净水技术 陪你去看流星雨——《运营人员需要了解的常规处理工艺》

原文链接：

https://awwa.onlinelibrary.wiley.com/doi/epdf/10.1002/opfl.1646

原文作者：

Hunter Adams,Steve Ash,Mark Southard

原文出处：J Opflow

翻译：阮辰旼

Operators Need to Know Conventional Treatment Processes

运营人员需要了解的常规处理工艺

Water treatment involves any process in which a source water's quality is improved for drinking, irrigation, industrial uses, and many other applications. Two main treatment categories include conventional and advanced treatment processes. Conventional water treatment processes are traditional, time-tested physical and chemical processes used to improve water quality from source to tap. To protect public health, these processes and water treatment techniques are in place to remove various drinking water contaminants in accordance with the US Environmental Protection Agency (EPA) National Primary Drinking Water Regulations.

任何可以改善原水质量以满足用于饮用、灌溉、工业使用和许多应用需要的处理过程都是水处理的范畴。水处理包括常规处理和深度处理两种分类。常规水处理工艺是传统的、久经历史考验的物理和化学工艺，能够用于改善从源头到龙头的饮用水水质。为了保护公众健康，这些工艺和水处理技术是根据美国环境保护署（EPA）的国家一级饮用水条例要求，能够去除各种饮用水污染物。

Treatment plant operators manage, maintain, and repair water treatment plant facilities and distribution systems. But to perform these duties successfully, an operator must possess good judgment and understand the fundamentals. This article provides a basic overview of conventional treatment processes (Figure 1) for new operators and those considering a career in the water industry as well as a review of fundamental concepts for more experienced operators. It's also becoming vital for operators to understand advanced treatment processes, as many utilities are starting to use newer technologies. A follow-up article focusing on advanced treatment will appear in Opflow’s April 2022 issue.

水厂运营人员需要管理、维护、维修水厂设施和输配系统。但为了顺利履行职责，运营人员必须很好的判断和理解基本的原因。本文为新入行的运营人员和那些正在考虑加入水行业的人提供了常规处理工艺的基本概述（图1），并为具有经验的运营人员提供了对基本概念的回顾。对运营人员来说，了解深度处理工艺也正在变得至关重要，因为许多水务公司开始使用深度处理，一篇侧重于介绍深度处理的后续文章将发表在Opflow期刊的2022年4月刊（即Opflow 2022,3期，参见本公众号所发布的“阿三书库|陪你去看满天星——《运营人员需要了解的深度处理工艺》”一文）。

Figure 1 Conventional Water Treatment Scheme

图1 常规水处理工艺路线

Conventional treatment effectively removes practically any range of raw water turbidity.

常规处理工艺几乎可以有效地去除任何范围的原水浊度。

Before treatment, water taken from the ground or from a surface source is called raw water. Water characteristics differ from one source to another. Each aquifer or surface source has water of a different quality and chemical profile that will determine what type of treatment it should receive.

在处理工艺前，从地下或者地表获取的水被称为原水。不同来源的原水水质特征各不相同。每一个不同的地下蓄水层或地表水源的水质以及化学性质都不相同，这将决定这些原水应该选择怎么样类型的处理工艺。

Groundwater  is raw water that's taken from wells and is usually clear enough and clean enough that the only treatment needed may be to just add a chlorine disinfectant. All water, regardless of its origin, requires disinfection before entering the distribution system. At times, however, groundwater may need additional treatment to address undesirable aesthetics: tastes, odors, or color.

地下水 原水通常通过水井取水，通常非常清澈和干净，以至于唯一需要的处理工艺就是添加氯消毒剂。所有的原水，不管从哪里取水，都需要在进入输配系统之前进行消毒。然而有时候，地下水可能需要额外的处理工艺来提升并不理想的感官问题，比如味、嗅或色。

Surface water  can come from lakes, rivers, reservoirs, or the ocean. Again, depending on the source, the water's characteristics will determine what type of treatment is necessary. Some waters that are low in pH may require pH adjustment at the treatment plant. Other waters may be high in salinity, requiring advanced membrane treatment to remove the salt. At the very least, raw surface water will need treatment to remove solids, followed by some form of filtration and chemical disinfection before entering the distribution system.

地表水 可以从湖泊、河流、水库，或者海洋中获取。同样的，原水的水质特性取决于它的来源，也会决定后续需要经过什么类型的处理工艺。一些原水的pH值偏低所以需要在水厂中调节pH值。另外一些原水可能盐度比较高，需要深度的膜处理工艺来去除盐分。最最基本的是，地表水原水都需要水处理工艺帮助去除固体物质，必须通过各种形式的过滤工艺和化学消毒工艺才可以进入输配系统。

Raw water may be stored, or impounded, in reservoirs, channels, or basins. This ensures an adequate supply is ready to be treated and turned into drinking water. When surface water is pumped from the source (lake, river, etc.), it's immediately treated with a strong oxidant to begin the disinfection process. Pathogens, such as harmful bacteria and viruses, are the target of this primary disinfection. Some of the more common oxidants used for primary disinfection are chlorine (Cl2), chlorine dioxide (ClO2), or ozone (O3). Introducing a predisinfectant or oxidant begins the water treatment process as the water makes its way to the treatment plant.

原水可以储存或蓄积在水库、管渠或洼地中。这是为了确保了足够的原水供应量，可以随时通过处理变成饮用水。当地表水从水源地（湖泊、河流等）抽出时，立即用强氧化剂进行处理并开始消毒过程。病原体，如有害细菌和病毒，是该预消毒工艺的目标。一些更常见的用于预消毒的氧化剂是氯气（Cl2）、二氧化氯（ClO2）或臭氧（O3）。当水进入水厂时，加入这些预消毒剂或氧化剂即开始水处理过程。

Water utilities may blend raw waters for any of the following reasons:

水务公司可以出于以下考虑对不同的原水进行混合：

△  T o make the source water easier to treat .  For example, a certain blend of waters may reduce the need for extensive treatment, thereby saving the utility money in treatment chemicals.

△  为 了使原水更容易处理 。  例如，某种情况下几种原水通过混合，可以减少对复杂的水处理工艺的需要，就可以为公用事业公司节省化学药剂的费用。

△  To reduce a naturally occurring constituent in one source water to safe levels by blending with a different source that has less of that particular constituent .  For example, well water with excess fluoride at >5 mg/L may be blended with fluoride-free water from another well to bring the fluoride concentration to an acceptable level.

△  通过与不同的原水进行混合，将某原水中特定的一个污染物成分降低到安全限值范围内的水平 。  例如，将氟化物含量超过5毫克/升的井水与另一个无氟的井水混合，可以使混合原水的氟化物浓度达到可接受的水平。

△  To allow a utility to supplement one source that may be insufficient in quantity or quality .  For example, during the summer, diminishing water levels in a small lake could make it impossible to supply enough water, so a portion of the lake water might be blended with water from a nearby river to help satisfy the increased seasonal water demand.

△  当水量和水质不能满足要求是，补充一个水源 。 例如，在夏季，一个较小的湖泊水位下降的时候，可能难以保证同充足的原水，因此可以将这个湖泊水中的一部分和附近的河水混合，来帮助满足季节性的水量需求。

△  To permanently increase the overall amount of water available to a community .  For example, if a town has grown and needs a larger raw water supply, an additional water source can be blended with an existing source on a permanent basis.

△  为了永久性地增加对一个社区的供水水量 。 例如，如果一个城镇的规模扩大需要更多的原水水量保障，一个额外水源的原水就需要和现有的原水进行混合，以满足这一永久性增长的需求。

Once raw water is drawn into a treatment plant, the first treatment process it undergoes is clarification. The main goal of this initial step is to clarify the water by removing most of the raw water's suspended solids. Another name for this process is sedimentation. Suspended solids are removed by the addition of chemical additives that cause the suspended solids to coagulate (clump) into larger particles referred to as floc. These larger, heavy floc particles then settle to the bottom of the clarification basin. Collectively, the steps in the clarification process are referred to as coagulation, flocculation, and sedimentation, and they may occur in one basic treatment unit or in separate basins, depending on plant design.

一旦原水进入了水厂，那第一道处理工序就行澄清。这一步的主要目的是通过去除大部分原水中悬浮的固体，来达到让水清澈的目的。这道工艺的另一种说法是沉淀。通过投加化学药剂，让悬浮固体集聚在一些较大的颗粒上形成混凝的絮体然后得以去除。这些较大、较重的絮体物质会沉降到澄清池的底部。澄清工艺中的各个步骤被称为混凝、絮凝和沉淀，它们可以在一个处理构筑物中进行，也可能发生在不同的构筑物里，这取决于水厂的设计形式。

The suspended solids in raw water are generally negatively charged, so a chemical coagulant is used that contains a positively charged metal, such as ferric sulfate (Fe ₂ (SO ₄ ) ₃ ); ferric chloride (FeCl ₃ ); or aluminum sulfate (Al ₂ (SO ₄ ) ₃ ), which is also known as alum. Coagulants are added into a clarifier's rapid-mix zone, to which positively charged coagulants are attracted, and connect with and neutralize negatively charged suspended solids. As the raw water becomes destabilized by this neutralization process, suspended solids clump together with the coagulant compounds. These coagulated clumps of floc become larger and larger and, as they become heavier, begin to settle to the bottom of the clarifier. Settled floc will be scraped out of the clarifier and moved into a sludge treatment process, which is described in a subsequent section.

原水中的悬浮固体通常带有负电，因此化学混凝剂一般都含有正价金属离子，例如硫酸铁、氯化铁，或硫酸铝，也就是俗称的明矾。混凝剂被投加到澄清池中快速混合的区域，带正电的混凝剂和水中带负电的悬浮固体连接中和。在这个连接中和的过程中，原水的化学性质变得不稳定，悬浮固体与已混凝形成的物质结合形成絮体，这些絮体越来越大，并且越来越重，开始向澄清池的底部沉降。沉淀下来的絮体被清除出澄清池，并被转移到污泥处理工艺中，在随后的章节中会进行论述。

This clarification process removes suspended solids from the raw water as they settle out and clarified water moves upward to the top of the clarifier. The clarified water then flows over the weirs and continues moving forward in the treatment process. As new operators are trained, they should learn to look down into a clarifier from the walkway to visibly inspect the formation of floc. This is an easy way to quickly assess the effectiveness of the clarification process. If there's no visible floc, the coagulation process is failing, and adjustments should be made (Photo 1).

澄清工艺将原水中的悬浮固体混凝沉淀后去除，澄清后的水从澄清池的上部流出。澄清后的水从澄清池上部的出水堰流出，然后继续进入后续的处理工艺。当一个新的运营人员在实习时，应该学习如何在澄清池的人行通道上观察池体内絮体生成的情况。如果池体内没有肉眼可见的絮体，就说明混凝过程失效了，必须对工艺进行调整（照片1）。

Photo 1   Poorly formed floc is typically the result of inadequate rapid mixing, improper coagulants or dosages, or improper flocculation. Here, jar tests show good floc formation on the left and poor floc formation on the right.

照片1 不够充分的快速混合、不够量的混凝剂投加浓度，或不当的絮凝过程，都是无法形成絮体的原因。图中，左边的烧杯显示了良好的絮凝形成效果，右边的烧杯则是不佳的絮凝表现。

Visual inspection should be confirmed with jar tests to determine the appropriate coagulant dosage to achieve the desired turbidity. A polymer may be added as a coagulant aid in the clarifier or in the clarifier effluent to increase filtration efficiency in the next process. When the treatment process is complete, the clarifier effluent should have low turbidity because most suspended solids are removed.

肉眼观察的结果还需要通过烧杯试验来判定所期望的浑浊度（目标）需要投加多少的混凝剂。可以在澄清池中或澄清池的出水处投加聚合物作为混凝的辅助来提高下一步过滤工艺的效果。当这部分工艺全部完成后，澄清池的出水应该只有很低的浑浊度，应为绝大部分的悬浮固体都已经被去除了。

Following clarification, filtration is the next step in the treatment process. At this point, a shift takes place from chemical treatment to physical treatment. Many treatment plant filters are open-air at this step in the process, and debris blown in by the wind can accumulate. Clarifier effluent enters the filters, which act as physical barriers to remove remaining suspended solids, leaving only dissolved solids.

在澄清工艺之后，过滤下一步的水处理该工艺环节。这个环节将从化学处理转向物理处理。许多水厂的滤池都是露天的，因为风的吹动可以让水中的絮体进一步凝结起来。

The two main types of conventional filters are sand filters and mixed-media (sand and anthracite) filters (Photo 2). Both types operate similarly: water enters and passes through the filter by gravity. Any remaining floc particles are trapped in the filter media as the water passes through. Filter effluent should have low turbidity, indicating that most pathogens (Cryptosporidium, Giardia, etc.) have been removed. EPA's surface water treatment rules require systems using surface water or groundwater under the direct influence of surface water to filter the water using conventional or direct filtration. At no time can turbidity (water cloudiness) go higher than 1 ntu, and samples for turbidity must be less than or equal to 0.3 ntu in at least 95% of the samples in any month. Filtration, combined with disinfection (discussed in the next section), ensures proper treatment and removal of pathogens.

两种最主要的常规滤池形式是砂滤池和混合填料滤池（砂和无烟煤，照片2）。两种形式滤池的运行是相似的：水流入并依靠重力通过滤池，水中的絮体都被截留在滤床填料中而水可以通过滤池。滤池的出水浑浊度非常低，表明大多数病原体（隐孢子虫、贾第虫等）已经被去除。美国环保总署的地表水处理规程要求以地表水或受地表水影响的地下水为原水的供水系统必须使用常规处理或直接过滤的方式来过滤水。在整个处理工艺流程中，水的浑浊度都不能高于1NTU，而且一个月内，最低95%的水样的浑浊度都应小于等于0.3NTU。过滤工艺配合消毒工艺（在下一节中讨论），能够确保水处理工艺对病原体的去除。

Photo 2  Multimedia (mixed-media) filters use three or more types of media of varying coarseness and specific gravity. Here, a filter cross-section of mixed media includes anthracite (top), sand (middle), and gravel (bottom).

照片2 混合填料滤池使用三种或更多种粗细粒度和密度不同的填料。混合填料滤池的滤料包括无烟煤（顶部）、沙子（中间）和砾石（底部）。

Over the course of a filter run, the efficiency will maximize and then decrease as the filter media become clogged with floc. When the efficiency has decreased to a certain point, the filter will need to be backwashed (cleaned) to remove the accumulated solids. Clean water is forced backward through the filter for a set period of time to remove clogged debris. This clean water removes the trapped solids and carries them to waste. Before being brought back online, freshly backwashed filters need to filter-to-waste to ensure no loose particles pass through to the clearwell. Filtering-to-waste ensures that the filtering efficiency increases, the filter media settle, and turbidity levels return to desired levels. A filter can be returned to service once the entire backwash cycle is complete, the filter media have settled, and normal turbidity levels are achieved. Rules allow for increased turbidity in the four hours immediately after a backwash because not all filters have filter-to-waste capability. This allows the filter to settle and resume normal operation by the four-hour mark.

在滤池整个运行的生命周期过程中，过滤效率会从最大然后逐渐降低，这是由于滤池中的滤料逐渐被絮体堵塞。当过滤效率降低到某一个临界点时，滤池就需要进行反冲洗以去除掉积累在滤料中的固体。干净的水通过加压，反方向冲洗滤料以达到去除堵塞的固体的目的，并带着这些固体成为滤池反冲洗废水。在重新投入运行之前，刚反冲洗过的滤池需要进行试运行性质的过滤（即过滤的水直接排放掉），以确保没有松散的颗粒可以穿透滤池。试运行性质的过滤一是确保过滤效率回升，二是确认填料都工作正常，三是出水浑浊度的水平可以满足要求。当上述要求都满足期望时，这个刚完成反冲洗的滤池就可以投入正常的生产运行。运行规则允许在一次反冲洗后的四个小时内，某个滤池的出水浑浊度可以适当有所增加，因为并非所有的滤池都能马上恢复到理想的过滤效率的，这就相当于允许滤池有一个四小时的周期来完成反冲洗到恢复正常运行。

Disinfection is a process in which a chemical or physical treatment is used to inactivate (destroy) harmful microorganisms. In conventional treatment, common disinfectants are ClO ₂ , Cl ₂ , and chloramines. After the water has been filtered, one of these final disinfectants is added to the filter effluent. The goal of this process is to remove pathogens such as Escherichia coli, Enterobacter, Naegleria fowleri, etc., remaining after filtration, not necessarily to completely sterilize the water. Disinfection means that some nonpathogenic microorganisms (like heterotrophic bacteria) could remain in the water.

消毒是一个通过化学或物理处理的方式达到有效灭活有害微生物的过程。在常规的处理工艺中，常见的消毒剂一般是ClO ₂ ，Cl ₂ 和氯胺。水经过过滤后，这些消毒剂中的某一种被加入到滤池出水中。这个工艺环节的目的是去除水中的病原体，比如大肠杆菌, 肠杆菌, 禽类奈格里菌等，这些病原体都是残留在过滤出水中的，但并不必要对水消毒的绝对彻底。因此，消毒工艺也意味着一些非病原体的微生物，比如异养菌是可能存在在水里的。

ClO ₂  is a preoxidant that's injected into raw water as it moves into the treatment plant. It's usually generated on-site, and the disinfection byproduct (DBP) chlorite must be closely monitored to ensure regulatory compliance. The maximum contaminant level (MCL) for chlorite is 1.0 mg/L. Cl ₂  and chloramines are used as final disinfectants of filter effluent. Cl ₂  is a strong oxidizer, making it effective at destroying pathogens in water. Cl ₂  is more effective at a lower pH, meaning it oxidizes organic material more quickly when the water is more acidic (e.g., 97% effective at pH 6, 50% effective at pH 7.5, and 24% effective at pH 8).

ClO ₂ 是一种预氧化剂，在原水进入水厂时被投加。它通常在现场制备，必须密切监测消毒副产品（DBP）亚氯酸盐，以确保符合法规要求。亚氯酸盐的最大污染物水平（MCL）是1.0毫克/升。Cl ₂ 和氯胺被用作滤池出水的最终消毒剂。Cl ₂ 是一种强氧化剂，能有效地破坏水中的病原体。Cl ₂ 在较低的pH值下更有效，也就是说，当水的酸性较强时，它能更快地氧化有机物（例如，在pH值为6时有效97%，在pH值为7.5时有效50%，而在pH值为8时有效24%）。

Most surface water systems will feed an ammonia product in addition to Cl ₂ , which can react with ammonia (NH ₃ ) to produce chloramines that are longer lasting than Cl ₂  and less likely to create DBPs (total trihalomethanes and haloacetic acids) but are less effective at oxidizing pathogens. Chloramine species (monochloramines, dichloramines, and trichloramines) should be monitored to ensure a correct Cl ₂ –NH ₃  ratio is being used in treatment to produce the desired monochloramine concentrations (Figure 2).

大多数地表水厂的处理工艺除Cl ₂ 外还会投加氨（NH ₃ ），Cl2可与氨反应产生氯胺，其持续时间比Cl ₂ 长，且不太可能生成DBP（总三卤甲烷和卤乙酸），但氧化病原体的效果相对较差。应监测氯胺种类（单氯胺、二氯胺和三氯胺），以确保在处理过程中投加正确的Cl ₂ 和NH ₃ 的比例，以产生理想的一氯胺浓度（图2）。

Figure 2 Chlorine Breakpoint Curve

图2 折点加氯曲线

A chlorine breakpoint curve illustrates the monochloramine peak.

折点加氯曲线说明了一氯胺浓度的峰值。

The clarification and filtration processes generate what's known as sludge, which is composed of the settled material from the clarification process and the material that the filters manage to accumulate during filtration. If sludge is allowed to accumulate in the sedimentation basin, it could cause a host of problems with the settling process and compromise the water quality.

澄清和过滤过程产生的污泥，是由澄清过程中的沉淀物和滤池在过滤过程中积累的固体组成。如果允许污泥长期在沉淀池中堆积，它可能导致沉淀过程中出现一系列问题，并影响出水水质。

The accumulated material, called a sludge blanket, builds up on the floor of the settling basin and must be removed periodically. This removal process, known as wasting, will remove a portion of the sludge blanket—a mixture of organic and inorganic solids—and reduce the chance that it creates a nuisance condition. The organic solids provide a food source for naturally occurring bacteria to thrive. When these bacteria consume this organic material, they release gases into the sludge blanket, causing the sludge to become buoyant and eventually break apart and float in pieces to the basin's surface.

积累的固体，被称为剩余污泥，堆积在沉淀池的底部，必须定期清除。这一清除污泥的过程，即排除剩余污泥的过程，排除剩余污泥这一有机和无机固体的混合物，能减少其对水质造成干扰的机会。其中有机固体可为水中的细菌提供营养来源，使其繁殖生长。当这些细菌消耗吸收这些有机物时，会在堆积在底部的剩余污泥中释放气体，让污泥具有浮力并最终破裂，成片地漂浮到沉淀池的表面。

The solids are resuspended in the basin and can easily carry over onto the filters, causing them to become dirty sooner, thereby shortening the filter run time between backwashes. In extreme situations, the oxygen in the sludge blanket may be totally consumed by bacteria, and the sludge blanket can become septic. When this happens, anaerobic bacteria can thrive, producing foul-smelling gases, such as hydrogen sulfide (H ₂ S), which has a rotten-egg odor. This situation can then impart taste and odors to the water as it flows through the basin.

如果固体物质重新在池体中变成悬浮状态，就很容易从池体中溢出，让水重新变脏，而且也会导致滤池正常运行的时间缩短，反冲洗变得更加频繁。在极端情况下，污泥中的氧气完全被细菌消耗掉，污泥就可能厌氧腐坏。当这种情况发生时，厌氧细菌会茁壮成长，产生恶臭的气体，如臭鸡蛋气味的硫化氢（H ₂ S）。这种情况下，如果水流经这样的池体，就会给水带来异嗅味。

Sludge must be disposed of once it's removed from the settling basin, and a variety of methods are used. The sludge may be pumped directly into a large lagoon where the solids settle and compact at the bottom and the water can evaporate. Other common disposal methods include sending the sludge to a wastewater treatment plant or using a belt filter press or centrifuge to remove the water from the sludge and then hauling the dried solids to a landfill. A more sustainable approach to sludge disposal is using the material as a soil amendment/conditioner, thereby recycling/reusing the sludge for beneficial purposes.

污泥从沉淀池中排出后必须进行处理，使用的方法有很多。污泥可能被直接泵入一个大的洼地，固体在底部沉淀和压实，水份可以通过蒸发去除掉。其他常见的处置方法包括将污泥送往污水处理厂，或使用带式压滤机或离心机从污泥中去除水分，然后将干燥的固体拖到垃圾填埋场。一个更可持续的污泥处理方法是将该材料作为土壤改良剂/调节剂，从而实现污泥的回收/再利用以达到有益的目的。

Water storage tanks serve several purposes. They provide additional storage capacity for the distribution system, ensuring that plenty of water is available for everyday use as well as for emergency needs, such as firefighting. Storage tanks also provide additional time for disinfection. By keeping the disinfectant chemical in the water for a longer period, the potential of pathogen contamination is reduced.

清水池有这样几个目的。一是为输配系统提供额外的储存能力，确保不论是水量充足的时期还是例如火灾消防等紧急需水的时间都能有足够的水量供给。二是清水池能够为消毒提供额外的反应时间，让消毒剂在水中拥有更长的化学反应时间，让病原体得到更好的去除。

Having additional storage tank capacity in the distribution system allows a plant operator to normalize the treatment plant flow and pressure into the distribution system. The ability of the operator to constantly keep an even flow rate through the plant helps to produce a more consistent product. Frequent changes in plant flow disrupt the water treatment process and can create inconsistent water quality. Having extra water storage space also decreases the need to constantly change plant flow rates, but the operator must properly manage how long the water resides in the tanks.

在输配系统中拥有额外的储水容量，可以让水厂的运营人员能够更为平常简单地控制水厂出水的流量和压力。运营人员能够持续保持水厂的流量的均态，也有助于生产更稳定的水。因为水厂流量的频繁变化可能会扰乱水处理工艺的过程，并可能导致水质的波动。拥有额外的储水空间可以减少水厂出水流量的波动，但前提是必须适当控制好水在清水池中的停留时间。

Water Age .  Minimizing and/or optimizing water age in the distribution system is important. Typically, an operator will fill up a utility's storage tanks overnight when water demand is lowest and let the storage tanks drain during the day when demand is highest. Whatever scheme the operator uses, cycling the storage tank water levels up and then back down keeps fresh water in the system. Keeping storage tanks full for extended periods and never letting them cycle lower can rapidly diminish disinfectant residual, creating conditions for microbial contamination, including nitrification and the creation of biofilms. These conditions could cause health concerns and/or violations of local, state, or federal water quality standards.

水龄 。 最小化或优化输配系统中的水龄是非常重要的。通常情况下，运营人员会在用水需求最低的晚上将清水池装满，并在白天需水最高的时候使用清水池中的水。不管采用什么样的运营方案，运营人员都会让那个清水池的水位在上升和下降中反复，以保持输配系统中的水足够“新鲜”。但如果长期保持清水池装满水，而不让水位下降带来用水循环，则会迅速降低消毒剂的残留量，为微生物污染创造条件，包括硝化反应和生物膜的产生。这些情况可能导致健康问题，和/或违反当地、州或联邦的水质标准。

Nitrification .  Nitrification is the process by which ammonia is oxidized. For systems that use chloramines as a disinfectant, this process can become problematic as water ages in the distribution system. Chloramines degrade over time, and NH ₃  levels can rise as dissociation occurs. NH ₃  can then be used as a food source for certain microorganisms, which leads to an overall degradation in water quality as nitrification progresses (Table 1). As microorganisms metabolize NH ₃ , nitrite (NO ₂ ^- ) is produced, which is then further metabolized and converted to nitrate (NO ₃ ^- ). Nitrate doesn't readily degrade and can build up in distribution systems to create water quality problems and cause harmful health effects. Water quality parameters, such as pH, temperature, alkalinity, chloramines, NH ₃ , NO ₂ ^- , and NO ₃ ^- , should be monitored so action can be taken if a nitrification event is detected.

硝化作用 。  硝化作用是氨被氧化的过程。对于使用氯胺作为消毒剂的处理该工艺，随着水在输配系统中的水龄延长，发生的硝化反应可能会成为问题。氯胺会随着时间的推移而逐渐降解，氨的浓度会随着解离的发生而上升。然后，氨可作为某些微生物的食物来源，随着硝化作用的进行，会导致水质的整体下降（表1）。当微生物对氨进行代谢时，会产生亚硝酸盐（NO ₂ ^- ），然后进一步代谢并转化为硝酸盐（NO ₃ ^- ）。硝酸盐不容易降解，会在输配系统中堆积，造成水质问题，并对健康造成有害影响。所以应当监测的水质参数，包括pH值、温度、碱度、氯胺、NH ₃ 、NO ₂ ^- 和NO ₃ ^- 等，以便当检测到硝化反应发生时可以采取行动。

Table 1. Nitrification Factors

表1 发生硝化反应的原因

Water quality degrades as nitrification progresses.

随着硝化反应的发生，水质相应变差

Elevated Storage Tanks .  What the public refers to as water towers, elevated storage tanks can improve distribution system water pressure by the weight of the water in the tank as it bears down on the system. The higher the water's elevation, the greater the downward pressure exerted by the water on the distribution system. For every added foot of water column elevation in a storage tank, the pressure at the base increases an additional 0.433 psi. For example, an elevated storage tank with a water column 100 feet tall would produce 43.3 psi at the base of the tank (100 ft ×?0.433 psi/ft = 43.3 psi).

高位储水池 。  高位储水池，也就是俗称的水塔、高位水箱，可以通过水箱中水的重力势能来提高输配系统的水压。水的高度越高，水对输配系统施加的向下的压力就越大。储水池的水位高度每增加一英尺，底部的压力就会增加0.433 psi。例如，一个水位高100英尺的高位储水池，在池底会产生43.3磅的压力（100英尺×0.433磅/英尺=43.3磅）。

Water may also be stored in  ground storage tanks , which are strategically sized and placed in various parts of the distribution system to ensure enough capacity to meet the daily water demand in those areas. Ground storage tanks can hold millions of gallons of water, so they can provide a lot of extra storage capacity. These tanks may rest on the ground, or they may be partially or completely below ground. Depending on the tank capacity and daily water usage, Cl ₂  levels in these large storage tanks may also diminish over time if they aren't properly cycled (allowed to regularly fill and drain). When Cl ₂  levels have diminished, it's convenient to be able to add Cl ₂  disinfectant to the water flowing in or out of the ground storage tank. Also, these large storage tank installations can serve as booster chlorination facilities to increase the Cl ₂  level of the water inside the tank or boost the Cl ₂  level as the water is being pumped to another area of town.

水也可以储存在 地面的储水池 中，这些储水池的尺寸是具有战略意义的，布置在输配系统的各个环节，以确保有足够的容量来满足这些地区的日常用水需求。地面的储水池可以储存数百万加仑的水，所以它们可以为输配系统提供大量额外存储容量。这些水箱可以布置在地面上，也可以部分或完全布置在地面以下。根据水池的容量和日常用水量需求，如果没有适当的循环（定期充满水和排放水），这些大型水池中的Cl ₂ 浓度也可能随着时间的推移而减少。当Cl ₂ 浓度减少时，需要方便地向水池的进水或出水中补充消毒剂。所以，这些大型水池还可以作为增压补氯的设施用来提高水池内的Cl ₂ 浓度，或者在水被抽到镇上另一个地区时提高Cl ₂ 的浓度。

Whichever type of storage is used—ground storage, elevated storage, or a combination of both—it's necessary to inspect storage tanks annually, both internally and externally. A water utility may conduct these inspections using in-house staff, or it may choose to hire a contractor to conduct the inspections.

不管是用那种储水的方式，地面水池、高位水池或组合形式，都必须每年对水池的内外部进行检查。水务企业可以委派自己的员工进行这些检查作业，也可以委派给第三方进行检查。

Water distribution systems begin when finished tap water leaves a water treatment plant at the system's point of entry. They consist of all the pipes, valves, pumping stations, and storage facilities outside of the water treatment plant, and their purpose is to convey uninterrupted pressurized drinking water to customers for consumption and to fire hydrants for fire protection.

输配系统指成品水离开水厂后的系统，以离开水厂的点为输配系统的入口。输配系统由水处理厂以外的所有管道、阀门、泵站和储水设施组成，其目的是将不间断的加压饮用水输送到用户，并输送到用于消防的消防栓。

Corrosion. Corrosion refers to how aggressive water is at corroding pipes. As shown in photos 3 and 4, it can be a major problem within distribution systems. Many types of corrosivity indices are available to determine how corrosive a water sample is (e.g., the Langelier Saturation Index, Ryznar Index, and Aggressiveness Index). These indices use the following measurements to determine corrosivity: pH, temperature, total dissolved solids, hardness, alkalinity, chloride (Cl ^– ), sulfate (SO ₄ ^2– ), and others. To halt or slow the effects of corrosion in the distribution system, parameters can be adjusted through treatment to produce water that's slightly scale-forming. This thin coating of scale inside the distribution system piping can create a barrier between the metal water mains and any corrosive water. For systems that blend multiple finished waters in ground storage before release to the distribution system, it's important to consider corrosivity parameters and plant flow blend percentages when determining the corrosion/scale-forming potential of the final product.

腐蚀。腐蚀是指水对管道的侵蚀程度。如照片3和4所示，腐蚀可能是输配系统中的一个主要问题。有许多的腐蚀相关的指标可用于确定水样的腐蚀性（例如，Langelier饱和度指数、Ryznar指数和侵蚀性指数）。这些指数使用以下参数来确定腐蚀性：pH值、温度、总溶解固体、硬度、碱度、氯化物（Cl ^- ）、硫酸盐（SO ₄ ^2- ），以及其他。为了阻止或减缓输配系统中的腐蚀影响，可以通过水处理来调整上述参数，以生产有轻微结垢倾向的水。输配系统管道内的这层薄薄的水垢可以在金属水管和任何带有腐蚀性的水之间形成一个屏障。对于在进入输配系统之前，要混合多个水厂来源成品水的系统，在确定最终的成品水的腐蚀/结垢潜力时，必须考要到虑腐蚀性参数和各个水厂流量的混合百分比。

Photos 3 and 4

Corrosion can occur outside (top) and inside (bottom) pipes and related structures as they are exposed to corrosive elements.

照片3和4 当管道和相关结构暴露在腐蚀性元素中时，会在其外部（顶部）和内部（底部）发生腐蚀。

Boil Water Notices .  A boil water notice or advisory is a public announcement initiated by a water system and disseminated via local news and social media. Such notices are issued when it's known or suspected that a water supply is contaminated, such as when a Revised Total Coliform Rule sample is positive for E. coli, when pressure in the distribution system drops below 20 psi, or when repeated chlorine samples indicate the disinfectant residual is below the required concentration. Once a boil water notice is issued, monitoring must be conducted to prove the distribution system's integrity before the notice can be lifted.

将水煮沸的提示 。 需要将水煮沸的通知或建议是由供水系统发起的社会公告，通过当地新闻和社会媒体进行传播。当已知或怀疑供水受到污染时，如按照修订后的总大肠菌群规则，水样的大肠杆菌呈阳性，输配系统的压力下降到20磅/平方英寸以下，或多次采样的样本表明消毒剂残留量低于所需浓度时，就会发布此类通知。一旦发布需要将水煮沸的通知，水务企业必须对输配系统进行检测以证明输配系统完好后，才能取消通知。