11
The Filter Beds Committee appointed by Government in G.O. No. 1012 W.,
dated 21st May 1914, under whose direction experiments are being conducted met
in February and Major Morison, I.M.S., was invited to offer his suggestions to the
Committee. He laid stress upon the value of chlorine solutions in the purifica-
tion of highly polluted water-supplies. On the question of standards for drinking
water in the tropics, he was of opinion that the conditions and surroundings
which affect the purity of natural water supplies in India were so unsatisfactory
and liable to such wide variations that it was not safe to place great reliance on
existing methods of water purification by filtration alone, much less to attempt to
fix any standard short of absolute freedom from bacteria of any sort. He was,
therefore, in favour of chlorination being adopted as a routine measure in
addition to filtration.
The Committee accordingly resolved to obtain sanction of Government for
installing a chlorination plant at Guindy or at Kilpauk, with a view to carry out
some experiments preliminary to adopting the system for the mufassal supplies.
As regards the Experimental Filter Installation at Guindy, it was resolved to
restrict the experiments to definite points raised by the Engineers for solution
as a result of their experiences in the working of mufassal water-supply installations.
Mechanical Filters.—Experiments with these filters carried out between 1913
and 1919 had shown that in dealing with turbid flood water these filters required
larger doses of alum than for the clearer water of the dry months. The latter is
comparatively free from suspended matter and consequently requires smaller doses
of alum for clarification.
The question of dosage of alum for the mechanical filters has been one of
great difficulty and during all these 7 years it was being dealt with more or less
empirically. Morison in 1916, working with the soft Poona water attempted to
place the determination of the dose of alum on a rational basis. He concluded
that " the best dose of alum for the perfect clarification of a soft water is obtained
by adding half the equivalent weight of alum necessary to react completely with
the alkalinity calculated as calcium carbonate and that the clarification obtained
by adding the optimum dose of alum is not affected by the turbidity of the water
within the wide limits of turbidity in the Poona water."
As Major Morison's findings were found to run contra to the results of
empirical dosage adopted here, it was considered necessary to institute a systema-
tic daily estimation of the alkalinity and turbidity of the Adyar water for a period
of at least one year. Experiments in this direction were started in October 1919
the flood season of that year and the alkalinity and bacterial content of the Adyar
water were systematically recorded, A Lovibond's tintometer, the instrument
which Major Morison used in his enquiry at Poona as being the most accurate,
was indented for from home but did not arrive till late in the year. It was not,
therefore, possible to estimate the turbidity along with the alkalinity.
The results obtained with the alkalinity test have been plotted out graphically
and are found in appendix IV.
It will be observed that the alkalinity of the Adyar river water follows a
curve bearing a definite relation to the rainfall and the depth of water in the river.
After every fall of rain the alkalinity went down and the turbidity as judged with
the naked eye and the ordinary glass cylinder in the absence of the tintometer
showed a corresponding increase. In fact the alkalinity varied inversely as the
turbidity and the rainfall.
The next step then, was to determine the existence of a definite relation (1)
between the alkalinity and the dose of alum required, (2) between turbidity and
the dose of alum, and (3) between alkalinity and turbidity. Experiments in this
direction have been projected and taken in hand.
Sand Filters .—Sir Alexander Houston's recent researches in England have
been directed towards chlorination as an auxiliary to sand filtration and in his latest
Research Report (1920) he recommends very rapid filtration of water through slow
sand filters, followed or preceded by chlorination as the safest and at the same
time the most economical of purification processes.