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CIVL 7062 > MIDTERM 2 CCHAN > Flashcards

MIDTERM 2 CCHAN Flashcards

1
Q

what are the different ways the stabilization (degradation) of wastewater is accomplished?

A
  • conversion of colloidal and dissolved carbonaceous organic matter into gases and biosolids (cell mass)
  • S.G. of biosolids > S.G. water, therefore biosolids can be removed via gravity settling or filtration
  • some specific types of microorganisms can also remove nutrients (N, P,) from wastewater
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2
Q

what is required for microorganisms grow?

A
  • carbon and energy
  • nutrients (N,P)
  • Trace elements (S, Mg, K)
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3
Q

classification based on O2 presence: Obligate aerobes

A

must have molecular O2 present

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4
Q

classification based on O2 presence: Obligate anaerobes

A

presence of O2 is toxic

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5
Q

classification based on O2 presence: Facultative aerobes

A

can grow in absence/presence of O2

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6
Q

classification based on O2 presence: Microaerophillic

A

obligate aerobes, but only in low O2 concentrations

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7
Q

what are some environmental factors to consider for functions of micro-organisms

A
  • pH
  • chemical composition of “food” (organic matter)
  • O2 concentration
  • temp.
  • light availability
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8
Q

true or false: identification and enumeration of all microorganisms present in water samples would be TEDIOUS, LONG AND VERY EXPENSIVE

A

true

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9
Q

what are the 3 types of indicator organisms (commonly used)

A
  1. total coliform (from soil, feces, other origins)
  2. Fecal coliform (from guts of humans, warm blooded animals)
  3. E. Coli> (one of the coliform bacteria group, more representative of fecal source than other coliform genre)
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10
Q

what is the criteria for the choice of indicator organisms?

A
  1. should always present when pathogenic organisms of concern is present, and absent in clean uncontaminated water
  2. should be present in fecal material in large quantity
  3. should respond to natural environmental conditions and to treatment processes in a manner similar to pathogens of interest
  4. easy to isolate identify and enumerate
  5. ratio of indicator to pathogen high
  6. indicator and pathogen should come from the same source
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11
Q

what are the different methods of counting the number of bacteria cells per milliliter, gram or cubic meter of a sample?

A
  1. membrane filtration technique
  2. presence and absence test
  3. fermentation tube technique
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12
Q

what are the water quality standards based on?

A

a) established or ongoing practice
b) technical attainability
c) economic attainability
d) ability to measure parameters reliably
e) evidence derived from accidental human exposure
f) educated guess based on available info and judgement
g) application of mathematical models (simulation of health risks)
h) legal enforceability

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13
Q

what are some methods for groundwater treatment?

A

aeration
lime soda ash addition
flocculation
sedimentation
recarbonation
filtration, disinfection and sludge processing

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14
Q

what is an intake facility?

A

facilities to divert and transport water from a supply source to a pumping station, collector well or directly to water treatment facility

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15
Q

what are some types of racks and screens?

A

intake bar rack (coarse screens)
fine screens travelling belt screen

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16
Q

what are some specifications for an intake bar rack?

A
  • located at water intakes from rivers and lakes to prevent entry of large materials
  • the clear spacing between bars composing the rack varies from 1 to 3 in
  • a trolley and hoist is often installed (manually or automated operation for cleaning
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17
Q

what are some specifications for fine screen travelling belt screen?

A
  • consists of wire mesh with opening sizes from 0.25 to 0.35 in.
  • often used following bar racks to prevent small fish from being drawn into the intake
  • can be hydraulically cleaned (back flush)
  • if fish present - fish lift buckets and low-pressure wash
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18
Q

what are some aspects regarding the design and operation of screens?

A

minimize head loss
average velocity
continuous cleaning

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19
Q

how are screens disposed?

A

usually disposed of in a landfill

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20
Q

what is an infiltration gallery?

A

natural pretreatment process
- collect water that naturally infiltrates through the soil allowing it to undergo natural filtration as it percolates through the ground
- removed suspended solids and to some extent, pathogens, making the water cleaner and easier to teat downstream

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21
Q

what is the theory of coagulation?

A

the process of adding chemicals to surface waters to collect small particulate matters (ie colloidal matters) into clusters that can be removed from solution by subsequent sedimentation and filtration through granular media

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22
Q

what are some characteristics of colloidal matters

A
  • for larger particles, the ratio of surface area to mass is low and mass effects such as sedimentation by gravity forces predominate
  • however, for colloids, the ratio of surface area to mass is high, and surface phenomena such as electrostatic repulsion and hydration become important
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23
Q

what is the principal phenomena that control the behavior of colloids?

A
  • electrical properties
  • van der waals forces
  • brownian motion
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24
Q

what are electrical properties in relation to colloids?

A

surface charge of colloids and suspended particles coause them to remain in suspension without aggregation for a long time - STABLE colloids

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25
Q

what are van der waal’s forces in relation to colloids?

A
  • the tendency of particles in nature to attract each other weakly if they have no charge
  • once the particles in water are not repelling each other, van der waal’s forces make the particles drift toward each other and join together into a group
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26
Q

what is particle stability?

A

colloids remain stable when there is a balance between the repulsive electrostatic force of the charged particle and attractive force of van der waals forces

26
Q

what is brownian motion in relation to colloids?

A

colloids have a sufficiently small mass that collision with molecular size particles in water will cause constant movement of the colloids

27
Q

what are some of the mechanisms of coagulation and flocculation

A
  • double layer compression
  • charge neutralization
  • enmeshment in precipitate (sweep coagulation)
28
Q

what do coagulants do?

A

reduce net electron repulsive force at particle surface + addition of counter ions (+ charged ions)

29
Q

what does flocculation do?

A

results in agglomeration of destabilized particles

30
Q

what is double layer compression

A

positive charged ions reduce/suppress double layer so that net repulsive charge is reduced

31
Q

what is charge neutralization?

A

absorption of hydrolyzed metal salts (+ ve ions) onto colloidal surface and neutralizing the negatively charged colloids

32
Q

what is enmeshment in precipitate (sweep coagulation)

A

add alum or iron ions (coagulants) at the right (something) to form flocs with colloids as its nulcei

33
Q

what is particle bridging?

A

adding polymers to enhance coagulation

34
Q

true or false, it is common that in practice 2-3 mechanisms of coagulation are used simultaneously in the coagulation process

A

FALSE!! its actually several mechanisms are used

35
Q

what does the removal of colloids by coagulation depend on?

A
  • their nature and concentration
  • the use of both coagulants and coagulant aids
  • pH
  • temperature
  • ionic strength
36
Q

what are the most widely used coagulants for water and wastewater treatment?

A

aluminum salts and iron salts

37
Q

what is aluminum sulphate?

A

the standard coagulant used in water treatment
- if sufficient alum is added and pH is adjusted to range of 6 TO 8, aluminum hydroxide precipitate is formed for the sweep floc coagulation mechanism

38
Q

when is lime added to water and wastewater treatment?

A

to provide the necessary alkalinity and control of pH of the coagulation process

39
Q

what are the advantages of ferric salts

A
  • coagulation is possible over a wide range of pH (4-9)
  • floc settles better than alum floc
  • better removal of NOM and odor/taste compounds
40
Q

what is a disadvantage of ferric salts?

A

it costs more than alum salts

41
Q

what are the advantages of using polymers for coagulants

A
  • for some waters, cationic polymers are effective as a primary coagulant, but more commonly are used as coagulant aids
  • do no affect pH, can be used in low alkalinity water
  • dosage of cationic polymer is much less than metal coagulants
  • anionic and non-ionic polymers are effective coagulant aids. promote larger and tougher floc by bridging mechanism
  • more effective in water containing higher concentration of divalent cations (calcium and magnesium)
  • reduce the amount of salt to be added
42
Q

how are acids and alkalies used to adjust water and wastewater

A
  • used to adjust the pH of water for optimum coagulation
  • typical acids usd to lower the pH are sulphuric and phosphoric acid
  • alkalies used to raise the pH are lime, sodium hydroxide, and soda ash
43
Q

in regards to mixing, what is rapid mixing (flash coagulation)

A
  • the process where the chemcials are quickly dispersed and mixed into the water
  • vigorous, turbulent mixing causes lots of particle collision - leads to coagulation
44
Q

in regards to mixing, what is gentle mixing (flocculation)

A
  • process by which these precipitates are brought in contact with one another so they can agglomerate and form larger particles called flocs
  • gentle (strong enough to form collisions but NOT strong enough to break apart flocs)
45
Q

what are the different types of mixers for rapid mixing (flash mixing)

A
  • in-line mechanical mixing (in-line blending)
  • in-line static mixing
  • mechanical mixing in stirred tanks
46
Q

what are the types of mixers for gentle mixing?

A
  • paddle flocculators
  • baffled chambers
  • axial flow impellers
47
Q

what is sedimentation?

A

suspended particles are removed from liquid phase by gravity settling

48
Q

what are the steps for sedimentation removal in water treatment?

A
  • pretreatment of surface waters
  • settling of coagulated/flocculated waters prior to filtration
  • settling of coagulated flocculated water chemical water softening
49
Q

what are the steps for sedimentation removal in wastewater treatment?

A
  • removal of grit and other coarse solids, suspended solids before biological treatment
  • removal of biological solids produced during biological treatment
50
Q

what are the 4 different types of settling classes for settling properties of particles?

A
  1. discrete settling (settling of non-flocculant particles) - TYPE 1
  2. flocculant settling - TYPE 2
  3. hindered settling - TYPE 3
  4. compression settling - TYPE 4
51
Q

what is type 1 discrete settling?

A

particles settle discretely at a constant settling velocity. They settle individually and do not flocculate

52
Q

what are some applications of type 1 settling?

A
  • presettling of grit or sand prior to water treatment
  • settling of sand particles during cleaning of rapid sand filters
  • in grit chambers in wastewater treatment
53
Q

what are some of the assumptions that we make for the ideal settling tank

A
  • type 1 discrete settling
  • four zones in basin: inlet, outlet, sludge, and settling
  • even distribution of flow entering and leaving settling zone
  • uniform particle distribution throughout
  • particles that enter outlet zone not removed from water
54
Q

true or false most actual settling systems do no behave like TYPE 1 (discrete settling) system

A

true

55
Q

what are the particle interactions for TYPE 2 (flocculent settling)

A

flocculation in which particles collide and adhere to other particles (particle growth)

56
Q

what are the particle interactions for TYPE 3 (hindered or zone settling)

A

fluidic in which particles are so close together that flow is restricted and particles move as a block

57
Q

what are the particle interactions for TYPE 4 (compression settling)

A

mechanical - particles physically interact in a compressive mode

58
Q

what are the two types of sedimentation tanks?

A

rectangular and circular

59
Q

some facts about rectangular sedimentation tanks

A
  • usually have chain driven scrapers for sludge removal
  • typically 3m deep for water treatment
60
Q

some facts about circular sedimentation tanks

A
  • inflow at center, outflow along perimeter weir or radial collection trough
  • circular rake arms for sludge collection
  • typically more than 3m deep
61
Q

what are the 4 zones for sediment tank design?

A

inlet zone
settling zone
outlet zone
sludge zone

62
Q

what are some considerations for sedimentation basin design?

A
  • overflow rate (surface loading rate) - for initial dimensions/sizing
  • detention time: need sufficient time for settling, if flocculation expected - need time for flocs to grow
  • scour velocity: particles settled at bottom may be re-suspended (scoured) if horizontal velocity too high
  • critical horizontal velocity (min. horizontal velocity that will produce scour)
  • horizontal flow velocity
  • weir loading rate (wastewater)
  • short-circuiting and hydraulic instability (L/W ratio, min. depth requirements

CIVL 7062 (5 decks)

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