Hazardous waste detoxification

Solidification/Stabilization technologies are techniques designed to be used as final waste treatment. A major role of these processes is posttreatment of residuals produced by other processes such as incineration or chemical treatment. In some cases, solidification/ stabilization processes can serve as the principal treatment of hazardous wastes for which other detoxification techniques are not appropriate. High volume, low toxicity wastes (such as contaminated soils) are an example of this application. 

It is not currently feasible to achieve a zero discharge of chemical pollutants from metal finishing operations. However, substantial reductions in the type and volume of hazardous chemicals wasted from most metal finishing operations are possible.8 Because end-of-pipe waste detoxification is costly for small- and medium-sized metal finishers, and the cost and liability of residuals disposal have increased for all metal finishers, management and production personnel may be more willing to consider production process modifications to reduce the amount of chemicals lost to waste. 

Table 20.5 lists the partition and transformation processes applicable in the deep-well environment and indicates whether they significantly affect the toxicity or mobility of hazardous wastes. None of the partition processes results in detoxification (decomposition to harmless inorganic constituents), but all affect mobility in some way. All transformation processes except complexation can result in detoxification however, because transformation processes can create new toxic substances, the mobility of the waste can be critical in all processes except neutralization. 

Polymerization is the formation of large molecules (polymers) by the bonding together of many smaller molecules. For example, styrene polymerizes to form polystyrene. Polymerization can enhance the tendency of a substance to be adsorbed on mineral surfaces by increasing the molecular weight, but is not likely to result in detoxification of hazardous wastes. 

Exner, J.H. Detoxification of Hazardous Waste, Ann Arbor Science Michigan, 1982. 

Alberti BN, Klibanov AM (1982) Peroxidase for removal of hazardous aromatics from industrial wastewaters. In Exemer JH (ed) Detoxification of hazard waste. Ann Arbor Science, Ann Arbor... 

Actions taken after a hazardous waste is generated. This clearly excludes any form of treatment (including detoxification, incineration, thermal, chemical or biological decomposition, stabilization through solidification, and embedding or encapsulation). 

Jorgensen, G. and Rangaprasad, G., Ultraviolet Reflector Materials for Solar Detoxification of Hazardous Waste, SERI/TP-257-4418, SERI, Golden, CO, 1991. 

Oxidation. Oxidation is a process that involves the transfer of one or more electrons. This can be carried out by adding an oxidizing agent or via electrochemistry. This process is used for the detoxification of hazardous waste the oxidation of cyanide to cyanate, and further decomposition into CO2 and N2 is a good example. Metals can be oxidized to their higher oxidation state, thus making them insoluble and recoverable as a precipitate. 

The change in oxidation state implies that an electron was transferred from the cyanide ion to the permanganate. The increase in the positive valence or decrease in the negative valence with oxidation takes place simultaneously with reduction in chemically equivalent ratios. Some oxidation reactions proceed readily to carbon dioxide (CO2). In other cases, the oxidation is not carried as far, perhaps because of the dosage of the oxidant, the pH of the reaction medium, the oxidation potential of the oxidant, or the formation of stable intermediates. The primary function performed by oxidation in the treatment of hazardous wastes is essentially detoxification. For instance, oxidants are used to convert cyanide to the less toxic cyanate or completely to carbon dioxide and nitrogen. A secondary function is to ensure complete precipitation, as in the oxidation of Fe " to Fe " and similar reactions, where the more oxidized material has a lower solubility under the precipitation reaction conditions (l-3,6,7). 

Sengupta, A.K. Millan, E. Roy, T. Potential of ion exchange resins and reactive polymers in elim-inating/reducing hazardous contaminants. Proceedings of the 2nd International Conference on Physicochemical and Biological Detoxification of Hazardous Wastes, Atlantic City, NJ, May 3-5, 1988 191. 

Havens, P.L., and H.F. Rase. 1991. Detoxification of organophosphate pesticide solutions Immobilized enzyme systems. Pp. 261-281 in Emerging Technologies in Hazardous Waste Management II, ACS Symposium Series No. 468. D.W. Tedder and F.G. Pohland, eds. New York, N.Y. Oxford University Press. 

Another problem is the detoxification of the hazardous wastes that are already present in the environment. Efforts are thwarted by the problan of how less toxic are the detoxification products in themselves Thus, in incineration, for instance, what are the toxicides of all the final combustion products Called products of incomplete combustion, or PlCs, these are the myriad by-products and coproducts of the competing reactions that occur during combustion, and for that matter, during any chemical conversion, more or less. Can they ever be fully detected and analyzed Or if selectively scrubbed, what is to be the disposition of the absorbed materials What is called detoxification may be merely a further dispersion throughout the ecosphere, and a process of trading one set of problems for another. 

Photolysis has had limited application for treatment of hazardous waste or detoxification of chemically contaminated materials. The susceptibility of chlorinated aromatics, including herbicides such as 2,4-D and 2,4,5-T, to UV-induced decomposition is well established (7,8). Photodecomposition of such compounds leads to successive dechlorination followed by condensation reactions to form phenolic polymers (7,8). Other research has demonstrated that CDD and CDF decompose in the presence of UV light (8,9,10) Development of a photochemical process for destroying 2,3,7,8-TCDD in a waste tar indicated similar dechlorination and condensation reactions and products (8). The high-molecular weight end products, which are similar in structure to humic acids, would be expected to have low toxicity and mobility. Therefore, essentially complete... 

Wang, Y. T., P. C. Pai, and J. L. Latchaw. 1989. Evaluating anaerobic biodegradability and toxicity of ozonation products of resistant phenolic compounds. Proceedings of the International Conference on Physicochemical and Biological Detoxification of Hazardous Wastes, 1988, Vol. 2, ed. Y. C. Wu, pp. 759-71. Lancaster, PA Technomic. 

Symons BD, Sims RC (1988) Assessing Detoxification of a complex hazardous waste, using the microtox bioassay. Arch Environ Contam Toxicol 17 497-505... 

E. Arvin, B. Jensen, E.M. Godsy and D. Grbic-Galic, in International Conference on Physiochemical and Biological Detoxification of Hazardous Wastes, Y.C. Wu (Ed.), 1988, p828. 

The use of PMDI as a binder for foimdry cores, rubber waste products, and solid rocket fuel are also known. Isocyanate-terminated prepolymers, often prepared from TDI or MDI with polyether polyols are also used as binders for composite products that require elastomeric properties. Athletic surfaces are sometimes prepared from groimd rubber tire scrap bonded with isocyanate-based prepolymers. Similarly, flexible polyurethane foam scrap is bonded with isocyanate prepolymers to form rebonded foam usefiil as carpet imderlay. Solidification of incineration ashes with PMDI-based binder systems is another waste disposal application. In this manner hazardous waste materials imdergo chemical fixation and detoxification. 

As applied to hazardous wastes in the biosphere, distinguish among biodegradation, biotransformation, detoxification, and mineralization. 

The photo-thennal detoxification unit uses photo-thennal reactions conducted at temperatures higher than those used in conventional photochemical processes (200 to 500°C, rather than 20°C) but lower than combustion temperatures (typically greater than 1000°C). At these temperatures the developer claims that photochemical reactions are energetic enough to destroy wastes quickly and efficiently without producing complex and potentially hazardous by-products. 

Ioannidis, T. A. Zouboulis, A. I. 2003. Detoxification of a highly toxic lead-loaded industrial solid waste by stabilization using apatites. Journal of Hazardous Materials, 97, 173-191. 

---