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ENCN281 > Wastewater Treatment > Flashcards

Wastewater Treatment Flashcards

1
Q

Problem with organic matter

A

oxygen depletion

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2
Q

problem with solids

A

turbidity, aesthetics

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3
Q

problem with nutrients

A

eutrophication

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4
Q

problem with pathogenic organisms

A

diseases

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5
Q

problem with organics/metals

A

toxicity

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6
Q

What is in wastewater

A
  • human feces and urine
  • food from sinks
  • soaps and cleaning agents
  • runoff from streets and lawns
  • industrial discharges
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7
Q

Objectives of wastewater treatment

A
  • reduce the load of contaminants
  • produce treated effluents that meet environmental protection regulations
  • produce effluents that can be safely disposed of in the environment or reused
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8
Q

Methods of wastewater treatment

A
  • Physical Unit Operations: treatment methods in which physical forces predominate
  • Chemical Unit Processes: removal or conversion of contaminants by addition of chemicals
  • Biological Unit Processes: removal of contaminants by biological activity
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9
Q

Physical Unit Operation

A
  • flow metering
  • screening
  • comminution
  • flow equalisation
  • mixing
  • flocculation
  • sedimentation
  • flotation
  • filtration
  • volatilisation and gas stripping
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10
Q

Chemical Unit Processes

A
  • chemical precipitation
  • adsorption
  • coagulation
  • ion exchange
  • chemical oxidation
  • chlorination
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11
Q

Biological Unit Processes

A
  • aerobic suspended-growth (activated sludge)
  • aerobic attached-growth (trickling filters)
  • anaerobic suspended-growth (contact reactor)
  • anaerobic attached-growth (anaerobic filter)
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12
Q

Levels of Treatment

A
  • Primary = Physical = removed solids, organic matter
  • Secondary = biological = organic matter, nutrients
  • Tertiary = various = nutrients, toxins
  • Disinfection = Various = pathogens
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13
Q

Preliminary Treatment

A

removal of wastewater constituents that may cause maintenance or operation problems with treatment operations (screening, comminution, grit removal, flotation)

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14
Q

Primary Treatment

A

portion of suspended solids and organic matter removed (sedimentation)

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15
Q

Secondary Treatment

A

biodegradable organics and suspended solids removed (activated sludge, fixed-film reactors, lagoon systems and sedimentation)

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16
Q

Tertiary Treatment

A

treatment beyond conventional secondary treatment removing constituents of concern including nutrients, toxic compounds and increased amounts of organic material and suspended solids

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17
Q

Disinfection

A

inactivation of pathogens by addition of disinfectant (chlorine, UV radiation)

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18
Q

Sludge Treatment and Disposal

A

anaerobic digestion, landfilling, incineration

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19
Q

Methods for Oxidation of Organic Compounds

A
  1. Chemical Oxidation = ozonation, peroxidation, chlorination
  2. Combustion
  3. Bacterial oxidation = microbial metabolism
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20
Q

Objectives of Biological Wastewater Treatment

A

coagulate and remove nonsettleable colloidal solids and stabilise organic matter. specifically:

  • transform/oxidise dissolved and particulat biodegradable constituents into suitable end products
  • capture suspended and nosettleable colloidal solids into a biological floc or biofilm
  • transform or remove nutrients such as N or P
  • remove trace organics and compounds
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21
Q

substrate

A

food to provide energy for microbial growth (most organic constituents in wastewater)
- organic growth measured as BOD, COD or TOC

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22
Q

Biomass

A
  • measured as volatile suspended solids (VSS)

- nutritional patterns or trophic levels distinguished based on two criteria - energy and carbon source.

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23
Q

Photoautotroph

A

organisms obtaining energy from light and carbon from CO2

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24
Q

Photoheterotroph

A

organism obtaining energy from light and carbon from organic material

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25
Q

Chemoautotrophs

A

organisms obtaining carbon from CO2 and energy from oxidation of inorganic compounds

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26
Q

Chemoheterotrophs

A

organisms obtaining both their energy and carbon from organic material

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27
Q

Respiratory metabolism

A

generate energy by enzyme - mediated electron transport from an electron donor to an external electron acceptor

28
Q

Fermentation metabolism

A

does not involve the participation of an external electron acceptor

29
Q

Aerobic respiration

A

when molecular oxygen is used as the electron acceptor in respiratory metabolism

30
Q

Anoxic respiration

A

when respiratory organisms use oxidised inorganic compounds such as nitrate and nitrite function as electron acceptors

31
Q

fermentation: Strict anaerobes

A

can exist only in environments devoid of oxygen and generate energy by fermentation

32
Q

fermentation: facultative anaerobes

A

have the ability to grow in either the presence or absence of molecular oxygen

33
Q

suspended growth

A

microorganisms responsible for treatment are maintained in liquid suspension - most common is activated sludge process

34
Q

attached growth process

A

microorganisms responsible for treatment are attached to packing material - most common is trickling filtration

35
Q

Biological Wastewater Treatment: 3 Steps

A
  1. Transfer of Food from Wastewater to Cell (adequate mixing and enough detention time)
  2. Conversion of Food to New Cells and Byproducts (acclimated biomass, useable food supply, adequate DO, proper nutrient balance)
  3. Flocculation and Solids Removal (proper mixing, proper growth environment, secondary clarification)
36
Q

BOD

A

Biochemical Oxygen Demand

  • quantity of oxygen used in the biochemical oxidation of organic material
  • best to use a “moving average” to determine the average impact on a treatment system
37
Q

Food to Microorganism ratio

A
  • ratio for best treatment will vary for different facilities
  • determined by regular monitoring and comparing to effluent quality
  • often will vary seasonally (higher rate in warmer temperature)
  • used to determine the kg of MLVSS needed at a particular loading rate
38
Q

Conventional Activated Sludge typical F:M range

A

0.25 - 0.45

39
Q

Extended Aeration Activated Sludge typical F:M range

A

0.05 - 0.15

40
Q

SA

A

sludge age

41
Q

CRT

A

Cell Residence Time

42
Q

MCRT

A

Mean Cell Residence Time

43
Q

MLVSS

A

Mixed Liquor Volatile Suspended Solids

44
Q

F:M

A

Food to Microorganism Ratio

45
Q

Young Sludge

A
  • start-up or high BOD load
  • few established cells
  • log growth
  • high F:M
  • low CRT
46
Q

Disadvantages of young Sludge

A
  • poor flocculation
  • poor settleability
  • turbid effluent
  • high O2 uptake rate
47
Q

Old Sludge

A
  • slow metabolism (less active=slower process)
  • decreased food intake
  • low cell production
  • oxidation of stored food
  • endogenous respiration
  • low F:M
  • high CRT
  • high MLSS
  • dense, compact floc
  • fast settling
  • straggler floc
48
Q

WAS

A

Waste Activated Sludge

- method for controlling the CRT for facility

49
Q

RAS

A

Return Activated Sludge

50
Q

Cell Residence Time

A

average length of time in days that an organism remains in the secondary treatment system

51
Q

VSS

A

volatile suspended solids

52
Q

Where to Waste Sludge

A

Primary Clarifiers
- advantage: co-settling
- disadvantage - are solids really wasted
Solids Handling
- advantage: know solids are out of the system
- disadvantage: thinner solids to solids process

53
Q

Y

A

Yield Coefficient: mass (kg) of biological solids produced per mass (kg) of BOD removed

54
Q

SVI

A

Sludge Volume Index: volume in millilitres occupied by one gram of activated sludge which has settled for 30 min

  • typical range for good settling = 80 - 120
  • higher the number, the less compact the sludge
  • large value = not settling at the bottom
  • small value = settling too fast
55
Q

SDI

A

Sludge Density Index: The grams of activated sludge which occupies a volume of 100 mL after 30 min. of settling

  • typical range for good settling = 0.8 - 1.2
  • lower the number the less compact the sludge
56
Q

SVI - SDI Relationship

A 
SVI = 100 / SDI
SDI = 100 / SVI
57
Q

Three areas of operation where Biomass normally settles well

A
  1. Extended Air
    - F:M less than 0.2
  2. Conventional
    - F:M 0.25 to 0.45
  3. High Rate
    - F:M 0.9 to 1.2
    - seldom used except when followed by additional treatment
58
Q

S(0)

A

substrate ( BOD(5) ) in the influent wastewater

59
Q

S(e)

A

or S: substrate ( BOD(5) ) in the effluent

60
Q

X

A

micro-organisms in the mixed liquor in the aeration tank (MLVSS)

61
Q

X(r)

A

the concentrated sludge (VSS) returned to the inlet of the aeration tank

62
Q

Q(r)

A

return activated sludge (RAS) flow which is the underflow from the final sedimentation tank

63
Q

Q(w)

A

waste activated sludge (WAS) flow which is a portion of the sludge underflow withdrawn for disposal to sludge digesters

64
Q

HRT

A

Hydraulic Retention Time, θ: the time required for the liquid to pass through the aeration tank

65
Q

SRT

A

Sludge Retention Time, θc: average time a bacteria spends in the system

66
Q

θ

A

Hydraulic Retention Time

67
Q

θc

A

Sludge Retention Time

ENCN281 (5 decks)

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