All living things require clean, uncontaminated water as  the most crucial compound for life on Earth Ideally, drinking water should be clear, colorless, and well aerated, with no unpalatable taste or odor, and it should contain no suspended matter, harmful chemical substances, or pathogenic microorganisms. Wastewater discharge from industries, agricultural pollution, municipal wastewater, and poor environmental sanitation are the main sources of water contamination

1. Water Supply and
Treatment Technology
(EHT 215)
LECTURER: SIR OAK

2. LECTURE 4
 Water treatment technology
Learning objective:
At the end of this topic, students should be able to:
• understand the concept of Water Treatment mimicking Earth’s
Hydrological cycle;
• describe the water treatment process work;
• list and explain the six (6) essential water treatment technologies;
• identify and explain why certain water treatment chemicals are
used.

3. Introduction
• All living things require clean, uncontaminated water as the
most crucial compound for life on Earth
• Ideally, drinking water should be clear, colourless, and well
aerated, with no unpalatable taste or odour, and it should
contain no suspended matter, harmful chemical substances, or
pathogenic microorganisms.
• Waste water discharge from industries, agricultural pollution,
municipal wastewater, and poor environmental sanitation are
the main sources of water contamination

4. Introduction cont…
• Water treatment is the removal of those impurities/contaminants
which makes the water undesirable for domestic, industrial and
other processes.
• Depending on the quality and type of the water entering a water
plant, treatment may vary.
• To ensure water do not present a health risk, nearly all water
sources require treatment before they can be consumed.
• Replicating the earth’s hydrological cycle in which water is
continuously recycled, treatment enables the same water to be
cleansed through several natural processes.

5. THE HYDROLOGICAL CYCLE
• Hydrological cycle also known as “water cycle” is the series of
natural processes by which water is recycled through the
environment.
• Due to solar radiation, water evaporates, generally from the
sea, lakes, etc.
• Water also evaporates from plant leaves through the
mechanism of transpiration.

6. The hydrological cycle cont…
• As the steam rises in the atmosphere, it is being cooled,
condensed, and returned to the land and the sea as
precipitation.
• Precipitation falls on the earth as surface water and result in
lakes and rivers which eventually leads to the sea.
• A part of the water precipitating penetrates the ground and
moves downward through the incisions, forming aquifers.

8. THE GLOBAL WATER CYCLE

9. THE GLOBAL WATER CYCLE

10. Water balance
• The water available to planet Earth is the same water that has
always been available and the only water that ever will be
available.
• Water is always on the move, traveling on a never-ending, cyclical
journey between earth and sky.
• It falls to the earth as rain, snow, sleet, or hail and evaporates
from the earth back into the atmosphere as water vapour.
• The availability of water changes with weather (eg. drought or
flooding), season, and human use

11. Water balance cont…
• Total amount of water (solid + liquid + vapour) is fixed
• Therefore, we can apply ‘accounting’ or ‘budgeting’ techniques
to water at any scale (in space or time)
• Considering inputs, outputs and storages of water; we can write
this as an equation:
• the difference between the sum of the inflows and the sum of
the outflows is equal to the change in storage

12. Water balance cont…
• The law of water balance states that the inflows to any water
system or area is equal to its outflows plus change in storage
during a time interval.
• A general water balance equation is: P = R + ET + ΔS
where
P is precipitation
R is streamflow
ET is evapotranspiration
ΔS is the change in storage (in soil or the bedrock / groundwater)
• A water balance can be used to help manage water supply and
predict where there may be water shortages.

13. Assignment II
Briefly explain five (5)
possible ways of restoring
the Hydrological Cycle.

14. Natural purification of water
Water purifies itself through some of the following ways:
• Sedimentation of impurities as the river flows along
• Percolation through layers of the earth (various aquifers).
• Aeration of the water (oxidation of chemicals) Eg. Iron,
Manganese and odour.
• Solar Radiation: Due to its germicidal effects, its reduces the
population of micro-organisms.

15. Natural purification of water cont…
• One easy and simple way to treat water is to use the SODIS
(SOlar DISinfection) system which has been tested both in the
laboratory and in the field.
• The principle underlying solar disinfection is that
microorganisms are vulnerable to light and heat.
• A transparent container is filled with water and exposed to full
sunlight for several hours.
• The inactivation process is accelerated when the water
temperature reaches 50 °C and usually leads to complete
bacteriological disinfection

16. WATER TREATMENT
• The water that comes out of your tap has been through various
processes that clean and change its original properties,
physically and chemically.
• A Water Treatment Plant aims to ensure that water is:
♦ safe for human consumption
♦ pleasant to consumers
♦ provided at a reasonable cost
• From the dam to the tap there is a vigorous process with many
steps that are all essential in assuring high quality water for
drinking.

17. Water Treatment Technology
• Water treatment technologies may be organize into three
general areas, namely: Physical Methods, Chemical Methods,
and Energy Intensive Methods.
• Physical Methods: solid-liquid separations techniques, of
which filtration plays a dominant role.
• Chemical Methods: the chemical interactions of the
contaminants we wish to remove from water.
• Energy Intensive Methods: Eg. thermal methods have a dual
role in water treatment applications – sterilization & volume
reduction.

18. The six (6) essential water treatment technologies
1. Screens
• Screens are used on many surface water intakes to remove
particulate material and debris from raw water.
• Weeds and debris can be removed using coarse screens,
whereas smaller particles including fish can be removed using
band screens and micro strainers.
• Ahead of coagulation or subsequent filtration, micro strainers
are used as a pre-treatment to reduce solids loading.

19. 2. Gravel filters
• Turbidity and algae can be removed using gravel filters, which
consist of a rectangular channel or a tank divided into several
sections and filled with graded gravel (size range 4 to 30mm).
• An inlet distribution chamber allows the raw water to enter
through and flow horizontally through the tank, encountering
first the coarse and then the finer gravel.
• An outlet chamber collects the filtered water with solids being
removed from the raw water accumulate on the floor of the
filter.

20. 3. Sand filters
• There are two main types of sand filters, namely: Slow Sand
Filters (SSF) and Rapid Sand Filters (RSF)
• SSF are so called because water moves down through the
sand at a rate of only 0.2m/hr.
• Slow sand filters usually consist of tanks containing sharp
sand (size range 0.15 - 0.30mm) to a depth of between 0.5 to
1.5m.
• Slow sand filters improves the micro-biological quality of water
considerably

21. • RSF is the most commonly used method of filtration in which
water passes downwards through a sand bed about 0.45 to 1m
thick at a rate of over 5m/hr.
• The water is driven through the bed either by gravity or by
pressure in a steel pressure vessel.
• However, due to the construction cost, complexity and other
need for regular backwashing, they are not appropriate for
applications in many developing countries

22. 4. Activated carbon
• Using physical adsorption, contaminants can be removed using
activated carbon.
• It is affected by the amount and type of the carbon, the nature
and concentration of the contaminant, retention time of water in
the unit and general water quality (temperature, pH, etc.).
• The most common mediums is granular activated carbon
(GAC), although powdered activated carbon (PAC) and block
carbon are also sometimes used.

23. 5. Aeration
• Aeration is designed to transfer oxygen into water and
remove gases and volatile compounds by air stripping.
• To achieve air stripping, various techniques can be used
including:
 counter current cascade aeration in packed towers,
 diffused aeration in basins and spray aeration.

24. 6. Membrane processes
• Reverse osmosis (RO), ultrafiltration (UF), microfiltration
(MF) and nanofiltration (NF) are the most commonly used
membranes for water treatment processes.
• Previously applied to the production of water for industrial or
pharmaceutical applications, membranes are being applied
to the treatment of drinking water.
• Membrane processes can provide adequate removals of
pathogenic bacteria, Cryptosporidium, Giardia, and
potentially, human viruses and bacteriophages.

25. Conventional Or Municipal Treatment Of Water
• It is the most common water treatment processes used for
treatment of raw water from a surface source.
• Conventional water treatment processes are aimed to remove
sediment, pollutants associated with sediment, and
microorganisms.
• It also involves improvement on the natural properties of water
by adding certain deficient ingredients.
• CWT involves the following steps:

26. Conventional Or Municipal Treatment Of Water cont…
(1) Collection
(2) Screening and Straining
(3) Aeration
(4) Coagulation and Flocculation
(5) Sedimentation and Clarification
(6) Filtration
(7) Disinfection
(8) pH adjustment
(9) Storage and Distribution

27. Collection
• This stage is also refer to as intake, impoundment, dams or
reservoir plain.
• The source water for a municipal surface water treatment plant
is typically a local river, lake, or reservoir.
• As a result of zero water velocity, pre-sedimentation take place
resulting in suspended solids and silt settle to the bottom.
• Large pumps are used to transfer the water up to the treatment
facility which are often engineered to utilize gravity water flow
as much as possible to reduce pumping costs.

30. Screening and Straining
• Surface water sources contain varying amounts of suspended
and dissolved materials. Eg. turbidity, color, taste, odour,
microorganisms, fish, plants, trees, trash, etc.
• Screen or strain are provided at intake points to remove larger
objects from the water. This protects the pumps and water
quality.
• This is often accomplished using a large metal screen, often
called a bar-screen, which trapped suspended objects as the
water passes through it.
• These screens must routinely be raked or cleaned off.

32. Aeration
This is a process whereby the water is brought into intimate contact
with air in accomplishing:
• Removal or reduction of taste and odour;
• Removal of gasses such as carbon dioxide, nitrogen, hydrogen
sulfide, methane, etc;
• Oxidation of iron and manganese;
• Introduction of oxygen into the water.

34. Coagulation and Flocculation
• Once the pre-screened source water is received into the treatment
plant, chemicals are added to aid in the formation of absorbent,
bulky precipitate known as flocs which in turn assist in the removal
of more finely divided sediments and colloids.
• These chemicals are called coagulants. Eg. aluminium sulfate
(alum), ferrous sulfate, ferric chloride, sodium aluminate, activated
silica, and polymers (cationic, anionic & nonionic).
• Flocculation is the process by which the agitation and velocity of
the water are reduced drastically to allow finely formed flocs to
coalesce with each other and aggregate into bigger flocs for easier
settlement.

36. Flocculation tank

37. Sedimentation and Clarification
• Once the flocculation process is complete, the water then passes over
to the center of the clarifier, or sedimentation basin.
• As the water makes its way towards the saw tooth weir at the perimeter
of the unit, the large floc particles are allowed to settle out to the bottom
of the clarifier.
• The water that passes over the weir is collected and transferred to the
filters.
• A rake continuously travels across the bottom of the clarifier and
scrapes the settled floc to the center of the unit.
• Pumps are used to pull the settled “sludge” out of the clarifier and send
it to a sedimentation / disposal pond.

38. Sedimentation and Clarification cont…
The reason clarification occurs
before filtration include:
• the removal of majority of
suspended material prior to
filtration,
• avoids overloading the filters
and thus allowing much more
water to be filtered before the
filters must be backwashed.

39. Filtration
• The process of filtration consist of passing the water through a bed
of sand or other suitable medium at a low speed.
• The sand retains fine suspended matter and some bacteria while
permitting the water to pass.
• The most common materials (media) used in filters are sand and
gravel.
• Many conventional plants are now using granular activated carbon
as the media of choice because it also removes organic
compounds which can cause taste and odour problems.

41. Disinfection
• This is the final process in water purification and is achieved in
the addition of certain chemicals especially chlorine.
• This is known as chlorination of water. The residual bacterial
are killed by the chlorine.
• Chlorine comes in many different forms including chlorine gas
(most common), chlorine dioxide, hypochlorite (bleach), and
others.
• Water plants monitor the chlorine levels continuously and very
carefully in the treated water.

43. Chlorine demand
• Chlorine is an oxidizing agent, if added to impure water, it will
quickly oxidize the impurities and no longer be available for
disinfection.
• It is therefore essential that chlorine dose should be greater than
the required to satisfy the immediate chlorine demand of the water.
• Water supplies in developing countries are frequently running
above their design capacity and cannot always guarantee this
minimum time before the water reaches the taps.
• If an adequate dose is used to satisfy the chlorine demand, a
residual of chlorine remains which provides protection against
contamination occurring during subsequent distribution of the
water.

44. pH adjustment
• This process involves the addition of enough lime/lime hydrated
to the filtered water to raise the pH and the alkalinity so that the
water reaches a state of equilibrium where it will neither deposit
nor dissolved carbonate scale.
• The normal pH range of drinking water is 6 – 8.5.
• The pH is mostly a result of natural geological conditions at the site
and the type of minerals found in the local rock.

45. Storage & Distribution
• Once the disinfection process is complete, the water is stored.
• Storage usually takes place in an underground storage tank
called a “clear well”, and also in elevated storage tanks that are
visible around town.
• The stored water is pushed through underground pipelines all
over town in what is called a “distribution system”.
• The distribution system consists of large water pumps at the
treatment plant, overhead water storage tanks, large pipelines,
smaller pipelines, fire hydrants, valves, and water meters in
your front yard.

46. OPTIONAL TREATMENT PROCESS
The following processes can be included depending upon the
quality of source of water:
• Pre-chlorination: This is the addition of chlorine to the water before
filtration. This oxidizes and precipitate iron and manganese, kills
algae and bacteria, reduces colour and slime formation and
generally assist settlement.
• Pre-liming and alkaline is added to the water to aid coagulation if
the water does not have enough alkaline to react with the
coagulant to form flocs.

47. WATER TREATMENT CHEMICALS
CHEMICAL FORMULA USE/APPLICATION
Aluminium Sulphate
(Alum)
Al2SO4 . (14 – 18) H2O Clarification of water
Lime Hydrated Ca(OH)2 pH correction,
corrosion prevention
Chlorine gas Cl2 Disinfection to kill
micro-organism
Bleaching powder CaOCl2 Disinfection to kill
micro-organism
Sodium Carbonate
(Soda Ash)
NaCO3 pH correction,
corrosion prevention.

48. The following chemicals are used on specific occasions:
CHEMICAL FORMULA USE/APPLICATION
Potassium Permanganate KMnO4 Oxidation and removal of
iron and manganese.
Sulpheric Acid H2SO4 Reduction of excess
alkalinity
Sodium Hydroxide NaOH Neutralization of acidity
Ozone O3 Disinfectants to kill
microbes/bacteria
Activated Carbon C Taste and odour removal
Chlorine dioxide CLO2 Disinfection to kill
microbes, etc.

49. Thank you