Dewatering waste handling

Table 28-2 lists some of the currently used pretreatments and ultimate disposal methods for hazardous wastes (6). Pretreatment refers almost entirely to thickening or dewatering processes for liquids or sludges. This process not only reduces the volume of the waste but also allows easier handling and transport. 

For the cement stabilization option, a facility would be constmcted to dewater and treat the wastes. There would be a 7- to 21-day staging period of wastes for quality assurance operations. An online rate of 250 days a year was assumed. It is estimated that cement stabilization would result in a volume factor increase roughly 3.75 times the total volume of waste treated. This increase in volume is necessary to immobilize technetium present in the wastes and to achieve a final waste form that could withstand pressures of 500 pounds per square inch (psi). The cement would be placed in 4-ft by 4-ft by 8-ft steel containers that would serve as a mold and to facilitate the handling of the finished blocks (D114432, Appendix A). 

A related area of research would include efforts to reduce the water requirements of flue gas treatment systems. This would be especially important to the wet throwaway systems most commonly used today. Research to improve the dewatering properties of scrubber sludge could be combined with the development of techniques to separate spent and unused sorbent, thus reducing both water and sorbent consumption while also reducing the volume and mass of solid waste to be handled. The use of waste or recycled water in flue gas treatment systems would also reduce water needs. Improved sludge stabilization methods that also remove water could also lower costs associated with both waste disposal and water consumption. 

Any waste-sludge handling requires separation of the maximum content of sludge water. It is necessary to differentiate the terms thickening and dewatering . 

In addition to the effluent limitations and the processes shown in Table 24 the degree of reduction in heavy metals waste loadings should consider the sludge handling and disposal methods used for the metal finishing wastewaters. Some processes (e.g., anaerobic digestion) concentrate these metals, and this can lead to process failure unless adequate pretreatment is provided. Dewatering operations discussed in Chapter 7 should be referred to. 

Process Description. An incineration system eonsists of three main units feed preparation and handling, primary combustion unit, and off-gas treatment. Feed preparation usually includes screening to remove oversized particles that could clog or jam the combustion unit. Oversized waste may be shredded so that it can be incinerated, or treated or landfilled separately. Sludge is usually dewatered to make the material easier to feed to the incinerator and to limit the fuel cost associated with heating, volatilizing, and treating the water in the incinerator. 

The 2 billion tons of waste coal fines existing in impoundments and ponds is an environmental and safety problem for the coal mining and coal preparation community. Coal fines do not readily dewater, and will remain in suspension in water—the primary transport medium in the coal cleaning processes— for long times. If stocked out and dried, these fines become a fugitive dust emissions source. Morc likely, however, they will be handled by being placed behind the many dams in impoimdments... 

Waste Type Handled. Pressurized and gravity-fed granular media filtration systems are used for waste streams containing suspended solids. Vacuum, belt press, and pressure chamber filtration processes are used primarily to dewater sludges. 

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