Chlorination of Water - Joseph Race

DIAGRAM III
EFFECT OF TEMPERATURE

DIAGRAM IV
EFFECT OF TEMPERATURE

Inefficient admixture leads to local concentration of the chlorine, a condition which (vide [p. 35]), results in a wastage of the disinfectant. Two practical examples of this effect may be cited. In one case the water was free from colour and contained very little organic matter. This water was chlorinated at one plant by allowing the bleach solution to drop into one vertical limb of a syphon approximately 6,000 feet long, the other vertical limb being used as a suction well for the pumps which discharged into the distribution mains. At the other plant the bleach solution was injected into the discharge pipe of a reciprocating pump through a pipe perforated with a number of small holes. The results for two typical months are given in [Table X].

TABLE X.—EFFECT OF EFFICIENT MIXING

Month.	Available Chlorine Parts Per Million.		Bacteria Per c.cm.			B. Coli Index Per 100 c.cms.
	Available Chlorine Parts Per Million.		Raw Water.	Treated Water.		B. Coli Index Per 100 c.cms.
	A.	B.	Raw Water.	A.	B.	A.	B.
July	0.20	0.25	864	27	93	< 0.2	8.5
August	0.20	0.27	1.108	12	120	< 0.2	10.2
A = efficient mixing. B = inefficient mixing.

The results with the “B” plant were very irregular. The hypochlorite and water did not mix thoroughly and, as several suctions pipes were situated in the suction shaft, there was no subsequent admixture in the pumps; this also caused complaints regarding taste and odour but the complaints were localised, and not general as would result from an overdose of solution due to irregularities at the plant.

The second example deals with a water containing 40-45 p.p.m. of colour. This supply was taken from the river by low-lift pumps and discharged into a header which was connected with the high-lift pumps by two intake pipes about 5,000 feet in length. During 1914 a baffled storage basin of two hours capacity was constructed and in June the hypochlorite was added at the inlet to this basin by means of a perforated pipe. The object was to increase the contact period prior to the delivery of the water into the header. The results for this month were as follows: