9
Samalkotah junction is supplied from a deep sub-artesian bore-hole. The
quality of the water is good but at the last examination it showed signs of
deterioration as a result of flooding.
The other stations obtain their supplies from wells. The quality of water
from these varies very considerably. (Vide Appendix III.)
(3) Research work in connection with the Experimental Filter Installation
.
Research work was continued with the Experimental Filters during the
year.
(a) Sand filters. —The effect of further reducing the sand layers which had
been shown to be possible by the introduction of a layer of fiat tiles between the
two grades of sand, was tested during the first half of the year. This experiment
was carried out in the covered filter and the topmost layer of sand was reduced to
12 inches. The results were eminently satisfactory.
The filter was started on 31st January 1919 and continued working until
25th June 1919 when it clogged. During this period of 145 days, which is a
record run for these sand filters, the filtrate maintained a high standard of purity
and compared very favourably with examinations of the unfiltered water which
were carried out as a control. (Vide Experiment I.)
Fluctuations in the filter-head continued to occur but these were not accom
- p a n i e d b y v a r i a t i o n s i n t h e p u r i t y o f t h e f i l t r a t e . T h e c a u s e o f t h e s e f l u c t u a t i o n s
is not apparent. Previous experience has shown that any sudden decrease in the
filter head is accompanied by a deterioration of the filtrate and has commonly been
ascribed to breaks in the biological film. Such an explanation is not however
applicable in this case and the true cause has still to be found.
Further experimentation in this direction is indicated but was not continued
at the time, owing to other questions engaging the attention of the Committee.
(b) Effects of storage and sunlight. —The next series of experiments were
designed to elucidate the effect of storage and sunlight as agents in the purification
of water.
During the course of certain experiments in 1918, designed to gauge the
efficacy of using stored in preference to unstored water for sand filtration, it was
noticed that after the eighth day of storage, there was a tendency for the quality
of the water to fluctuate. Specialised experimental work on this particular point
had not been carried out here, although Houston and Clemesha had, as a result of
their experiments, come to certain conclusions. Houston has pointed out that in
England a period of three weeks is required to achieve the best results in rendering
a polluted water comparatively safe. Clemesha showed a similar change occurs
in this country in about eight days. The value of this method of treatment was
reinvestigated. The experiments were so designed as to make it possible to
distinguish between the effect of storage alone and storage in combination with
sunlight. Samples were drawn thrice daily for 27 days at 3 different depths
(surface, middle and bottom) from each of the covered and open tanks and the
daily condition of the sky and hours of bright sunshine noted. Three such sets of
experiments were conducted and the results point to the following conclusions:
—
(1) During the first four days of storage the number of bacteria diminishes
rapidly and to a considerable extent; after this period the process of reduction is
less marked or may be absent altogether.
(2) The maximum reduction is reached either before or about the
8th day.
(3) Considerable fluctuations were found to occur in the bacterial content
of water stored for longer periods.
(4) Lactose fermenters are similarly reduced by storage and the reduction
of these organisms goes on to a greater extent than that of the other bacteria.
(5) No consistent difference has been noted between the combined action
of sunlight and storage and storage alone. (Video Experiment II.)
It would appear therefore that, under tropical conditions similar to those
obtaining in Madras, storage of raw water for a short period antecedent to