Water is one of the most important things in our life. There are two sources of water, one is the surface water and the other is the groundwater. The river plays a major role in the surface water source. In India, the Ganges, Brahmaputra and Indus river water systems are the largest as they drain almost half of the country, carrying more than forty percent of the utilizable water. The rivers are also used to dispose of the waste which deteriorates the quality of the river but due to self-purification technology present in rivers, the rate of deterioration gets slow.
Self Purification Technology of Rivers
It is a very basic technique in the self-purification of the river. When a river containing a very high content of sewage, mixes with another fresh stream then the overall waste content decreases, or in the case when the river water gets diluted with the rainy water the overall volume of the river gets increased, reducing the concentration of pollutants. It increases the dissolved oxygen (DO) content and aerobic condition always exists.
It is a mechanism that occurs when stream velocity is less than the scour velocity of particles it causes the bigger particles to settle down at the bottom. Sand in the river-bed acts as a sink for the pollutants. Basically, due to the low velocity of the streams the pollutants settle down. The suspended solids get removed contributing to improved water quality. The anaerobic decomposition of the settled solid takes place.
The aerobic bacteria present in the river use the dissolved oxygen and oxidize the organic matter present in the river and convert it into stable compounds. The process continues until the oxidation of organic matter takes place. The stream which can absorb more oxygen through the reaeration process will be able to purify the water on a large scale.
In this case hydrolysis of organic matter takes place. Hydrolysis refers to the reaction of organic matter with water resulting in the formation of new simpler compounds. It can take place biologically or chemically. Anaerobic bacteria split the organic matter into liquid and gases thus easing the stabilization of the pollutants by oxidation.
Aquatic plants are present in water, these plants absorb the sunlight and use it for the process of photosynthesis that means it consumes the carbon-dioxide and releases the oxygen. This process increases the dissolved oxygen content of the river. Therefore, the oxidation of organic matter gets quicker. The drawback with this mechanism of water purification is that it can be only done during the day-time since the sun is only present then.