Wastewater Story

Water – Our Lifeline

• Water is used for a variety of purposes in our everyday life. When used, this water becomes adulterated and is called waste water.
• Polluted water leads to people suffering from water-related diseases.
• Water gets polluted due to several factors such as increase in population, industrial development and mismanagement.
• Waste water is subjected to a cleaning process often referred to as sewage treatment.

Sewage

• Sewage is liquid waste; most of it is water which has dissolved and suspended impurities.
• Water which washes off the roads and roofs carries harmful substances and impurities called contaminants.

Types of Impurities	Examples
Organic impurities	Human faeces, animal wastes, oil, urea, pesticides, herbicides, fruit and vegetable wastes
Inorganic impurities	Nitrates, phosphates, metals
Nutrients	Phosphorus and nitrogen
Bacteria	Those which cause diseases such as cholera, dysentery and typhoid

• A sewer is an underground passage for carrying off drainage water and waste matter.
• The provision of drainage at a place by laying sewers under the ground is called sewerage. It takes the waste water to the point of disposal, i.e. a treatment plant.
• A manhole is a covered vertical hole in the ground, pavement or road. Manholes are located every 50-60 m in a sewerage system, at the junction of two or more sewers and at points where there is a change in direction of the sewer line.

Sources of wastewater:

• Sewage water contains detergents, toxic chemicals food wastes, paper, human faeces, plastics, metal objects, microorganisms, blood, human/animal tissues, etc. These kinds of materials present in wastewater are called contaminants.
• In agricultural practices, pesticides and fertilizers are used, which gets mixed with fresh water during rains or flood, thereby contaminated the river and ponds.
• The wastewater from the industries may contain lubricant oil, paint, dye, chemicals and metals. These are also called Industrial effluents.
• Construction of buildings, mining leads to the generation of wastewater containing cement, paints, metals and chemicals.
• Abattoirs (slaughterhouses), animal farms and veterinary hospitals too contaminate water and contribute to sewage.
• One of the major sources of wastewater is domestic sewage from homes.

Treatment of sewage in cities and towns:

• If sewage water is allowed to directly flow into the water bodies, it would pollute water. Such polluted water is not suitable for human consumption or for growing crops. It will also harm all kinds of plants and animals living in this water.
• Thus, Wastewater must be cleaned before it is released into the water bodies. This is done in Sewage treatment plant or wastewater treatment plant. Treated wastewater can be used for various purposes.

Effects of improper sewage management:

• Many places in our country have open drains in the streets. These serve as breeding places for mosquitoes, which cause diseases like malaria and Chikungunya.
• Untreated wastewater or sewage contains nutrients which are beneficial for the growth of algae. If this untreated wastewater is let off into the water bodies then it leads to an increase in algal growth called algal blooms. This causes depletion of oxygen in the water bodies making them unable to support aquatic life such a condition is called eutrophication.
• The overflowing drains can contaminate wells and streams too.
• The contamination can cause water- borne diseases such as Cholera, typhoid, Hepatitis and dysentery.

Methods of sludge management:

• Sludge can be incinerated in sludge incinerators to convert it into ashes, which can be used in construction purposes or to supplement the nutrients in the soil.
• Dewatering of the sludge can be done by sludge- drying machines. The leftover solid waste is used in the manufacture of fertilizers.
• The gas produced by aerobic bacteria acting on the sludge in the aeration tank is used as biogas, which is a source of energy for cooking and electricity.

Wastewater Treatment Plant (WWTP)

• Physical, chemical, biological processes are employed to remove physical, chemical and biological matter from the water.

• The dried sludge is now used as manure, thereby returning the organic matter and nutrients to the soil.
• The treated water has a very low level of organic and suspended matter and is hence discharged into seas, rivers or into the ground.
• Sometimes, chemicals such as chlorine and ozone are used to disinfect water before releasing it into the distribution system.

Primary treatment process:

• In this process, the sewage flows through the grit chamber very slowly so that the sand, pebbles and soil settle down at the bottom.
• It is a mechanical process; the sewage flows into the settling tank of sedimentation tank where the solid wastes like faeces are allowed to settle down.
• The waste material that settle down at the bottom is called the sludge and the floatable material is called the scum.
• The sludge at the bottom is removed with a scrapper every few days and treated further. The water then is left out is called the clarified water.

Secondary treatment process:

• It is a biological process. This is done by transferring the clarified water into an aeration tank where air blowers bubble air, which helps the aerobic bacteria to grow and feed on the organic contaminants.
• Microorganisms decompose most of the organic matter still present in the sewage.
• The leftover liquid waste is allowed to remain in time so that microscopic organisms settle down at the bottom. This is called the activated sludge. This activated sludge is then left in sand dry beds.

Tertiary treatment process:

• The leftover liquid waste is transferred to another large tank where the decomposed waste settles at the bottom. These tanks too are called sedimentation tanks.
• At this stage, most of the solid substance from the water are removed.
• The water is then shifted to a tank where it is treated with chlorine to kill all the microorganisms present in the wastewater and to remove the Phosphorus compounds and nitrogen compounds. Addition of chlorine to wastewater to kill germs is called chlorination. It is a chemical process.
• The dirty water that was brought to the sewage treatment plant is now clean and can be used to cultivate crops, maintain large gardens, and manufacture goods in industries.
• The water can also be discharged into oceans, rivers and lakes or used to recharge groundwater.

Alternative Arrangement for Sewage Disposal

Sanitation and Disease

• A large number of diseases are caused by poor sanitation and contaminated drinking water.
• Water contaminated with untreated human excreta causes diseases such as cholera, typhoid and dysentery.

Good Practices of Waste Disposal

Control of sewage at homes:

• Do not drain off cooking oil, paints and automobile oils. it leads to blockage.
• Chemical like paints, insecticides, medicines may kill decomposer microbes that help purify water, so, these must never be thrown down the drain.
• Do not drain the tea leaves, vegetable and animal food waste and egg shell. Solid waste clogs drains and make surrounding dirty.