Content Writer-SME
Sewage is domestic household waste which includes the hospital wastes, the residue products which remain after washing clothes. The health of humans and the environment are majorly affected by the direct disposal of industrial wastes and the pollution created by the humans. The sewage treatment plant treats sewage in two stages : primary and secondary sewage water treatment. The toxicity of sewage can be reduced only through proper sewage water treatment.
What is Sewage Treatment?
[Click Here for Sample Questions]
A large amount of wastewater is released from the houses and industries every day, they are referred to as sewage. Sewage must be treated in the sewage treatment plants before permitting into rivers and streams to restrict the pollution. Microorganisms are widely used to treat wastewater in sewage treatment. The process of sewage treatment takes place in two stages: firstly, the primary treatment, and second is the biological treatment.
Sewage Water Treatment
Process of Sewage Treatment
[Click Here for Sample Questions]
The entire process of sewage water treatment is done to reduce the toxixity of sewage water. There are two stages of treatment- Primary sewage water treatment and secondary sewage water treatment.
Primary Sewage Water Treatment
In primary treatment filtration and sedimentation occurs together. Both large and small objects found in the sewage are removed at this stage. In the primary stage, floating scrap is removed by sequential filtration. The grit such as the coarse soil or the pebbles is removed through sedimentation in the primary settling tank. The settled or sorted-out organic and inorganic solids are known as primary sludge. The floating greases and all the plastic materials present in the water are transferred for the secondary treatment which is also referred to as biological treatment.
Secondary Sewage Water Treatment
In Secondary treatment, the liquid wastes are diminished. In this stage known as the biological stage, the effluents are unsettled mechanically with the supply of oxygen in the aeration tanks. Flocs in a sewage treatment plant are mesh-like structures. In the wastewater treatment plants or the sewage treatment plant, the degradation of complex compound substances that contaminates the water is carried out by microorganisms.
The second stage uses oxygen (O2) which helps in reducing the sewage from the water. Aerobic organisms or aerobic microbes are organisms that are capable of surviving and are able to grow in an oxygenated habitat.
The aerobic microbes present in the tank make use of oxygen and break down the organic matters that are currently present in the effluents or in the liquid waste. BOD that is the biochemical oxygen demand refers to the amount of oxygen required by the microbes to oxidize each and every organic matter in one litre of water. The BOD is an indicator that indicates the amount of organic matter present in the water. The BOD of raw sewage can be as much as six hundred milligrams per litre (mg/L).
As the decrement in the BOD of water is achieved, the effluents of the pollutants are transmitted to another tank, the aeration tank. In this tank, the bacterias are cautiously and gradually permitted to sediment. The sedimented activated sludge in the secondary settling tank is pumped into anaerobic sludge digesters.
In anaerobic sludge digesters, the anaerobic bacteria digest all the organic matter present in the sludge and produce a mixture of gases. Gases such as methane ( CH4), hydrogen sulphide (H2S), and carbon dioxide (CO2) are produced. This combination of gases is also referred to as biogas. Biogas is used as a fuel, and the sludge is used as manure. The pollutants from the secondary treatment plant are released into the natural water bodies.
Advantages of a Sewage Treatment Plant
[Click Here for Sample Questions]
- It is an easy and effective method to reduce the amount of sewage and pollutant from the water. It minimizes wastes.
- Wastewater treatment is the best option to use the contaminated water in a better way.
- It provides clean and safe water and with the help of a sewage treatment plant the water can be reused.
- A technique that is used in order to save water.
Disadvantages of Sewage Treatment Plants
[Click Here for Sample Questions]
- It requires a large space for the setup.
- The Installation cost and the power supply are very much high.
- The use of bacteria makes the plant smelly.
- Wastewater absorption can affect the wet areas or during excessively rainy periods.
Sample Questions
Ques. Why is secondary treatment called biological treatment? (1 mark)
Ans. The secondary treatment after the primary treatment is known as the biological treatment because there is an involvement of oxygen ( O2) in this treatment.
Ques. What is the use of an aeration tank in sewage treatment? (1 mark)
Ans. An aeration tank is a big chamber or an area where aeration work takes place. The aeration tank is used to supply oxygen in the water.
Ques. What does a Flocs do? (1 mark)
Ans. Flocs help in reducing the BOD i.e, the Biochemical oxygen demand of the water. In other words, flocs help to remove the impurities from the water. The BOD of water that is used for drinking must be less than 0.5.
Ques. What is the Activated Sludge? (1 mark)
Ans. When the Flocs are allowed to rest or sediment in the secondary settling tank then these sediments are known as activated sludge or secondary sludge sediment.
Ques. What is used in sewage treatment plants? (1 mark)
Ans. Microorganisms are widely used in sewage treatment plants in order to remove toxic organic matter.
Ques: What are the flocs formed during secondary treatment of sewage? (2019)
Ans. There are three stages of sewage treatment known as primary, secondary and tertiary stages. Flocks can be termed as the groups of bacteria that are formed as a sludge in structure and are bound together with the help of slime. They help in the increment of the decomposition rate and are kept in the aeration tank during the secondary stage of the sewage treatment procedure.
Ques: Explain the effects on the characteristics of a river when urban sewage is discharged into it. (2018)
Ans. When the sewage from the urban areas inclusive of the sewage from hospitals, houses and industries are dumped into the rivers, there is certain kinds of effects on the aquatic life which are as follows:
- Houses/hospitals: Sewage from such places may contain various kinds of pathogenic bacteria that can cause the rise of certain types of diseases.
- Industries: The sewage discharges by industries can lead to the pollution of the water as they contain certain harmful toxic material such as powerful metals. Such types of materials are very dangerous for aquatic animals. These kinds of sewage can lead to a change in the colour of the river as they may turn dark as they contain waste products and lead to an end of the aquatic life present in the waterbody.
Ques: Secondary treatment of the sewage is also called biological treatment. Justify this statement and explain the process. (2017)
Ans. In the secondary stage of sewage treatment the organic matters are broken down with the help of biological agents. Thus it is also known as the biological treatment. This can be done by the use of microbes that can help in consuming and degrading the organic matter and turning it to CO?, H?O and energy for the reproduction and growth of their own kind. This leads to the reduction of biochemical oxygen demand of the sewage water.
Ques: "Determination of Biological Oxygen Demand (BOD) can help in suggesting the quality of a water body." Explain. (2015)
Ans. BOD or biological oxygen demand helps in the measurement of the oxygen that is used by the microorganisms such as aerobic bacteria to oxidise the organic substance. The natural water bodies have certain types of organic matter that the microorganisms help in decomposing. Calculating the BOD level of the water body helps in attaining the level of organic matter it contains. The existence of increased amounts of organic wastes leads to the increase in the biological activity which in turn leads to the algal blooms. High level of biological oxygen demand measurement shows an increase in the microbial activity showing that the water has been polluted.
Ques: Name two commonly used bioreactors. State the importance of using a bioreactors. (2013)
Ans. The two common types of bioreactors are:
- Sparged stirred-tank bioreactors
- Simple stirred tank bioreactors
The importance of using a bioreactors include the following:
- The processing of very large quantities of culture can be done in bioreactors that can be upto 100 to 1000 litres.
- Appropriate products can be obtained through the help of bioreactors as they provide the ideal conditions for development such as salts, oxygen, temperature, vitamins, pH and substrate.
Ques: Name any two sources of e waste and write two different ways for their disposal. (2013)
Ans. Two sources of e-waste includes:
- Computer parts
- Electronic devices such as mobile phones
The different ways for their disposal:
- Buried in landfills
- Incinerated
Comments