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3.—THE EFFECT, AS REGARDS THE RESULTANT QUALITY OF THE EFFLUENTS
FROM THE BACTERIAL BEDS, OF THE ADDITION OF CERTAIN CHEMICAL
SUBSTANCES TO THE BARKING CRUDE SEWAGE.
It is known that some species of micro-organisms act with great vigour in the presence of a
large excess of certain basic substances. For example, the nitrifying germs show increased
bacterial activity when grown in liquid media containing an excess of magnesium or calcium
carbonate. It is supposed that the solid grains besides neutralising the products of bacterial
actilvity, act as what may be termed "contact points," enabling the bacteria to localise and concentrate
themselves at a multitude of different spots. Further, if the liquid is in motion the
grains may act as "carriers" of the microbes and their products from one place to another.
It is a matter of controversy among those who have practical concern with bacterial beds
which is the best material to use. Some assert that the actual chemical composition of the
substance is of no importance, that it is the physical qualities (e.g., whether smooth or jagged,
pervious or impervious) of the material which is all essential. Others believe that certain
substances are preferable to all others in virtue of their ability of exerting a basic action on the
products of bacterial growth and of encouraging the active growth of special micro-organisms.
However this may be, it is of interest to note that Mr. E. Brooke Pike, the chemist in charge at
Barking, suggested the trial of ragstone as a better material in respect of its chemical composition
than coke. This was agreed to by Dr. Clowes, and accordingly a trial was made of the comparative
values of ragstone and coke bacterial beds. The outcome of these experiments seemed to be that
the ragstone coke-beds did encourage the growth of the nitrifying germs (as evidenced by an increased
production of oxidised nitrogen), but that the effluents, as regards the removal of dissolved oxidisable
and putrescible matter, were not so satisfactory from the ragstone as from the coke-beds.
Although it is quite conceivable that the actual chemical composition of the material in a
bacterial bed, quite apart from its physical characters, may play a definite part in influencing the
biological processes at work in the bed, it is evident that the action, whatever it may be, cannot be
expected to persist for an indefinite period.
With this idea in view, I suggested the trial of the artificial addition, in small amounts, of
some such substance as magnesium carbonate or calcium carbonate to the sewage as it flowed on
to the beds, as likely to produce a beneficial effect by its diffusion throughout the liquid in the
beds and also by its settling on the surface of the fragments of coke and effecting a lodgement
there. It was hoped that not only would the result be immediately beneficial, but that the good
effect would be maintained for a considerable period after the addition of the substance had been
abandoned. In short, that it would only be necessary to occasionally and very rarely resort to
such an artificial measure in order to obtain uniformly good results. With Dr. Clowes' permission
Mr. E. Brooke Pike was good enough to carry out some very careful experiments in this direction.
In the first series of experiments he added magnesium carbonate emulsion to the crude
sewage as it flowed on to the beds in such strength as to correspond to O'OOl part of magnesium
carbonate to every 100 parts of raw sewage.* This was done each time the beds were filled, viz.,
twice a day between Wednesday, 21st March, and Wednesday, March 28th, 1900, both days
inclusive.

* This minimal quantity (.0001 per cent.) was used as a preliminary, as it did not seem desirable to
materially increase the suspended matters in the sewage.