Septic tanks

Septic tanks are the simplest and most commonly used unit for wastewater treatment, especially human sanitation. Septic tanks have different applications. Septic can be used for sewage sump tank to pump it to main treatment package. It can be pre-treated in septic tank by processes such as settling, floating process. These septic tanks are widely used in residential and villa units, residential and office complexes, construction workshops, manufacturing plants, hotels, restaurants, and recreational and sports complexes.

Septic Tank Components:

As shown below, each septic tank is made up of different components. Important components of any septic tank include:

  • Wastewater Inlet System: Includes pipe and baffle inlet.
  • Primary septic tank: It has the largest volume of septic tanks and is usually 65 to 75% of the total septic tank volume.
  • Separator wall: This prevents the entry of sludge and grease and floating oils into the clearing tank.
  • Clearance Tank: This tank contains approximately 35% of the total volume of septic tank. In that wastewater accumulates free of sediment and floats.
  • Biogas Exhaust (Ventilation): Through this conduit, the air generated by the anaerobic wastewater treatment processes that is mainly methane is released from the septic.
  • Sewage Output System: Contains baffle and septic outlet pipe

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Wastewater first enters the septic tank through the inlet pipe. This section, separated by a separating wall from the second part of the tank, comprises a volume equal to two-thirds of the total volume of septic tank. As the sewage enters this section, the suspended matter and foreign particles move downstream due to their greater weight and settle on the bottom of the tank. Oils and fats also move upward and float on the surface because they are less specific in weight than sewage.
The accumulation of sediments on the floor of the tank causes a mass of sludge to grow and grow in microorganisms and bacteria. The biological reactions that occur during their reproduction and growth cause the organic matter to be decomposed and the wastewater treated. Performing these reactions also results in a considerable volume of sludge being converted to biogas and reducing the volume of sludge. The produced biogas, which is mainly methane, flows out of the septic tank through the biogas outlet pipe.

The effluent of the first section then enters the second part of the septic tank by passing the connecting path embedded in the separator wall. In this section very fine particles of oil and fat left in the sewage float on the surface. Finally, the clarified effluent is discharged through the outlet pipe into the septic tank. Sludge accumulated in septic
The tank needs to be discharged after about two years. Better to discharge, leave some of the sludge in the septic tank. Because the sludge contains microorganisms and bacteria that are effective in filtration and their complete discharge prolongs the restart time of the biological part of the septic tank.

Uses of septic tank:

The septic tank properties have made them widely used in various home, health and industrial sectors. Some of the main uses of septic tanks are:

  1. Pre-treatment and pre-treatment of sanitary sewage in residential units, commercial and office complexes, hotels and restaurants due to municipal and environmental regulations
  2. Removal of sediment, grease and oils in sewage in restaurants and dining halls to prevent rapid filling of absorption wells and clogging pipes due to accumulation of fat and coarse sediment particles.
  3. Wastewater Balancing and Pumping in Wastewater Treatment Systems

Septic tanks are commonly used for sanitation. So here’s how to calculate septic tank capacity for sanitation. According to BS6297 standards, the septic tank capacity can be calculated from the following equation.

(V) = (2000) + (C × P)

In the above relation, V is the minimum septic tank volume per liter, C is the number of wastewater per day per liter, and P is the number of persons covered per person. Therefore, to determine the required septic tank capacity, the volume of daily wastewater produced must first be calculated. The volume of sanitary sewer usually depends directly on the number of people covered.

Typically, if the collected sewage discharge is about 2 cubic meters per day, septic capacity of 3 cubic meters is considered. If the collected sewage discharge is about 2 to 6 cubic meters per day, the septic capacity is about 1.5 times the discharge rate.

Filtration efficiency:

Much of the residual suspended solids (ss), oils and fats eliminates floating objects and junk in the effluent at an efficiency of about 65 to 85%. Following removal of these pollutants, other pollutant parameters such as COD, BOD5 and TSS are also reduced. The portion of solids removed from wastewater that is more dense than water. The floor part of the reservoir accumulates and forms a layer of sludge.
Another part of the solid material removed from the wastewater, which is less dense than water, forms a layer on the surface of the wastewater, which mainly contains oil, grease, and other floating objects, including plastic particles. These layers grow due to the favorable conditions of the bacteria and digest or soluble some of these solids. Solve
The incorporation of some solids into the wastewater and passing them through the septic tank makes the BOD5 removal efficiency of the septic tank usually less than the initial settling tank. But in general, the BOD5 septic removal efficiency is 35 to 55 percent.

Biological reactions produce gases such as methane that bubble upwards from the bottom of the tank and prevent part of the material from settling. Adhering these bubbles to solid particles sometimes suspends the particle and causes it to pass through the septic. In fact, the most important reason that a middle wall is embedded in the septic is to fix this problem. Because of this wall, it does not accumulate in the second sludge tank and thus does not produce gas bubbles. Failure to produce the gas bubble also prevents disruption of the particle deposition process and increases filtration efficiency.
Usually the septic tank volume is such that the wastewater has a storage time of about 24 hours. The longer the wastewater retains in the septic tank, the better the wastewater treatment efficiencies will be due to the improvement of its treatment processes. Therefore, sometimes to increase the efficiency of septic treatment, septic capacity is considered above standard. Of course, the graph of increasing efficiency is not linear with increasing retention time.

So, for a 155 percent increase in septic tank capacity, its purification efficiency will only increase by about 25-45 percent. Therefore, it is not usually the case that enlarging the septic tank is aimed at increasing the efficiency of the economic treatment.