3.1介紹

The purpose of this chapter is to present a treatment process-oriented review of thechemistry and biochemistry of nitrification and denitrification. An understanding of thissubject is useful for developing an appreciation of the factors affecting the performancedesign, and operationof nitrification and denitrification processes.Subsequent chapters dealwith design aspects of nitrification (Chapter 4) and denitrification (Chapter 5). Since theselatter chapters are laid out to be used without reference to this chapter, review of thetheoretical material in this chapter is not mandatory.

----

本章的目的在于提供一種針對(duì)處理過程的化學(xué)和生物化學(xué)性質(zhì)對(duì)硝化和反硝化進(jìn)行評(píng)述。對(duì)于理解影響硝化和反硝化過程的性能設(shè)計(jì)和操作因素，了解這一主題是非常有用的。后續(xù)的章節(jié)將涉及硝化（第四章）和反硝化（第五章）的設(shè)計(jì)方面。由于這些后續(xù)章節(jié)的目的是不參考本章的，因此本章中理論資料的回顧并非強(qiáng)制要求。

Biological processes for control of nitrogenous residuals in effluents can be classified in twobroad areas. First, a process designed to produce an effluent where influent nitrogenammonia and organic nitrogen) is substantially converted to nitrate nitrogen can beconsidered. This process, nitrification, is carried out by bacterial populations thatsequentially oxidize ammonia to nitrate with intermediate formation of nitrite. Nitrificationwill satisfy effluent or receiving water standards where reduction'of residual nitrogenousoxygen demand due to ammonia is mandated or where ammonia reduction for other reasonsis required for the treatment system. The second type of process, denitrification, reducesnitrate to nitrogen gas and can be used following nitrification when the total nitrogenouscontent of the effluent must be reduced.

----

在處理廢水中的氮?dú)埩粑飼r(shí)，可以將生物過程分為兩個(gè)廣泛的領(lǐng)域。首先，可以考慮一種旨在產(chǎn)生出水，其中影響氮（氨和有機(jī)氮）在相當(dāng)程度上轉(zhuǎn)化為硝酸鹽氮的過程。這個(gè)過程叫做硝化，是通過細(xì)菌族群完成的，它們將氨氧化成硝酸鹽，中間還有亞硝酸鹽的形成。硝化將會(huì)符合出水或接收水體標(biāo)準(zhǔn)，這些標(biāo)準(zhǔn)要求必須減少由于氨引起的殘留氮氧需求，或者需要出于其他原因降低氨的含量。第二種類型的過程是反硝化，將硝酸鹽還原為氮?dú)?，可以在硝化之后使用，?dāng)必須減少出水中總氮的含量時(shí)。

3.2 Nitrification

The two principal genera of importance in biological nitrification processes are Nitro-somonas and Nitrobacter. Both of these groups are classed as autotrophic organisms. Theseorganisms are distinguished from heterotrophic bacteria in that they derive energy forgrowth from the oxidation of inorganic nitrogen compounds, rather than from theoxidation of organic matter, Another feature of these organisms is that inorganic carbon(carbon dioxide) is used for synthesis rather than organic carbon. Each group is limited tothe oxidation of specific species of nitrogen compounds. Nitrosomonas can oxidizeammonia to nitrite, but cannot complete the oxidation to nitrate. On the other handNitrobacter is limited to the oxidation of nitrite to nitrate. Since complete nitrification is asequential reaction, treatment processes must be designed to provide an environmentsuitable to the growth of both groups of nitrifying bacteria.

----

3.2 硝化

生物硝化過程中的兩個(gè)主要屬是氧化亞氮單胞菌和硝化藍(lán)光菌。這兩個(gè)組是自養(yǎng)生物。它們與異養(yǎng)細(xì)菌的不同之處在于，它們從無機(jī)氮化合物的氧化中獲得生長必需的能量，而不是從有機(jī)物的氧化中獲得能量。這些生物的另一個(gè)特征是使用無機(jī)碳（二氧化碳）進(jìn)行合成，而不是有機(jī)碳。每一組生物只能氧化特定種類的氮化合物。氧化亞氮單胞菌能將氨氧化為亞硝酸鹽，但不能將氧化完全為硝酸鹽。同時(shí)，硝化藍(lán)光菌則僅限于將亞硝酸鹽氧化為硝酸鹽。由于完全的硝化是一個(gè)連續(xù)的反應(yīng)，處理過程必須設(shè)計(jì)成適合兩種硝化細(xì)菌生長的環(huán)境。

3.2.1 Biochemical Path ways

On a biochemical level, the nitrification process is more complex than simply the sequentialoxidation of ammonia to nitrite by Nitrosomonas and the subsequent oxidation of nitrite to nitrate by Nitrobacter. Various reaction intermediates and enzymes are involved,1 Moreimportant than an understanding of these pathways is knowledge of the response ofnitrification organisms to environmental conditions.

----

3.2.1 生物化學(xué)途徑

在生化層面上，硝化過程比 Nitrosomonas 順序氧化氨到亞硝酸鹽，然后 Nitrobacter（硝化桿菌） 氧化亞硝酸鹽到硝酸鹽更為復(fù)雜。這涉及到各種反應(yīng)中間體和酶。比了解這些途徑更重要的是了解硝化微生物對(duì)環(huán)境條件的響應(yīng)。

3.2.2. Energy and Synthesis Relationships

The stoichiometric reaction for oxidation of ammonium to nitrite by Nitrosomonas is:

----

3.2.2. 能量和合成關(guān)系

Nitrosomonas（亞硝化單胞菌）將氨氧化為亞硝酸的化學(xué)反應(yīng)的化學(xué)計(jì)量式為:

The loss of free energy by this reaction at physiological concentrations of the reactants hasbeen estimated by various investigators to be between 58 and 84 kcal per mole ofammonia.?

----

各種研究者估計(jì)，在反應(yīng)物的生理濃度下，這種反應(yīng)失去的自由能大約在58到84千卡每摩爾氨之間。

The reaction for oxidation of nitrite to nitrate by Nitrobacter is:

This reaction has been estimated to release between 15.4 to 20.9 kcal per mole of nitriteunder in vivo conditions. Thus, Nitrosomonas obtains more energy per mole of nitrogenoxidized than Nitrobacter. If it assumed that the cell synthesis per unit of energy producedis equal, there should be greater mass of Nitrosomonas formed than Nitrobacter per mole ofnitrogen oxidized. As will be seen, this is in fact the case.

----

據(jù)估算，該反應(yīng)在體內(nèi)條件下每摩爾亞硝酸根釋放15.4至20.9千卡。因此，相較于硝化細(xì)菌，氨氧化菌在氧化每摩爾氮時(shí)獲得更多的能量。假定單位能量產(chǎn)生的細(xì)胞合成相等，則每摩爾氧化氮產(chǎn)生的氨氧化菌質(zhì)量應(yīng)大于硝化細(xì)菌。如下將看到，事實(shí)上是這種情況。

As previously mentioned, these reactions furnish the energy required for growth of thenitrifying organisms. Assuming that the empirical formulation of bacterial cells isC5H7NO2, the equations for the growth of Nitrosomonas and Nitrobacter are shown inEquations 3-4 and 3-5,respectively:

----

正如先前所述，這些反應(yīng)為硝化微生物生長所需的能量提供了基礎(chǔ)。假設(shè)細(xì)菌細(xì)胞的實(shí)驗(yàn)配方為C5H7NO2，則Nitrosomonas和Nitrobacter的生長方程式如方程式3-4和3-5所示：

Equations 3-1, 3-4 and 3-5 have terms showing the production of free acid (H+) and theconsumption of gaseous carbon dioxide (CO2). In actual fact, these reactions take place inaqueous systems in the context of the carbonic acid system. These reactions usually takeplace at pH levels less than 8.3. Under this circumstance, the production of acid results inimmediate reaction with bicarbonate ion (HCO3) with the production of carbonic acid(H2CO3). The consumption of carbon dioxide by the organisms results in some depletion ofthe' dissolved form of carbon dioxide, carbonic acid (H2CO3). Table 3-1 presents themodified forms of Equations 3-1 to 3-5 to reflect the changes in the carbonic acid system.As will be later described in Sections 3.2.3 and 3.2.5.6, the variations occurring in pHresulting from changes in the carbonic acid system can significantly affect nitrificationprocess performance.

方程式3-1、3-4和3-5具有顯示自由酸（H +）的產(chǎn)生和吸收氣態(tài)二氧化碳（CO2）的術(shù)語。實(shí)際上，這些反應(yīng)在炭酸酸系統(tǒng)的水系中發(fā)生。這些反應(yīng)通常發(fā)生在pH小于8.3的水平。在這種情況下，酸的產(chǎn)生會(huì)立即與碳酸氫根離子（HCO3）反應(yīng)，生成碳酸（H2CO3）。生物體對(duì)二氧化碳的消耗導(dǎo)致一些溶解的二氧化碳形式，即碳酸（H2CO3）的消耗。表3-1呈現(xiàn)了修改后的方程式3-1至3-5的形式，以反映炭酸酸系統(tǒng)中的變化。正如稍后在3.2.3和3.2.5.6節(jié)中所描述的那樣，由于炭酸酸系統(tǒng)的變化而導(dǎo)致的pH變化可以顯著影響硝化過程的性能。

The equations for energy yielding reactions (Equations 3-1 and 3-2) can be combined withthe equations for organism synthesis (Equations 3-4 and 3-5) to form overall synthesisoxidation relations by knowledge of the yield coefficients for the nitrifying organisms.Experimental yield values for Nitrosomonas range from 0.04 to 0.13 1b VSS grown per lbammonia nitrogen oxidized, Experimental yields for Nitrobacter are in the range from 0.02to 0.07 lb VSS grown per lb of nitrite nitrogen oxidized,Values based on thermodynamictheory are 0.29 and 0.084 for Nitrosomonas and Nitrobacter, respectively.Theexperimentally based yield may be lower than theoretical values due to the diversion of aportion of the free energy released by oxidation to microorganism maintenance functions.
Equations for synthesis-oxidation using representative measurernents of yields and oxygenconsumption for Nitrosomonas and Nitrobacter are as follows:

能量產(chǎn)生反應(yīng)的方程式（方程式3-1和3-2）可以與有機(jī)體合成的方程式（方程式3-4和3-5）結(jié)合起來，通過對(duì)硝化有機(jī)體的產(chǎn)量系數(shù)的了解，形成總體合成氧化關(guān)系。Nitrosomonas的實(shí)驗(yàn)產(chǎn)量值范圍為0.04至0.13磅VSS/磅氨氮氧化，Nitrobacter的實(shí)驗(yàn)產(chǎn)量范圍為0.02至0.07磅VSS/磅亞硝酸氮氧化，基于熱力學(xué)理論的值分別為0.29和0.084。由于將一部分由氧化釋放的自由能轉(zhuǎn)向微生物維護(hù)功能，基于實(shí)驗(yàn)的產(chǎn)量可能低于理論值。使用對(duì)Nitrosomonas和Nitrobacter的產(chǎn)量和氧消耗的代表性測(cè)量值的合成-氧化方程式如下：

In these equations, yields for Nitrosomonas and Nitrobacter are 0.15 mg cells/mg and 0.02 mg cells/mg NO2-N, respectively. On this basis, the removal of twenty mg/l ofammonia nitrogen would yield only 1.8 mg/l of nitrifying organisms. This relatively lowyield has some far reaching implications, as will be seen in Section 3.2.7. Oxygenconsumption ratios in the equations are 3.22 mg O2/mg NH4-N oxidized and 1.11 mgO2/mg ? oxidized, which is in agreement with measured values.

在這些方程中，亞硝酸鹽氧化細(xì)菌和硝酸鹽氧化細(xì)菌的收益分別為0.15 mg細(xì)胞/mgNH和0.02 mg細(xì)胞/mg NO2-N?；诖?，去除20 mg/l氨氮只會(huì)產(chǎn)生1.8 mg/l的硝化生物。這種相對(duì)較低的收益率具有一些“深遠(yuǎn)的影響，這將在第3.2.7節(jié)中看到。方程中的氧消耗比為3.22 mg O2/mg 氧化和1.11 mg O2/mg NO2-N氧化，與測(cè)量值相符。

3.2.3Alkalinity and H Relationships

Equation 3-3A (Table 3-1) shows that alkalinity is destroyed by the oxidation of ammoniaand carbon dioxide (H2CO3 in the aqueous phase) is produced, When synthesis is neglectedit can be calculated that 7.14 mg of alkalinity as CaCO3 is destroyed per mg of ammonianitrogen' oxidized, The effect of synthesis is relatively small; in Equation 3-8, the ratio is7.07 mg of alkalinity per mg of ammonia nitrogen oxidized. Experimentally determinedratios are presented in Table 3-2; differences between the experimental and theoreticalratios are due either to errors in alkalinity or nitrogen analyses or the inadequacy of theory to completely explain the phenomenon. A ratio of 7.14 g alkalinity destroyed per mg ofammonia nitrogen oxidized may be used for engineering calculations.

方程式3-3A（表3-1）表明，堿度會(huì)因氨的氧化而被破壞，同時(shí)產(chǎn)生二氧化碳（水相中的H2CO3）。如果忽略綜合效應(yīng)，每毫克氨氮被氧化，7.14毫克以CaCO3計(jì)的堿度會(huì)被破壞。綜合效應(yīng)對(duì)結(jié)果的影響相對(duì)較??；在方程式3-8中，比例是每毫克氨氮被氧化，7.07毫克的堿度被破壞。實(shí)驗(yàn)確定的比率列在表3-2中；實(shí)驗(yàn)和理論比率之間的差異可能是由于堿度或氮分析誤差或理論無法完全解釋現(xiàn)象造成的。在工程計(jì)算中，可以使用每毫克氨氮被氧化，7.14克堿度被破壞的比率。

These changes may have a depressing effect on pH in the nitrification system, as therelationship for pH in the system is:

這些變化可能會(huì)對(duì)硝化系統(tǒng)中的pH值產(chǎn)生抑制作用，因?yàn)樵撓到y(tǒng)中pH關(guān)系為：

Since nitrification reduces the level and increases the H2CO3 level, it is obvious that the pH would tend to be reduced. The effect is mediated by stripping of carbon dioxidefrom the liquid by the process of aeration and the pH is elevated upwards. If the carbondioxide is not stripped from the liquid, such as in enclosed high purity oxygen systems, thepH can' be depressed as low as 6.0. lt has been calculated that to maintain the pH greaterthan 6.0 in an enclosed system, the alkalinity of the wastewater must be 10 times greaterthan the amount of ammonia nitrified。

由于硝化反應(yīng)降低了碳酸氫鹽（）的水平并增加了二氧化碳（H2CO3）的水平，因此pH明顯會(huì)趨于降低。通過曝氣過程將溶液中的二氧化碳除去，可以提升pH值。如果不除去溶液中的二氧化碳，例如在密閉的高純度氧氣系統(tǒng)中，pH可能會(huì)降低至6.0以下。據(jù)估算，在密閉系統(tǒng)中維持pH大于6.0，廢水的堿度必須是氨氮祛除量的十倍。

Even in open systems where the carbon dioxide is continually stripped from the liquid.severe pH depression can occur when the alkalinity in the wastewater approaches depletion by the acid produced in the nitrification process. For example, if in a.wastewater20 mg/l of ammonia nitrogen is nitrified, 143 mg/l of alkalinity as CaCO3 will be destroyed.In many wastewaters there is nsufficient alkalinity initially present to leave a sufficientresidual for buffering the wastewater during the nitrification process. The significance of pHdepression in the process is that nitrification rates are rapidly depressed as the pH is reduced below 7.0 (see Section 3.2.5.6). Procedures for calculating the operating pH in aeration
systems are presented in Section 4.9.
----
即便在二氧化碳不斷從液體中溢出的開放系統(tǒng)中，當(dāng)廢水中的堿度逐漸耗盡時(shí)，硝化過程中產(chǎn)生的酸會(huì)導(dǎo)致嚴(yán)重的pH下降。例如，如果廢水中20毫克/升氨氮被硝化，將破壞143毫克/升以CaCO3表示的堿度。在許多廢水中，最初存在的堿度不足以在硝化過程期間提供足夠的緩沖。pH下降的重要性在于，當(dāng)pH降至7.0以下時(shí)，硝化速率迅速下降（請(qǐng)參閱第3.2.5.6節(jié)）。在航空設(shè)備中計(jì)算操作pH的程序?qū)⒃诘?.9節(jié)中介紹。