The settling tanks now being altered are Nos. 2 and 3, in 1927 it Is proposed to adapt No. 1 tank and, in 1933, No. 4 tank. The output of these four tanks will be increased from 1,600,000 to 3,100, 000 gallons per hour and, from urge scale experiments already jearried out, it is expected that fter clarification will be obtained with a reduced alum dosage. Water] will be passed continuously' through, these settling tanks, Nos. 1 and 2 tanks being worked in parallel and then in series with Nos. 3 and The raw water will be admitted at two points, where the necessary alum dose will be added and an intimate mixture will be obtained by then passing the water throug a mixing chamber which consists of baffle walls so placed as to give a velocity of 6 inches per second and A contact period of 15 minutes. The combination of the alum and raw water results in the formation of particles of floc and it is anticipated that the design of this niixing chamber will give what required, particles of the most effective size uniformly distributed.
From the mixing chamber the water will pars through each of Nos. 1 and 2 tanks in each of which a bate wall will be constructed; the partly clarified water will then be conveyed by channels to No. 3 tunk, which will be unbaffled, and will the No. 4 tank is' used continuously in 1933, flow from there through another channel direct to the pump wells.
The arrangement of bates gives} the following velocities and contact! periods, which approximate very] nearly to the velocities found de sirable by experiments carried out a large scale and under, as nearly as possible, the same conditions:— in/sec—eontact period 80 mins. in./s0e. 100
Text read from the printed page and cleaned; old type leaves the occasional error.