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System Up-Gradation

PHASE: I

Objectives of up-gradation:

In view of the constraints / limitations associated with the CETP hard ware as well as the process parameters it was decided to implement up-gradation in the CETP to achieve the following objectives…

  • To improve the biodegradation by being able to maintain MLVSS level at the desired value in the Aeration Tank.
  • To improve oxygen transfer efficiency by up-grading / augmenting the present aeration system.

In order to achieve the above objectives aimed to improve biodegradation, the up gradation programme was divided in two phases. In the Phase: I up-gradation programme the CETP was up-graded from the hard ware point of view while in Phase: II programme new processes were incorporated with the existing biological treatment to enhance biodegradability of the organic pollutants and to achieve the specified outlet norms.

Phase: I Up-gradation Programme:

Installation of Separate Secondary Clarifiers:
In order to accomplish desired MLVSS level in the Aeration Tank it was decided to provide two separate Secondary Clarifiers in replacement to the existing peripheral Integrated Clarifier. The Clarifiers are of the conventional gravity type with sludge scrappers at the bottom. The mixed liquor from the existing aeration basin would flow to the Clarifiers by gravity. The clarified effluent overflows over a weir system to the outside   launder and then to the Final Receiving Sump from where it is pumped to mega pipeline for final disposal.

The sludge settled at the bottom is collected in a bio sludge sump from where it is recycled to the aeration basin. Excess sludge is wasted to the existing Sludge Holding Tank for eventual dewatering in the Centrifuge. The filtrate is returned to the primary treatment unit and the dewatered sludge / solids are taken to Common Secured Landfill Site.

Up-gradation and Augmentation of Aeration System:

In view of the limitations of the existing coarse bubble diffuser aeration system it was decided to replace it with a medium bubble diffuser aeration system. The hole size of the aeration grid was reduced from 10 mm to 5 mm. The entire grid system was changed to implement this up-gradation. This up-gradation resulted in increasing the number of holes by a factor of four. This would cover the bottom area of the tank more uniformly.  The bubble size is also much smaller than the previous diffuser system. This would enhance oxygen transfer as well as mixing in the tank. It was observed that it was not advisable to blow the entire quantity of required air through the aeration grids because of heating of air. The resulting hot air raised the temperature of the mixed liquor in the Aeration Tank which ultimately reduced solubility of oxygen and oxygen transfer efficiency. The hot air also adversely affected the piping and grid system. It was therefore decided to use the grid system for the partial fulfillment of the aeration requirement and augment it with the other type of system. After carrying out a detailed survey, study and evaluation of different types of aeration systems, the Triton type Aerators manufactured and supplied by  Aeration Industries International Inc., Minneapolis,  Minnesota,  USA were  selected for  augmenting the oxygen supply. Initially a total number of 12 such aerators each of 60 HP were installed with a provision of adding 6 nos. in the central region of the tank. Necessary bridges and columns were constructed to support these aerators.

After implementation of these measures the reduction achieved in COD and BOD was in the range of 60 – 75% and 90 – 95% respectively. This performance was satisfactory and met with our expectations.
The investment made towards Phase: I up-gradation programme was Rs. 67046693.
The detailed break-up is as under…

SR. NO.

ITEM

COST Rs.

1

Two nos. Secondary Clarifies and Final Pumping Station 

Civil Work, Mechanical and Piping Work, Electrical Work Instrumentation Work, Integration with Existing Installation etc.

18274927

2

New Aeration Grid System

24271766

3

New Aerators (12 Nos.)Installation of New Aerators (12 nos.), Civil Work, Mechanical Work, Electrical Work, Instrumentation Work, Conversion of Integrated Clarifier to Aeration Tank.

24500000

TOTAL COST

67046693