氮控制手册-第三章化学和生物的硝化反硝化过程（3.1）
3.1介绍
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.
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本章的目的在于提供一种针对处理过程的化学和生物化学性质对硝化和反硝化进行评述。对于理解影响硝化和反硝化过程的性能设计和操作因素，了解这一主题是非常有用的。后续的章节将涉及硝化（第四章）和反硝化（第五章）的设计方面。由于这些后续章节的目的是不参考本章的，因此本章中理论资料的回顾并非强制要求。
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.
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在处理废水中的氮残留物时，可以将生物过程分为两个广泛的领域。首先，可以考虑一种旨在产生出水，其中影响氮（氨和有机氮）在相当程度上转化为硝酸盐氮的过程。这个过程叫做硝化，是通过细菌族群完成的，它们将氨氧化成硝酸盐，中间还有亚硝酸盐的形成。硝化将会符合出水或接收水体标准，这些标准要求必须减少由于氨引起的残留氮氧需求，或者需要出于其他原因降低氨的含量。第二种类型的过程是反硝化，将硝酸盐还原为氮气，可以在硝化之后使用，当必须减少出水中总氮的含量时。
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.
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3.2 硝化
生物硝化过程中的两个主要属是氧化亚氮单胞菌和硝化蓝光菌。这两个组是自养生物。它们与异养细菌的不同之处在于，它们从无机氮化合物的氧化中获得生长必需的能量，而不是从有机物的氧化中获得能量。这些生物的另一个特征是使用无机碳（二氧化碳）进行合成，而不是有机碳。每一组生物只能氧化特定种类的氮化合物。氧化亚氮单胞菌能将氨氧化为亚硝酸盐，但不能将氧化完全为硝酸盐。同时，硝化蓝光菌则仅限于将亚硝酸盐氧化为硝酸盐。由于完全的硝化是一个连续的反应，处理过程必须设计成适合两种硝化细菌生长的环境。
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.
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3.2.1 生物化学途径
在生化层面上，硝化过程比 Nitrosomonas 顺序氧化氨到亚硝酸盐，然后 Nitrobacter（硝化杆菌） 氧化亚硝酸盐到硝酸盐更为复杂。这涉及到各种反应中间体和酶。比了解这些途径更重要的是了解硝化微生物对环境条件的响应。
3.2.2. Energy and Synthesis Relationships
The stoichiometric reaction for oxidation of ammonium to nitrite by Nitrosomonas is:
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3.2.2. 能量和合成关系
Nitrosomonas（亚硝化单胞菌）将氨氧化为亚硝酸的化学反应的化学计量式为:
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.
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各种研究者估计，在反应物的生理浓度下，这种反应失去的自由能大约在58到84千卡每摩尔氨之间。
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.
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据估算，该反应在体内条件下每摩尔亚硝酸根释放15.4至20.9千卡。因此，相较于硝化细菌，氨氧化菌在氧化每摩尔氮时获得更多的能量。假定单位能量产生的细胞合成相等，则每摩尔氧化氮产生的氨氧化菌质量应大于硝化细菌。如下将看到，事实上是这种情况。
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:
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正如先前所述，这些反应为硝化微生物生长所需的能量提供了基础。假设细菌细胞的实验配方为C5H7NO2，则Nitrosomonas和Nitrobacter的生长方程式如方程式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具有显示自由酸（H +）的产生和吸收气态二氧化碳（CO2）的术语。实际上，这些反应在炭酸酸系统的水系中发生。这些反应通常发生在pH小于8.3的水平。在这种情况下，酸的产生会立即与碳酸氢根离子（HCO3）反应，生成碳酸（H2CO3）。生物体对二氧化碳的消耗导致一些溶解的二氧化碳形式，即碳酸（H2CO3）的消耗。表3-1呈现了修改后的方程式3-1至3-5的形式，以反映炭酸酸系统中的变化。正如稍后在3.2.3和3.2.5.6节中所描述的那样，由于炭酸酸系统的变化而导致的pH变化可以显著影响硝化过程的性能。
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:
能量产生反应的方程式（方程式3-1和3-2）可以与有机体合成的方程式（方程式3-4和3-5）结合起来，通过对硝化有机体的产量系数的了解，形成总体合成氧化关系。Nitrosomonas的实验产量值范围为0.04至0.13磅VSS/磅氨氮氧化，Nitrobacter的实验产量范围为0.02至0.07磅VSS/磅亚硝酸氮氧化，基于热力学理论的值分别为0.29和0.084。由于将一部分由氧化释放的自由能转向微生物维护功能，基于实验的产量可能低于理论值。使用对Nitrosomonas和Nitrobacter的产量和氧消耗的代表性测量值的合成-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.
在这些方程中，亚硝酸盐氧化细菌和硝酸盐氧化细菌的收益分别为0.15 mg细胞/mgNH和0.02 mg细胞/mg NO2-N。基于此，去除20 mg/l氨氮只会产生1.8 mg/l的硝化生物。这种相对较低的收益率具有一些“深远的影响，这将在第3.2.7节中看到。方程中的氧消耗比为3.22 mg O2/mg
氧化和1.11 mg O2/mg NO2-N氧化，与测量值相符。
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，碱度会因氨的氧化而被破坏，同时产生二氧化碳（水相中的H2CO3）。如果忽略综合效应，每毫克氨氮被氧化，7.14毫克以CaCO3计的碱度会被破坏。综合效应对结果的影响相对较小；在方程式3-8中，比例是每毫克氨氮被氧化，7.07毫克的碱度被破坏。实验确定的比率列在表3-2中；实验和理论比率之间的差异可能是由于碱度或氮分析误差或理论无法完全解释现象造成的。在工程计算中，可以使用每毫克氨氮被氧化，7.14克碱度被破坏的比率。
These changes may have a depressing effect on pH in the nitrification system, as therelationship for pH in the system is:
这些变化可能会对硝化系统中的pH值产生抑制作用，因为该系统中pH关系为：
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。
由于硝化反应降低了碳酸氢盐（）的水平并增加了二氧化碳（H2CO3）的水平，因此pH明显会趋于降低。通过曝气过程将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，例如在密闭的高纯度氧气系统中，pH可能会降低至6.0以下。据估算，在密闭系统中维持pH大于6.0，废水的碱度必须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.
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即便在二氧化碳不断从液体中溢出的开放系统中，当废水中的碱度逐渐耗尽时，硝化过程中产生的酸会导致严重的pH下降。例如，如果废水中20毫克/升氨氮被硝化，将破坏143毫克/升以CaCO3表示的碱度。在许多废水中，最初存在的碱度不足以在硝化过程期间提供足够的缓冲。pH下降的重要性在于，当pH降至7.0以下时，硝化速率迅速下降（请参阅第3.2.5.6节）。在航空设备中计算操作pH的程序将在第4.9节中介绍。
