Difficult waste

An innovative technology called the "lasagna" process is based on the electrokinetic phenomenon called electro osmosis. The lasagna process was created to treat difficult wastes in low permeabiUty, sdt- and clay-laden soils (40). The lasagna process is so named because it consists of a number of layered subsurface electrodes and treatment zones. These layers can be constmcted either horizontally where contaminants are forced to more upward or in vertical position where lateral contaminant movement is desired. 

One of the most difficult wastes for industry to dispose of is that of solutions of inorganic salts [270]. Unlike organic salts which can be treated by various methods to convert the organic species into carbon dioxide and water, inorganic salts can rarely be broken down. 

The wastewater field has more than 100 years of treating difficult waste materials in an aqueous environment. There are sophisticated models for wastewater treatment which can be applied to the remediation field, and the methods and the approaches are also useful. The introduction of a C N P ratio or the introduction of various simple operating parameters has been cost effective, and may be applicable in the remediation field as well. From some of the new reactor designs and applications, it appears that some remediation problems may be those which have already been studied by the wastewater field, and that there are lessons to be learned as well as new and innovative approaches still remaining to be evaluated. 

With the proper emission controls, burning tires for their fuel energy can be an environmentally sound method of disposing of a difficult waste. It can also be financially advantageous and can improve the operating characteristic of a number of processes. 

Unlike Portland cement, the Ceramicrete slurry sets into a hard ceramic even in the presence of salts such as nitrates and chlorides hence, the Ceramicrete process has a great advantage over conventional cement technology with respect to the stabilization of some difficult waste streams, such as those from Hanford and Savannah River tanks. Wagh et al. demonstrated this advantage in several studies, wherein they produced monolithic Ceramicrete solids by using concentrated sodium nitrate and sodium chloride solutions in place of water to stabilize the waste streams. Details of some of these studies may be found in Ref. [21]. 

Glearly, ion exchange methods can overcome what would otherwise be a difficult waste disposal problem, and the bonuses of recovering reagents and process water are valuable economically. A diagrammatic representation of the ion exchange route is shown in Figure 8.21. 

The most difficult waste disposal problems arise from the effluents produced during the processing of spent nuclear fuel where liquid-liquid extraction techniques are used to recover fissile and fertile material from the various fission products. 

Note that the pathological waste in the waste stream in this problem is the most difficult waste to destroy since its heating value is low. Hospital waste incinerators must be designed to destroy pathological and infectious waste, not paper waste alone. The contents of a hospital waste stream are normally more complex than shown in this problem. Other hazardous components may include pentane, diethyl ether, acetone, methyl cellosolve, and other laboratory wastes. 

These solutions can contain as much as 60 percent (by volume) hydrochloric or sulfuric acid, depending on the shape of the steel and type of steel (high carbon or low carbon) to be cleaned. The solutions are used until either the acid content is too low (Baume gravity scale), or the iron content is too high (titration technique). By the time it is ready to be discarded, pickling solutions can have very high iron concentrations (60 g/L or 0.5 Ib/gal total dissolve iron). These solutions pose one of the most difficult waste disposal problems for the steel industry. There are a few other industries that can use the solutions (mainly for the acid content), but the volume of the solutions can literally flood the market. 

The recently adopted landfill directive (a) demands high standards of landfill management, and also seeks to ban certain difficult wastes from landfill, and (b) seeks a progressive reduction in the land-filling of biodegradable wastes which account for a high percentage of wastes sent to sites. 

However, in order to expand the recovery and recycling of plastics and decrease the amount of waste disposed in landfills, it will be necessary to overcome these difficulties. Because of its heterogeneous nature and the amount of contaminants present, separation of post-consumer mixed plastic waste is the most difficult. Waste plastics from industrial operations are cleaner and more homogeneous in resin type and scrap form than postconsumer plastics. The term "mixed plastics" has been used to describe broad scale processing of post-consumer plastic waste, although no formal definition yet exists. In its broadest sense, mixed plastics means a collection of a mixture of plastic resins or a mixture... 

Today, chemical decladding and total dissolution processes are generally avoided because of the difficult waste-disposal problems they engender. The preferred head-end treatment involves the disassembly or dismantling of irradiated fuel assemblies, followed by shearing individual rods. Subsequently, the sheared fuel is leached with boiling nitric acid to produce a dissolver solution suitable for downstream solvent extraction operations. 

Difficult waste is a term used to describe wastes that could in certain circumstances be harmful to human healtii or the environment in the short or long term due to their chemical or biological properties. This term incorporates wastes whose physical properties present handling problems at the point of disposal. 

---