Municipal solid waste stream

Mercury thermometers have been used for decades. In some instances their use has been discontinued, such as in infant incubators where it was found that significant mercury vapor concentrations could be achieved if the thermometers were broken in this enclosed environment. Disposal of thermometers and thermostats continues to add significandy to the toxicity of municipal waste. In 1995, discarded thermometers contributed 16.9 tons of mercury to municipal solid waste stream. 

Universal waste rule was an amendment to the Resource Conservation and Recovery Act regulations. It is designed to reduce the amount of hazardous waste items in the municipal solid waste stream. The rule encourages the recycling of certain common hazardous wastes and their proper disposal. Another objective of this rule is to reduce paperwork and other administrative requirements and regulatory burden on businesses that generate these wastes, and to save them compliance costs. 

There are two basic types of solid waste combustors currently in operation in the United States, mass burn facilities and refuse derived-fuel (RDF) facilities. Mass burn facilities manage over 90% of the solid waste that is combusted in the United States. Mass burn facilities are designed to handle unsorted sohd waste, whereas RDF facilities are designed to handle preprocessed trash. The ash produced by RDF facilities, where the incoming municipal solid waste stream is shredded and presorted to remove ferrous metal and in certain cases nonferrous metal prior to combustion, can be expected to have different physical and chemical properties from ash generated at mass burn facilities [115-118]. 

Figure 4.1. Packaging in U.S. municipal solid waste stream, 1998 [1].

FIGURE 9.2 Generation and recovery of the plastics in municipal solid waste stream in the United States. Source USEPA. 

The forest products companies, on the other hand, see plastics as a way to expand sustainable forest resource utilization through the use of wood waste, fibers from underutilized species, and reclamation and recycling of wood, other agricultural species and waste, and paper materials from municipal solid waste streams (62), as well as a way to make new construction materials with attributes that wood does not have (56). 

Paper-contaminated plastics waste collected from the municipal solid waste stream is a potentially inexpensive source of cellulose for bulk composite applications. However, the processing of such waste stream is very difficult because of a high melt viscosity and agglomaration of the cellulose phase. A method for the hydrolytic pretreatment with acid in gas phase of such waste has been recently developed in our laboratories (11). 

Injection molding of samples containing more than 40% cellulose is limited by the high viscosity of the filled melt. This limit is reached at about 60% by hydrolyzing the fibers. Prehydrolytic treatment has been further optimized in our laboratory and has been applied in a pilot plant for the processing of paper-contaminated plastics waste collected from a municipal solid waste stream. The application of this method to the waste stream not only contributes to a decrease in the amount of of waste but at the same time creates novel composite materials at a very attractive price. Table II demonstrates the differences between the mechanical properties of composites manufactured by treatment of paper-contaminated plastics waste collected fi om different sources and illustrates the benefits of prehydrolytical treatment. 

In the municipal solid waste streams in 1999, plastics amounted to about 10.5% by weight of the 459.8 billion pounds of municipal solid waste (55). The waste plastic collected from the solid waste stream is a contaminated, assorted mixture of a variety of plastics. This makes their identification, separation, and purification very challenging. In the plastic waste stream, polyethylene forms the largest fraction, which is followed by PET. 

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