Emerging Technologies for Hazardous Waste Management - ACS

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Emerging Technologies for Hazardous Waste Management An Overview 1

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Downloaded by 80.82.77.83 on January 3, 2018 | http://pubs.acs.org Publication Date: March 10, 1994 | doi: 10.1021/bk-1994-0554.ch001

D. William Tedder and Frederick G. Pohland

1School of Chemical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0100 2Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15261-2294 Hazardous waste management and the remediation of contaminated environments continue to command priority attention and the mobilization of the collective capabilities of scientists, engineers and related disciplines in the private and public sectors of society. This emphasis, and the recognition of a need to efficiently and economically resolve hazardous waste management problems, has led to an emergence of an array of innovative technologies with applications in a variety of environmental settings. Indeed, the focus on hazardous waste management and remediation technology has been the subject of numerous national and international workshops, symposia, conferences and associated activities, as exemplified by the Wastech® initiative of the American Academy of Environmental Engineers(1). Our current contribution to the advancement of knowledge and its application to the solution of hazardous waste management challenges focuses on selected technologies currently under development, and showing particular promise in terms of new approaches as well as advancing the application of fundamentals of science and technology. As such, it is an extension of and an embellishment to the continuum of topics presented in previous volumes of the series (2-4), with an attempt to highlight those that have taken on particular contemporary significance. Therefore, perusal of this overview will serve to demonstrate the importance of soils and sediments as crucial remediation horizons, the inextricable linkage between waste minimization and management technologies, and the renewed emphasis on the pervasive challenges of radioactive wastes. Remediation Technologies for Soils and Sediments

The discovery and environmental impacts of contaminated soils and sediments have catalyzed an aggressive search for innovative technologies for both access and remediation, employing physical, chemical and/or biological techniques. In Chapter 2, Chesnut recognizes the consequences of the usual heterogeneity encountered in porous geologic media, including effects on porosity, permeability, mineralogy, and contaminant concentrations, and presents a model for quantifying effects of heterogeneity on vapor extraction, where a single parameter, a, is used. The resulting model is sufficiently simple to apply in Monte Carlo and similar sampling procedures for estimating the 0097-6156/94/0554-0001$08.00/0 © 1994 American Chemical Society

Tedder and Pohland; Emerging Technologies in Hazardous Waste Management IV ACS Symposium Series; American Chemical Society: Washington, DC, 1994.


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EMERGING TECHNOLOGIES FOR HAZARDOUS WASTE MANAGEMENT

uncertainty in cost or duration of a remediation project. The model, originally developed to determine the effect of heterogeneity on waterflooding for secondary oil recovery, has also been extended elsewhere (5) to estimate travel time distribution for radionuclides dissolved in water moving through fractured porous rock. Recognizing that soils and groundwater may be contaminated with heavy metals, requiring extensive excavation for removal and management, Lingren, et al. (Chapter 3) developed and tested an electrokinetic process for in situ remediation of anionic contaminants in terms of electromigration rate through unsaturated media at varying moisture contents. Decreases in rate at low and high moisture contents were explained by increases in pore tortuosity and decreases in pore water current density, respectively. Experiments with food dye and chromate ions provided the basis for developing a simple experimental model capable of predicting dependence on soil moisture content and pore water chemistry. Knowledge of biodegration kinetics can also facilitate decisions on in situ remediation of soils, sediments and aquifers. Tabak, et al. (Chapter 4) investigated adsorption/desorption equilibria and kinetics in soil slurry reactors for phenol and alkyl phenols. A mathematical model incorporating effects of adsorption/desorption and biodegradation in the liquid and solid soil phases, as well as protocols for measuring biomass adsorption in soil and bioconversion by radiolabeled carbon dioxide evolution, were presented and advocated for use in determining the extent of bioremediation at contaminated sites. As such, this contribution complements the overview presented by Eckenfelder and Norris (6) in the previous volume of this symposium series. Tsang, et al. (Chapter 5) also focused on the need for re-mediation of soils and sediments contaminated by activities such as mining, electroplating and other manufacturing and industrial processes. Sterile and nonsterile soil, experimentally contaminated with bismuth, cadmium, lead, thorium and uranium, containing cysteine, glycine, or thioglycolate, and inoculated with pure cultures of soil bacterial isolates, indicated the promotion of releases of all contaminants. It was concluded that viable and active microorganisms influence the ability of soil to retain or release metals, and that cysteine is effective in this process, operating as a reducing agent as well as a metal complexing agent and nutrient Enhancement of microbially-mediated removal was considered due to changes in pH and/or Eh near the soil colloid, alteration of the valence state of the metals, and decomposition of the organic matter in the soil. These findings again emphasize the necessity of providing favorable growth conditions supportive of biological activity on a continuum. Waste Minimization and Management Technologies

The recognition of waste minimization as an essential element in the hierarchial approach to hazardous waste management continues to foster developments in responsive methodologies. Edgar and Huang (Chapter 6) advocated a systematic module-based synthesis approach to the design of environmentally clean processes with minimal waste generation. The approach adds the dimension of structural controllability to the conventional capital and operating cost functions, and elaborates waste minimization strategies as constraints. In the absence of sufficient data on waste generation at the process design step, artificial intelligence techniques are used to represent waste minimization strategies and evaluate controllability. The efficacy of the proposed waste minimization approach is illustrated using a phenol-containing waste in an oil refinery as an example. Therefore, the generic features of the approach would enhance its applicability to other industrial settings. Recognizing the increasing difficulty of meeting more stringent effluent quality requirements by conventional treatment technologies, Gaarder, et al. (Chapter 7) Tedder and Pohland; Emerging Technologies in Hazardous Waste Management IV ACS Symposium Series; American Chemical Society: Washington, DC, 1994.


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Hazardous Waste Management: Overview 3

selected a crystallization technology for the concentration of mechanical pulp mill effluents, and the subsequent recovery and reuse of water. After screening other separation technologies, clathrate hydrate concentration, a variant of freeze concentration, was selected using carbon dioxide and propane to control the temperature and pressure conditions at which hydrates form. The results of the studies were considered essential to the development of large-scale crystallization units applied to pulp mill effluents where impurities did not adversely affect pressuretemperature equilibria. The control of mercury in aquatic environments and sediments continues to receive attention, and methods for its removal and recovery have been a subject of considerable scientific inquiry. Larson and Wiencek (Chapter 8) review the various management techniques and advocate the utilization of a microemulsion containing a cation exchanger to extract mercury from water. In order to successfully model the extraction process, both the equilibrium and kinetics of the metalrliquid ion exchange were determined, and a diffusion/reaction model for extraction of mercury with oleic acid in a batch STR (stirred reactor) is presented. Many hazardous waste constituents are volatile as well as biodegradable, and various methods to capture and convert these fractions have emerged. Apel, et al. (Chapter 9) have focused on the use of laboratory and full-scale biofilters for remediation of gasoline vapors using a proprietary bed medium. Removal occurred over temperature ranges of 22 to 40° C, and removal rate was a function of gasoline concentration and microbial viability. Removal of benzene in field tests was approximately 10 - 15%, with total BTEX (benzene, toluene, ethylbenzene, xylene) removal of 50 - 55%. Optimum contact opportunity between the gas stream and microbial consortia was considered essential and an important design variable. The recovery and processing of petroleum produces organic and oily wastes requiring appropriate management to comply with regulations. Majid, et al. (Chapter 10) focused on the feasibility of introducing finely divided sulphur dioxide capture agents into high sulphur fuels to demonstrate sulphur capture during combustion process. By using liquid phase agglomeration and comparison of the results of static muffle furnace combustion tests at 850° C with bench-scale fluidized bed results, cogglomeration of petroleum cokes and lime resulted in sulphur capture of over 80 to 30%, depending on the source of carbon and respective test conditions. A Ca:S molar ratio in the range of 1 to 2 was capable of reducing SO emissions sufficiently to meet USA and Canadian standards. Organic aqueous contaminants may exist as nonionic species and may be treated by sorption and subsequent partitioning for removal and/or recovery. Park and Jaffe (Chapter 11) recognized the ability of anionic surfactant monomers to adsorb onto mineral oxides (organo-oxide) and act as a sorbent for nonionic organic pollutants, with the advantage of in situ regeneration. Using batch and column experiments with aluminum oxide, carbon tetrachloride and an anionic surfactant, sorption was shown to be highly pH-dependent, with partitioning linearly dependent on concentration and proportional to the adsorbed mass of surfactant. High energy election-beam irradiation is also an emerging technology for removing hazardous organic contaminants from water. To explore the effectiveness of this technique, Rosocha, et al. (Chapter 12) formulated a simple kinetic model for removing TCE and CC1 from water, examining the production, recombination and reaction of free radicals. Simulations indicated that low pulse intensities were more efficient in producing radicals, however, a train of short, high-dose, repetitive pulses could approach the removal efficiency of a continuous dose profile. Therefore, repetitively pulsed accelerators were considered preferable for future applications because of specific machine advantages. 2

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The ubiquitous distribution of pesticides in the USA and throughout the world has focused attention on their environmental and health effects. Pentachlorophenol (PCP) is the second most widely-used pesticide in the USA and, because of its biocidal properties, it has many industrial applications. Therefore, focus on effective methods of conversion and removal from environmental media remains high. Carberry and Lee (Chapter 13) used Fenton's Reageant to enhance degradation potential for PCP through partial chemical oxidation followed by biological oxidation with selected microbial consortia. Chemical oxidation at a level of only 3% tripled the rate of biological conversion and reduced the toxicity index to a level four times less. It was concluded that the mechanism of enhancement was due to a reduction in PCP toxicity and cometabolism of the PCP and partial oxidation products. Pesticides can also be oxidized with ozone, and Hapeman (Chapter 14) studied the aqueous ozonation of s-triazine pesticides and the dependence of conversion product formation structure and abundance on the duration of ozonation. Using chemical methods, HPLC, mass and NMR spectroscopy, a proposed degradation pathway for s-triazines was described, together with a reaction product profile of atrazine. The technique was considered of value in developing methods for triazine residue removalfromground and surface waters. Radioactive and Mixed Waste Management

The storage and long-term management of nuclear wastes remains a difficult challenge, and increased attention is being given to the assessment and maintenance of facilities at existing sites. Reynolds and Babad (Chapter 15) have described the Hanford Site complex and its facilities for storage of radioactive wastes. Of the 177 existing tanks for storage of radioactive wastes, 53 have been identified as having potential safety issues. The monitoring for generation and release of hydrogen from one of the tanks and minimization of theriskof a hydrogen burn are presented, together with steps for mitigation of hydrogen release. The storage challenges at the Hanford complex are more explicitly elucidated by mechanistic studies on the thermal chemistry of simulated aqueous nuclear waste mixtures by Ashby, et al. (Chapter 16). This incisive and detailed study of factors affecting the reaction by which H gas is formed from the degradation product, formaldehyde, and OH" provides a mechanism consistent with results obtained from radiolabelling experiments. Moreover, the amount of hydrogen produced was found to be substantially larger under oxygen than under an argon atmosphere, which has new and important ramifications with regard to mitigation procedures that would introduce Ο into the waste mixture and thereby intensify the rate and concern associated with Η formation. Vitrification is an innovative technology applicable for the immobilization of high-level radioactive isotopes in borosilicate glass. Bannochie, et al. (Chapter 17) present results of bench-scale acid hydrolysis tests for defining factors affecting removal of aromatic carbon from aqueous slurries of Cs-137 and other tetraphenylborates prior to vitrification at the Savannah River Site. Since hydrolysis is performed with formic acid and Cu(II) as a catalyst, the eventual rate of conversion to the primary products of benzene and boric acid is influenced by the need to balance the Cu(II) and total acid ratio, and the presence or absence of oxygen, nitrite, complexing agents and other potential reaction catalysts or inhibitors. Solidification and stabilization of hazardous and radioactive wastes are being advanced as viable management techniques. Darnell (Chapter 18) presents the potential of sulfur polymer cement (SPC) or sulfur polymer cement concrete (SPCC) asfinalwaste forms for such applications. Based on a summary of a series of tests in 2

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5 Hazardous Waste Management: Overview

the USA and abroad, guidance is provided for applications of the technology, including a discussion of advantages and disadvantages in terms of waste type and exposure condition.


Summary

The control and remediation of hazardous and radioactive wastes, and their environmental and health consequences, continue to challenge scientific and engineering ingenuity as environmental regulations become more stringent and industrial productivity continues to accelerate commensurate with the needs and aspirations of a growing consumer population. Therefore, it is appropriate that new and innovative management techniques are sought and developed for application, including emphasis on waste minimization and pollution prevention. Indeed, the transformation of an end-of-thepipe approach to one that prevents pollution and promotes innovation in design and processing, as well as resource conservation and recycle, has shifted much attention to problems involving environmental and health impairment due to past waste management practices. Accordingly, the new emerging technologies in hazardous waste management have become consequences of the challenges of this focus on situations where waste source and environmental setting are more obscure and less explicitly defined. Therefore, it is appropriate to embrace such facets of the challenge, whether related to soils and sediments as a target matrix, waste minimization and ex situ management, or the special characteristics of a segregated waste requiring isolation and/or long-term storage. Each of these broader generic topics is addressed with specific selected examples in this volume of theSERIES,and while definite progress is being made in all cases, additional improvements are necessary, whether in the basic science or technology, or its application in practice. As developments proceed both reactively as a consequence of regulatory inertia, but also proactively and in an anticipatory fashion, a change in protocol will be required, including the development and nurturing offinancialand personnel resources capable of managing and sustaining the technology. Therefore, it is anticipated that these issues will collectively contribute, not only to the substance of continuing symposia in print, but to the overall advancement and transfer of the knowledge needed to sustain progress in hazardous waste management in the future. Literature Cited 1. 2. 3. 4. 5.

Anderson, W. C., Wastech® - Assessing Innovative Waste Treatment Technology. Waste Management, 13, 205-206, 1993. Tedder, D. W. and Pohland, F. G., Eds. Emerging Technologies in Hazardous Waste Management, ACS Symposium Series 422, American Chemical Society, Washington, DC, 1990. Tedder, D. W. and Pohland, F. G., Eds. Emerging Technologies in Hazardous Waste Management II, ACS SymposiumSeries468, American Chemical Society, Washington, DC, 1991. Tedder, D. W. and Pohland, F. G., Eds. Emerging Technologies in Hazardous Waste Management III, ACS SymposiumSERIES518, American Chemical Society, Washington, DC, 1993. Chesnut, D. Α., Characterizing the Altered Zone at Yucca Mountain; The Beginning of a Testing Strategy. Proceedings Third International High-Level Radioactive Waste Management Conference, 1026-1039, American Nuclear Society, Inc., Las Vegas, NV, 1993.


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Eckenfelder, W . W., Jr. and Norris, R . D . , Applicability of Biological Processes for Treatment of Soils. In Tedder, D . W . and Pohland, F . G . , Eds., Emerging Technologies in Hazardous Waste Management III. Chapter 8. pages 138-158, ACS Symposium Series 518, American Chemical Society, Washington, D C , 1993.


R E C E I V E D December 3, 1993


Emerging Technologies for Hazardous Waste Management - ACS

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