Solid waste separation, unit

SOLID WASTE DISPOSAL AND RECYCLING AN OVERVIEW OF UNIT OPERATIONS AND EOUIPMENT IN SOLID WASTE SEPARATION... 

A continuous flow of the solid waste stream, from its initial feeding into the processing plant until its exit in the form of final products, is necessary so that separation is efficient and economically viable. Among other factors, the uniform and controlled feeding of process units and equipment as well as the continuous handUng of the products secure the efficient operation of a solid waste separation plant. 

When processing municipal solid wastes, an eddy current separation unit is often used to separate aluminum and other nonferrous metals from the waste stream. This is done after removal of the ferrous metals (see Fig. 1). The eddy current separator produces an electromagnetic field through which the waste passes. The nonferrous metals produce currents having a magnetic moment that is phased to repel the moment of the appHed magnetic field. This repulsion causes the nonferrous metals to be thrown out of the process stream away from nonmetallic objects (13). 

Centrifugation is performed in a closed system and is therefore an excellent choice for treating volatile fluids. The liquid and solid are mechanically separated by centrifugal force. The removal of most of the liquid increases the solid concentration in, and reduces the volume of, the waste stream. The collected solid waste may then be treated and disposed of or recovered. Three types of units are available for centrifugation the solid bowl, the disk, and the basket. The first two are used in large plants, the third in smaller plants. 

This wastewater is often cleaned further by other treatment systems (filters, impoundments, etc.). The solids separating in these systems continue to be API separator sludge, a listed hazardous waste. Therefore, all downstream wastewater treatment systems are receiving and treating a hazardous waste and are considered hazardous waste mauagement units subject to regulation. 

Solid-liquid separations are important operations in chemical engineering ranging from upstream raw material purification, to downstream product separation and waste managements. They are usually low cost, and low energy consumption. A successful operation of a SLS system upstream a major chemical engineering unit such as a catalyst bed will help to improve the efficiency the catalyst, and decrease overall cost of the whole process. 

Classification or size separation is the unit operation that separates the particles according to their size. In general, it can be carried out dry or wet. The fraction of the feed having size less than the size of the screen aperture is the undersize, while that of greater size is the oversize. The fraction of the undersize that flows through the apertures is called underflow (or passing), while the particles that do not pass are called overflow (or remaining). In solid-waste treatment, classification is carried out almost always on screens and in dry, because the particles to be classified are relatively coarse and wet processes are undesirable. 

Magnetic separation is a unit operation that is applied whenever metals with magnetic properties participate in the composition of the commingled waste. Magnetic separators are encountered in almost all the recycling plants, as they are very simple in operation, have a relahvely lower cost compared to the other equipment of a solid-waste processing plant, have a high efficiency (80 to 95 percent) and production rates, and short pay-hack period. 

Research on solvent based polymer separation processes is by no means in its infancy. One of Ae first studies on mixed plastics was conducted by Sperber and Rosen [24,25] in the mid 1970 s. These investigators used a blend of xylene and cyclohexanone to separate a mixture of polystyrene (PS), poly(vinyl chloride) (PVC), high density polyethylene (HOPE), low density polyethylene (LDPE), and polypropylene (PP) into three separate phases. In adAtion, many United States and foreign patents dating from the 1970 s were granted for the solvent recovery of thermoplastic jwlymers [26-30]. The interest in solvent processes waned in the late 1970 s as the oil crisis eased, but the growing need to develop solutions to Ae solid waste problem has renewed Ae research effort [31-33]. 

The possibility of separating batteries from MSW needs to be considered within the context of MSW processing as a whole. Some data from the United States may be of Interest. In 1988 the average rate of accumulation of municipal solid waste amounted to 1.8 kg per person per day (16), and it was expected to increase rather than decrease during subsequent years. (The amounts of domestic waste... 

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