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ENCN281 > Wastewater Treatment > Flashcards

Wastewater Treatment Flashcards

1
Q 
What are its physical characteristics?
Colour
Odour
Temperature
Solids
A

Colour - grey to light brown

Odour - “fresh” - musty, “old” rotten egg

Temperature: varies seasonally

Solids: floatable, dissolved, suspended, settleable

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2
Q

What are its chemical characteristics?
Organics
Inorganics

A

Organics - Human, animal, vegetable waste

Measured as BOD and COD

Alkalinity

Inorganics - nitrogen, phosphorous, dissolved material

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3
Q

Biological characteristics:

Define Pathogenic and Non-pathogenic

A

Pathogenic - disease producing

Non-pathogenic - harmless, most prevalent

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4
Q

What are the stages in preliminary treatment and are the three functions?

A

Screening and Grit removal

  • removal of untreatable solids
  • protection of subsequent equipment
  • improvement of the performance of other processes

Notes:
• A portion of suspended solids and organic matter
(BOD) is removed from the wastewater
• this is usually accomplished with physical operations
such as: settling ,sedimentation, clarification

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5
Q

What is grit?

A
  • Sand
  • Cinders
  • Rocks
  • Cigarette filter tips
  • Coffee grounds
  • Non-putrescible material
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6
Q

Why is grit removed?

A

• Prevent clogging of the subsequent unit
operations

• Avoid overloading biological reactors

• Avoid damaging mechanical parts of the WWT
process (grits are abrasive)

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7
Q

How to remove grit?

A
  1. Aerated grit chamber
  2. Non- aerated grit chamber
    (old wastewater can be odorous)
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8
Q

What are Biological Unit Processes?

A

• Biological Unit Processes: Consist of treatment
methods whereby the removal of contaminants is
brought about by biological activity.

• Used to remove colloidal and dissolved biodegradable
organics.

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9
Q

What is Substrate?

A

• Most organic constituents in wastewater can serve as food (substrate) to provide
energy for microbial growth.

• Organic substrate is measured as BOD, COD or alternatively as TOC

Organic substrate is a mixture of sugars, fats, proteins, etc.

Denoted by generic “S”
eg. BOD5(initial) = S0

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10
Q

What is Biomass?

A
  • Biomass is measured as volatile suspended solids (VSS).
  • Biomass nutritional patterns or trophic levels are distinguished on the basis of two criteria: the energy and carbon source.
  • Mostly bacteria
    Denoted by generic “X” (Micro-organisms)

How do we measure bacteria? Mixed liquor volatile solids (MVLSS) = 80% of TSS

Growth of bacteria:

1) Water treatment - Number(i.e # coliforms/100mL)
2) Wastewater Treatment - Mass (i.e mg/L)

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11
Q

Biomass Classification o Trophic Levels: Energy Source

What are Phototrophs?

A

If light is the primary energy source, micro-organisms are known as phototrophs.

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12
Q

Biomass Classification o Trophic Levels: Energy Source

What are Chemotrophs?

A

If redox reactions extract energy from chemicals, micro-organisms are known as chemotrophs.

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13
Q

Biomass Classification o Trophic Levels: Carbon Source

What are Autotrophs (or lithotrophs)?

A

If CO2 or HCO3- is the principle carbon source, micro-organisms are known as autotrophs (or lithotrophs).

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14
Q

Biomass Classification o Trophic Levels: Carbon Source

What are Heterotrophs (or organotrophs)?

A

If organics are the principal carbon source, micro-organisms are known as
heterotrophs (or organotrophs).

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15
Q

What are photoautotrophs?

Give examples

A

• Organisms obtaining energy from light and carbon from CO 2 .

• Ex: Algae, plants, Chlorobium (green sulfur bacteria), Chromatium (purple sulfur bacteria)
and Cyanobacteria (blue-green algae).
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16
Q

What are photoheterotrophs?

Give examples

A

• Organisms obtaining energy from light and carbon from organic material (ex: alcohols,
carbohydrates, fatty acids etc.)

• Ex: Rhodospirillium (purple non-sulfur bacteria) and green non-sulfur bacteria.

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17
Q

What are chemoautotrophs?

Give examples

A

• Organisms obtaining carbon from CO 2 and energy from the oxidation of inorganic
compounds.

• Ex: Beggiatoa (H 2 S oxidized to SO 4-2 ), Thiobacillus (elemental sulfur S to H 2 S), Nitrosomonas
(NH 3 to NO 2- ), Nitrobacter (NO 2- to NO 3- ), Hydrogenomonas (H 2 to H 2 O), and Thiobacillus
ferrooxidans (Fe +2 to Fe +3 ).

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18
Q

What are Chemoheterotrophs?

Give examples

A

• Organisms obtaining both their energy and carbon from organic material.

• Ex: The majority of bacteria (Eschericia coli, Desulfovibrio, Pseudomonas, Clostridium,
Methanogens), all fungi, slimes, protozoa and animals.
• They also include saprophytes and parasites

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19
Q

Aerobic Processes

A

Free (molecular) O2 is present.

  • Carbon degradation is done by chemoheterotrophic bacteria
  • Nitrification is done by chemoautotrophic bacteria
20
Q

Anoxic Processes

A

Bound oxygen forms

  • Denitrification is done by chemoheterotrophs.
  • Sulphate reduction (i.e. sulphanogenesis) is done by chemoautotrophs.
  • Sulphate reduction is most often classed as an anaerobic process.
21
Q

Anaerobic Processes

A

No free or combined oxygen

• Done by two groups of chemoheterotrophic bacteria.

a) Liquefaction (acidogenesis)
b) Gasification (methanogenesis)

22
Q

What is the Trickling Filter (TF)?

A
  • An aerobic, fixed-growth process in which the biomass grows on a media and the wastewater trickles down over the media allowing the BOD to be removed.
  • A fixed growth process because the micro-organisms grow as a film and are “fixed” on to the media.
23
Q

What is the Rotating Biological Contactor (RBCs)?

A

• An aerobic process in which the biomass grows on a media but this time the media is rotated into a pool of wastewater allowing the BOD to be removed.

24
Q

What is Activated Sludge (AS)?

A

• An aerobic suspended growth process.

• The micro-organisms are grown in suspension forming brown flocculent suspended
particles.

  • Often modelled as a completely-mixed reactor (CMR) with recycle.
  • The model is also known as a continuous-flow, stirred tank reactor (CFSTR)
25
Q

What is the goal of the AS Process?

A

• To remove (reduce) or stabilize organic (and inorganic) matter in the wastewater using suspended growth, aerobic microorganisms

26
Q

What is Anaerobic Digestion (AD)?

A

• An anaerobic suspended growth process in which WAS is digested by cannibalisation
by other bacteria.

27
Q

What is Fluidized Bed (FB)?

A

• An anaerobic process in which bacteria grow on media but this time the media is kept in suspension.

28
Q

What is Upflow Anaerobic Sludge Digestion (UASBs)?

A

• An anaerobic process where the bacteria form large granules (rather than flocs) and the granules cluster in a blanket.

29
Q

How is a water’s quality measured?

A

By chemical, physical and biological parameters.

30
Q

What is the order of how contaminants are removed from a water/wastewater?

A

(i) increasing difficulty; and

(ii) decreasing size.

31
Q

What is the nutrient ratio for biological growth in a sewage treatment plant? BOD5:N:P

A

BOD5:N:P = 100:5:1

You add nutrients to promote biomass growth

32
Q

Model for Microbial Growth:

What is the name of the concept when the output is less than the input?

A

Microbial growth kinetics is described in terms of a Yield Coefficient (Y).

33
Q

What is r(s)?

( ) = subscript

A

Substrate Destruction Rate (oxidation)

34
Q

what is r(g)?

( ) = subscript

A

Biomass growth rate (synthesis)

35
Q

What is k(d)X?

( ) = subscript

A

Endogenous Metabolism Rate (autooxidation)

36
Q

Whats is k(d)?

( ) = subscript

A

starving factor coefficient

37
Q

What is Y?

A

Yield coefficient = mass biomass produced/mass substrate destroyed i.e. Y = r(g)/r(s)

38
Q

What is K(s)?

A

the one half velocity coefficient (half-saturation constant)

39
Q

What is Mu(m)?

A

maximum specific growth rate = r(g,max)/X

40
Q

What is k?

A

Max specific substrate destruction rate

k=Mu(m)/Y = r(s,max)/X

41
Q

Treatment Models: Completely Mix with No Recycle

What processes are in involved?

A

Aerobic and anaerobic digesters

Aerated lagoons:
• A biological treatment process consisting of a CFSTR (Continuous Flow Stirred Tank Reactor)

• Properties are uniform throughout @ steady-state.

42
Q

What is U?

A

The Specific Utilization Rate

U=k*S/(K(s)+S)

43
Q

What is r(g)’?

A

Net sludge production when multiplied by volume

44
Q

High F/M (food to microorganism ratio)

A
  • > Low growth phase, maximum rate of metabolism
  • > settling poor, BOD removal efficiency is low

Thus

  • > excess BOD passes out through effluent
  • > lots of sludge produced
45
Q

Low F/M (food to microorganism ratio)

A
  • > endogenous phase, metabolic rate is low
  • > small(food) + large(bugs) = starvation
  • > settling is good, BOD removal efficiency is high

ENCN281 (6 decks)

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