The Providence news. (Providence [R.I.]) 1891-1906, 1893-02-22
easss
A. inlet; y. outlet; C. drains.

another reason in favor OF the natural OIL
gravity filter be and that is that the
efficiency Of any filter is dependent upor
rate OF liberation" Scientific ex.
| periments go to show that any properly
constructed sand filter bed will entirely
remove all impurities ana all bacteris
provided the water Is filtered slowly
| enough.
The important question therefore is to
| get system that will comb blue the maxi :
mum efficiency with the maximum
rapidity.
had experience. The remains OF one that
cost the city $4,000 are to be- seen today
near the pumping station. But the fail
ure in this line did not deter the city
engineer from making provisions for
other systems, II occasion should arise.
He foresaw tn 1t filtration was inevitable,
aud the present reservoir was constructed
on one side 80 that the addition of a
mechanical filter plant would be an easy
matter.
Mr.. Shedd now proposes to utilize this
reservoir aud he has mapped out a plan
the cost of which he estimates at not to
exceed Sl05, 900.
1t consists Of sixty mechanical filters
placed side by side along the upper edge
supplied from n brick conduit, and the
connection with each filter is separate so
that il one gets out of order the rest can
be- kept working.
These filters, one of which is shown
here. are Constructed on a plan already
In practical use in Wellington. Kansas.
and are giving good satisfactioi.
They consist of a cylindrical chamb er
forty feet long by nine feet. iour inches
in diameter, giving n filterlng surface Of
$40 feet each, or little over a half acre
Tor the sixty.
The filter bed Is constructed rs follows:
Across the filter chamber and little be-
low its broadest point are laid series Of
iron bars with hanges eight inches apart.
On these flauges are laid rows of especially
selected bricks. Over these for a thick
ness of two feet Is spread filtering sand
of various degrees OF ilneness, the finest
being not more than one thirty second of
an inch In size. The water is first forced
in from the reservoir and backed up
through the bricks until il is of su tiicient
height and then the water Is supplied to
the filter from above by means of n
trough so that the even surface Of the
sand will not be disturbed by water
dropping on it.
This Is a gravity filter, and does not, as
now planned, provide Tor the use Of
alumina. The head or the distance
which the water falls in order to force it's
way through the filter will be seen TO be
about half the diameter of the filter, or
four feet. With that force the filters
Will purify Is, 100000 gallons daily.
1t will be. however, an easy matter
both to make the saud bed thicker and to
Increase the force, thus making a more
rapid filter. In Philadelphia the filter is
three feet thick and the water has a head
OF nine feet
But Mr.. Shedd. believing In a slow
process of filtration. would much prefer
To build twice the number OF filters now
proposed and have only two feet OF fail
for the water. 1t is universally conceded
that this would be the more perfect plan
Of the two, but its expense would be
great.
On the other hand NJ Shedd does not
believe In the use OF alumiua and is anx-
ious to construct a filter bed thet will
obviate the necessity OF using either that
or any other coagulent. He points out
that alumina ~ great astringeut and
even in small quantities will have very
serious effect upon the city health He
believes that IL is impossible to exercise
80 continuous and due care AS l. necessary
to- insure perfection In the use of alumina
and he is afraid of carelessness such as h.
knows has occurred at various places now
using the alumina. 1T is not positively
dangerous" said Mr.. Snedd, but it is
suspicious
The cost Of alumina is s35 per ton and
the cost 20 the city for ton per day
would be including waste, etc, about
$4,000 per year. The opponents OF the
system call attention TO the fact that
sl5, 900 represents the interest on at least
$3.50, 900. aud they claim that IT would be
better To expend that much more on A
filter plant tnat would be equally efficient
without alumina than To build small
plant and use alumina
Thus perfect plaut TO use alumina
would cost probably 100000 aud one
without alumina, but more inexpensive
in maintenance could cost S4OV, 600 and
save mouey To the city.
Mr.. Shedd's filter il washed by me-
chauical pump which forces the filtered
water back through the sand bed lie
claims that the impucity collects on the
top surfaco OF "a slow filter and looks not
unlike "A thin sheet of rubber. When the
water is forced upward from the lower
surface this blanket rises all in one
piece aud breaks up in water
aud flows out through the es-
cape piIe This Is the only part
Of the filter that is as yet uutried. In
the rapid filters the pressure Of the water
forces the imp Irities down into the sand
and I'm order To wash the filter me-
chanical appliance for stirring up the
sand is usei The plan OF Mr.. Snedd.
however, dOes not provide for stirring
the sand because he hopes to filter the