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Self Depuration Competence of Natural Streams

Published on Nov 30, 2023


The process of purification mainly depends on absorption and dissolution of atmospheric oxygen from the water body surface. This absorbed and Dissolved Oxygen is necessary for the growth of bacteria to break down the biological and chemical pollutants thereby reducing its strength for a period of time. Self-purification capacity of water bodies mainly depends on natural factor. These include the water velocity, depth, discharge and temperature. The turbulence nature of water bodies helps the river to very clean because of the natural capacity to absorb and digest pollutants at a very high rate. Stagnant water bodies tend to become septic because of the low rate of oxygen absorption.

The self purification of natural water systems is a complex process that often involves physical, chemical, and biological processes working simultaneously. The amount of Dissolved Oxygen (DO) in water is one of the most commonly used indicators of a river health. As DO drops below 4 or 5 mg/L the forms of life that can survive begin to be reduced. A minimum of about 2.0 mg/L of dissolved oxygen is required to maintain higher life forms.

Vrishabhavathi River is the fundamental surface water source which is tributary of waterway Arkavathy, which joins the Cauvery River. It depletes a noteworthy parts of Bangalore city and is an outlet for household and mechanical profluent of that region. Today this water is utilized for rural purposes which are likewise not protected.

Keywords : Self-depuration, Dissolved Oxygen, Contamination, Environmental degradation, River Vrishabhavathi


The work has been taken up with the following objectives:

 To determine the physical parameters (Temperature, turbidity) of river water sample at selected points in Vrishabhavathi river.

 To determine the chemical parameters (pH, Hardness, Alkalinity, TDS, DO, BOD, COD) of water sample at selected points in Vrishabhavathi River.

 To determine the percentage of purification that is been taken place at each interval, in accordance with the selected points.

The scope of this study is the find out the self depuration competence of the River Vrishabavathi. The project will estimate the ability of the river for self purification of the environmental degradation due to the pollutants which are directly or indirectly discharged.

The gradual deterioration in the water quality makes the river lose its efficiency of self purification. This experimentation will lead to suggest the installation of efficient effluent treatment plants to the government bodies.


 The river is divided into zones according to our convenience as

 Residential Zone

 Industrial Zone

 Forest Zone

 Zone of Dilution

 We have divided the streams into zones and indentified few points based on the estimated pollution from nearby areas and will be testing the samples for few of the parameters.

 The course of the river flows through the south of the Bangalore city. The river originates near the Kadumalleshwara temple near malleshwaram and flows through major areas like Guddadahalli, Rajarajeshwari Nagar, Kengeri. The river then culminates at a reservoir named as Vrishabhavathi reservoir. It will then join to river Arkavathi near Kanakpura which will later join the major river Kaveri.

 The total course of the river is divided into the specified zones and apparently the points are selected along the river for the collection of the samples. The sampling is done as per the regulations of „Grab Sampling‟.

 Few parameters are tested on spot such as temperature and colour. And the samples are then kept under incubation till they are tested for all other parameters. All the tests are performed according to the IS standards.

 A grab sample is a sampling technique in which a single sample is taken at a specific time and a place.

 We chose this technique because of its low cost and immediate results.


To bring out the advantage of Self-Purification, the testing was conducted for water samples at different zones. The results of the tests conducted from the current project shows that there is self purification happening at a longer distance than in the expected sampling point. The main objective of this investigation is to study the relation between DO and BOD using Oxygen Sag Curve. Based on the results of the tests conducted, an attempt has been made to the competence of self depuration in river Vrishabhavathi.

The samples collected are stored at low temperature and tested for the following parameters on the same day of sample collection.

1. Temperature

2. pH

3. DO

4. BOD

5. COD

6. Hardness

7. Solids

8. Turbidity

9. Heavy metals

 Lead

 Chromium

The samples were tested for the above parameters as per Standard test procedures as mentioned in IS 10500 in environmental laboratory, Civil Department, RNSIT. Results of some important parameters are stated. Our primary objective is to study the behavior of DO and BOD obtained from various locations.

Self Depuration


As per the analysis made on the results obtained, the river Vrishabhavathi has a good Self-Purification efficiency as it runs through a long distance in forest covered region where the inclusion of waste water is less and also the river bed is basically a combination of course sand, fine sand and pebbles, where the impurities are held between spaces of media and also the course of river helps in aeration of the water. We see that, as the river course joins Arkavathi, there is dilution process which has a prominent effect on the purification of water.

Whereas, the 1st 4 sampling stations display a very less self purification efficiency because of the river bed properties and also the continuous disposal of waste in the city from industries and residential areas

We can conclude that the Self-Purification competence of river Vrishabhavathi can be improved by adopting some of the remedial measures which are as follows:

 In Bengaluru city region, the river bed should be replaced for concrete to coarse sand, fine sand and pebbles.

 The existing river bed which basically acts as a strainer should be backwashed periodically by the method of “Scraping The Media”.

 As it was found that, stagnation of sewage water was happening at many locations, the river has to be De-silted periodically.

 Cascades has to be constructed at every interval along the coarse of river in city limits to naturally increase the oxygen levels by the process of aeration.

 Waste water disposal points along the river has to be minimized and regularized with alternative disposal points.

Scope for Future Work:

 By determining the velocity of the flow of the river the Oxygen Sag Curve can be further improved by adding Re-oxygenation Curve.

 The degree of sewage treatment required can be found out by knowing the discharge of waste water to the station per day or second.

Project Done By Mr. Nagarjuna R, Mr. Paladugu Akash Venkat, Ms. Shilpa H, Mr. Hithaish P