Steps of Sewage Treatment
The process of sewage treatment is an important one for any city. It ensures that the water in your drinking glass is safe to drink. It’s also necessary to ensure that the environment doesn’t get polluted by human waste.
The process of sewage treatment starts with a bit of history. People believed in natural purification through “sewage farming” or using animal manure as fertilizer long ago. But this practice was abandoned when it became clear how destructive it was to humans and animals alike.
The three stages of sewage treatment are primary, secondary, and tertiary treatment. Each stage has several steps that the sewage goes through to leave behind clean water.
Today, modern-day sanitation practices collect raw sewage in pipes before treating it chemically or biologically (or simply dumping it into rivers). This process may be complicated because each type of wastewater requires different chemicals to remove the pollutants.
Raw sewage can contain both harmful chemicals and microbes. Toxic chemicals come from treated water, commercial products, agricultural wastes, solid human waste, runoffs from streets containing metals, oils, salts, and organic chemicals. You can now imagine how much waste and harmful chemicals one must eliminate to ensure clean and safe water.
So let us discuss some of the helpful and harmless methods of Sewage water treatment.
What Are The Three Main Stages/Steps of Sewage Water Treatment?
Three different steps to treat sewage water are primary, secondary, and tertiary wastewater treatment.
1) Primary treatment is the first step in wastewater treatment, and however, screening is always the primary stage of sewage treatment. The first step of this primary treatment is to use aeration tanks that let the liquid settle, and the liquid will then flow into more aeration tanks, where bacteria help remove dirt and debris particles from water.
2) Secondary treatment is the next stage in the sewage water treatment process. Primary sludge is first thickened by adding more floc to it. It aids in the settling of other particles, which one should remove from the wastewater. The aeration step is repeated with another addition of floc to assist in the removal of these particles.
3) Tertiary treatment is the last and final stage where all the filtering processes are done to further reduce organics and other chemical components.
Primary Wastewater Treatment
In the aspect of water resources pollution, primary treatment is a basic necessity for water resource conservation. The concept and function of primary sewage treatment plant (also called POT (Primary Oxygen Treatment)) will be introduced here briefly:
Stages of primary wastewater treatment
Primary Wastewater treatment consists of several stages, and we will brief them so that you can understand them properly.
1. Screening and pumping
Screening is done by passing the sludge through sieves of different sizes so that only solids are leftover while liquid moves on to the pump stage. Using centrifugal force or suction devices removes liquids from solid matter to create cleaner effluent for reuse in other processes, such as irrigating agricultural fields or watering lawns.
2. Grit removal
Grit removal is removing sand, grit, and other coarse material from water. Grit removal machines typically use screens with openings 0.5mm in diameter – 1mm in diameter, which can be made up of stainless steel wire mesh or plastic foam blocks fused into a honeycomb shape. This opening size will allow most sand grains to pass through but capture stone fragments, etc., too big to fit through it.
3. Primary settling
This process is typically the third step in an effluent purification system. The primary settling tank can be either gravity or mechanical, and it depends on what other methods are included in the wastewater treatment system design.
The immediate settling process removes larger solids from wastewater through sedimentation and provides cleaner effluents for further processing.
4. Aeration/activated sludge
Activated sludge plants use a variety of processes to remove organic material from the water, and these include clarification, gas stripping, chemical oxidation, nitrification, and denitrification. Activated sludge is also used to treat sewage or industrial wastewater where it reduces organic material and biochemical oxygen demand (BOD).
5. Secondary settling
The secondary settling process is conducted by removing residues that may have been deposited in the primary settler. These sediments consist of the more finely divided particles of solids and greases and colloidal matters such as clays, shales, silts, etc. These were not removed in the primary settler.
These residues are given a final separation from the clear water. It is done through a slow-moving layer of water on top of a faster-moving layer underneath.
6. Filtration
Filtration can be defined as a process of separating particles from a liquid. The liquid will pass through a medium where particles are collected on the surface or inside the medium. There are many types of filtration based on the type of media used. These media include sand, diatomaceous earth, and anthracite coal.
7. Disinfection
The primary purpose of disinfection in the wastewater treatment process is to kill microorganisms. Microorganisms like bacteria, viruses, and protozoa can cause disease. The goal of adding disinfectants is not only to provide safe drinking water.
In addition to that, to avoid spreading diseases through sewers and waterways, disinfectants are used. Disinfectant chemicals include chlorine, chloramines, ozone, and ultraviolet light.
8. Oxygen uptake
This step is effective at removing nitrogen compounds from wastewater. Oxygen uptake can be defined as air passage through wastewater via diffusion, air stripping, or both. The oxygen diffuses into the wastewater and reacts with the organic compounds to form carbon dioxide.
This reaction is known as aerobic digestion and is a biologically mediated process. In addition, the oxygen that diffuses into the wastewater can react with nitrogen present in the wastewater to form nitric acid—the formation of nitric acid results in the loss of nitrogen from wastewater.
9. Sludge treatment
Sludge treatment is a process that turns sewage, wastewater, and other forms of water into clean water. The sludge treatment process includes the following steps:
● Dewatering the sludge by removing as much liquid from it as possible.
● Batching up the dewatered sludge in tanks or pits for anaerobic digestion or aerobic decomposition.
● In some cases, drying out the sludges produce a more stable material when it’s sent offsite for long-term storage.
● Sometimes, it is incinerated in a sewage sludge treatment facility.
The end product is clean water that we can safely release into the environment.
know more about Primary Wastewater Treatment here.
Secondary Wastewater Treatment
The secondary wastewater treatment is a process that separates the organic solids from the wastewater to form effluent, which is treated and safe to release, and solids that can be used as a fertilizer. It is achieved through the following ways:
Ways of secondary waste treatment
1. Biofiltration
In biofiltration, many organisms are involved. They may be active or passive filter feeders such as bacteria, protozoa, algae, and fungi. They may be attached to inert particles, then removed with the treated water.
They may adhere to surfaces inside active filters (e.g., rotating discs). In this way, microorganisms remove dissolved substances from wastewater by adsorption/absorption on their cell surface or by ingestion of suspended solids within the water stream.
Biochemical reactions also occur between these microorganisms and organic matter in the wastewater. These biochemical reactions lead to the removal of pollutants. The production of gases such as carbon dioxide, methane, and hydrogen sulfide is also stopped.
2. Aeration
The process involves mixing air with sewage to oxidize the organic matter. It will remove some harmful substances in the wastewater, including hydrogen sulfide and ammonia. It also helps with odor control by removing methane gas generated by bacteria during treatment.
3. Oxidation ponds
In Oxidation ponds, pollutants are eliminated or reduced by exposing them to sunlight and air. The sunlight helps break down the contaminants, while the air helps to disperse them. This type of treatment is often used for wastewater that contains organic pollutants, such as municipal wastewater and agricultural runoff.
Know more about Secondary Wastewater Treatment here.
Tertiary Wastewater Treatment
The tertiary phase includes chemical treatments to stabilize the water for discharge into waterways or reuse within the industry.
Tertiary treatment reduces or removes substances from shots, so they are less harmful to human health and natural ecosystems. One substance that you must remove from wastewater is phosphorus.
Phosphorus is an element that stimulates algae growth and can lead to excessive aquatic plant life, depleting dissolved oxygen in the water. Phosphorus can be removed or destroyed before the release of wastewater. The water is exposed to chemicals that precipitate the dissolved phosphorus, making it less damaging to the environment.
How does tertiary wastewater treatment work?
1. Filters
In tertiary wastewater treatment, filters are vital for removing solids from wastewater. For example, retention time can be increased to allow more solid particles to settle out, or filtration membranes could remove dissolved solids.
Bag filters
The frame is constructed and filled with medium-sized gravel in a typical application, washed clean beforehand. The frame is then assembled into a tank or basin where the wastewater enters at one end and flows down over the rock.
This process removes most of the suspended solids from wastewater before leaving through an outlet pipe at the bottom of the filter bed to enter a clarifier for further processing before being discharged into surface waters downstream. The size range for this type of bag filter depends on how many suspended solids we must remove from the wastewater.
Drum filters
The drum filter process begins by pumping raw sewage into a rotating cylinder with vertical slots cut out of its shell. These slots form channels where solids can accumulate and settle as it rotates. The sludge that collects at the bottom is removed periodically for disposal or processing, while clean water continues through with fewer suspended solids than when entered.
Disc filters
Disc filters are most often used in tertiary wastewater treatment systems because they can remove bacteria with low-pressure loss. They are commonly used to remove fine particles and microorganisms (bacteria) from wastewater.
A disc filter works using centrifugal forces arising from a rotating disc to separate waste matter from clean water. There are many different disc filters, but the two most common types include hydraulic and non-hydraulic filters.
2. Disinfecting
Chlorine treatment
Tertiary wastewater treatment involves adding chlorine to clean the water before releasing it into the environment. This process makes sure that all of the dangerous organisms are killed off, so they don’t infect other people or animals downstream. Chlorine is also added to raw sewage coming out of homes and businesses, preventing mosquitoes’ infestation.
Ultraviolet light treatment
Ultraviolet light is a disinfectant, and it is used to treat water for human consumption. The UVA and UVB rays in ultraviolet light inhibit the growth of bacteria that can cause diseases such as cholera, typhoid fever, and polio.
Ozone treatment
Ozone treatment is used to control wastewater’s biochemical oxygen demand (BOD) levels. BOD measures the amount of oxygen required by microorganisms to break down organic matter in a water quality test. The lower the BOD, the better the wastewater treatment process is working, and hence cleaner water is discharged.
3. Discharge
Discharging the pollutants in the right way is very important. Some of the discharged pollutants are toxic to the environment and human health. The contaminants released into the atmosphere can contaminate soil, water, and air and harm plants, animals, and humans.
The correct way to discharge the pollutant is to control their concentration in wastewater. The amount of contaminant discharged into the environment should not exceed the environmental standard for that pollutant. If the concentration of contaminants is too high, it can be diluted to be safe for the environment for human health level.
4. Reuse
You can reuse the wastewater to save the environment. Using wastewater causes the saving of clean water and also helps in conserving natural resources. The use of domestic sewage decreases the pollution load on freshwater sources, rivers, and the sea. Moreover, disposal of wastes becomes easy and economical by this method.
In the past, sewage from toilets and bathrooms was dumped into rivers or directly into oceans. Wastewater treatment plants were not present to treat the sewage before it went into natural waterways in those days.
These circumstances caused a severe environmental problem that threatened human health and animal and plant species living in the water.
For a sustainable environment, you must treat wastewater before releasing it in the background. This treatment system has been developed called wastewater recycling. Most big cities have sophisticated sewage systems that treat the wastewater from homes and industries before dumping them into oceans in today’s world.
After the water is treated, you can use it for various purposes. For example watering the lawns, irrigation of farms and industries. It also reduces contamination in oceans and rivers, and it is done by eliminating toxic materials like pesticides, arsenic, mercury, and lead. All these steps are practical enough to take care of our planet’s precious resources, which will bring long-term benefits.
The need for wastewater treatment has become increasingly important today as the amount of wastewater generated by human activities continues to grow.
The main objective of wastewater treatment is to protect the environment and public health by reducing the adverse effects of wastewater. Several different technologies are available for treating wastewater, and each has its advantages and disadvantages.
Conclusion
It is essential to select the right technology for a particular application based on the characteristics of the wastewater and the desired results.
Advanced treatments such as reverse osmosis and activated carbon can help reduce the level of pollutants in wastewater to below detectable levels. These treatments also effectively remove harmful compounds such as pharmaceuticals and endocrine disruptors.
Wastewater treatment technologies are constantly changing to keep up with the latest developments in wastewater treatment. The current trend is towards more sustainable forms of wastewater management, particularly energy usage and climate impact. Future demand for clean water means it will become even more critical to treat wastewater properly before returning it to the environment.
