Every evening, Wilmington daily commercial., 1906-01-18
FILTRATION Oh WATER


Of new water works at Wilmington necos.
sorily brings up as a question of much
interest whether slow sand or mechani-
cal filtration shall be used The writer,
as an engineer has made a long and deep
study of systems of filtration and with
your indulgence he viii set out here a
number of conclusions by him and other
engineers, showing, SO far as they 60,
that the mechanical system Of filtration
is by far the preferable process in every
way.
Many times the question is asked,
why did such and such a city adopt
slow sand liltrationg' The reason for
some of them may be given with a
reasonable degree OF accuracy by reading
over Che reports of the engineering COM
missions and considering them in the
light of later developments.
All the questions might consistently be
answered by asking another: "Nhy is &c
that there have been about twenty times
the number of mechanical plants as slow
sand plants installed in the United
statosl Why is IL that mechanical filter
plauts were recommended and are being
butt at New Orleans, Cincinnati, Toledo,
Columbus, Louisville Troy N. ", and
number OF other places, all Of large ca
pacityi"
However, there are more specific an
swers. Slow sand plants are few in num-
Der and in the cities in which they are
being installed, the agitation concerning
hltmtion was begun al a time long prior
TO the knowledge Of the completeness of
the efficiency and full development Of
ffHUNNutH.II
employed whose technical training had
been principally in connection with slow
sand filter plants in New England where
there are more of this type of plant in
use
Mechanical filter construction in those
days was looked upon as a manufactur-
ing product, was not considered or studied
as an engineering problem to any great
extent and engineering study was gen
orally directed TO that type of constiuc-
tion which had heen known and in opera
uon for period of fifty or seventy five
years and which was looked upon purely
as an engineering study.
Professional etiquette. undoubtedly.
played a large part in recommendations Of
carly engineering commissions. Profess
sional men are notoriousiy Jealous in
guarding the domains of their profession
ana in cndcaYoring to avoid even to a
slight degree. the endorsement of any
particular make or brand of manufact-
ufei articles such as mechanical filters
were regarded In the early DAYS. II is
now fact that almost all the engineers.
who, m the early DAYS, would have hesi-
mted or refused to endorse the installa-
ton Of a mechanical plant, now heartily
commend same.
Another consideration is that in almost
every case i'm which this query is referred
10 tne engineering commission, as stated.
that as tar as meteorological results were
concerned either type of filter would give
an equally good average result while in
me matter of appearance the mechanical
hiter would give superior looking water.
the recommendation in most cases com
ing down 70 o question of cost, that cost
being equnlized By the capitalization of
tne larger operating costs of mechanical
plants. Almost universally the operating
costs were based on the use Of sulphat,.
OF aluima at cost of about S25 per ton.
As this same material can be procured to.
day for SIS ton, taking the same basis
Of estimated costs, they would now show
the decreased cost in favor of the me.
chanical filter with use of alum as a
coagulant.
In the last two years, a new coagulant
lsulphate of ironl at cost Of about So
or $40 per ton is being used in practi-
caliy an the later plants which further
reduces it's operating cost on mechanical
filters so that, using the same basis of
estimates, the cost would be largely in
iaNor OF mechanical plants with the new
coagulant. IL has also been demonstrated
oy the construction OF large plants that
have been built In the last few wears that
the construction costs of the plants for
mechanical plants as given in those esti.
mates were more than liberal while in
the case of the slow sand plants. thev
have proven generally inadequate.
Careful review of these various reports
VIII clearly Indicate TO any investigation
tnat while there are certain waters TINT
either slow sand plants or mechanical
plants will give satisfactory results. If
used, IN the majority of waters in this
country, slow sand plants are not adapt-
anie 40 ali in other words, a mechanical
plant cam he used with practically any
character of water, while with the slow
sand plant it is limited TO waters of a
certain character; that this is univer.
sally agreed viii De borne out bv "a prefer
ence made later in this communication.
ln TINS connection, the writer desires
Co cali attention TO q quotation from a
paper by Mr. Nicholas Simin. chief enqi.
neer of Moscow, Russia, before dc
American Society Of Civil Engineers in
July, 1905 80
"Ihe method Of water publication with
SLOW sand filters has been used in Europe
about seventy years. Il has been proven
that good results can be obtained bv
llem 40 the same time. they are not
always obtained. In Russia. not a sinole
case OF slow sand filters can be consid-
cred as a whole successful"
The writer has seen certain criticisms
on mechanical filters in which it was
quoted that the German government
would not allow their construction I'm
6ermany, as being unable to comply with
ineir sanitary requirements. In this con.
necton desire Co state that "a mechoni-
cal hlter plant has been in operation in
Germany under the direct supervision of
the Nerman government for moro than /.
year, and I'M report lust issued bv them
~ o. stated that the sanitary results oc.
complished were entirely satisfactory and
that M appearance the water was su
perior. Ihee are now being Constructed
ln Germany two mechanical plants for
hitering municipal supplies.
The question has been asked frequent
ly' Why have such and sucuh cities
adopted the slow sand filtration in nref.
erenee TO the mechanical process ~ AZ
The writer is pleased TO set forth the
following, in respect 10 certain cities
which are referred 10 at times:
Pittsburq-lf any iuonirer vii t.i-. D..