Richmond dispatch. [volume] (Richmond, Va.) 1884-1903, 1898-08-25
JAMES RIVER WATER.

re feel that we could not do our citizens
a better service than give editorial prom
inence to the subjoined communication
from Professor Mallet, his second OF
recent date on the subject treated.
University of Virginia,
August q. 1898.
To the Editor of the Dispatch
The sample of James-river water sent
me by you came TO hand yesterday, and
this morning ! return part of it filtered,
without addition Of alum or any other
clarifier. Tho result is rather better
than in the case OF sample previously
sent you Of our local water supply. main
~ because the filter has been kept run
ming, and its pores are not 50 open as
when 1t was first used.
In your remarks on Saturday last upon
the previously sent sample you seem TO
have been under the impression that L
ignored the scale upon which filtration
would have TO be carried on for the gene
raj supply Of Richmond. in sending you
that sample, however, / said distinctly
that It was not intended as an illustration
OF the method of filtration 20 be adopted
upon the larger scale. but merely to re-
flute the erroneous assertion that Rich
mond water cannot be filtered clear with
out the use Of alum.
Two different methods have chiefly
been used for the filtration of large guam
titles of water for the public supply Of
cities one of these being more largely
employed in Europe, the other more OK
tensvely in the United States.
The former of these involves the con-
Structon of large shallow. rectangular
basin5, ten or twelve feet deep, of stone
lrf ,VLy
work. with impervious lining. in which
are disposed layers. first of broken stone,
then. in order. coarse gravel, fine gravel,
coarse sand, and finally on top not less
than three feet of fine sliceous sand
Into these the water is run, so that il
always stands at a depth Of three or four
feet above the uppermost layer OF sand
Properly constructed drains carry off
the filtered water from beneath the bot
tom layer of broken stone In view Of
the irregular demand for water through
a day of twenty-four hours, a supply-ba-
sin TO hold the filtered water is needed.
and in case the original water is notably |
turbid. II is we'll 10 interpose a settling-ba- |
sin between the source of supply and the |
flter-beds. so as TO admit of the filters |
being less frequently cleaned, but both |
settling and supply-basins may be small !
holding not more than, say, a single days |
supply. Such filtration will from the first |
render the water clear as far as the |
grosser mud is concerned. but after being
in use for little while the upper surface
of the sand. and the surface OF the sand
grains to the depth of two or three inches.
will become covered with a ielly-like
slime. the accumulation Of bacterial or
ganisms, and thenceforth the far more
important result Is accomplished Of filter
ing out the bacteria themselves. BY no
means all OF these minute living organ
isms are harmful. but IL is well known
that amongst their countless hOrdes oc-
cur species from which the grayest dam
gers 10 health arise If they be swallowed.
il has been shown that by means OF
such filtration as has been described
from 9S5 10 995 of the bacterial and
other microbes present may be removed
from originally very foul water. After 4 |
couple OF weeks use In winter. or say u |
months use In summer. each flter be-
comes 30 far choked as 10 require clean ,
ing. by letting the water run down and
removing with shoves an inch ,
or two from the top layer of sand. and al
much longer intervals either new sand I
or the old scrapings cleaned must be
laid down so as 10 maintain "A proper
minimum thickness for the filtering layer.
In connection with this system there Is j
no use made OF alum or other coagu- q
lants.
TWO principal variations OF the ar
rangement require notice: In the first
pace, The hlter-beds may be uncovered ~ b
IN climate so mild that ice never or n
ou, rarely interferes with filtration I'm
winter, though occasional ice NAV he
Se~,. Win Cat some additional expense) D
py breaking IT up or partly removing II {
or, on the other hand trouble from =,
ireezihg may be avoided by roofing over
me beds In the second place. the ultra.
lion may be continuous water being kent n
s,aholhs on me sand at all times save 4
dur1ns cleaning. or may be intermi,,ent
the water being from time 10 nine ailon''
ed to drain of. and air allowed 20 renlaco Il
IL In the pores Of the filter Win a yie,. a
OF aiding the process OF destruction OF Il