Water quality, water treatment method and explanation of water treatment terms

1. 9 kinds of impurities in water 

1. Particulate Matter 
includes particulate impurities such as sediment, rust, algae, suspended solids, and microfibers, which are visible to the naked eye. These particles are often suspended in the water flow, causing the turbidity of the water. These particles are very unstable and can be removed by sedimentation and filtration. As the water sits, heavy particles (mainly inorganic substances such as sand and clay) settle. Light particles (mainly a class of organic compounds of animals, plants and their remains) will float on the water surface and can be removed by pre-sedimentation, filtration and other separation methods. 
Particulate matter is a major contributor to turbidity, color, and odor. It may exist in tap water, secondary supply tap water, rivers and lakes. 

2. Colloidal substances 
Colloidal substances are particles that are larger than ionic substances and smaller than granular substances, with a diameter between 10-4 and 10-6 mm. Colloids are collections of many molecules and ions. Inorganic mineral colloids in natural water are mainly compounds of iron, aluminum and silicon. The organic colloidal substances in the water are mainly the humus produced by the decay and decomposition of plant or animal limbs. Among them, the humus content in the lake water is the most, so the water is often yellow-green or brown. 
Colloidal particles cannot be removed by self-sedimentation by gravity. Generally, chemicals are added to water to destabilize them, so that the colloidal particles are enlarged and removed by sedimentation. 
Colloidal substances may be present in surface water or groundwater. 

3. Ionic materials 
include: cations and anions. Cations such as calcium ions, magnesium ions, iron ions, etc.; anions such as chloride ions, sulfate ions, phosphate ions, etc. 
Ionic substances are usually easily soluble in water, and dissolved substances can be removed by ion exchange or desalination. 
  
4. Non-reactive dissolved gases 
such as nitrogen in the air, etc. 

5. Reactive dissolved gases 
Common dissolved gases in natural water include oxygen (O2), carbon dioxide (CO2), and sometimes hydrogen sulfide (H2S), sulfur dioxide (SO2), and ammonia (NH3). Most of these gases dissolved in water have a corrosive effect on metals and are an important factor causing metal corrosion in water systems. 
CO2 in the air has the greatest impact on pure water. CO2 exists in the air and easily dissolves in water, making the water acidic, ie a pH value below 7. The purer the water quality, the more susceptible it is to the influence of the air. The influence is mainly manifested in pH value and conductivity (resistance) rate. 

6. Microorganisms 
mainly refer to the bacteria content in water. The allowable content of conventional bacteria in tap water in CHINA is <100cfu/ml; the allowable content of conventional bacteria in pure water is less than 1cfu/ml. 

7. Heat source 
Heat source, also known as bacterial endotoxin, is mainly used for medical water, especially water for injection, and the content control of heat source should be considered. When there are biological applications such as cell culture in the laboratory, there are requirements for content control of heat sources. 

8. Organic substances 
Organic substances in water mainly refer to pollutants of humic acid, domestic sewage and industrial wastewater. Humic substances are the products of life activity processes such as aquatic organisms. These organic substances pollute water bodies and deteriorate water quality. 
The organic matter in water has a common feature, that is, to carry out biological oxidation and decomposition, it needs to consume dissolved oxygen in the water, which leads to the lack of oxygen in the water. At the same time, corruption and fermentation will occur, causing bacteria to grow, deteriorating water quality, and destroying water bodies; organic pollution of industrial water will also reduce the quality of products. Organic matter is one of the main causes of water pollution. 
The content of organic matter in surface water is usually higher than that in ground water. 

9. Residual disinfectant 
In order to control the bacteria content in the water, the tap water company will add disinfectant to control the total number of bacteria. Commonly used disinfectants are chlorine-containing preparations. When chlorine is added to water, highly oxidizing compounds such as residual chlorine will be produced to play a role in disinfection and sterilization. 
For water treatment equipment using reverse osmosis technology, highly oxidative residual chlorine will cause great damage to the RO membrane, so it needs to be strictly removed during pretreatment. Commonly used activated carbon adsorption removal. 

two. 10 Common Water Treatment Methods 

1. Sedimentation filtration method 
This is the most primitive filtration method, which relies on the sinking of the particulate impurities in water to achieve the purpose of separation. It is often used in places with large impurity particles in water, such as preliminary natural clarification and filtration of rivers and lakes. 

2. Distillation 
Distillation is to heat water to turn it into a gas, separate out the low boiling point components or droplets mixed into the gas phase, and put the low boiling point gas in the atmosphere. Non-volatile impurities remain in the liquid phase and are discharged as a concentrated liquid. In this way, the water is refined into high-purity water. 
This method consumes a lot of electricity and water, and needs someone to guard it when it is used. It is inconvenient to use and is less used now. 

3. Membrane microfiltration (MF) method 
The membrane microfiltration method includes three forms: depth filtration, screen filtration, and surface filtration. 
Depth filtration is a matrix made of woven fibers or compressed materials, using inert adsorption or capture methods to retain particles, such as commonly used multimedia filtration or sand filtration; depth filtration is a more economical method that can remove 98 % of suspended solids, while protecting the downstream purification unit from being blocked, so it is usually used as pretreatment. 
Surface filtration is a multi-layer structure. When the solution passes through the filter membrane, particles larger than the internal pores of the filter membrane will be retained and mainly accumulated on the surface of the filter membrane, such as the commonly used PP fiber filter. Surface filtration can remove more than 99.9% of suspended solids, so it can also be used for pretreatment or clarification. 
The sieve filter membrane basically has a consistent structure, just like a sieve, leaving particles larger than the pore size on the surface (the pore size of this filter membrane is very accurate), such as the terminal use of ultrapure water machines Point-of-use security filter; screen filter microporous filter is generally placed at the end-use point of the purification system to remove the last residual traces of resin chips, carbon dust, colloids and microorganisms. 

4. Activated carbon adsorption method 
Activated carbon mainly removes organic impurities such as color, odor, residual chlorine, and residual disinfectants in water by means of adsorption and filtration. 

5. Electrodialysis 
Dialysis is a physical phenomenon. For example, two brines with different concentrations are separated by a permeable membrane, and the solutes in the brine with high concentration, such as inorganic salt ions, permeate into the brine with low concentration through the membrane. This phenomenon is called dialysis. This dialysis is caused by the difference in salt concentration and is called concentration dialysis. Because the concentration difference is used as the driving force, the diffusion rate is always relatively slow. If you want to speed up this speed, you can add a DC electrode on both sides of the membrane. Under the action of an electric field, the electrolyte will accelerate the migration speed, which is called electrodialysis. 
Electrodialysis consumes a lot of power, and the dialysis membrane is fragile, so it is rarely used after the appearance of reverse osmosis technology. 

6. Ion exchange (IX) method
The principle of the ion exchange method is to exchange the anions and cations of inorganic salts in the raw water*, such as calcium ions Ca2+, magnesium ions Mg2+, sulfate SO42-, nitrate NO3-, etc., with ion exchange resins, The anions and cations in the water are exchanged with the anions and cations in the resin, so that the water is softened or purified. 
Note 1: Raw water refers to the incoming water of each filter unit is called raw water. 
Ion exchange resins* are divided into anion resins (R-OH) and cationic resins (HR and Na-R), among which cationic resins are divided into sodium type resins (Na-R) and hydrogen type resins according to their active groups. Resin (HR). Sodium type resin is often used for water softening, and hydrogen type resin is often used together with anion resin R-OH to remove inorganic salt anions and cations in water and purify water into ultrapure water. 
Note 2: Ion exchange resin refers to the polymer group of ion exchange resin, which is usually represented by R. 
Purification process: 
If HR represents hydrogen-type cation resin, the exchange process of purified water quality is as follows: 
2H-R+Ca2+= R2Ca+2H+ 
2R-OH+ SO42- = R2SO4 + 2OH-   
The H+ and OH- generated in the above process react again: 
H++ OH - =H2O     
means that after the water quality passes through the ion exchanger, the anions and cations of inorganic salts in the water are replaced with H2O to achieve the purpose of purification. 
Softening process: 
If Na-R represents sodium resin, the exchange process is as follows: 
2Na-R+Ca2+=R2Ca+2Na+ 
2Na-R+Mg2+=R2Mg+2Na+, 
that is, after the water passes through the sodium ion exchanger, Ca2+ and Mg2+ in the water are replaced with Na+ to achieve softening Purpose. 
Regeneration process: 
After the ion exchange resin has been used for a period of time, the ions in the resin have been completely exchanged, reaching saturation and losing ion exchange capacity. At this time, the resin needs to be regenerated. 
The softening resin needs to be regenerated with NaCl instant salt solution, and the chemical reaction of the regeneration process is just opposite to the ion exchange reaction of the above-mentioned softening process. 
The cation resin for purified water needs to be regenerated with acid, and the anion resin needs to be regenerated with alkali. The chemical reaction of the regeneration process is the opposite of the ion exchange reaction of the purification process described above. 

7. The ultrafiltration (UF)
microporous membrane removes particles according to the size of the filter pore size, while the ultrafiltration (UF) membrane is like a molecular sieve, which uses the size as a basis to allow the solution to pass through extremely fine pores to separate the solution. The purpose of molecules of different sizes. 
Ultrafiltration membrane is a strong, thin, and selective permeable membrane. It is generally considered that its filtration pore size is about 0.01 μm, and it can retain molecules above a certain size, including: colloids, microorganisms, and heat sources. Smaller molecules, such as water and ions, pass through the membrane. 
Ultrafiltration is commonly used in fruit juice concentration, Chinese herbal medicine extraction, reverse osmosis pretreatment, ultrapure water terminal security filtration, etc. 

8. Reverse osmosis (RO) method
is a high-tech membrane separation technology. It is a material separation process in which pure water is extracted from water containing various inorganic substances, organic substances, and microorganisms, using pressure as the driving force, using the selectivity of reverse osmosis membranes that can only permeate water but not solutes. The pore size of the reverse osmosis membrane is less than 10 angstroms (1 angstrom is equal to 10-10 meters), which has a strong screening effect, its desalination rate is as high as 99%, and the sterilization rate is greater than 99.5%. It can remove inorganic salts, sugars, amino acids, bacteria, viruses and other impurities in water. It has been widely used in the desalination of seawater, the production of pure water, the preparation of ultrapure water, and other professional processes for the removal of bacteria, pyrogens, colloids, particles and organic matter. 
If the raw water quality and product water quality are taken as the benchmark, RO is an economical and effective method to purify tap water after proper design, and it is also a good pretreatment method for ultrapure water systems. 

9．紫外线(UV)、臭氧灭菌法
紫外灯所放射出来的254nm的紫外线是一种有效的杀菌方法，因为细菌中的DNA及蛋白质会有吸收紫外线导致死亡。 
紫外线灭菌法 
臭氧灭菌法：采用臭氧发生器产生臭氧，加入纯水中，灭菌效果极好。 

10、EDI法
一种新的去离子水处理方法。又称连续电除盐技术，EDI装置将离子交换树脂充夹在阴/阳离子交换膜之间形成EDI单元。这种方法不需再用酸碱对树脂进行再生，环保性好。现已广泛应用。 

三、各种水处理方法与处理对象的比较 

符号标注：◎表示优良，○表示良，△表尚可，×表不好.

四、水处理常用名词解释 

1.什么是水的浑浊度？ 
答：由于水中含有微粒杂质，使得原是无色透明的水产生浑浊现象，其浑浊的程度称为浑浊度。浑浊度的单位是用“度NTU”来表示的。 
控制浑浊度是工业水处理的一个重要内容，According to水的不同用途，对浑浊度有不同的要求：生活饮用水的浑浊度不得超过5度； 
在工业水处理中，主要是采用混凝、澄清和过滤的方法来降低水的浑浊度。

 
2.什么是水的硬度？ 
答：水中有些金属阳离子，同一些阴离子结合在一起，容易形成水垢，附着在物体表面，我们把水中这些金属离子的总浓度称为水的硬度。如在天然水中常见的金属离子是钙离子(Ca2+)和镁离子(Mg2+)、它与水中的阴离子如碳酸根离子(CO32-)、碳酸氢根离子(HCO3-)、硫酸根离子(SO42-)、氯离子(Cl-)、以及硝酸根离子(NO3-)等结合在一起。形成钙镁的碳酸盐、碳酸氢盐、硫酸盐、氯化物、以及硝酸盐等硬度。水中的铁、锰、锌等金属离子也会形成硬度，但由于它们在天然水中的含量很少，可以略去不计。因此，通常就把Ca2+、Mg2+的总浓度看作水的硬度。 
通常，地下水、井水等的硬度较大，地表水的硬度较小。中国北方地区的水质较硬，南方地区的水质较软。 
若水质的硬度较大，则在反渗透处理之前需要对原水进行软化，否则易在RO膜表面结垢，影响RO膜的产水质量及使用寿命。 
水的硬度对锅炉用水的影响很大，因此，锅炉用水时需要进行软化或除盐处理。 

3.什么是水的总固体、溶解固体和是悬浮固体？ 
答：水中除了溶解气体之外的一切杂质称为总固体。而水中的固体又可分为溶解固体和悬浮固体。这二者的总和即称为水的总固体。 
溶解固体是指水经过过滤之后，那些仍然溶于水中的各种无机盐类、有机物等。悬浮固体是指那些不溶于水中的泥砂、粘土、有机物、微生物等悬浮物质。 
总固体的测定是蒸干水分再称重得到的。 
  
4.什么是水的含盐量？TDS值？ 
答：水的含盐量(也称矿化度)是表示水中所含盐类的的总含量。由于水中各种盐类一般均以离子的形式存在，所以含盐量也可以表示为水中各种阳离子的量和阴离子的量的和。 
水的含盐量与溶解固体的含义有所不同，因为溶解固体不仅包括水中的溶解盐类，还包括有机物质。同时，水的含盐量与总固体的含义也有所不同，因为总固体不仅包括溶解固体、还包括不溶解于水的悬浮固体。所以，溶解固体和总固体在数量上都要比含盐量高。但是，在不很严格的情况下，当水比较清净时，水中的有机物质含量比较少，有时候也用溶解固体的含量来近似地表示水中的含盐量。 
水质的TDS值是指溶解性总固体含量。在水处理计算中，通常被用作水质含盐量的代替值，常可用TDS笔作快速测得，其单位为。通常TDS、电导率间的关系可简易换算为：1ppm=2us/cm 

5.水的电阻率、电导率？二者的关系？ 
答：水的电阻率和电导率的大小,与水中含盐量的多少、水中离子浓度、离子的电荷数以及离子的运动速度有关。水越纯，电阻率越大，电导率越小。电阻和电导是成反比的关系。目前最纯的水质电阻率为18.25MΩ.cm。需了解中国实验室水质标准GB6682-92的PH、电阻等指标。 
水质越纯，电阻率和电导率越易受空气中的CO2的影响，因此超纯水的电导电阻检测需要在线检测，才可保证其准确性。 

6.什么是水的PH值？有什么意义？ 
答：水的PH值是表示水质酸碱性的相对值。PH值范围规定在1-14之间，以7为中性的界限，1＜PH＜7时水质为酸性，PH值越小，酸性越强；7＜PH＜14时水质为碱性，PH值越大，碱性越强。 
纯水的PH值很容易受空气中的CO2的影响，水质越纯，对CO2的溶解性越强，因此中国实验室水质标准GB6682-92对一、二级纯水的PH值不作规定。 

7.什么是ppm、ppb？ 
答：1ppm(parts per million)就是指1毫克/升。即表示1升水中含有多少毫克的杂质，故1毫克／升的杂质相当于水中含有百万分之一份杂质。 
1微克／升相当于水中含有十亿分之一份的杂质，也可以ppb来表示。 
1mg/L=1ppm   1μg/L=1ppb   1ppm=1000ppb 

8. What is water pretreatment? What are the main methods of preprocessing? 
Answer: Water pretreatment is the preliminary treatment before water refining treatment, so as to achieve good results in water refining treatment, improve water quality and prolong the service life of fine treatment equipment. 
There are many pretreatment methods, mainly pre-sedimentation, coagulation, clarification, filtration, softening, disinfection and so on. After pretreatment with these methods, impurities such as suspended solids (turbidity), chromaticity, colloids, organic matter, iron, manganese, temporary hardness, microorganisms, volatile substances, and dissolved gases in water can be removed or reduced to a certain level. degree. 
Pre-sedimentation is natural sedimentation treatment with large volume and low flow rate, such as grit chamber and pre-sedimentation tank. 
Coagulation Use coagulants such as iron salts, aluminum salts, and polymers to form large-grained sediments through flocculation and bridging with impurities in the water, and then remove them through other equipment, such as clarification tanks and filter tanks. 
Clarification The large-grained sediment formed by the action of the coagulant is separated in the clarification tank, and the sediment is removed to obtain clarified water. 
Filtration The water to be treated flows through devices equipped with special filter materials, such as various filters, etc., to trap impurities in the water and remove them.   
Softening Use chemical agents, such as lime water, soda powder, etc., to remove the hardness of bicarbonate in water; or use cation exchange resins to remove calcium, magnesium, and iron ions in water. This process is called softening. 
Disinfection Add fungicides, such as liquid chlorine, bleaching powder, etc., to kill microorganisms in the water. 

9. Explanation of the abbreviated names of commonly used experimental items: 
PCR——molecular biology test. Gene research and cell culture, etc. 
IVF --- Fertilized egg culture 
AA --- Atomic absorption analyzer 
HPLC --- Effective liquid chromatography 
ICP --- Inductively coupled plasma spectroscopy 
TOC --- Total organic carbon