3.1 WASTEWATER TREATMENT

Wastewater treatment

a process

to convert wastewater - which is

water no longer needed or suitable

for its most recent use - into an

effluent that can be either returned

to the water cycle with minimal

environmental issues or reused.

PHYSICAL WATER TREATMENT
BIOLOGICAL WATER TREATMENT
CHEMICAL WATER TREATMENT

TYPES OF WASTEWATER TREATMENT

Physical water treatment

physical methods are used for

cleaning the wastewater. No chemicals are involved in this

process such as screening, and sedimentation. Aeration is

also a physical treatment process.

Biological water treatment

This uses various biological

processes to break down the organic matter present in

wastewater, such as soap, human waste, oils and food.

Microorganisms metabolize organic matter in the

wastewater in biological treatment.

Aerobic processes

Bacteria decomposes the organic matter

and converts it into carbon dioxide that can be used by

plants. Oxygen is used in this process.

Anaerobic processes

fermentation is used for

fermenting the waste at a specific temperature. Oxygen is

not used in anaerobic process.

Composting

A type of aerobic process where wastewater is

treated by mixing it with sawdust or other carbon sources.

Chemical water treatment

this treatment involves the use of

chemicals in water.

Chlorine

an oxidizing chemical, is commonly used to kill bacteria

which decomposes water by adding contaminants to it.

Ozone

is an effective disinfectant to oxidize organic compounds

and reduce microorganisms.

Neutralization

is a technique where an acid or base is added to

bring the water to its natural pH of 7. Chemicals prevent the

bacteria from reproducing in water, thus making the water pure.

Pre-treatment

Preliminary treatment

Primary treatment

Secondary treatment

Tertiary treatment

Sludge (biosolids) disposal

STAGES OF WASTE WATER TREATMENT

PRE-TREATMENT

waste water moves towards the

plant by means of gravity. Lift

station pump water are used

from low lying areas.

removes large objects and non-

degradable materials.

bar screen and grit chamber

BAR SCREEN

catches large objects that have gotten into sewer

system such as bricks, bottles, pieces of wood, etc.

GRIT CHAMBER

removes rocks, gravel, broken glass, etc.

MESH SCREEN

removes diapers, combs, towels, plastic bags,

syringes, etc.

PRIMARY TREATMENT

Involves sedimentation of solid waste after

filtering large contaminants.

Wastewater is passed through several tanks and

filters that separate water from contaminants.

The resulting “sludge” is then fed into a digester,

in which further processing takes place.

This primary batch of sludge contains nearly 50%

of suspended solids within wastewater.

PRE-SETTLING BASIN

primary sedimentation tanks or primary clarifiers

wherein two hours of detention takes place for

sewage for gravity settling. The tanks are used to

settle sludge while grease and oils rise to the surface

and are skimmed off.

RAPID MIXING

A process of applying turbulence on the tank adding

chemicals that encourages coagulation to water

streams.

FLOCCULATION

A gentle mixing stage, increases the particle size from

submicroscopic microfloc to visible suspended

particles. Microfloc particles collide, causing them to

bond to produce larger, visible flocs called pinfloc

SECONDARY TREATMENT

It removes the soluble organic matter that

escapes primary treatment.

It also removes more of the suspended

solids.

Removal is usually accomplished by

biological processes in which microbes

consume the organic impurities as food,

converting them into carbon dioxide, water,

and energy for their own growth and

reproduction.

TRICKLING FILTER

tank filled with a deep bed of stones.

Settled sewage is sprayed continuously over

the top of the stones and trickles to the

bottom, where it is collected for further

treatment. As the wastewater trickles

down, bacteria gather and multiply on the

stones.

ACTIVATED SLUDGE

consists of an aeration tank followed by a

secondary clarifier. Settled sewage, mixed

with fresh sludge that is recirculated from

the secondary clarifier, is introduced into

the aeration tank. The mixture then flows

from the aeration tank into the secondary

clarifier, where activated sludge settles out

by gravity.

OXIDATION POND

also called lagoons or stabilization ponds, are

large, shallow ponds designed to treat

wastewater through the interaction of

sunlight, bacteria, and algae. Mechanical

aerators are sometimes installed to supply

yet more oxygen. Sludge deposits in the pond

must eventually be removed by dredging.

Algae remaining in the pond effluent can be

removed by filtration or by a combination

TERTIARY TREATMENT

to raise the quality of

the water to domestic and industrial standards, or to meet

specific requirements around the safe discharge of water.

More than one tertiary treatment process may be used at any

treatment plant. If disinfection is practiced, it is always the final

process. It is also called "effluent polishing".

FILTRATION

It is a process that removes particles and

other media of a certain size and larger from

liquids. Removing these particles and debris

from a wastewater system allows the water

BIOLOGICAL NUTRIENT REMOVAL

regarded by some as a type of secondary

treatment process, and by others as a tertiary (or "advanced") treatment

process

ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL

Phosphorus can be removed biologically in a process called enhanced

biological phosphorus removal. In this process, specific bacteria, called

polyphosphate-accumulating organisms (PAOs).

DISINFECTION

to substantially

reduce the number of microorganisms in the water to be discharged back into

the environment for the later use of drinking, bathing, irrigation, etc.