The Memphis appeal. [volume] (Memphis, Tenn.) 1886-1890, 1886-12-05
Engineer CrOs's Report.

NEW York, November 20, 1886.
Gen. Cotton Greene, Of the Memphis Water
Committee:
SRI have examined at your request the
plans and method of operation of the plant
proposed by the Newark Filtering Company
supply to the city of Memphis.
This plant consists Of three cylin drical
tanks, each containing filter bed of sand
and coke, six feet deep, and having fourteen
terisl. The aTrar gements for feeding and
drawing of the water and for washing the
filter bed, ore fully described in the specifi-
cations and plans submitted by the COM
pany.
ating the filter are ingenious and effective.
In some details think improvement might
be made in the direction Of oonvenisnoe of
operation, but these are not essential parts
OF the scheme.
The area of fltsring surface in the three
tanks is 2l5o square feet, and it is proposed
to pass through the filters 1880 900 gal ,ons a
day.
The time occupied in washing the filter bed
is assumed to be one hour q day, leaving
twenty-thrse hours for q teripg.
This rate of filtration will require the pas
sage Of the water through the sand at the
rate Of about l52 gallons per hour per square
foot Of filter surface.
believe tho malnten anco of this rate of
hltraton for twenty three hours to be i'm
possible under the conditions Such expert
ments on the rate OF percolation of water
through sand. as have been able to find re-
corded, leaJ me to believe that with head
Of fourteen feet Y is possible to pass clear
water through ski ct of sand at n somewh at
greater speed than that proposed in this case
for short time, but the invariable rule is
that the rate of perculation decreases rapid
ly in consequence Of the competing of the
whole mass, and particularly Of the finer
up er strata.
Where the water filtered is turbid, the rate
OF Depreciation diminishes more rapidly from
the deposit OF the su' pc nded matter in the
interst'ces OF the tering material.
With the Wolf river water this will occur
avery great extent in your works, and
am of the opinion that to full II the require
ments OF the guarah tee il will be necessary
toso erraDgs the tanks thai head of at least
fifty ieetcan be put on the filter. This opin-
ion is confirmed by tests which have ma de
Of the operation Of one of the largest plat Is
which the Newark Filter ng Company have
built, that at the Norfolk and New Bruins.
wick Hosiery Company, at New Brunswick.
n. j. Lack of time has prevented making as
thorough an examination of this subject as
is desirable, but no doubt exists in my mind
that the proposed rate will be found i'm
practicable under the proposed conditions.
The operation Of the proposed Memphis
litter is entirely different from that Of a
closed litter placed between pump and the
lower end OF force main or stand pipe,
hltering material from the bottom and make
1t always open a d porvious. In your case
there will lie no back pressure and the tend
eney of the water will always be to compact
and consolidate the upper strata of the
filter and make il LEES perviOus. The puri-
hcation Of water by filtration at the pro-
posed rate of perc0lation is, / believe, I'M
exampled prior to Mr. Hyatts ingenious
water Just before its passing on to the fl ter
bed This appears to have increased the
capacity Of filtration of a eiven area to
ABOUT seVenty-hvo times what is possible by
Asimple filtration. The Tracticability of the
method is, Think, fully proved.
The asratien Of the filtered water is essen
tial TO remaining pure 10 the reservoir, The
proposed ethod Of charging the water with
air is ingenious and likely to prove eGica-
cious.
There is some doubt as to whether the
duration Of the period of intimate contact
between the air and the water under high
pressure Will be sufficient in passing through
lOOfeet Of pipe to produce the oxidation nee
essary to preserve the water pure for any
length OF time. The combined air and water
Will be under pressure { over twenty pounds
for only lew seconds. The process of alb
.orption Of oxygen from the air BY the water
contact under pressure will pTobs bly not do
as much good rs is anticipated, although il
will unquestiOnably be of some benefit.
The method of washing the otter beds Is
uuNOl hnu lukbulOues 1uo WISHING lTOm De-
low in sections of one quarter Of the area at
time, appeared TO me on examining its
operation, TO be exceedingly effective and to
have the great adVan age Of causing the
altering material to be deposited when the
washing ceased, in perfect graduation as re-
CARDS Its specific gravity, the coarser pebbles
falling 70 the bottom and the finest particles
remaining at the surface where they are
1t is open to the objection that a certain
y nFODOPkiOn of tho nd and danoait Waahad
out viii remain in the filter and be deposited
on the surface OF the unwash, d segments.
But this will probably be so small a not to
seriously intertere, with the filtration, 1
agree with Mr.. Wilson in the opinion that
the quantity, Of water required for washing
the filter beds will be considerably in excess
oi2 per ceRt. OF the amount filtered.
The computations Of Dir. Wilson Of the
cost OF pumping the water are based on the
sup POSITION that the average level Of the
water will be nine feet over the liter beds
or twenty-one feet above the reservoir. As
above stated, / think tho average head to be
pumped against will be fifty 1. ct above the
filter b. ds, or sixty-two feet above the reser-
voir. This would increase the annual cost
Of pumping about $500 above Mr.. Wilson's
eltimates, and would make the annual cost
ofhltering, including all expense and inter
est on cost, about SIS, $50, which is squiva-
lent TO so cents per 100, 200 gallons filtered.
The cost of filter beds, such as those in
POuRhkeepsie and Hudson and English
towns, would be about $4,000, and
the cost Of maintenRnce 81 50 per
100000 gallons Uttered. total Of
about y per 100000 gallons, or four
times 80 mach as the greatest estimated cost
oithe proposed works In conclusion, am
th9 opinion that the general plan OF
hltIaton proposed 10 entirely practicable,
and Will be eeonomical, and | recommend
adoption: The particular plant described
A the specihcatione, consider insuthcient
gpeot to the head Of water provided for on
the Alter beds, which should be greatly in
creased. The auxiliary stand pipe also APP
pears to me 10 be too small for the object
sought 70. be attained by II. Respectfully
submitted. SQ,a. J,R. ORuES,