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REHS Study > Wastewater > Flashcards

Wastewater Flashcards

1
Q

Water is a universal _______________

A

universal solvent

most abundant element on earth

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2
Q

Why do we treat waste water?

A

To accelerate the natural purification process of water.

Water self recycles, however humans are easily polluting more water than they can purify.

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3
Q

What is a sanitary sewer system

A

The underground carriage system that transports sewage to the treatment or disposal

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4
Q

Fraction of US population that is on an individual sewage disposal system

A

1/3

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5
Q

Most sewer systems move waste products at what rate?

A

two feet per second or faster

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6
Q

Ideal sewage systems move waste products to the treatment facility within _____ days

A

within 2 days

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7
Q

Manholes are placed every ________ feet apart in a sewage system to ___________

A

300-500 feet

to monitor for sewage leaks

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8
Q

Heaviest flow of sewage through the waste water treatment plant is during what hours?

A

3-9 PM

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9
Q

What are the 5 types of waste water

A 
domestic waste
industrial waste
ground water
storm drain runoff
municipal waste
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10
Q

What is domestic waste

A

sanitary waste out of a home, business or institution

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11
Q

What is industrial waste

A

from a manufacturing plant, hospital, restaurant etc.

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12
Q

What is ground water waste

A

ground water can infiltrate into the sewer system by cracks in the sewer pipe

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13
Q

What is storm drain runoff

A

water from rainstorms and runoff from the streets

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14
Q

What is municipal waste

A

Any sewage or waste water that is going to be treated. Can be sewage from both domestic and plant sources)

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15
Q

Define leachate

A

Water that has percolated through a solid and leach out some of the constituents

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16
Q

What percent of raw waste water is solids?

A
  1. 2%

98. 8% water

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17
Q

What is gray water

A

a term for fresh waste water

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18
Q

What is septic water

A

Black colored waste water with rotten egg smell (hydrogen sulfide) undergoing decomposition. waste water becomes septic when it is not moving and anaerobic decomposition occurs.

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19
Q

What percentage of solids in waste water are organic vs inorganic

A

75% organic

25% inorganic

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20
Q

Average pH of wastewater

A

6-9

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21
Q

What are the 3 temperature zones of bacteria

A

Thermophillic zone
Mesophillic zone
Psychrophillic zone

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22
Q

What is the thermophillic zone

A

hot zone. bacterial grow in 113F to 158F

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23
Q

what is the mesophillic zone

A

medium zone. bacteria grow in 59F to 112F

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24
Q

What is the psychrophilic zone

A

cold zone. bacteria grow 35F to 50F

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25
Q

What are saprophytic bacteria

A

bacteria that feed on all types of dead organic matter

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26
Q

What percent of pathogens die off within 10 hours of being in waste water?

A

40%

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27
Q

What is anoxia

A

an absence of oxygen. waste water is said to be anoxic when the dissolved oxygen level falls below 4mg/l

Anoxic waters can no longer support fish life

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28
Q

What does absorption mean

A

something is taken into the material

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29
Q

What does adsorption mean

A

something adheres to the material

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30
Q

What is the weight in lbs of one gallon of water

A

8.34 lbs

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31
Q

One cubic foot of water contains how many gallons?

A

7.48 gallons

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32
Q

What is the main purpose of waste water disposal

A

To keep a certain level of dissolved oxygen in the waste water during the treatment process. You don’t want the water to become septic.

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33
Q

What is effluent

A

The waste water going into the treatment plant

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34
Q

What are the treatment steps

A

preliminary treatment
primary treatment
secondary treatment
tertiary treatment

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35
Q

What is the communitor?

A

A heavy duty garbage disposal that grinds up the solids from the bar screens.

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36
Q

What are most of the solids in waste water?

A

paper and rags

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37
Q

What are grit chambers

A

Part of preliminary treatment

They slow down the velocity of the waste water to allow heavier solids to settle out quickly.

Usually consists of 2 chambers

removes grit and sand

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38
Q

Where is the grit disposed of?

A

a sanitary landfill

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39
Q

Primary treatment removed what percent of BOD

A

40%

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40
Q

What is secondary treatment

A

BIOLOGICAL process that removes another 55% of the BOD

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41
Q

What is BOD?

A

Biological oxygen demand. It’s a measurement of raw sewage strength. The strength of sewage is dependent upon the oxidation reduction potential of the bacteria in the sewage.

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42
Q

What is the maximum dissolved oxygen concentration in water at 40F?

A

10mg/l

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43
Q

If left untreated, raw sewage can use up _____mg/l of dissolved oxygen to purify itself

A

21 mg/l

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44
Q

What is the BOD test

A

measures BOD. It’s measured over 5 days period at 20C to determine strength of or potency of sewage.

higher BOD = more oxygen is being used = stronger sewage

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45
Q

BOD is (high/lower) in summer?

A

BOD is higher. Sewage is stronger.

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46
Q

Quality of waste water is judged by what three qualities?

A

BOD
Total Solids
Volatile Solids

treatment reduces all three

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47
Q

What is chemical flocculation/coagulation

A

A process that clumps up harder to settle solids. Alum, polymers and bentonite are often used. Chemical method of flocculating/coagulating.

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48
Q

What is an aeration tank?

A

A way to oxygenate the waste water. This is the biological method of flocculating/coagulating.

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49
Q

What is a trickling filter or bio-filter

A

rotary arm sprays waste water over plastic filter beds (use to be rocks). large surface areas have aerobic organisms that consume and oxidize organic wastes. Water trickles down.

can handle 10-30 million gallons/acre/feet/per day

good for large volumnes, large system.

waste water must be carefully maintained as high concentrations of hazardous chemicals can kill off the beneficial bacteria

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50
Q

What are the two ways to flocculate/coagulation?

A

Chemically (mix chemicals in)

Biologically (aeration tank)

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51
Q

What are some of the things that can occur in tertiary treatment?

A 
rapid sand filter
chlorine treatment
activated charcoal filtration (removes odor and chemicals)
ozone disinfection
UV light disinfection
nitrate and phosphate removal.
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52
Q

How does aeration work?

A

Adding oxygen activates growth of aerobic bacteria. The bacteria grow and clump together (aka flocculate) and they get heavier and sink to the bottom.

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53
Q

Three types of sand filters

A

intermittent
slow
rapid

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54
Q

Intermittent sand filter

A

sand bed inside shallow trough. 30’’ varied media from sand to gravel

filtration rate of 100,000 acre/feet/per day for 24 hours.

typically facilities have three and they are used one at a time for 24 hours then shut down for 48 so the filter can reabsorb oxygen and maintain it’s aerobic environment

good for smaller systems.

can clog easily and messy to clean

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55
Q

slow sand filter

A

24’’ of increasing sand sizes and then 15-24’’ of gravel particles

.4 to .8mm sand size
1/8’’ to 2’’ gravel particle size

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56
Q

rapid sand filter

A

anthracite coal (a form of activated charcoal) then gravel. expensive but works quickly and well.

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57
Q

in extremely large systems which is used more? aeration or filtration?

A

aeration

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58
Q

Average americans use how many gallons of water per day for personal use

A

50-100 gallons

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59
Q

What are two pathogenic bacteria known to survive up to two weeks in wastewater?

A

typhoid and dysentery

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60
Q

What are 4 ways that waste water is reintroduced into the environment

A

surface disposal (no longer allowed)
tile fields disposal - shallow in ground disposal
subsurface disposal - leach lines 2-5 feet underground
dilution disposal - into large body of nearby water (no longer allowed)

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61
Q

Preliminary Treatment - Name 5 concepts

A 
Bar screening
grit removal
pre-aeration - helps remove oil and scum
flow meter
chlorine - can be used for highly active wastewater
62
Q

What are bar screens

A

Used in preliminary treatment

metal grates with bars spaced 1-3 inches.

removes paper, rags, roots, refuse debris, and any other large objects entering the treatment plant

63
Q

What is primary treatment

A

influent now enters treatment facility. The main thing that happens in primary treatment is sedimentation. solids and floating debris are removed.

also happening:

scum/foam/oil removal
flocculation/coagulation

64
Q

What is secondary treatment

A

further removal of solids and dissolved solids by biological, chemical and physical treatments

bio-filtration
flocculation/coagulation

65
Q

What is tertiary treatment?

A

Further use of filters to remove particles, color and odors.

Disinfection

Waste water leaves the treatment plant

66
Q

Tertiary treated water is considered by many to be what type of water?

A

drinking water

67
Q

What is a scum skimmer

A

device used in primary treatment to remove scum, foam and oil that is floating in the waste water

68
Q

What are sedimentation or clarification tanks

A

part of primary treatment. tanks where solids and suspended particles are settled to the bottom and removed.

sludge is the term for what settles out at the bottom. chemical additives can be used to help flocculate fine particles.

69
Q

Treating waste water increases or decreases the BOD?

A

decreases the BOD. if there is less demand for dissolved oxygen by aerobic bacteria than there is more dissolved oxygen to support life to the water and it can then be recycled.

70
Q

Water holds more dissolved oxygen at warmer or cooler temperatures?

A

holds more at cooler temperatures

71
Q

What are the two main types of filters used in waste water treatment

A

sand filters

bio-filtersr

72
Q

How long does waste water typically remain in an aeration tank?

A

4 hours.

73
Q

The solids that accumulate at the bottom of an aeration tank are called what?

A

raw sludge

74
Q

What is a stabilization pond?

A

Can be part of tertiary treatment to further purify the water source.

shallow pond 3 to 5 feet. promotes aerobic activity.

aka: lagoonization.

shallow depths promote temperature mixing and aeration.

water will remain here for 45 to 60 days, thus it’s only practical for smaller systems

75
Q

What is reclaimed water?

A

Water that has gone through tertiary treatment and can be recycled for use. At this time it’s only used for irrigation purposes.

76
Q

The pipes that carry reclaimed water are what color?

A

purple

77
Q

What are the two most common treatments at the tertiary level?

A

filtration through activated charcoal and chlorination

78
Q

Why can’t tertiary treated water be drinking water?

A

Although it can sometimes be more physically attractive than tap water, it may still have some viruses, so it can only be used for irrigation.

79
Q

What is eutrophication?

A

an enrichment of nutrients, typically phosphate and nitrate. The over abundance of these nutrients leads to huge algal blooms which can deplete dissolved oxygen in water.

80
Q

What are the three types of sludge?

A

raw sludge
activated sludge
digested sludge

81
Q

What is raw sludge

A

Sludge from sedimentation and aeration tanks.

fresh sludge.

most reactive.

has not begun to decay.

82
Q

What is activated sludge?

A

aka: mixed liquor

When raw sludge is mixed with bacteria that will break it down into CO2, water and inorganic materials (phosphates and nitrates)

83
Q

What is digested sludge

A

The most stable version.

sludge has been totally digested. anaerobic bacteria have oxidized the organic matter.

resembles used coffee grounds.

can be added to soil

84
Q

What is a digester?

A

A huge tank for raw sludge treatment.

Sludge enters the tank and oxygen is removed to create an anaerobic environment.

heat is added to promote bacterial activity and digestion

acid forming anaerobic bacteria are added

as the sludge turns acidic, gas forming anaerobic bacteria take over digestion.

typically takes 21 days total.

85
Q

What is the “healthy state” of digestion

A

When the ideal percentages of gases are produced.

methane CH4 65%
CO2 34%
H2S Hydrogen Sulfide Gas less than 1%

86
Q

What is a sick state of sludge

A

When the gas percentages are not ideal. Usually when Hydrogen sulfide gas is more than 1%. a perfect balance must be maintained

87
Q

What is humus

A

organic matter which is anaerobically digested into inorganic material.

it’s an excellent soil conditioner

88
Q

Sludge incineration

A

Digested sludge can burn if most of the water is removed. HERS project in LA wanted to burn sludge for energy. Due to cost it hasn’t been in practice yet.

89
Q

What are some alternative disposal systems?

A

pit privy
cesspools
seepage pits
septic tank system

90
Q

What is a pit privy

A

most primitive method. simple hole dug in the ground. should only be used for emergency

91
Q

What is a cesspool

A

a vault in the ground where waste water seeps into the ground.

illegal to build, but legal to have if existing.

solids must be pumped out
too much liquid saturates the ground

sewage is not “treated”

92
Q

If cesspool wastewater is “treated” then it would be called a ________

A

seepage pit

93
Q

What is a septic tank system

A

Preferred domestic treatment of sewage if one can’t connect to the municipal sewer system.

consists of the septic tank and leach fields.

94
Q

Describe the typical septic tank construction

A

concrete box placed underground. Raw sewage from the house goes directly into the tank.

95
Q

What is the main purpose of the septic tank? How long does waste water remain in the tank (net time) for a single family capacity vs. a larger capacity?

A

Main purpose is to separate liquid from solids. solids fall to the bottom (sludge). solids floating on top are called scum.

single family waste water remains for 24 hours net time
larger systems hold waste water for 12 hours net time

96
Q

What are the advantages of a septic tank

A
  1. stores solids on the bottom of the tank
  2. anaerobic environment promotes decomposition
  3. sedimentation pumped out periodically
97
Q

What are some disadvantages to a septic tank

A

Sludge or scum can block off the system.

improperly operating system can over saturate the surrounding ground water causing system overflow

may not work properly due to poor design or poor soil porosity conditions

Will not work in areas with high ground water

98
Q

How often should septic tanks be pumped?

A

every 3 years at least.

99
Q

A two bedroom house should have a minimum septic tank size of

A

750 gallons

100
Q

A 3 bedroom house should have a minimum septic tank size of

A

1,000 gallons

101
Q

From a well, a septic tank must be ____feet away and a leach field must be ___ feet away

A

50 feet from tank

100 feet from leach field

102
Q

What is the purpose of the perc test?

A

to check the ground is suitable to absorb waste water. checking the porosity of the soil.

103
Q

Do bacterial levels decline or incline as soil levels grow deeper

A

Bacterial levels decline

104
Q

Typically there are no bacterial at ____ feet and below the surface level

A

7 -10 feet below

105
Q

What is an auger?

A

A tool used to dig a hole for a perc test

106
Q

Shape of hole for a perc test

A

2 to 3 feet
4 to 12 inches wide
two inches of gravel on bottom

107
Q

What is a saturation period?

A

When water is placed in the perc test hole for 24 hours prior to the test.

108
Q

How many inches of water are placed for the perc test after the saturation period?

A

12’’ over the gravel

109
Q

For how many hours is the test water observed and how often are measurements taken?

A

4 hours

measurements every 30 minutes

110
Q

during the test how many inches of water must maintain in the test hole?

A

6’’ of water

111
Q

How are the test results recorded?

A

time it takes for 1’’ of water to fall

112
Q

1 minute per inch fall requires ____ sq ft disposal area per bedroom

A

1 minute requires 70 sq ft of disposal area per bedroom

113
Q

5 minute per inch fall requires ____ sq ft disposal area per bedroom

A

125 sq ft

114
Q

15 minutes per inch fall requires ____ sq ft disposal area per bedroom

A

190 sq ft

115
Q

Would a perc rate of 60 minutes allow for a disposal trench?

A

no. over 60 minutes is unsuitable for a proper waste water disposal area

116
Q

30 minutes perc result requires ___ sq ft per bedroom

A

250 ft per bedroom

117
Q

Describe the construction of leach lines

A

leach pipes 2 to 3 feet under ground and sloping. holes on top and bottom for seepage.

6’’ of rock lie under the pipes. rocks with a minimum of 1.5 diameter

black construction paper is placed over the pipes to prevent soil from intrusion

118
Q

What is a distribution or junction box

A

where effluent is diverted into different areas of the absorption field

119
Q

A single leach line should typically not exceed what length?

A

100 feet long

120
Q

The slope of leach lines should be what?

A

6’’ for every 100 foot distance

121
Q

What is a tracer dye

A

fluorescent dye to detect direct sewage leaks.

usually green or orange tables placed in sink drain or toilet to detect for leaks.

122
Q

Why would pH meters be used throughout some sanitary sewer systems?

A

to detect for illegal hazmat dumping

123
Q

What do the following pipe colors indicate

red
yellow
green
blue
purple
white
A 
red - electrical
yellow - steam, gas or oil
green - sewer
blue - potable water
purple - reclaimed water
white - leach line
124
Q

Soil Type I is composed of what? Is it good for leach lines?

A

sand with a little silt. excellent for subsurface systems

125
Q

What are soil types IV and V made up of? Are they good for sewage disposal?

A

mostly clay. Not suitable because of the low absorption capacity.

126
Q

Septic tank effluent goes to either ______ or _______

A

leach lines or seepage pit

127
Q

absorption field typical dimensions

A

12-18’’ deep and 12-36’’ wide

128
Q

The bottom of leach trenches must be how many inches above the ground water level

A

at least 24’’

129
Q

When would seepage pits be used over leach lines?

A

when ground water table is very deep and area is limited in size or inadequate. can be 20 feet deep.

130
Q

What is a sand filter

A

an alternative system used in subsurface sewage treatment systems.

sand filters provide secondary waste water treatment after the septic tank and before the leach field.

131
Q

The wastewater from the flushing of a water closet, latrine or privy is referred to as______

gray water
black water
green water
brown water

A

black water

132
Q

If a septic tank is pumped during a wet period, the:

water may flow into the tank
field may flood the tank
tank may float out of the ground
tank may be crushed by the wet earth

A

tank my float out of the ground

133
Q

Nutrient associated with eutrophication include all of the following except:

organic carbon
potassium
nitrogen
phosphates

A

potassium

134
Q

Which of the following is least important when reducing sewage to gases?

anaerobic bacteria
earthworms
protozoa
aerobic bacteria

A

anaerobic bacteria

135
Q

A septic tank maintenance worker has checked an empty tank for the presence of H2S. The test was negative, and there are no odors indicating the presence of other hazardous gases. Is the tank safe to enter without a respirator and supplied air?

yes, because H2S and odors were not detected
no, because oxygen content and methane were not tested
yes, because absence of odors and H2S indicates acceptable confined space entry conditions
no, because a lack of H2S is a sign of a hazardous confined space atmosphere

A

no, because oxygen and methane content were not tested

136
Q

All of the following are true about ozone as a disinfectant except which one?

nontoxic to aquatic organisms
source of dissolved oxygen
excellent viricide
long-lasting residual

A

long-lasting residual

137
Q

Aerobic bacteria require all of the following nutrients except:

carbon
magnesium
phosphorus
nitrogen

A

magnesium

138
Q

What does a mottled brown and red soil indicate?

unsuitability for absorption due to chemical composition
suitability for absorption due to granular structure
inadequate aeration methods
adequate agglomeration

A

inadequate aeration methods

139
Q

Alternative small waste water treatment systems are considered unless:

impervious formation are found at a depth of 10 feet
space is limited and surface water supplies are inadequate
highly porous formations exist
high ground water exists

A

impervious formations are found at a depth of 10 feet

140
Q

Lime coagulation, mixed media filtration, and activated carbon filtration will greatly reduce:

heavy metals
biological contaminants
EPA priority pollutants
EPA listed hazardous wastes

A

EPA priority pollutants

141
Q

It is known that some common pathogenic organisms found in waste water will survive more than _______ of harsh temperature extremes

2 months
5 months
2 years
5 years

A

2 years

142
Q

A storm sewer is used to:

remove rain and other standing surface water
remove sewage and storm water
remove household water waste and gutter drain water
remove non-toxic, non-hazardous wastewater

A

remove rain and other standing surface water

143
Q

Stream pollution is sometimes apparent by:

increased levels of available oxygen in the water
a zone of degradation
large numbers of crayfish and cristivomer species
large numbers of small fish

A

a zone of degradation

144
Q

A young lake is considered to be:

eutrophic
mesotrophic
oligotrophic
ohytrotrophic

A

oligotrophic (low levels of nutrients)

145
Q

If a septic tank will also have a garbage disposal unit feeding into it the:

size of the tank should be increased 50 percent
tank should have an agitator
tank should not be equipped with a gas baffle
tank should not be constructed with precast concrete

A

size of tank should be increased 50 percent

146
Q

Sludge accumulation in a tank serving a normal home has been estimated at:

40 to 50 liters per person per year
69-80 gals per person per year
18-21 gals per person per year
2.2 gals per person per year

A

18 to 21 gals per person per year

147
Q

How often should a septic tank for a private home be serviced?

every year
every 5 to 10 years
every 3 to 5 years
every 10 years

A

Every 3 to 5 years

148
Q

Human diseases from aerosols of wastewater:

is primarily related to wastewater treatment by the activated sludge, trickling filter, and spray irrigation processes

has been demonstrated from pathogens recovered in aerosols from the spray irrigation of treated wastewater

may be caused by very small numbers of organisms

is a hazard even to those who have had subclinical infections, and thus should have been immunized

A

may be caused by very small numbers of organisms

149
Q

Plants absorb certain constituents of wastewater; using wastewater for irrigation of consumable plant products may present a health hazard to humans if the water contains

nitrates
iron
cadmium
chlorides

A

cadmium

150
Q

After servicing (pumping) a septic tank, it is essential that the tank or lid be:

cleaned with a bleach or chlorine product
scrubbed to remove hardened sludge
recolonized with a commercial biological product containing yeast
replaced and secured for safety purposes

A

replaced and secured for safety reasons

REHS Study (20 decks)

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