Millions from Waste

by Frederick Arthur Ambrose Talbot

At the large cattle-slaughtering establishments of North and South America, and at the sheep-killing stations in Australia and New Zealand, the residues from which the edible fat has been recovered by the open steam process are turned over to the solvent extraction plants which have now been introduced to form an integral part of the waste-recovery system, the value of the invention being fully appreciated. At first the practice was to dry the residues from the digesters before committing them to the extraction plant, but since it was found superfluous to carry out such a preliminary, the residue is turned over from the open steam digester where the edible fats are obtained to the solvent extraction plant, the idea of course being to secure the proportion of fat escaping recovery in the digester. In this manner 99 per cent. of the fat contained in the crude waste is obtained, but the proportion reclaimed from the practice of the solvent extraction process is set aside for manufacturing purposes—conversion into soap and other utilitarian commodities.

In the course of digesting the fresh fat with open steam a considerable quantity of the “stick” liquor is precipitated, and its recovery for size is fully justified. In the crude form this liquor is somewhat weak, but by means of the Scott multiple-effect vacuum evaporating plant it can be concentrated to any required degree of density. This product is blended with the meat-meal from the solvent extraction plant in a suitable vessel and is then dried to a powder, the ultimate meal being high in ammonia.

In the case of the offal which is not suitable for the production of an edible fat, recourse to the open steam digester is eliminated. The refuse, along with the condemned meat, is consigned directly to the extraction plant to be dealt with in one operation. A similar practice is followed at the large pig-killing establishments. At one installation in South America, where there is an impressive illustration of British ingenuity and enterprise in regard to waste recovery upon the Scott principle, the tallow produced is immediately dispatched to the adjoining soap works—also a British installation—where the glycerine is recovered and soap is produced. In this instance therefore we have a powerful example of a self-contained establishment completely equipped for the recovery of the whole of the by-products incurred in the course of its normal operations and to the utmost advantage.

The Germans have been extremely active in advancing the possibilities of the solvent extraction process. Several large plants are in operation in the Fatherland, of which we heard a good deal during the war, but the character of the operations of which were grossly misrepresented and exaggerated. Those behind the lines were reserved exclusively for the disposal of fallen horses as well as the offal and other wastes resulting from the feeding of the troops. The fat, immediately upon its extraction, was treated for its glycerine, which was dispatched to the explosive manufactories in Germany, while the residues were converted into soap upon the spot. This practice was followed because the glycerine was the staple in most urgent demand, and the transport of which was far simpler than the movement of the crude reclaimed fats. So far as soap was concerned the German soldiers, even up to the front lines, had little or no room for complaint, for the simple reason that it was prepared in their midst at the plants which were installed within easy access of the centres of suitable raw material supply.

British manufacturers, although somewhat conservative, are becoming alive to the fact that only by the solvent extraction process can the utmost wealth be won from fats derived from waste materials, and many interesting expressions of enterprise in this direction may be recorded. For instance, the manufacture of maize flour has made decided strides in these islands during the past five years, doubtless owing to the deficiency in connection with the wheaten product. However, before this grain can be converted into the farinaceous form the germ must be extracted, otherwise the keeping qualities of the flour are seriously impaired. But, seeing that the germ represents approximately 20 per cent. of the whole grain, it will be seen that the industry has to face a loss of one-fifth of its raw material in preparing the flour—an imposing quantity. However, the germ is rich in oil, this constituting approximately 20 per cent. of its bulk. The demand for oil, particularly those of vegetable origin, is such that the maize germ, instead of being turned over directly to cattle, is now being exploited for its oil. By the solvent extraction process 99 per cent. of this available 20 per cent. of oil is being extracted, the resultant meal thus being virtually free of oil.

When the idea was first taken in hand it was maintained that the withdrawal of the oil would imperil the feeding qualities of the meal residue. This being conclusively disproved it was then argued that the employment of benzine for the purpose would depreciate its cattle-food value, the idea doubtless being entertained that it must be associated with a certain benzine flavour from coming into contact with the solvent. But here again practice did not coincide with precept, because horses will devour the meal, freshly drawn from the extractor, with avidity, and look round for more, proving very convincingly that the benzine is completely exhausted from the extractor after having fulfilled its designed function. Experience has shown that meal made from the de-oiled maize germ is every whit as good and as nourishing as, if not actually superior to, that which has not been subjected to the oil-recovery process.

The solvent extraction process has proved to be of incalculable value to the firms specializing in the dry-cleaning of clothes, fabrics, and textiles in general. When the articles are likely to be charged with appreciable quantities of dirt, such as carpets, they are first subjected to a dusting treatment which removes the superfluous or free dirt. Wearing apparel, except in a few instances, does not require submission to this preliminary operation and so is passed into the washing machine, which contains only benzine, together with a slight proportion of ammoniacal liquor. The garments are passed through several successive washings and rinsings in various machines, to be submitted finally to the hydro-extractor, where practically the whole of the benzine is recovered, the goods being delivered practically dry. But to be positive upon this point they are hung for three or four hours in a drying room. The articles are then examined for any stains, such as blood and grease marks, which have resisted elimination in the mechanical cleaning process. These are removed by hand—“hand-spotting” as it is called, either with water, or with benzine and a little soluble soap and a brush.

The dirt and other deleterious matter removed by the benzine in the washing and rinsing machines is separated from the solvent, which undergoes a simple treatment, bringing about its complete purification, when it is returned to the service-tanks for further use. The process is one of continuous distillation, the benzine, as previously mentioned, being used over and over again, it only being necessary to add certain quantities from time to time to remedy the unavoidable losses incurred. The wastage of benzine averages about 15 per cent. of the weight of the goods treated. Seeing that about 4,500 gallons may pass hourly through the machines and the circuit, the loss is relatively low. The quantity of dirt removed, despite the thoroughness of the process, is comparatively trifling.

One interesting phase of the dry-cleaning process deserves mention, if only to bring home the assiduity with which the reclamation of grease from every conceivable source is now being prosecuted. Some of the firms are devoting attention to the separation of the grease removed from the clothes by the benzine. Seeing that the only likely contribution of grease is that removed from the hands or other part of the body coming into contact with the fabric, and that the grease in question is only natural perspiration, it will be seen that, under the most favourable conditions, such deposit must necessarily be exceedingly trifling. That it should be deemed worthy of recovery seems almost incredible. But it is being done, though the yield is low, and it is proving profitable.

Probably no other waste is to be found in such a multiplicity of forms and in such unexpected quarters as that capable of yielding grease, but that it should pay to recover natural perspiration to assist in the lubrication of a railway locomotive, or some other piece of machinery, serves to emphasize the extremely fine limits to which fat-reclamation science has been carried. It is admitted that, in the majority of cases, the possible yields are so small as to render reclamation absolutely impossible by any but the solvent extraction process, which undoubtedly constitutes the highest testimony to the efficiency and value of this wonderful British invention it is possible to advance.