short-flow.This agrees with the previous result that the SS concentration

80、 of the EGSBc effluent increased rapidly when the Vup exceeded 5.0 m/h(as shown in Fig.2). For the EGSBm, the D/UL kept increasing(or</p><p>　　3 Conclusions </p><p>　　This study showed that muni

81、cipal sewage could be treated eficiently and stably with the EGSBm reactor through recirculating its mixed liquid at ambient temperatures,by contrast,effluent recycling was adopted by EGSBc. The EGSBm could achieve impro

82、ved treatment efficiencies in terms of COD,CODfilt and SS in comparison with the EGSBc .The washout of granular sludge from the EGSBm was much less than that from the EGSBc at high Vup values. </p><p>　　Thro

83、ughout the reactor height, anaerobic microorganisms maintained a stable microbial community in the EGSBm regardless of the changes of wastewater quality and hydrodynamic characteristics. thus ensuring the effective degra

84、dation of organic pollutants. Though a small portion of granular sludge disaggregated after the EGSBm reactor was started up,new granular sludge gradually aggregated as the anaerobic microorganisms were acclimated to the

85、 operational conditions. </p><p>　　The hydrodynamic analysis using the RTD model revealed that the D/UL of the EGSBm kept increasing as the Vup increased.The Vd was as low as 0.87% at the Vup of 10.3 m/h whi

86、ch corresponded to a D/UL value of 0.15.However,the maximal D/UL(0.18)for the EGSBc was found at the Vup of 5 m/h.Either decreasing or increasing the Vup in the EGSBc would result in a decrease of the D/UL due to insufic