Sunday 4 October, 2015

AN STP DESIGN WITH A LITTLE HELP FROM GOOGLE

60. AN STP DESIGN WITH A LITTLE HELP FROM GOOGLE


Regular followers and readers of my blogs would have no doubt read the piece about an STP titled  “Designing by the Book”.  In keeping with advancement of technology, here is an STP proposed to be designed with a little help from Google.

Many well wishers have often asked me why I do not respond to RFQ’s ( Request for Quotation) for STP’s floated by Architects and their Plumbing Consultants. I present to you below a recent RFQ I came across for a High end apartment complex of a Grade I Builder sent out by a leading Architect and his Plumbing consultant.  The specifications for the STP in the RFQ will accept  anything from a SIPANI BADAL three wheeled car to a PORSCHE 911 and everything in between if I were to borrow the equivalent from the automobile world.



Under the circumstances, dear reader you will agree that the odds of a snowflake in hell are infinitely higher than Ecotech ( our Company) landing a contract through this tender route.

The following is a true, entirely authentic and unedited extract from an RFQ we were regaled with from a respected Architectural firm in Bangalore.  The only camouflaging I have done is to the names of the actors in this farce and some figures to protect their identity and their good name ( although I am not entirely sure why).  The camouflaged bits are in red font by me..


XXXXXXX APARTMENTS”
BY
M/S YYYYYY DEVELOPERS
at BANGALORE

REQUEST FOR QUOTATION ON DESIGN BUILD BASIS FOR


230KLD SEWAGE TREATMENT PLANT


Date  : Does it really matter for this kind of trash ?
Client: M/s. YYYYYYYY ( same as above)
Architects:  ZZZZZZZZ ( In sleep mode)
PHE Consultants: 000000000.... ( Not enough zeroes in this world for ranking)


Introduction:

The proposed project is a residential Apartment located  Anywhere in Bangalore comprising of 999 Flats with common amenities like clubhouse, Gym & swimming pool etc.
The total water requirement is as mentioned in the below table.

Description
Values
Units
No. of Flats
999
Nos.
No. of persons per  villa
5
Nos.
Water Usage per person per day
200
LPCD
Water used for domestic uses
2,21,000
LPD
Design factor for additional reserve capacity
5%

Additional reserve capacity
11,050
LPD
Total Flow in ltrs/Day
2,32,050
LPD
Total Design Capacity of Plant
230
KLD
                                                         
The project is a gated community which has no access to sewer system hence requires establishing a STP onsite. Further it is also envisaged to use the reclaimed water for landscaping by spray or drip kind of irrigation system and if need be for flushing in future.

Plant design parameters:

Influent to the STP shall be domestic sewage generated in the Flats and common amenity areas, an approximate characteristics of the likely expected sewage is given below. The influent sewage parameters may vary time and season, the plant shall be capable of accommodating organic loading to the tune of 30% and a hydraulic shock load of 30 to 40% with minor operational adjustments.

Parameters
Inlet (Expected)
Outlet (Required)


Reuse
Landscaping
BOD, ppm
250
<10
<20
COD, ppm
500
<100
<200
TSS, ppm
500
<10
<20
Oil & Grease, ppm
>10
<3
<5
pH         
6.5 - 8.5
6.0 - 9.0
6.0-9.0
E-Coli
NA
NIL
NIL
Residual chlorine, PPM
-
<1 mg/lt
1 mg/lt

The expected outlet water requirements shall be met by the plant while operating in the range up to the designed capacity. The output performance shall not vary by more than 20% under shock loads.
The output is to be treated as 50% for reuse and 50% for landscaping quality water generation.

Sewage treatment processes:

The vendor may select any process as per their area of expertise / proprietary design. The vendor shall submit a detailed process description and flow sheet considering the site conditions.
The vendor may also choose from the list of available methods for treatment or propose any other alternative.

Biological:  Aerobic
  • Extended aeration
  • SBR (Sequential Batch Reactor)
  • FAB (Fluidized Aerobic bed)
  • SAFF (Suspended Aeration Fixed Film)
  • FBBR (Fluidized bed Bio Reactor)
  • RBC (Rotating Biological Contactor)
  • MBR (Membrane Bio Reactor)

Biological Anaerobic systems
  • UASB
  • Septic tank

Physical / Chemical:
  • Enzyme activated treatment
Electrical:
  • Electrolysis

The sludge generated in the STP shall be suitably treated to ensue that it can be properly disposed along with municipal solid waste. Sludge drying beds are not permitted. Sludge volume reduction by aerobic / anaerobic digestion in small plants are not viable hence the same may be considered for plants above 250 kld.

The vendor shall also furnish detailed design calculations along with the offer which shall be scrutinized by the PHE consultants. In the event of the vendor not willing to share the design calculations they shall guarantee the performance of the system by a Bank Guarantee of a value as per the client discretion and shall be decided based on the vendors reputation and the performance of the existing plants.


NOW SOME PERTINENT OBSERVATIONS AND QUESTIONS FROM ASK ( that is me : of      “ When Kodavasal talks, people listen” fame)

( Pls. note I have overlooked and condoned some minor lapses in this document which may have crept in due to a mindless cut and paste job done by the Consultant : Ex : “No. of persons per villa”.  Is this not an apartment ?)

1. Since when has Karnataka State Pollution Control Board ( KSPCB)  relaxed its Rules and left toilet use option of treated water to the discretion of the plumbing consultant ?

2. What can be the seasonal variation in the characteristics of domestic sewage from an apartment complex ?  Due to variations in Temperature ? The monsoons ? Seasonal changes in dietary pattern of the residents ?

3. Why must the STP accommodate and handle only 30 % of the organic load ? Why not 100 % ?  And where does one offload the balance 70 % ?

4. 30 – 40 % of excess Shock loads are better handled by proper Design and Engineering  of the STP rather than by twiddling with some unspecified and abstruse  “minor operational adjustments”

5. Obviously the Consultant is not wise to the KSPCB “ Urban Reuse Standards” for quality of treated water enforced now for more than 6 years, and has prescribed his own set of standards.

6. I fail to understand the grammar of the consultant’s 50 % for Reuse and 50 % for landscaping jargon.  In Technical papers and documents one expects exactitude and precision and not vague descriptions.

7. About the wide choice of STP technologies left to the bidder, less said the better.  One wonders however at these possibilities and has these nagging questions :

  -  Had there been a more powerful search engine, say Google +++,  would the list have been longer ?

- Does the Consultant possess adequate knowledge, competence, skill and expertise to assess the pros and cons of the various technologies that may be proposed by sundry bidders.  And if the answer is YES,  why has he not done this exercise and homework himself and Zeroed in on the one most Optimal and Practicable technology option for an STP of this size in this setting ?

- Under the Biological aerobic options, what is the difference between an FAB and FBBR ?  Am I missing some key but obscure differences in Design and engineering between the two competing technologies ?

- A septic tank option for a 230 KLD STP ?????

… and so on.  Professional  etiquette and decency prevents me from completely disrobing the consultant.

UPSHOT OF THE STORY

My Company steadfastly refuses to participate in such open tenders for precisely the above reasons.  What chance does a good STP with proper scientific design and engineering features have against these odds and at the hands of an incompetent consultant ?


Dr. Ananth S Kodavasal                                                                        October 04, 2015
Director – Ecotech Engg. Consultancy Pvt. Ltd.
Bangalore 560 066

Mob : 98450-62033

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