TOI : Govt-run RCF does it, with water from sewage : Sept 6, 2007
Govt-run RCF does it, with water from sewage
Sunil Nair | TNN
Mumbai: A sluggish 1992 monsoon, which forced the BMC to impose a 30 per
cent water cut on the city, set the Rashtriya Chemicals and Fertilisers on
its way to establishing the country’s largest sewage treatment plant.
The RCF at Trombay, which needed 7 million gallons (26.5 million litres)
of water daily to keep the factory’s cooling towers running 24×7, was forced
to shut down some units for two weeks as the BMC began slashing supply.
The consequent loss in production bled the state-run undertaking by Rs
50 crore and forced its management to look for innovative solutions. Two of
them seemed the most viable: desalinating water from the sea or cleaning up
sewage. RCF, eventually, plumped for a project to purchase raw municipal
waste water and treat it for use in its industrial processes.
The sewage is cleaned, aerated, filtered, chlorinated and made virtually
fit to drink using a five-stage recycling technique (see box) that is a
shining example of environmentfriendly practice in a city struggling to
ensure non-stop supply of drinking water.
“It took us eight years and Rs 40 crore to commission it. Today the
plant can treat about 5 million gallons (19 million litres) of sewage a day,”
deputy general manager and part of the team that spearheaded the project, P
T Desai, said. “We don’t use the plant to full capacity as we get 3 million
gallons daily from the BMC.”
Part of the reason the project took so long to commission was the fact
that the BMC was not entirely enthused by the fact that it would lose a
large chunk of its revenue from the RCF. The BMC cross-subsidises its
operations by charging industrial users more in order to supply to
residences at concessional rates. So it was not keen on the fertiliser plant
cutting back on water bills but finally relented when the RCF agreed to pay
60 paise per litre of sewage treated.
Tenders were invited and a 5-km pipeline was laid from Ghatkopar to
Trombay to pump the sewage in from a collection point in the eastern
suburbs. The factory now receives 1 per cent of the 3,300 million gallons of
raw waste generated every day in Mumbai.
FROM WASTE TO WATER
Waste becomes water in a five-stage process at the Rashtriya Chemicals and
Fertilisers
STAGE I
The sludge flows over a sieve for removal of floating material like cloth,
plastic wrappers and grit.
STAGE II
The waste is then aerated by pumping oxygen into it in a tank; the sewage,
at this point, generates its own form of biomass.
STAGE III
The middle stage of the process involves the use of a clarifier where the
sludge settles at the bottom.
STAGE IV
The water is dispatched for further cleaning with sand filters.
STAGE V
A process of reverse osmosis helps achieve removal of dissolved sonlids like
carbon and salt.