On the day of 21st of February, Saturday sharp at 10 o'clock morning, the lake conscious team gathered at Cubbon Park with an agenda of more familiarity with Cubbon park Sewage Treatment Plant. The purpose is to evaluate the technology for its viability for sourcing treated sewage water to the lake rejuvenation.
In a gist “The Cubbon park treatment plant is 1.5 MLD capacity using MBR (Membrane Bioreactor) coupled with aeration technology, setup in 2004/2005, at a cost of > Rs 4 Cr with a footprint of 0.8 acres on a 2 acres plot”. The idea was to tap 1.5 MLD sewage from neighboring drain and use the cleaned water for gardening purposes of the park. This was achieved by letting out clean water of < 2 BOD consistently. The plant spends Rs 2 lakhs per month on electricity. Simplified cost is Rs 12/- per KL. The STP is completely automated and most operations can be carried out from the office using SCADA systems, leaving human factors to 15 employees only. For 2004/2005 it was surely efficient enough, to see if this holds good in 2014/2015 let us see the operational details below:
Step 1: Sewage is let to flow from the drain to wet settler tank by screening through a 3 cm gap screen, To stop the bigger objects like blanket, utensils, dead animals etc.
Step 2: Four pumps are then engaged in pulling the water from the tank to two new chambers say ‘A’ and ‘B’. The total flow capacity of the 4 pumps is 55.25 cu.meter.
Step 3: Both chamber “A” and “B” has a 6 mm screen each to further filter out heavy particles before letting in a common chamber say “C”.
Step 4: From “C” then with the help of two pumps it again passed to two chambers say “D” and “E” having 0.8 mm filtration screen each.
Step 5: From “D” and “E” via a distribution channel it then passed in two big aeration tank say “M” and “N”. The depth of each of the tank is 4.29 meter. Air is passed into each of the tank from two air blowers. Here the aerobic digestion takes place. From this tank the final sludge is removed.
Step 6: Following that the treated water is passed through Chlorine bed for disinfection by passing jet of Sodium hypochlorite.
Step 7: Further it is made to pass through Activated carbon filter for odour removal and dechlorination. Because Chlorine is a toxic substance which makes it ideal for killing harmful pathogens, but it does not stop there. If chlorinated water were released into the garden it would also be harmful to soil,plants and any other living organisms it contacts.
Step 8: While the Treated water is stored in a tank for irrigation, The obtained sludge is removed and dried in sludge bed and generally used for landfilling.
Quality: less than 2 BOD but contains Nitrate and Phosphates which is not a threat in this case as it is considered that both will be absorbed by plant as nourishment.
Maintenance: Major action involves cleaning up the clogged membrane. It is achieved by backwash technique. Sodium hypochlorite and Citric Acid jet is used for this purpose.