Lecture 6 P3

Question 1

What are the objectives of municipal treatment?

Answer 1

to provide a potable supply of water, which is chemically and microbiologically safe for human consumption and to provide water that aesthetically acceptable (free from apparent turbidity, color, odor, and objectionable taste

Question 2

What are the general considerations for selecting technology?

Answer 2

Water source (deep & shallow wells, rivers, and natural lakes)
and quality (depends on agricultural practices in the watershed, location of the municipal and industrial outfall sewers, river developments such as dams, and season of the year and climate conditions
as well as the drinking water standards

Question 3

What are the two sources of water pollution? Explain them

Answer 3

Point source- (from a single identifiable source, ex from a factory, municipal sewer system, is easy to find, regulate, treat, and monitor)
Non point source (from a vast area (ex: agricultural runoff or industrial storm water, is hard to measure control, treat, and monitor

Question 4

What are the seven characteristics of ground water as it pertains to water quality?

Answer 4

• higher levels of dissolved solids
• may contain an abundance of the minerals that can
  contribute to hardness problems
• low levels of dissolved oxygen
• constant cool temperature
• less vulnerable to contamination
• higher quality
• requires less intensive treatment than other types
  of water

Question 5

What are the seven characteristics of surface water as it pertains to water quality?

Answer 5

accumulates mainly as a result of direct runoff from
rain or snow
* it does not pick up the elevated levels of dissolved
minerals that contribute to water hardness
* for the most part, surface water is referred to as
“naturally soft”, although it is not mineral-free
* high turbidity and suspended solids
* more vulnerable to contamination
* rapid temperature fluctuations
* high levels of dissolved oxygen

Question 6

What are common stages of drinking water treatment? (4)

Answer 6

Coagulation, flocculation, sedimentation
Filtration
Taste and odor control
Disinfection

Question 7

What is coagulation?

Answer 7

a process consisting of the addition and mixing of a chemical
reagent to water to destabilize colloidal and fine solids suspended in water
(turbidity)

Question 8

What is flocculation?

Answer 8

involves slow stirring to promote agglomeration of the destabilized
particles formed during coagulation

Question 9

What is filtration?

Answer 9

some cities (including Calgary) filter water using fine sand,
gravel, and anthracite to remove non-settleable floc remaining after
chemical coagulation and sedimentation

Question 10

How do you perform taste and odor control?

Answer 10

Activated carbon filters (charcoal) is used to
remove organic contaminants (taste and odor)

Question 11

How do you perform disinfection?

Answer 11

Chlorination

Question 12

What are four common drinking water treatment systems?

Answer 12

Iron and manganese removal (involves aeration)
Softening
Arsenic and nitrate removal

Question 13

What is aeration?

Answer 13

It removes dissolved gases like H2S and volatile organic compounds

Question 14

What is softening?

Answer 14

phosphate or lime/soda ash is added to water to ppt Ca and Mg

Question 15

What happened in walkerton On 2000?

Answer 15

E coli entered the water system from manure that had been spread on a farm near their water wells, seven people died and more than 2300 became ill from drinking tap water

Question 16

What are the types of microorganisms that causes disease?

Answer 16

Bacteria- E coli and salmonella cause food poisoning
Viruses- Hep A virus cause Hep A
Protozoa- giardia lambia causes giardiasis

Question 17

What are the three disinfection techniques?

Answer 17

1. Membrane Technology
2. UV radiation
3. Chemical methods
4. a Ozonation
5. b Chlorination

Question 18

How does membrane technology work?

Answer 18

Water goes through microfiltrations (removes bacteria and suspended solids)
then ultrafiltration (removes viruses)
then nanofiltration (removes multivalent ions
then reverse osmosis (removes monovalent ions)

Question 19

How does UV radiation work?

Answer 19

The UV energy attacks DNA/RNA, destroying pathogens

Question 20

What are the advantages of UV radiation? (6)

Answer 20

UV disinfection is effective at inactivating most viruses, spores, and cysts
* No chemical is required
* There is no residual effect that can be harmful to humans or aquatic life
* UV disinfection is user-friendly for operators
* UV disinfection has a shorter contact time (approximately 20 to 30 seconds)
* UV disinfection equipment requires less space than other methods

Question 21

What are the disadvantages of UV radiation?

Answer 21

Low dosages may not effectively inactivate some viruses, spores, and cysts
* A preventive maintenance program is necessary to control the fouling of tubes
* Turbidity and total suspended solids (TSS) in the wastewater can render UV disinfection
ineffective
* UV disinfection is not as cost-effective as chlorination

Question 22

How does ozonation work?

Answer 22

ozone gas is generated onsite by discharge, it reacts with pollutants or generates radicals such as OH in the water, 10 min contact with concentrated O3 destroys bacteria and viruses

Question 23

What are the downsides of ozonation?

Answer 23

It’s energy intensive to generate O3, and ha sa shirt half-life so there’s no residual protection

Question 24

How does chlorination work?

Answer 24

CL in HOCL is in a +1 oxidation state which is readily reduced to CL-. HOCL diffuses through cell walls and oxidizes vital molecules.

Question 25

What is the advantage of chlorination over other methods?

Answer 25

there is chlorine residually left

Question 26

What is the disadvantage of chlorination?

Answer 26

There's formation of disinfection by-products such as: - haloacetic acids and haloacetonitriles -chlorinated phenols and halomethanes (ex: chloroform)

Question 27

How is chloroform produced through chlorination?

Answer 27

HOCL reacts with humic acids, and CCL3 group is displaced by OH in water to yield chloroform

Question 28

What disinfection system has the lowest capital cost?

Answer 28

chlorination

Question 29

What disinfection system has the lowest operating cost?

Answer 29

UV

Question 30

What disinfection system has the best ease of installation and maintenance?

Answer 30

UV

Question 31

What disinfection system has the least contact time required?

Answer 31

UV

Question 32

What are the objectives of wastewater treatment (4)?

Answer 32

To remove from wastewater: - Dissolved biodegradable organics (BOD) - Suspended solids - Pathogenic micro-organisms - N and P removal if eutrophication is a concern

Question 33

Draw schematic of municipal waste water treatment plant (Slide 30)

Answer 33

Slide 30

Question 34

What is the purpose of the pre-treatment?

Answer 34

to remove debris, grit, and oily scum - to avoid shock loadings - to condition the wastewater for subsequent treatment processes

Question 35

Why are coarse objects and grit removes during the pre-treatment?

Answer 35

because they: Damage equipment Reduce treatment efficieny Clog pipes and meters and interfere with the treatment process (such as digesters)

Question 36

What happens during the screening in the pre-treatment? Why and what is used?

Answer 36

Large objects are removed, downstream mechanical equipment is protected, and mechanical bar screens are usually used to do this

Question 37

What happens during the Pre-treatment Grit Removal?

Answer 37

Grit such as sand, broken glass, silt, and pebbles is removed in order to protect pump and avoid clogging pipes and channels

Question 38

What happens during the flotation step of pre-treatment?

Answer 38

Fats, oils, and greases are removed using air flotation

Question 39

What happens during the primary treatment of wastewater?

Answer 39

Solids are physically seperated from wastewater via sedmentation tanks

Question 40

Are soluble pollutants removed in primary treatment?

Answer 40

No

Question 41

How much BOD is removed by the primary treatment process?

Answer 41

30%

Question 42

What is the purpose of the secondary treatment? What is removed during it?

Answer 42

The purpose of the secondary treatment is to remove BOD, COD and additional removal of TSS It partially removes N, P, and heavy metal, some biological degradation of organic matter by oxidation and part of organic suspended solids - reduced pathogens

Question 43

How does biological treatment work?

Answer 43

In aerobic treatments, organic materials is degraded and theres a production of more biomass In anaerobic treatments the organic matter is degraded and the biomass is reducted

Question 44

What are the five phases of the aeration tank?

Answer 44

Lag phase Exponential Growth Phase Declining Growth Phase Stationary Phase Endogenous Phase

Question 45

What is the goal of the aeration tank? How is this accomplished?

Answer 45

Goal is to maximize the number of microbes in the stationary growth phase to maximize BOD removal, this is done by - good supply of aeration to support growth - Appropriate retention time - Waste loading to feed the microbes - wasting of sludge to remove aging populations

Question 46

What is the activated sludge aeration tank?

Answer 46

Aerated sewage containing aerobic microorganisms which help to break down organic compounds in wastewater)

Question 47

What happens during the secondary treatment?

Answer 47

Air is injected into the tank to accelerate biological degradation of organic matter

Question 48

What are the costs and treatment efficiencys of the aeration tank?

Answer 48

high

Question 49

What is advanced waste water treatment?

Answer 49

Any process/system after conventional secondary treatment to remove remaining contaminants

Question 50

What are the purposes of advances wastewater treatment?

Answer 50

To meet stringent discharge limits * To reclaim or reuse wastewater

Question 51

What is the most popular source of wastewater to be used for reclamation?

Answer 51

Municipal wastewater

Question 52

What is removed during AWT?

Answer 52

nitrogen * phosphorus * total dissolved solids and suspended solids * micro-organisms and * refractory organics

Question 53

How do you remove phosphorus in AWT?

Answer 53

- Chemical precipitation ▪ Ferric chloride FeCl3 ,Alum Al2(SO4)3 and Lime Ca(OH)2 ▪ Biological

Question 54

How do you remove nitrogen in AWT?

Answer 54

- Nitrification/denitrification (Biological) ▪ Nitrification: oxidation of ammonia to NO3- ▪ Denitrification: convert NO3- to nitrogen gas under anoxic condition ▪ Ammonia stripping

Question 55

What are the types of filtration in AWT?

Answer 55

- Granular filtration (multimedia filter) ▪ Membrane filtration

Question 56

What is the carbon adsorption in AWT?

Answer 56

Remove persistent soluble organics (refractory organics- poorly biodegradables

Question 57

What is the microorganism removal in AWT?

Answer 57

Target to kill pathogens using chemical processes (oxidation) – disinfection or UV irradiation

Question 58

What are advanced oxidation processes?

Answer 58

They mineralize the pollutants (CO2 & H2O as products)

Question 59

Give two examples of AOP's?

Answer 59

Hydrogen peroxide + UV Ozone + UV

Question 60

What has the highest oxidation potential?

Answer 60

the hydroxyl radical

Question 61

What are the four things the choice of AOP's depends on?

Answer 61

Effectiveness (doesn't degrade atrazine) Economics (treats only the wastes that resistant to the cheaper conventional treatment processes) Operation and maintenance issues Pathway (doesnt make more toxic byproducts)

Question 62

What is sludge?

Answer 62

residues from wastewater treatment in the form of liquid or semisolid, odious and difficult to manage

Question 63

What are the objectives of sludge treatment (3)?

Answer 63

* Volume reduction * Safe disposal * Resource & reuse

Question 64

How does sludge digestion work?

Answer 64

Through anaerobic digestion, there is a decomposition of sludge in the absence of oxygen to gaseous products, it reduces the mass of sludge.

Question 65

What are the five ultimate disposals of sludge?

Answer 65

Land application Landfilling Ocean Disposal Incineration Deep Well Injection

Question 66

Where is treated wastewater disposed?

Answer 66

Disposed into rives, lakes, seas and lands sometimes as irrigation or into soils and wetlands for additional treatment

Question 67

Where is treated wastewater reused?

Answer 67

* Fire fighting, cleaning, cooling, steam generation * Aquifer (groundwater) recharge * For nutrient recovery – aquatic plants are allowed to grow and then harvested for animal food * Others (habitat restoration)