Sewerage - Nagar Nigam Raipur

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Detailed Design Report - Sewerage
Chapter 9: Design of Sewage Treatment Plant
The above costs are presented for two cases, namely ultimate requirement and intermediate
requirement. ASP and SBR are almost identical in cost though the civil component is less in SBR.
Operation & Maintenance cost: The technological options under consideration require various
mechanical equipments (pumps, aerators) for aiding the biological process. These equipments or
their parts are in continuous touch with sewage and due to corrosive nature / contents of
sewage, they get clogged and/or are damaged. This needs periodic maintenance to upkeep their
useful life and utility in the process. The piping, valves, gasholders, etc, need periodic
maintenance for efficient working of the reactors. In ASP large machinery is at work that
requires O&M. In mechanized processes category SBR requires minimum O&M because the
plant is working under controlled processes. On the basis of literature and experience in Indian
conditions, for various technologies, the annual O&M percentage cost with respect to capital
cost (for intermediate stage of year 2027) is presented in Table 9.11.
Table-9.11: O&M Cost for STPs with SBR & ASP
O& M cost
Rank Process % (Lakh Rs.)*
1 Sequential Batch Reactor (SBR) 4 819.28
2 Activated Sludge Process 8 1588.4
* Intermediate year 2027
For the intermediate stage of year 2027, a total of 209 Mld sewage would be available for
treatment. The capital cost and annual O&M cost along with capitalized O&M cost (for 15 years
with 12% interest) for ASP and SBR technologies is computed and presented in Table 9.12 below.
Table-9.12: O&M Cost for ASP and SBR STPs (Intermediate Stage – 209 MLD)
Rank Process
Cost (Lakh Rs.)
Capital O&M Capitalized Total
Per O&M - 15
year yrs
(i) (ii) (iii) (i+iii)
1 Sequential Batch Reactor (SBR) 19855 819.28 5580.01 26062.01
2 Activated Sludge Process 20482 1588.40 10818.38 30673.38
9.5.3 Total Cost of STP
Using the computations of land cost, capital investment cost and annualized O&M cost for the
selected options, a final ranking is presented in Table 9.13.
Table 9.13 : Total Cost For STPs (Intermediate Stage)
Rank Process
Cost (Lakh Rs.)
Land Capital Capitalized O&M
for 15 yrs
Total
1 Sequential Batch Reactor (SBR) 31.65 19855.00 5580.01 25466.66
2 Activated Sludge Process 79.12 20482.00 10818.38 31379.5
As seen from the above comparison, SBR technology is cheaper than Activated Sludge Process
and becomes the economical option considering cost of land, capital investment and annualized
O&M for 15 years tenure. The life cycle analysis of ASP and SBR plants for all three zones is
presented in Annexure – 6 and the hydraulic design of SBR plants is given in Volume – III.
9.5.4 Recommendation on Treatment Technology
On the basis of information presented in section 9.4, a summary of technical and economical
comparison is presented in Table 9.14.
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