Waste Reduction And Materials Recovery

Proper solid waste management should first prevent and reduce the generation of solid wastes, reduce their hazardous characteristics, and recover and recycle waste to the extent practicable and then dispose of the remaining wastes in a manner that does not endanger public health or the environment. The focus of this section is on waste reduction and the recovery and recycling of materials.

Platform scales (optional)
Waste Transfer Station

FIGURE 3.12 Definition sketch for two most common types of transfer stations: (a) direct discharge; (b) storage-discharge. (Source: LaGrega, M. D., P. L. Buckingham, and J. C. Evans, Hazardous Waste Management, 2nd ed., McGraw-Hill, New York, 2001.)

Property lint

Property lint

Malcolm Pirnie Inc

Property line

Site Plan

Property line

Site Plan

Section A-A Section B-B

FIGURE 3.13 Direct-discharge transfer station equipped with stationary compactors. (Courtesy of Malcolm Pirnie, Inc. Reproduced with permission.)

Section A-A Section B-B

FIGURE 3.13 Direct-discharge transfer station equipped with stationary compactors. (Courtesy of Malcolm Pirnie, Inc. Reproduced with permission.)

Waste Reduction

The extent to which solid wastes can be reduced, recovered, and recycled should be an integral part of every solid waste management system study, whether involving composting, a sanitary landfill, or an incinerator. Composting is also considered a form of recycling. The first step, however, should be waste reduction at the point of generation or product formulation. Industrial material, process, and packaging changes can minimize the waste or substitute a less toxic or objectionable material. The amount of waste can then be reduced, and what waste is produced can be recovered, reused, or recycled to the extent feasible, thereby reducing the amount for final disposal. Additional details on source reduction may be found elsewhere.9

There has been considerable interest in a returnable bottle deposit law in some states to reduce highway litter, conserve resources, and reduce the volume

Transfer Landfill Stations

FIGURE 3.14 Small direct-discharge transfer stations: (a) convenience type located in rural areas at entrance of landfill disposal sites. (b ) individuals unloading waste materials into a convenience type transfer station located at the entrance to a landfill.

FIGURE 3.14 Small direct-discharge transfer stations: (a) convenience type located in rural areas at entrance of landfill disposal sites. (b ) individuals unloading waste materials into a convenience type transfer station located at the entrance to a landfill.

Garbage Transfer Trailer

FIGURE 3.15 Typical examples of transfer trailers used to transport waste over large distances to (a) single large trailer with drop bottom and (b) tractor trailer combination in process of being unloaded at landfill.

FIGURE 3.15 Typical examples of transfer trailers used to transport waste over large distances to (a) single large trailer with drop bottom and (b) tractor trailer combination in process of being unloaded at landfill.

of solid wastes for disposal. The bottle law is usually applicable to all types of beverage containers, including glass, metal, and plastic, but not to other types of containers such as food jars, plastic and paper cups, wine and liquor bottles, and the like. The effectiveness of the bottle deposit law has been debated by some considering its limited application, the handling involved, and total cost, tangible and intangible. A substantial number of deposit containers are not returned by the consumer. This results in an unintended income to the supermarket or other retailer and what amounts to an additional cost to the consumer. Other alternatives should be considered. The reduction of all types of litter and insults to the landscape, including spillage from uncovered vehicles, elimination of junked cars, debris, and illegal dumps, and education of the public to promote a clean environment such as through Keep America Beautiful, requires greater support. Some returnable bottle laws are being amended to include liquor, wine, and wine cooler bottles and possibly other containers.

Materials Recovery and Recycling

Recovery of materials and energy from solid wastes is not new. Scavengers have salvaged newsprint and cardboard, rags, copper, lead, and iron for years. These materials, together with aluminum, glass, plastics, and wood, are being reclaimed at central collection and processing stations to a greater or lesser extent, depending on the available market, tax policies, and public interest. Energy recovery, where feasible, has been an important consideration in which unsorted solid waste and shredded solid waste, referred to as refuse (solid-waste) derived fuel (RDF), is burned to produce steam or electricity.

Recycling can effect savings in landfill space and in energy. One ton of newspapers can save 3.0 to 3.3 yd3 of landfill space. It is estimated that 95 percent less energy is required to produce aluminum from recycled aluminum than from bauxite. Crushed recycled glass melts at a lower temperature than virgin raw material, thereby conserving energy. Unfortunately, the recycling of glass has essentially ceased because of a glut of material available, the high cost of handling and processing recycled glass, and the cost associated with pollution control.

Resource recovery is not a municipal operation to be entered into just because it seems like the logical or proper thing to do. It is a complex economic and technical system with social and political implications, all of which require competent analysis and evaluation before a commitment is made. Included are the capital and operating costs, market value of reclaimed materials and material quality, potential minimum reliable energy sales, assured quantity of solid wastes, continued need for a sanitary landfill for the disposal of excess and remaining unwanted materials and incinerator residue, and a site location close to the centroid of the generators of solid wastes. Not all concepts are viable. Incentives and monetary support may be required to obtain an acceptable site.

Resource recovery is a partial waste disposal and reclamation process. Materials not recovered may amount to 40 to 55 percent of the original waste by weight, although a resource recovery system can theoretically be used to separate up to 90 percent of the municipal waste stream into possibly marketable components. It has been estimated that under the best conditions only about 50 to 60 percent of the solid waste will be recovered. In 1979, 7 percent was being recycled for materials or energy. In 1990, the national average was estimated to be 11 percent. In the year 2000, the average was about 26 percent. In 2008, the average is close to 50 percent. As noted previously, the Board of Supervisors of the City of San Francisco has mandated a goal of 75 percent waste diversion by the year 2010. In general, it has been found that the recovery of materials from municipal solid waste is not a paying proposition. Most materials recovery operations are subsidized, in part, by the collection fees or by added monthly charges. In most communities, materials recovery facilities are used to help meet mandated diversion (from landfill disposal) requirements.

Processing Technologies for the Recovery of Materials

In the not-so-distant past, solid-waste processing and disposal methods have included the open dumping, hog feeding, incineration, grinding and discharge to a sewer, milling, compaction, sanitary landfill, dumping and burial at sea (prohibited in the United States), incineration, reduction, composting, pyrolization, wet oxidation, and anaerobic digestion. Currently, the most commonly accepted processing technologies involve the recovery of materials at materials recovery facilities and composting. Materials recovery facilities are considered next; composting is considered in the following section.

Implementation of Materials Recovery Facilities

Because the EPA has mandated diversion goals, most communities have developed a variety of materials recovery facilities. The purpose of this section is to define the type of materials recovery facilities now in use, to review the principal unit operations and processes used for the recovery of materials, and to highlight the planning issues associated with the implementation of a materials recovery facility. Additional details on materials recovery facilities may be found in Ref. 10.

Types of Materials Recovery Facilities (MRFs) The separation of household and commercial waste can be done at the source, at the point of collection by collection crews or at centralized materials recovery facilities or large integrated materials recovery/transfer facilities (MR/TFs). The type of MRF will depend on the type of collection service provided and the degree of source separation the waste has undergone before reaching the MRF. The two general types of MRFs are (1) for source-separated material and (2) for commingled solid waste. The functions of each of theses types of MRFs are reviewed in Table 3.12. As reported in Table 3.12, may different types of MRFs have been developed, depending on the specific objective. Further, as reported in Table 3.13, materials recovery facilities can also be classified in terms of size and the degree of mechanization. Small MRFs associated with the further processing of source-separated materials tend to be less highly mechanized.

TABLE 3.12 Typical Examples of Materials and Functions/Operations of MRFs Used for Processing of Source-Separated Recyclable Materials and Commingled Solid Waste

Materials

Function/Operation

MRFs for Source-Separated Recyclable Materials

Mixed paper and Manual separation of high-value paper and cardboard or cardboard contaminants from commingled paper types; baling of separated materials for shipping; storage of baled materials Manual separation of cardboard and mixed paper; baling of separated materials for shipping; storage of baled materials Manual separation of old newspaper, old corrugated cardboard, and mixed paper from commingled mixture; baling of separated materials for shipping; storage of baled materials Manual separation of PETE and HDPE from commingled plastics; baling of separated materials for shipping; storage of baled materials

Manual separation of PETE, HDPE, and other plastics from commingled mixed plastics; baling of separated materials for shipping; storage of baled materials Manual separation of PETE, HDPE, and glass by color from commingled mixture; baling of separated materials for shipping; storage of baled materials Manual separation of clear, green, and amber glass; storage of separated materials Storage of separated mixed glass

Magnetic separation of tin cans from commingled mixture of aluminum and tin cans; baling of separated materials for shipping; storage of baled materials Manual or pneumatic separation of polyethylene terepholate (PETE), high-density polyethylene (HDPE), and other plastics; manual separation of glass by color, if separated; magnetic separation of tin cans from commingled mixture of aluminum and tin cans; magnetic separation may occur before or after the separation of plastic; baling of plastic (typically two types), aluminum cans and tin cans, and crushing of glass and shipping; storage of baled and crushed materials Yard wastes Manual separation of plastic bags and other contaminants from commingled yard wastes, grinding of clean yard waste, size separation of waste that has been ground up, storage of oversized waste for shipment to biomass facility, and composting of undersized material Manual separation of plastic bags and other contaminants from commingled yard wastes followed by grinding and size separation to produce landscape mulch; storage of mulch and composting of undersized materials Grinding of yard wasted to produce biomass fuel; storage of ground material

PETE and HDPE plastics

Mixed plastics

Mixed plastics and glass

Mixed glass With sorting Without sorting Aluminum and tin

Plastic, aluminum cans, tin cans, and glass

TABLE 3.12 (continued)

Materials

Function/Operation

MRFs for Commingled Solid Waste

Recovery of recyclable materials to meet mandated first-stage diversion goals Recovery of recyclable materials and further processing of source-separated materials to meet second-stage diversion goals Preparation of MSW for use as fuel for combustion Preparation of MSW for use as feedstock for composting Selective recovery of recyclable materials

Bulky items, cardboard, paper, plastics (PETE, HDPE, and other mixed plastic), glass (clear and mixed), aluminum cans, tin cans, other ferrous materials

Bulky items, cardboard, paper, plastics (PETE, HDPE, and other mixed plastic), glass (clear and mixed), aluminum cans, tin cans, other ferrous materials; additional separation of source-separated materials, including paper, cardboard, plastic (PETE, HDPE, other), glass (clear and mixed), aluminum cans, tin cans

Bulky items, cardboard (depending on market value), glass (clear and mixed), aluminum cans, tin cans, other ferrous materials

Bulky items, cardboard (depending on market value), plastics (PETE, HDPE, and other mixed plastic), glass (clear and mixed), aluminum cans, tin cans, other ferrous materials

Bulky items, office paper, old telephone books, aluminum cans, PETE and HDPE, and ferrous materials; other materials, depending on local markets

Source: Adapted from H. Leverenz, G. Tchobanoglous, and D. B. Spencer, "Recycling," in G. Tchobanoglous and F. Kreith (Eds.), Solid Waste Handbook, 2nd ed., McGraw-Hill, New York, 2002, Chapter 8.

Methods and Equipment for the Separation and Recovery of Materials

Methods and processes used singly and in various combinations to recover and prepare wastes for reuse and/or disposal are summarized in Table 3.14. Of the methods reported in Table 3.14, manual sorting is by far the most commonly used method for processing waste materials (see Figure 3.16). It is interesting to note that no machine has been developed to date that can match the eye-hand coordination of humans. The particulate grouping of unit processes and operations will depend on the characteristics of the material to be separated.

MRF Process Flow Diagrams Once a decision has been made on how and what recyclable materials are to be recovered, MRF process flow diagrams must

TABLE 3.13 Typical Types of Materials Recovery Facilities, Capacity Ranges, and Major Functions and System Components Based on Degree of Mechanization

System Type

Capacity (tons/day)

Major System Components

Materials recovery

Organic Gardeners Composting

Organic Gardeners Composting

Have you always wanted to grow your own vegetables but didn't know what to do? Here are the best tips on how to become a true and envied organic gardner.

Get My Free Ebook


Post a comment