3.1 WASTEWATER TREATMENT SYSTEM

Wastewater treatment

is 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.

Suspended solids

Total suspended solids
Aesthetic problems

Sludge deposits

Pollutants adsorption

Protection of pathogens

Biodegradable organic matter

Biochemical oxygen demand

Oxygen consumption

Death of fish

Septic condition

Nutrients

Nitrogen

Phosphorus

Excessive algae growth

Toxicity to fish (ammonia)

Illness in new-born infants (nitrate)

Pollution of groundwater

Pathogens

Coliforms
Water-borne diseases

SOURCES OF WASTES

RESIDENCES

COMMERCIAL INSTITUTIONS

INDUSTRIAL ESTABLISHMENTS

AGRICULTURAL ESTABLISHMENTS

PHYSICAL WATER TREATMENT

BIOLOGICAL WATER TREATMENT

CHEMICAL WATER TREATMENT

TYPES OF WASTEWATER TREATMENT

PHYSICAL WATER TREATMENT

Screening

Sedimentation

Filtration

Aeration

BIOLOGICAL WATER TREATMENT

Aerobic Process

Anaerobic Process

Composting

CHEMICAL WATER TREATMENT

Chlorination

Ozonation

Neutralization

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

Here, 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

s 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 nondegradable 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.

BAR SCREEN

GRIT CHAMBER

MESH SCREEN

PRE-TREATMENT

PRE-SETTLING BASIN]

CLARIFIER

RAPID MIXING

FLOCCULATION

PRIMARY TREATMENT

RAPID MIXING

A process of applying turbulence on the tank adding chemicals that encourages coagulation to water streams

aluminum coagulants (aluminum sulfate, aluminum chloride and sodium aluminate)

iron coagulants (ferric sulfate, ferrous sulfate, ferric chloride and ferric chloride sulfate)

other chemicals (hydrated lime and magnesium carbonate)

Primary coagulants

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

ACTIVATED SLUDGE

OXIDATION POND

SECONDARY TREATMENT

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 of chemical treatment and settling

TERTIARY TREATMENT

The aim of tertiary wastewater treatment is 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".

The treatment process is chemic/physical process to remove remaining inorganic compounds, and substances, such as the nitrogen and phosphorus

FILTRATION

BIOLOGICAL NUTRIENT REMOVAL (BNR)

ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL

DISINFECTION

TERTIARY TREATMENT

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 to be reused within that system.

.

Sand filtration

removes much of the residual suspended matter

carbon adsorption

Filtration over activated carbon, also called —, removes residual toxins

BIOLOGICAL NUTRIENT REMOVAL (BNR)

regarded by some as a type of secondary treatment process, and by others as a tertiary (or "advanced") treatment process .

● Wastewater may contain high levels of the nutrients nitrogen and phosphorus. Excessive release to the environment can lead to a buildup of nutrients, called eutrophication.

biological oxidation

● Nitrogen is removed through the — of nitrogen from ammonia to nitrate (nitrification), followed by denitrification.

ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL

Phosphorus can be removed biologically in a process called —- . In this process, specific bacteria, called polyphosphate-accumulating organisms (PAOs).

● Phosphorus removal can also be achieved by chemical precipitation, usually with salts of iron (e.g. ferric chloride), aluminum (e.g. alum), or lime.

● Once removed, phosphorus, in the form of a phosphate-rich sewage sludge, may be dumped in a landfill or used as fertilizer.

DISINFECTION

● The purpose of — in the treatment of waste water is 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.

● Common methods of disinfection include ozone, chlorine, ultraviolet light, or sodium hypochlorite