Primary Treatment of Wastewater
One of the most common industrial waste management processes is recycling. As technology progresses and new needs arise, recycling will become more critical to meet those needs.
It is usually accomplished by allowing special sedimentation tanks or basins where the organic matter in the waste settles as sludge, and the inorganic matter remains in suspension. This septic tank effluent is then discharged to a secondary treatment facility.
One instance of this process is manufacturing facilities that use recycled material to create new goods. These manufacturing facilities need to properly treat wastewater before discharging it to a local sewer system.
This article will cover all about primary wastewater treatment. So let’s start.
Primary Treatment of Wastewater Definition
Primary wastewater treatment is a process to remove settleable and floating solids before the wastewater is discharged to surface water. The immediate treatment removes about 30 to 50 percent of the Biological Oxygen Demand (BOD) and 30 to 60 percent of suspended solids.
Objectives of Primary Treatment
In a sequence of operations, wastewater is treated primarily through physical, chemical, and biological processes. These are applied to domestic sewage to reduce its pollution hazards as much as practicable, and all this is done before discharging it into receiving waters.
->The main objective of this process is to remove floating materials or “scum” that float on the surface. Scums can be made up of organic matter, oils, grease, and other lighter solids.
-> The primary treatment is usually a preliminary stage to further wastewater treatments.
-> Primary treatment of wastewater has been demonstrated by research to improve the quality and settling characteristics of wastewaters that are otherwise difficult to treat.
-> In addition, this process will be beneficial for reducing the BOD (Biological Oxygen Demand) of wastewater.
-> Removal of settleable solids is the most crucial objective of this process
What is a Primary Sedimentation Tank?
A primary sedimentation tank is a holding tank for contaminated water to settle the solids before entering the secondary treatment stage. It is the first stage of the three-stage process for controlling pollution.
Primary sedimentation tanks are used to remove floating oil and other matter on the tank’s surface. Oil removal is usually achieved with an oil-water interface skimmer, which takes floating oil out of the water. The removed fat is stored in a separate tank to be disposed of later.
Primary sedimentation tanks are usually constructed of concrete, masonry, or metal. The tank is open at the top. There is a hatch cover to close the lid after the water has been allowed to settle.
Primary sedimentation tanks come in several different sizes and shapes. A common one is a rectangular tank with an air dome roof located in the center to settle.
Primary Sedimentation Tank Design Specification
Sedimentation tanks are large, circular vessels. Here sludge is allowed to settle out of wastewater under the influence of gravity.
Primary sedimentation tanks are employed in large wastewater treatment plants, and it’s usually the first step in any wastewater treatment process.
Primary sedimentation tanks specifications are given below:
1. Primary sedimentation tank volume is usually 1/3 to half of the plant’s total volume.
2. The surface area of the primary sedimentation tank depends on its flow and (height).
3. The depth is about 1 meter or 3 feet. The slope of the floor is 1/40 to 1/30. The tank can be divided mainly into three parts. They are bar screen area, clear water zone (no solids), and sludge zone (solids dropping down).
4. The bar screen separates the first zone from the other parts. The bar screen is flexible.
5. It can be inserted or removed into the wall of the tank. The area where the bar screen is located needs to be cleaned and maintained, and it is done by removing any accumulated sediment.
6. The primary tank should have good capacity. It ensures that there is enough time for the solids to settle at the bottom of the tank. It will help divert the excess flow to a side-channel or equalization tank before it flows through the bar screen.
7. The outlet channels from the primary sedimentation tank should have a minimum capacity of 2 to 3 times the inlet, and the outer flow does not have a constant limit.
8. It depends on the number of suspended solids in the influent wastewater. More suspended solids are carried over to the primary sedimentation tank for settlement with the increased flow.
Types of Primary Sedimentation Tank
There are several types of primary sedimentation tanks. Here we are going to discuss only three types.
1. Typical primary sedimentation tank
A typical primary sedimentation tank is a large rectangular or cylindrical tank. It is used to remove large particles from wastewater. The wastewater flows into the tank, and the larger particles settle to the bottom.
The water on top flows out of the tank, and it leaves behind a cleaner wastewater stream that can be treated further.
Wastewater enters the vessel through an inlet connected to the sewer system. It is treated by having sediment settle out of it at the bottom of the tank. The contaminants in the wastewater settle out. Then it forms a layer on top of the vessel’s bottom called primary sludge.
The water on top of the vessel flows out for further treatment. Under this category, we get two other types of sedimentation tanks: rectangular tanks and Hopper bottom tanks.
2. Circular Radial Flow Tank
Circular radial-flow sedimentation tanks are the sedimentation tanks used for continuous vertical flow. In this arrangement, the influent is sent through the main pipe. It results in radial flow.
Mechanical scrapers collect sludge. The accumulated sludge is carried through a sludge pipe at the bottom of the tank. Circular radial-flow sedimentation tanks are less economical than rectangular sedimentation tanks. They usually have a lower loading rate and less easy sludge removal.
The diameter of the tank is the primary factor. The greater the diameter of the tank, the larger volume of solids it will be able to hold.
An active stable radial flow pattern is necessary, and it ensures that there is not much turbulence in the sedimentation process. A hopper removes the sludge sedimented at the bottom at the end.
3. Up-flow tanks
Up Flow Tanks are a type of wastewater tank. It allows wastewater to be pumped up from the bottom and then flow out of the tank through an outlet at the top.
It allows the solids to settle at the bottom of the tank and the clarified water to flow out at the top. This type of tank is aerated, usually with an air pump.
In up-flow tanks, the hopper is present at the bottom. From there, the wastewater is taken in and then allowed to flow upward. The main tank or reservoir is PVC pipes covered with a geomembrane sheet. An aeration pump (or air blower) has also been provided to improve its efficiency.
It is to ensure that enough oxygen levels are inside the tank for proper treatment. The polythene sheets cover the entire bed area completely. It is done to allow maximum sunlight for the reduction of BODs.
Up-flow tanks are used mainly by small communities or individual homes, and the waste that the tanks treat are toilet waste, shower, and sink wastewater. However, there are two types of UpFlow Tank for larger gatherings: a Rapid Mixing Type (RMT) and a Slow Mixing Type (SMT).
The SMT allows all the solids to settle before the water is pumped out, and later it is reused by underground irrigation systems. Whereas in RMT’s, this separation is impossible, so the water has to be treated through disinfection before being sent to another process.
Steps in Primary Wastewater Treatment
There are several methods and steps included in Primary wastewater treatment. Primary wastewater is treated through multiple phases to safely return water to the natural environment.
A wastewater treatment facility provides an acceptable quality of effluent for release into rivers, lakes, or oceans.
Primarily wastewater is treated in three stages: physical, biological, and chemical processes.
The proper working of primary wastewater treatment is essential, and it ensures that the final effluent discharged from the plant meets the government’s water quality standards.
The process of primary wastewater treatment can be explained in a detailed manner as follows:
1. Physical Treatment
This stage removes large debris, oil, and grease from the sewage. In some cases, one may add sand or coal to the wastewater. Removing large particles ensures that equipment and machinery in the biological stage are not damaged.
Filtration is the removal of solid material from a liquid or gas stream. In the wastewater industry, it’s the process of removing suspended solids from wastewater. Filtration can be done in various ways, with the most common being through the use of a Basket or Screen Filter.
The grit removal process is the most common in wastewater treatment.
Grit is removed through three steps, i.e., physically, chemically, and biologically. Physical grit removal is done through flotation.
Chemical grit removal is done through coagulation. Biological grit removal is done by using activated sludge which produces bio sludge.
In designing a wastewater treatment plant, a sedimentation process is always necessary. It is used to remove the solid materials in the wastewater. In the sedimentation tank, the wastewater will be passed through the tank, the solids will settle down, and it will remove the clear water from the tank.
Sedimentation can also create the biggest problems in the wastewater treatment industry. Some of the particles may not be genuinely settled and may float back up to the top of the tank. In this case, you may not have treated the wastewater thoroughly.
When you have a wastewater treatment plant, you need to be aware of the level of sediments that settle in primary treatment. If you don’t give this treatment the right level of sedimentation, it can harm the wastewater treatment plant.
2. Biological process
At this stage, bacteria and algae degrade organic matter. Human waste, soap, detergents into carbon dioxide, and mineral salts are included. Most of the organic matter found in wastewater is either suspended or dissolved.
The biological process reduces alkalinity and helps keep pH levels low, decreasing chemical oxygen demand (COD).
Primary treatment of wastewater can be problematic in terms of odor problems and the release of toxic gases. Aeration is used to treat wastewater with the assistance of air bubbles.
Aeration is one of the processes used in wastewater treatment to improve water quality. Aeration refers to the process of transferring oxygen into the water. The oxygen is transmitted as a pressurized gas released into the water. As a result, the water reacts with oxygen in the air.
After that, it carries out a series of reactions like hydration and oxidation. Aeration breaks down the wastewater, allowing bacteria to consume it.
Aeration also produces nitrogen and oxygen used in the production cycle. Without aeration, the organic mass would clog the pipes and other equipment in the wastewater treatment plant.
3. Chemical process
Two types of chemical treatment may be used. It includes removing nitrogenous components by sedimentation or chlorination. It is also done by precipitation of dissolved iron and manganese.
Sedimentation for removing suspended particles is used as the first stage of treatment. It is responsible for converting organic matter in wastewater into biogas and carbon dioxide.
Later they are released into the atmosphere. Aeration is also a process required for nitrogen removal.
Chlorination is a water purification process in which chlorine is used to kill harmful organisms in a water supply. It happens through a reaction of chlorine with natural organic compounds or ammonia.
In simple words, chlorination is just adding chlorine to the water. It is the most widely used method of chlorination. It is used in water treatment and disinfection to kill pathogenic microbes.
Adding chlorine to the water kills most germs and bacteria in the water. It is called the disinfection process. Chlorine is added to water at many stages in the water treatment process.
It is added to water upstream of the area that water will be used, such as a water tank, swimming pool, or a household tank.
Better housekeeping practices to maintain sanitation
We all know that sanitation is an essential part of our day-to-day lives. One must follow a disciplined and systematic approach to maintain cleanliness.
In the absence of this, several diseases may likely attack. Here we will discuss the importance of housekeeping practices and help maintain sanitation.
Cleanliness is next to godliness, and this is a well-known saying. This saying should be a mantra to maintain a clean and healthy environment around us.
We should focus on different areas to make sure that we can keep a clean and healthy environment for our loved ones.
Maintaining sanitation in housekeeping is a challenge for most of us. Maintaining good housekeeping practices is not an easy task, and it involves a lot of discipline, hard work, and time.
Yet, it does not end there. If you do not maintain sanitation, you will be plagued by diseases. It is why you need to put in place a good sanitation plan and follow specific hygiene procedures.
As you know by now that wastewater management is very crucial, we hope you enjoyed our article about the primary treatment of wastewater. We are excited to provide this information on our blog so that you can learn more about water treatment systems.
We are glad you liked the article about the steps of primary treatment of wastewater.
Please note that it is essential to treat the waste before being discharged into the environment. We hope this article helped. Don’t hesitate to contact us anytime if you have questions about water treatment. Thank you for reading!