Hazardous Industrial Waste Treatment - Chapter 11 potx

Table 2 Properties of Important Explosive Wastes Chemical name 2,4,6-Trinitrotoluene Hexahydro-1,3,5-trinitro-s-triazine, cyclotrimethylenetrinitramine, 1,3,5-trinitro-1,3,5-triazocycloh

Explosive Waste Treatment

J Paul Chen, Shuaiwen Zou, and Simo Olavi Pehkonen

National University of Singapore, Singapore

Yung-Tse Hung

Cleveland State University, Cleveland, Ohio, U.S.A

Lawrence K Wang

Zorex Corporation, Newtonville, New York, U.S.A., and

Lenox Institute of Water Technology, Lenox, Massachusetts, U.S.A

In the early 20th century, more than 60 highly explosive compounds were developed Testing and use of high explosives has extensively contaminated soil, sediments, and water with toxic explosive residues at a large number of government installations The end of the Cold War resulted in a significant surplus of both conventional and nuclear weapons The United States and the former Soviet Union, together with their allies and the People’s Republic of China are destroying large quantities of weapons As a result, a great many high explosives are being released directly and indirectly to the environment These are highly toxic and mutagenic and classified as environmental hazards and priority pollutants by the U.S Environmental Protection Agency (USEPA) [1 – 3]

Large amounts of highly explosive wastes (HEWs) need to be treated The United States, Europe, and the former Soviet Union have produced more than 360,000 tons of HEW per year

It is estimated that 2,4,6-trinitrotoluene (TNT) alone is produced in amounts close to 1,000,000 kg a year It has been well documented that the toxicity of these energetic chemicals can be accumulated in bodies of aquatic organisms and terrestrial species such as earthworms and mammals Under the Intermediate-Range Nuclear Forces Treaty (INF) and Strategic Arms Reduction Treaties, the U.S Department of Defense demilitarization program destroys a significant amount of weapons, which generates large amounts of high explosive contaminated wastewaters that needs to be treated [4 – 6] In this chapter, we will discuss the generation of HEWs, and the respective treatment technologies

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“Explosive waste” normally refers to propellants, explosives, and pyrotechnics (PEP), which belong to the more general category of energetic materials These materials are susceptible to initiation, or self-sustained energy release, when they are present in sufficient quantities and exposed to stimuli (e.g., heat, shock, and friction) Each reacts differently; all will burn, but explosives and propellants can detonate under certain conditions (e.g., confinement) Figure 1 outlines the various categories of energetic materials

Wastewaters containing explosives are produced at military installations carrying out manufacturing, and loading, assembly, and packing (LAP) of munitions, as well as washout

or deactivation/demilitarization operations The LAP generates wastewater from cleanup and washdown operations Deactivation is accomplished by washing out or steaming out the explosives from bombs and shells Explosives contaminated waters are normally subdivided into two categories based on the color of the wastewater:

and

deactivation of munitions involving contact with finished TNT

(XACs) enter the natural subsurfaces from several types of sources:

The wastewater from manufacturing and packing operations has posed the greatest threat

to groundwater In the United States, royal demolition explosives (RDX) is presently the most important military high explosive because TNT is no longer manufactured, although it is a

Figure 1 Categories of energetic materials

widely used military explosive Energetic materials are classified into propellants, explosives,

summarized below

Explosives are commonly classified as primary and secondary based on their susceptibility to initiation Primary explosives such as lead azide and lead styphenate are highly susceptible to initiation; as they are used to ignite secondary explosives, they are referred to as initiating explosives

Secondary explosives include TNT, cyclotrimethylenetrinitroamine or cyclo-1,3,5-trimethylene-2,4,6-trinitramine or royal demolition explosives (RDX or cyclonite), cyclote-tramethylenetetranitramine (cyclo-1,3,5,7-tetramethylene-2,4,6,8-tetranitramine or high melting explosives (HMX), and tetryl They are much more prevalent at military sites than primary explosives As they are formulated to detonate only under specific circumstances, they are used

as main charge or bolstering explosives Secondary explosives can be loosely categorized into melt – pour explosives, which are based on TNT, and plastic-bonded explosives (PBX), which are based on a binder and crystalline explosive such as RDX They can also be classified according to their chemical structure as nitroaromatics such as TNT, and nitramines such as RDX

Trinitrotoluene can have three structural isomers: 2,3,5-TNT, 2,4,6-TNT and 2,4,5-TNT The symmetrical 2,4,6-trinitrotoluene is the most commonly found form and thus in most publications that discuss munitions compounds, the simple name TNT refers to this isomer TNT

is still the most widely used military explosive due to its low melting point of 80.18C, stability, low sensitivity to impact, and relatively safe methods of manufacture RDX, or cyclonite as it is commonly referred to, is an explosive used extensively as a propellant for propelling artillery shells and in projectiles It is used in the above applications because it offers higher energy, higher density, and lower flame temperatures It is often used in binary mixtures with TNT It finds its way into the munition wastewaters during manufacturing and blending operations [3]

The nitro-organics found in the waste streams from army ammunition plants (AAPs), are resistant to aerobic biodegradation and are toxic in nature in addition to being suspected carcinogens These waste streams, if released untreated, would cause serious contamination in natural surface and subsurface systems, thereby affecting the health of humans and may have a detrimental effect on the environment For example, HMX has adverse effects on the central nervous system (CNS) in mammals and has also been classified as a class D carcinogen by the USEPA Therefore, army installations are prohibited from discharging wastewater into the environment prior to meeting a low interim discharge limit of 1 ppm of total nitrobodies The USEPA has ambient criteria of 0.06 mg/L for TNT and 0.3 mg/L for RDX/HMX, and drinking water criteria of 0.049 mg/L for TNT and 0.035 mg/L for RDX/HMX [4 – 7]

Table 1 List of High Explosives

RDX (Cyclo-1,3,5-trimethylene-2,4,6-trinitramine) TNB (Trinitrobenzenes)

Tetryl (N-Methyl-N,2,4,6-tetranitrobenzeneamine) DNB (Dintrobenzenes)

HMX (1,3,5,7-Tetranitro-1,3,5,7-tetraazocyclooctane) AP (Ammonium perchlorate)

Table 2 Properties of Important Explosive Wastes

Chemical name 2,4,6-Trinitrotoluene Hexahydro-1,3,5-trinitro-s-triazine,

cyclotrimethylenetrinitramine, 1,3,5-trinitro-1,3,5-triazocyclohexane, Hexogen, cyclonite, and T4

Octahydro-1,3,5,7-tetranitro-1,3, 5,7-tetrazocine,

cyclotetramethylene-tetramine, and octogen

Chemical formula C7H5N3O6 C3H6N6O6 C4H8N8O8

Molecular weight 227.15 222.26 296.16

Physical property Light yellow or buff crystalline solid;

soluble in alcohol, ether and hot water;

detonates at around 2408C

Colorless polycrystalline material;

soluble in acetone; insoluble in water, alcohol, carbon tetrachloride, and carbon disulfide; slightly soluble in methanol and ether

Colorless polycrystalline material;

similar to replaced RDX but has a higher density and much higher melting point;

highly soluble in dimethylsulfoxide Usage TNT is the most common military

explosive because of its ease of manufacture and its suitability for melt loading, either as the pure explosive or as binary mixtures with RDX or HMX

RDX is used extensively as the base charge in detonators Its most common uses are as an ingredient in castable TNT-based binary explosives and as the primary ingredient in plastic-bonded explosives Mixtures are used as the explosives fill in almost all types of munitions

Because of its high density, HMX has replaced RDX in explosive applications for which energy and volume are important It is used in castable TNT-based binary explosives, as the main ingredient in high-performance plastic-bonded explosives, and in high-performance solid propellants Hazard Flammable, dangerous fire risk,

moderate explosion risk Toxic by ingestion, inhalation, and skin absorption

High explosive, easily initiated by mercury fulminate Toxic by inhalation and skin contact 1.5 times as powerful

as TNT

High explosive; toxic inhalation and skin contact

11.2.3 Propellants

Propellants include both rocket and gun propellants Most rocket propellants are either based on: (a) a rubber binder, ammonium perchlorate (AP) oxidizer, and a powdered aluminum (Al) fuel; or (b) a nitrate ester, usually nitroglycerine (NG), nitrocellulose (NC), HMX, AP, or polymer-bound low NC If a binder is used, it is normally an isocyanate-cured polyester or polyether Some propellants contain combustion modifiers, such as lead oxide

Gun propellants are usually single base (NC), double base (NC and NG), or triple base [NC, NG, and nitroguanidine (NQ)] Some of the newer, lower vulnerability gun propellants contain binders and crystalline explosives and are similar to PBX

Pyrotechnics include illuminating flares, signaling flares, colored and white smoke generators, tracers, incendiary delays, fuses, and photo-flash compounds Pyrotechnics are composed of an inorganic oxidizer and metal powder in a binder Illuminating flares contain sodium nitrate, magnesium, and a binder Signaling flares contain barium, strontium, or other metal nitrates

Owing to the nature of explosive wastes, strict safety precautions must be taken at sites contaminated with explosive wastes to avoid initiation The U.S Army Environmental Center (USAEC) has developed protocols for identifying sites that require explosives safety precautions and for handling explosives wastes at these sites

With the protocol, people can determine quickly and inexpensively whether materials are susceptible to initiation and propagation by analyzing the composition of samples from the site According to the deflagration-to-detonation test, soils containing more than 12% secondary explosives by weight are susceptible to initiation by flame; according to the shock gap test, soils containing more than 15% secondary explosives by weight are susceptible to initiation by shock

As a conservative limit, USAEC considers all soils containing more than 10% secondary explosives by weight to be susceptible to initiation and propagation and exercises a number of safety precautions when sampling and treating these soils Sampling and treatment precautions are exercised when handling soils that contain even minute quantities of primary explosives Work, sampling, and health and safety plans for explosives waste sites should incorporate safety provisions that normally would not be included in work and sampling plans for other sites The most important safety precaution is to minimize exposure, which involves minimizing the number of workers exposed to hazardous situations, the duration of exposure, and the degree of hazard

Based on treatment location, there are in situ and ex situ treatments Each treatment includes physical, chemical, and biological processes, which are discussed in Sections 11.4 and 11.5 There are many technologies available in the market for remediation of contaminated sites We can classify them into three categories They can be used separately and in most of cases in conjunction to remediate explosive waste contaminated sites They are: (a) alteration of contaminants; (b) separation of contaminants from environmental media; and (c) immobilization

of contaminants As no single technology can remediate an entire site, several treatment technologies must usually be combined for cost-effective treatment

Alteration of contaminant is usually referred to as destruction of the contaminant in most environmental engineering text books Strictly speaking, the term alteration is more suitable, because treatment technologies in most cases are not able to eliminate the contaminants There is always a question of treatment efficiency In addition, a series of byproducts may be produced during the treatment Destruction of contaminant can be fulfilled by altering the chemical structures of the contaminants by physical, biological, and chemical treatment approaches These destruction technologies can be applied in situ or ex situ to contaminated media Separation of contaminants from environmental media includes physical and chemical processes The separated pollutants are eventually transported to treatment stations for their final destruction This process is applied to contaminated sites Typical examples are soil washing and pump-and-treat technologies The technologies and the possible integration must be carefully selected based on the natural characteristics of water, soil, and sediment in order to achieve the most cost-effective treatment For example, more air than water can be moved through soil Therefore, for a volatile contaminant in soil that is relatively insoluble in water, soil vapor extraction would be more efficient than soil flushing or washing

Immobilization of contaminants includes stabilization, solidification, and containment technologies, such as placement in a secure landfill or construction of slurry walls As no immobilization technology is permanently effective, monitoring and maintenance are important

to prevent secondary pollution, such as leaching

In in situ treatment or disposal, contaminated surface water, groundwater, soil, and sediment are treated directly in contaminated sites This method does not require movement of contaminated materials The main advantage is significant cost savings; however, it generally requires longer time periods In addition, there is less certainty about the uniformity of treatment because of the variability in water and soil characteristics and because the efficacy of the process is more difficult to verify Like treatment technologies for other contaminants, physical, physico-chemical, and biological processes are available

In Situ Physical and Physicochemical Treatment Physical and physicochemical treatments use the physical and chemical properties of the contaminants or the contaminated medium to destroy and separate the contamination For con-taminated surface and subsurface waters, and leachate, the following technologies can be used: adsorption, membrane separation, air sparging, bioslurping, chemical oxidation, directional wells, dual phase extraction, thermal treatment, hydrofracturing enhancements, in-well air stripping, and passive/reactive treatment walls For contaminated soil, sediment, bedrock, and sludge, the available technologies include: chemical oxidation, electrokinetic separation, fracturing, soil flushing, soil vapor extraction, solidification/stabilization, and thermal treatment [3,8–13] Physical and physicochemical treatment technologies are normally costly even though removal of contaminants can be completed in short time periods in comparison with biological treatment Residuals after treatment will require further disposal, which will add to the total project costs

In Situ Biological Treatment

In in situ bioremediation processes, microorganisms are stimulated to grow and use the organic contaminants (e.g., TNT) as a food and energy source In order to facilitate the processes, a

favorable environment for the microorganisms must be provided and maintained This can

be done by providing sufficient oxygen, nutrients, and moisture, and controlling the temperature and pH Sometimes, microorganisms adapted for degradation of the specific contaminants are added to enhance the process

Bioventing, enhanced bioremediation, and phytoremediation are commonly used to treat contaminants in soil, sediment, bedrock, and sludge, while enhanced bioremediation, monitored natural attenuation, and phytoremediation are employed to remediate contaminated surface and subsurface waters [3] These bioremediation techniques have been successfully used in the remediation of various contaminated sites; they have very limited effect on inorganic contaminants Compared to physicochemical treatments, the operating costs for biological treatments are typically lower The residuals after biological treatments are normally less harmful and thus no further treatment or disposal is required However, in a few cases, the biological residuals could

be more toxic and may be mobilized in natural subsurface waters if no careful control is performed If it occurs, in situ bioremediation must be performed above a low permeability soil layer in order to avoid further groundwater pollution In addition, a good groundwater monitoring system must be installed in the treatment site

In ex situ treatment or disposal, contaminated surface water, groundwater, soil, and sediment are first transported from the contaminated sites and subsequently treated by various processes Unlike in situ treatment, ex situ treatment requires shorter time periods Ex situ remediation can

be easily monitored and controlled, which is much better than in situ treatment However, it requires transportation of contaminated substances, such as pumping of groundwater, which can lead to significantly higher operating costs Like treatment technologies for other contaminants, physical, physico-chemical, and biological processes are available

Ex Situ Physical and Physicochemical Treatment

Ex situ physical and physicochemical treatment processes destroy, separate, or concentrate contaminants based on the physical properties of the contaminants or the contaminated medium For contaminated soil, sediment, bedrock, and sludge, chemical extraction, chemical reduction/oxidation, dehalogenation, soil washing, solidification/stabilization, hot-gas decon-tamination, incineration, open burn/open detonation, pyrolysis, thermal desorption, and landfill cap can be used Contaminated groundwater, surface water, and leachate can be remediated

by adsorption, advanced oxidation processes, air stripping, coagulation, and flocculation Among the above technologies, advanced oxidation processes (e.g., UV oxidation) and thermal treatment processes (e.g., incineration) are destruction technologies; all other technologies are separation technologies, which either separate or concentrate pollutants

Ex situ physical and physicochemical remediation can be completed in shorter time periods than biological treatment Treatment residuals from separation techniques will require treatment or disposal, which will add to the total project costs and may require permits For example, adsorption can remove TNT species from aqueous solutions The water after treatment becomes less contaminated; however, further disposal of TNT adsorbed chemically onto activated carbons is problematic

Ex Situ Biological Treatment

In ex situ biological treatment, wastewater, soil, and sediment are first moved to treatment stations and treated biologically For soil, sediment, bedrock, and sludge, biopiles, composting,

landfarming, slurry phase biological treatment can be used; natural subsurface and surface waters can be remediated by bioreactors and constructed wetlands A series of bioreactors have been widely studied and applied [12] If based on oxygen environments, there are aerobic and anaerobic treatments; if based on reactor configuration, there are continuously stirred tank reactors (CSTR), plug-flow reactors (PFR), fixed-bed reactors (FBR), and fluidized-bed reactors

Ex situ biological remediation generally requires shorter time periods than in situ remediation There is more certainty about the uniformity of treatment because of the ability to monitor and manage the treatment However, ex situ treatment requires transportation of contaminated water, soil, and sediment (e.g., pumping of groundwater), leading to increased costs and inconvenience in management Other properties of ex situ biological remediation are similar to those of in situ treatment as discussed previously

The most common method for transformation of nitro-aromatics at present is incineration However, while incineration has been demonstrated to be an effective technology, issues such as safety, noise, air emissions, costs, regulatory requirements, etc., have motivated research in physical and physico-chemical treatment technologies Several commonly used technologies are summarized below

Oxidative processes have been used for the treatment of wastewater contaminated with organic compounds Direct oxidation of aqueous solutions containing organic contaminants can be carried out under a variety of conditions Catalytic oxidation of aromatics contaminated waste-water has shown that the ring cleavage step is very fast at moderate pressures and temperatures Oxidation may also be carried out by enervation of hydroxyl radicals in sufficient quantities by

oxidation processes (AOP)

Hydrogen peroxide is a relatively inexpensive and readily available chemical Photolysis

following reaction:

The excited hydrogen peroxide molecule is cleaved into two hydroxyl radicals, which initiate the chain decomposition:

†

At the same time, these radicals initiate the degradation process by abstracting a hydrogen atom from a high explosives molecule:

Direct ultraviolet photolysis and a combination of ultraviolet photolysis with hydrogen peroxide oxidation have been used to treat TNT, RDX, and HMX wastewater [13] With a

low-pressure mercury UV lamp, more than 70% of RDX/HMX can be oxidized in about

10 min Complete oxidation is achieved in 25 min When ultraviolet oxidation is applied, 70% degradation of TNT is achieved; however, the process takes a rather long period due to the complicated structure of TNT

Hydrogen peroxide in combination with UV radiation does not significantly enhance degradation of RDX/HMX However, it greatly improves the photolytic degradation of TNT

on the UV photolytic process [13]

The adsorption of TNT and other explosive wastes on activated carbon has been one of the most common treatment technologies used by military ammunition plants This technology is effective at removing a wide variety of explosive contaminants from water, but is nondestructive and expensive to operate Moreover, after the carbon is exhausted, it has to be incinerated or disposed of into a hazardous waste disposal site The disposal of used carbon is very costly Batch reactors and fixed-bed reactors can be used for the remediation The batch reactor is flexible to operate; the fixed-bed reactor is more convenient to use The adsorption capacity and treatment efficiency are dependent on physical and chemical properties of carbon, solution chemistry, as well as operating conditions [3,8,9,12,14,15]

A successful example was illustrated in McAlester Army Ammunition Plant (McAAP) [7] A process for pink water treatment includes storage tanks, coagulation/flocculation, settling tanks, sand filters, and activated carbon adsorption columns When the concentration approaches the pretreatment discharge limit of 1 mg/L TNT, the carbon columns are replaced [7] Heilmann and coworkers [5] used a combination of adsorption and alkaline hydrolysis to treat HMX and other explosive waste The waste first enters the adsorption reactor, where the contaminants are adsorbed The spent carbons are then sent to alkaline hydrolysis reactors for desorption This system provides a better treatment result and can provide a higher degree of flexibility in operation

Biological remediation of explosive wastes mainly occurs via compound oxidation and reduction Oxidation takes place when oxygen is the reactant and oxygenase or peroxidase enzymes act as catalysts to cleave the aromatic ring Reduction is the more common mechanism for nitroaromatics and occurs when the nitroaromatic compound is reduced to arylamines via hydrolytic deamination, acetylation, reductive deamination, and finally cyclization

It was found that the Pseudomonas species degraded both DNT and TNT aerobically with supplemental glucose as a carbon source [16,17] Reduction of the nitro groups took place only at the para position and proceeded through hydroxylamino-nitrotoluene to aminonitrotoluene Haidour and Ramos [18] observed 2-hydroxylamino-4,6-dinitrotoluene,4-hydroxylamino-2,6-dinitrotoluene, 4-amino-2,6-2-hydroxylamino-4,6-dinitrotoluene,4-hydroxylamino-2,6-dinitrotoluene, 2-amino-4,6-2-hydroxylamino-4,6-dinitrotoluene,4-hydroxylamino-2,6-dinitrotoluene, and 2,4-diamino-nitro-toluene as the products of TNT degradation with Pseudomonas sp Boopathy et al [19] reported the anaerobic degradation of TNT under different electron accepting conditions by a soil bacterial consortium Hughes et al [20] demonstrated the ability of Clostridium acetobutylicum to reduce TNT to 2,4-dihydroxylamino-6-nitrotoluene and then to phenol products via the Bamberger

Biotransformation of RDX has been observed by a number of researchers Young et al [21] found a bacterial consortium in horse manure capable of degrading RDX at the rate of 0.022 L/g cells per hour Most of the research in the biological degradation of RDX has been carried out under anaerobic conditions

Kitts et al [22] isolated three different genera of bacteria, which were able to degrade RDX The most effective degrader of these three isolates was identified as Morganella morganii One pathway for the biotransformation of RDX is a stepwise reduction of each of three nitro groups in RDX to form nitroso groups, as shown in Figure 3 [22,23] Detail of site remediation and ground water decontamination technologies are presented in another chapter by Wang [27]

As with other organics, biodegradation of explosive wastes is influenced by temperature, oxygen supply, nutrient supply, pH, the availability of the contaminant to the microorganism, the concentration of the wastes, and the presence of substances toxic to the microorganisms (e.g., Figure 2 Pathway of TNT transformation observed in Clostridium acetobutylicum crude cell extracts

Figure 3 Stepwise reduction of RDX through reduction of nitroso groups