Wastewater Flashcards
Water is a universal _______________
universal solvent
most abundant element on earth
Why do we treat waste water?
To accelerate the natural purification process of water.
Water self recycles, however humans are easily polluting more water than they can purify.
What is a sanitary sewer system
The underground carriage system that transports sewage to the treatment or disposal
Fraction of US population that is on an individual sewage disposal system
1/3
Most sewer systems move waste products at what rate?
two feet per second or faster
Ideal sewage systems move waste products to the treatment facility within _____ days
within 2 days
Manholes are placed every ________ feet apart in a sewage system to ___________
300-500 feet
to monitor for sewage leaks
Heaviest flow of sewage through the waste water treatment plant is during what hours?
3-9 PM
What are the 5 types of waste water
domestic waste industrial waste ground water storm drain runoff municipal waste
What is domestic waste
sanitary waste out of a home, business or institution
What is industrial waste
from a manufacturing plant, hospital, restaurant etc.
What is ground water waste
ground water can infiltrate into the sewer system by cracks in the sewer pipe
What is storm drain runoff
water from rainstorms and runoff from the streets
What is municipal waste
Any sewage or waste water that is going to be treated. Can be sewage from both domestic and plant sources)
Define leachate
Water that has percolated through a solid and leach out some of the constituents
What percent of raw waste water is solids?
- 2%
98. 8% water
What is gray water
a term for fresh waste water
What is septic water
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.
What percentage of solids in waste water are organic vs inorganic
75% organic
25% inorganic
Average pH of wastewater
6-9
What are the 3 temperature zones of bacteria
Thermophillic zone
Mesophillic zone
Psychrophillic zone
What is the thermophillic zone
hot zone. bacterial grow in 113F to 158F
what is the mesophillic zone
medium zone. bacteria grow in 59F to 112F
What is the psychrophilic zone
cold zone. bacteria grow 35F to 50F
What are saprophytic bacteria
bacteria that feed on all types of dead organic matter
What percent of pathogens die off within 10 hours of being in waste water?
40%
What is anoxia
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
What does absorption mean
something is taken into the material
What does adsorption mean
something adheres to the material
What is the weight in lbs of one gallon of water
8.34 lbs
One cubic foot of water contains how many gallons?
7.48 gallons
What is the main purpose of waste water disposal
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.
What is effluent
The waste water going into the treatment plant
What are the treatment steps
preliminary treatment
primary treatment
secondary treatment
tertiary treatment
What is the communitor?
A heavy duty garbage disposal that grinds up the solids from the bar screens.
What are most of the solids in waste water?
paper and rags
What are grit chambers
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
Where is the grit disposed of?
a sanitary landfill
Primary treatment removed what percent of BOD
40%
What is secondary treatment
BIOLOGICAL process that removes another 55% of the BOD
What is BOD?
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.
What is the maximum dissolved oxygen concentration in water at 40F?
10mg/l
If left untreated, raw sewage can use up _____mg/l of dissolved oxygen to purify itself
21 mg/l
What is the BOD test
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
BOD is (high/lower) in summer?
BOD is higher. Sewage is stronger.
Quality of waste water is judged by what three qualities?
BOD
Total Solids
Volatile Solids
treatment reduces all three
What is chemical flocculation/coagulation
A process that clumps up harder to settle solids. Alum, polymers and bentonite are often used. Chemical method of flocculating/coagulating.
What is an aeration tank?
A way to oxygenate the waste water. This is the biological method of flocculating/coagulating.
What is a trickling filter or bio-filter
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
What are the two ways to flocculate/coagulation?
Chemically (mix chemicals in)
Biologically (aeration tank)
What are some of the things that can occur in tertiary treatment?
rapid sand filter chlorine treatment activated charcoal filtration (removes odor and chemicals) ozone disinfection UV light disinfection nitrate and phosphate removal.
How does aeration work?
Adding oxygen activates growth of aerobic bacteria. The bacteria grow and clump together (aka flocculate) and they get heavier and sink to the bottom.
Three types of sand filters
intermittent
slow
rapid
Intermittent sand filter
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
slow sand filter
24’’ of increasing sand sizes and then 15-24’’ of gravel particles
.4 to .8mm sand size
1/8’’ to 2’’ gravel particle size
rapid sand filter
anthracite coal (a form of activated charcoal) then gravel. expensive but works quickly and well.
in extremely large systems which is used more? aeration or filtration?
aeration
Average americans use how many gallons of water per day for personal use
50-100 gallons
What are two pathogenic bacteria known to survive up to two weeks in wastewater?
typhoid and dysentery
What are 4 ways that waste water is reintroduced into the environment
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)
Preliminary Treatment - Name 5 concepts
Bar screening grit removal pre-aeration - helps remove oil and scum flow meter chlorine - can be used for highly active wastewater
What are bar screens
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
What is primary treatment
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
What is secondary treatment
further removal of solids and dissolved solids by biological, chemical and physical treatments
bio-filtration
flocculation/coagulation
What is tertiary treatment?
Further use of filters to remove particles, color and odors.
Disinfection
Waste water leaves the treatment plant
Tertiary treated water is considered by many to be what type of water?
drinking water
What is a scum skimmer
device used in primary treatment to remove scum, foam and oil that is floating in the waste water
What are sedimentation or clarification tanks
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.
Treating waste water increases or decreases the BOD?
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.
Water holds more dissolved oxygen at warmer or cooler temperatures?
holds more at cooler temperatures
What are the two main types of filters used in waste water treatment
sand filters
bio-filtersr
How long does waste water typically remain in an aeration tank?
4 hours.
The solids that accumulate at the bottom of an aeration tank are called what?
raw sludge
What is a stabilization pond?
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
What is reclaimed water?
Water that has gone through tertiary treatment and can be recycled for use. At this time it’s only used for irrigation purposes.
The pipes that carry reclaimed water are what color?
purple
What are the two most common treatments at the tertiary level?
filtration through activated charcoal and chlorination
Why can’t tertiary treated water be drinking water?
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.
What is eutrophication?
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.
What are the three types of sludge?
raw sludge
activated sludge
digested sludge
What is raw sludge
Sludge from sedimentation and aeration tanks.
fresh sludge.
most reactive.
has not begun to decay.
What is activated sludge?
aka: mixed liquor
When raw sludge is mixed with bacteria that will break it down into CO2, water and inorganic materials (phosphates and nitrates)
What is digested sludge
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
What is a digester?
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.
What is the “healthy state” of digestion
When the ideal percentages of gases are produced.
methane CH4 65%
CO2 34%
H2S Hydrogen Sulfide Gas less than 1%
What is a sick state of sludge
When the gas percentages are not ideal. Usually when Hydrogen sulfide gas is more than 1%. a perfect balance must be maintained
What is humus
organic matter which is anaerobically digested into inorganic material.
it’s an excellent soil conditioner
Sludge incineration
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.
What are some alternative disposal systems?
pit privy
cesspools
seepage pits
septic tank system
What is a pit privy
most primitive method. simple hole dug in the ground. should only be used for emergency
What is a cesspool
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”
If cesspool wastewater is “treated” then it would be called a ________
seepage pit
What is a septic tank system
Preferred domestic treatment of sewage if one can’t connect to the municipal sewer system.
consists of the septic tank and leach fields.
Describe the typical septic tank construction
concrete box placed underground. Raw sewage from the house goes directly into the tank.
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?
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
What are the advantages of a septic tank
- stores solids on the bottom of the tank
- anaerobic environment promotes decomposition
- sedimentation pumped out periodically
What are some disadvantages to a septic tank
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
How often should septic tanks be pumped?
every 3 years at least.
A two bedroom house should have a minimum septic tank size of
750 gallons
A 3 bedroom house should have a minimum septic tank size of
1,000 gallons
From a well, a septic tank must be ____feet away and a leach field must be ___ feet away
50 feet from tank
100 feet from leach field
What is the purpose of the perc test?
to check the ground is suitable to absorb waste water. checking the porosity of the soil.
Do bacterial levels decline or incline as soil levels grow deeper
Bacterial levels decline
Typically there are no bacterial at ____ feet and below the surface level
7 -10 feet below
What is an auger?
A tool used to dig a hole for a perc test
Shape of hole for a perc test
2 to 3 feet
4 to 12 inches wide
two inches of gravel on bottom
What is a saturation period?
When water is placed in the perc test hole for 24 hours prior to the test.
How many inches of water are placed for the perc test after the saturation period?
12’’ over the gravel
For how many hours is the test water observed and how often are measurements taken?
4 hours
measurements every 30 minutes
during the test how many inches of water must maintain in the test hole?
6’’ of water
How are the test results recorded?
time it takes for 1’’ of water to fall
1 minute per inch fall requires ____ sq ft disposal area per bedroom
1 minute requires 70 sq ft of disposal area per bedroom
5 minute per inch fall requires ____ sq ft disposal area per bedroom
125 sq ft
15 minutes per inch fall requires ____ sq ft disposal area per bedroom
190 sq ft
Would a perc rate of 60 minutes allow for a disposal trench?
no. over 60 minutes is unsuitable for a proper waste water disposal area
30 minutes perc result requires ___ sq ft per bedroom
250 ft per bedroom
Describe the construction of leach lines
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
What is a distribution or junction box
where effluent is diverted into different areas of the absorption field
A single leach line should typically not exceed what length?
100 feet long
The slope of leach lines should be what?
6’’ for every 100 foot distance
What is a tracer dye
fluorescent dye to detect direct sewage leaks.
usually green or orange tables placed in sink drain or toilet to detect for leaks.
Why would pH meters be used throughout some sanitary sewer systems?
to detect for illegal hazmat dumping
What do the following pipe colors indicate
red yellow green blue purple white
red - electrical yellow - steam, gas or oil green - sewer blue - potable water purple - reclaimed water white - leach line
Soil Type I is composed of what? Is it good for leach lines?
sand with a little silt. excellent for subsurface systems
What are soil types IV and V made up of? Are they good for sewage disposal?
mostly clay. Not suitable because of the low absorption capacity.
Septic tank effluent goes to either ______ or _______
leach lines or seepage pit
absorption field typical dimensions
12-18’’ deep and 12-36’’ wide
The bottom of leach trenches must be how many inches above the ground water level
at least 24’’
When would seepage pits be used over leach lines?
when ground water table is very deep and area is limited in size or inadequate. can be 20 feet deep.
What is a sand filter
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.
The wastewater from the flushing of a water closet, latrine or privy is referred to as______
gray water
black water
green water
brown water
black water
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
tank my float out of the ground
Nutrient associated with eutrophication include all of the following except:
organic carbon
potassium
nitrogen
phosphates
potassium
Which of the following is least important when reducing sewage to gases?
anaerobic bacteria
earthworms
protozoa
aerobic bacteria
anaerobic bacteria
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
no, because oxygen and methane content were not tested
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
long-lasting residual
Aerobic bacteria require all of the following nutrients except:
carbon
magnesium
phosphorus
nitrogen
magnesium
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
inadequate aeration methods
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
impervious formations are found at a depth of 10 feet
Lime coagulation, mixed media filtration, and activated carbon filtration will greatly reduce:
heavy metals
biological contaminants
EPA priority pollutants
EPA listed hazardous wastes
EPA priority pollutants
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
2 years
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
remove rain and other standing surface water
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 zone of degradation
A young lake is considered to be:
eutrophic
mesotrophic
oligotrophic
ohytrotrophic
oligotrophic (low levels of nutrients)
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
size of tank should be increased 50 percent
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
18 to 21 gals per person per year
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
Every 3 to 5 years
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
may be caused by very small numbers of organisms
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
cadmium
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
replaced and secured for safety reasons
