No_7_July_1968 — Page 38

no pretreatment plant at the treatment works.

(ii) Sedimentation

Four circular, radial flow tanks, 87 ft. 6 in. internal dia- meter with a bottom slope of 71⁄2 in. and side water depth of 4 ft. 9 in., are provided initially. The tanks were de- signed for retention periods of two hours at D.W.F. and quick sludge removal,

me-

The weirs of the tanks are fitted with adjustable aluminium vee-notched weir plates. Elec- trically operated scraper chanisms are provided to re- move sludge from the floor of the tanks by means of a scrap- ing mechanism, scum from the surface of the contents of the tanks by means of a skimming mechanism, and algal growth from the side walls of the tanks and inverts and weir side walls of the effluent peri- pheral channels by

means

of adjustable contra-rotating brushes.

(d) Aeration tanks

Initially, four units of aeration tanks, with two sets of mixed liquor and returned sludge channels, all hav- ing an overall capacity of 71⁄2 hours D.W.F. are constructed. The tank is of the flat floor type, and each unit is divided into seven channels by means of precast prestressed r.c. col- umns and planks.

Each channel is provided with four lines of 7 in, diameter dome diffus- ers, supplying air from the air com- pressing plant at the maximum rate of 0.3 cu. m./sq. ft. of surface area.

Four axial flow pumps installed in

Primary sedimentation tank under construction; four bays ready for concreting

pairs, each pair serving two units, are provided to deliver return sludge up to 1.25 D.W.F.

(e) Final separating tanks

Eight final separating tanks are constructed at this stage. These tanks are of 70 ft. internal diameter with a floor slope of 30° and a side water depth of 4 ft. Each has a capacity of 4 hours D.W.F.

To combat algal growth as with the primary sedimentation tanks, the weirs are fitted with aluminium vee- notched weir plates. Scraping me- chanisms are provided to remove ac- tivated sludge from the sloping sloping floors of the tanks and brush algal

growth from the side walls of the tanks and the inverts and weir side walls of the effluent peripheral chan- nels.

Mixed liquor is fed into the cen- tre of the tank by a 24 in. dia. c.i. pipe and an aluminium diffuser box is provided to dissipate the energy of the incoming flow to prevent the creation of eddy currents от other distur- bances to the settling of the activated sludge in the tank.

(f) Sludge disposal

Provision is made for primary digestion tanks at the works. Digested sludge will be pumped to Serangoon sludge disposal works, where plans

MAIN SEWER

24&39 & RISING BRADOEL ROMAINS |PUMPING STATION

393 AM(FUTURE)

„2-639ERISING

GRAVITY SEVERBAŘILEY RD MAINS

PUMPING

WORKS PUMPING

STATION

SLUDGE TO STAGE 1 AERATION TANKS

SLUDGE DRAINS FROM EXISTING WEST WORKS (FUTURE DIVERSION

v v h

WORKS DRAINS FROM EXISTING WEST WORKS (FUTURE DIVERSIONY RAW SLUDGE TO WEST WORKS DIGESTORS

STATION

139 0 RM(FUTURE)

SURPLUS ACTIVATED SLUDGE

RAW SLUDGE

OVERSION EXISTING WEST W

WCRI

SETTLED SEWAGE

SEDIMENTATION

TANKS & MOS

78-6 DIAMETER

|RETURN EFFLUENT

CAPACITY 150,330 GALLONS EACH

FRCH WEST WORKS

AIR TO EAST WORSĄ AT 6 PSI IN 5-4

AIR MAIN

SLUDGE GAS FROM WESTERN DIGESTOPS

AIR TO WEST WORKS AT 7% PSÍ IN 263 A'R MA'N

COMPRESSOR

HOUSE

RAW SLUDGE

DIGESTED SLUDGE FROM WEST WORKS,

Flow diagram. Toa Payoh sewage treatment works

40

PERATION TANKS

4 UNITS TO TAL SAPAC TY

3.250.000

GALLONS

MIXED LIQUOR

ETURNĄ"

-FINAL SEPARATION TANKS

# NOS 70FT DIA

CAPACITY

250,000 GALLONS EACH

FINAL EFFLUENT TO EFFLUENT OUTFALL

SLUDGE GAS

GAS HOLDER

PRIMARY DIGESTION TANKS

--6 NOS

CAPACITY

885,000 GALLONS EACH

D.GESTED SLUDGE

OSUMPING STATUNGE PUMPING PAIN

TO SERANGOON SLUDGE DISPOSAL WORKS

Far East BUILDER, July 1968.