Correct Answer - Option 1 : dilution, sedimentation and oxidation
Explanation:
Self-purification of running stream:
When the sewage effluent is disposed of in a river stream it undergoes the process of self-purification by the following natural mechanism;
Dilution & Dispersion:
In real terms, it is not the mechanism of self-purification it only reduces the potential hazard of the sewage effluent into the river stream.
Sedimentation:
As per the turbulence available in the river stream organic suspended particles get settled in it thereby helping the river water to get self purified.
Sunlight:
In the presence of sunlight, a photosynthesis reaction takes place during which O2 is released which is utilized by the micro-organism for the decomposition of organic matter thereby helping the river water to get self purified.
Oxidation & Reduction:
Decomposition of the organic matter by the action of micro-organism over the surface of the river stream and by the anaerobic micro-organism on the bed of the river collectively helps the river to get self purified.
