1. What is water self-purification?

Water self-purification: Polluted rivers, through physical, chemical, and biological processes, reduce or transform pollutant concentrations, restoring the water body to its original state or reducing it from exceeding water quality standards to meeting them.

 

2. What are the basic methods of wastewater treatment?

Basic methods of wastewater treatment: It involves using various methods and technologies to separate and remove pollutants from wastewater, recycle them, or convert them into harmless substances, thus purifying the wastewater. It is generally divided into water supply treatment and wastewater treatment.

 

3. What wastewater treatment technologies are currently available?

Modern wastewater treatment technologies can be classified according to their working principles as: Physical treatment methods, chemical treatment methods, biological treatment methods.

 

4. Five water measurement indicators

Biochemical Oxygen Demand (BOD): It refers to the amount of oxygen required to degrade organic matter due to microbial action under aerobic conditions. It is a comprehensive indicator of organic pollution in wastewater.

Theoretical Oxygen Demand (ThOD): The theoretical oxygen demand of a certain organic substance in water. It usually refers to the theoretical value of the oxygen required to completely oxidize the carbon and hydrogen elements in the organic matter into carbon dioxide and water (i.e., the oxygen demand calculated according to the complete oxidation reaction formula).

Total Oxygen Demand (TOD): It refers to the amount of oxidizable substances in water, mainly the amount of oxygen required for organic substances to become stable oxides during combustion, expressed as mg/L of O2.

Chemical Oxygen Demand (COD): It is the amount of reducible substances in a water sample that need to be oxidized using chemical methods. In wastewater, wastewater treatment plant effluent, and polluted water, it represents the oxygen equivalent of substances (generally organic matter) that can be oxidized by strong oxidants.

Total Organic Carbon (TOC): It refers to the total amount of carbon in dissolved and suspended organic matter in a water body.

 

5. Under what circumstances is biological treatment used?

It is generally considered that only wastewater with a BOD/COD value greater than 0.3 is suitable for biological treatment.

 

6. What are the hygiene standards for drinking water?

Physical indicators of drinking water hygiene standards: Color, turbidity, odor, and taste.

 

7. What is eutrophication of water bodies?

Eutrophication of water bodies It is a natural phenomenon that occurs in freshwater, caused by excessive nitrogen, phosphorus, and potassium in the water body, leading to a sudden overgrowth of algae.

The main cause of eutrophication is the discharge of nitrogen, phosphorus, and potassium into slow-flowing surface waters with long renewal cycles, causing excessive growth of algae and other aquatic organisms, resulting in the rate of organic matter production far exceeding the rate of consumption, accumulation of organic matter in the water body, and disruption of the aquatic ecological balance.

 

8. What is dissolved oxygen?

Oxygen dissolved in water is called Dissolved oxygen . Aquatic organisms and aerobic microorganisms rely on dissolved oxygen for survival. Different microorganisms have different requirements for dissolved oxygen.

 

9. What are the basic methods of modern wastewater treatment?

Modern wastewater treatment technologies can be classified according to their working principles as: Physical treatment methods, chemical treatment methods, biological treatment methods.

 

10. What is the stability of colloids?

Stability of colloids: It refers to the characteristic of colloidal particles remaining dispersed and suspended in water for a long time.

 

11. What is electrokinetic potential?

Electrokinetic potential: The electric potential on the slip plane of the colloid, i.e., the zeta potential.

 

12. How do hydrophobic colloids form large particles?

For hydrophobic colloids, to allow colloids to collide with each other through Brownian motion and form large particles, the repulsive energy peak must be reduced or eliminated. The way to reduce the repulsive energy peak is to reduce or eliminate the zeta potential of the colloid particles.

 

13. What is the role of adsorption bridging?

Adsorption bridging refers to the adsorption and bridging of macromolecules with colloid particles.

 

14. What is the function of a screen?

Function of a screen: To intercept larger suspended solids or floating impurities.

 

15. What are the main factors affecting coagulation efficiency?

Main factors affecting coagulation efficiency: Water temperature, water pH and alkalinity, suspended solids concentration in water, and hydraulic conditions.

 

16. How many types of sedimentation are there? What are they?

There are four types of sedimentation , which are:

Free settling : Particles are in a discrete state during sedimentation, their shape, size, and mass do not change, the settling velocity is not affected, and each particle completes the sedimentation process independently.

Flocculent settling: During sedimentation, the size, mass, and settling velocity of the particles increase with depth.

Hindered settling: 颗粒在水中的浓度较大，在下沉的过程中彼此干扰，在清水与浑水之间形成明显的交界面，并逐渐向下移动。

压缩沉淀： 颗粒在水中的浓度很高，沉淀过程中，颗粒相互接触并大部分地受到压缩物支撑，下部颗粒的间隙被挤出。 

 

17、按池内水流方向，沉淀池可分为哪几种？

按池内水流方向的不同，沉淀池可分为 平流式、斜流式、辐流式、竖流式。

 

18、滤料层内杂质分布有什么规律？

滤料层内杂质分布规律： 在过滤开始阶段，滤料比较干净，孔隙也较大，水流剪切力较小，粘附作用较强，此时，水中颗粒首先被表层滤料截留，随着过滤时间延长，滤层中杂质增多，孔隙率逐渐减小，特别是表层细滤料，水流剪切力增大，脱落作用增强，最后被粘附上的颗粒首先脱落向下层移动并被下层滤料截留。

 

其结果是： 在一定过滤水头下，滤速将急剧减小，或者在一定得滤速下水头的损失达到极限值，或者由于滤层表面受力不均匀而使泥膜产生裂缝时，大量的水流自裂缝中流出，造成水中杂质颗粒穿透滤层使出水水质恶化。

 

19、提高过滤效率的途径有哪些？

提高过滤效率的途径： 为了改变这种状况提高滤层含污能力，便出现了“反粒度”过滤，即顺水流方向，滤料粒径由大到小，由于上向流及双向流滤池结构复杂，不便冲洗等原因。

 

20、均质滤料由什么组成？

均质滤料组成： 均质滤料是指整个滤层深度方向的任一横断面，滤料组成和平均粒径均匀一致，而并非指滤料粒径完全相同。

 

21、什么是负水头现象？避免的方法有哪些？

负水头现象： 在过滤过程中，当滤层截留了大量杂质，以致砂面以下某一深度处的水头损失超过该处水深时出现的现象。

避免出现负水头的方法： 是增加砂面上水深，或者滤池出水位置等于或高于滤层表面。虹吸滤池和无阀滤池不会出现负水头即是这个原因。

 

22、普通快滤池反冲洗水供给方式有几种？

普通快滤池反冲洗水供给方式 有两种：冲洗水泵和水塔。

 

23、什么是这点加氯？

当水中有机物主要为氨和氮化物，其实际需氯量满足后，加氯量增加，余氯量增加，但是后者增长缓慢，一段时间后，加氯量增加，余氯量反而下降，此后加氯量增加，余氯量又上升，此折点后自由性余氯出现，继续加氯消毒效果最好，即折点加氯。

 

24、活性污泥法有哪几个系统？

活性污泥法是由 曝气池、沉淀池、污泥回流、剩余污泥 排除系统组成。

 

25、什么是污泥沉降比？

污泥沉降比（SV%）： 是指曝气池混合液，在1000ml量筒中静置沉淀30min，沉淀污泥与混合液的体积比（%）。 

 

26、什么是污泥指数？

污泥指数(SVI)： 是指曝气池出口处混合液经静置沉淀30min后，每克干污泥所占的容积，以mL计。    

SVI值过低，说明泥粒细小紧密，无机物多，缺乏活性和吸附能力；SVI值过高，说明污泥难于沉降分离，即将膨胀或已经膨胀，必须查明原因，并采取措施。        

 

27、什么是污泥膨胀、解体、腐化、上浮和泡沫？

污泥膨胀： 当污泥变质时，污泥不易沉淀，SVI值增高，污泥的结构松散，体积膨胀，含水率上升，澄清液少，颜色也有异变。       

污泥解体： 处理水水质浑浊，污泥紊凝微细化，处理效果变坏等则是污泥解体的现象

污泥腐化： 在二次沉淀池有可能由于污泥长期滞留而产生厌氧发酵，生成气体，从而出现大块污泥上浮的现象。

污泥上浮： 污泥在二次沉淀池呈块状上浮的现象。

泡沫问题：曝气池中产生泡沫，主要原因是污水中存在大量合成洗涤或其他起泡物质。

 

28、什么是活性污泥增长曲线？

Activated sludge microorganisms are a mixed population of multiple species, their growth patterns are complex, but can also be expressed by their growth curve. This curve shows that when environmental conditions such as temperature and dissolved oxygen meet the growth requirements of microorganisms, and there is a certain amount of initial microbial inoculation, after a sufficient addition of nutrients, the proliferation and attenuation of the number of microorganisms over time.

The change in the growth rate of activated sludge is mainly caused by the ratio of nutrients or organic matter to microorganisms (usually expressed as F/M), and the F/M value is also an important influencing factor of the organic substrate degradation rate, oxygen utilization rate, and the coagulation and adsorption performance of activated sludge.

The four stages of the activated sludge growth curve: adaptation phase, logarithmic growth phase, deceleration growth phase (maximum biomass), endogenous respiration phase (best treated water quality).

 

29. How many processes are involved in the purification of activated sludge?

Activated sludge purifies wastewater through three stages:

In the first stage, wastewater is mainly purified through the adsorption of activated sludge. Adsorption is very rapid, generally completed within 30 minutes, and the BOD5 removal rate can reach up to 70%. It also has a partial oxidation effect, but adsorption is the main effect.

The second stage is also called the oxidation stage. It mainly continues to decompose and oxidize the organic matter adsorbed and absorbed in the previous stage, while continuing to adsorb some residual dissolved substances.

The third stage is the solid-liquid separation stage. In this stage, activated sludge is precipitated and separated in the secondary sedimentation tank. Both the anabolism and catabolism of microorganisms can remove organic pollutants from wastewater, but the products are different.

 

30. What are the characteristics of the secondary sedimentation tank?

Characteristics of the secondary sedimentation tank: In terms of function, in addition to solid-liquid separation, it also performs sludge concentration, and due to changes in water quality and quantity, it also temporarily stores sludge.

 

31. What is a slow sand filtration system for wastewater?

Slow sand filtration is the process of allowing wastewater to slowly pass through the land, purifying the wastewater through natural seepage and filtration. It is suitable for areas with good soil permeability, low evaporation, and humid climate.

 

32. What is a rapid sand filtration system for wastewater?

Suitable for soils with very good permeability, such as sandy soil and gravelly sandy soil. After the wastewater flows to the surface of the rapid infiltration field, it quickly infiltrates into the ground and eventually enters the groundwater layer.

 

33. How many stages are there in anaerobic reaction? What are they?

Anaerobic reaction is divided into three stages:

The first stage is the decomposition of organic matter into fatty acids and other products under the action of hydrolytic and fermentative bacteria.

The second stage is the further conversion of hydrogen and acetic acid into hydrogen, carbon dioxide, and acetic acid under the action of bacteria.

The third stage is the methanogenic fermentation stage (alkaline fermentation stage), through the action of two different groups of methanogens, one group converts hydrogen and carbon dioxide into methane, and the other group produces methane from acetic acid.

 

34. What is two-phase digestion?

Two-phase digestion is to separate the acid-producing stage and the methane-producing stage of anaerobic digestion of organic substrates.

 

35. What are the material components of sludge?

The material components of sludge can be divided into organic sludge and inorganic sludge.

According to the source of sludge, it can be divided into primary sedimentation sludge, excess activated sludge, humus sludge, digested sludge, and chemical sludge.

 

36. What kind of water does sludge contain?

The water contained in sludge is divided into four categories: Intergranular pore water, capillary water, sludge particle adsorption water, and intracellular water.

Removal methods: Gravity, flotation, centrifugation.

 

37. What does mechanical dewatering include?

Mechanical dewatering: Vacuum filtration dewatering, pressure filtration dewatering, roll pressing dewatering, and centrifugal dewatering of sludge.

 

38. What is the purpose of sludge stabilization?

Purpose of sludge stabilization: It is to eliminate the odor emitted from the sludge and kill the pathogenic microorganisms in the sludge.

 

39. What is adsorption?

Using porous solids (such as activated carbon) or flocculant substances (such as polyferric) to adsorb toxic and harmful substances in wastewater on the surface or micropores of solids or flocculants to achieve the purpose of water purification. This treatment method is called adsorption treatment. The object of adsorption can be insoluble solid substances or soluble substances.

 

40. What are the characteristics of physical adsorption and chemical adsorption?

Characteristics of physical adsorption: The adsorption heat is small, it can be carried out at low temperatures, the adsorption is reversible, and the adsorption has basically no selectivity.

Characteristics of chemical adsorption: The adsorption heat is large, the adsorption is irreversible, and the adsorption is selective.

 

41. What is resin density?

Resin density: Generally refers to two representation methods: wet true density and wet apparent density. Wet true density is related to the resin layer's backwashing strength, expansion rate, and resin stratification in mixed beds and double-layer beds, while wet apparent density is used to calculate the amount of wet resin required for ion exchanger loading.

 

42. What is the function of the water spray packing?

The function of the water spray packing: It is to disperse the water droplets falling from the water distribution system into fine droplets or water films through multiple dispersions, increasing the contact area between water and air, extending the contact time, and thus ensuring good heat and mass exchange between air and water.

 

43. What is mixed liquor volatile suspended solids?

Mixed Liquor Volatile Suspended Solids (MLVSS) Refers to the weight of volatile matter in the dry sludge contained in a unit volume of biochemical pool mixed liquor. The unit is also mg/L. Since it does not include the inorganic matter in the activated sludge, it can more accurately represent the number of microorganisms in the activated sludge.

 

44. Why is there excess sludge?

In the biochemical treatment process, the microorganisms in the activated sludge continuously consume the organic matter in the wastewater.

Of the organic matter consumed, some is oxidized to provide energy for the life activities of microorganisms, while the other part is used by microorganisms to synthesize new cytoplasm, thus enabling microorganisms to proliferate and reproduce. At the same time as the metabolism of microorganisms, some old microorganisms die, thus producing excess sludge.

 

45. What is the needle carbon technology?

Iron-carbon treatment, also known as iron-carbon micro-electrolysis or iron-carbon internal electrolysis, is an application of metal iron wastewater treatment technology. Using the iron-carbon method as a pretreatment technology to treat toxic and harmful wastewater with high COD has a unique effect.

 

46. Why should the effluent pH of the neutralization sedimentation tank be adjusted to above 9?

The iron-carbon effluent contains a large amount of ferrous sulfate, which, if not removed, will affect the growth and reproduction of microorganisms in the subsequent bioreactor.

Therefore, we must use lime to increase the pH of the wastewater from 5-6 to above 9, converting the water-soluble ferrous sulfate into insoluble ferrous hydroxide and calcium sulfate, and then using coagulation sedimentation to precipitate them, ensuring that the wastewater entering the bioreactor does not contain ferrous sulfate.

 

47. What are the types of flotation?

Flotation is divided into: Dissolved air flotation (divided into vacuum dissolved air flotation and pressure dissolved air flotation), dispersed air flotation, and electrolytic flotation.

 

48. What is flocculation?

Flocculation is the addition of high-molecular flocculants to wastewater. After dissolution, high-molecular flocculants form high-molecular polymers. The structure of this polymer is linear. One end of the line pulls a tiny particle, and the other end pulls another tiny particle, playing a bonding bridging role between two particles that are far apart, causing the particles to gradually become larger and eventually form large flocculates (commonly known as alum flowers), accelerating particle sedimentation.

 

49. Why is wastewater treated with polyferric sulfate for flocculation and adsorption?

The ferric hydroxide flocs formed during the coagulation process of polyferric sulfate have a good ability to adsorb organic matter in wastewater. Experimental data show that after flocculation and adsorption with polyferric sulfate, 10%-20% of COD in wastewater can be removed, which can greatly reduce the operating burden of the bioreactor and is conducive to the discharge of treated wastewater that meets standards.

In addition, coagulation pretreatment with polyferric sulfate can remove trace substances that are toxic and inhibitory to microorganisms in wastewater, ensuring that the microorganisms in the bioreactor can operate normally. Among many coagulants, the price of polyferric sulfate is relatively cheap (25-300 yuan/ton), so the treatment cost is relatively low, making it suitable for the pretreatment of process wastewater.

 

50. Why are colloidal particles in wastewater not easily naturally settled?

Many impurities with a specific gravity greater than 1, large particles, and easily settling suspended solids in wastewater can be removed by natural sedimentation and centrifugation.

 

However, suspended particles with a specific gravity less than 1, tiny or even invisible to the naked eye, are difficult to settle naturally. For example, colloidal particles are micro-particles with a size of 10-4-10-6 mm, which are very stable in water, and their sedimentation rate is extremely slow, taking 200 years to settle 1 m.