51
REPORT ON THE WORKING OF THE KING INSTITUTE, GUINDY
the previous week, was rendered sufficiently clear within the first four days of starting the
filters. The clarity continued to be satisfactory during the rest of the run. The organic
matter was reduced by about one-half and the total number of bacteria was reduced by
.about 70 per cent and there was at least a fifty-fold improvement with regard to the lactose
fermenters. The same experiment was repeated twice between September and November
1921. The second experiment carried out between 14th October and 12th November 1921 is
alone taken into account, as the conditions present during the first were not comparable.
During this period there was a comparatively heavy and well-distributed rainfall (between
16th October and 5th November 1921). This rain produced a very turbid initial feed water;
the filters however functioned very satisfactorily and not only rendered the water clear but
also removed the excess of organic and bacterial pollution to an appreciable extent. This
experiment fully confirmed the results obtained in the first experiment. It was now
decided by the Committee that even while the rains lasted, some experiments on a rate
higher than 8 inches should be tried. Further experiments with 8 inches, under fair weather
and high flood conditions, were therefore postponed until later.
In December 1921 both the filters were started at a rate of 12 inches vertical per hour.
The rainfall during this period was not so great as in the preceding experiments. There
was however, an increased turbidity in the water of the river on 9 out of the 19 days
during which the filters were worked. This increase was not quite so great as was
anticipated. The results, as far as both clarification and filtration were concerned, were
satisfactory. The yield of filtered water in gallons for the entire period, while working at
this rate, compared very favourably with that at 8 inches. At the end of this experiment it
was apparent that there would be no more rainfall and therefore it was next decided to raise
the rate of filtration to 16 inches vertical per hour, for it was considered that, if the results
of filtration with that rate, with an initially clear water were not satisfactory, there would be
no necessity for trying the higher rate with a flood water. The filters worked for only eleven
days at this rate (16 inches), and although the results of filtration were satisfactory from
the bacteriological point of view, the total yield in gallons of the filtered water during the
period of the run had dwindled down by about 30 per cent, as compared with the 8 and.
12-inch rates. The experiment was again repeated in February 1922 with identical results.
The Committee therefore considered that the 1.6-inch rate was not of practical value on
account of the rapidity with which the filters went out of action, no advantage in the
quantity of the filtered. water being obtained as a possible set-off against the increased cost of
maintenance. Experiments at a 16-inch rate with turbid water were therefore not
considered necessary.
Between March and June experiments with the 8-inch rate were repeated in the hopes
that local thunder-storms, which are usual at this time of the year, would bring the necessary
conditions of the raw water. No rain however fell, while the experiments were in progress.
The results of these experiments have not therefore been discussed as they are not comparable
with the remainder.
Towards the end of August 1922 the experiments were again commenced. Except
for a few slight falls in the month of September, there was little appreciable rainfall. The
filters ran at a rate of 8 inches vertical per hour for 30 days and then clogged. The raw
water was for the most part only hazy. The clarity effected by the filters was satisfactory.
The percentage removal of bacteria and the reduction of lactose fermenters were very
marked (90 per cent reduction in the total count and a 5,000-fold reduction of lactose
fermenters on an average).
With the setting-in of the monsoon, satisfactory conditions for the continuation of the
experiments were established. The two filters were started on 27th October at a rate of
8 inches vertical per hour. They ran for 33 days. On this occasion the filters failed to effect
complete clarification. The filtrate remained slightly hazy during the entire period of the
run. The amount of haziness however, was not considered sufficient to condemn the filtrate
from the point of view of the experiments. A similar condition has been recorded by Sir
Alexander Houston in the case of the Thames water, during certain seasons. Sir Alexander
Houston considers, that a hazy filtrate is unavoidable under such conditions.
The filters were found to have effected a 64 per cent reduction in the total number of
bacteria and a 1,000- fold improvement on an average, with regard to lactose fermenters.
The reduction in the quantity of organic matter was also quite satisfactory. This experiment
conclusively proved that, even under extreme conditions, the rate of filtration could be
increased to 8 inches vertical per hour, while at the same time, a filtrate could be obtained
which was satisfactory both as regards yield and quality for subsequent chemical treatment.
The next was a repetition experiment in which the 12-inch rate was tested with both the
filters. The Adyar River water was very turbid at the beginning of the experiment but
gradually cleared up so that at the end of the experiment, the filters were dealing with a
fairly clear water. The filters ran for 17 days and the filtrates were satisfactory in
every way.