Explain the methods of disposal of liquid wastes.
Most liquid wastes contain both dissolved and suspended matters. Treatment of such effluent involves the removal of contaminants and is done to prevent any adverse effects on receiving water or allow its reuse. Three steps are usually followed in the treatment of effluents:
Sewage water is treated in three steps:
(i) Primary treatment - In this, the coarse and fine suspended solids are removed by sedimentation, coagulation and precipitation.
(ii) Secondary treatment - It is essentially a biological treatment process which involves removal of colloidal and dissolved organic substances and some toxic chemicals.
(iii) Tertiary treatment - Here, excess nutrients are removed to allow the reuse of that water.