EDWARD A. PATERSON, chemical engineer, London, England, appeared
before the commission and said:
After I received the telegram from the secretary of the Canadian
section of the commission asking me to come here I cabled to London
for certain plans and models and additional samples, as I only had a
few samples on this side and a few notes. These samples and reports
have not yet got here, I suppose owing to the war conditions. I
therefore have to rely upon rough laboratory notes, which I hope to
augment with further information as soon as the data arrive here. I
hope you will excuse me for not having the short report which I have
made in fuller detail. I shall be glad to give you more interesting
information later.
I may state, first, that my remarks are purely from the British point
of view; I am not at all familiar with the conditions on this side,
except as to a few of the plants, such as the Baltimore plant and
others, where they have erected up-to-date plants for the collection
of the solids. I have been investigating this matter for about six
years purely from the point of view of the disposal of the solids,
and I have looked upon it from the utilization point of converting
waste products into a commercial enterprise. Our difficulty in Great
Britain is that we have an enormous accumulation of what we call
sludge cake or sewage cake, which comes mostly from the filter press,
and in some cases it is taken out to sea and in others it is disposed
of on the land and in other cases they burn it. In England alone
we have enormous quantities of this material, which costs from 1
shilling to 5 shillings--that is, from 25 cents to $1.25--per ton of
wet sludge. When I refer to “wet sludge,” I mean sludge that contains
from 50 to 60 per cent of water.
As to the raw material, the process to which I will refer deals with
the raw sewage which has been precipitated or agglomerated by means
of lime, “ferro-alumina,” or other agent, and rendered solid either
by filter pressing or “lagooning” at the sewage-disposal works. This
solid material contains on an average 50 to 55 per cent moisture and
must, owing to its nature, be quickly disposed of, because for about
six months in the year it becomes extremely offensive, and they have
in England a very small area in which to dispose of it. It has to be
taken away by railway trains and in boats and such like conveyances.
In Great Britain the amount of solid material--containing 50 per cent
moisture--produced by each 1,000 inhabitants is approximately 100
tons per annum, and, for the purposes of this report, those towns in
the United Kingdom having a population of over 100,000 people produce
annually 1,800,000 tons.
In disposing of it we look upon it from the commercial point of view,
and, therefore, the composition of the sewage is very important.
The composition of raw sewage, of course, must vary very
considerably, depending on the time of year and the district which it
is derived from--trades waste, and so forth, e. g., paper factories,
iron works, dye works, render it very complex, and an ever-varying
mixture, but the following analysis will give a very general idea of
its character and composition in Great Britain:
_Analysis of raw sewage per 100,000 parts as solids._
In solution, 125.4 }
In suspension, 62.9 } 188.3
Chlorine 8.9
Free ammonia 2.1
Organic (albuminoid). Ammonia 76
I have a sample here of the material that is generally produced at
the sewage works.
(Sample produced and shown to the commissioners.)
That sample contains from 55 to 60 per cent of water and is as it
comes from the filter press, and it is called filter-press cake.
Mr. GARDNER. That is not in commercial form?
Mr. PATERSON. No; that is in the form, as it comes from the sewage
works, and it is material that gives us much trouble to dispose of.
The analysis of that material, not air dried, is approximately--by
“approximately” I mean the general analysis of that class of material
over the United Kingdom--as follows:
_Analysis of press cake (not air dried)._
--------------------------------+-----------+-----------+-----------
| London. | Leeds. | Wimbledon.
--------------------------------+-----------+-----------+-----------
|_Per cent._|_Per cent._|_Per cent._
Water | 50.00 | 58.05 | 56.15
Organic matter | 15.40 | 16.69 | 11.36
Silica | 6.40 | 8.08 | 7.10
Carbonate of lime | 10.30 | 7.94 | 11.14
Nitrogen in sewage sludge (dry) | 1.63 | ... | ...
To ammonia | 1.95 | ... | ...
To ammonia sulphate | [2]7.67 | ... | ...
--------------------------------+-----------+-----------+-----------
[2] Or per ton sludge, 171.8 pounds.
The ordinary air-dried sewage--we do not have very much of it in
England--mostly comes from the small towns, in which the sludge is
pumped up into lagoons and allowed to dry there, and the composition
of that material is, generally speaking, as follows:
----------------------------+-----------+-----------
Air dry. | London. | Leeds.
----------------------------+-----------+-----------
|_Per cent._|_Per cent._
Water | 11.86 | 16.40
Organic matter | 24.61 | 27.92
Phosphoric acid (P₂O₅) | 1.04 | .75
Sulphuric acid | 1.12 | 1.02
Carbonic acid | 10.98 | 13.11
Lime | 14.33 | 17.51
Magnesia | 2.34 | 7.67
Oxide of iron | 3.02 | 2.32
Alumina | 4.13 | 6.33
Nitrogen | .86 | .70
----------------------------+-----------+-----------
These analyses will give a general idea of the composition of
filter-pressed sewage cake, which we treat in Great Britain, and of
which we have 1,800,000 tons per annum.
The object of the process under consideration is to dry the solids
so that they may be available either for a fertilizer or, secondly,
to be in a condition that by-products of commercial value can be
recovered. The greatest difficulty with which we have had to contend
was to provide a way of liberating the moisture, of which the pressed
cake contained from 55 to 60 per cent, without volatilizing valuable
material, and at the same time achieve the object in a short space of
time and at low cost. One of the difficulties that has caused a great
deal of time and trouble to solve is how to get rid of that moisture
and dry the material at a moderate cost without losing any of the
valuable constituents, because the valuable products are volatilized
at a very low temperature. A very large amount of money and time has
been spent in Great Britain in trying to dry sewage pressed cake, or
sewage sludge, economically, and many ingenious mechanical appliances
have been invented to try and solve the difficulty, but they have
not been a success, as they have been costly to operate and required
high temperature, with consequent loss of some of the valuable
constituents of the sewage. This is due to the water in the sewage
being in so many different forms, namely, hydroscopic water, water of
combination, and water of crystallization; the first being easy to
drive off and the two latter extremely difficult. So it is recognized
now that the problem is one of chemistry and mechanics applied, and
I can safely say that there is now a satisfactory solution of these
difficulties on a practical scale.
Further on in this report I will give you some figures as to the cost
of plant and cost per ton of drying pressed cake.
Having dried the material, it is in a condition to be treated by
destructive distillation, whereby ammonia, oil, gas, fat, phenols,
and other materials suitable for drugs and dye making may be
extracted.
I show you a sample of the material as dried. It appears in that form
[specimen exhibited], and it contains 50 to 55 and 60 per cent of
water. After it is dried it becomes absolutely, as you see it there.
That specimen is practically free from water; it contains only about
2 per cent of water. That material is valuable as a fertilizer, and
it is sold in the form of a butter. [Butter specimen exhibited.]
The value of the material, as any chemist knows, is in its
fertilizing contents for particular purposes. For certain purposes,
the merchants who deal in the product add the necessary quantities
of phosphoric acid that the material is deficient in, to bring it up
to Government standard. That material is worth to-day on the English
markets from $12 to $15 a ton.
Mr. GARDNER. What is the relative proportion of potash to phosphoric
acid in that sample?
Mr. PATERSON. It varies very much, indeed. In small towns where it
does not pay to extract--where there is not sufficient tonnage to pay
for extracting the oil and the fat from these other products--they
are either put into this form, or, if the towns are sufficiently near
a large center, it is shipped on the railway to central works where
it is treated for these products. But in isolated cases they simply
dry the material by a special process, and they have local sale for
it, and it is cheap to operate, so that where a man is usually
employed in these plants the man can do the whole thing, and you can
practically make a small number of people the limit of cost. Taking
about 1,000 as being about the limit, or 500 persons, they can put it
into this form and use it for manure purposes.
Oils are interesting to the British people, because we have no oil
in England outside of the oils which are obtained in very small
quantities from the Scottish shale deposits, so that when you are
dealing with several million tons of material which will produce a
very large quantity of oil per ton it becomes a matter of extreme
interest to the Admiralty.
Sir Boverton Redwood, Bart., D. Sc., F. I. C., and Alfred Gordon
Salamon, A. R. S. M., F. I. C., the former of whom is one of the
consulting chemists of the British Government, state in a report on
this process, made two years ago:
1. That the process is capable of furnishing valuable
commercial products for which there is a practically
unlimited market. In this connection, we may state that
the sample of crude oil distillate which was subjected
to test remained fluid until cooled to 20° F., had a
specific gravity of 0.971 at 60° F., and a flash point of
256° F. A sample of the redistilled oil previously tested
by us contained only 0.24 per cent of sulphur, and had a
calorific value of 10,230 calories per gram, or 18,415
British thermal units. It is evident that a product similar
to the crude oil examined would be a fuel oil complying
with the contract requirements of the Admiralty.
2. That very large supplies of the raw material, viz,
sewage-sludge press cake, would be available in this
country as soon as it became recognized that such press
cake could be disposed of.
3. That it may be reasonably anticipated that a substantial
profit would result from the general application of the
process.
The yields of valuable products, of course, vary within very wide
limits, depending upon the composition of the sewage, but, speaking
broadly, the amount of ammonia as sulphate ranges between 60 and 130
pounds per ton of sewage containing 5 to 10 per cent of moisture.
Oil, from 18 to 40 gallons per ton; fat, from 5 to 10 per ton; gas,
from 14,000 to 17,000 cubic feet per ton. The rare products, it is
difficult to give any reasonable figures. Then, after these products
have been extracted, there is a residue which has a commercial
value as a fertilizer base, as it contains products valuable for
agricultural purposes. It is an inodorous grayish-black friable
substance having the following general composition.
Siliceous matter 66.30
Iron oxide and alumina 7.30
Calcium carbonate 3.44
Carbon 20.40
Magnesia .07
Phosphoric acid 1.14
Moisture
Sulphur 1.09
-----
99.74
The commercial value of sulphate of ammonia may be usually taken at
2 cents a pound, in Great Britain. It is difficult to say what the
commercial value of these products is to-day, in war time. We obtain
from 5 to 10 per cent of fat, and under special conditions, such as
they have at Bradford, which is a wool-washing place, the amount of
fat runs up to 20 per cent. It is difficult to give any definite
figures as to the value of other products, because they vary in
different localities, but there is a fair amount of substances which
are used in drug making.
That butter, or residue, after these other products are taken out, is
absolutely innocuous, and quite a deodorizer because of the amount of
carbon it contains.
That material is used by the fertilizing companies and they add to
it the requisite amount of ammonia or phosphoric acid, or potash, or
what is required for particular kinds of agriculture.
One of the chief products is oil, and the analysis of the crude oil
obtained from the process is as follows:
By volume.
Specific gravity at 15° C per cent 9.931
Light oil boiling under 170° C do 5.0
Light oil boiling between 170-230° do 19.6
Light oil boiling between 230-270° do 18.7
Light oil boiling between 270-350° do 29.9
Residue, a soft pitchy substance, do 26.8
valuable for many purposes -----
100.0
The crude oil is a very dark thick-looking substance, very much like
what you would see lubricating any bearing of engines, and very
much like the crude oil that is obtained from the oil wells of this
country. It can be split up and fractionated into different parts.
It has not a very pleasant smell or a very unpleasant smell; it is
quite different from the ordinary crude oil you get from the earth,
but several different spirits can be obtained, which are useful for
driving motor cars, internal combustion engines, and so on.
After that black crude oil has been split up into these various
grades, and various other compounds taken out, there remains in
the still a pitch which is practically animal pitch, and which is
useful for all kinds of things for which bone pitch is used. [Sample
produced.]
The extraordinary thing is to think that that comes through a human
being, but it does.
I have no sulphate of ammonia with me; it is such a common thing, you
will see it in any drug store, it is used in most households, and it
is known to everybody. The mean calorific value of the gases after
the extraction of all condensible oils in the process was found to
be 130 British thermal units. It will be noted that all the products
mentioned in this analysis are easily salable, and always in demand.
These products are extracted in this way: The chief process is drying
material, which has been one of the greatest difficulties in solving
the sewage problem.
Mr. TAWNEY. What is the device used?
Mr. PATERSON. They have revolving cylinders, they have chambers,
they have glass houses, they have towers that it is worked down
through; all these sorts of things. In this process they take the
gases which are coming from the garbage plant, and pass them through
a brick chamber in which there is an endless belt made of wire-woven
mesh. That travels a distance of about 120 feet in 20 minutes, and
the carbonic-acid gas from the furnace, in conjunction with certain
other material, creates a chemical reaction which breaks up these
various forms of water, and in 20 minutes the material is dry, and in
that condition in which you now see it. Having obtained it in that
condition, if it is not used for fertilizing, it is put into a gas
plant, which consists of retorts, in which the coal is thrown, the
door closed, and heat applied. The volatile matter, gas and tar and
so on, goes over in the condensers and the gas passes on and leaves
behind it a tar and ammonia and liquor, etc. This process is very
similar to the ordinary gas process, with this exception, that the
ordinary gas retorts are not suitable, owing to the extremely low
heat-conducting properties of dry sewage. So, special retorts have
had to be constructed, and they are mostly vertical and in benches
of 4 or 8 or 12 or 16. The material is taken along an automatic feed
and pumped into these retorts and the top closed, and then the oil
goes through a condenser and is thrown down in that form in which you
see it. Steam is introduced and the ammonia runs over, the steam is
condensed, and the ammonia is in that ammoniacal liquid. The ammonia
is extracted from that liquid and the oil floats on the top and flows
into these fractionating stills. Then the gas which passes on, 14,000
to 17,000 cubic feet, comes around again and is used for doing the
distillation, so that practically the amount of gas in the sewage
will complete the operation. In other words, it costs practically
nothing for heat for doing the distillation.
The cost of one of these plants will depend on several factors,
the chief of which is the population of the place. To deal with a
small tonnage costs more per ton than to deal with a very large one,
the overhead charges have to be taken into account, so that one is
limited to a certain population for extracting the by-products.
As to whether a drying plant is installed alone or in conjunction
with a distillation plant, this of course could only be decided by
the careful examination of local conditions. Broadly speaking, a
drying plant to treat 30 tons of sewage, containing 55 to 60 per cent
of water, would cost approximately for the machinery $2,500.
Mr. MCGRATH. For what population?
Mr. PATERSON. For 1,000 people making 100 tons a year. Usually,
around a municipality, they have buildings and garbage plants and
structures of different kinds, so that practically in most of the
towns I have visited in England that is about the total expense for
machinery, after putting the material into the condition you see it,
without practically any extra labor. The cost of drying in England,
for the plant at Wimbledon is $1.50 per ton. A larger plant would
cost relatively less, as certain mechanical parts that would be
necessary for a small plant would serve a much larger one. In London,
as I have said, it is costing us for drying per ton of sewage about
$1.50, and the value of the product as a fertilizer, which naturally
depends on its chemical composition, is from $12 to $15 per ton, and
as a matter of fact on its chemical contents it is worth more than
that. That is a very conservative figure to put upon it, because the
fertilizer people want profits.
The cost of the distillation plant will, of course, vary in different
towns and different localities. It is extremely difficult to give
estimates on the cost of a distillation plant on this continent as
the conditions vary to a large extent, but to generalize, a plant is
not expensive and we consider in England a unit for treating, say, 40
tons a day of dried sewage would be in the neighborhood of $40,000,
most of which plant would be suitable for treating 100 tons per day
with only the addition of retorts, which is the least expensive part
of the plant.
I have gone into the subject in this report in a quite general
and untechnical way, and I shall be pleased to answer any further
questions which you wish to ask me.
Mr. TAWNEY. Where are the plants, which you speak of, situated?
Mr. PATERSON. At Wimbledon, which is part of London.
Mr. TAWNEY. Are they operated by the municipality or by private
interests?
Mr. PATERSON. They are operated by private interests.
Mr. TAWNEY. Do these private interests buy the sewage?
Mr. PATERSON. The sewage is delivered to the works free of charge.
Speaking from memory, the cost at Wimbledon is about 75 cents a ton.
They are getting rid of it for nothing, and, in addition to that,
they give the land necessary for the treatment.
Mr. TAWNEY. How long has that plant been in operation?
Mr. PATERSON. About a year. On account of the war it has been shut
down two or three times by the Government taking the men away; but
now it is practically under Government control, for it comes under
the Munitions Department. It is now looked upon by the Government
as a necessary national project, and comes under the munitions
department.
Mr. POWELL. Because of the gasoline they get?
Mr. PATERSON. Yes.
Mr. TAWNEY. From your knowledge, what do you estimate the cost of a
plant would be for a city of, say, from 50,000 to 100,000 people?
Mr. PATERSON. I should say from about $40,000 to $50,000.
Mr. TAWNEY. That would be about $1 per capita.
Mr. PATERSON. About that; but less per capita for a population of
over 50,000.
Prof. PHELPS. What is the cost of operation?
Mr. PATERSON. From 35 cents to 50 cents a ton; that, of course,
depends on circumstances and conditions.
Mr. TAWNEY. What are the elements of cost?
Mr. PATERSON. The elements of cost, after the material is dried, are
simply the cost of distillation, which is the principal cost, and
there is also the cost of the maintenance of the plant.
Mr. TAWNEY. What labor cost is involved?
Mr. PATERSON. The labor cost is about 2 shillings per ton.
Mr. DALLYN. Does the fertilizer possess a solid residue devoid of
organic life; do the seeds germinate at all?
Mr. PATERSON. That is not our experience; of course, there is bound
to be organic life.
Mr. DALLYN. I mean, as you deliver it from your plant?
Mr. PATERSON. Not so far as we have found.
Mr. DALLYN. I speak of disease germs.
Mr. PATERSON. We have not found it so. That dry piece of sewage which
you see there has been in my bag for five months.
Mr. MAGRATH. This process deals entirely with the solids?
Mr. PATERSON. Yes; it deals entirely with the solids.
Mr. MAGRATH. And it does not include any treatment of the liquid
sewage.
Mr. PATERSON. No.
Mr. MAGRATH. What would be the minimum population that you consider
it would be feasible to erect a system for?
Mr. PATERSON. Do you mean commercially?
Mr. MAGRATH. Yes.
Mr. PATERSON. Well, on the dry process, I should think down to 1,000
people, or probably 500 people. In England, the War Office, at two
of their camps, have put in small plants for about 1,000 men. They
call them field destructors, and they get sufficient oil to run the
machines, but they do not save the products.
Mr. MCCULLOUGH. What process of sedimentation do you use?
Mr. PATERSON. They have a series of sedimentation tanks, and they use
both lime and alumina to precipitate.
Mr. TAWNEY. Are the costs of the precipitants included in the cost
you have mentioned?
Mr. PATERSON. No; this is purely for the treatment of the solids.
Mr. POWELL. It includes the drying?
Mr. PATERSON. Yes.
Mr. DALLYN. The use of chemicals for precipitating in your
sedimentation tanks would make it cost more.
Mr. PATERSON. In certain cases they do not use a precipitant at all,
but in other places they do. In places they use lime and alumina, and
that is expensive: It does not affect the process at all if lime or
any other agglomerant is not used, you still have the solids left.
They are rather getting away from lime precipitation on account of
its cost, but, on the other hand, where they have it for a fertilizer
they are getting the value back that they paid for their lime to
a very large degree, and possibly they are making a profit out of
it. There is no doubt that lime does give more rapid precipitation,
and it has its advantages, but it does not affect the solids for
treatment or the by-products that you get from the solids.
Mr. MAGRATH. Do I understand that none of the important centers have
yet taken this matter up?
Mr. PATERSON. They have signified their intention to take it up.
Glasgow and Sheffield are contemplating putting in a plant, and
Derby and Leeds. The plants would have been built this year, but
the condition in England now is that no municipality can lend money
without the sanction of the treasury. The plans are drawn for
Glasgow, Leeds, and Sheffield.
Mr. TAWNEY. Is this a patented process?
Mr. PATERSON. In part; the distillation part is not patented.
Mr. MIGNAULT. Did you tell us what profit is realized out of the
disposal of the sludge?
Mr. PATERSON. That could only be given in a general way, depending
on the quantity which is treated. In London, which has 100,000
tons a year, you would naturally make a very large profit there in
comparison to a city of 3,000 or 4,000 or 20,000 people.
Mr. MIGNAULT. Take a city of 100,000 people.
Mr. PATERSON. It leaves a fair margin of profit.
Mr. MIGNAULT. What do you mean by a fair margin of profit?
Mr. PATERSON. A fair margin of profit, and to pay for the
depreciation of the plant, the redemption of the plant, the money
that is necessary to keep it up, the cost that the city has gone
to, and leave interest on the money plus decrease of capital, plus
profit, I should think $1 a ton profit on 100,000 people, after
paying all this, would be quite a good thing.
Mr. MAGRATH. I suppose, as a matter of fact, this process is in
the experimental stage, or do you consider it is now sufficiently
established?
Mr. PATERSON. It is sufficiently established, because the plant is
paying. It went from the laboratory to a small plant at the rate of a
ton a day, and now it has gone to a bigger one and a bigger one. We
practically hope, and we are pretty sure, that we are going to take
over the London sewage, which would be a very large plant.
Mr. MIGNAULT. How much money has been invested in these plants?
Mr. PATERSON. The one at Wimbledon is not a fair criterion, because
it has been in operation for a long time, and it has gone through all
the initial stages of a new process. Now, of course, it is in perfect
order, and running smoothly, and giving good results, but it has
come up from a smaller plant to a large degree, and there were lots
of difficulties encountered which have been surmounted. I suppose it
might be said to cost $300,000 now.
Mr. GARDNER. And, in the light of your experience, what do you
estimate you could duplicate that plant for?
Mr. PATERSON. The same plant could be put in to-day easily for
$40,000 or $50,000. Of course, in a new process we are continually
putting in different things and trying different things, and also
extracting things which we never dreamed of were in the material.
Mr. DALLYN. Is it not a fact that when the pressed sludge was first
offered to the agricultural interests in England it was taken up and
they paid a certain amount for it?
Mr. PATERSON. Yes.
Mr. DALLYN. And, after the system was generally adopted, is it not so
that they could find no demand for it? Do you not think that if this
process were generally adopted the value of the by-products would
decrease on account of the large volume offering?
Mr. PATERSON. I do not think so, because of the nature of the
by-products. Take this continent, and you import an enormous amount
of sulphate of ammonia. The recovery of nitrogen is one of the
problems which the United States Government has taken up within the
last year. We have to have nitrogen, and you can not get it much
cheaper than you can out of sewage, because you have to get rid of
the sewage anyway. I do not think that nitrogen will ever depreciate
in value. They are trying to take it from the air to-day, and have
been fairly successful. Oil will always be valuable, gas will always
be valuable, potash, phosphorus are all absolutely essential for the
human race, and everybody is straining his brains and experimenting
genius in trying to discover methods of getting oil and nitrogen.
It seems to me to have been wicked that the English-speaking races
should have been throwing this material away for so many years and
looking upon it as a curse instead of a blessing. We can imitate the
Germans in a great many respects, and that is one of them--to keep
what is valuable instead of throwing it away.
Mr. MIGNAULT. Did you read the testimony of Mr. Hatton given before
the commission?
Mr. PATERSON. Yes.
Mr. MIGNAULT. Comparing your process to the one he spoke of, what
would you say?
Mr. PATERSON. I came to the conclusion, in reading Mr. Hatton’s
report, that he had the same difficulty which we had in Great
Britain--that is, as to treating sewage. He complained that there
was not sufficient sun. He said that after he had dried it that it
was worth $20 a ton--I think he placed the minimum at $15 a ton.
But his difficulty seemed to be with the process of drying and the
difficulty of drying. In some of the plants I visited--in the plant
at Baltimore--they have a drying plant there, and, perhaps I should
not say it, but they have not got any further than we did four years
ago. They had not discovered yet how to get over the difficulty in
drying this material. If you have to wait in the summer time for the
material to air dry, then you have the difficulty of bad smells,
putrescent material lying about, and complaints. The material should
be treated as soon as it is recovered.
Mr. MIGNAULT. According to your system, do you get rid of these
difficulties?
Mr. PATERSON. Yes; we get over the difficulties. Formerly it used to
take us two months to dry it, and if we tried to force the drying by
most of the machines that have been invented we would lose most of
the valuable constituents. Glasgow spent £6,000 on a drying machine,
and then it had difficulty, and they were still in that difficulty
five months ago. The difficulty about drying the material is that you
must not drive off the valuable constituents, because if you do you
lose money--you lose the volatile oils, you lose several things of
value--and after it gets dry to a certain extent it becomes extremely
inflammable. This material here that I have shown you could be used
quite suitably as a fuel. It burns beautifully. That brick there, if
you put a match to it, will burn quite easily and make an excellent
fuel. If you want to augment the heating qualities of it, you can
add coal or slack or anything like that to it, because it is a very
excellent fuel.
Mr. MIGNAULT. Has this system any distinctive name?
Mr. PATERSON. I do not think it has. We have a company in England, we
call it the S. O. S.; not the call for help--it is quite accidentally
called that--but it means Sewage Oil Syndicate.
Mr. POWELL. I suppose the difficulty in drying is that if you use
heat to expedite the drying you are apt to drive out the volatile
constituents?
Mr. PATERSON. Yes.
Mr. POWELL. You must dry at a reduced heat?
Mr. PATERSON. Yes; it dries at a very low temperature. Another
difficulty with the drying is that this sewage cake is so extremely
nonconductive. You could heat it up to a temperature in the retort
of 2,000 F., a piece the size of your fist, and the center will come
out exactly as you put it in the retort. It will retain the moisture
still, almost in the same condition as it went in, after receiving
that high temperature for six hours.
Mr. TAWNEY. Has the development of this system proceeded beyond the
experimental stage, or has it yet reached the commercial stage?
Mr. PATERSON. Yes, sir; it has reached the commercial stage. You have
to take into consideration that the conditions in Canada and in the
United States are considerably different from what they are in Great
Britain. Great Britain is a smaller country, thickly populated, and
I would want to point out that isolated towns would not have the same
facility of working that we have here. Take a town like Rochester,
and Buffalo, the next town, is 70 or 80 miles away. A town like
Indianapolis, with a population of 300,000, has around it many towns
of 20,000 or 25,000 people which radiate out from that center, and it
would mean an absolutely sure profitable proposition. In other towns,
like in Ontario, where they are isolated, you could not expect to
make as large profits as in these well-situated towns.
Mr. POWELL. What is the highest percentage of net profit on capital
expenditure? Maybe you do not wish to disclose that.
Mr. PATERSON. I do not think that would be wise at the present stage.
Before answering that, I would like to know the conditions in this
country better. One might make a statement as to that and then fall
down lamentably on it after he understood the conditions.
Mr. TAWNEY. Do you think that a city of 25,000 inhabitants could
install a plant of this kind for the disposal of sewage at a profit,
or without a loss?
Mr. PATERSON. And using the by-product as a fertilizer?
Mr. TAWNEY. Yes.
Mr. PATERSON. If a town is situated like Hamilton, in Ontario,
with respect to a large city like Toronto, yes. But not to put up
a by-product plant for itself. It certainly could make a profit.
I think Mr. Hatton bears me out in that, that there is almost an
unlimited demand for this material at about $15 or $20 a ton in
America.
Mr. MIGNAULT. I think Mr. Hatton stated that there was a very small
percentage of fat in the sewage of Milwaukee. I would like to know
whether this system can be applied anywhere, or does it depend on the
nature of the sewage?
Mr. PATERSON. In England we take out the fats first in any case, but
where it is used for fertilizing alone, Mr. Hatton is quite correct
in what he says. In England, where we are dealing with large tonnages
and taking out the other by-products, yes, it pays. Generally
speaking, small towns of 25,000 people, unless they are well
situated with relation to larger towns, the only way they can make a
profit, so far as I know, is by drying the product and selling it as
fertilizer, and that they can do at a very moderate cost. A drying
plant will not cost more than $2,500, and the operating expenses are
practically all done with the staff they have; that is, for a small
city.
Mr. GARDNER. I wish, Mr. Paterson, on behalf of the commission, to
express to you their thanks, and to say how much we appreciate that
you have come before us from Indianapolis on our invitation and given
us the valuable information which you have.
Mr. PATERSON. We professional chemists look upon it that we should
render your commission the most useful information which we have in
our possession, and I am sure we are all glad to do so. If I can be
of any further assistance to the commission, I shall be glad.
Mr. GARDNER. We appreciate that.
Mr. PATERSON. If I can give you further information, I shall be only
too pleased to do so.
Mr. TAWNEY. Mr. Paterson stated at the beginning of his statement
that he had a full report on this matter on its way from England,
or that he expected one before long. I would suggest that when he
receives that report he should forward it to the commission, with any
additional data that he wishes to submit to us. I am sure we would
appreciate it.
Mr. PATERSON. I shall be very pleased to do so.