Every evening, Wilmington daily commercial., 1906-01-18


On page 50 -1he question Of the use
of other coagulauts and sulphate OF
aluminium has not been considered by us.
The report Of Mr. Fuller upon expert
ments at Louisville treats this matter
quite fully There is no reason TO sup
pose that any either coagulant could be
substituted 20 advantage for the sulphate
of aluminium used in our experiments
which serves as a basis of our estimates
[ lsulphate of iron at SO and $40 per ton is
used to purify many millions Of gallons
daily at present)"
Turning to page So;
"ln final conclusion the two methods of
filtration have been examined, either of
which is capable of furnishing at all
times sufficient water free from mud or
Objectionable turbidity. OF these sys-
TENS, one, namely sand filtration removes
more completely the effects OF pollution
than the other,I therefore, recommend
the adoption Of sand filtration" lin this
connection refer 10 Efficiency Clause"
page 81, where il is shown that properly
operated, they would be practically on an
equal basis)
On page 65 is given the cost of con-
struction of mcdaniel and sand plants.
In mechanical plants the cost is 81 ,64l,-
730 at one location, and 81 ,720, ,920 at the
other location. OF sand filters, SILL
800 and S2,56s.93O. The contract price of
the slow sand plant for Pittsburgh was
something over S600OO00 The question
Of which type Of plant should be finally
installed was practically decided by the
opinion of city officials in authority. AZ
one time it was determined TO use the
mechanical plant Before this could be
carried out, the political parties in power
were superseded by a faction which de-
sired the slow sand filter plant, which
was finally installed.
Philadelphia.-Ihe progress of this
work has demonstrated clearly that the
slow sand filters were unable TO handle
the water satisfactorily and to the origi-
nal scheme was added system of pre-
liminary filtration at a high rate to pre-
pare the water for the slow sand beds,
making a double filtration system which
was not contemplated in the original
/ plant. IL was also notorious that the
cost of construction at Philadelphia has
been many millions of dollars in excess
Of the original calculations One very
potent reason for the installation of a
plant costing the greatest amount Of
money has certainly become apparent to
everybody in the last few months.
Washington.-lt is a fact that the op-
position to mechanical filtration there
was originated by the medical fraternity,
one of whom was DIR. Lockwood. IL is
certainly also a fact that the average
medical man, professional OF business
man, is not capable Of passing judgment
on the ordinary engineering problem that
the arguments brought by them did not
sustain their position. 1t is also a fact
that the medical profession in matters
hygiene vii probably be more influential
in moulding public opinions than the best
scientific or engineering authorities, and
this was very largely the case at that
point.
Col. Miller, who had charge of the
original Investigations of the water sup
! ply problem for Washington, recommend
ed the mechanical filters, basing the re-
concentrations on the results obtained in
this experimental plant. While it is a
fact that the later commission reversed
this, we quote from their report and also
from the report of the proceedings of the
| Congressional committee several para
! graphs which are worthy of study;
Experience with sand filters is much
I
that of mechanical filters. Our knowledge
of what they will do rests not alone upon
experimental investigations, but upon
actual use for many years by some of the
largest cities I'm the world. The force of
this statement is somewhat reduced,
however, by the fact that the raw water
at Washington is more turbid than the
raw water at places where sand filters
have been used"
1t apepars from consideration of the
evidence at our disposal that the average
yearly bacterial efficiency of the two sys-
TENS would be about equal. During the
warmer months of the year this efficiency
would probably be greatest in the case Of
the sand filters. When river water is at
or near the freezing point, the condition
upon which the sand filters are taken are
less effective and the eniciencies of me-
chanical filters would probably be q little
| greater This deterioration of sand filters
would not be materially changed by COW
ering them"
Following this; There will be but
little difference in the cost of the two
systems. The cost Of constructing sand
filters is larger than the cost of con-
structing mechanical filters, but the lat
ter are very expensive TO operate, and
when interest and depreciation charges
on investment are added TO the cost of
operation, the difference between the
total cost is within limit of accuracy Of
the two systems Ut will be noted here
that the cost Of operation is based on
the use Of alum at S25 per ton. Sulphate
OF iron now used at cost of SO TO $40
per toni.
mo such representative gathering Of
experts ever took place in this country" /"
A little later, "the result of this discus
sion established the fact that the slow
sand filters wherever they have been nut
In operation have produced uniformly
good results, both from clearing water
from turbidity and also IN removing bac-
teria.' The theory was maintained. how
ever, that different types of water re-
quire different treatment. and that for
waters that are simply polluted, the slow
sand filters would be preferred. whereas
for very turbid waters containing fine
particles Of clay, the use of coasulant
IS necessary. From this theory but one
expert dissented. The experts were oil
the opinion that the mechanical system
when properly operated, was capable OF
producing superior results as 70 the clear
ness OF the water and equally good re-
suits with the sand filter as TO bacterial
aihcieney. The further fact was devol-
| oped that the cost OF the two systems
during a series Of years, is about equal.
The first cost Of lands necessary for slow
sand filters, being Offset by annual cost of
alum used as q coagulant lalum figured
at s25 per tonl.' Mechanical filters built
according TO practice at that date figured