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Wastewater > Secondary Treatment > Flashcards

Secondary Treatment Flashcards

1
Q

Organic loading to a wastewater treatment pond is expressed in these units.

A

Pounds BOD- / acre * day or “pounds of BOD per day per acre”

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2
Q

The major by-product produced by algae in a wastewater treatment pond

A

Oxygen

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3
Q

Oxygen in wastewater may be found in these two forms.

A

□ Free oxygen, as dissolved molecular oxygen (02)
* Combined oxygen, which is oxygen in the form of nitrates or sulfates

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4
Q

Terms that are used for impoundments that are usedto treat raw sewage through natural
biological processes.

A
  • Stabilization ponds
  • Lagoons
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5
Q

Characteristics of facultative treatment ponds:
Water depth, feet
Detention time, days
Organic loading, lb BOD/day/acre

A
  • Water depth: 3-4ft.
  • Organic loading: 60 - 120 lb/day/acre
  • Detention time: 30 to more than 100 days
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6
Q

Types of media that may be used in trickling filters.

A

Sorted river rock
* Plastic media
* Redwood slats

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7
Q

Typical changes in pH and dissolved oxygen that occur over a 24-hour time period in an
un-aerated sewage lagoon

A

Dissolved oxygen and pH move up and down together during a 24 hr. period.
Photosynthesis activity of algae during the daylight hours causes the pH and D.O. to rise,
and respiration by bacteria and algae during the dark hours results in a drop in pH and
D.O.

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8
Q

Maximum and minimum values for pH and D.O. occur during this period of time in an un
aerated sewage lagoon

A
  • Maximum pH and D.O.: late afternoon during peak algae photosynthesis
  • Minimum pH and D.O.: 4-5 A.M. just prior to daylight hours
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9
Q

The types of organisms important in the operation of a facultative sewage lagoon

A
  • Aerobic bacteria
  • Facultative bacteria
  • Anaerobic bacteria
  • Single-celled algae
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10
Q

The density of primary clarifier sludge solids and solids produced during secondary
treatment.

A

Primary clarifier sludge solids are slightly more dense than secondary solids.
Primary clarifier sludge: 1.05 specific gravity
Secondary biological solids: 1.02 - 1.04 specific gravity

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11
Q

The function of sodium nitrate, when it is added to a waste stabilization pond.

A

Sodium nitrate may be used to minimize odor problems during brief overload
conditions in an un-aerated waste stabilization pond. The nitrate supplies a chemically
bound source of oxygen that helps to keep the upper layers of the pond aerobic, and aids
aerobic bacteria in stabilizing the wastewater loading.

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12
Q

Photosynthesis is an essential part of the biological activity of this secondary treatment
process.

A

Facultative waste treatment ponds/lagoons utilize oxygen produced as a byproduct of
photosynthesis.

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13
Q

The basic laboratory tests used to monitor the operation of a wastewater treatment lagoon

A

pH, D.O., and temperature

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14
Q

Typical oxygen conditions in an un-aerated wastewater treatment lagoon

A
  • The upper surface of the pond is aerobic
    0 The middle layer of the pond is anoxic (no free D.O.)
  • The bottom of the pond is anaerobic
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15
Q

Time of year that is best for wastewater treatment pond start-up.

A

Summer is the ideal time for wastewater treatment pond start-up due to the increase of
biological activity that occurs during the warmer temperatures.

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16
Q

Operators must minimize or eliminate these conditions in a waste stabilization pond.

A
  • Burrowing rodents in the pond embankment
  • Rushes, cattails, and other aquatic weeds growing along the pond bank
  • Mosquito and other insect larvae multiplying in the pond
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17
Q

The normal color of a wastewater treatment pond, especially during the summer months.

A

Green, due to the growth of algaenear the pond surface

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18
Q

An aerobic process requires this.

A

Oxygen

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19
Q

An abundance of the aquatic weed called “duckweed” can cause this problem in
wastewater treatment ponds.

A

Duckweed” floats on the surface of the pond and can shade the pond water so that normal
single-celled algae are unable to develop.

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20
Q

Oxygen is produced by algae during this period of the day, and oxygen is consumed by
algae during this period of the day.

A
  • Algae produce excess oxygen during the day, through the process of photosynthesis.
  • Algae consume oxygen atnight, through the process of respiration.
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21
Q

The typical foam produced during periods when the activated sludge F/M ratio is very
high, and during start-up.

A

White crisp billowy foam

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22
Q

This process may be used to reduce the BOD of high strength wastewater before treatment
by the activated sludge process.

A

A trickling filter “roughing tower”

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23
Q

Major factors that affect the treatment by a high rate trickling filter.

A
  • Filter recirculation ratio
  • Ambient air temperature
  • Wastewater strength
  • Organic loading to the filter (lb BOD/day/lOOO cu ft media)
    □ Hydraulic loading to the filter (mgd/acre filter surface)
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24
Q

Factors that promote the process of nitrification in an activated sludge aeration basin.

A
  • Warm sewage temperature
  • Long aeration basin detention time
  • Low F/M ratio
  • High D.O. in the aeration basin
  • High Sludge age and/or MCRT
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25
Q

Denitrification may occur in an activated sludge secondary clarifier if these conditions
occur.

A
  • Excessive clarifier sludge detention time
  • Clogged or plugged clarifier sweep arm draft tubes
  • Excessive clarifier blanket depth
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26
Q

Activated sludge modification best suited to handle shock loads

A

Complete mix modification. Shock loads are rapidly diluted as they are mixed across the
entire aeration basin volume

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27
Q

The relationship between F/M, MCRT and sludgeage

A
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28
Q

Operation changes that can stop or reduce nitrification in an activated sludge aeration
basin.

A
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29
Q

The three common F/M loading classifications of the activated sludge process:
Conventional loading
Extended aeration loading
High rate loading

A
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30
Q

Characteristics of a conventional activated sludge process:
F/M loading
Return percent
Aeration basin detention time
Clarifier loading

A
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31
Q
A

F/M: 0.05 -0.15
□ Return rate: 50 - 150%
* Aeration basin detention time: 12 - 24 hours
□ Clarifier loading: 300 - 500 gal/day/sq. ft. clarifier surface

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32
Q
A

Aeration basin detention time
□ Clarifier sludge detention time
* Solids distribution between aeration tank(s) and clarifier(s)
* RAS (return activated sludge) concentration

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33
Q
A

Plug flow

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34
Q
A

Step feed/aeration

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35
Q

Conditions indicated by activated sludge foam:
Excessive tan “greasy” foam
White crispy billowy foam
Moderately light brown foam

A
  • Possible Nocardia infestation
  • Start-up or recovery from upset condition
  • Normal operation
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36
Q

The F/M ratio is determined by measuring the following:
“Food”
“Microorganism”

A
  • The F/M “food” is measure by BOD, or COD
  • The F/M “microorganism” is measured by MLSS or MLVSS
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37
Q

The extended aeration process is often used in these activated sludge plants.

A
  • Oxidation ditch treatment plants
    □ “Package” activated sludge treatment plants
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38
Q

Year-around nitrification may occur when an activated sludge plant is operated in this
loading range.

A

Extended aeration loading, F/M: 0.05 - 0.15

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39
Q

Factors that can cause a waste treatment pond to “short circuit.”

A
  • Excessive growth of aquatic weeds
  • Irregular pond bottom
  • Poor arrangement of pond inlet and outlet
40
Q

Aquatic plants that are a nuisance or interfere with the proper operation of a waste
stabilization lagoon.

A
  • Cattails or rushes
  • Duckweed
  • Water lilies
41
Q

Conditions considered ideal for the operation of a waste stabilization pond

A
  • Warm climate conditions (increases biological activity)
  • Moderate breeze (aids oxygen transfer to pond surface)
    □ Bright sunlight (stimulates algae photosynthesis)
42
Q

Process control test most often used to determine the settling characteristics of activated
sludge.

A

Sludge Volume Index (SVI)

43
Q

Factors that would indicate a need to increase sludge wasting in the activated sludge
process

A
  • Appearance of dark brown, greasy/scummy foam on the aeration basin
  • F/M is too low
  • MCRT and/or sludge age is too high
44
Q

The characteristics of a good quality activated sludge

A

Light brown, with a slight musty odor

45
Q

The application of septic sewage to trickling filter may result in this

A

Trickling filter may emit severe odors

46
Q

Ponding may develop in a trickling filter due to these conditions

A
  • Uneven flow distribution over the surface of the trickling filter
  • Breakdown of the filter rock media
  • Excessive organic loading to the trickling filter
47
Q

Failure to adequately pump settled sludge from the secondary clarifier in a trickling filter
process could result in this.

A

Gasification of the sludge in the clarifier bottom, resulting in the rising sludge and/or
septic odor from the clarifier

48
Q

The function of the underdrain in a trickling filter.

A
  • Collect wastewater that has trickled down through the filter media
  • Provide air ventilation through the filter media
49
Q

The loading to a rotating biological contactor is measured in these units.

A

Pounds of Soluble BOD,/day/1000 sq ft of surface area

50
Q

It is important to maintain the rotation of a rotating biological contractor shaft because of
this.

A

If the shaft is stopped for prolonged periods, the shaft and bearing may become flattened
and permanently damaged

51
Q

Aerobic biological treatment process capable of at least 85% removal of BOD. and total
suspended solids.

A

Secondary treatment

52
Q

The end products produced when aerobic bacteria assimilate organic material.

A

Carbon dioxide and water

53
Q

A sludge volume index (SVI) that is in excess of 200 may result in this

A

Bulking conditions in the secondary filter

54
Q

This small fly may breed large numbers around trickling filters

A

The Psychoda fly

55
Q

This small fish is used to control mosquito larvae in waste stabilization ponds

A

The Gambusia minnow

56
Q

The underdrain in a trickling filter is designed to flow no more than 50% full, to provide
for this.

A

Adequate air ventilation to the trickling filter

57
Q

Techniques used by operators to minimize Psychoda fly populations around a trickling
filter.

A
  • Remove shrubs and/or brush adjacent to the trickling filter
  • Routinely open the trickling filter distributor arm endgates to flush the filter side walls
58
Q

A typical range for MLSS and D.O. in a conventional activated sludge plant.

A

□ MLSS: 1200 - 2000mg/L
□ D.O.: 1 - 3 mg/L

59
Q

MLSS and MLVSS are measured for the purpose of estimating this.

A

The population of active microorganisms in the activated sludge process

60
Q

Bacteria that can live in the presence or absence of free dissolved oxygen

A

Facultative

61
Q

Sludge volume index (SVI) of less than 100 could result in this

A

Too rapid settling, leaving “straggler” floc in the secondary clarifier

62
Q

Microorganisms associated with good quality activated sludge.

A
  • Predominate microorganisms: free swimming ciliates and stalked ciliates
  • Minor abundance: flagellates and amoeba
63
Q

Bubbles and/or rising sludge in an activated sludge secondary clarifier indicate this.

A

Denitrification is occurring in the secondary clarifier

64
Q

When these microorganisms are abundant, it normally indicates problems with the
activated sludge process.

A

An abundance of amoeba and flagellates

65
Q

Snow and ice cover on a waste treatment pond surface will have this effect on the oc and BODs level.

A

The pond BOD will increase due to poor surface oxygen transfer to the pond

66
Q

The pounds of oxygen produced by one pound of algae during a sunny day.

A

1.6 pounds of oxygen

67
Q

RBC

A

Rotating biological contactor

68
Q

RBC shafts are covered for these reasons

A

□ Protects media from sunlight UV damage
□ Provides insulation againstextreme cold temperatures
* Prevents algae growth
* Prevents intense rain fromstripping growth from media

69
Q

The most likely cause of massive sloughing of the biological slime growth from an RBC
shaft

A

Toxicity in wastewater, including extreme pH

70
Q

The function of the curved baffles placed between the center island and outside wall of an
oxidation ditch.

A
  • Deflect linear velocity around the end of the island
  • Provide uniform velocity throughout the cross sectional area of the ditch
  • Reduce the settling of solids along the inside radius of the curve
71
Q

Nitrification and denitrification normally occur in this secondary treatment process.

A

Activated sludge oxidation ditch treatment

72
Q

Oxygen concentration in an oxidation ditch can be controlled by adjusting this.

A

Controlling the water level in the ditch, which adjusts the submergence of the brush
aerators

73
Q

Activated sludge process modification best suited to provide adequatetreatment during
severe hydraulic overload conditions

A

Contact stabilization

74
Q

“Rule of thumb” for pounds of activated sludge produced per pound of BOD removed

A

0.5 lbof sludge produced/lb of BODs removed

75
Q

“Rule of thumb” for pounds of oxygen required to treat one pound of BOD.

A

1.0 lb0,/lb of BOD, removed

76
Q

Membrane biological reactor (MBR) characteristics:
solids - liquid separation occurs here
problems avoided
membranes utilized
removal efficiency

A

Membranes located in the aeration tank or in a separate tank replace the activated
sludge secondary clarifier
* Process not affected by sludge settleability problems (high SVI, filaments, etc.)
* Microfiltration and ultrafiltration membranes utilized
* Removal exceeds 95% BOD, and TSS

77
Q

Membrane terms:
Permeability
Flux

A
  • Ability of membrane surface to allow passage of water
  • Flow rate of water across membrane measured as gallons/day/ sq ftof membrane
    surface
78
Q

Memory aid for membrane filter types

A

Maryln “M-U-N-RO” The sequence is in order of increasingly smaller pore size.
* Microfiltration
* Ultrafiltration
* Nanofiltration
* Reverse Osmosis

79
Q
  • Microfiltration membranes:
    Pore size
    Application
    Material removed
  • Ultrafiltration membranes:
    Pore size
    Application
    Material removed
  • Nanofiltration membranes:
    Pore size
    Application
    Material removed
A
  • 0.1 - 2 micrometers, um
    □ Membrane biological reactor (MBR)
  • Suspended solids, bacteria
    □ 0.005 - 0.1 micrometers, um
  • Membrane biological reactor (MBR) 1
  • Suspended solids, protozoa, bacteria, viruses, large organic molecules
  • 0.0005 - 0.005 micrometers
  • Water treatment and wastewater reuse
  • Suspended solids, protozoa, bacteria, viruses, organics, hardness, iron and
    manganese
80
Q

RBC slime growth appearance:
Shaggy, brown-gray
White
Black

A
  • Shaggy, brown-gray … Healthy normal appearance of biofilm growth
  • White …………………………… Excess sulfide in wastewater promotes growth of
    sulfur bacteria Beggiatoa
  • Black …………………………… Oxygen starved or organically overloaded
81
Q

Activated Sludge parameters directly controlled by operators

A

□ D.O.
* Return rate
* Wasting rate

82
Q

Standard rate trickling filters:
hydraulic loading
organic loading
filter depth
recirculation
characteristic operation

A
  • Hydraulic loading … 25 - 100 gal/day/sq ft media
  • Organic loading……………….. 5 - 25 lb BOD/day/1 000 cu ft media
  • Filter depth……………………………
  • Recirculation ………………… no
  • Characteristic operation
    1. Sloughing occurs intermittently (fall and spring)
    2. Sloughed solids are dense and settle readily
    3. Nitrification occurs during warm weather conditions
    4. Psychoda flies are common problem
83
Q

High rate trickling filters:
hydraulic loading
organic loading
filter depth
recirculation
characteristic operation

A

□ Hydraulic loading 100 - 1000 gal/day/sq ft media
* Organic loading ………………… 25 - 100 lb BOD/day/lOOO cu ft of media
* Filter depth……………………….. 3 - 5 ft
* Recirculation……………………… yes, a portion of filter effluent is recirculated back to filter influent
* Characteristic operation:
l. Sloughing is uniform and continuous
2. Sloughed solids are light and low density. Effluent is typically turbid with TSS.
3. Nitrification does not occur
4. Filter odors occur when filter is organically overloaded
5. Filter ponding can occur when organically overloaded or uneven flow distribution results from plugged
distributor arm orifices

84
Q

Roughing filters:
organic loading
characteristic operation

A
  • Organic loading
    greater than 100 lb BOD/day/lOOO cu ft media
  • Characteristic operation
    Used to reduce or trim the organic loading to a downstream treatment process. Often used when strong
    industrial wastes are part of the wastewater influent.
85
Q

Trickling filter ponding: causes and cures

A

Causes:
* Debris accumulation on filter surface from poor or missing primary clarification
* Filter media too small or non-uniform
* High organic loading followed by massive sloughing of filter growth

Cures:
* Breakup and flush clogging with a high pressure hose on the media surface
* Physically rake filter media surface and remove accumulated debris
* Dose the filter with chorine (5 mg/L) for several hours
* Flood the filter (submerge the media) for 24 hours to cause growth to slough stop flow to the filter for 1-2
days to allow the growth to dryout

86
Q

RBC loss of treatment efficiency and/or excess sloughing

A
  • Organic or hydraulic overloading
  • Toxic influent wastewater, (industrial chemicals, including extreme pH)
  • Shockhydraulic or organic loading
  • Extreme cold weather causing influent temperature drop
87
Q

Filter fly (Psychoda fly) causes and cures

A

Causes:
* Common problem in low ratefilters due to inadequate hydraulic flushing volumes
* May be problem in high rate filters if flow distribution is uneven due to plugged orifices

Cures:
* Increase the recirculation rateor add additional filter pumps to increase flushing hydraulics
* Use insecticide around filter perimeter and filter wall
* Flood filter for 24 hr to disrupt fly life cycle in the eventof infestation
* Remove shrubs, weeds and tall grass around filter perimeter

88
Q

These solids pass through a wastewater treatment plant largely unchanged.

A

Dissolved Solids

89
Q

This problem may occur in the clarifier if nitrification is occurring in the aeration basin

A

Denitrification producing bubbles and rising / rafting sludge in the secondary clarifier

90
Q

Natural ventilation in a trickling filter.

A

Ventilation is designed to flow upward as ambient air is warmed by the wastewater

91
Q

Common wastewater lagoon algae.

A

Chlorella, Chlamydomonas, and Euglena

92
Q

Why constant rate return activated sludge is not recommended

A
  • During low influent flows the return rate is excessive - does not produce adequate
    blanket level for proper thickening

□ During peak influent flows the return rate is inadequate - pushing excessive biological
solids to the clarifier when they are needed in the aeration basin to stabilize the organic
load in the influent. In addition, thehigher sludge blanket can threaten clarifier
performance during peak flow.

93
Q

Return activated sludge flow rate control methods

A
  • Constant rate - not recommended
  • Percent of influent flow - most common
  • Adjusted to match settled sludge concentration ratio (percent settleometer sludge at 60
    minutes settling)
94
Q

Sludge Volume Index:
Units of expression
Needed for calculation
Factors that can cause high (greater than 200) SVI
Clarifier response to high SVI

A

Sludge Volume Index:
* ml/ gram MLSS
* 30 min. settle volume and MLSS
* High F/M, high organic load, young sludge age, excessive filament growth in mixed liquor floc
* Clarifier may undergo bulking and solids loss over the weirs

95
Q

Five steps common to all Sequencing Batch Reactors (SBRs)

A
  • iF …………………………. Influent vastewater added
  • React ………………. Aeration c nixed Iquor
  • Settle ……………….. MLSS ©ttle to leave clear supernate
  • Draw or decant . Clarified effluent is removed and sent to downstream disinfection
  • dle………………….. Portion c sttled sludge wasted from tank
96
Q

SBR process characteristics:
1. Operating principle
2. Optimum size
3. Why footprint is small
4. Operating flexibility
5. Necessary instrumentation
6. Important routine maintenance

A
  1. Operates on a sequential “fill and draw” principle
  2. Appropriate for small flows: 5 mgd or less
  3. No separate primary or secondary clarifier is required
  4. Process can be controlled to achieve biological nutrient removal of nitrogen and phosphorus
  5. Requires SCADA system for timing and control of treatment process
  6. Maintenance on monitoring instruments, controllers and valves

Wastewater (10 decks)

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