ENVIRONMENTAL ENGINEERING - II

Water Treatment Process &

Supply
ENVIRONMENTAL ENGINEERING - II Water supply- Water Quality

• Water for human consumption must be:

• Free from harmful bacteria & suspended matter
• Colorless
• Pleasant to taste
• For health reasons, moderately hard
• Water storage & treatment process to ensure good
water quality
ENVIRONMENTAL ENGINEERING - II Typical water treatment process
ENVIRONMENTAL ENGINEERING - II
Water supply- Treatment Process 1

Process 1 - Raw Water

The raw water treated by the A Treatment Works comes

from different sources, including Reservoir lakes and
Rivers etc.
ENVIRONMENTAL ENGINEERING - II
Water supply- Treatment Process 2

Process 2- Mixing

The raw water is dosed at the inlet of the mixing chamber

with the following chemicals:-

➢Hydrated Lime to precondition the raw water

➢Chlorine at initial stages to control algae
➢Alum to coagulate impurities
➢Polyelectrolyte to improve the coagulation and
flocculation of impurities
ENVIRONMENTAL ENGINEERING - II
Water supply- Treatment Process 3

Process 3 - Flocculation and Sedimentation

After mixing, water is passed to the clarifiers where

coagulation and flocculation of the impurities in the water
will occur.
The dissolved alum coagulate impurities in the water into
large particles where settle as sludge.
The sludge is collected and conveyed to sludge thickening
tanks for further treatment before disposal.
ENVIRONMENTAL ENGINEERING - II
Water supply- Treatment Process 4

Process 4 - Rapid Gravity Filtration

Settled water from the clarifiers flows to

the constant rate sand filters for removal of
more finely divided suspensions.

Periodically the filter beds are cleaned by

backwashing with air and then water.
ENVIRONMENTAL ENGINEERING - II
Water supply- Treatment Process 5

Process 5 - Clear Water Tanks

Chorine, fluoride and lime are dosed into the filtered

water in the contact tanks and disinfect, fluoridate and
control the alkalinity of the final treated water.

The treated water is stored in the clear water tank before

conveying to Primary Service Reservoir for distribution
to People.
ENVIRONMENTAL ENGINEERING - II
Water supply- Treatment Process 6

Process 6 - Pumping Facilities

The pumping stations have sufficient

number of pumps with an installed
pumping capacity according to the
demand of the community
considering future demands as well.
ENVIRONMENTAL ENGINEERING - II
Water supply- Treatment Process 7

Process 7 - Environmental Friendly

Facilities
The wash-water is collected in the
recovery tanks for re-pumping to the
inlet for recycling.
Sludge produced in the treatment works
is thickened by three circular sludge
thickening tank using electrolyte as
coagulant.
Thickened sludge is compressed by
membrane type filter presses into cakes
for disposal at landfill sites.
ENVIRONMENTAL ENGINEERING - II
Water supply- Treatment Process 8

Process 8 - Water Quality Control

The quality of water is closely monitored by means

of chemical, bacteriological and biological
examinations of water samples taken

To comply with the Guidelines for Drinking Water

Quality recommended by World Health
Organization, to ensure a safe and wholesome
potable supply.
ENVIRONMENTAL ENGINEERING - II Water supply- Network

• Distribution network of water supply

• Main reservoir
• Pumping stations
• Water treatment plants
• Pumping substations
• Service reservoirs
• Trunk mains or service trunks
• Street mains or water mains (into buildings)
ENVIRONMENTAL ENGINEERING - II Water supply- Pressure & Piping

• Mains water supply

• Size of the water mains
• Pressure (or head) of water in them
• Such as a 75 mm diameter pipe fed from both ends
or a 100 mm diameter pipe fed from one end
• Min. head of 30 m for firefighting purposes
• Max. head of 70 m to limit wastage and pipe noise
• A ring circuit & a grid of pipes
• To increase reliability & facilitate maintenance
ENVIRONMENTAL ENGINEERING - II
Ring main distribution
ENVIRONMENTAL ENGINEERING - II
Distribution systems

•Direct supply
system: conveys
water directly from
water mains to the
point of usage
without any transit
water storage tanks

Direct supply system (without storage tank)

ENVIRONMENTAL ENGINEERING - II
Distribution systems

Direct supply system (with storage tank)

ENVIRONMENTAL ENGINEERING - II
Distribution systems

•Indirect
supply system:
conveys
water from
water mains
to the point of
usage through
a transit water
storage tank

Indirect supply system (with sump and pump)

ENVIRONMENTAL ENGINEERING - II
Distribution systems

Indirect supply system (with pneumatic vessel)

ENVIRONMENTAL ENGINEERING - II
Comparison of direct and indirect water supply systems

Direct supply Indirect supply

- Less pipe work, smaller or no - More pipe work, large water

water tank storage tank
- No storage to satisfy peak - Water storage to meet peak
demand period demand
- Risk of contamination and - Less risk of adverse effects by
pressure fluctuation of mains water mains

- Not feasible for high-rise - Can be used in high-rise

buildings due to main pressure buildings
ENVIRONMENTAL ENGINEERING - II Water supply- Piping

• Components and materials

• Pipe materials & fittings
• Suit the purpose & conditions
• Decision factors:
• Effect on water quality
• Cost, service life and maintenance needs
• For metallic pipes, internal and external corrosion
• Compatibility of materials
• Ageing, fatigue and temperature effects, especially in plastics
• Mechanical properties and durability
• Vibration, stress or settlement
• Internal water pressure
ENVIRONMENTAL ENGINEERING - II
Water supply- Piping

• Commonly used pipe materials, such as:

• Cast iron (BS 4622)
• Copper (BS EN 1057)
• GI with PVC-C lining (BS 1387)
• PVC, un-plasticized PVC, PB, PE, PE-X
• Stainless steel (BS 4127)
ENVIRONMENTAL ENGINEERING - II Water supply- Other Components

• Commonly used fittings

• Ball valve
• Butterfly valve
• Gate valve
• Non-return valve
• Pressure reducing valve
• Pressure relief valve
• Stopcock
• Float switch
• Expansion vessel
ENVIRONMENTAL ENGINEERING - II
Water supply- Components

Gate valve Water tap

Ball valve
ENVIRONMENTAL ENGINEERING - II Water supply- Storage Cistern

• Water tanks
• Materials: reinforced concrete, fibre glass, etc.

• Reinforced concrete is the most common material

used.

• Fiberglass storage cistern for potable water shall be

of an approved type or certified, with no toxic
materials and suitable for storage of potable water.
ENVIRONMENTAL ENGINEERING - II Water supply- Storage Cistern

Overflow pipe
• to discharge overflow water to a conspicuous position
easily visible and accessible by the occupants.
• at least one commercial size larger than the inlet pipe
(min. 25 mm in diameter)
• A grating and a self-closing non-return flap at the
overflow pipe outside the storage cistern.
ENVIRONMENTAL ENGINEERING - II Water supply- Storage Cistern

Warning pipe
• min. 25 mm in diameter
• at a level below the overflow pipe and be extended to
outside of the building periphery for roof cistern or
outside the pump room for sump cistern.

Outlet pipe
• Outlet pipes from the storage cistern be at the opposite
side to the inlet supply pipe to prevent stagnation of
water.
ENVIRONMENTAL ENGINEERING - II Water supply- Storage Cistern

• Storage capacities:
• Assessment of water consumption & demand
• Sump tank : roof tank = 1:3
• Recommend to meet one-day demand
• Domestic supply – follows WSD recommendations
ENVIRONMENTAL ENGINEERING - II
Water tank basic requirements (for a gravity supply)
ENVIRONMENTAL ENGINEERING - II
Recommended storage capacities in water supply systems

Domestic water supply with Flushing Temporary

sump and pump supply using mains fresh
salt water water for
flushing
Up to 10 flats > 10 flats (TMF)

135 liters/flat 90 liters for Minimum 1/2 45 liters per

(total storage each day flushing
including additional flat consumption apparatus,
sump tank) minimum 250
liters
ENVIRONMENTAL ENGINEERING - II Water supply- Pumping System

• Water pumps
• Provide a duplicate set
• Pumping capacity >= designed out-flow of tank
• Minimize vibration and noise problems
• Adequate pipe work support & anchor
• Solid foundation

• Common pump types

• Horizontal end suction centrifugal
• Vertical multistage centrifugal
ENVIRONMENTAL ENGINEERING - II Water supply- Pumping System

• Pump control
• Automatic control using pressure switches, level
switches, high-level & low-level electrodes
• Pump selector switch & ON/OFF/AUTO
• Low-speed preferred (longer life & quiet)

• Pump motor
• Such as squirrel cage induction type
• Overload protection
ENVIRONMENTAL ENGINEERING - II
Typical pump room
ENVIRONMENTAL ENGINEERING - II
Typical pump room
ENVIRONMENTAL ENGINEERING - II
Water supply - General Principles

The followings are the general principles for installing

plumbing works :-

▪ All water fittings and pipe work shall comply with the
relevant Waterworks Regulations;
▪ All plumbing works shall be carried out in accordance
with the relevant Waterworks Requirements;
▪ All plumbing works shall be carried out by a licensed
plumber.
▪ System main pipes should preferably not be run through
the individual premises.