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REPORT ON THE WORKING OF THE KING INSTITUTE, GUINDY
APPENDIX No. VII.
REPORT ON THE EXPERIMENTS CARRIED OUT AT THE GUINDY
EXPERIMENTAL FILTERS BETWEEN 1921 AND 1923.
Experiments on the rapid filtration of water through sand filters as a preliminary to
suitable chemical treatment, were carried out with the experimental filter plant at Guindy,
as opportunity offered between 1921 and 1923, under the direction of the Committee on
Water Filtration.
These experiments were completed in May of the present year (1923). The detailed
report on these, experiments which had been promised in the last annual report of the
King Institute of Preventive Medicine, is now submitted for the information of Government.
The idea of carrying out these experiments first originated from similar experiments
performed by Sir Alexander Houston, who in his research report published in 1920
strongly advocated very rapid filtration of water through slow sand filters, followed or pre
- c e d e d b y c h e m i c a l t r e a t m e n t , a s t h e s a f e s t a n d a t t h e s a m e t i m e t h e m o s t e c o n o m i c a l o f
purification processes. When chemical means of purification is resorted to, some form of
filtration is necessary in most cases for preliminary clarification, sterilization being subse
- q u e n t l y c a r r i e d o u t b y t h e a d d i t i o n o f t h e c h e m i c a l .
In these circumstances the rate of filtration can be increased to an unlimited extent, so
long as the preliminary clarification is satisfactory.
As the Committee had no information as to the behaviour of sand filters when used for
this purpose, it was considered advisable to divide the investigation into the chemical treat
- m e n t o f w a t e r i n t o t w o p a r t s ,v
i z . ,
(1) The discovery of the best and most economical means of using sand filters as a
preliminary to chlorination.
(2) The best and most effective method of chlorination.
It is obvious that the experiments initiated to decide part I, must be the necessary
precursors to the second part of the investigation. The Committee have therefore devoted
their time to experiments on rapid filtration in the first instance and the results obtained
from these experiments form the subject matter of the present report.
In order to determine the extent of clarification effected by rapid sand filtration, apart
from considerations of bacterial purification, the sand filters at Guindy which had been
subjected in the previous year to certain structural alterations were utilised in their altered
condition for the present experiments.*
The present series of experiments were carried out at rates of filtration varying from 8 to
16 vertical inches per hour. The thickness of the fine sand layer was 12 inches in both the
filters. It appears necessary at this stage, to mention one important factor which constituted
a serious handicap to the continuity of the experiments and caused considerable delay in
their execution. The results obtained with each series of experiments to be of comparable
value, should be derived from experiments carried out, and repeated for confirmation, under
identical conditions of the raw water. Now, the raw water of the Adyar River changes
continually as the result of local and general storms. Almost every experiment has therefore
had to await the necessary conditions of the raw water before repetition was justified.
Fourteen separate experiments have been carried out in all. Ten of these, which are strictly
comparable with each other have been described.
Tables I and II give full details of the bacteriological and chemical examination of the
various samples taken during experimentation.
The Chart gives a measurement of the turbidity, the composition of the filters, the
lengths of the runs and other engineering details. These have been prepared and recorded
by M. R.Ry. K. V. Narasimha Ayyangar, Superintendent, Experimental Filters, Guindy.
The earliest experiment carried out in June 1921 was of the nature of a preliminary
trial and is not included in the present series. In this experiment the rate of filtration was
gradually increased from 4 inches to 8 inches vertical per hour, and the results obtained
justified the adoption of 8 inches as the rate for the first series of experiments, now recorded.
The first definite experiment was conducted with both filters in August of the same year,
a uniform rate of filtration, viz., 8 inches vertical per hour being maintained from the begin
- n i n g t o t h e e n d o f t h e r u n . T h e f i l t e r s r a n f o r 2 9 d a y s a n d t h e w a t e r o f t h e A d y a r R i v e r
which at this period was whitish and opaque as a result of a moderately heavy rainfall during
N
ote. —A single layer of tiles was included in one filter 6 inches below the upper surface of the fine sand
layer with the idea of forming a possible supporting layer.