4. Flash mixer:
Coagulants were added to the effluents:
- Lime: (800-1000 ppm) To correct the pH upto 8-9
- Alum: (200-300 ppm) To remove colour
- Poly electrolyte: (0.2 ppm) To settle the suspended matters & reduce SS, TSS.
The addition of the above chemicals by efficient rapid mixing facilitates homogeneous combination of flocculates to produce microflocs.
In the clarriflocculator the water is circulated continuously by the stirrer.
- Overflowed water is taken out to the aeration tank.
- The solid particles are settled down, and collected separately and dried this reduces SS, TSS.
- Flocculation provides slow mixing that leads to the formation of macro flocs, which then settles out in the clarifier zone.
- The settled solids i.e. primary sludge are pumped into sludge drying beds.
6. Aeration tank
- The water is passed like a thin film over the different arrangements like staircase shape.
- Dosing of Urea and DAP is done.
- Water gets direct contact with the air to dissolve the oxygen into water.
- BOD & COD values of water is reduced up to 90%.
- The clarifier collects the biological sludge.
- The overflowed water is called as treated effluent and disposed out.
- The outlet water quality is checked to be within the accepted limit as delineated in the norms of the Bureau of Indian standards.
- Through pipelines, the treated water is disposed into the environment river water, barren land, etc.
- ETP Plant Operation
8. Sludge thickener
- The inlet water consists of 60% water + 40% solids.
- The effluent is passed through the centrifuge.
- Due to centrifugal action, the solids and liquids are separated.
- The sludge thickener reduces the water content in the effluent to 40% water + 60% solids.
- The effluent is then reprocessed and the sludge collected at the bottom.
9. Drying beds
- Primary and secondary sludge is dried on the drying beds.