Refuse Disposal

Feeding to Swine.

The U.S. Department of Agriculture es timates that the garbage of more than 8,000,000 people is fed to hogs. A survey of 200 cities by Public Works showed that 39% of them fed all or part of their garbage to hogs. It is estimated that 5o lb. of garbage will produce i lb. of pork. Based on a live market price of i o cents a pound for pork, garbage is therefore worth $4 per ton, from which must be deducted the costs of la bour and hauling, interest and depreciation on equipment, and other items. While some of the food value in the garbage is util ized, in very few cases is the return sufficient to pay for both col lection and disposal, though the revenue received may reduce materially these costs.

For utilization of the garbage by hog feeding, frequent collec tion is necessary. In the summer, collections should be made at least three times a week. Careful separation of the garbage is necessary, since its value as a food depends upon the care with which rubbish, glass, crockery, soap and other harmful materials are excluded. It is always difficult to find a suitable situation for a farm, as there is always objection to its establishment in settled areas; as a result an isolated place usually must be chosen, with a resultant long and costly haul. Dry and well-drained sites, pre ferably with sandy or gravelled soil, and with plenty of water, are almost a necessity. Hogs should be fed on platforms, which should be of impervious materials, and so arranged as to reduce spillage and waste. The refuse remaining from the feeding, which, with the droppings from the pigs, amounts to 4o to so% of the original volume of the garbage, must be removed daily. Disposal of this waste is difficult ; composting, burial and incineration have been used in various places with some success. Cooking of the garbage is not desirable, as the hogs are less able to choose the materials most suited to them. Hogs fed on garbage are liable to suffer from cholera, and immunization is necessary to prevent loss.

Incineration.

The complete destruction by fire of all wastes in specially constructed furnaces called incinerators has several advantages. It permits the collection of mixed refuse, thereby without added fuel, but when garbage is burned, some additional fuel must be supplied. When garbage alone, or very wet refuse is to be burned, a drying hearth is provided upon which the garbage or wet refuse is placed. The flames from the burning material on the grate pass over this material, drying it.

Either natural or forced draft may be employed in operation, but unless the refuse is unusually heavy and compact, natural draft is sufficient, the air being supplied to the furnace pre-heated to a temperature of about 400° F. The furnace is commonly mechanically charged.

Both high and low temperature incinerators are used, local con ditions usually dictating the choice of type. With the high temper ature plants in which the interior of the furnace is maintained at 1,600 to 2,00o° F, odours are effectively destroyed; low tempera ture plants operate at 5,250 to 1,400° F, which does not always prevent the emission of odours. The high temperature plant,

therefore, is especially suited for use in closely built up sections where discharge of odours cannot be permitted. Low temperature plants do not emit odours at all times, but may do so when the fire is cooled below the safety point. In 1927 about 4o cities in the United States installed incinerators, and this method is increasing.

Reduction.—Some of the fats and food values in garbage may be recovered by the reduction process. The products of reduction are grease and tankage. The grease, which is of low grade, is used in making soap, candles and similar products, while tankage forms a base or filler for fertilizer. Reduction is applicable only to gar bage and dead animals, and other wastes must be collected and dis posed of separately. Because of the costly and complicated equip ment required for this process, the necessity for skilled opera tion, and the large overhead costs, reduction is not commercially feasible for cities having a population less than about ioo,000.

There are two general processes of reduction, the drying method and the cooking method. Though the latter process is higher in first cost and operating cost, more grease is recovered and the by products are in somewhat better condition. The yield of grease ranges from 2 to 3% of the original weight of the garbage, while from 15o to 225 lb. of tankage per ton are produced. The value of the grease varies with the market; tankage value is de termined by its content of ammonia, potash and bone phosphate of lime, which carry the same values as in commercial fertilizers. To be commercially saleable, tankage must not contain more than io% of moisture.

In the cooking method, the garbage is cooked in digester tanks for five or six hours, and then pressed. The grease that rises to the top is skimmed off and the solid matter dried and percolated with a solvent to remove the remaining grease. In the drying process, the garbage is crushed or ground and passed through driers, then being percolated to remove the grease. Odours are troublesome in both methods, but are perhaps less difficult to control in the cooking method. Washing with a fine spray of water, burning and treating with chlorine gas are among the methods employed to destroy odours, but none of these has been fully effective. Care and cleanliness in operation are important factors.

Solid and liquid wastes also result from these processes. The former consist largely of the rubbish sorted from the garbage, and are usually buried or burned. The liquid wastes include floor washings, waste liquors and drainings. They may be discharged into the sewer system or treated in an individual plant. Because of the likelihood of odours, re duction plants, like hog farms, must be situated in thinly settled areas, usually far from the city limits. This requirement of situa tion necessitates long hauls, which often materially increase the cost of disposal. (W. A. HAR.)