How to treat Sewage

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How to treat Sewage

Treating sewage is very important. Sewage is the waste material from residential, commercial, and industries that can be decomposed. Now import is why we have to treat sewage and what's in the process.

As you know sewage is the waste material mixed with all impurities with water, we can't mix the sewage in the river or all accumulate in some area.  We have to segregate the waste and remove the water.

Now there are many methods of sewage treatment, but we will discuss simple two methods, that is conversational and nonconventional  

Conventional sewage treatment:- In this process treatment of biological method is used and it reduces the BOD and COD aerobically. after that Chlorination is done.  Please read the last phrase for a detailed system.

NonConventional sewage treatment:- Is to just pass the sewage from multilayers. like charcoal, sand, and pebbles. 



1. WASTE WATER TRANSPORT: The raw wastewater which is generated from various sources is collected at the source and routed towards the treatment plant. All the wastewater is allowed to flow by gravity through close / open drains passing through the course respectively. 
 2. SCREENING: Screening is done in the bar screen chamber to retain large-sized particles / Fibrous material which cannot be equalized and treated.
 3. OIL & GREASE TRAP:  The screened influent enters the O & G trap, where the free-floating oil rises to the surface and is removed periodically. 
 4. COLLECTION / EQUILISATION TANK ( EQT ): The Sewage underflows to the Equalization Tank. The untreated water is retained in this tank with sufficient capacity. This tank acts as a balancing/reaction tank where the hydraulic and organic loading to the subsequent units can be controlled. The Equalization tank is fitted with coarse aeration at the bottom of the tank. As the effluent from various sources carries a large number of suspended solids, the Coarse aeration keeps these solids in suspension to avoid any formation of anaerobic zones in the tank, which can lead to a foul smell. The homogeneous effluent from the collection cum equalization tank is pumped to Bioreactors.
 5. BIOLOGICAL TREATMENT:  The equalized effluent is pumped to the biological treatment aeration tank(s) for biological degradation of available organic matter to reduce the BOD and COD aerobically. The biological treatment tank is designed on the extended aeration principle. The fluidized aerobic bioreactor tank is filled up with small carrier elements. The carrier elements or the media are made up of special grade plastic of specific density that can be fluidized using an aeration device. In course of treatment, a biofilm develops on the carrier elements which move along with the effluent in the bioreactor. The movement within the reactors is generated by providing aeration with the help of diffusers placed at the bottom of the reactor. The thin bio-film on the carrier elements enables the microorganisms to act upon the biodegradable matter in the effluent and reduce the BOD content.
6. TUBE SETTLER:  From the biological reactor the treated effluent flows by gravity to the tube settler. The biological solids generated are removed in the tube settler with the help of tube settler media. 
7. CHLORINATION:  Sodium Hypochlorite solution is used as a sterilizer to remove the residual microbial load. A small amount of residual chlorine in the water will prevent any algae/micro-organism growth during further treatment. 
8. TERTIARY TREATMENT:  Dual Media Filter – The sterilized effluent is pumped to the sand filter to remove any fine suspended particles to achieve filtered water. This filter will also have an Activated Carbon media for the removal of excess chlorine and any odor. The effluent from the activated carbon filter will be clear and odorless.
 9. SLUDGE DRYING BED (SDB): In the process, the sludge is sufficiently mineralized and requires no further treatment before Dewatering and disposal. In the sludge drying bed, sludge is dewatered by filtration through a sand bed and Drying of the dewatered sludge by solar radiation naturally. The dewatered sludge cake is then dried and disposed of. The filtrate from the sludge drying bed is recycled back to the equalization tank.

Residential sewage system 

The most important criteria to be considered for the construction of sewage water drains in a residential area is per day water discharge, normally 250 liter/ day is considered. So, for example, 4 members are staying in one home, the total discharge of wastewater will be 4 x 250 liter = 1000 liters, hence we have to make a septic tank of 3 times the discharge water that is 3000 liters, and then a soak pit for 1.2 times of discharge that is 1200 liters.

Quick conversions 

  1m3 = 1000 litres 

How to calculate tank size

   1m width x 1m length x 1m height = 1m3

Design of ST and Soak pit

1. What is Bio-Chemical Oxygen Demand (BOD)?

Bio-Chemical Oxygen Demand (BOD) testing is widely used in water treatment plants. The test determines the amount of oxygen used up by biodegrading microorganisms during a given time in the presence of oxygen. The BOD test is part of a wastewater treatment plant’s routine monitoring. The test is usually performed at least once a month to ensure the treatment plant is doing its job efficiently and effectively. The results of the BOD test are used to monitor the treatment plant’s operational parameters, to perform minor process adjustments, and generate reports that are submitted on a monthly, quarterly, and yearly basis. The biochemical oxygen demand (BOD) is a measure of the amount of oxygen required by microorganisms in a given water sample to break down organic material (BOD). The BOD test is an analysis performed to determine the amount of oxygen required for the biochemical oxidation of organic matter in an aerobic wastewater sample. The BOD test is the most widely used laboratory test for the measure of the oxygen demand of a wastewater sample.

2. What is Chemical Oxygen Demand (COD)?

What does COD mean? COD, or chemical oxygen demand, is a measure of the amount of oxygen needed to chemically oxidize the contaminants in wastewater. It is an indicator of organic pollutants or other compounds in water. There are many types of pollutants that can cause a high COD level, including organic pollutants from domestic wastewater or industrial waste. One common pollutant is organic material from food, such as food scraps, vegetable peelings, and egg shells. Another common pollutant is the organic matter that comes from leaves, grass, and tree trimmings. The organic material that goes down the drain or toilet and ends up in the sewage treatment plant is known as biochemical oxygen demand or BOD. This is the reason why sewage treatment plants have to be equipped with a system called activated sludge, as the sludge converts the organic matter found in the water into carbon dioxide, water, and bacteria. The bacteria are then used to treat the water, which is then returned to the environment.

3. How to Treat Sewage Water?

Sewage treatment plants are used to treat sewage water from homes and businesses. The sewage water is treated and made good enough to be released into the environment. Wastewater can be treated by a number of different processes. Each one uses different processes to remove different types of waste from the water. The goal of most sewage treatment plants is to give people clean water to use for things like drinking and bathing. There are actually two kinds of water that come from our homes and businesses: wastewater and stormwater. Stormwater is used for watering plants, lawns, gardens, and cars. It's also used for cooling equipment in factories, refineries, and power plants. While wastewater is the water that is used for flushing the toilets, doing the laundry, and washing the dishes. Collectively, wastewater and stormwater are called wastewater.

Conclusion: The toxicity of water can be tested by its BOD and COD values.

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