1 Water cycle and water quality standards

1 Water cycle and water quality standards

1、The challenges of urban water resources include ( )
    A、Urban water distribution renders large energy consumption.
    B、Capital and operational costs of water supply for long distance transportation are high.
    C、High risk of urban water pollution.
    D、The standards of urban water quality are high due to the increasing concerns about the safety of urban water sources.

2、It is relatively hard to separate salt from water, because ions such as Ca2+,Mg2+,K+ are tightly surrounded by water molecules.

3、Lakes and reservoir waters usually have low water mobility, high turbidity, and relatively stable water quality.

4、Heavy metals can be concentrated in plant roots or aquatic animals, causing great danger to living organisms.

5、In the US, different sewage plants follow the same discharge standards.

1 Water cycle and water quality standards

1、How can we classify the pollutants in natural basing on particle size?

2 Coagulation theory and technology

2 Coagulation theory and technology

1、Which one below belongs to organic coagulant ( )
    A、polyacrylamide (PAM)
    B、aluminum sulfate
    C、lime glue
    D、poly aluminum chloride (PAC)

2、There are many ways for the control of coagulant dosage and automatic detection, including ( ).
    A、establishing a mathematical model according to the quantity and quality of raw water
    B、streaming current detector (SCD)
    C、dosing according to experience
    D、light transmission pulsation detector

3、Increasing ionic strength would compress the electric double layer and increase the stability of the colloid.

4、G value and GT value are employed to design coagulation tanks, because they can describe the coagulation process comprehensively.

5、The hydraulic condition of the rotary baffle plate flocculation tank is better than that of the reciprocating type, and head loss of the rotary type is 40% less than that of the reciprocating type.

2 Coagulation theory and technology

1、Please discuss the factors influencing the performance of coagulation. How to enhance the performance of coagulation process.

3 Theory and technology of sedimentation

3 Theory and technology of sedimentation

1、Which of the following measure could not improve the settling efficiency in sedimentation tank? ( )
    A、To recycle the sludge to improve the size of particles
    B、To increase the surface area of the tank
    C、To increase the flow rate
    D、To improve the performance of flocculation before sedimentation

2、Which of the following methods can recover the adsorption capacity of sludge in clarifier process? ( )
    A、To generate a pulse to break the large flocs
    B、To circulate the sludge mechanically
    C、To discharge the sludge completely in the clarifier
    D、To circulate the sludge by a water jet

3、θ presents the contact angle of water on the solid surface. Which of the pollutant(s) with the following value of the contact angle cannot be removed by air flotation process. ( )
    A、θ=95°
    B、θ=85°
    C、θ=1°
    D、θ=150°

4、The feed water will go into the upper part of the sedimentation tank under the case of density current of high turbid water, leading to the deterioration of the effluent quality.

5、There is an ineffective zone exists in the inclined tube/ plate sedimentation tank. The ineffective zone would increase if the settling zone is small in the tank.

3 Theory and technology of sedimentation

1、Please analyze the advantages and disadvantages of air flotation process.

4 Filtration theory and technology

4 Filtration theory and technology

1、The effective particle size of filter media refers to the particle size of filter media less than ( ) percent of the total weight after screening.
    A、5
    B、10
    C、75
    D、80

2、The negative water head will not appear in ( ) process(es)?
    A、Conventional rapid filter
    B、Siphon filter
    C、Valveless filter
    D、V-shaped filter

3、The biofilm in slow sand filtration has negative effect on water quality because it may increase the load of disinfection.

4、The expansion rate of single-layer quartz sand is usually about 40%-45%.

5、Supporting layer in the filter can also contribute to the uniform distribution of water to some extent.

4 Filtration theory and technology

1、Please discuss the advantages and disadvantages of slow filter.

5 Adsorption technology

5 Adsorption technology

1、Langmuir isotherm assumes that all surface sites have equal activity, which means adsorption energy is independent of the extent of surface coverage θ.

2、In sorption process, film diffusion transport or pore transport is usually the rate limiting step.

3、Activated carbon can react with water treatment agents such as coagulants and disinfectants.

4、Adding granular activated carbon in intake structure can extend contacting time.

5、In drinking water treatment, activated carbon can be regenerated by organic solvent extraction, such as methanol, ethanol, benzene, acetone, and ether.

5 Adsorption technology

1、What are the assumed conditions of Langmuir model?

6 Oxidation and disinfection technology

6 Oxidation and disinfection technology

1、Usually, ozone and chlorine dioxide are much more effective than chlorine, while chloramine is a weaker disinfectant compared with chlorine.

2、80℃ water spray is usually employed to promote the evaporation of chlorine.

3、Security protections for chlorine leakage include positive-pressure chlorine absorption equipment and negative-pressure chlorine absorption equipment. Lime or reductants can also be used to adsorb chlorine.

4、Ozone pre-oxidation can enhance coagulation through destroying the organic coating on the surface of inorganic matters.

5、The chemicals and materials used in water treatment can be the precursors of disinfection by-products.

6 Oxidation and disinfection technology

1、What measures can be implemented to reduce DBPs in drinking water?

7 Membrane technology

7 Membrane technology

1、Microfiltration (MF), ultrafiltration (UF) and reverse osmosis (RO) are all separation processes that utilize pressure difference as the driving force to make solvent (water) pass through the membrane. In general, what is the order of the molecular sizes retained by MF, UF and RO? ( )
    A、UF>MF>RO
    B、MF>UF>RO
    C、MF>RO>UF
    D、MF>RO>UF

2、Which of the following is not a feature of membrane separation technology? ( )
    A、Easy to operate
    B、Low energy consumption
    C、High efficiency
    D、Long lifespan

3、Which of the following is not an effective measure to reduce the resistance of concentration polarization? ( )
    A、To increase the flow rate and mass transfer coefficient
    B、To reduce the temperature of feed water
    C、To install a turbulence promoter
    D、To clean the membrane regularly

4、The filtration rate is constant under constant-pressure filtration mode.

5、In general filtration operations, the cake layer is actually the main filter media instead of the membrane itself.

7 Membrane technology

1、How to control membrane fouling during ultrafiltration process?

Final examination

Final examination

1、Which of the following statements is false about the characteristics of water: ( )
    A、Water has a very high boiling point and high heat of vaporization.
    B、The maximum density of liquid water is near 0 ℃
    C、The volume of water increases as it becomes ice.
    D、The dew on leaves appears spherical mainly because of the high surface tension of water.

2、In the following picture indicating the natural cycle of water, “a, b, c, d” respectively represent: ( )
    A、Atmosphere, surface runoff, ocean, underground runoff.
    B、surface runoff, ocean, Atmosphere, underground runoff.
    C、underground runoff, Atmosphere, surface runoff, ocean.
    D、Atmosphere, surface runoff, underground runoff, ocean.

3、Which of the following statements is false: ( )
    A、Suspended solids are unstable and can be easily removed from the water.
    B、The colloidal particles are usually charged by adsorbing ions.
    C、The sizes of dissolved matters are less than 1 nm.
    D、The pollution of natural water only comes from the natural environment.

4、Which of the following statements is false: ( )
    A、Colloids are all inorganic matters.
    B、Ions existed naturally in water make natural water obtaining different salinity, hardness, pH and electrical conductivity, and thus showing different physicochemical properties.
    C、Humic substances, polysaccharides, and proteins are commonly-found organic pollutants in natural water.
    D、Microorganisms would cause odor in water, increase water color and turbidity, and cause various diseases.

5、Which of the following item is not the usual feature of river water: ( )
    A、Low salinity
    B、Low hardness
    C、High turbidity
    D、Stable water quality

6、The salt content in seawater is mainly: ( )
    A、MgCl2
    B、CaSO4
    C、NaCl
    D、NaBr

7、Which of the following statements is false about the common contaminants in water: ( )
    A、Perfluorocarboxylic acid could be degraded as inorganic substances by microorganisms.
    B、Although some contaminants are non-toxic, they could affect physical properties such as transparency and fluidity of water and cause negative effects.
    C、Nitrogen and phosphorus are the main substances that cause eutrophication and the outbreak of algae in lakes, reservoirs, bays, and other water.
    D、Despite low concentrations, heavy metal ions show toxicity and can accumulate in human body, causing chronic hazards.

8、Which of the following statements is false about the water quality indicators: ( )
    A、The drinking water indicators can be divided into four categories: microbiological indicators, sensory index and chemical index, toxicological index, radioactivity index.
    B、Drinking water should not contain pathogenic microorganisms or organisms.
    C、Drinking water should be transparent, not turbid, and without smell or unpleasant color.
    D、Chemical indicators are unrelated to the sensory properties of water.

9、The water flow is stirred violently at mixing stage, so that the chemicals can be quickly and evenly dispersed into water. During the rapid hydrolysis, particle destabilization accelerates. G value at this stage should be as ( ) as possible, and the time of this stage is usually ( )
    A、high;short
    B、high;long
    C、low;short
    D、low;long

10、Poly aluminum is prepared by adding alkali into the aluminum salts, and then species with ( ) are preformed, which have great ability to compress double layer.
    A、high charge and low degree of polymerization
    B、low charge and low degree of polymerization
    C、low charge and high degree of polymerization
    D、All above

11、The settling efficiency of particle in ideal sedimentation tank is related to ( )
    A、Surface loading
    B、Sedimentation time
    C、Depth of tank
    D、Horizontal flow velocity

12、The included angle between inclined tube/plate and horizontal plane is usually ( )
    A、30°
    B、45°
    C、60°
    D、75°

13、How many valves should be switched on in conventional rapid filter during the filtration period and backwashing period, respectively. ( )
    A、1;3
    B、2;2
    C、3;2
    D、2;3

14、Which of the following statement is false about adsorption model:( )
    A、Friedrich adsorption isotherm is an empirical formula.
    B、Langmuir isotherm assumes that the adsorption process is monolayer adsorption.
    C、Langmuir isotherm considers the interaction between adsorbed molecules.
    D、Langmuir isotherm assumes that all surface sites have equal activity.

15、Which of the following statement is false about the preparation of activated carbon:( )
    A、The process of preparing activated carbon mainly contains two steps: carbonization and activation.
    B、The non-carbon components are removed and graphite structures are formed through carbonization.
    C、The aims of activation are enlarging the specific area of carbon material and generating functional groups which act as adsorption sites.
    D、During the activation procedure, the carbonized material is heated in the presence of oxidants.

16、The adsorption kinetics of powdered activated carbon (PAC) is (), and it is () to regenerate. The adsorption kinetics of granular activated carbon (GAC) is (), and it is () to regenerate.( )
    A、slow; easier; slow; more difficult
    B、fast; more difficult; fast; easier
    C、slow; easier; fast; more difficult
    D、fast; more difficult; slow; easier

17、Which of the following statement is false about the characteristics and application of activated carbon:( )
    A、Activated carbon has well-developed pore structure
    B、Generally, the powered activated carbon is used for adsorption columns and the granular activated carbon is used for batch reactor.
    C、Acidic groups on activated carbon such as carboxyl groups can easily adsorb polar compounds, but restrain the adsorption of nonpolar ones.
    D、Iodine value can represent the adsorption capacity for small molecules, while molasses value can represent the adsorption capacity for large molecules.

18、Which of the following statement is false about the selection of activated carbon in drinking water treatment:( )
    A、Through adsorption kinetic experiment, we can determine the time required to reach equilibrium and then determine the position to dose the activated carbon.
    B、In drinking water treatment, what we need is the activated carbon with high adsorption capacity for the adsorbate at high equilibrium concentration.
    C、In drinking water treatment, the slope of the adsorption isotherm of activated carbon should not be too large.
    D、Powdered activated carbon is often used to prevent accidental pollution.

19、Which of the following statement is false about the regeneration of activated carbon:( )
    A、Chemical regeneration——decrease pH, organic solvent extraction and oxidation
    B、Biological regeneration——in-situ regeneration, low cost but slow.
    C、Physical regeneration——microwave and ultrasonic wave
    D、The activated carbon in drinking water treatment can be reused in wastewater treatment.

20、The common adsorbents used in drinking water treatment except activated carbon include:( ) ①kaolin; ②bentonite; ③activated alumina; ④zeolite;⑤resin
    A、①②⑤
    B、②③④
    C、①③④⑤
    D、①②③④⑤

21、Which of the following statement is false about zeolite, diatomaceous earth and fly ash:( )
    A、zeolite is a nonpolar adsorbent like activated carbon.
    B、Diatomaceous earth is mainly used for industrial wastewater treatment.
    C、Fly ash cannot be applied to drinking water treatment because it usually contains heavy metal ions.
    D、Zeolite is a great cation exchanger and can be used to soften water.

22、Which of the following statement is false about chlorination:( )
    A、When chlorine dissolves in water, it generates hypochlorous acid and hydrochloric acid.
    B、The disinfection ability of hypochlorite ion is usually relatively limited because it is difficult to dissolve in water.
    C、Hypochlorous acid plays major roles in chlorine disinfection.
    D、The lower the pH and temperature are, the more hypochlorous acid molecules are formed, and the stronger the disinfection effect is.

23、Which of the following statement is false about breakpoint chlorination curve:( )
    A、When the chlorine dosage is low, there is no residual chlorine due to the consumption by organic or inorganic compounds and microorganism in water.
    B、In the second zone, chlorine reacts with ammonia, the residual chlorine is mainly chloramine. When the amount of combined residual chlorine reaches a maximum, the corresponding H point on the curve is called the peak point.
    C、In the third zone, with the further increase of chlorine dosage, the chloramine decomposes.
    D、In the fourth zone, CA represents combined chlorine, while CB means free residual chlorine.

24、Which of the following statement is false about the toxicity of disinfection by-products:( )
    A、N-DBP>C-DBP
    B、Halogenated DBPs>Non-halogenated DBPs (except nitrosamines)
    C、The toxicity of halogenated disinfection by-products increases with the decrease of atomic number
    D、Emerging DBPs>Conventional DBPs.

25、1、The pore size range of ultrafiltration membrane is ( ).
    A、0.1-10 mm
    B、10-100 nm
    C、0.5-5 nm
    D、0.1 nm

26、In recent years, ( ) has played an important role in seawater desalination
    A、Ultrafiltration membrane
    B、Nanofiltration membrane
    C、Reverse osmosis membrane
    D、Microfiltration membrane

27、The functions of water cycles include: ( )
    A、Conservation of groundwater resources.
    B、Water purification.
    C、Maintain the terrestrial water environment.
    D、Maintain a well ecosystem.
    E、Support the sustainable development of human society by water resources.

28、The pollutants during water social circulation usually contain: ( )
    A、Gas pollutants such as nitrogen oxides.
    B、Heavy metal ions.
    C、Organic matters and nutrients.
    D、Radioactive substances and pathogenic microorganisms
    E、Humus

29、The reasons for the stability of colloids include ( )
    A、Brownian motion of water molecules
    B、The electrostatic repulsion between colloidal particles
    C、Hydration shell effect
    D、The hydrogen bond between colloids

30、The mechanisms of coagulation include ( )
    A、Double layer compression
    B、Adsorption and charge neutralization
    C、Adsorption and interparticle bridging
    D、Enmeshment by a precipitate (sweep-floc coagulation)

31、Coagulation operational indexes include ( )
    A、G value
    B、GT value
    C、GTCV value
    D、GCV value

32、Velocity gradient can be generated by ( )
    A、Mechanical mixing
    B、Consumption of the potential energy of water (i.e. water head)
    C、Decrease of water temperature
    D、Brownian motion of water molecules

33、he advantages of poly aluminum chloride are ( )
    A、large and heavy particles; high settling velocity
    B、strong adaptability to various water bodies and a wide optimal pH range
    C、less alkalinity consumption
    D、low dosage (about 1/2-1/3 of the aluminum sulfate dosage)

34、Which one or ones are coagulant aids below ( )
    A、polyacrylamide (PAM)
    B、activated silica gel
    C、lime glue
    D、poly aluminum chloride (PAC)

35、The efficiency of coagulation process is not good during the condition of low temperature, because ( )
    A、coagulants will not hydrolyze completely
    B、the hydration of colloidal particles is enhanced, which hinders the coagulation process
    C、the viscosity of water is high, so the Brownian motion is weak, making it difficult for colloids to aggregate
    D、The rate of coagulants hydration is too high

36、Which one or ones are the hydraulic flocculation equipment ( )
    A、Baffle plate flocculation tank
    B、Grid flocculation tank
    C、Folded plate flocculation tank
    D、Mechanical flocculation tank

37、The conditions of the ideal sedimentation zone include ( )
    A、The horizontal flow rate over the whole tank is constant
    B、Particles are in the state of free settling
    C、When the particles settle to the bottom of tank, the particles are considered to be removed
    D、The value of surface loading is unequal to critical settling velocity

38、The methods to reduce the effect of density current of turbid water include ( )
    A、increasing horizontal flow velocity
    B、increasing vertical grids in sedimentation zone
    C、decreasing depth of tank
    D、installing perforated wall on the influent zone

39、According to the way of influent entering into the sedimentation tank, inclined tube/ plate sedimentation tank can be classified into ( )
    A、horizontal (side) flow
    B、upward flow
    C、downward (parallel) flow
    D、oblique flow

40、The inclined plate sedimentation tank consists of ( ) along the height
    A、super elevation
    B、clear water zone
    C、inclined tube/ plate zone
    D、water distribution zone
    E、sludge zone

41、Which one(s) belong(s) to sludge reflux clarifier ( )
    A、vacuum pulse clarification tank
    B、bell-jar pulse clarification tank
    C、mechanically accelerated clarifier
    D、hydraulic circulating clarifier

42、The equipment in mechanically accelerated clarifier does not include ( )
    A、water jet
    B、vacuum pump
    C、vane
    D、sludge discharge pipe

43、The requirements of air flotation process include ( )
    A、The size of the bubble usually ranges from 10 to 100 micrometers
    B、The density of the pollutant should be lower than (or close to) water
    C、There should be a strong adhesion between the bubble and pollutant
    D、The pollutant should be hydrophobic

44、The application of air flotation in water treatment mainly includes ( )
    A、algae laden water
    B、oil wastewater
    C、sludge thickening
    D、pretreatment of high-turbidity water

45、The following statement about slow filters, which ones are correct ( )
    A、Biological process exists in slow sand filtration, and the quality of the effluent is high
    B、Slow filter is the first filtration equipment for water treatment process, which can effectively remove the particles, smell and taste.
    C、The surface load of the slow sand filtration is high and the footprint is small
    D、Bank river filtration is a green process, and is cost-effective for water purification

46、Requirements for filter media include ( )
    A、Mechanical strength
    B、Chemical stability
    C、Gradation and porosity
    D、Obtaining of the filter material should be as convenient as possible

47、The removal mechanisms of suspended particles in the filter include ( )
    A、Mechanism of screening
    B、Mechanisms of adsorption and contact flocculation
    C、Mechanism of migration
    D、Mechanism of stripping

48、The slow sand filtration usually has two working stages, including ( )
    A、mature period of the filter layer
    B、the aging period
    C、the filtration period
    D、the backwash period

49、Negative water head will not occur in the following rapid filter listed below ( )
    A、Conventional rapid filter
    B、Siphon filter
    C、Valveless filter
    D、V-shaped filter

50、The consequences of uneven water distribution include ( )
    A、"mud ball" or "mud cake" will form, which can cause a short-circuiting phenomenon during filtration
    B、the filter media may break during filtration and backwash periods
    C、backwash pipes may be destroyed
    D、The particles of the local support layer will move and mix with the filter media, and the filter media will run off under this situation if a large amount of uneven backwash water come through

51、Valveless filter has many advantages include ( )
    A、it does not need large valves
    B、backwash is completely automatic
    C、negative water head will not appear in the filtration process
    D、the structure of the filter is simple, loading and unloading of the filter media are very convenient

52、There are two functions for the water purification in slow sand filtration, including ( )
    A、mechanical interception
    B、biological adsorption and bio-degradation
    C、chemical oxidation
    D、the inactivation of bacteria near the surface of filter media

53、The main characteristics of V-shaped filter include ( )
    A、It can use a thick filter layer with coarse filter media to extend the filtration cycle
    B、Gas and liquid backwash are applied, combined with the transverse surface cleaning, which greatly reduces the amount of backwash water
    C、High backwash efficiency with small amount of clean water can be achieved
    D、It is easy to realize automatic filtration and backwash

54、Which of the following statements are true about the application of activated carbon:( )
    A、Activated carbon can remove odor compounds effectively.
    B、Activated carbon can remove the macromolecule natural organic matters in raw water effectively.
    C、Through adsorption, activated carbon can avoid generating disinfection by-products to a large extent.
    D、Activated carbon is an efficient way to remove synthetic organic compounds (SOCs).

55、Which of the following statements are true about the method of activated carbon application:( )
    A、Granular activated carbon can be used individually after filtration.
    B、Granular activated carbon can be combined with ozone or permanganate.
    C、Membrane filtration technologies such as ultrafiltration can be used after ozone-activated carbon process to ensure the biosecurity of drinking water.
    D、Activated carbon can be used to alleviate membrane fouling

56、Which of the following technologies can be used in drinking water disinfection:( )
    A、Hydrogen peroxide
    B、Chlorine
    C、Fluorine
    D、Permanganate
    E、Ozone

57、The functions of pre-oxidation include:( )
    A、Alleviate organism.
    B、Remove odor compounds, plankton, color, etc.
    C、Destroy the precursors of disinfection by-products.
    D、Enhance coagulation.

58、Which of the following statements are true about disinfection:( )
    A、Disinfection efficiency is determined by disinfectant concentration C, contact time T, water quality, and the type of disinfectant.
    B、CT is considered to have a close relationship with the disinfection efficiency, and the minimum CT value is required to ensure the safety of drinking water.
    C、The higher the CT value, the easier for the specific microorganism to be inactivated.
    D、The practical retention time of disinfectants is sometimes lower than the theoretical value because of short flow.

59、Which of the following statements are true about ozonation:( )
    A、Ozone can effectively convert soluble substances into insoluble oxides and precipitate out of the water.
    B、Ozone can dissolve in water reacts directly with the organic pollutants, and the reaction is kinetically fast and has no selectivity.
    C、Ozone can decompose into hydroxyl radicals which indirectly interact with organic pollutants in water.
    D、Ozone can also have negative effect on coagulation in some situations.

60、The advantages of ozonation include:( )
    A、Remove pollutants that cannot be easily removed through traditional methods.
    B、Coagulation aid.
    C、Control disinfection by-products (DBPs).
    D、Strong oxidation capacity and decolorization ability.

61、The limitations of ozonation include:( )
    A、High operating cost.
    B、Generate bromate and bromo trihalomethane.
    C、If ozone is excessively dosed, it will have negative effect on coagulation.
    D、Cannot oxide or remove some persistent organic pollutants when used alone.

62、Which of the following technologies can avoid generating disinfection by-products:( )
    A、Ozone pre-oxidation
    B、Air floatation
    C、Membrane filtration
    D、Adsorption

63、According to the source of membrane, it can be classified into ( ).
    A、Hollow fiber membrane
    B、Porous membrane
    C、Synthetic membrane
    D、Natural membrane

64、The two operation models of the microfiltration process are ( ).
    A、Dead-End Filtration
    B、Constant pressure filtration
    C、Cross-Flow Filtration
    D、Constant rate filtration

65、The two necessary conditions for reverse osmosis process are ( ).
    A、Membrane with selective solvent permeation
    B、The static pressure difference between the two sides of the membrane must be greater than the osmotic pressure difference
    C、Applied DC electric field
    D、Keep the filtration rate constant

66、1、The main reasons for the decrease of membrane flux are ( ).
    A、Membrane aging
    B、Concentration polarization
    C、Membrane injury
    D、Membrane fouling

67、The purification mechanism of ultrafiltration membrane includes ( ).
    A、Physical rejection
    B、Chemical reaction
    C、Biological degradation
    D、Adsorption bridging

68、Membrane foulants include ( ).
    A、Particulates
    B、Organics
    C、Inorganics
    D、Micro-biological organisms

69、The mechanisms of membrane fouling include ( ).
    A、Adsorption
    B、Pore blocking
    C、Cake layer formation
    D、Gel formation

70、Generally, the cleaning of membrane can be divided into two categories: ( ).
    A、Ultrasonic cleaning
    B、Physical cleaning
    C、Chemical cleaning
    D、Pickling

71、H2O molecular has asymmetric structure and dipolar character.

72、As a result of hydrogen bond, larger clusters of water are formed in liquid water, and the cluster structure is stable and invariable.

73、Nitrobenzene and alcohol can interact with water molecular through hydrogen bond, which increases their solubility.

74、Ions can dissolve in liquid water because of ion-dipole bonds between ions and water.

75、Dilution mostly provides complete recovery of the original water quality.

76、The colloidal particles are charged by adsorbing ions, so they are often unstable in water.

77、Lakes are usually more suitable for plankton or algae growth and reproduction than rivers.

78、Groundwater has relatively lower salt content and hardness than those of surface water because it is less affected by surrounding environment.

79、The main process of water self-purification is to oxidize and decompose the organic matter through chemical and biological action, and the self-purification capacity of water is usually unlimited.

80、Only the water which belongs to Class I~Class III can be used as drinking water source.

81、Coagulation process, which is the combination of agglomeration and flocculation, is mainly used to remove colloids.

82、According to DLVO theory, particle repulsion due to electrostatic interaction is counteracted by attraction due to van der Waals interaction.

83、Perikinetic flocculation is caused by hydraulic fluid flow, while orthokinetic flocculation is caused by Brownian motion.

84、The performance of coagulation process will be better when low-turbidity water is treated.

85、PAM should by pre-hydrolyzed before it can be used.

86、Water pump-mixing exhibits high mixing efficiency and low energy consumption, which is suitable for the situation of long distance between intake pumping station and water treatment plant.

87、Streaming current detector (SCD) monitors the performance of coagulation process by measuring the zeta potential directly.

88、The coating of organic matters on the surface of inorganic colloids will lead to a high dosage of coagulants. Pre-oxidation would be a good choice to destroy the organic coating, when raw water with high organics is treated.

89、Algae-laden water can be easily controlled by coagulation process.

90、To avoid the flocs being destroyed, the number of grids should be decreased as well as the size of grids should be increased with increasing the flocculation time during the coagulation process.

91、The colloidal nucleus is thermodynamically stable, resulting in the high stability of colloids in water.

92、The collision rate of perikinetic flocculation is inversely proportional to the particle size.

93、Ferrous sulfate is very cheap and can be applied directly to coagulation process.

94、The objectives of enhanced coagulation technology are to thoroughly remove the colloids during the coagulation stage, as well as to maximize organic matter removal and to reduce DBP precursors.

95、The head loss of tubular-mixing is low.

96、The sedimentation efficiency of aggregated particles is affected by the depth of the tank.

97、In ideal sedimentation tank, only the particles with settling velocity higher than critical settling velocity can be removed.

98、There is an intermediate transition stage between flocculation tank and sedimentation tank.

99、Froude number reflects the ratio of inertia force and viscous force. If Froude number is large enough, the water flow will have strong resistance to the variances of temperature, density, wind and waves.

100、The Reynolds number of inclined plate sedimentation tank is smaller than horizontal flow sedimentation tank.

101、In vertically rotational flow of sludge separation of inclined plate sedimentation tank, sludge separation zone is set at the boundary of the sedimentation zone, where sludge is separated by rotational side-flow. The settling of sludge in separation zone is not affected by the water flow, so the settled sludge will not be disturbed.

102、The adsorption of large flocs to small flocs in clarifier will increase the particle size of the floc, leading to the increase of sedimentation efficiency.

103、Hydraulic circulating clarifier is more adaptable to the variation of the raw water than mechanically accelerated clarifier.

104、Hydrophobic particles can attach to the air bubble more tightly. Therefore, air flotation is suitable for the removal of hydrophobic particles.

105、In air flotation process, the smaller bubble can always result in a better performance.

106、The value of critical settling velocity of particles is equal to the value of surface loading of an ideal sedimentation tank.

107、The actual residence time is shorter than theoretical value because of the density current in the actual sedimentation tank.

108、When the included angle between inclined tube/plate and horizontal plane increases, the area of the horizontal projection plane and the settling efficiency will increase.

109、In mechanically accelerated clarifier, the flow of recycled sludge is four to five times that of the influent.

110、Air floatation process can be applied to desalination.

111、Slow sand filtration can be applied to large-scale water supply system because of the high-quality effluent and high surface load.

112、The principle of water purification by riverbank filtration is the same to slow sand filtration.

113、The quartz sand filter material has great chemical stability, which can be stable under various background conditions of water.

114、The filter material with larger K80 has higher uniformity.

115、The porosity of the filter can reflect the capacity of the impurity removal.

116、The use of coarse filter media in V-shaped filter can extend the filtration cycle, and make the filter layer thinner.

117、When the size and density of filter media, as well as the water temperature are fixed, expansion rate will increase with backwash intensity.

118、The applied transverse surface cleaning in V-shaped filter may increase the amount of backwashing water.

119、Siphon filter is generally composed of six to eight grids, and the effluents of all grids are connected with each other.

120、Supporting layer can prevent the loss of filter media from the collecting system during water filtration.

121、Slow sand filter needs backwash after running for a long time.

122、The filtration rate of rapid filtration process is much higher than slow filtration process, and needs frequent backwash.

123、Screening effect is the only mechanism during the entire filtration process.

124、Usually, uniformity coefficient K80 is lower than 2.

125、To prevent the loss of filter media from the collecting system during backwashing, a supporting layer is needed.

126、Adsorbent is the substance onto which the adsorbate is accumulated, and it can be solid, liquid or gas.

127、Adsorption can be sorted into physical adsorption and chemical adsorption, and both of them are nonselective.

128、Activated carbon can be sorted into GAC and PAC according to their particle sizes.

129、The activated carbon prefers to adsorb hydrophobic molecules.

130、The calcium and magnesium ions can increase the amount of organics adsorption through coordinating with carboxyl groups in organic compounds and decreasing their polarity.

131、For activated carbon, the process of adsorption can be divided into four steps: solution transport, film diffusion, pore diffusion, and adsorption. In water treatment, film diffusion transport or pore transport is usually the rate limiting step.

132、The adsorption kinetics of PAC is much faster than those of GAC, however, PAC may penetrate the filter.

133、If pH increases, it will be easier for activated carbon to adsorb organic acid.

134、Wet oxidation regeneration needs high temperature and pressure.

135、Only stable and nontoxic materials can be used as adsorbents in drinking water treatment.

136、Coagulation and filtration cannot sufficiently remove the pathogenic microorganisms in raw water.

137、Besides drinking water disinfection, chlorine dioxide can also be applied for sewage treatment.

138、Intermediate oxidation is usually located after precipitation or filtration, and ozone, ultraviolet, chlorine dioxide can be used.

139、Free chlorine includes Cl2, HOCl, and OCI-, and the effect of free chlorine disinfection is much higher than that of compound chlorine, but less sustainable.

140、According to the adding position of chlorine, chlorination of microorganisms can be sorted into pre-chlorination, intermediate chlorination and post chlorination.

141、The dosage of chlorine is determined according to the requirement that 0.05 mg/L residual chlorine should be remained at the end of the water plant (GB5749-2006).

142、Hydroxyl radical oxidation is selective towards certain pollutants.

143、Ozonation will not form any harmful by-products.

144、Organics in surface water are the primary reason of the formation of disinfection by-products (DBPs).

145、All DBPs can be removed by boiling water.

146、Traditional membrane separation technologies include microfiltration, ultrafiltration, nanofiltration, reverse osmosis, and electrodialysis.

147、At present, reverse osmosis devices mainly include four types: plate and frame, tubular, spiral-wound and hollow fiber modules.

148、Organic membranes include cellulose membrane, polysulfone membrane, polyamide membrane and ceramic membrane.

149、UF, like RO, NF and MF, belongs to pressure driven membrane separation technology.

150、Taking hollow fiber membrane module as an example, according to the way of water inflow, it can be classified as outside-in type: raw water enters from the outside of membrane, and purified water flows out from the inside of membrane. On the contrary, it is inside-out type. The working pressure of the inside-out type is higher than that of the outside-in type.

151、Chemical cleaning is usually based on the degree of membrane fouling, using oxidant (sodium hypochlorite, etc.), acid (hydrochloric acid, sulfuric acid, nitric acid, etc.), alkali (sodium hydroxide, etc.), complexing agent, surfactant, enzyme, detergent and other chemical cleaning agents to soak and clean the membrane.

152、Large membrane pore size usually leads to a high permeate flux. Narrow pore size distribution usually results in a low selectivity.

153、In the reverse osmosis process, water pass through the membrane from the low concentration side to the high concentration side.

154、According to the alleviation of membrane fouling by hydraulically cleaning, membrane fouling is divided into two categories: reversible fouling and irreversible fouling. Irreversible membrane fouling can be eliminated by physical cleaning.

155、The control strategies of membrane fouling include pretreatment of the feed streams, chemical modification of membrane and optimization of the operational conditions.

156、Reverse osmosis process generally includes two parts: pretreatment and membrane separation.

157、Nanofiltration can be used to soften and purify water, as well as the separation and purification the raw water with substances such as dyes, antibiotics, peptides, and polysaccharides.

158、The cation membrane of ion exchange membrane contains acidic active groups, which dissociate cations to make the membrane negative and selective permeate anions.

159、The surface layer of nanofiltration membrane is much denser than that of RO membrane, but it is much looser than that of UF membrane.

160、When high-strength retention of NaCl with a higher concentration is required, a reverse osmosis membrane is the best choice. When low concentration, divalent ions, and solutes with a molecular weight of 500 to several thousand are required for rejection, nanofiltration membranes are the best choice.