Chapter - 18 Wastewater Story

• Population growth, pollution, industrial development, mismanagement and other factors contribute to an increasing scarcity in freshwater.
• Used water is wastewater. Wastewater could be reused.
• Cleaning of water is a process of removing pollutants before it enters a water body or is reused. This process of wastewater treatment is commonly known as “Sewage Treatmentâ€�. It takes place in several stages.

SEWAGE:

Sewage is wastewater released by homes, industries, hospitals, offices and other users. It also includes rainwater that has run down the street during a storm or heavy rain. The water that washes off roads and rooftops carries harmful substances with it. Sewage is a liquid waste. Most of it is water, which has dissolved and suspended impurities. These impurities are called contaminants.
Sewage is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease causing bacteria and other microbes.

• Organic impurities – Human feces, animal waste, pesticides, herbicides, fruit and vegetable waste, etc.
• Inorganic impurities – Nitrates, Phosphates, metals.
• Nutrients – Phosphorus, Nitrogen.
• Bacteria – which causes cholera and typhoid.
• Other microbes – Which cause dysentery.

Sewerage is a transport system that carries sewage from the point of being produced to the point of disposal, i.e. treatment plant. It is made up of a network of pipes called as sewers.
Manholes are located at every 50 m to 60 m in the sewerage, at the junction of two or more sewers and at points where there is a change in direction.

WASTEWATER TREATMENT PLANT:

Treatment of wastewater involves physical, chemical, and biological processes, which remove physical, chemical and biological matter that contaminates the wastewater.

1. Wastewater is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed.
2. Water then goes to a grit and sand removal tank. The speed of the incoming wastewater is decreased to allow sand, grit and pebbles to settle down.
3. The water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faeces settle at the bottom and are removed with a scraper. This is the sludge. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water .The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The biogas produced in the process can be used as fuel or can be used to produce electricity.
4. Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water. After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top. The activated sludge is about 97% water. The water is removed by sand drying beds or machines. Dried sludge is used as manure, returning organic matter and nutrients to the soil. The treated water has a very low level of organic material and suspended matter. It is discharged into a sea, a river or into the ground. Sometimes it may be necessary to disinfect water with chemicals like chlorine and ozone before releasing it into the distribution system.

BETTER HOUSE-KEEPING PRACTICES:

One of the ways to minimize or eliminate waste and pollutants at their source is to see what you are releasing down the drain.

• Cooking oil and fats should not be thrown down the drain. They can harden and block the pipes. In an open drain the fats clog the soil pores reducing its effectiveness in filtering water. Throw oil and fats in the dustbin.
• Chemicals like paints, solvents, insecticides, motor oil, and medicines may kill microbes that help purify water. So do not throw them down the drain. Used tealeaves, solid food remains, soft toys, cotton, sanitary towels, etc. should also be thrown in the dustbin. These wastes choke the drains. They do not allow free flow
of oxygen. This hampers the degradation process.

VERMI-PROCESSING TOILET

A design of a toilet in which humans excreta is treated by earthworms has been tested in India. It has been found to be a novel, low water-use toilet for safe processing of human waste. The operation of the toilet is very simple and hygienic. The human excreta is completely converted to vermi cakes — a resource much needed for soil.

SANITATION AND DISEASE:

• Poor sanitation and contaminated drinking water is the cause of a large number of diseases including water borne diseases like cholera, typhoid, polio, meningitis, hepatitis and dysentery.
• Where underground sewerage systems and refuse disposal systems are not available, the low cost on-site sanitation system can be adopted. Examples are septic tanks, chemical toilets, composting pits. Septic tanks are suitable for places where there is no sewerage system, for hospitals isolated buildings or a cluster of 4 to 5 houses.
• Some organizations offer hygienic on-site human waste disposal technology. These toilets do not require scavenging. Excreta from the toilet seats flow through covered drains into a biogas plant. The biogas produced is used as a source of energy.