- World Water Day : 22 March
- On World Water Day, 22 March 2005, the General Assembly of the United Nations proclaimed the period 2005–2015 as the International Decade for action on “Water for life”. All efforts made during this decade aim to reduce by half the number of people who do not have access to safe drinking water.
- 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 Treatment”. It takes place in several stages.
WHAT IS 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
Organic impurities –Human faeces, animal waste, oil, urea (urine),pesticides, herbicides, fruit and vegetable waste, etc.
Inorganic impurities –Nitrates, Phosphates, metals.
Nutrients –Phosphorus and Nitrogen.
Bacteria –Such as which cause cholera and typhoid.
Other microbes –Such as which cause dysentery.
WASTEWATER TREATMENT PLANT (WWTP)
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. Nature cleans it up further. Sometimes it may be necessary to disinfect water with chemicals like chlorine and ozone before releasing it into the distribution system.
- It has been suggested that we should plant eucalyptus trees all along sewage ponds. These trees absorb all surplus wastewater rapidly and release pure water vapour into the atmosphere.
- The water in a river is cleaned naturally by processes that are similar to those adopted in a wastewater treatment plant.
- 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.
