Wastewater Story

IMPORTANT TERMS

 

Scum                           Lighter impurities that rise to the top and float during wastewater treatment.

Sludge                         Solids waste which settle at the bottom of tank during primary treatment of wastewater.

Skimmer                      A skimmer is used to remove floatable solids like oil and grease       present in the wastewater.

Sewage                       Wastewater that is generated from household activities is called sewage.

Scraper                       Solid waste that settles at the bottom in the primary treatment is removed with a scraper.

Eutrophication              The process of nutrient enrichment of water bodies and the subsequent growth of plants on the surface of water.

Anaerobic Bacteria       Anaerobic organisms are those which can survive in the absence of air.

 

 

WASTEWATER AND ITS SOURCES

 

The water which is generated from various household activities such as washing clothes, dishes, bathing, mopping, etc. gets dirty and is called wastewater.

Wastewater is also generated from other activities such as construction of houses, buildings, shops etc.

It is also generated from agricultural activities such as irrigation.

 

WASTEWATER TREATMENT PLANT

 

The wastewater generated from various activities contains suspended and dissolved impurities. Untreated sewage water can contaminate water bodies and ground water and causes various water borne diseases. Sewage treatment refers to the process of removing contaminants from the wastewater, so that it can be reused for various purposes. Wastewater is treated in a sewage treatment plant. Sewage or wastewater reaches the treatment plant by a network of big and small pipes.

 

There are mainly three stages involved in the treatment of wastewater:

 

Primary Treatment

 

The primary treatment of wastewater is a mechanical process which involves removing of large particles.

The wastewater is passed through bar screens for removing the large objects such as rags, sticks, metal cans, and plastic bags etc. from the sewage.

After removing the larger impurities, the wastewater is passed through a tank called grit chamber to remove sand, pebbles and grit. The speed of the incoming wastewater is decreased so that sand, grit and pebbles settle down.

After the sand and grit settle down, the wastewater is passed through sedimentation tanks. Sedimentation is the process in which insoluble impurities are allowed to settle down at the bottom of the container to form sediments.  Here, solids such as faeces settle down at the bottom and the light waste such as oil and grease rise. The solid waste called sludge is removed with a scraper and the light waste is removed with a skimmer.

Water which comes out of the sedimentation tanks is known as clarified water.

 

Secondary Treatment

 

Secondary treatment is a biological process in which organic matter present in the sludge is broken down with the help of bacteria. The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria.

The water is allowed to flow into aeration tanks, where air is pumped into the clarified water. This promotes the growth of microbes in the wastewater. The microbes feed on the organic material present in the water.

After the action of aerobic bacteria, for several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is removed from the top.

 

Tertiary Treatment

 

Tertiary treatment is mainly a chemical process during which chemicals such as chlorine are used to remove phosphorous and nitrogen from the water. After cleaning of water, chlorine is added to the water. This destroys the harmful microorganisms and germs present in the water.

The treated water is discharged into water bodies such as rivers, streams and seas.

 

METHODS OF TREATING THE SLUDGE

 

The sludge is treated by the following methods:

 

Incineration

Incineration is a method of disposing the sludge, which involves burning the sludge into ashes. The ash can be used as a construction material.

 

Dewatering

Dewatering is a process by which, the sludge is thickened and then it is combined with other wastes to make fertilisers. Water content of the sludge is reduced by filtration or evaporation. 

 

Composting

Composting of sludge is an aerobic process of mixing sewage sludge with plant materials such as straw and leaves. In the presence of oxygen, the bacteria digest both the sewage sludge and the plant material and generate heat to kill disease-causing microorganisms.

 

CONTROLLING SEWAGE GENERATION

There are several ways which can be adopted to control sewage generation.

Cooking oils should not be thrown in the drains as they can harden and block the pipes. They should always be thrown in the dustbin.

Food waste should always be thrown in the dustbin to avoid blockage of sewage pipes.

Medicines and insecticides should not be thrown down the drains as they might kill the microbes that help to purify water.

Drain should always be covered otherwise, garbage such as plastic bottles etc. can enter the sewerage and clog the pipes.

ALTERNATIVE METHODS OF SEWAGE DISPOSAL

Onsite sewage disposal systems are an alternative arrangement for sewage system. They are used at places where there is no sewerage system.

Septic Tanks

Septic tanks are alternative methods of sewage disposal. In this method, household wastewater is allowed to flow into an underground septic tank.  The sludge settles down at the bottom of the tank and the lighter waste floats on the surface. Bacteria present in the sewage help in decomposing the solid waste.

Biogas Plants

Biogas plants are set up usually in villages and small towns. In this method, human excreta flow through covered drains into biogas plants. It is broken down by the microorganisms and biogas is produced.

Vermi-composting Toilets

Vermi-composting toilets use earthworms to decompose faecal matter. It is a safe and hygienic way of processing human waste.

Chemical Toilets

A chemical toilet collects human excreta in a holding tank and uses chemicals to minimize odors. These toilets are usually self-contained and movable.

SANITATION AT PUBLIC PLACES

Proper sanitation should be maintained at public places as sanitation and diseases are closely related.

Defecating in the open and throwing garbage in the water bodies are some of the poor habits which cause water pollution.

Sewage and garbage should be disposed properly, or they can be breeding places of flies and mosquitoes and microbes. Thus, they become the cause of various water-borne diseases. Diseases like typhoid, cholera and dysentery are caused by drinking contaminated water.

One should not scatter the litter anywhere at public places but should throw the waste only in the dustbin to maintain cleanliness.

One should not spit on roads and walls in public places. Spitting leads to the breeding of bacteria and also causes infections. Therefore, the habit of spitting should be changed to maintain cleanliness.

INTERESTING FACTS

·       Only 20% of wastewater produced receives proper treatment worldwide.

·       The global burden of human disease caused by sewage pollution of coastal waters has been estimated to be 4 million people lost annually.

• Typical family of four produces about 360 L/day of grey water = 135,000 L/year.
• 15 million children under the age of five die each year because of diseases caused by drinking water.
• Over 30 billion tons of urban sewage is discharged into lakes, rivers and oceans each year.
• India accounts for nearly 600 million of the 1 billion people in the world who have no access to toilets.
• 1.1 million litres of raw untreated sewage flows into river Ganga every 60 seconds.
• 82% of those who lack access to improved water, live in rural areas, while just 18% live in urban areas.