Lecture 6 P3 Flashcards
What are the objectives of municipal treatment?
to provide a potable supply of water, which is chemically and microbiologically safe for human consumption and to provide water that aesthetically acceptable (free from apparent turbidity, color, odor, and objectionable taste
What are the general considerations for selecting technology?
Water source (deep & shallow wells, rivers, and natural lakes)
and quality (depends on agricultural practices in the watershed, location of the municipal and industrial outfall sewers, river developments such as dams, and season of the year and climate conditions
as well as the drinking water standards
What are the two sources of water pollution? Explain them
Point source- (from a single identifiable source, ex from a factory, municipal sewer system, is easy to find, regulate, treat, and monitor)
Non point source (from a vast area (ex: agricultural runoff or industrial storm water, is hard to measure control, treat, and monitor
What are the seven characteristics of ground water as it pertains to water quality?
- higher levels of dissolved solids
- may contain an abundance of the minerals that can
contribute to hardness problems - low levels of dissolved oxygen
- constant cool temperature
- less vulnerable to contamination
- higher quality
- requires less intensive treatment than other types
of water
What are the seven characteristics of surface water as it pertains to water quality?
accumulates mainly as a result of direct runoff from
rain or snow
* it does not pick up the elevated levels of dissolved
minerals that contribute to water hardness
* for the most part, surface water is referred to as
“naturally soft”, although it is not mineral-free
* high turbidity and suspended solids
* more vulnerable to contamination
* rapid temperature fluctuations
* high levels of dissolved oxygen
What are common stages of drinking water treatment? (4)
Coagulation, flocculation, sedimentation
Filtration
Taste and odor control
Disinfection
What is coagulation?
a process consisting of the addition and mixing of a chemical
reagent to water to destabilize colloidal and fine solids suspended in water
(turbidity)
What is flocculation?
involves slow stirring to promote agglomeration of the destabilized
particles formed during coagulation
What is filtration?
some cities (including Calgary) filter water using fine sand,
gravel, and anthracite to remove non-settleable floc remaining after
chemical coagulation and sedimentation
How do you perform taste and odor control?
Activated carbon filters (charcoal) is used to
remove organic contaminants (taste and odor)
How do you perform disinfection?
Chlorination
What are four common drinking water treatment systems?
Iron and manganese removal (involves aeration)
Softening
Arsenic and nitrate removal
What is aeration?
It removes dissolved gases like H2S and volatile organic compounds
What is softening?
phosphate or lime/soda ash is added to water to ppt Ca and Mg
What happened in walkerton On 2000?
E coli entered the water system from manure that had been spread on a farm near their water wells, seven people died and more than 2300 became ill from drinking tap water
What are the types of microorganisms that causes disease?
Bacteria- E coli and salmonella cause food poisoning
Viruses- Hep A virus cause Hep A
Protozoa- giardia lambia causes giardiasis
What are the three disinfection techniques?
- Membrane Technology
- UV radiation
- Chemical methods
- a Ozonation
- b Chlorination
How does membrane technology work?
Water goes through microfiltrations (removes bacteria and suspended solids)
then ultrafiltration (removes viruses)
then nanofiltration (removes multivalent ions
then reverse osmosis (removes monovalent ions)
How does UV radiation work?
The UV energy attacks DNA/RNA, destroying pathogens
What are the advantages of UV radiation? (6)
UV disinfection is effective at inactivating most viruses, spores, and cysts
* No chemical is required
* There is no residual effect that can be harmful to humans or aquatic life
* UV disinfection is user-friendly for operators
* UV disinfection has a shorter contact time (approximately 20 to 30 seconds)
* UV disinfection equipment requires less space than other methods
What are the disadvantages of UV radiation?
Low dosages may not effectively inactivate some viruses, spores, and cysts
* A preventive maintenance program is necessary to control the fouling of tubes
* Turbidity and total suspended solids (TSS) in the wastewater can render UV disinfection
ineffective
* UV disinfection is not as cost-effective as chlorination
How does ozonation work?
ozone gas is generated onsite by discharge, it reacts with pollutants or generates radicals such as OH in the water, 10 min contact with concentrated O3 destroys bacteria and viruses
What are the downsides of ozonation?
It’s energy intensive to generate O3, and ha sa shirt half-life so there’s no residual protection
How does chlorination work?
CL in HOCL is in a +1 oxidation state which is readily reduced to CL-. HOCL diffuses through cell walls and oxidizes vital molecules.
What is the advantage of chlorination over other methods?
there is chlorine residually left
What is the disadvantage of chlorination?
There’s formation of disinfection by-products such as:
- haloacetic acids and haloacetonitriles
-chlorinated phenols and halomethanes (ex: chloroform)
How is chloroform produced through chlorination?
HOCL reacts with humic acids, and CCL3 group is displaced by OH in water to yield chloroform
What disinfection system has the lowest capital cost?
chlorination
What disinfection system has the lowest operating cost?
UV
What disinfection system has the best ease of installation and maintenance?
UV
What disinfection system has the least contact time required?
UV
What are the objectives of wastewater treatment (4)?
To remove from wastewater:
- Dissolved biodegradable organics (BOD)
- Suspended solids
- Pathogenic micro-organisms
- N and P removal if eutrophication is a concern
Draw schematic of municipal waste water treatment plant (Slide 30)
Slide 30
What is the purpose of the pre-treatment?
to remove debris, grit, and oily scum
- to avoid shock loadings
- to condition the wastewater for subsequent treatment processes
Why are coarse objects and grit removes during the pre-treatment?
because they:
Damage equipment
Reduce treatment efficieny
Clog pipes and meters
and interfere with the treatment process (such as digesters)
What happens during the screening in the pre-treatment? Why and what is used?
Large objects are removed, downstream mechanical equipment is protected, and mechanical bar screens are usually used to do this
What happens during the Pre-treatment Grit Removal?
Grit such as sand, broken glass, silt, and pebbles is removed in order to protect pump and avoid clogging pipes and channels
What happens during the flotation step of pre-treatment?
Fats, oils, and greases are removed using air flotation
What happens during the primary treatment of wastewater?
Solids are physically seperated from wastewater via sedmentation tanks
Are soluble pollutants removed in primary treatment?
No
How much BOD is removed by the primary treatment process?
30%
What is the purpose of the secondary treatment? What is removed during it?
The purpose of the secondary treatment is to remove BOD, COD and additional removal of TSS
It partially removes N, P, and heavy metal, some biological degradation of organic matter by oxidation and part of organic suspended solids
- reduced pathogens
How does biological treatment work?
In aerobic treatments, organic materials is degraded and theres a production of more biomass
In anaerobic treatments the organic matter is degraded and the biomass is reducted
What are the five phases of the aeration tank?
Lag phase
Exponential Growth Phase
Declining Growth Phase
Stationary Phase
Endogenous Phase
What is the goal of the aeration tank? How is this accomplished?
Goal is to maximize the number of microbes in the stationary growth phase to maximize BOD removal, this is done by
- good supply of aeration to support growth
- Appropriate retention time
- Waste loading to feed the microbes
- wasting of sludge to remove aging populations
What is the activated sludge aeration tank?
Aerated sewage containing aerobic microorganisms which help
to break down organic compounds in wastewater)
What happens during the secondary treatment?
Air is injected into the tank to accelerate biological degradation of organic matter
What are the costs and treatment efficiencys of the aeration tank?
high
What is advanced waste water treatment?
Any process/system after conventional secondary treatment to remove remaining contaminants
What are the purposes of advances wastewater treatment?
To meet stringent discharge limits
* To reclaim or reuse wastewater
What is the most popular source of wastewater to be used for reclamation?
Municipal wastewater
What is removed during AWT?
nitrogen
* phosphorus
* total dissolved solids and suspended solids
* micro-organisms and
* refractory organics
How do you remove phosphorus in AWT?
- Chemical precipitation
▪ Ferric chloride FeCl3 ,Alum Al2(SO4)3 and Lime Ca(OH)2
▪ Biological
How do you remove nitrogen in AWT?
- Nitrification/denitrification (Biological)
▪ Nitrification: oxidation of ammonia to NO3-
▪ Denitrification: convert NO3- to nitrogen gas under anoxic condition
▪ Ammonia stripping
What are the types of filtration in AWT?
- Granular filtration (multimedia filter)
▪ Membrane filtration
What is the carbon adsorption in AWT?
Remove persistent soluble organics (refractory organics- poorly biodegradables
What is the microorganism removal in AWT?
Target to kill pathogens using chemical processes (oxidation) – disinfection or
UV irradiation
What are advanced oxidation processes?
They mineralize the pollutants (CO2 & H2O as products)
Give two examples of AOP’s?
Hydrogen peroxide + UV
Ozone + UV
What has the highest oxidation potential?
the hydroxyl radical
What are the four things the choice of AOP’s depends on?
Effectiveness (doesn’t degrade atrazine)
Economics (treats only the wastes that resistant to the cheaper conventional treatment processes)
Operation and maintenance issues
Pathway (doesnt make more toxic byproducts)
What is sludge?
residues from wastewater treatment in the form of
liquid or semisolid, odious and difficult to manage
What are the objectives of sludge treatment (3)?
- Volume reduction
- Safe disposal
- Resource & reuse
How does sludge digestion work?
Through anaerobic digestion, there is a decomposition of sludge in the absence of oxygen to gaseous products, it reduces the mass of sludge.
What are the five ultimate disposals of sludge?
Land application
Landfilling
Ocean Disposal
Incineration
Deep Well Injection
Where is treated wastewater disposed?
Disposed into rives, lakes, seas and lands sometimes as irrigation or into soils and wetlands for additional treatment
Where is treated wastewater reused?
- Fire fighting, cleaning, cooling, steam generation
- Aquifer (groundwater) recharge
- For nutrient recovery – aquatic plants are allowed
to grow and then harvested for animal food - Others (habitat restoration)
