Accepted Papers - 3.pdf - UNESCO

3. Sewage Water Recycling System
The objective of industrial liquid Sewage
treatment plant (STP) is to treat the canteen waste
and sewage from the power plants to meet
environmental regulations and use the treated water
for horticulture, thus reducing the load on the raw
water from the river and the residue for land filling
as a manure.
In NALCO CPP, for an employee strength of
3000 (including Contract worker) and for nearly 100
quarters in the Vidyut Nagar Township around 18
M 3 /hr sewage water is generated. The internal
canteen and kiosks are generating around 3 M 3 /hr
of canteen waste. The sewage Water recycling
system is installed to recycle back 8 M 3 /hr of water
from this area .
After primary treatment at the source of their
generation of the canteen waste by Garbodrain ,
the effluents are sent to the STP for further treatment
along with the sewage. The composite liquid effluent
treatment plant has been designed to treat all liquid
effluents, which originate within the power station
and re-circulation of the treated effluent for various
plant uses mainly for coal yard fire quenching and
Horticulture purpose. The Capacity of the system
is as below -
a) FLOW :
i) Canteen Waste - 3 M3 / hr
ii) Sewage Flow - 18 M3 / hr
Total - 21 M3 / hr
b) RAW EFFLUENT CHARACTERISTICS :
i) Canteen Waste Water
BOD 500 mg/lit
SS 600 mg/lit
Oil & Grease 50 – 100 mg / lit
ii) Combined Waste Water
BOD 600 mg/lit
SS 1000 - 1500 mg/lit
Oil & Grease 600 mg / lit
410
c)TREATED EFFLENT CHARACTERISTICS:
pH 7 – 7.5
BOD < 30 mg/lit
COD < 250 mg /Lit
SS 100 mg/lit
Oil & Grease < 10 mg / lit
DO 0.20 mg/ Lit
Residual Free Chlorine 1 mg/ Lit
Process Description
The canteen waste is processed through a
GARBODRAIN, where the screened solids, grits
and other kitchen waste are ground and then led to
the BAR SCREEN –I. There, the Canteen
wastewater is screened off and the floating matter
is collected in a channel fitted with fine bar screen.
The bar Screen consists of equispaced parallel bars
inclined to horizontal. The screenings arrested on
Bar Screens are raked manually at intervals. The
raked screenings are collected on perforated
platform to allow effluent to drip in to the channels.
The semi-dried screenings are then carted out for
land filling or incinerated. The canteen waste water
is then conveyed to the GRIT REMOVAL
CHANNEL, designed to remove grit consisting of
sand, gravel or other heavy solids. The GRIT
REMOVAL CHANNEL constructed in RCC is
designed to maintain horizontal velocity close to
0.6 m/sec. so as to settle the grit particles to bottom
of the channel. Settled grits are scooped manually
from bottom and collected in a wheel barrow and
disposed off as land filling. The degrited canteen
waste water is then passed to OIL REMOVAL
UNIT for removal of oil. It consists of baffles and
an Oil skimming pipe to skim off the floating oil
into an oil drum.
The raw sewage along with preliminary treated
canteen waste water is screened Off in the BAR
SCREEN-II .As in BAR SCREEN -1,,the
screenings are arrested on bar screen and raked
manually at interval depending on clogging frequency.
The raked screenings are collected on perforated
platform to allow sewage to drip in to the channels.
The semidried screenings are then carted out for
land filing or incinerated. The waste water is then