corner of the settling tanks, where the water is dosed with aluminium sulphate to promote flocculation of the fine particles, a coagulant aid such as activated silica, and an alkali to adjust the acidity of the water to ob- tain optimum flocculation. The mix- ing race contains a series of baffles to promote thorough mixing of the chemicals.
After mixing, the dosed water is distributed by channels to the 24 upward flow hopper-bottomed settling tanks by means of inlet pipes dis- charging in the bottom of the tanks. A sludge blanket is formed in each tank and clarified water is decanted at the top by means of concrete troughs supported on a prestressed concrete beam.
Sludge is both intermittently bled off through a small valve, and periodically drawn off through a larger valve when heavy sludge accumula- tion requires this. The sludge is dis- charged into a drainage system lead- ing back to the river downstream of the intake.
The clarified water flows by gravity to the filter block through an open channel provided with an overflow weir, which when in use discharges into the wash-water drainage system.
Each of the scheme's eight filter beds consist of sand 3ft. thick con- tained in a concrete tank. One ex-
perimental filter has anthracite sub- stituted for part of the sand layer.
The clarified water enters the upper part of the filter tank and after perco- lating through the filter media is col- lected in an earthenware pipe system in the base of the tank and thence led to the central filtered water chan- nel beneath the filter operating gallery.
The first stage of filter cleaning is to scour the filter media by blowing compressed air through nozzles to break up consolidated matter retained in the upper layers. Filtered water is then pumped through the filter bed to wash away the agitated retained material to the washwater drainage system. A steel weir prevents signi- ficant loss of filter media.
Compressed air system
Operation of the filter valves and penstocks is by a compressed air sys- tem controlled manually from indivi- dual consoles in the upper filter gal- lery.
The position of the outlet valves of the filters in service is ad- justed automatically from a transmit- ter in the settled water channel to compensate for variations in the quantity of settled water entering the filters.
In addition, the pneumatic filter flow control system compensates automatically for the increasing loss
of head of individual filters as they become dirty.
Filtered water passes beneath the administration building in a concrete channel where it receives dosages of lime for alkalinity adjustment, chlo- rine and ammonia for sterilisation, and sodium silico fluoride as an optional additive.
Dosing is carried out in the chemi- cal building and the chemicals are conveyed by hose to their injection points.
Finally, treated water passes to a clear water tank by means of twin short lengths of 48in. steel pipe, each fitted with isolating butterfly valves. The clear water tank is of reinforced concrete construction, and the walls are partly restrained by fill.
The treated water delivery system comprises the high lift pumping sta- tion and the delivery main to the connection with the Tebrau mains some 17 miles away.
High lift station
In the high lift pumping station, two 48in. dia. steel pipes lead from the two halves of the post-filtration treatment clear water tank to the suc- tion manifold for the five high lift pumps (two more pumps will be re- quired for stage 2 output). Both pipes are fitted with butterfly valves
Reinforcement placing nearing completion at a downstream
RC cross-connection support slab
Far East BUILDER, August 1968.
Top right: Intake coffer dam showing the top frame at + 7ft. and part of the middle frame at -2ft. 6in. Bottom right: 36in. diameter siphons in the intake structure
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