Primary, Secondary, and Tertiary Wastewater Treatment: How Do They Work?
- Primary Wastewater Treatment. Primary treatment of wastewater involves sedimentation of solid waste within the water. ...
- Secondary Wastewater Treatment. Secondary treatment of wastewater makes use of oxidation to further purify wastewater. ...
- Tertiary Wastewater Treatment. ...
What is the primary treatment of wastewater?
Jun 27, 2017 · Primary treatment of wastewater involves sedimentation of solid waste within the water. This is done after filtering out larger contaminants within the water. 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.
What happens to materials in the wastewater treatment process?
Primary treatment removes material that will either float or readily settle out by gravity. It includes the physical processes of screening, comminution, grit removal, and sedimentation. Screens are made of long, closely spaced, narrow metal bars. They block floating debris such as wood, rags, and other bulky objects that could clog pipes or pumps.
How long does it take for wastewater to be treated?
The main objectives of primary treatment of wastewater are: To reduce the strength of sewage to the extent 30% to 50%. To remove settleable solids by 80% to 90%. To reduce BOD by 30% to 35%. To make the sewage fit for further treatment process. Primary Sedimentation Tank. Primary sedimentation tank is also known as primary clarifier and is located just after grit chamber.
What are the stages of wastewater treatment?
Dec 06, 2018 · What is primary wastewater treatment? During primary treatment, wastewater is temporarily held in a settling tank where heavier solids sink to the bottom while lighter solids float to the surface. Once settled, these materials are held back while the remaining liquid is discharged or moved through to the more rigorous secondary phase of wastewater treatment.
What happens during primary treatment of wastewater?
Primary treatment of wastewater involves sedimentation of solid waste within the water. This is done after filtering out larger contaminants within the water. Wastewater is passed through several tanks and filters that separate water from contaminants.Jun 27, 2017
What are the steps of primary water treatment?
Wastewater Primary Treatment ProcessScreening: Wastewater entering the treatment plant includes items like wood, rocks, and even dead animals. ... Pumping: ... Aerating: ... Removing sludge: ... Removing scum: ... Killing bacteria: ... Wastewater Residuals:
What steps are taken during secondary treatment of waste water?
The secondary stage of treatment removes about 85 percent of the organic matter in sewage by making use of the bacteria in it. The principal secondary treatment techniques used in secondary treatment are the trickling filter and the activated sludge process.
What is the purpose of primary sewage treatment?
The purpose of primary treatment is to settle material by gravity, removing floatable objects,and reducing the pollution to ease secondary treatment. Primary Treatment aims to reduce the Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) in the wastewater.
What is the purpose of sewage treatment plant?
The sewage treatment plant provides a suitable environment , albeit of steel and concrete , for this natural biological process. Removal of soluble organic matter at the treatment plant helps to protect the dissolved oxygen balance of a receiving stream, river, or lake.
How does removal of impurities work?
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.
How long does it take for a primary clarifier to settle?
These tanks, also called primary clarifiers, provide about two hours of detention time for gravity settling to take place. As the sewage flows through them slowly, the solids gradually sink to the bottom. The settled solids—known as raw or primary sludge —are moved along the tank bottom by mechanical scrapers.
How much of the secondary sludge must be treated?
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 ( see Sludge treatment and disposal ).
How long does activated sludge stay in the aerator tank?
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.
What is the purpose of a secondary clarifier?
Air circulating upward through the spaces among the stones provides sufficient oxygen for the metabolic processes. Settling tanks, called secondary clarifiers, follow the trickling filters. These clarifiers remove microbes that are washed off the rocks by the flow of wastewater.
What is activated sludge?
activated sludge process. Primary and secondary treatment of sewage, using the activated sludge process. Encyclopædia Britannica, Inc. Grit chambers are long narrow tanks that are designed to slow down the flow so that solids such as sand, coffee grounds, and eggshells will settle out of the water. Grit causes excessive wear and tear on pumps ...
How does a water treatment facility get rid of sewage?
One of the first steps that a water treatment facility can do is to just shake up the sewage and expose it to air. This causes some of the dissolved gases (such as hydrogen sulfide, which smells like rotten eggs) that taste and smell bad to be released from the water. Wastewater enters a series of long, parallel concrete tanks. Each tank is divided into two sections. In the first section, air is pumped through the water.
Where are wastewater treatment plants located?
Pumping: The wastewater system relies on the force of gravity to move sewage from your home to the treatment plant. So wastewater-treatment plants are located on low ground, often near a river into which treated water can be released.
How is scum pumped to digesters?
Scum is thickened and pumped to the digesters along with the sludge. Many cities also use filtration in sewage treatment. After the solids are removed, the liquid sewage is filtered through a substance, usually sand, by the action of gravity.
What is scum in sedimentation tanks?
Removing scum: As sludge is settling to the bottom of the sedimentation tanks, lighter materials are floating to the surface. This 'scum' includes grease, oils, plastics, and soap. Slow-moving rakes skim the scum off the surface of the wastewater.
How does aeration work?
In the first section, air is pumped through the water. As organic matter decays, it uses up oxygen. Aeration replenishes the oxygen. Bubbling oxygen through the water also keeps the organic material suspended while it forces 'grit' (coffeegrounds, sand and other small, dense particles) to settle out.
What is a process.png?
Process.PNG. 1. Screening: Wastewater entering the treatment plant includes items like wood, rocks, and even dead animals. Unless they are removed, they could cause problems later in the treatment process. Most of these materials are sent to a landfill. 2. Pumping:
How long is treated water kept in a digester?
7. Wastewater Residuals: Another part of treating wastewater is dealing with the solid-waste material. These solids are kept for 20 to 30 days in large, heated and enclosed tanks called 'digesters.'.
How to treat wastewater?
The main objectives of primary treatment of wastewater are: 1 To reduce the strength of sewage to the extent 30% to 50%. 2 To remove settleable solids by 80% to 90%. 3 To reduce BOD by 30% to 35%. 4 To make the sewage fit for further treatment process.
What are the main objectives of primary treatment?
The main objectives of primary treatment of wastewater are: To reduce the strength of sewage to the extent 30% to 50%. To remove settleable solids by 80% to 90%. To reduce BOD by 30% to 35%. To make the sewage fit for further treatment process.
What is primary sedimentation tank?
Primary sedimentation tank is also known as primary clarifier and is located just after grit chamber. It may be rectangular, circular or square shape. The principle and construction details are same as that of plain sedimentation tank W.T.P.
What are the stages of wastewater treatment?
What Are the Three Stages of Wastewater Treatment? There are three main stages of the wastewater treatment process, aptly known as primary, secondary and tertiary water treatment. In some applications, more advanced treatment is required, known as quaternary water treatment.
What is the process of removing sediment from a wastewater system?
1. Biofiltration. Bio filtration uses sand filters, contact filters or trickling filters to ensure that any additional sediment is removed from the wastewater. 2. Aeration. Aeration is a lengthy process which increases oxygen saturation by introducing air to wastewater.
Where is wastewater held?
During primary treatment, wastewater is temporarily held in a settling tank where heavier solids sink to the bottom while lighter solids float to the surface. Once settled, these materials are held back while the remaining liquid is discharged or moved through to the more rigorous secondary phase of wastewater treatment.
What is tertiary treatment?
In the case of water treated by municipalities, tertiary treatment also involves the removal of pathogens, which ensures that water is safe for drinking purposes.
What happens when wastewater enters the secondary clarifier?
When the wastewater enters the two Secondary Clarifiers, it still contains lots of microorganisms from the Aeration Basins and looks brown and murky. The Secondary Clarifiers are identical to the Primary Clarifiers; materials in the wastewater sink and float and rotating arms remove this material from the water.
What is the process of aeration of wastewater?
From the Primary Clarifiers, the wastewater flows into large, rectangular tanks called Aeration Basins, where a biological treatment called the “activated sludge process” occurs. The wastewater flows slowing through a series of chambers as large volumes of air are bubbled up through the water. There is so much air added that it looks as if the water is boiling. In these basins, the wastewater is mixed with the “activated sludge;” hundreds of millions of actively growing single-celled microorganisms (mostly bacteria and protozoa) referred to as “bugs.”
How long does it take for wastewater to leave the aeration basin?
When all of the food (waste) is gone, after about eight hours, the wastewater leaves the Aeration Basins.
How much water does a secondary clarifier hold?
The Secondary Clarifiers each hold 800,000 gallons of water.
What is considered preliminary treatment?
Preliminary Treatment: Physical. When wastewater arrives at the treatment plant, it contains many solids that cannot be removed by the wastewater treatment process. This can include rags, paper, wood, food particles, egg shells, plastic, and even toys and money.
How many gallons of water can a primary clarifier hold?
Primary Clarifiers: Physical. From the Headworks, the wastewater flows into two huge circular tanks called Primary Clarifiers. These tanks can hold 600,000 gallons of water each. Here the wastewater slows down and remains in the tanks for about two hours.
Screening
Most sewer systems operate by gravity flow, which pulls wastewater toward the treatment plant. It first enters the plant at the headworks and passes through the preliminary treatment called screening where large objects are trapped and removed for landfill disposal.
Aeration and Sedimentation
The wastewater leaving primary treatment then enters the secondary treatment process which is a two-phase process. In the first phase, also called aeration, the wastewater is mixed with air and cultivated microorganisms that consume suspended organic matter such as food particles, human waste, and other organic matter.
Disinfection
The fairly clean water from the secondary treatment process is sent through a filtration system to remove any fine particles remaining, and then it is ready for disinfection. The most common form of disinfection is chlorine inside a chlorine contact chamber, but other disinfection methods also work such as ozone, ultraviolet light, and peroxide.
What is primary wastewater treatment?
The primary wastewater process utilizes equipment to break up larger particles and then uses sedimentation or a floating process for extraction. Many treatments that use the primary method then proceed to the secondary treatment process.
How is wastewater treated?
The primary treatment of wastewater occurs through sedimentation with filtering out large contaminant particles within the liquid. The contaminants separate as they are passed through several tanks and other filters. Leftover sludge filters through a digester to suspend solids from the wastewater.
How to get rid of sediment in sewage?
The first is biofiltration that uses filters with sand, contact filters or trickling filters that remove sediment from the sewage. Aeration is the next step. It mixes the wastewater with a microorganism solution. Then, this treatment uses an oxidation pond to pass the wastewater through a body for up to two or three weeks.
What is the process of removing impurities from water?
The removal in the secondary wastewater treatment process generally occurs through a biological process with consumption of impurities in water by microbes, converting the matter into energy, carbon dioxide gases, and water. AOS can help with municipal wastewater treatment services in both primary and secondary processes.
What is primary treatment?
Through the primary treatment, it is possible to remove materials that float and settle on top of water. Through primary treatment, it is possible to implement screening water treatment, reduce particles to fragments, remove grit and initiate sedimentation. The primary treatment pushes sewage through screens into the comminutor for grip disposal ...
What is the difference between primary and secondary treatment?
The principal difference in primary and secondary treatment is the process that breaks down the sewage in wastewater. In the primary method, the waste processes through a physical procedure with equipment and filtration. While secondary treatment may use similar items, this method uses biological treatment through microbes.
What is the difference between filtration and sedimentation?
Another difference between these processes is how much time they take to complete.
