What Is Waste Water and How Does the Waste Water Treatment Process Work
It is a type of water which is contaminated by human use like washing of clothes, industrial discharge, commercial as well as agricultural activities. As all these contaminating sources disturb the quality of water which leads to contamination of water. Contamination also depends on various sources or products such as domestic wastewater, municipal wastewater i.e sewage and industrial waste of chimanies. Wastewater mainly contains physical, chemical and biological pollutants. We can purify this contaminated water by various methods, there are so many power plants which do purification processes.
Effects of Contaminant on Quality of Water:
There are various harmful result noticed due to contamination of water, some of them are listed below:
Loss of Aquatic Organisms: Aquatic organisms are harmed due to contaminated water. As discharges and runoff of harmful contaminants like pesticides into waterways can be lethal to aquatic life, causing death of fishes, prawns, etc.
Loss of Local Invertebrate Species: As these small invertebrates are food for fishes and other aquatic organisms. Death of these invertebrates lead to starvation for those aquatic organisms who are dependent on them for food and they start migrating to other water bodies exposing them to greater risk and stress.
Decrease in Biochemical Oxygen Demand(BOD): Due to waste or harmful contaminants they use up natural oxygen present in the water body. Excess nutrients can also lead to algal blooms and oxygen is used up when the algae die and decompose. Decrease in available oxygen causes difficulty in breathing to aquatic organisms.
Contaminant increases turbidity and decreases water clarity of water thus making water murky. So this aquatic organism is not able to find their prey and detect predators.
Contaminated water causes internal damage to aquatic organisms as they reduce the reproductive ability of aquatic organisms, decrease in immunity, causes disorder in the central nervous system, etc.
Types of Water Pollution Depending on Different Source:
Surface Water Pollution: This type of pollution includes pollution in rivers, lakes and oceans. Here water sources are contaminated by various means like industrial waste, release of sewage waste, etc.
Marine Pollution: one of the common ways by which contaminants enter the sea are rivers. Here directly discharging sewage and industrial waste into the ocean causes pollution into oceans. Plastic debris can absorb toxic chemicals from ocean pollution, potentially poisoning any creature that eats it.
Groundwater Pollution: Use of pesticides and insecticides causes contamination of groundwater. Groundwater pollution is directly connected to soil pollution.
Wastewater Management:
Wastewater treatment is a several step process and by going through these process we purify contaminant water:
Steps performed during purification of contaminated water:
Wastewater Collection
Screening
Primary Treatment
Secondary Treatment
Final Treatment
Wastewater Collection:
Very first step in the purification process is collection of water in a storing tank which further goes through various filtration steps.
Screening:
This is the very first step of water treatment. In this process large objects are removed from wastewater and then moved into the grit and sand removal tank, where they are further treated.
Primary Treatment:
After going through screening water is taken to primary treatment where all organic waste present in water is removed and this process is done by pouring the wastewater into a big tank where solid matthew style down at the base.
The settled solids, after primary treatment, are called the sludge. This sludge is decomposed by bacteria and the gas emitted by this decomposition is known as biogas, which can be used as a fuel or can be used to generate electricity.
Secondary Treatment:
After primary treatment water is passed to an aeration tank where air is tapped into water to increase the growth of aerobic bacteria in the water. These bacteria break down small particles of sludge that are not broken during primary treatment. These broken slugs are known as activated sludge. These activated sludge contain air in them.
Final Treatment:
This activated sludge is passed through a bed of sand drying machine where the sludge is dried up and from the water is filtered out. This water is filtered and then released into the river.
How to Control Water Pollution:
There are several way to prevent water pollution, some of them are below:
Industrial Wastewater Treatment:
As industrial waste is discharged into water bodies which causes contamination of water.
So by using pre-treatment plants for reducing harmful chemicals present in industrial waste, this process will decrease contamination of water.
Agriculture Wastewater Treatment:
By reducing use of pesticides and weedicides we can reduce underground water pollution. As these chemicals contaminantes water which causes various health related issues.
Municipal Wastewater Treatment:
Instead of discharging sewage waste directly into water bodies treat it in separate sewage treatment plants to reduce water pollution.
FAQs on Waste Water Story and the Science of Sewage Treatment
1. What is wastewater in chemistry?
Wastewater is used water containing dissolved and suspended impurities such as organic matter, chemicals, microbes, and toxic substances. In chemistry, wastewater includes domestic sewage, industrial effluents, and agricultural runoff that contain:
- Organic pollutants (proteins, carbohydrates, oils)
- Inorganic salts (nitrates, phosphates, chlorides)
- Pathogenic microorganisms
- Toxic heavy metals like Pb2+ and Hg2+
2. What is sewage and how is it different from wastewater?
Sewage is wastewater that comes specifically from homes and municipal sources, containing human waste, food residues, and soaps. The key difference is:
- Sewage → Domestic wastewater from toilets, kitchens, and bathrooms.
- Wastewater → A broader term including sewage, industrial waste, and agricultural runoff.
3. What are the main stages of wastewater treatment?
Wastewater treatment occurs in three main stages: primary, secondary, and tertiary treatment. These stages include:
- Primary treatment – Physical removal of large solids by screening and sedimentation.
- Secondary treatment – Biological degradation of organic matter using aerobic bacteria.
- Tertiary treatment – Chemical or advanced treatment to remove nutrients and disinfect water.
4. What happens during primary treatment of sewage?
Primary treatment is the physical removal of suspended solids from wastewater by sedimentation and filtration. It involves:
- Screening to remove plastics, rags, and large debris.
- Grit chambers to settle sand and small stones.
- Sedimentation tanks where heavier solids settle as sludge.
5. How does secondary treatment remove organic pollutants?
Secondary treatment removes organic pollutants using aerobic bacteria that decompose biodegradable matter. In aeration tanks:
- Air (oxygen) is pumped into wastewater.
- Bacteria oxidize organic matter into CO2, water, and biomass.
6. What is Biochemical Oxygen Demand (BOD)?
Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen required by microorganisms to decompose organic matter in water. It is measured in mg/L and indicates pollution level:
- High BOD → High organic pollution.
- Low BOD → Cleaner water.
7. How is water disinfected during wastewater treatment?
Water is disinfected by adding chlorine, ozone, or using ultraviolet (UV) radiation to kill pathogens. In chlorination, chlorine reacts with water as:
Cl2(g) + H2O(l) ⇌ HCl(aq) + HOCl(aq)
- HOCl (hypochlorous acid) acts as a strong disinfectant.
- It destroys bacteria and viruses by oxidation.
8. What are common pollutants found in wastewater?
Common wastewater pollutants include organic matter, nutrients, pathogens, and toxic chemicals. Major categories are:
- Organic waste – Food particles, oils, proteins.
- Nutrients – Nitrates (NO3-), phosphates (PO43-).
- Heavy metals – Pb2+, Cd2+, Hg2+.
- Microorganisms – Bacteria and viruses.
9. Why is wastewater treatment important for the environment?
Wastewater treatment is important because it prevents water pollution, protects aquatic life, and reduces the spread of diseases. Untreated sewage can:
- Increase BOD and deplete dissolved oxygen.
- Cause eutrophication due to excess nitrates and phosphates.
- Spread waterborne diseases like cholera and typhoid.
10. What is sludge and how is it treated?
Sludge is the semi-solid residue formed during primary and secondary wastewater treatment. It contains organic matter and microorganisms. Sludge treatment involves:
- Anaerobic digestion to produce biogas (mainly methane, CH4).
- Drying and dewatering.
- Safe disposal or use as manure if treated properly.
