第二章 环境中的含氮物质及控制废水排放的必要性

2.1 Introduction
Various compounds containing the element nitrogen are becoming increasingly important inwastewater management programs because of the many effects that nitrogenous materials inwastewater effluent can have on the environment. Nitrogen, in its various forms, can depletedissolved oxygen levels in receiving waters, stimulate aquatic growth, exhibit toxicitytoward aquatic life, affect chlorine disinfection efficiency, present a public health hazard.and affect the suitability of wastewater for reuse. Biological and chemical processes whichoccur in wastewater treatment plants and in the natural environment can change thechemical form in which nitrogen exists Such change may eliminate one deleterjous effect ofnitrogen while producing, or leaving unchanged, another effect. For example, by convertingammonia in raw wastewater to nitrate, the oxygen-depleting and toxic effects of ammmoniaare eliminated, but the biostimulatory effects may not be changed signiicantly.
lt is important, therefore, prior to the detailed discussions of nitrogen removal processeswhich form the principal content of this manual, to review the chemistry of nitrogen andthe effects that the various compounds can have. Several speciic aspects are discussed inthis chapter. First, the nitrogen cycle for both surface water and soil/groundwatercnvironments is described, with emphasis on the important compounds and reactionsassociated with cach. Second, sources of nitrogen, both natural and man-caused, arediscussed. Important elements of the latter category include domestic and industrialwastewater, urban and suburban runoff, surface and subsurface agricultural drainage, andemissions to the atmosphere which may eventually enter the aquatic environment througlprecipitation or dustfall Then, the effects of nitrogen discharge to Surface watergroundwater, and land are summarized. And finally, introductory to the following chapters.a brief discussion is presented on the relationship between the various nitrogen compoundsand process removal efficicncy.
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2.1 引言
含氮元素的各种化合物在废水管理计划中变得越来越重要，因为废水中氮素材料对环境可能产生的影响很多。氮在其各种形式下会降低接收水体的溶解氧水平、促进水生生物生长、对水生生物具有毒性、影响氯消毒效率、构成公共卫生危害，并影响废水再利用的适用性。在废水处理厂和自然环境中发生的生物和化学过程可以改变氮的存在形式。这种改变可能消除一种有害氮素的影响，同时产生或保持另一种影响不变。例如，通过将原始废水中的氨转化为硝酸盐，可以消除氨的耗氧和毒性作用，但生物刺激作用可能不会显著改变。
因此，在详细讨论氮去除过程之前，本手册的主要内容之前，回顾氮的化学和其可能的影响至关重要。本章节讨论了几个具体方面。首先，描述了表面水体和土壤/地下水环境的氮循环，重点关注与每种循环相关的重要化合物和反应。其次，讨论了氮的来源，包括自然和人为因素。后者的重要元素包括家庭和工业废水、城市和郊区径流、表面和亚表面农业排水以及通过降水或灰尘沉降最终进入水生环境的大气排放。然后，总结了氮排放对表面水、地下水和土壤的影响。最后，在下一章之前，简要讨论了各种氮化合物与处理效率之间的关系。

2.2 氮循环

22. The Nitrogcn Cycle
Nitrogen exists in many compounds becatse of the high number of oxidation states it canassume. In ammonia or organic compotnds, the form most closely associated with plantsand animals, its oxidation state is minus 3. At the other extreme its oxidation state is plus 5when in the nitrate form. In the environment, changes from one oxidation state to anothercan be brought about biologically by living organisms The rclationship between the variouscompounds and the transformations which can occur are often presented schematically in adiagram known as the nitrogen cycle. Figure 2-1 shows a common manner of presentation.The atmosphere serves as a reservoir of N2 gas from which nitrogen is removed naturally by electrical discharge and nitrogen-fixing organisns and artificially by chemical manufacturing. Nitrogen gas is returned to the atmosphere by the action o denitrifying organisms. Inthe fixed state, nitrogen can undergo the various reactions shown. A general desciption olthe nitrogen cycle is presenfed here, and aspects of particular importance to surface waterand soil/groundwater environmtents are discussed in the following sections.
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氮循环

氮的氧化状态可以假定很高，因此它存在于许多化合物中。在植物和动物所密切关联的氨或有机化合物中，它的氧化状态为负3；而在硝酸盐形式中，它的氧化状态则是正5。在环境中，生物可以通过生物途径将一种氧化态转换成另一种；其中化合物间的关系及其转化通常以氮循环的方式图示呈现。图2-1展示了常见的图例呈现方式。大气作为氮气的储量，自然地通过电放电和固氮微生物以及人工地通过化学制造来去除氮。通过反硝化微生物作用，氮气返回大气。在固定状态中，氮可以经历各种反应。本文介绍了氮循环的一般描述，并探讨了对地表水和土壤/地下水环境至关重要的方面。

Transformation reactions  of importance include fixation, ammonification, assimilationnitrification and denitrification.2 These reactions can be carried out by particularmicroorganisms with either a net gain or loss of energy; energy considerations often play animportant role in determining the reaction which occurs. The principal compounds olconcern in the nitrogen cycle are nitrogen gas, ammonium, organic nitrogen, and nitrate.These compounds and their oxidation states are shown below:
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重要的转化反应包括固定、氨化、同化、硝化和反硝化。2 这些反应可以由特定的微生物进行，其能量净增益或净损失；能量考虑经常在确定发生的反应时发挥重要作用。氮循环中的主要化合物是氮气，铵，有机氮和硝酸盐。下面显示了这些化合物及其氧化态：

It is important to note that at neutral pH values there is very little molecular ammonia(NH3) in wastewater as most is in the form of the ammonium ion (NH4). The distributionof ammonia and ammonjum as a function of pH is discussed in Section 6.1.1.
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需要注意的是，在中性pH值下，废水中分子氨（NH3）含量非常少，而大部分都是以铵离子（NH4）的形式存在。关于氨和铵在pH值变化下的分布情况详见第6.1.1节。

Fixation of nitrogen from N2 gas to organic nitrogen is accomplished biologically byspecialized microorganisms. This reaction requires an investment of energy. Biologicalfixation accounts for most of the natural transformation of nitrogen to compounds whichcan be used by plant and animal life, Lightning fixation has been estimated to account forapproximately 15 percent of the total which occurs naturally.3 Industrial fixation wasinitially developed in the early 20th Century for manufacture of both fertilizer andexplosives. Presently, nitrogen fixed by industry is about half the amount that is removedfrom the atmosphere by natural means.
Ammonification is the change from organic nitrogen to the ammonjum (NHa/NH) formThis occurs to dead animal and plant tissue and to animal fecal matter.
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生物学上由特定微生物通过将N2气体转化为有机氮实现氮固定。这种反应需要投入能量。生物学固定过程占了氮转化为可以供植物和动物利用的化合物的自然过程的大部分。闪电固定被估计占了自然过程总量的约15％。20世纪初，工业固定最初被开发用于生产肥料和炸药。目前，工业固定的氮量约为自然方式从大气中移除的氮量的一半。腐烂是有机氮转化为铵（NH4 / NH）形式的过程，这发生在死亡的动物和植物组织以及动物粪便中。

Nitrogen in urine exists principally as urea. Urea is hydrolyzed by the enzyme urease toammonium carbonate.
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尿液中的氮主要存在于尿素中，尿素会被酶酰胺酶水解生成碳酸铵。

Assimilation is the use of ammonium or nitrate compounds to form plant protein and othernitrogen-containing compounds.
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同化是利用铵或硝酸盐化合物形成植物蛋白质和其他含氮化合物的过程。

Animals require protein from plants or from other animals. With certain specific exceptions.
they are incapable of converting inorganic nitrogen forms into organic forms.
The term “nitrification” is applied to the biological oxidation of ammonium, first to thenitrite, then to the nitrate, form. The bacteria responsible for these reactions are termedchemoautotrophic because they use inorganic chemicals as their source of energy. Generally.the Nitrosomonas genera are involved in conversion of ammonium to nitrite under aerobicconditions as follows:
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动物需要从植物或其他动物中获取蛋白质，除一些特殊例外外，它们无法将无机氮形式转化为有机形式。术语“硝化”适用于氨的生物氧化，首先形成亚硝酸盐，然后形成硝酸盐。负责这些反应的细菌被称为化能自养细菌，因为它们使用无机化学物质作为能源。通常，在有氧条件下，氨转化为亚硝酸盐的过程中，Nitrosomonas属参与其中，具体过程如下：

硝酸盐则通常由亚硝酸盐经由Nitrobacter菌株氧化而来，其反应式为：

整个硝化反应式如下：

To oxidize 1 mg/l of ammonia-nitrogen requires about 4.6 mg/l of oxygen when synthesis ofnitrifiers is neglected. The nitrate thus formed may be used in assimilation as describedabove to promote plant growth, or it may be used in denitrification, wherein throughbiological reduction, first nitrite and then nitrogen gas are formed, A fairly broad range ofbacteria can accomplish denitrification,including Psuedomonas, Micrococcus， Achromobacter. and Bacillus In simplified form, the reaction steps are as follows:
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氨氮1毫克每升的氧化需要约4.6毫克每升的氧气，假设不考虑硝化细菌的合成。因此产生的硝酸盐可用于同化，如上所述，以促进植物生长，也可用于反硝化作用，其中通过生物还原作用，首先形成亚硝酸盐，然后形成氮气。相当广泛的细菌可完成反硝化作用，包括铜绿假单胞菌、微球菌、黄色杆菌和芽孢杆菌。简化形式的反应步骤如下：

Here methanol is used as the example organic carbon source, although many natural andsynthetic organic compounds can serve as the carbon source for denitrification.
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在这里，甲醇被作为有机碳源的示例，虽然许多天然和合成的有机化合物都可以作为反硝化的碳源。

Oxidation of organic atter to carbon dioxide and water furnishes energy for bacteria.Either oxygen or nitrate may be used for the oxidation, but the use of oxygen results in therelease of more energy. When both oxygen and nitrate are present, bacteria preferentiallyuse oxygen. Therefore, use of nitrate for denitrification can only occur under anoxicconditions, an important consideration when attempting to remove nitrate from wastewater.
Nitrite, since it is an intermediate in the nitrification and denitrification processes, can linkthe nitrification and denitrification steps directly without passing through nitrate. First.nitrite is formed from oxidation of ammonium by Nitrosomonas, then nitrite can bedenitrified to nitrogen gas. By this route less oxygen is required for nitrification and lessorganic matter (energy) is required for denitrification. This is a special case, however, andnot broadly applicable to municipal wastewater treatment.
In discussing the nitrogen cycle, it is useful to differentiate between the surface water andsediment environment and the soil/groundwater environment. This aids in understanding theroles that nitrogenous compounds play in each and the problems which can be encountered
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有机物质氧化成二氧化碳和水为细菌提供能量。氧气或硝酸盐都可以用于氧化，但使用氧气会释放更多的能量。当同时存在氧气和硝酸盐时，细菌优先使用氧气。因此，在尝试将硝酸盐从废水中去除时，硝化只能在缺氧条件下进行，这是一个重要的考虑因素。

硝酸盐中间产物亚硝酸盐可以直接将硝化和反硝化步骤联系起来而不经过硝酸盐。首先，氨经Nitrosomonas氧化生成亚硝酸盐，然后亚硝酸盐可以被反硝化成氮气。通过这种方式，硝化所需的氧气较少，反硝化所需的有机物（能量）也较少。但这是一个特殊情况，不适用于城市废水处理。

在讨论氮循环时，区分水表和沉积物环境与土壤/地下水环境是有用的。这有助于理解氮化合物在各种情况下所扮演的角色以及可能遇到的问题。