Millions from Waste

by Frederick Arthur Ambrose Talbot

In deciding the type of plant suited to the recovery of military organic waste regard was specially devoted to two governing principles. The one was the standardization of plant, so far as was practicable, to facilitate duplication and installation of the machinery in the various camps. The second was the selection of such plant as could be installed readily and cheaply in an improvised building, and which, if the conditions warranted, would enable a standard type of cheap and simple building to be adopted.

So far as the initial plants were concerned dependence had to be placed upon existing structures, otherwise delay in putting the scheme into practical application would have been inevitable, owing to the difficulty attending the acquisition of constructional material. But the installation of the plants in extemporized buildings sufficed to establish the applicability of the idea to any type of building of adequate dimensions, and in such a manner as to impose only the minimum of structural alterations to secure the requisite efficiency. This adaptability is an outstanding feature, because it indicates how the recovery of organic waste may be attacked along the most economical yet comprehensive lines, and with the minimum of capital expenditure and its concomitant amortization charges.

Two types of plant were adopted, both being standardized. One coincided with what might be described as the central or permanent waste-recovery station, while the second presented all the necessary elements of portability with the added advantages of inexpensive dismantling, removal, and expeditious reassembling at another point according to exigencies. But the processes are common to both types.

In the case of the permanent mill which I visited structural alterations had been reduced to the absolute minimum, the most conspicuous outlay being the provision of a simple form of elevator to lift the swill to a level above the plant to permit of gravity feed. The total cost of this station, including the installation of the necessary machinery, which included a steam-boiler, bone-crusher, small engine, melter, centrifugal or turbine fat extractor, and settling tanks, with one or two further accessories, was only £2,500—$12,500.

The swill is brought to the mill by motor-lorry. Operations are commenced at an early hour, because health considerations demand that waste of this character shall be handled with all possible promptitude in a big camp. The clearance is carried out daily and is complete, including all garbage, bones and other profit-yielding organic residue from the cook-house. Segregation is conducted as far as practicable at the source, special sanitary vessels for distinctive residues being provided. The mill continues working throughout the day until the whole of the morning’s collection has been duly treated. No accumulation or carrying-over of some of one day’s swill to the next day is permitted. Swill is susceptible to speedy fermentation, especially during hot and sultry weather, and so would become noisome within a very short period, as well as developing into an ideal breeding-ground for flies and other pests.

The contents of the collecting lorries are distinctly heterogeneous, the vehicles being laden with swill, bones, empty tins, jam and pickle jars, bottles—in short, anything possessing an element of salvage value. In segregating the waste at the cook-house special stress is laid upon the necessity to keep all green vegetable matter, such as outer leaves, stumps and other inedible trimmings, distinct from the general swill for the reason explained later.

The swill is transferred by the elevator to the upper level, where it is dumped into a capacious sink to drain. The proportion of free liquid is not pronounced, the swill being rather in the nature of a slush, whatever fat there may be present, apart from the solid pieces, being either congealed in flakes and globules, either free or clinging to the more stable substance. The superfluous water having run off the residue is permitted to fall through a trap into a hopper feeding the capacious cooker or melter. Where the height of the building does not permit the provision of an elevated draining sink the swill, dumped at ground-level, is shovelled into the melter.

The melter is a cylindrical vessel or drum fitted with a steam jacket, the steam circulating at a pressure of about 80 lb. per square inch through the annular space between the inner and outer jackets. The capacity of the vessel is approximately 1,700 pounds, and the contents are kept agitated during the process by paddles mounted upon a revolving shaft forming the longitudinal axis of the drum.

The cooking process drives off all remaining moisture in the form of steam, and, at the same time, liberates whatever fat may be present by melting and rendering it fluid. It gravitates to the bottom of the cylinder to make its escape through a suitable vent and pipe into the settling tank. The last-named is also steam-heated by a coiled pipe system which not only sterilizes but clarifies the reclaimed fat, which is then permitted to cool and to solidify.

The swill remains in the drum for 70 to 90 minutes. By the end of this period the contents have been practically cooked, while all free fat has effected its escape. It will be observed that the steam does not come into contact with the contents, but is confined to circulation between the jackets. When withdrawn from the melter the swill resembles a stiff slush. This is transferred to a canvas bag to be dropped into a wire cage forming the inner vessel of the second machine, which is a vertical turbine extractor. The vessel when charged is closed by clamping down the lid.