氮控制设计手册2.4氮排放的影响

It was previously noted that nitrogenous compounds discharged from wastewater treatmentfacilities can have several deleterious effects. Although biostimulation of receiving watershas generated the most concern in recent years, other less well publicized impacts can be ofmajor importance in particular situations. These impacts include toxicity to fish lifereduction of chlorine disinfection efficiency, an increase in the dissolved oxygen depletionin receiving waters, adverse public health effects - principally in groundwater, and areduction in the suitability for reuse.
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先前已指出，从废水处理设施排放出来的含氮化合物可能产生多种有害影响。虽然最近几年接收水体的生物刺激引发了最大的关注，但在特定情况下，其他不太为人知的影响可能具有重要作用。这些影响包括对鱼类生命的毒性、氯消毒效率降低、接收水体中溶解氧消耗增加、对公共健康的不良影响——主要出现在地下水中，以及减少再利用的适用性。

2.4.1 Biostimulation of Surface Waters
A major problem in the field of water pollution is eutrophication, excessive plant growthand/or algae “bloomsresulting from over-fertilization of rivers, lakes, and estuaries. Resultsof eutrophication include deterioration in the appearance of previously clear waters, odorproblems from decomposing algae, and a lower dissolved oxygen level which can adverselyaffect fish life.
Four basic factors are required for algal growth: nitrogen, phosphorus, carbon dioxide, andlight energy. The absence of any one will limit growth. In special cases, trace micronutrientssuch as cobalt, iron, molybdenum and manganese may be limiting factors under naturalconditions.
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2.4.1 表面水的生物刺激作用

水污染领域中的主要问题是富营养化，即由于对河流、湖泊和河口的过度施肥导致植物生长和/或藻类“水华”过度增长。富营养化的结果包括先前清澈水体的恶化外观，由腐烂藻类产生的异味问题，以及溶解氧水平降低，可能对鱼类生命产生不利影响。

藻类生长需要四个基本因素：氮、磷、二氧化碳和光能。缺乏其中任何一个都会限制生长。在特定情况下，微量营养元素，如钴、铁、钼和锰，可能是自然条件下的限制因素。

Good generalizations concerning which factor is growth limiting and at what concentrationare difficult to make. Light and carbon dioxide are essentially impossible tocontrol. Bothnitrogen and phosphorus are present in waste discharges and hence subject to control. Thequestions which must usually be answered when faced with a eutrophication problem are: isnitrogen or phosphorus (or neither) the limiting nutrient, and if either one is, can theamount entering the receiving water be significantly reduced by removing that nutrient fromthe waste stream? In some cases algal assay procedures may allow a conclusion as to whichnutrient is limiting. Under some circumstances, however, removal of both nitrogen andphosphorus may be undertaken to limit algal growth.
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关于哪种因子是生长限制因素以及何种浓度为限制因素的充分归纳总结是困难的。光和二氧化碳基本上是无法控制的，而氮和磷则存在于废水排放中，因此受到控制。通常面临营养过度问题时必须回答的问题是：氮或磷（或两者皆是）是否为限制养分，如果是，则是否可以通过从废水中去除这些养分显著降低污水处理后排放的进水中的限制养分含量？在某些情况下，藻类鉴定过程可以确定是哪种养分限制因素。但是，在某些情况下，需要同时去除氮和磷以限制藻类生长。

Eutrophication is of most concern in lakes because nutrients which enter tend to berecycled within the lake and build up over a period of time.9 A river, by contrast, is aflowing system, Nutrients are always entering or leaving any given section. Accumulationstend to occur only in sediment or in slack water, and the effects of these accumulations arenormally moderated by periodic flushing by floods.
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富营养化对湖泊的影响最为关注，因为流入湖泊的营养物质在湖内循环并逐渐积累。与之相反，河流是一个流动的系统，任何给定区域营养物质都在进出。积累往往仅出现在沉积物或缓流水中，并且这些积累的影响通常会被洪水的周期性冲刷所缓解。

In estuaries and oceans, nitrogen compounds are often present in very low concentrationsand may limit the total biomass and the types of species it contains.9 Thus, upwelling,which brings nutrient-rich waters to the surface, may result in periodic blooms of algae orother aquatic life. While in some estuaries discharges from wastewater treatment plants mayincrease nitrogen concentrations to the level where blooms occur, the high dilution providedby a direct ocean discharge probably eliminates the danger of algae blooms caused by sucldischarges.In summary, while nitrogen in wastewater treatment plant effluents can inparticular cases cause undesirable aquatic growths, determination of the limiting constituentand other sources of that constituent (such as feedlot runoff or fixation) should be madebefore the decision is made to require nitrogen removal from municipal wastewaters.
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在河口和海洋中，氮化合物通常存在非常低的浓度，可能会限制总生物量和其中包含的物种类型。因此，上升流将营养丰富的水带到表面，可能会导致周期性的藻类或其他水生生物的繁殖。虽然在一些河口中，来自废水处理厂的排放可能会增加氮浓度，并导致藻类繁殖，但直接向海洋排放的高稀释率可能会消除由此类排放引起的藻类繁殖的危险。

总之，在某些情况下，废水处理厂排放的氮可能会导致不良的水生生长现象，但在决定要求从市政污水中去除氮之前，应确定限制构成因素和其他来源（如饲料料场径流或固定）。
2.4.2 Toxicity
The principal toxicity problem is from ammonia in the molecular form (NHa) which canadversely affect fish life in receiving waters. A slight increase in pH may cause a greaincrease in toxicity as the ammonium ion (NHn is transformed to ammonia in accordancewith the following equation.
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2.4.2 毒性问题
主要毒性问题来自于分子形式下的氨（NH3），它可能会对接受水域中的鱼类生命产生负面影响。pH值的轻微增加可能会导致毒性的急剧增加，因为氨盐离子（NH4+）会根据如下反应式转化为氨。

Factors which may increase ammonia toxicity at a given pH are: greater concentrations ofdissolved oxygen and carbon dioxide; elevated temperatures; and bicarbonate alkalinity.Reported levels at which acute toxicity is detectable have ranged from 0.01 mg/19 to over2.0 mg/120 of molecular ammonia-nitrogen.
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在特定的 pH 值下可能增加氨毒性的因素包括：溶解氧和二氧化碳的浓度更高；温度升高；以及碳酸盐碱度。报道的急性毒性可检测水平范围从 0.01mg/19到超过 2.0 mg/1分子氨氮。

2.4.3 Effect on Disinfection Efficiency
When chlorine, in the form of chlorine gas or hypochlorite salt, is added to wastewatelcontaining ammonium, chloramines, which are less effective disinfectants, are formed.Themajor reactions are as follows;
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2.4.3 消毒效率影响
当氯以氯气或次氯酸盐的形式被添加到含有氨、氯胺等物质的废水中时，会产生一种消毒效果较差的化合物——氯胺。其主要反应如下：

Only after the addition of large quantities of chlorine does free available chlorine exist. Ifthe effluent ammonia-nitrogen concentration were 20 mg/l, about 200 mg/l of chlorinewould be required to complete the reactions with ammonium and organic compounds. Onlrarely in wastewater treatment is this level of chlorine addition (“breakpoint” chlorination)used. Therefore, as a practical matter, the less effective combined chlorine residuals(monochloramine and dichloramine) must be relied upon for disinfection. This results irincreased chlorine dose requirements for the same level of disinfection. Further informationon the relative effectiveness of free chlorine and combined residuals is presented in Section
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只有添加大量氯气后才会存在可用自由氯。如果废水中氨氮浓度为20毫克/升，则需要约200毫克/升的氯气与铵离子和有机物反应。在废水处理中很少使用这种氯气添加水平（“断点”氯化），因此，作为实际问题，必须依靠不太有效的复合氯余量（一氯胺和二氯胺）来进行消毒。这会导致相同消毒水平需要增加氯气用量。有关自由氯和复合余量相对有效性的进一步信息请参见本节6.2.7.

2.4.4 Dissolved Oxygen Depletion in Receiving Waters
Ammonium can be biologically oxidized to nitrite and then to nitrate in receiving watersand thereby add to the oxygen demand imparted by carbonaceous materials. Table 2-2shows a typical example of the removal of total oxygen demand obtainable with varyingdegrees of treatment. If either conventional biological treatment or physical-chemica!treatment is utilized to provide 90 percent BODs removal, an effluent will be dischargedwhich still contains over 100 mg/l of oxygen demand. This high level of oxygen demandmay cause significant oxygen depletion in the receiving water if insufficient dilution isavailable. Nitrification (or ammonia nitrogen removal) will reduce the total oxygen demandof the effluent to less than 40 mg/l.
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2.4.4 溶解氧在受纳水体中的耗竭问题
氨可以在受纳水体中被生物氧化为亚硝酸盐，接着再被氧化为硝酸盐，从而增加碳质材料所施加的氧需求。表2-2展示了在不同程度的处理下总氧需求的去除典型例子。如果采用传统的生物处理或物理-化学处理实现90%的BOD去除率，则排放出的废水中仍包含100 mg/l以上的氧需求。如果受纳水体中的稀释不足，则这种高水平的氧需求可能会导致显著的氧耗竭。硝化（或氨氮去除）可将废水的总氧需求降至少于40 mg/l。

The Potomac Estuary in the United States and the Thames Estuary in Great Britain areexamples of estuaries which are greatly affected by nitrification. Figure 2-4 shows, as afunction of the degree of nitrification provided by wastewater treatment facilities, theestimated discharge into the Thames Estuary which will cause the maximum oxygendepletion to be 10 percent of saturation, The calculation assumes an effluent BODs of 20mg/l, an effluent organic plus ammonia-nitrogen concentration of 19 mg/l, and discharge ata point 10 miles above London Bridge. From the figure, the allowable discharge fornon-nitrified effluent is about 12 mgd, while for completely nitrified effluent, over 40 mgdcan be discharged.
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波托马克河口在美国和泰晤士河口在英国是受硝化作用影响较大的河口的例子。图2-4显示，根据污水处理设施提供的硝化程度，估计向泰晤士河口排放将导致最大氧饱和度降至10％的排放量。该计算假定出水BOD为20mg/l，出水有机物加氨氮浓度为19mg/l，并在伦敦桥上游10英里的一点排放。从图表中可以看出，未经硝化处理的出水允许排放量约为12 mgd，而完全经过硝化处理的出水可以排放超过40 mgd。

2.4.5 Public Health
The public health hazard from nitrogen is associated with the nitrate form and is limitedprincipally to groundwater where high concentrations can occur. Nitrate in drinking water was first associated in 1945 with methemoglobinemia, a sometimes fatal blood disorderwhich affects infants less than three months old. When water high in nitrate is used fororeparing infant formulas, nitrate is reduced to nitrite in the stomach after ingestion. Thenitrites react with hemoglobin in the blood to form methemoglobin, which is incapable ofcarrying oxygen. The result is suffocation accompanied by a bluish tinge to the skin, whichaccounts for the use of the term “blue babies”in conjunction with methemoglobinemia. Insuspect areas water should be analyzed for both nitrite and nitrate since either form willcause methemoglobinemia.
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2.4.5 公共卫生学
氮的公共卫生风险主要与硝酸盐形式有关，其限制性主要在地下水中高浓度存在。饮用水中的硝酸盐最初与一种有时会影响3个月以下婴儿的致命血液疾病——高铁血红蛋白症关联。当富含硝酸盐的水用于制备婴儿配方奶粉时，硝酸盐在摄入后在胃中被还原为亚硝酸盐。然后，亚硝酸盐与血液中的血红蛋白反应形成高铁血红蛋白，该物质不能传递氧气。其结果是窒息并伴有皮肤呈蓝色，这就是“蓝色婴儿”术语在高铁血红蛋白症中的使用原因。在可疑的地区，应分析水中的亚硝酸盐和硝酸盐，因为任一形式都会导致高铁血红蛋白症。

Since 1945 about 2,000 cases of methemoglobinemia have been reported in the U.S. andEurope, with a mortality rate of seven to eight percent. Because of difficulty in diagnosingthe disease and because no reporting is required, the actual incidence may be many timeshigher.10
The EPA's interim primary drinking water standard (40 CFR Part 141) for nitrate is 10 mg/las nitrogen, This standard is exceeded most often in shallow wells in rural areas.
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自1945年以来，在美国和欧洲大约报告了2,000例的高铁血红蛋白血症，其中死亡率为7%至8%。由于该疾病的诊断困难，而且没有报告要求，实际发病率可能高出许多倍。环保局的暂行饮用水主要标准（40 CFR第141部分）中亚硝酸盐的浓度为10毫克/升作为氮。这一标准最常在农村地区的浅井里被超过。

2.4.6 Water Reuse
While direct wastewater reuse for domestic water supply is not yet a reality because ofpublic health considerations, plans for industrial reuse are being carried out in several areasWhen reclaiming wastewater for industrial purposes, ammonia may need to be removed inorder to prevent corrosion. Further, nitrogen compounds can cause biostimulation incooling towers and distribution structures.
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2.4.6 水的再利用
尽管受制于公共健康考虑，直接将废水再利用于生活用水目前还未成为现实，但在几个领域中已经开始执行废水产业再利用计划。在回收废水用于工业目的时，为了防止腐蚀，可能需要去除氨。此外，氮化合物可能会在冷却塔和配水结构中引起生物刺激反应。