The process is very simple. The refuse is dumped into the digester which, upon being filled, is sealed. Steam is turned on, and the resultant cooking releases all the oleaginous constituents of the contents, which are floated off through the cock to be led to the fat-recovery tanks. The cooking is continued until the raw waste has shed every drop of recoverable oil and grease. The digester is then emptied, pressed, and the cooked material passed to the dryer to be dried, thence to the disintegrator to be pulverized or ground to the required degree of fineness.
The fatty and oil liquors drawn from the digester fall into a tank, and the fat and grease collecting on the surface are skimmed off to be passed to a lower tank. All tanks are kept at a certain degree of temperature by means of a steam-heated coil. The fat and oil reclaimed in this manner are subsequently treated for their yield of glycerine, the final residue entering into the preparation of soap and other articles.
The solid residues recovered from the disintegrator, representing the fibres from the meat, fish offal and other solid matter, constitute an excellent poultry food. According to the analyses which have been made it is rich in the albuminoids and phosphates.
While the foregoing naturally represents the foremost and greatest phase of salvage activity pursued by the Liverpool Corporation it by no means exhausts their efforts in this direction. Other refuse is recovered and treated for some one or other specific commercial purpose. All bones are collected, washed, and boiled to secure the fat, the solid matter afterwards being ground into meal. Vegetable refuse, of which large quantities are forthcoming, especially from the markets, are dried and stored, having been found useful as a constituent for poultry foods. Fish, both offal and unsold inedible surplus, is converted directly into fertilizer. Wooden refuse, recovered from dust-bins and other sources, is heated at low temperature to allow carbonization for sale as charcoal. Large quantities of straw, both clean and soiled, are also brought in, being recovered from packing-cases and crates. The clean straw is segregated to be chopped finely, and as such meets with a ready sale among poultry-raisers because it constitutes a very effective scratching material. The dirty straw, together with soiled paper and old wooden boxes incapable of other treatment, as well as other light refuse, are burned in a special furnace which has been installed, care being observed to collect the ash. As the latter contains approximately 12 per cent. potash it forms a first-class fertilizer. Banana stalks are likewise rich in potash, and so, by submitting the stalks, large quantities of which are forthcoming from the fruit markets under normal conditions, to a special treatment, this potash is recovered and is turned over to the soap-makers. Oyster shells are washed, calcined, and then ground for sale as grit to poultry-raisers.
Damaged and condemned eggs are frequently received in large quantities from the docks, warehouses and wholesale establishments. One consignment numbered no fewer than a quarter of a million. Instead of being used as fuel for the destructor, these eggs are boiled, then chopped, dried and together with the shells are finely ground into meal for use as chicken food.
Consignments of ham and bacon are often received in heavy quantities at times from the docks. This inedible food is submitted to treatment to secure the various commercial by-products such as oil and grease, the residue being ground up into meal.
From the foregoing it will be realized that Liverpool is not permitting much waste of any commercial character to find its way to the incinerator. The wise policy now being pursued is bearing fruit. The prices which have been, and still are being, realized, render the trouble and effort expended well worth while. The meal made from fish offal, after the extraction of the oil, has fetched as much as £25—$125—per ton, while the butchers’ offal, after similar treatment, has commanded an equally satisfactory price. Even the refuse gathered from the households of the city, and capable of being turned into poultry-meal, which exceeds 20 tons a week, is promptly sold at prices ranging up to £15—$75—per ton. The possibilities attending systematic collection from private residences have also been conclusively established, and at the moment the Corporation is gathering a round 1,000 tons of such waste from certain houses in the course of the year. Reclaimed tins, after being washed and dried, have realized up to £8—$40—per ton, while, to meet the enhanced request for organic manure, an excellent fertilizer is being prepared from certain materials which come into the hands of the authorities, or accrue from the practice of waste-reclaiming. The Corporation are able to dispose of this fertilizer with comparative ease at the rate of 50,000 tons during the year.
Other towns are able to point to comparable achievements in connection with the exploitation of waste incurred within their areas. Some of the small communities are even able to produce some startling records in this connection. If all our civic and municipal authorities could be brought into line and raised to the productive level of Glasgow or Liverpool, the cumulative benefits to the nation would be enormous and far reaching. But, as yet, only a fraction of what might be secured is being turned to useful account. For instance, it is computed that 3,000 tons of first-class pig-food could be recovered from London alone every week—this in itself would show a heavy yield of fats and greases if properly treated—but at present it is being wasted.
Merely because foodstuffs—meat, fish, eggs, fruit, and other commodities innumerable of a perishable nature—are condemned as being unfit for the service of man, that is not to say they have completed their mission in the scheme of things ordained by a so-called high civilization. Doubtless they assist in the manufacture of excellent paving-stones, but although we are in dire need of houses and this is the concrete age, that is not a sufficiently reasonable excuse for withdrawing nitrogenous products from the cycle of Nature.