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Main Stages of Wastewater and Sewage Treatments - Coggle Diagram
Main Stages of Wastewater and Sewage Treatments
Tertiary Treatment
process and is employed to further polish the effluent that has undergone primary and secondary treatment
achieve higher levels of water quality by addressing remaining impurities, nutrients, and pathogens.
The specific methods used in tertiary treatment can vary, but they often include the following processes:
filtration
This step helps remove any remaining suspended particles and solids, improving the clarity of the water.
Nutrient Removal
Nutrient removal is important to prevent excessive nutrients, such as nitrogen and phosphorus, from being discharged into receiving water bodies.
Methods like chemical addition (using chemicals like alum or ferric chloride) or biological processes (such as denitrification) may help to reduce nutrient levels.
Disinfection
Common disinfection methods include chlorination, ultraviolet (UV) irradiation, and ozonation.
Advanced Oxidation Processes (AOPs)
AOPs involve the use of advanced chemical oxidation techniques to break down persistent organic pollutants.
Examples include ozonation, advanced UV treatment, and hydrogen peroxide addition.
Adsorption
Adsorption involves the use of adsorbent materials (such as activated carbon) to remove remaining organic compounds, colour, and odour from the water.
Membrane Filtration
Membrane filtration processes, including microfiltration, ultrafiltration and nanofiltration, can be used to achieve high-quality water by physically separating particles and impurities.
Reverse Osmosis (RO)
RO is a specific membrane filtration process that uses a semi-permeable membrane to remove ions, molecules, and larger particles, producing high- quality water.
Primary Treatment
physical processes to remove large solids and reduce the biochemical oxygen demand (BOD).
Here are the typical stages of primary treatment:
Screening
passes through screens to remove large objects such as sticks, leaves, plastic, and other debris.
This step helps protect downstream equipment from damage and prevents clogging.
Grit Removal Chambers
the wastewater may be directed to a grit chamber where heavy, inorganic materials like sand, gravel, and other gritty particles settle to the bottom.
Uses of grit removal chambers:
Protects equipment and prevents abrasion
Used to slow down the flow with the objective of settling heavy solids.
Used for saving the waste treatment cost.
Types of Grit Removal Chambers
Aerated grit chamber
Vortex-type grit chamber
Detritus Tanks
Horizontal Flow Grit Chambers
Inclined Plate Grit Chambers
Primary Sedimentation
The screened and grit-removed wastewater flows into primary settling tanks, also known as primary clarifiers
In these large tanks, the speed of the water is reduced, allowing heavier particles to settle to the bottom as sludge.
Sludge is a semi-solid substance comprising a mixture of solid particles and water, It contain organic and inorganic materials, along with pollutants.
The clarified water, or effluent, is then collected from the top.
Secondary Treatment
crucial step that follows the primary treatment process, it involves biological processes.
reduce the concentration of organic pollutants and suspended solids in the water
The three most common methods for secondary treatment are:
Activated sludge process
The activated sludge treatment system consists of an aeration tank
Settled sewage, mixed with fresh sludge that is recirculated from the secondary clarifier, is introduced into the aeration tank.
Compressed air is then injected into the mixture through porous diffusers located at the bottom of the tank. As it bubbles to the surface, the diffused air provides oxygen and a rapid mixing action.
Under such oxygenated conditions, microorganisms thrive, forming an active, healthy suspension of biological solids mostly bacteria called activated sludge.
About six hours of detention is provided in the aeration tank, this gives the microbes enough time to absorb dissolved organics from the sewage, reducing the BOD.
The mixture then flows from the aeration tank into the secondary clarifier, where activated sludge settles out by gravity.
Clearwater is skimmed from the surface of the clarifier, disinfected, and discharged as secondary effluent.
The sludge is pumped out from a hopper at the bottom of the tank. About 30 percent of the sludge is recirculated back into the aeration tank, where it is mixed with the primary effluent.
The recycled microbes are well acclimated to the sewage environment and readily metabolize the organic materials in the primary effluent. The remaining 70 percent of the secondary sludge must be treated and disposed of in an acceptable manner
Oxidation pond
shallow ponds designed to treat wastewater through the interaction of sunlight, bacteria, and algae.
Algae grow using energy from the sun and carbon dioxide and inorganic compounds released by bacteria in water.
During the process of photosynthesis, the algae release oxygen needed by aerobic bacteria.
Mechanical aerators are sometimes installed to supply yet more oxygen, thereby reducing the required size of the pond.
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.
Trickling filter process
The primary effluent is distributed over a bed of rocks, plastic media, or other support materials forming a trickling filter.
Microorganisms form a biofilm on the media's surface and metabolize organic pollutants
The treated water from the trickling filter flows into a secondary clarifier.
In a secondary clarifier, solids settle and clarified water is separated from the sludge.
These microorganisms form a biofilm on the surface of the filter media, where they break down and consume organic pollutants present in the wastewater.
The most common types of microbes found in trickling filters include:
Nitrifying bacteria
Nitrifying bacteria are responsible for the conversion of ammonia into nitrites and then into nitrates. This process, known as nitrification, is important for reducing the nitrogen content in the wastewater
Heterotrophic bacteria
Heterotrophic bacteria are diverse microorganisms that obtain their carbon and energy from organic compounds. They contribute to the decomposition of complex organic substances in the wastewater.
Fungi
Fungi can also be present in trickling filters. While not as dominant as bacteria, certain fungal species may contribute to the breakdown of organic matter.
Aerobic bacteria
require oxygen for their metabolic processes. They play a key role in oxidizing and breaking down organic matter