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ENVISCI > Lesson 5: Part 2 > Flashcards

Lesson 5: Part 2 Flashcards

1
Q

In addition to the CBOD and NBOD measures already presented, two other indicators are sometimes used to describe the oxygen demand of wastes. These are the:

A

Theoretical Oxygen Demand (ThOD)
Chemical Oxygen Demand (COD)

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2
Q

It is the amount of oxygen required to oxidize completely a particular organic substance, as calculated from simple stoichiometric considerations.

A

Theoretical Oxygen Demand (ThOD)

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3
Q

_____________ _______, however, for both the carbonaceous and nitrogenous components, tends to overestimate the amount of oxygen actually consumed during decomposition.

A

Stoichiometric analysis

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4
Q

What are the organic matter that resist biodegradation?

A

cellulose, phenols, benzene, and tannic acid

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5
Q

What are the other types of organic matter that are nonbiodegradable because they are toxic to microorganisms?

A

pesticides and various industrial chemicals

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6
Q

TRUE OR FALSE:

Some organic matter, such as pesticides and various industrial chemicals, resist biodegradation.

A

FALSE

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7
Q

TRUE OR FALSE:

Organic matter, such as cellulose, phenols, benzene, and tannic acid, are nonbiodegradable because they are toxic to microorganisms.

A

FALSE

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8
Q

It is a measured quantity that does not depend either on the ability of microorganisms to degrade the waste or on knowledge of the particular substances in question.

A

Chemical Oxygen Demand (COD)

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9
Q

In this test, a strong chemical oxidizing agent is used to oxidize the organics rather than relying on microorganisms to do the job.

A

COD test

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10
Q

This test is much quicker than a BOD test, taking only a matter of hours.

A

COD test

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11
Q

TRUE OR FALSE:

The BOD test is much quicker than a COD test, taking only a matter of hours.

A

FALSE

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12
Q

This test does not distinguish between the oxygen demand that will actually be felt in a natural environment due to biodegradation and the chemical oxidation of inert organic matter.

A

COD test

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13
Q

This test does not provide any information on the rate at which actual biodegradation will take place.

A

COD test

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14
Q

TRUE OR FALSE:

The measured value of COD is higher than BOD, though for easily biodegradable matter, the two will be similar.

A

TRUE

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15
Q

This test is sometimes used as a way to estimate the ultimate BOD.

A

COD test

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16
Q

The amount of dissolved oxygen in water is one of the most commonly used indicators of a __________.

A

river’s health

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17
Q

TRUE OR FALSE:

The amount of dissolved oxygen in water is one of the most commonly used indicators of a river’s health.

A

TRUE

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18
Q

As _________ drops below 4 or 5 mg/L, the forms of life that can survive begin to be reduced.

A

Dissolved Oxygen (DO)

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19
Q

In the extreme case, when these conditions exist, most higher forms of life are killed or driven off.

A

Anaerobic Conditions

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20
Q

These conditions then prevail, including floating sludges; bubbling, odorous gases; and slimy fungal growths.

A

Noxious Conditions

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21
Q

What are the five (5) factors that Affect the Among of Dissolved Oxygen (DO) in a River?

A

1) Oxygen demanding wastes remove dissolved oxygen (DO).

2) Photosynthesis adds DO during the day, but those plants remove oxygen at night.

3) The respiration of organisms living in the water as well as in sediments removes oxygen.

4) In addition, tributaries bring their own oxygen supplies, which mix with those of the main river.

5) In the summer, rising temperatures reduce the solubility of oxygen, while lower flows reduce the rate at which oxygen enters the water from the atmosphere.

6) In the winter, ice may form, blocking access to new atmospheric oxygen.

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22
Q

Oxygen demanding wastes remove __________.

A

dissolved oxygen (DO)

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23
Q

It adds DO during the day, but those plants remove oxygen at night.

A

Photosynthesis

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24
Q

TRUE OR FALSE:

The respiration of organisms living in the water as well as in sediments removes oxygen.

A

TRUE

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25
Q

They bring their own oxygen supplies, which mix with those of the main river.

A

Tributaries

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26
Q

TRUE OR FALSE:

In the summer, falling temperatures reduce the solubility of oxygen, while higher flows reduce the rate at which oxygen enters the water from the atmosphere.

A

FALSE

(rising, lower)

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27
Q

During this season, ice may form, blocking access to new atmospheric oxygen.

A

Winter

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28
Q

This can provide insight into the most important parameters that affect DO.

A

Simple Analysis

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29
Q

TRUE OR FALSE:

We should remember, however, that our results are only a first approximation to reality.

A

TRUE

30
Q

The simplest model of the oxygen resources in a river focuses on two key processes:

A

1) the removal of oxygen by microorganisms during biodegradation.

2) The replenishment of oxygen through reaeration at the liquid surface.

31
Q

In this simple model, it is assumed that there is a continuous discharge of waste at a given location on the river.

A

Point-Source Plug Flow Model

32
Q

In this simple model, as the water and wastes flow downriver, it is assumed that they are uniformly mixed at any given cross section of river, and it is assumed that there is no dispersion of wastes in the direction of flow.

A

Point-Source Plug Flow Model

33
Q

The rate of _______ at any point in the river is assumed to be proportional to the BOD remaining at that point.

A

deoxygenation

34
Q

It is often assumed to be the same as the (temperature adjusted) BOD rate constant obtained in a standard laboratory BOD test.

A

Deoxygenation Rate Constant

35
Q

For deep, ____________, this seems to be a reasonable approximation.

A

slowly moving rivers

36
Q

In these movements of streams, the approximation is less valid.

A

turbulent, shallow, rapidly moving streams

37
Q

Such _______ have deoxygenation constants that can be significantly higher than the values determined in the laboratory.

A

streams

38
Q

The rate at which oxygen is replenished is assumed to be proportional to the difference between the actual DO in the river at any given location and the saturated value of dissolved oxygen.

A

Reaeration

39
Q

The difference between the actual DO in the river at any given location and the saturated value of dissolved oxygen is called?

A

oxygen deficit

40
Q

It is very much dependent on the river conditions.

A

Reaeration Constant

41
Q

A fast-moving river will have a much _______________ than a sluggish stream or a pond.

A

higher reaeration constant

42
Q

Range of kr at 20°C (day-1) of small ponds and backwaters.

A

0.10—0.23

43
Q

Range of kr at 20°C (day-1) of sluggish streams and large lakes.

A

0.23—0.35

44
Q

Range of kr at 20°C (day-1) of large streams of low velocity.

A

0.35—0.46

45
Q

Range of kr at 20°C (day-1) of large streams of normal velocity.

A

0.46—0.69

46
Q

Range of kr at 20°C (day-1) of swift streams.

A

0.69—1.15

47
Q

Range of kr at 20°C (day-1) of rapids and waterfalls.

A

> 1.15

48
Q

The saturated value of dissolved oxygen varies with __________, _________, and ________.

A

temperature, atmospheric pressure, and salinity

49
Q

Both the wastewater that is being discharged into a stream and the stream itself are likely to have some ________.

A

oxygen deficit

49
Q

TRUE OR FALSE:

Both the wastewater that is being discharged into a stream and the stream itself are likely to have some dissolved oxygen.

A

FALSE

(oxygen deficit)

50
Q

TRUE OR FALSE:

The oxygenation caused by microbial decomposition of wastes and deoxygenation by reaeration are competing processes that are simultaneously removing and adding oxygen to a stream.

A

FALSE

51
Q

What are the two (2) competing processes that are simultaneously removing and adding oxygen to a stream.

A

Deoxygenation
Oxygenation

52
Q

It is caused by microbial decomposition of wastes.

A

Deoxygenation

53
Q

It is caused by reaeration.

A

Oxygenation

54
Q

It is the difference between the saturation value of dissolved oxygen and the actual value.

A

Deficit

55
Q

When was the classic Streeter-Phelps oxygen sag equation first described?

A

1952

56
Q

This equation was first described in 1925.

A

Streeter-Phelps Oxygen Sag Equation

57
Q

At the _________ downstream, dissolved oxygen reaches its minimum value and river conditions are at their worst.

A

critical point

58
Q

Beyond this point, the remaining organic matter in the river has diminished to the point where oxygen is being added to the river by reaeration faster than it is being withdrawn by decomposition, and the river begins to recover.

A

Critical Point

59
Q

TRUE OR FALSE:

Beyond the critical point, the remaining organic matter in the river has diminished to the point where oxygen is being added to the river by reaeration slower than it is being withdrawn by decomposition, and the river begins to recover.

A

FALSE

(faster)

60
Q

When this rate exceeds the rate of reaeration, the DO in the river drops.

A

Rate of Deoxygenation

61
Q

When the rate of deoxygenation exceeds this rate, the DO in the river drops.

A

Rate of Reaeration

62
Q

At the critical point, those rates are equal.

A

Rate of Reaeration
Rate of Deoxygenation

63
Q

Beyond the critical point, it exceeds decomposition, the DO curve climbs toward saturation, and the river recovers.

A

Reaeration

64
Q

It can then be found by substituting the value obtained for the critical time into the Streeter-Phelps oxygen sag equation.

A

Maximum Deficit

65
Q

This curve should make some intuitive sense, even without the mathematical analysis.

A

Oxygen Sag Curve

66
Q

TRUE OR FALSE:

Near the outfall, there is so much organic matter being degraded that the rate of removal of oxygen from the water is higher than the rate that it can be returned by reaeration, so the dissolved oxygen drops.

A

TRUE

67
Q

TRUE OR FALSE:

As we move further downstream, more and more organic matter remains, so the rate of removal of oxygen keeps dropping as well.

A

FALSE

(less and less)

68
Q

As we move further downstream, less and less organic matter remains, so this rate keeps dropping as well.

A

Rate of Removal of Oxygen

69
Q

At this point, the rate of removal of oxygen equals the rate of addition of oxygen by reaeration.

A

Critical Point

70
Q

Beyond the critical point, it begins to dominate, returning oxygen to the river at a faster rate than the bacteria remove it, so the dissolved oxygen begins to climb back to the saturation value.

A

Reaeration

ENVISCI (7 decks)

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