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CIVE40010 - Energy and environmental engineering > Biological wastewater management > Flashcards

Biological wastewater management Flashcards

1
Q

What is the biggest organic constitute of domestic wasteand thier %?

A
  • 30% carbohydrates
  • 28% other fats, grease and micropollutants
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2
Q

What microorganisms cause intestinal disease?

A
  • Salmonella spp
  • Listeria spp
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3
Q

How much of sewage is water?

A

99.9%

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4
Q

What is the pollution control objective in terms of health?

A

Minimise risk of disease transmission by water-borne route

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5
Q

What is the pollution control objective in terms of ecology?

A

Minimise risk to the natural ecological balance of receiving water (eutrophication)

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6
Q

What is the pollution control objective in terms of aesthetic?

A

Maintain value of water for recreational activities/tourism

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7
Q

What is the pollution control objective in terms of economics?

A

Provide an appropriate level of treatment to achieve environmental protection at reasonable cost, GDP will suffer

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8
Q

What steps are involved in waste water treatment?

A
  • Barscreening
  • Grit removal
  • Primary clarifier
  • Aeration
  • Secondary clarifier
  • Chlorination
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9
Q

What does the secondary clarifier do?

A
  • Separates biological floc from the treated liquid waste stream.
  • Reduces organic matter content
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10
Q

What does the primary clarifier do?

A
  • The major function of the primary clarifier is the removal of all settleable and floating solid waste that has a high oxygen demand – BOD.
  • Water is stilled so tiny particles are suspended
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11
Q

What does preliminary screening do?

A
  • Removes solid matter
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12
Q

What does the primary clarifier typically remove?

A
  • 40% of BOD
  • 60% of suspended solids
  • 17% of nitrogen
  • 20% of phosphorus
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13
Q

What des the secondary biological treatment typically remove?

A
  • 95% of BOD
  • 95% of suspended solids
  • 29% of nitrogen
  • 35% of phosphorus
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14
Q

What is effluent?

A

Effluent is sewage that has been treated in a septic tank or sewage treatment plant.

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15
Q

What does the tertiary treatment do?

A
  • Reduce the load of micro-organisms and nutrients in the effluent
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16
Q

What does the tertiary treatment usually remove?

A
  • 100% BOD
  • 100% of suspended solids
  • 33% of nitrogen
  • 38% of phosphorus
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17
Q

What is biological oxygen demand?

A

BOD, also called biological oxygen demand, is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time.

18
Q

What microorganisms are involved in wastewater treatment?

A

Bacteria, algae, and fungi

19
Q

What are attached growth processes?

A

Wastewater treatment processes in which the microorganisms and bacteria treating the wastes are attached to the media in the reactor.

20
Q

What are some attached growth processes?

A

Trickling/percolating biological filter

21
Q

What are some suspended growth processes?

A
  • Activated sludge process
  • Main process employed at major wastewater treatment plant
22
Q

What are suspended growth processes?

A

Wastewater treatment processes in which the microorganisms and bacteria treating the wastes are suspended in the wastewater.

23
Q

What’s good about biological filters?

A
  • Very successful wastewater treatment system
  • Widespread use for >120 years
  • Less energy required than activated process (30-50% less)
24
Q

What’s the negatives for biological filters?

A
  • Superseded by activated sludge process at larger treatment facilities
  • Larger footprint
25
Q

How is the settled sewage supplied?

A

Through a distributor

26
Q

What are the shapes of the aggregate beds usually?

A

Circular or rectangular aggregate bed

27
Q

Why does the beds need to be a specific depth?

A
  • Need to be 1.5-2.0m deep otherwise, you will introduce an anaerobic community
28
Q

What happens in the attached growth process, biofilm development and purification process?

A
  • Soluble organics and O2 diffuse into biofilm
  • Direct ingestion by metazoa and protozoa
  • Nitrification
29
Q

What is nitrification?

A
  • The process in which bacteria in the soil use oxygen to change compounds of nitrogen in dead plant material into nitrates which plants can then absorb as food.
30
Q

What’s some advantages of attached growth processes?

A
  • Simple operation
  • Low maintenance
  • Low energy use (30-50%
    less than activated sludge)
  • Reliable
  • Treat industrial WW
31
Q

What are some negative of attached growth processes?

A
  • Filter clogging due to excessive microbial growth
  • Potential odors
  • Fly nuisance
  • Difficult to control
  • Poorer operation in cold conditions
32
Q

What is involved in activated sludge process?

A
  • Continuous aerated reactor with feedback of biomass providing inoculum source and sites of biological activity → continuously stirred
  • Excess sludge washed away to treatment - digester
33
Q

What is a floc?

A

A large number of cells glued together

34
Q

What is mixed liquor?

A

biomass + wastewater

35
Q

How is mixed liquor suspensions maintained?

A

Turbulence

36
Q

What achieves maximum rate of decomposition?

A

High microbial population

37
Q

What is supernatant?

A
  • The relatively clear water layer between the sludge on the bottom and the scum on the surface of an anaerobic digester, septic tank
  • Discharged effluent
38
Q

What are the purification mechanisms?

A
  • Rapid stage
  • Oxidation stage
39
Q

What is involved in the rapid stage?

A
  • Due to properties of floc
  • Rapid adsorption + flocculation of soluble & colloidal matter
  • Capture of particulate solid matter
  • Rapid reduction in BOD
40
Q

What is involved in the oxidation stage?

A
  • Respiration at the inlet increased as organic matter oxidized
  • Rapid oxidation of readily degradable organics
  • Respiration < 1/10 initial rate at end of the tank
41
Q

What are advantages of suspended growth processes?

A
  • Increased process control
    – Flexible as different redox environments created by
    reactor design
    – Reduced odor and fly problems
    – Smaller footprint (10%) than attached growth systems
42
Q

What are disadvantages of suspended growth processes?

A

– Susceptible to shock loads and contaminants
– Susceptible to biomass wash-out
– A more complex operation

CIVE40010 - Energy and environmental engineering (21 decks)

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