OLID wastes, often called refuse, include a wide

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solid wastes is carried out principally by unskilled and semiskilled laborers, a class of personnel seldom found in health agencies, which are predominantly professional. INADEQUACY OF CURRENT WASTE-HANDLING

METHODS The traditional method of handling domestic food wastes has been to use them as feed for animals, usually hogs. Solid, non food wastes have been dumped into conveniently located, but useless, land sites such as marshes, old quarry pits or ravines. By design, or through accident, these dump sites frequently ignited and bumed, and much dumping capacity was reclaimed in this manner. Indeed. burning, in spite of unpleasant smoke and odors, was thought to be an effective method of destroying vermin within the dump site. Although these are very crude disposal methods by modern standards, they probably seemed much less so to earlier generations, who lived closer to the earth and who were accustomed to close proximity with animals and the utilization of animal manures and compost for fertilization of the soil. Even in cities, horses were quartered close to residences. In those days, methods of handling human excrement left much to be desired in comparison with modem practices, so that the unsightly presence of waste accumulations and accompanying odors, flies and so forth was less likely to be viewed as out of the ordinary.

It is hardly necessary to point out that the United States is now an urban society (approximately two thirds of the population lives on less than I per cent of the land area), that with the exception of small dogs and cats, animals have disappeared from daily life, and that an affluent economic status has permitted the benefits of modern plumbing and sewage become virtually universal. In fact, Americans have become so sensitive to the presence of a “fresh" atmospheric environment that they sup port handsomely an industry devoted to supplying products that purport to mask the odors of stale tobacco smoke, automobile exhaust fumes and toilets. Although esthetic considerations have played a large part in making the population acutely aware of environmental problems, other changes of a fundamental nature that have occurred in recent years have had a direct and generally detrimental effect on solid-waste management. These are as follows,

The concentration of population into high-den


materials resulting from normal community activities. Garbage and rubbish from households, institutions and commercial establishments comprise the largest fraction of municipal waste collections, but bulky objects, such as stoves and refrigerators and, especially, abandoned automobiles, represent more difficult municipal collection and disposal problems. Industrial refuse from factories, power plants and food-processing plants may contain waste materials not usually found in municipal collections, but more often the difference is quantitative rather than qualitative since industrial processes, by their very nature, generate large amounts of one, or a few, kinds of waste products. By contrast, ordinary municipal collections tend to be extremely diverse.

PUBLIC-HEALTH ASPECTS The public health aspects of solid wastes are not as well defined as those for liquid wastes, or sewage, and public health authorities in the United States have been content in recent years to delegate handling of solid wastes to departments of public works. Although it is commonly understood that accumulations of garbage and rubbish that have been poorly handled are likely to attract and provide breeding places for vermin and to produce malodors and unsightly dumps, modern epidemiologic evidence that disease is spread from such sources is largely lacking. Rats, insects and birds are known to be carriers of disease under certain circumstances (for example, the association of rodents and lice with plague, Aies with intestinal disease and birds with psittacosis come easily to mind), but in none of these cases is the poorly handled waste the reservoir of the disease, with the exception of the transmission of trichinosis to man through the feeding of uncooked garbage to hogs. Other reasons why public health directors have been reluctant to accept collection and disposal of garbage and trash as a health-department function are, first of all, that the costs of municipal solid-waste handling usually far exceed those of all public health functions combined. Therefore, disposal of solid wastes would tend to emphasize in the health department budget their least important function. Secondly, handling of

* Assixiate professor, Department of Industrial Hygiene. Kresge Environmental Health Center, Harvard School of Public Health

Reprinted from the New England Journal of Medicine

275: 1478-1485 (December 29), 1966

sity, geographically extensive metropolitan areas tuas engulted once remote trash-disposal sites in a way of residential and commercial developments. Traditional disposal practices are anathematic to the new neighbors at their gates. In addition, because dump sites often represent a major fraction of all remaining open urban land available for recreatonal, residential, commercial and industrial use there are strong pressures to convert them to these higher economic uses as rapidly as possible.

The population explosion has increased the tumber of people generating wastes.

Prosperity has increased per capita waste produ ton enormously Modern packaging practices, spate of periodical literature, almost instant abralescence of an endless variety of material requisitions and the enormous growth of industry here combined to increase the daily per capita dostoon of solid wastes in the United States him ! pounds in 1920 to 4.5 pounds in 1965. Smail zr increases are now occurring in western Esope The present trend is equivalent to an

] increase of 25 pounds of waste per capita. Paper consumption alone increased 16.6 per cent from 1955 to 1960 although the population of the triped States increased only 7.5 per cent during the same interval.: Even more impressive is a bgure of pounds for the total paper and paper board products consumed during 1963.2

Eftertive research and development programs for sted-waste handling were virtually nonexistent up to five or ten years ago, and the national annual investment in this activity was less than **0000 as recently as a year ago, in spite of the fact that “Amencans living in cities pay each year roughly $3-billion for the collection, transportamm prxessing, and the disposal of solid wastes." The truth of the matter is that research on solidwaste technology has never been a "respectable" activity at universities, technical schools and reSearch foundations although, fortunately, this attiMade is undergoing rapid alteration. The penalty best thus niggandliness and lack of vision is the PUITEN dependence solid-waste hudling methods that are largely obsolescent (when not baitally obsoletel inadequate for coping with the puan* *ses of material that will be generated soon,

problems of a noninfectious nature. Air pollution problems associated with burning open dumps, poorly constructed and operated incinerators and a variety of salvage operations, ranging from recovery of lead and copper from old electric cables to production of edible and nonedible substances from rendering plants, have become increasingly grave as the volume of wastes and the pressure on the self-cleansing properties of the air environment have increased simultaneously. It is only now, however, that the potential for ground water and surface water pollution associated with leaching of undesirable products from raw or improperly incinerated wastes spread in or on unsuitable ground is beginning to be recognized. Ground pollution occurs when waste-disposal practices place restrictions on the subsequent use of the disposal site. When buildings are erected on old landfills, for example, care must be taken to prevent migration of toxic and explosive gases from the subterranian fill to the interior of the buildings..

u un suitable for the rapid and safe disposal of man new materials rapidly coming into common s Eumples of substances in this category are gasto products that are fire resistant and proof

US mirobiologic and chemical disintegration and aluminum, which, unlike iron and steel, re asta rusting and disintegration for very long periand earn torn buned in the ground or under water.

l' has been recognized, belatedly, that although surplugs wastes muy rate low on a scale of sources of pur.mussable disease, improper disposal practices an aume serious ait, water and land pollution

SOLID-WASTE DISPOSAL ACT OF 1965 Recognition of a worsening situation regarding the level of technology associated with solid-waste collection and disposal practices and an awareness that it is no longer possible in a crowded urban society to treat the 3 broad classifications of pollution (air, water and land) separatelys have directed advanced thinking along channels that can be most accurately labeled "solid-waste management." The intention is to provide the widest possible scope for co-operative studies of basic interdisciplinary solidwaste problems by urban planners, social scientists, sanitary engineers and public-works specialists. In addition, the methods of operations research and high-speed computation are being explored to determine what assistance they can provide to researchers, planners and managers of solid waste collection and disposal systems. Finally, only a cursory look at solidwaste systems currently in operation throughout the United States is required to reveal a pressing need for participation of specialists in municipal, state and federal law in the planned research studies.

The situation in research on problems of solidwaste management and technologic development improved enormously with the passage and signing of the Solid Waste Disposal Act (Public Law 89.272) in October, 1965. The administration of this law is under the direction of a newly established Office of Solid Wastes located in the United States Public Health Service, and substantial funds have been designated for the following activities, research and development in new and improved methods of disposal, including studies directed toward the conservation of natural resources by reducing the amount of waste and unsalvagable materials and by recovery and utilization of potential resources in solid




because of the widespread use of new inorganic substances such as plastics and from a large de

in the collections of domestic, commercial and institutional garbage because of the introduction of garbage grinders and a tremendous increase in the use of prepackaged, ready-to-cook and readyto-eat foods. This, combined with the almost coun. trywide requirement that garbage be cooked before being fed to pigs, a trichinosis-control measure, is making it difficult to salvage and reuse food wastes by this method and is rapidly eliminating garbagefed pig farms from the fringes of cities. No one is sorry to see them disappear, for they produce in tense odos nuisances that extend over long distances. Other traditional salvage and recovery operations utilizing food wastes rendering and tanning of hides. Collectively, and with good redson, they have been known as the "noxious trades." More modern additions to this list include the fol. lowing: fish-oil and fish-meal processing utilizing trash fish and the remains from fish-filleting plants, manure drying, to prepare from cow dung a powdered, deodorized fertilizer suitable for in-town lawns and flower gardens, and the conversion of chicken feathers into a proteinaceous animal feed. Although, in each process, one may be in sympathy with the attempt to utilize a conservable resource, one is unable to direct these processors to suitable locations for carrying on their activities in peace, for the sad fact is that the installation and operation of effective de vices for control of air and water pollution usually make these salvage operations uneconomic. Nor is this situation confined to the processing of animal and vegetable residues because similar restrictions appear to apply to the recovery of scrap rubber from used automobile tires and the recovery of lead and copper from rubber and resin-coated wire and cable when these metals are in poor demand. Operation of a free commodity market in the United States means that, each year, the metals in 48,000,000,000 cans will be returned to the ground at widely dis. persed locations because it is now cheaper to mine concentrated ores and produce new metals than to gather together and refine for reuse an equivalent weight of used containers. It appears to be national policy, though seldom stated explicitly, to rely on the discovery of suitable substitute materials before the sources of traditional ones become impossibly degraded and completely exhausted,

wastes; and technical and financial assistance to state and local governments for planning, development, and conduct of solid-waste disposal programs. Appropriations up to $60,000,000 were authorized for the period October 20, 1965, to June 30, 1969, to carry out the provisions of this act.

WASTE-DISPOSAL METHODS All procedures for solving solid-waste problems involve the use of one or more of these 3 basic methods: reduction of waste production; reclamation, utilization and recycling of waste products, and returning the wastes to the environment via land, air or water. There seems to be little quarrel with the first 2 proposals, and, indeed, conservationists have been advocating them for many years, but major problems arise in attempting to put them into practice. For example, complex product distribution and sales mechanisms favor the extravagant use of packaging materials for preservation and selling appeal. In many cases the cost of packaging is a small proportion of the total price, and this is more than compensated for by a reduction in spoilage, breakage, soiling and other losses. It is difficult to foresee any factor in the immediate future that is likely to reverse this trend. Similar considerations apply to all classes of reading matter, and this type of consumption is not likely to call for curtailment in an increasingly literate society. Modern manufacturing technics have, in part, reached their present advanced state by the application of automatic, continuous processing machinery. Because close quality control of mass-produced items calls for an endless supply of very uniform raw materials, the use of heterogeneous scrap materials introduces character. istic excess costs that exceed savings in raw materials. The successes of on-line computer-operated refineries and chemical plants illustrate clearly the advantages of continuous large-scale production processes that utilize uniform product inputs and indicate the poor prospects that heterogeneous scrap materials have now and will continue to experience in the raw-materials markets of the future. As a consequence, only one third of the 86,000,000,000 pounds of paper products reaching the United States market annually is salvaged to make new items, 48,000,000,000 cans and 26,000,000,000 bottles are produced annually and virtually all are discarded promptly; 8,000,000,000 pounds of new plastics are produced annually, and only 10 per cent is recovered.“ Most of the small percentage of useful materials now recovered for reuse comes from manufacturing processes producing scrap that is clean, of identifiable composition and in large quantities, making it unusually valuable for reprocessing. Almost none of the same products are salvaged after they find their way into municipal or private refuse collections.

The composition of municipal wastes has changed radically during the past thirty years - from 65 to 35 per cent organic matter. This has come about

It seems clear that for the foreseeable future all but a small fraction of the total quantity of solid wastes will be returned to the environment as a means of final disposal. The current tendency to regard each element of the environment as a resource makes it very clear that each becomes most valuable when exploited to the maxinum degree compatible with prudent safeguards for human health, well-being and preservation of property. A distinction must therefore be made between contamination of the environment - that is, addition of foreign substances - and pollution

that is, accu

mulation of contaminants to the point where undesirable effects begin to occur. It is naïve to maintain that nothing whatsoever can be added to the environment, for even if it became technically possible to achieve such an ideal, the human and material resures that would have to be committed to this single purpose would be so great that the quality of daily life would be substantially impoverished. Instead, the obpective should be to utilize to the fullest the self-punhing properties of the environment. which are enormous when properly understood and sanaged. In Los Angeles County, for example, all wid waste collections are used for landfill to transbom steep, dry hills and canyons into public parks and golf courses Most citizens appear well pleased with this decision although a few express a prefereure for preservation of the waste lands. Similar considerations and differences of opinion apply to the management of tidal fats. Even staunch conservahetats may concede, in good conscience, that not stery single acre of tide land is best utilized by bring left alone. As poorly located and badly pol. tated tide lands can be drained, filled and utilized for many good purposes, so, in like manner, can new da anda be created in ideal locations to fill needs Emain nya satısbed by natural geologic processes.

At present, there are 2 satisfactory methods in greral use for disposing of the fraction of municipa wastes not Hushed into the sewer via the gartuage pnnder Both methods return wastes to the entrament One is the sanitary land fill, and the they tugh temperature incineration and ground disposal of the residue.

Sanitary landfilling. often referred to as cut-andover burial, overcomes almost all the objectionable beatures assocuated with open dumping. When the FLEXS 15 properly operated, each day's refuse collections are compacted and completely covered with

least 6 inches of compacted clean fill. This prerents hures, suppresses odors of decomposition and puttrtation, eliminates much of the unsightliness aruncated with open dumps and destroys feeding and breeding places that would otherwise be open k rodents, birds and insects. This method of waste dupmonal produces no air pollution problems, except bove the generation of some local dustiness during peruds of prolonged dryness. Problems of water paluation can be avoided by provision of drainage for the site, the waters being conducted to an adjacent sute-water disposal facility. This is an impor. samt beature of a sanitary landfill since it guards unut water pollution and prevents erosion of the tantall by surtace runoff of rainwater and melting reduction in bulk is more important than residual weight when the effect of incineration on the life of a sanitary land fill site is assessed. Tins and bottles, which come through the incineration process largely unchanged, make up a large proportion of the combustible weight and bulk of domestic refuse. If these items were segregated by the householder they could be hauled directly to a landfill site and thereby effect a considerable saving in incineration cost and the cost of residue hauling. However, the housewife finds the practice of segregating solid wastes into separate refuse containers (for example, garbage, combustible refuse and incombustible refuse) onerous and objects very vigorously to such a system. Therefore, the usual practice is to collect mixed refuse and haul the small incombustible items to the dump after they have passed through the incinerator,

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disposal site, thereby greatly reducing handling costs. In addition to handling large tonnages of wastes rapidly and cleanly, these large, heavy machines are especially effective for compacting the waste and clean cover, thereby conserving fill volume. Usually, a completed fill is topped with a foot or more of clean earth. When properly graded, finished with loam, seeded and planted, it may be converted to public use or sold for commercial development. The increased value of the filled land, whether retained for public use or sold, may properly be treated as a credit when the net cost of refuse disposal is calculated.

A rule of thumb for landfill requirements is 1 acre per 10,000 population per year when the depth of compacted refuse is about 7 feet.* Greater fill depths, possible in canyons, quarry pits and similar deep holes, reduce land requirements and conserve fill capacity. Although this is a preferred method of disposal when land is available, suitable sites and cheap cover materials are disappearing rapidly within economic haul distances of almost all large metropolitan areas, and this is especially true for the older cities along the eastem seaboard and Great Lakes. Under these circumstances, remaining close-in fill sites are generally reserved for disposal of noncombustibles and for incinerator residues in an effort to extend their useful life.

Incineration reduces refuse to between one fifth and one tenth its original volume and thereby de. creases many times the land area required for final disposal. This means that during the combustion process, 80 to 90 per cent of the volume (50 to 75 per cent by weight) is converted to gaseous products that are discharged to the air environment. When incineration is complete, well over 99 per cent of the gases formed by combustion are carbon dioxide and water vapor. These 2 compounds are found in the normal atmosphere in abundance and are not usually considered to be pollutants although there is considerable current interest in the longterm (one hundred to three hundred years) climatologic effects that may result from an increase in the carbon dioxide content of the atmosphere

Although a reduction in volume of four fifths to nine tenths may be achieved by incineration, solid wastes include many items that are incombustible (such as old refrigerators and junk automobiles) and others that, though combustible, are nonincinerable in existing incinerators (such as tree stumps and urban-renewal demolition wastes).

Recent figures from Los Angeles Countyø show that 36 per cent of their solid wastes are nonincinerable or noncombustible. When the residue from the incineration of the remainder is added, the total amount of raw waste that must be disposed of in the ground, even when modern incineration plants are employed, is slightly greater than 50 per cent by weight. Because household and commercial refuse contains large amounts of bulky paper products that are almost totally consumed by incineration, the

Sanitary landilling. when suitable land is avail. atbe to the cheapest method of solid-waste disposal

**" entirely satistactory from sanitary and esthet kemuderations The use of large earth-moving eta benes adapted from equipment designed for was cleaning and road building, has made it possihole fur a single skilled operator to manage a large

Incineration, including burial of the residues, is a relatively expensive disposal method and costs about $5 per ton, as compared to $1 or $2 per ton for sanitary landfilling without incineration when conveniently located large tracts of cheap waste land are available for this purpose. When remote landfill sites must be utilized, transportation costs become an important fraction of the total disposal cost, and transfer of loads from 5-ton or 8-ton packer pickup trucks to 20-ton trailer trucks at intown locations becomes an economical procedure. The experience of Los Angeles shows that transfer operations increase handling costs by $1.25 per ton of refuse. Haulage costs are $12 per hour for an 8-ton truck ($1.50 per ton per hour) and $15 per hour for a 20ton trailer load ($0.75 per ton per hour).* Operating time has been found to be a more reliable guide to costs than the mileage covered, for per mile costs Huctuate widely, depending on local terrain and traffic conditions.

The small percentage of combustion products emitted to the atmosphere from waste incineration that is not carbon dioxide or water vapor consists of particulate matter (soot, smoke and gas-entrained solid residues), organic gases (hydrocarbons or aldehydes) and inorganic gases (sulfur dioxide, hydrogen chloride or oxides of nitrogen). These are all recognized as air pollutants. Under ideal operating conditions, a modern high-temperature municipalwaste incinerator totally destroys all organic matter, and the emissions that are of special interest because of their effect on the air environment will be inorganic - principally, particles of solid residue, oxides of sulfur and nitrogen and hydrogen chloride.

All particulate emissions, including smoke, can be eliminated or greatly reduced, even from old incinerators, by the use of dust collectors between the burning units and the discharge stack. Most incinerator dust collectors in current use are either dry cyclones or simple washers. Neither of these devices is capable of removing particies less than 10 M in diameter from the flue gases at high efficiency, and neither is in any manner effective for smoke

and soot. Washers have the added disadvantage of cooling the flue gases and greatly increasing their density by the addition of water vapor so that they lose their buoyancy when released to the atmos phere and fail to become dispersed and diluted as they do when released in a hot, dry state. High-energy scrubbers, electrostatic precipitators and industrial cleanable cloth filters are the only kinds of collecting equipment capable of reducing particle emissions from incinerators to a low level consistant with modern concepts of acceptable control of air pollution. Of the 3, industrial cloth filters are preferred because they are capable of cleaning the flue gases to the point where no visible emission occurs (greater than 99.9 per cent efficiency), and the cost is no greater than for electrostatic precipitation or high energy scrubbing. At present no municipal incinerator in the United States is equipped with any of these devices except for 1 or 2 small-scale pilot test units. In Germany electrostatic precipitators are used on combination coal-burning and refuse-burning municipal central-station steam plants, but they would have been required, in any case, for burning coal.

The equipment and installation cost of first-class Ay-ash collection equipment for an incinerator suit. able for a city of 100.000 to 200,000 population is presently about $500,000. When amortized over the life of the incinerator (twenty or more years) this is just a few pennies added to the tax rate. Therefore, it is difficult to understand why affluent suburban communities are eager to build multimillion dollar, campus-type schools containing swimming pools and other amenities of modern "education" while remaining content to build new incinerators that have been obsolete for twenty years. Unlike educa. tion and dogs, waste disposal fails, so far, to arouse aggressive interest among the citizenry, but perhaps a current concern for maintaining the quality of the environment will change this attitude.

Even with the best possible dust collectors to remove all incineration Ay ash and complete destruction of all organic matter by high-temperature combustion, contamination of the air may still occur from inorganic gaseous compounds. Oxides of sulfur are formed from the burning of sulfur-containing substances such as protein in food wastes and vulcanized rubber. Most of the sulfur will be in the form of sulfur dioxide, but a small percentage will be converted to sulfur trioxide, and this fraction combines with water vapor in the flue gases to form submicron-sized sulfuric acid mist droplets. Hydrogen chloride is formed during the burning of chlorine-containing synthetic plastics, principally poly. vinyl chlorides. The occurrence of hydrogen chloride is increasing with the greater use of plastic materials of all kinds but is not yet thought to be a serious problem of air pollution. Oxides of nitrogen. principally nitric oxide and nitrogen dioxide, are formed by the fixation of nitrogen from the air in the high-temperature combustion zone.

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