Part 20

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?