Effluent is generated in many manufacturing industries like textile, pharmaceuticals and chemicals, tanneries etc. Contaminated water cannot be released without treatment as it contains toxic and non-toxic chemicals. Releasing it may cause contamination of the existing pure water and will affect the environment. As a result ETP’s are installed in most manufacturing industries. The Effluent treatment plants (ETP) are used for the removal of high amounts of organic compounds, debris, dirt, grit, pollution, toxic, non-toxic materials and polymers etc. from industrial effluent. The ETP plants use evaporation and drying methods and other auxiliary techniques such as centrifuging, filtration , incineration for chemical processing and effluent treatment.
ETP Plant Operation
- Screen Chamber : This chamber removes relatively large solid to avoid abrasion of mechanical equipment and clogging of hydraulic system.
- Collection Tank : The collection tank collects the effluent water from the screening chamber, stores and then pumps it to the equalization tank.
- The effluents do not have similar concentration at all the time; the pH will vary time to time.
- Effluents are stored for up to 8 to 12 hours in an equalization tank resulting in the homogenous mixing of effluents and helping in neutralization.
- Continuous mixing also eliminates settling of solids within the equalization tank.
Reduces SS, TSS.
Flash mixer:- Coagulants are added to the effluents
- Lime:(800-1000 ppm) To correct the pH upto8-9
- Alum: (200-300 ppm) To remove colour
- Poly electrolyte : ( 0.2 ppm) to settle the suspended matters and reduce SS, TSS.
- The addition of the above chemicals by efficient rapid mixing facilitates homogeneous combination of flocculates to produce micro flocs.
- In the clarriflocculator the water is circulated continuously by a stirrer.
- Flocculation provides slow mixing that leads to the formation of macro flocs, which then settles in the clarifier zone.
- Overflowing water goes out to the aeration tank.
- The solid particles settle down, and are collected separately; this reduces SS, TSS.
- The settled solids i.e. primary sludge is pumped into sludge drying beds.
- The effluent after clarification flows to an aeration tank for aerobic treatment.
- This tank is equipped with air blowers or diffusers using which air is passed through the tank.
- This air is required to maintain the desired dissolved oxygen (DO) level required for bacteria to grow and remove BOD and COD by breaking down the matter.
- BOD and COD values of effluent are reduced up to 90%.
- The overflow from aeration tank is led into the secondary clarifier where solid liquid separation takes place.
- The settled solids in secondary clarifier are called biological sludge, a part of which is recycled back into the aeration tank to maintain the desired MLSS level and remaining sludge is conveyed to sludge collection tank for further treatment.
- The outlet water quality is checked if it’s within the accepted.
- The treated water is disposed through pipelines.
- The inlet sludge consists of 60% water + 40% solids.
- The effluent is passed through a 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 is collected at the bottom.
Primary and secondary sludge is dried on the drying beds to further reduce the water content.