2. What is Wastewater Treatment?
īŽ Wastewater treatment is also referred to as
sewage treatment
īŽ Process of removing physical, chemical, and
biological contaminants from wastewater and
household sewage
īŽ Goal is to separate wastewater into:
īŽ Environmentally-safe fluid waste stream
īŽ Solid waste to be disposed or reused
4. What Needs to be Removed?
īŽ Wastewater may contain a variety of substances:
īŽ trash and debris
īŽ human waste
īŽ food scraps
īŽ oils
īŽ grease
īŽ soaps
īŽ chemicals (cleaning, pesticides, industrial)
īŽ pharmaceuticals and personal care products
http://www.westfield.ma.edu/personalpages/draker/edcom/final/webprojects/sp11/triparoundworld/Marine.html
5. What Needs to be Removed?
īŽ Wastewater from both domestic and industrial sources
may contain a variety of potentially harmful
contaminants, including:
īŽ Bacteria
īŽ E. coli (right), Giardia, Hepatatis A
īŽ Viruses
īŽ Nitrates
īŽ Metals
īŽ mercury, lead, cadmium, chromium, arsenic
īŽ Toxic materials
īŽ Salts
http://www.anh-usa.org/the-european-e-coli-outbreak-the-real-story/
6. Example 1: Concentration
īŽ A 4.2 mL wastewater sample was tested and
found to contain 7.6 ng of lead (II) ions. What
is the molarity of lead (II) ions in this solution?
7. Example 1 Solution
7.6 ng Pb x 10-9 g x 1 mol Pb x 1 mL soln
4.2 mL 1 ng 207.2 g Pb 10-3 L
= 9.1 x 10-9 mol/L
= 9.1 x 10-9 M Pb
8. Why Treat it?
īŽ The environment is able to naturally dilute and degrade
water contaminants, but only in small amounts
īŽ Wastewater
treatment reduces
pollutants to levels
that the
environment can
safely handle and
process
9. Why Treat it?
īŽ Decaying solid matter left in water consumes
dissolved oxygen from the water
īŽ Known as Biochemical Oxygen Demand (BOD):
the amount of dissolved oxygen needed by aerobic
organisms to break down organic matter
īŽ Lack of oxygen can kill plants and aquatic life
īŽ Excessive nutrients (nitrogen and phosphorous)
can also lead to deoxygenation
īŽ Increased plant and algae growth, which eventually
die and decompose, lead to an increased BOD
10. Process of Water Treatment
īŽ Water which enters a water treatment facility
undergoes a series of steps to cleanse the water
using physical, chemical, and biological
processes
īŽ Upon exiting the water treatment facility, the
decontaminated water is released into rivers or
streams, entering again into the environment
īŽ Sometimes used specifically for agriculture and
irrigation
īŽ Possible to purify into clean drinking water again
11. Steps of the Wastewater Treatment
Process
īŽ 1. Pretreatment
īŽ 2. Primary Treatment
īŽ 3. Secondary Treatment
īŽ 4. Tertiary Treatment
īŽ 5. Sludge Processing
13. Treatment Process
Step 1: Pretreatment
īŽ Prepares waste water for entering
the treatment plant
īŽ Removal of larger debris by
screening (shown right)
īŽ Trash
īŽ Tree limbs
īŽ Removal of grit and gravel by
screening and settling
īŽ Gravel must be removed early as it
can damage machinery and
equipment in the treatment plant
http://www.alard-equipment.com/wastewater/index.htm
14. Treatment Process
Step 2: Primary Treatment
īŽ In Primary Treatment, as much solid material is
removed as possible by relying on gravity
īŽ Removes most of the sludge and scum
īŽ Sludge: Organic and inorganic materials which will
naturally settle
īŽ removed by sedimentation
īŽ Scum: Materials which will float (oil, grease, soap)
īŽ removed by skimming
īŽ This step successfully removes 50 to 70% of suspended
solids and up to 65% of oil and grease
īŽ Colloidal and dissolved materials are not affected by
this step
15. Separation of Oil and Grease
īŽ Oil and grease will naturally separate from water due to
differences in polarity
īŽ This is also known as the hydrophobic effect
īŽ Water is considered a polar substance, while oils and grease are
considered nonpolar substances
īŽ A polar molecule is one in which
electrons are unevenly
distributed within the molecule
due to differing
electronegativities
īŽ Nonpolar molecules generally
have evenly distributed electrons
andhave no areas of partial
charges
http://novocreamseparators.com/blog/clean-separation/
16. Separation of Oil and Grease
īŽ Water molecules have regions of differing electron
density, making one end of the molecule have a
partially negative side, while the other is partially
positive
īŽ Water molecules are attracted to one another due to
attractions between these positive and negative regions
(hydrogen bonding) http://marineodyssey.co.uk/abioticoceans.html
http://bioweb.wku.edu/courses/biol115/Wyatt/Bonds.htm
17. Separation of Oil and Grease
īŽ Oil and grease are typically long chains of
hydrocarbons, making them nonpolar,
hydrophobic substances
īŽ Mixing a hydrophobic substance such as oil
into water disturbs the attractions between
polar water molecules
īŽ Hydrophobic substances tend to aggregate
together in water in order to minimize the
surface area that contacts the water which
minimizes the disturbance
īŽ Oils and grease rise to the top of water due
to a difference in density
http://en.wikibooks.org/wiki/Structural_Biochemistry/Chemical_Bonding/Hydrophobic_interaction
18. Primary Treatment:
Physical Separation
īŽ Sewage flows through large tanks known as primary
clarifiers or primary sedimentation tanks
īŽ Round or rectangular basins, 3 to 5 meters deep
īŽ Water retained here for 2 to 3 hours
īŽ Sludge will settle toward the bottom of tanks, while
scum will rise to the top. Both are removed and
pumped to sludge treatment tanks
īŽ Mechanical scrapers continuously drive sludge into a
well at the bottom of the tanks to be removed
īŽ Mechanical skimmers or rakes remove oils and grease
from the surface.
īŽ May be recovered to use in saponification
20. Primary Treatment: Aeration
īŽ Another process during primary treatment is
aeration
īŽ Water is agitated and exposed to air, which
serves two purposes:
īŽ Allows some dissolved gases to escape, such as foul
smelling hydrogen sulfide gas
īŽ Allows more oxygen to be dissolved into the water.
Oxygen may be bubbled into water at this point.
īŽ Increasing dissolved oxygen in water
compensates for the increased BOD and helps
with the sludge settling process
21. Example 2: Concentration
īŽ 9 ppm is considered a healthy dissolved oxygen
concentration in water. What is this
concentration expressed in molarity?
22. Example 2 Solution
9 g O2 x 1000 g H2O x 1 mol O2
1000000g H2O 1 L H2O 32 g O2
= 3 x 10-4 M O2
23. Treatment Process Step 3:
Secondary Treatment
īŽ Secondary treatment is designed to remove
residual organic materials and suspended solids
that were not removed during primary treatment
īŽ Works to degrade the biological content of the
sewage that comes from human waste, food
waste, soaps and detergent.
īŽ Removal of biodegradable dissolved and
colloidal organic matter using aerobic
biological treatment and flocculation
24. Secondary Treatment:
Aerobic Biological Treatment
īŽ performed in the presence of oxygen by aerobic
microorganisms
īŽ Aerobic = in presence of oxygen
īŽ principally bacteria and protozoa
īŽ metabolize the organic matter in the wastewater,
including sugars, fats, and short-chain
hydrocarbons
īŽ Results in production of several inorganic
products, including CO2, NH3, and H2O, as well
as reproduction of more microorganisms
25. Secondary Treatment:
Flocculation
īŽ Process in which colloids
come out of suspension
to form flakes, or floc
īŽ Differs from
precipitation!
īŽ Precipitation involves particles which are dissolved
in a solution
īŽ Flocculation involves particles that are suspended
within a liquid, not dissolved
http://www.tech-faq.com/flocculation.html
26. Colloid Properties
īŽ Colloids contain microscopic particles
dissolved evenly throughout a substance
īŽ Particles finer than 0.1 Âĩm in water remain
in constant motion because they often
carry an electrostatic charge which causes
them to repel each other.
27. Colloids and Flocculation
īŽ If the electrostatic charge of colloid
particles is neutralized, the finer particles
start to collide and combine together into
larger groups of particles
īŽ Due to the influence of Van der Waals forces:
īŽ These larger and heavier particles are called
flocs
īŽ Floc can either be filtered out of
wastewater or left to settle out as sludge
28. Colloids and Flocculation
īŽ Flocculants, or flocculating agents are
chemicals that promote flocculation by
causing colloids and other suspended
particles in liquids to combine, forming a
floc.
īŽ Many flocculants are multivalent cations
such as aluminum, iron, calcium, and
magnesium
īŽ Often, colloid particles carry a negative charge
īŽ These positively charged flocculant
molecules interact with negatively charged
colloid particles and molecules to reduce
the barriers to aggregation.
http://water.me.vccs.edu/courses/env110/lesson4.htm
29. Colloids and Flocculation
īŽ Many flocculating agents
under appropriate
conditions (such as pH,
temperature and salinity)
will react with water to
form insoluble hydroxides
īŽ These hydroxides will
precipitate from solution
and link together to form
long chains or meshes
īŽ physically traps small
particles into the larger floc
īŽ Polymers can also be
used as flocculants
http://www.kolonls.co.kr/eng/product/pop02_16.asp
30. Common Flocculants
Chemical Flocculating
Agents:
īŽ Alum
īŽ Aluminum chlorohydrate
īŽ Aluminum sulfate
īŽ Calcium oxide
īŽ Calcium hydroxide
īŽ Iron (II) sulfate
īŽ Iron (III) chloride
īŽ Polyacrylamide
īŽ Sodium silicate
Natural Products Used as
Flocculants:
īŽ Chitosan
īŽ Isinglass
īŽ Horseradish tree seeds
īŽ Gelatin
īŽ Guar Gum
īŽ Alginates (from brown
seaweed)
31. Treatment Process
Step 4: Tertiary Treatment
īŽ Tertiary treatment (also known as advanced
treatment) includes the remaining processes necessary
to remove the following from wastewater:
īŽ Nitrogen
īŽ Phosphorus
īŽ additional suspended solids
īŽ remaining organics
īŽ heavy metals
īŽ dissolved solids
īŽ Final treatment stage before water is released into
rivers, lakes, or groundwater
32. Example 3: Dilution and Concentration
īŽ Nitrogen is usually present in wastewater as
ammonia. 3.5 million L of wastewater entering
a treatment plant have an initial ammonia
concentration of 0.75 mM. By the time the
wastewater reaches the tertiary treatment phase,
the volume has been reduced to 2.9 million L.
What is the concentration of ammonia at this
point?
34. Tertiary Treatment
īŽ Depending on the types of contamination and
the desired end use, one or more processes may
be used in tertiary treatment:
īŽ Sand filtration
īŽ Nutrient removal (nitrogen and phosphorous)
īŽ Odor removal
īŽ Disinfection (via chlorination, ozone, or UV
radiation)
35. Tertiary Treatment
īŽ Sand filtration
īŽ Removes any remaining suspended solids not
removed by sedimentation and flocculation
īŽ May be combined with filtering over activated
carbon to remove toxins and odors
http://water.me.vccs.edu/concepts/filters.html
36. Tertiary Treatment
īŽ Nutrient Removal
īŽ Excessive release of nitrogen and phosphorous leads
to a condition known as eutrophication (presence of
excessive nutrients)
īŽ Eutrophication
encourages excessive
algae and weed growth
īŽ Leads to
deoxygenation of
water
īŽ Some algae can
release toxins into
water
http://05lovesgeography.blogspot.com/2011/02/eutrophication.html
37. Tertiary Treatment
īŽ Nutrient removal may be accomplished through
biological processes by passing wastewater through 5
different chambers:
1. Anaerobic fermentation zone
very low dissolved oxygen levels and the absence of
nitrates
2. Anoxic zone
low dissolved oxygen levels but nitrates present
3. Aerobic zone
4. Secondary anoxic zone
5. Final aeration zone
39. Nutrient Removal: Nitrogen
īŽ The majority of nitrogen in wastewater is in the
form of ammonia, NH3
īŽ Nitrogen removal takes place in two parts:
īŽ Nitrification: oxidation of ammonia to nitrate
īŽ Denitirication: reduction of nitrate to nitrogen gas
īŽ Nitrogen gas is then released into the
atmosphere
40. Nutrient Removal: Nitrogen
Nitrification
īŽ Nitrification occurs in the 3rd zone (aerobic zone)
īŽ Two step process
īŽ Each step carried out by a unique bacteria
īŽ Step 1: oxidation of ammonia to nitrite (NO2
-1)
NH3 ī NO2
-1
īŽ Step 2: oxidation of nitrite to nitrate (NO3
-1 )
NO2
-1 ī NO3
-1
41. Nutrient Removal: Nitrogen
Denitrification
īŽ After nitirification in the 3rd zone, wastewater rich in
nitrates is recycled back to the 2nd zone (first anoxic
zone)
īŽ The recycled nitrates, in the absence of dissolved
oxygen, are reduced by bacteria to nitrogen gas
NO3
-1 ī N2
īŽ Incoming organic carbon compounds present in this zone
act as hydrogen donors
42. Nutrient Removal: Nitrogen
īŽ Denitrification
īŽ In zone 4, the second anoxic zone, any nitrates
not reduced in zone 2 are reduced by the
respiration of bacteria present
īŽ In zone 5, the re-aeration zone, oxygen levels are
increased to stop the denitirication process
īŽ Stopping denitirification prevents problems with
settling
43. Example 4: Redox Reactions
īŽ Redox Reactions: Balance the three redox half
reactions associated with nitrogen removal:
īŽ Nitrification Step 1
īŽ Nitrification Step 2
īŽ Denitrification
45. Nutrient Removal: Phosphorous
īŽ Phosphorous may occur as organic or inorganic forms
īŽ Of the 5 to 20 mg/L total phosphorous content in
wastewater, 1 to 5 mg/L is organic
īŽ Phosphorous is typically present in the form of
phosphates
īŽ Typical forms include:
īŽ Orthophosphates: easily used in biological metabolism
īŽ Polyphosphates: contain two or more phosphorous atoms
in a complex molecule. Can slowly undergo hydrolysis to
orthophosphates
īŽ Phosphorous may be removed biologically or
chemically
46. Nutrient Removal: Phosphorous
īŽ Biological Removal:
īŽ Biological phosphorous removal takes place in Zones 1 and 2
of the five zone system mentioned earlier
īŽ In Zones 1 and 2, the anaerobic fermentation zone and first
anoxic zone, bacteria are stressed by the low oxygen
conditions and release phosphorous to maintain cell
equilibrium
īŽ When these bacteria reach later zones with higher oxygen
supplies, they rapidly accumulate phosphorous in excess of
what they normally would
īŽ Removed along with sludge
47. Nutrient Removal: Phosphorous
īŽ Chemical Removal
īŽ Phosphorous can be precipitated out of the wastewater
mixture using salts of iron, aluminum, or calcium
īŽ Some of this is accomplished during flocculation
īŽ Produces more sludge due to precipitate formation
īŽ More expensive than biological removal (added cost of
chemicals)
īŽ Usually more reliable and more effective than biological
removal
48. Chemical Removal of Phosphorous
Using Calcium
īŽ Usually added in the form of lime, Ca(OH)2.
īŽ Reacts with the natural alkalinity in the wastewater to
produce calcium carbonate
Ca(HCO3)2 + Ca(OH)2 ī 2CaCO3 + 2H2O
īŽ As the pH value of the wastewater increases past 10,
excess calcium ions will then react with the phosphate, to
precipitate in hydroxylapatite:
10 Ca2+ + 6 PO4
3- + 2 OH- â Ca10(PO4)*6(OH)2 (s)
īŽ Amount of lime required depends on pH of water rather
than amount of phosphate present
īŽ Neutralization may be required to lower the pH before
further treatment or disposal, typically by recarbonation
with carbon dioxide
49. Example 5: Acids, Bases, and pH
īŽ The pH of domestic wastewater is about 7.2.
īŽ What are the concentrations of hydronium and
hydroxide ions in water at this point?
īŽ Lime is only effective in removing phosphorous at a
pH higher than 10. What is the pH of 9800 L of
water treated with 50 g Ca(OH)2?
50. Example 5 Solution
Part 1:
[H3O+] = 10 -pH
= 10 -7.2
= 6.3 x 10-8 M
[H3O+] [OH-] = 1 x 10-14
[OH-] = 1 x 10-14
6.3 x 10-8
= 1.6 x 10-7M
Part 2:
50.0 g x 1 mol Ca(OH)2 x 2 mol OH
9800 L 74.1 g 1 mol Ca(OH)2
= 1.38 x 10 -4 M OH-
[H3O+] = 1 x 10-14
1.38 x 10 -4
= 7.25 x 10 -11 M H3O+]
pH = -log[H3O+]
= -log (7.25 x 10 -11 M)
= 10.1
51. Chemical Removal of Phosphorous
Using Aluminum
īŽ Typically use alum or hydrated aluminum sulfate
to precipitate aluminum phosphates (AlPO4).
Al3+ + HnPO4
3-n â AlPO4 + nH+
īŽ Reaction affected by pH, equilibrium of
competing reactions, and presence of trace
elements in wastewater
īŽ Aluminum may adversely affect some of the
bacteria used in sludge and digestion and should
be used carefully
52. Chemical Removal of Phosphorous
Using Iron
īŽ Iron (III) chloride or sulfate or iron (II) sulfate
can be used to form iron phosphate precipitates
Fe3+ + HnPO4
3-n â FePO4 + nH+
īŽ Lime is usually added to raise the pH to enhance
the reaction
53. Example 6: Solubility and Net Ionic
īŽ Write the full balanced equation (including
states) and the net ionic equation for the
reaction of iron (III) sulfate with sodium
phosphate.
55. Tertiary Treatment: Disinfection
īŽ Disinfection of wastewater reduces the number of
microorganisms in water that may lead to disease
before discharging back into the environment
īŽ Usually the very last step before discharge
īŽ Effectiveness depends upon conditions of treated
water at this point, including cloudiness and pH
īŽ Three major strategies: chlorination, ozone, and UV
radiation
http://www.purewater2000.com/Ultraviolet.html
56. Disinfection: Chlorination
īŽ Most commonly used form
of disinfection due to low
cost and high effectiveness
īŽ The exact mechanism by
which chlorine disinfects is
not fully understood. It
likely involves oxidative
damage to microbial cell
membranes and vital
protein systems
īŽ Chlorination also helps to
reduce any odors in the
water
īŽ Drawbacks:
īŽ may create chlorinated organic
compounds that may be carcinogenic
īŽ Residual chlorine is toxic to aquatic life
īŽ May be necessary to dechlorinate
water before release
http://chlorination.us/chlorination/chlorination/
57. Disinfection: Chlorination
īŽ When chlorine (Cl2) is injected into water, it forms
hypochlorous acid and hydrochloric acid in a pH
dependent equilibrium
Cl2 + H2O â HOCl + HCl
īŽ Depending on the pH, the hypochlorous acid will partly
dissociate to hydrogen and hypochlorite ions:
HClO â H+ + ClO-
īŽ In acidic solution, the major species are Cl2 and HOCl
while in basic solution only ClO- is present.
īŽ Very small concentrations of ClO2
-, ClO3
-, ClO4
- are
also found
58. Disinfection: UV Radiation
īŽ Ultraviolet radiation damages the genetic structure of bacteria
and viruses which makes them incapable of reproduction
īŽ Since no chemicals are used, UV disinfection poses no risk to
organisms which will later encounter the treated water
īŽ Requires highly treated water
with little cloudiness.
Suspended solids in the water
may block out the UV rays
īŽ Maintaining UV lamps can be
costly
http://www.blog.waterfilters.net/uv-technology-explained/1207
59. Disinfection: Ozone
īŽ Ozone (O3) is generated by passing oxygen gas
(O2) through a high voltage potential. Voltage
breaks O2 into oxygen atoms which will
recombine as O3 gas
O2 + electricity ī O3
īŽ Ozone is very unstable. Generated as needed
rather than stored
īŽ Produces fewer by-products than chlorination,
but much more costly
60. Example 7: Reaction Stoichiometry
īŽ Write the balanced equation for the synthesis of
ozone from oxygen
īŽ If 56.8 g of ozone must be synthesized, how
many moles of oxygen gas are required?
61. Example 7 Solution
3 O2 ī 2 O3
56.8 g O3 x 1 mol O3 x 3 mol O2
48 g O3 2 mol O3
= 1.78 mol O2
62. Disinfection: Ozone
īŽ Ozone is very effective in destroying viruses and
bacteria and may act by several mechanisms:
īŽ Direct oxidation and destruction of the cell wall with
leakage of cellular components
īŽ Reactions with radical by-products of ozone
decomposition
īŽ Damage to the constituents of the nucleic acids (purines
and pyrimidines)
īŽ Breakage of carbon-nitrogen bonds leading to
depolymerization
63. Tertiary Treatment: Odor Removal
īŽ Odor in waste water typically form as a result of
anaerobic conditions
īŽ Most common odor is hydrogen sulfide gas
īŽ Odor is eliminated along the way by aeration,
chlorination, biological degradation, and circulation of
fluids
īŽ Other methods to eliminate hydrogen sulfide are by
adding iron salts, hydrogen peroxide, or calcium nitrate
64. Treatment Process
Step 5: Sludge Treatment
īŽ Sludge consists of all the solid material removed from
wastewater during the water treatment process
īŽ While the water in treatment is ready for release into
streams and groundwater, sludge requires further
treatment before it can be disposed or used
īŽ Must reduce the amount of organic matter
īŽ Must reduce the number of disease causing microbes
īŽ Remove as much remaining liquid as possible
īŽ Sludge treatment options include:
īŽ Aerobic digestion
īŽ Anearobic digestion
īŽ Composting
īŽ Incineration
65. Sludge Treatment
īŽ Sludge is most often processed by biological
anaerobic digestion
īŽ Bacteria metabolize the organic material in the
sludge
īŽ Occurs over a period of 10 to 60 days, depending on
the capabilities of the digesting tanks
īŽ Reduces the volume of sludge that requires disposal
īŽ Makes the sludge more stable
īŽ Improves the dewatering characteristics of the sludge
īŽ Shorter retention time and smaller tanks required
īŽ Requires higher temperatures, resulting in a higher
energy cost
66. Sludge Treatment
īŽ One byproduct of
anaerobic sludge digestion
is the production of
biogas
īŽ Biogas contains about 60
to 65% methane (CH4)
and can be recovered as
an energy source.
īŽ Methane is a combustible,
renewable fuel
CH4 + O2 ī CO2 + H2O
http://home.comcast.net/~hollywastewater/Process.htm
67. Sludge Treatment
īŽ In small sewage treatment plants, sludge is
processed using aerobic digestion
īŽ Under aerobic conditions, bacteria will consume
organic material and convert it into carbon
dioxide
īŽ Energy cost associated with adding oxygen to
process and blowers to remove CO2
68. Sludge Treatment
īŽ Composting of sludge is similar to aerobic digestion,
except other organic materials such as sawdust are
mixed in with the sludge
īŽ Incineration is the least used method of sludge
treatment.
īŽ Sludge burns poorly due to low calorific value, so extra
fuels must be added
īŽ Worries of emissions associated with sludge
īŽ High energy cost to vaporize residual water present in
sludge
69. Sludge Treatment
īŽ Sludge that does not originate from
highly industrialized areas and is
for the most part free of toxic
chemicals can be used as fertilizer
īŽ Water is removed
from sludge by
centrifugation and
addition of chemicals
that aid in polymer
formation
īŽ Dried sludge can be
converted into
fertilizer pellets
which are usually rich
in phosphorous
http://www.thewatertreatmentplant.com/sludge-treatment-equipment.html
70. Water Treatment
īŽ View the entire process in action
http://photosmynthesis.wordpress.com/2010/09/16/wetland-services/water-treatment-plant/
71.
72. Sources
īŽ Severn Trent Water. âThe Water Treatment Processâ Online. 9 July 2011.
īŽ http://www.youtube.com/watch?v=9z14l51ISwg
īŽ United States Geological Survey. âWastewater Treatment: Water Useâ Online. 9 July 2011.
http://ga.water.usgs.gov/edu/wuww.html
īŽ South Carolina Office of Regulatory Staff. âOverview of Basic Wastewater Treatment Processâ
Online. 9 July 2011. http://www.regulatorystaff.sc.gov/orscontent.asp?pageid=654
īŽ Author Unknown. âSewage Treatmentâ Online. 8 July 2011.
http://en.wikipedia.org/wiki/Sewage_treatment
īŽ United States Geological Survey. âA visit to a wastewater-treatment plant: Primary treatment of
wastewaterâ Online. 9 July 2011 http://ga.water.usgs.gov/edu/wwvisit.html
īŽ Natural Resources Management and Environment Department. âWater Treatmentâ Online. 10
July 2011. http://www.fao.org/docrep/t0551e/t0551e05.htm
īŽ Environmental Protection Agency. âWater Treatment Processâ Online. 8 July 2011.
http://water.epa.gov/learn/kids/drinkingwater/watertreatmentplant_index.cfm
īŽ Environmental Protection Agency. Wastewater Technology Fact Sheet: Ozone Disinfection.
(1999) Online. 11 July 2011
http://water.epa.gov/scitech/wastetech/upload/2002_06_28_mtb_ozon.pdf
īŽ Author Unknown. âChlorinationâ Online 11 July 2011.
http://water.me.vccs.edu/courses/ENV149/chlorinationb.htm
īŽ Lenntech Water Treatment Solutions. âPhosphorous removal from wastewaterâ. Online 10 July
2011. http://www.lenntech.com/phosphorous-removal.htm#ixzz1RpIsY55O
īŽ Author Unknown. âFlocculationâ Online 9 July 2011.
http://en.wikipedia.org/wiki/Flocculation