Hearings of the International Joint Commission in re remedies for the pollution of boundary waters between the United States and Canada

by International Joint Commission

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.