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Environmental Engineering 3 > Water Treatment > Flashcards

Water Treatment Flashcards

1
Q

When are coagulation and flocculation typically used?

A

For industrial wastewater where biological treatment is difficult to use

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2
Q

How can lead pipes be kept from contaminating drinking water?

A

Adding a coating agent to the water to prevent the lead from dissolving

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3
Q

What is a potential use of sludge removed during water treatment?

A

It can be dried into bricks, used as fertiliser or fermented for energy

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4
Q

What is the limit for defining grit?

A

Particles 212 micro meters or greater in diameter

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5
Q

How are fats removed from wastewater?

A

Foaming with soap by air injection

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6
Q

How is groundwater commonly aerated? Why?

A

Cascade aeration is used to remove dissolved gases such as sulphur

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7
Q

What are the metallic salts commonly used for coagulation?

A

Aluminium sulphate
Ferric sulphate
Ferric chloride

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8
Q

An additional compound must often be added when aluminium sulphate is used as a coagulant. What is this and why?

A

Lime, used to counteract the decrease in alkalinity

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9
Q

What is hydraulic retention time?

A

Volume / flow rate

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10
Q

What is the definition of disinfection?

A

The partial destruction of disease causing organisms

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11
Q

How does sterilisation differ to disinfection?

A

Disinfection only targets pathogens, sterilisation targets all microbes

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12
Q

What is the primary indicator for faecal contamination in water?

A

E. Coli

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13
Q

When does disinfection come on the treatment process?

A

Typically last, at the very least after flocculation and filtration

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14
Q

What is log removal?

A

The logarithm of the number s of pathogens at time t / number of pathogens at time zero

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15
Q

According to the Chick and Watson model, what is the relationship between log removal and concentration time?

A

Log10(Nt/N0) = -k Cn t log10e

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16
Q

What is disinfection lag?

A

When disinfectants react with impurities such as ammonia before killing the pathogens

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17
Q

How does flow cytometry work?

A

A 488nm laser is fired at the sample and scatter is used to detect cells based on fluorescent staining

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18
Q

What are trihalomethanes and why must they be limited?

A

They are byproducts of disinfection that are carcinogenic

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19
Q

In the equivalent curve for HOCl, H+ and OCl-, when is disinfection most effective?

A

When HOCl dominates

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20
Q

If you do not know the flow regime, how do you discover it?

A

Assume laminar flow then check the Reynolds number. If Re > 1, repeat until it matches

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21
Q

Compare rectangular and circular sedimentation tanks

A

Rectangular tanks are cheaper and take up less space. Circular tanks are easier to maintain. Rectangular tanks are cleaned by conveyor, circular tanks by funnelling

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22
Q

What is assumed when designing a settlement tank?

A

Uniform horizontal velocity
Uniform concentration of same-size particles
Particles removed at base
Settlement of particles occurs independently

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23
Q

What is the limit for turbidity before disinfection?

A

< 0.3

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24
Q

Which type of gravity filter uses less space for the same volume of water?

A

Rapid gravity filtration

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25
How can water treatment plants be easily upgraded?
Introducing membrane filters
26
Why is reverse osmosis often used in desalination?
It is able to remove ions from the water such as metal salts
27
Why should water flow be directed tangential to a membrane?
Perpendicular flow causes pores to clog very quickly
28
What is the mass balance equation?
Flux (concentration x flow rate) = concentrate (concentration x flow rate) + permeate (concentration x flow rate)
29
What can nanofiltration remove? What can in not be used for?
Pathogens and hardness | Desalination
30
When a filter has been fouled too much for backwashing to improve permeability, what must be done?
A deep clean with acids
31
Once a filter had been fouled, can it ever return to 100% efficiency?
No
32
What do membrane bioreactors remove the need for?
Clarifiers or tertiary treatments
33
Define adsorption
The loose adhesion of particles to the surface of another solid or liquid phase
34
Why is activated carbon very effective at adsorption?
It has a very large surface area
35
How can a polar compound be defined?
Polar compounds dissolve in water
36
What are the positives of powdered activated carbon?
Low initial cost | Flexible dosage
37
What are the downsides of powdered activated carbon?
``` High continuous cost Unable to be regenerated Large sludge output Can cause damage to filters Flammable ```
38
What is biological activated carbon?
Biodegradation by bacteria in the activated carbon pores following adsorption
39
Define ion exchange
Ions of a given species are displaced from an insoluble medium by ions of a different species in solution
40
What is a Chelant?
A type of ion bonding dealing specifically with heavy metals
41
What is nitrate dumping?
When an exhausted resin starts to replace nitrate with sulphate and nitrate ions are released in greater quantity than unfiltered water
42
Why can electrolyte coagulation not be used in drinking water?
It produces high levels of salt
43
When is pH correction employed?
Before disinfection
44
Why is ion exchange often impractical to use in large scale water treatment plants
It is very expensive on a large scale
45
What is the difference between primary and secondary disinfection?
Primary is disinfection applied at the source to inactivate pathogens Secondary is residual to protect water as it is transported
46
In the equation Pi = i theta C R T, what does each letter stand for?
``` Pi - osmotic pressure i - ions produced in dissociation Theta - osmotic coefficient (usually 1) C - concentration R - gas constant T - temperature in Kelvin ```
47
In the equation Fw = Kw (Pa - Pi), where pi is osmotic pressure, what do the other letters represent?
Fw - flux Kw - mass transfer coefficient Pa - pressure in pascals
48
What is the translation ratio of bar to pascals
1 bar = 1e5 pascals
49
How can you estimate membrane area?
Permeate flow rate divided by trans-membrane flux
50
What is the recovery rate equation?
Qp/Qf
51
What is the rejection rate equation?
(Cf-Cp)/Cf
52
What is the concentration factor equation?
Cc/Cf
53
What should water discharged into a sensitive area take care to remove?
Nutrients such as nitrogen and phosphorus, COD and BOD
54
How do nano and RO filtration differ from other filters?
Particles are adsorbed into the membrane rather than sieved
55
How does aluminium sulphate coagulate suspended solids?
Charge neutralisation
56
How does conductivity removal compare to turbidity removal?
Usually lower as coagulation and sedimentation are better at removing suspended solids than dissolved solids
57
What is the efficiency of of removing particles of settling velocity Vs compared to a system with overflow rate OR
Vs/OR
58
How do calculate the radius of a cylindrical tank given OR and flow rate?
R = sqrt(Q/ORpi)
59
What is the camp number?
Mean velocity gradient x hydraulic retention time
60
What is hydraulic retention time?
Tank volume divided by flow rate
61
Knowing velocity gradient, what is the power required to drive the fluid?
P = velocity gradient squared x viscosity x volume
62
What is the equation for empty bed contact time?
Resin volume/flow rate
63
How do you find dosage needed to reach a specific alkalinity?
Use TIC to find alkalinity before Use additional compound equation to find drop in alkalinity Subtract drip from initial for current alk Find target alkalinity in equivalents Subtract current from goal alk Convert these equivalents into ppm of dosing substance
64
What is the efficiency of removal of a particle type with settling velocity V in a tank with overflow rate OR?
V/OR x100%
65
What is the “breakthrough volume”?
Breakthrough time (aka time to regeneration) x flow rate

Environmental Engineering 3 (2 decks)

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