氮控制手册2.5脱氮处理工艺
In the past several years the number of processes utilized in wastewater treatment hasincreased rapidly. Many of these processes have been developed with the specific purpose oftransforming nitrogen compounds or removing nitrogen from the wastewater stream. Otherscan remove several compounds, including significant amounts of nitrogen. Still others mayremove only a small amount of nitrogen or a particular form of nitrogen which is a smallfraction of the total. In determining which method is most suitable for a particular application, considerationmust be given to six principal aspects: (1) form and concentration of nitrogen compounds inthe process influent, (2) required effluent quality, (3) other treatment processes to beemployed, (4) cost,(5) reliability, and (6) flexibility. Great care must be taken indeveloping and evaluating alternatives. Presented below are brief descriptions of the various processes employed in wastewatertreatment facilities which, to varying degrees, remove nitrogen from the waste stream.Process characteristics, compound selectivity, and normal range of efficiency are presented.It is stressed that this discussion is descriptive and is intended only to provide anintroduction to the following chapters of this manual.
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在过去的数年间，废水处理中使用的处理过程数量迅速增加。很多这样的过程是针对转化氮化合物或从废水流中去除氮的特定目的而开发的。其他过程则可去除多种化合物，包括大量的氮。还有一些过程可能只去除少量的氮或一种特定形式的氮，而这种形式只是总氮的一小部分。在确定哪种方法最适合特定应用时，必须考虑六个主要方面：（1）处理原料中氮化合物的形式和浓度，（2）要求的出水水质，（3）其他要使用的处理过程，（4）成本，（5）可靠性和（6）灵活性。必须十分谨慎地发展和评估替代方案。以下是污水处理设施中使用的各种过程的简要说明，这些过程在不同程度上都可去除废水流中的氮。介绍了其特性、化合物的选择性和正常效率范围。强调这讨论仅仅是描述性的，并旨在为本手册的下一章节提供引言。
2.5.1常规处理工艺
Nitrogen in raw domestic wastewaters is principally in the form of organic nitrogen, bothsoluble and particulate, and ammonia. The soluble organic nitrogen is mainly in the form ofurea and amino acids. Primary sedimentation acts to remove a portion of the particulateorganic matter. This generally will amount to less than 20 percent of the total nitrogenentering the plant.
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生活污水中的氮主要以有机氮形式存在，包括可溶性有机氮和颗粒有机氮以及氨。可溶性有机氮主要以尿素和氨基酸的形式存在。初级沉淀作用能够去除一部分的颗粒有机物，通常只占进一厂总氮负荷的不到20%。
Biological treatment will remove more particulate organic nitrogen and transform some toammonium and other inorganic forms A fraction of the ammonium present in the wastewili be assimilated into organic materials of cells formed by the biological process. Solubleorganic nitrogen is partially transformed to ammonium by microorganisms, but concentrations of to 3 mg/l are usually found in biological treatment effluents.24 Through theseprocesses, an additional 10 to 20 percent of the total nitrogen is removed when biologicaltreatment and secondary sedimentation follows primary sedimentation. Thus, total nitrogenremoval for a conventional primary-secondary facility will generally be less than about 30percent.
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生物处理将去除更多颗粒状有机氮并将一部分转化为铵和其他无机形式。废水中存在的铵的一部分将被生物过程形成的细胞有机材料吸收。可溶性有机氮部分通过微生物转化为铵，但是生物处理出水中通常仅发现3mg / l的浓度。通过这些过程，在化学处理和二级沉淀跟随初级沉降时，附加10％至20％的总氮可被去除。因此，对于传统的初级-次级设施，总氮去除通常不超过30％。
2.5.2废水深度处理工艺
Advanced treatment processes designed to remove wastewater constituents other thannitrogen often remove some nitrogen compounds as well Removal is often restricted toparticulate forms, and overall removal efficiency is rarely high.
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设计用于去除废水中除氮以外其他成分的高级处理工艺，通常也会去除一些氮化合物。去除通常限于颗粒形式，总体去除效率很少是高的。
Tertiary filtration can remove a significant fraction of the organic nitrogen present. Overallremoval depends on the amount of nitrogen in the suspended organic form, As noted above.most of the organic nitrogen in secondary effluent is insoluble, but ammonium usuallyaccounts for the majority of the total nitrogen. Carbon adsorption, used to remove residualorganics, will also remove organic nitrogen. The amount of organic nitrogen remaining atthat point in the treatment scheme will generally be quite small.
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高等过滤技术可以有效去除有机氮的显著比例。总的去除量取决于含悬浮有机物形式的氮的数量，如前所述，大多数二级废水中的有机氮是不溶性的，但氨通常占总氮的大部分。碳吸附技术用于去除残留的有机物也可以去除有机氮。在处理过程中，剩余的有机氮通常会很小。
Electrodialysis and reverse osmosis are tertiary processes used primarily for reduction oftotal dissolved solids. Nitrogen entering such systems is mainly in the ammonjum or nitrateform. Electrodialysis can be expected to remove about 40 percent of these forms; reverseosmosis, 80 percent. However, these processes are not currently in use for treatment ofmunicipal wastewater.
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电渗析和反渗透是主要用于降低总溶解固体的三级处理过程。进入这些系统的氮主要以铵或硝酸盐形式存在。电渗析可以预期去除约40％的这些形式，而反渗透可以去除约80％。然而，这些过程目前不适用于处理市政污水。
Chemical coagulation, often utilized for phosphate removal, also aids in removal ofparticulate matter,including particulate organic nitrogen. While chemical coagulation doesnot remove ammonium directly, lime addition is used prior to ammonia stripping (discussedin Section 2.5.3.4) in order to raise the pH and allow the process to proceed.
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化学混凝是通常用于磷的去除的方法，同时也有助于去除颗粒物，包括颗粒性有机氮。虽然化学混凝不能直接去除铵，但在铵中和之前添加石灰以提高 pH 值，使该过程得以进行，是常见的铵去除方法（如第2.5.3.4章节所述）。
Land disposal may be used to remove nitrogen. Removal occurs when the effluent is usedfor irrigation purposes with the nitrogen assimilated by growing crops which aresubsequently harvested. However, nitrogen removal by land treatment systems is not withinthe scope of this manual.
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土地处置可以用于去除氮。当废水用于灌溉目的时，氮被吸收到种植作物中，随后被收获收取实现去除。然而，土地处理系统的氮去除不在本手册的范围内。
2.5.3主要脱氮工艺
The major processes considered in this manual are nitrification-denitrification, breakpointchlorination (or superchlorination), selective ion exchange for ammonium removal, and air stripping for ammona removal (ammonia stripping). These are the processes which aretechnically and economically most viable at the present time.
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本手册所讨论的主要过程包括硝化反硝化、断点氯化（或超氯化）、针对铵离子的选择性离子交换和氨气去除的气体脱附（氨气蒸发）等。这些是目前技术上和经济上最为可行的过程。
2.5.3.1生物硝化-反硝化
Biological nitrification does not increase the removal of nitrogen from the waste stream overthat achieved by conventional biological treatment. The principal effect of the nitrificationtreatment process is to transform ammonia-nitrogen to nitrate. The nitrified effluent canthen be denitrified biologically. Nitrification is also used without subsequent biologicaldenitrification when treatment requirements cal for oxdation of ammonia-nitrogenOxidation of ammonium can be as high as 98 percent. Overall transformation to nitratedepends on the extent to which organic nitrogen is transformed to ammonia-nitrogen in thesecondary stage or is removed by another process. Nitrification can be carried out inconjunction with secondary treatment or in a tertiary stage;in both cases, either suspendedgrowth reactors (activated sludge) or attached growth reactors (such as trickling filters) canbe used.
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生物硝化并不能比传统的生物处理方式更有效地去除废水中的氮。硝化处理的主要效果是将氨氮转化为硝酸盐。硝化后的出水可以通过生物脱氮来处理。当需要处理氨氮氧化时，也可以使用硝化而无需进行后续的生物脱氮。氨的氧化率可以高达98％。总的硝化转化取决于有机氮在二次处理阶段被转化为氨氮还是被另一个过程去除。硝化可以在二次处理阶段或第三级阶段进行。在两种情况下，都可以使用悬浮生长反应器（活性污泥）或固定生长反应器（如滴滤池）进行处理。
Biological denitrification can also be carried out in either suspended growth or attachedgrowth reactors. As previously noted, an anoxic environment is required for the reactions toproceed. Overall removal efficiency in a nitrification-denitrification plant can range from 70to 95 percent.
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生物反硝化可以在悬浮生长反应器或附着生长反应器中进行。如前所述，需要一种缺氧环境来促进反应的进行。在硝化-反硝化工厂中，总体去除效率可在70至95％之间变化。
2.5.3.2折点加氯
Breakpoint chlorination (or superchlorination) is accomplished by the addition of chlorineto the waste stream in an amount sufficient to oxidize ammonia-nitrogen to nitrogen gasAfter sufficient chlorine is added to oxidize the organic matter and other readily oxidizablesubstances present, a stepwise reaction of chlorine with ammonium takes place. The overalltheoretical reaction is as follows:
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断点氯化（或超氯化）是通过向废水中添加足够的氯，使氨氮氧化为氮气而实现的。在添加足够的氯气氧化有机物和其他易于氧化物质后，氯气会逐步与铵发生反应，从而实现氮气氧化。总体的理论反应式如下：
In practice, approximately 10 mg/l of chlorine is required for every 1 mg/l ofammonia-nitrogen, In addition, acidity produced by the reaction must be neutralized by theaddition of caustic soda or lime. These chemicals add greatly to the total dissolved solids andresult in a substantial operating expense. Often dechlorination is utilized followingbreakpoint chlorination in order to reduce the toxicity of the chlorine residual in theeffluent.
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实际操作中，每1毫克/升氨氮需要约10毫克/升氯。此外，反应产生的酸度必须通过加入氢氧化钠或石灰进行中和。这些化学物质大大增加了总溶解物的含量，导致了大量的运营费用。通常，在进行断点氯化处理后，会采用脱氯技术，以减少排放物中残留的氯毒性。
An important advantage of this method is that ammonia-nitrogen concentrations can bereduced to near zero in the effluent The effect of breakpoint chlorination on organicnitrogen is uncertain, with contradictory results presented in the literature. Nitrite andnitrate are not remoyed by this method.
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这种方法的一个重要优势是，在废水中氨氮浓度可以降至接近于零。而断点氯化对有机氮的影响尚不确定，文献中也存在着相互矛盾的结果。此方法无法去除亚硝酸盐和硝酸盐。
2.5.3.3选择性离子交换除
Selective ion exchange for removal of ammonium from wastewater can be accomplished bypassing the wastewater through a column of clinoptilolite, a naturally occurring zeolitewhich has a high selectivity for ammonium ion. The first extensive study was undertaken in1969 by Battelle Northwest in a federally sponsored demonstration project, Regeneration ofthe clinoptilolite is undertaken when all the exchange sites are utilized and breakthroughoccurs.
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通过将废水通过自然产生的沸石之一的斜十字沸石的柱体中，可以实现有选择性地进行铵离子去除的离子交换。斜十字沸石因具有极高的铵离子选择性而被广泛应用，关于其首次广泛研究是在1969年由Battelle Northwest进行的联邦赞助演示项目。当所有交换位点被利用完毕并出现突破时，便对斜十字沸石进行再生。
Filtration prior to ion exchange is usually required to prevent fouling of the zeolite.Ammonium removals of 90-97 percent can be expected. Nitrite, nitrate, and organicnitrogen are not affected by this process.
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在离子交换之前，通常需要进行过滤以防止沾污分子筛。预计可达到90-97％的铵离子去除率。该过程不会影响亚硝酸盐、硝酸盐和有机氮。
2.5.3.4气相吸附去除氨
Ammonia in the molecular form is a gas which dissolves in water to an extent controlled bythe partial pressure of the ammonia in the air adjacent to the water. Reducing the partialpressure causes ammonia to leave the water phase and enter the air. Ammonia removal fromwastewater can be effected by bringing small drops of water in contact with a large amountof ammonia-free air. This physical process is termed desorption, but the common name isammonia stripping.
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氨分子形式的气体可溶于水中，且溶解度由氨在水旁的空气中产生的分压控制。降低分压会导致氨从水相离开，进入空气中。通过将小水滴接触大量无氨气体，可实现将氨从废水中去除。这种物理过程被称为解吸，常用名为氨气剥离。
In order to strip ammonia from wastewater, it must be in the molecular form (NH3) ratherthan the ammonium ion (NH4 form. This is accomplished by raising the pH of thewastewater to 10 or 1l, usually by the addition of lime. Because lime addition is often usedfor phosphate removal, it can serve a dual role. Again, nitrite, nitrate, and organic nitrogenare not affected.
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为了从废水中剥离出氨，必须将其转化为分子形式（NH3），而非铵离子（NH4）形式。通常通过加入石灰，将废水的pH值升至10或11来实现此目的。由于石灰补加常常用于磷的去除，因此它可以发挥双重作用。需要重申的是，亚硝酸盐、硝酸盐和有机氮不会受到影响。
The principal problems associated with ammonia stripping are its inefficiency in coldweather, required shutdown during freezing conditions, and formation of calcium carbonatescale in the air stripping tower.
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氨脱除的主要问题包括其在寒冷天气下的低效率、需要在冰冻条件下停机以及空气脱除塔中钙碳酸盐形成。
The effect of cold weather has been well documented at the South Lake Tahoe PublicUtility District where ammonia stripping is used for a 3.75 mgd tertiary facility. Thestripping tower is designed to remove 90 percent of the incoming ammonium during warmweather. During freezing conditions, the tower s shut down. One echanism of scaleformation is attributed to the carbon dioxide in the air reacting with the alkaline wastewaterand precipitating as calcium carbonate. In some instances, removal with a water jet hasbeen possible; in other applications the scale has been extremely difficult to remove. Somefactors which may affect the nature of the scale are: orientation of air flow, recirculation ofsludge, pH of the wastewater, and chemical makeup of the wastewater.
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南莱克塔霍公共事业区使用氨气脱除法处理污水，冷天气的影响已有充足的文献记录。这座处理厂紧急脱氨设备在炎热天气中的目标是脱除进水中90%的铵。在冰冷的气温下，设备必须关闭。由于空气中的二氧化碳与碱性废水反应并析出碳酸钙，这是结垢的一个机制。有时可以用水喷射法去除结垢，而在其他情况下，结垢非常难以去除。影响结垢特性的因素包括：气流方向、污泥再循环、废水pH值和化学成分。
2.5.4其他脱氮工艺
In addition to the processes listed above, there are other methods for nitrogen removalwhich might usefully be discussed. Most are in the experimental stage of development oroccur coincidentally with another process.
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除了上述列出的过程外，还有其他一些氮去除方法值得探讨。这些方法大多处于实验开发阶段或与其他过程偶然出现。
Use of anionic exchange resins for removal of nitrate was developed principally fortreatment of irrigation return waters. Two major unsolved problems are the lack of resinswhich have a high selectivity for nitrate over chloride and disposal of nitrogen-ladenregenerants.
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离子交换树脂是一种主要用于处理灌溉回灌水中硝酸盐去除的方法。其中，存在两个主要的未解决问题：一是缺乏高选择性去除氯化物的树脂，二是氮负荷再生剂的处置。
Oxidation ponds can remove nitrogen through microbial denitrification in the anaerobicbottom layer or by ammonia emission to the atmosphere. The latter effect is essentiallyammonia stripping but is relatively inefficent due to a low surface-volume ratio and low pHIn a study of raw wastewater lagoons in California, removals of 35-85 percent were reportedfor welloperated lagoons.
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氧化池可以通过微生物反硝化在厌氧底层将氮去除，或通过氨排放到大气中去除氮。后一种效应本质上是氨剥离，但由于低表面积-体积比和低pH而相对低效。在加利福尼亚对原始废水塘的研究中，对于运营良好的池塘，报道了35-85％的去除效果。
Nitrogen in oxidation ponds is assimilated by algal cultures. If the algal cells are removedfrom the pond effluent stream, nitrogen removal is thereby effected. Methods for removalof algae are summarized in the EPA Technology Transfer Publication, UpgradingLagoons,
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氧化池中的氮被藻类文化同化。如果从池的排放流中移除藻细胞，则从而实现了氮的去除。除藻的方法总结在EPA技术转移出版物《升级沼泽》中。
It was noted previously that in secondary biological treatment and in nitrification, somenitrogen is incorporated in bacterial cells and is removed from the waste stream with thesludge. If an organic carbon source such as ethanol or glucose is added to the wastewaterthe solids production will be increased and a greater nitrogen removal will be effectedDisadvantages are that large quantities of sludge are produced and that difficulties occur inregulating the addition of the carbon source, with high effluent BODs values or highnitrogen levels resulting.
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先前已经指出，在第二级生物处理和硝化过程中，部分氮被细菌细胞吸收并随着污泥从废水中去除。如果添加可作为有机碳源的乙醇或葡萄糖到废水中，则会增加固体产量并促进更大的氮去除。缺点是会产生大量污泥，并且在调节碳源添加时会出现困难，从而导致出水BOD或氮含量较高。
2.5.5 总结
Table 2-3 summarizes the effect of various treatment processes on nitrogen removal. Shownis the effect that the process has on each of the three major forms: organic nitrogen.ammonium, and nitrate. In the last column is shown normal removal percentages which canbe expected from that process. Overall removal for a particular treatment plant will dependon the types of unit processes and their relation to each other For example, while manyprocesses developed for nitrogen removal are ineffective in removing organic nitrogenincorporation of chemical coagulation or multimedia filtration into the overall flowsheetcan result in a low concentration of organic nitrogen in the plant effluent. Thus, theinterrelationship between processes must be carefully analyzed in designing for nitrogenremoval. Further discussion of process interrelationships is presented in Chapter 9
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表2-3总结了各种处理工艺对氮去除的影响。显示了处理过程对三种主要形式（有机氮、铵和硝酸盐）的影响。最后一列显示的是该过程可以期望的正常去除百分比。对于特定处理厂的总体去除效果将取决于单元处理类型及其相互关系。例如，尽管为了氮去除而开发的许多处理过程在去除有机氮方面无效，但将化学凝聚或多介质过滤体系纳入总流程中可以使工厂废水的有机氮浓度降低。因此，在设计氮去除时必须仔细分析处理过程之间的相互关系。详细讨论处理过程的相互关系将在第9章中进行。
