Sewage is the detergent-rich liquid waste from households, agricultural farms, cowsheds, poultry farms, excreta and bathhouses. Deadly diseases like cholera, diarrhoea, typhoid, jaundice, measles etc. are caused by using polluted water.
Currently, all over the world, treated sewage is discharged into rivers or lakes through activated sludge processes. Aeration tanks and sedimentation tanks are used in this method. Bacteria, fungi and other microorganisms live in aeration tanks. These microorganisms break down organic matter in sewage into CO2 and water. The water is kept stable in the sedimentation tank. This tank contains purified water and the bottom accumulates under the water. Treated water is discharged into rivers or lakes. The bottom is used as fertilizer. Zooglea ramigera bacteria play a significant role in this.
In the developed countries of the world, sewage is mixed with other wastes and assimilated in three ways.
- Mechanical method: Water insoluble solids and large sewage are separated by high pressure and chemically converted into a sterile powder. Valuable organic and inorganic fertilizers are made from this powder.
- Biotechnology: Water soluble sewage is decomposed by air flow and bacteria. Chlorine is then added to this solution. As a result, the water becomes free of bacteria.
- Chemical Purification: In the next stage, the water is purified by chemical means to remove nitrates and phosphates.
All these wastes accumulate in water bodies and pollute the water.
All these wastes are assimilated using Pseudomonas, Achromobacter, Enterobacter, Flavobacterium, Zooglea, Micrococcus, Arthrobacter, Sphaerotilus etc. Methane and carbon dioxide are produced by breaking down organic waste in sewage. The methane produced is used as fuel in refineries.