U.S. patent application number 10/097089 was filed with the patent office on 2003-09-18 for process and system for treating waste from the production of energetics.
Invention is credited to Cha, Daniel K., Chiu, Pei C., Kim, Byung Joon, Oh, Seok-Young.
Application Number | 20030173306 10/097089 |
Document ID | / |
Family ID | 28039114 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030173306 |
Kind Code |
A1 |
Cha, Daniel K. ; et
al. |
September 18, 2003 |
Process and system for treating waste from the production of
energetics
Abstract
A waste stream from energetics processing is treated using a
pre-filter having media, preferably sand, and a metal that has a
reducing potential, preferably elemental iron (Fe.sup.0). The
pre-filter is connected to a zero-valent metal column reactor. The
waste stream is pumped through the pre-filter to trap solids and
deoxygenate it, then enters the reactor and is subjected to a
reducing process. Most of the Fe.sup.0 is transformed to the
ferrous ion (Fe.sup.+2), added to the resultant product, and fed to
a continuous stirred tank reactor (CSTR) in which Fenton oxidation
occurs. This product is then sent to a sedimentation tank and
pH-neutralized using a strong base such as sodium hydroxide (NaOH).
The aqueous portion is drawn off and the sludge pumped from the
sedimentation tank. Both tanks are monitored and controlled to
optimize required additives, while monitoring of pressure drop
across the pre-filter and column reactor establishes replacement
requirements.
Inventors: |
Cha, Daniel K.; (Newark,
DE) ; Chiu, Pei C.; (Hockessin, DE) ; Oh,
Seok-Young; (Newark, DE) ; Kim, Byung Joon;
(Champaign, IL) |
Correspondence
Address: |
HUMPHREYS ENGINEER CENTER SUPPORT ACTIVITY
ATTN: CEHEC-OC
7701 TELEGRAPH ROAD
ALEXANDRIA
VA
22315-3860
US
|
Family ID: |
28039114 |
Appl. No.: |
10/097089 |
Filed: |
March 14, 2002 |
Current U.S.
Class: |
210/743 ;
210/202; 210/206; 210/259; 210/757; 210/758; 210/804; 210/96.1 |
Current CPC
Class: |
C02F 1/001 20130101;
C02F 2305/026 20130101; B09C 1/002 20130101; C02F 1/008 20130101;
C02F 1/722 20130101; C02F 9/00 20130101; C02F 1/66 20130101; Y10S
588/90 20130101; C02F 1/705 20130101; B09C 1/08 20130101; C02F 1/70
20130101; Y10S 210/909 20130101; C02F 1/72 20130101; C02F 1/725
20130101; C02F 2101/003 20130101 |
Class at
Publication: |
210/743 ;
210/757; 210/758; 210/804; 210/259; 210/202; 210/206; 210/96.1 |
International
Class: |
C02F 001/70 |
Goverment Interests
[0001] The invention described herein may be manufactured and used
by or for the Government of the United States of America for
governmental purposes without the payment of any royalties thereon
or therefor.
Claims
We claim:
1. A system for treating a waste stream that may contain suspended
and colloidal solids, comprising: a pre-filter containing a
zero-valent metal and media suitable for filtering at least some of
said solids from said waste stream; a zero-valent metal column
reactor operably connected to said pre-filter, wherein after said
waste stream is treated therein and a first treated waste stream is
output; a first vessel in which initial contents include an
oxidizer to be combined with said first treated waste stream,
wherein said contents of said first vessel are adjusted to optimize
the amount of said oxidizer and a metal ion resultant from
processing said waste stream with said zero-valent metal in said
zero-valent metal column reactor, wherein said contents of said
first vessel are further adjusted to optimize the pH of said
contents of said first vessel, and wherein said contents of said
first vessel are stirred as part of treating said contents prior to
output as a second treated waste stream; and a second vessel for
accepting said second treated waste stream as at least part of its
contents, wherein said second treated waste stream is
pH-neutralized, wherein said contents of said second vessel are
further adjusted to optimize pH of said contents of said second
vessel, and wherein said second treated waste stream is permitted
to settle prior to drawing off at least one final product suitable
for reuse.
2. The system of claim 1 in which said waste stream results from
operations involved with the handling of energetic materials.
3. The system of claim 2 in which said energetic materials are
composed of constituents selected from the group consisting
essentially of TNT, RDX, HMX, nitroglycerin (NG), and constituents
and combinations thereof.
4. The system of claim 1 in which said filter media is a naturally
occurring material
5. The system of claim 4 in which said naturally occurring material
is sand.
6. The system of claim 1 in which said filter media is manmade.
7. The system of claim 1 in which said metal is selected from the
group consisting of: iron, tin, aluminum, zinc, magnesium, nickel,
palladium, platinum, and combinations thereof.
8. The system of claim 7 in which said metal is predominantly
elemental iron (Fe.sup.0), wherein, upon reaction of said elemental
iron with said waste stream, at least part of said elemental iron
is converted to the ferrous ion (Fe.sup.+2) and combined with said
first treated waste stream.
9. The system of claim 1 in which said pre-filter is a replaceable
cartridge.
10. The system of claim 1 in which said zero-valent metal column
reactor is vented to reduce accumulation of gasses that may result
from reactions therein.
11. The system of claim 1 further comprising a mix control module,
wherein automated control of the characteristics of said contents
of said first and second vessels is accomplished via said mix
control module, wherein said mix control module at least monitors
and controls the pH of each of said first and second vessels, and
wherein said mix control module controls the amount of said metal
ion and said oxidizer in said first vessel.
12. The system of claim 1 further comprising an impeller mixer for
use in said first vessel.
13. The system of claim 1 in which said first vessel is a
continuously stirred tank reactor (CSTR).
14. The system of claim 1 in which said oxidizer is hydrogen
peroxide (H.sub.2O.sub.2).
15. The system of claim 1 in which said second vessel is a
pH-neutralizing and sedimentation tank, wherein the pH of said
second treated waste stream is neutralized within the range of
6.0-8.0 by adding a base, and wherein any said suspended solids
within said second treated waste stream are permitted to settle,
forming sludge.
16. The system of claim 15 in which said base comprises at least
some sodium hydroxide (NaOH).
17. The system of claim 15 further comprising at least one sludge
pump for emptying said sedimentation tank of sludge.
18. The system of claim 1 in which said first vessel is positioned
lower than said zero-valent metal column reactor thus enabling
gravity feed of said first treated waste stream from said
zero-valent metal column reactor, and further positioning said
second vessel at a position lower than said first vessel thus
enabling gravity feeding of said second treated waste stream to
said second vessel.
19. A method for treating a waste stream containing at least some
highly oxidized suspended and colloidal solids, comprising:
physically filtering at least some of said solids in a pre-filter;
establishing a reducing environment for removing oxygen via use of
at least one zero-valent metal as a reducing agent, wherein the
output of said physical filtering and reducing environment is a
first treated waste stream; subjecting said first treated waste
stream to a Fenton oxidation reaction in a first vessel, wherein
said Fenton oxidation reaction is monitored and controlled, and
wherein the output of said Fenton oxidation reaction is a second
treated waste stream; and pH-neutralizing said second treated waste
stream in a second vessel prior to reclaiming at least a portion of
said second output waste stream's constituents; wherein said second
waste stream is permitted to settle in a tank to precipitate any
remaining said solids in sludge.
20. The method of claim 19 in which said solids comprise at least
one energetic material.
21. The method of claim 20 in which said energetic material is
selected from the group consisting of: TNT, RDX, HMX, nitroglycerin
(NG), and constituents and combinations thereof.
22. The method of claim 19 in which said metal is selected from the
group consisting of: iron, tin, aluminum, zinc, magnesium,
palladium, nickel, platinum, and combinations thereof.
23. The method of claim 22 in which said metal is predominantly
elemental iron (Fe.sup.0), wherein, upon reaction of said elemental
iron with said waste stream, at least part of said elemental iron
is converted to the ferrous ion (Fe.sup.+2) and combined with said
first treated waste stream.
24. The method of claim 19 in which said pH neutralizing is
accomplished by adding a base.
25. The method of claim 24 in which said base is at least some
sodium hydroxide (NaOH).
26. The method of claim 19 in which said sludge is pumped from said
tank.
27. The method of claim 19 in which at least one of said reclaimed
constituents is water suitable for reuse.
28. The method of claim 19 in which said first vessel is positioned
lower than said zero-valent metal column reactor thus enabling
gravity feed of said first treated waste stream from said first
vessel, and further providing said second vessel at a position
lower than said first vessel thus enabling gravity feeding of said
second treated waste stream to said second vessel.
29. The method of claim 19 further comprising optimizing
performance of said system by monitoring and controlling: pH of
each of said first and second vessels; amount of said oxidizer in
said first vessel; and amount of said metal ion in said first
vessel.
30. A processing plant that incorporates a system for remediating a
waste stream containing at least some suspended and colloidal
solids, the system comprising: a pre-filter containing a
zero-valent metal and media suitable for filtering at least some of
said solids from said waste stream; a zero-valent metal column
reactor operably connected to said pre-filter, wherein after said
waste stream is treated therein and a first treated waste stream is
output; a first vessel in which initial contents include an
oxidizer to be combined with said first treated waste stream,
wherein said contents of said first vessel are adjusted to optimize
the amount of said oxidizer and a metal ion resultant from
processing said waste stream with said zero-valent metal in said
zero-valent metal column reactor, wherein said contents of said
first vessel are further adjusted to optimize the pH of said
contents of said first vessel, and wherein said contents of said
first vessel are stirred as part of treating said contents prior to
output as a second treated waste stream; and a second vessel for
accepting said second treated waste stream as at least part of its
contents, wherein said second treated waste stream is
pH-neutralized, wherein said contents of said second vessel are
further adjusted to optimize pH of said contents of said second
vessel, and wherein said second treated waste stream is permitted
to settle prior to drawing off at least one final product suitable
for reuse.
Description
BACKGROUND
[0002] Carbon sorption is the conventional method for treating
munitions manufacturing waste containing explosive compounds such
as 2,4,6 trinitrotoluene (TNT), trimethylenetrinitronitramine
(RDX), and tetramethylenetetranitramine (HMX). The liquid form of
this waste is termed "pinkwater." Typically using granulated
activated carbon (GAC) filters, the waste is passed through the GAC
with the explosive constituents removed by sorbing onto the carbon.
This method is non-destructive, i.e., the sorbed molecules of
contaminant remain intact chemically. Thus, the process generates
spent contaminant-laden GAC filters that require further treatment,
to include regeneration of the carbon filter for re-use or safe
disposal at the end of the filter's useful life. The U.S. military
and its contractors generate substantial amount of spent GAC from
pinkwater treatment and would save considerable resources by
replacing the GAC filtration process with a process that actually
destroys or neutralizes energetic contaminants.
[0003] Thus, it is a given that conventional sorbing processes have
several disadvantages that are immutable. Further, direct oxidation
by chemical or biological processes is not as efficient as
sequential reduction/oxidation processes due to the relatively
oxidized nature of energetics.
[0004] It is known to use the Fenton reaction for oxidizing
hydrocarbons to their constituents. Typically, the oxidizing agent
used in the reaction is hydrogen peroxide, H.sub.2O.sub.2. Mixed
with a metallic salt, H.sub.2O.sub.2 produces a free radical that
breaks the bonds of a hydrocarbon molecule in an exothermic
reaction. This results in a low-free-energy-state generally
associated with the production of carbon dioxide (CO.sub.2) and
water.
[0005] Elemental iron (Fe.sup.0) oxidizes to Fe.sup.+2 in the
presence of oxygen. This removes most of the oxygen from the
solution and contributes to the solution attaining an anaerobic
state.
[0006] Zero-valent iron has been used in permeable reactive
barriers (PRBs), an emerging technology that has been applied in
recent years to remediate groundwater contaminated with a wide
range of pollutants. Permeable Reactive Barrier Technologies for
Contaminant Remediation, EPA/600/R-98/125, U.S. EPA, Sep. 1998;
Field Applications of In Situ Remediation Technologies: Permeable
Reactive Barriers, EPA/542/R-99/002, U.S. EPA, June 1999. Iron is a
strong reducing agent (E.sup.0=-0.44V) and can reduce relatively
oxidized pollutants, including chlorinated solvents, metals,
nitrate, and radionuclides. U.S. EPA (Sep. 1998).
[0007] Researchers have shown that iron can reduce TNT, RDX, and
HMX at high rates. Hundal, L. S., et al., Removal of TNT and RDX
from Water and Soil Using Iron Metal, Environmental Pollution, 97:
55-64, 1997. Further, the Fenton reaction is an established process
applied to treat a wide variety of pollutants in hazardous wastes,
wastewater, and groundwater. Eckenfelder, W. W., The Role of
Chemical Oxidation in Waste Treatment Processes, Proceedings of the
First International Symposium on Chemical Oxidation, Technomic
Publishing Co., Inc., Lancaster, Pa., pp. 1-10, 1992; Huang, C. P.
et al., Advanced Chemical Oxidation: Its Present Role and Potential
Future in Hazardous Waste Treatment, Waste Management, 16: 361-377,
1993.
[0008] The well-known Fenton reaction has been used in a number of
recent patents dealing with environmental remediation. For example,
for in-situ subterranean treatment of contaminated ground water or
soil, the following employ the Fenton reaction as at least a part
of their process: U.S. Pat. No. 6,206,098, In situ Water and Soil
Remediation Method and System, to Cooper et al., Mar. 27, 2001
using a catalyst prior to injection of an oxidizer to initiate the
Fenton reaction; U.S. Pat. No. 5,967,230, In situ Water and Soil
Remediation Method and System, to Cooper et al., Oct. 19, 1999; and
U.S. Pat. No. 5,611,642, Remediation Apparatus and Method for
Organic Contamination in Soil and Groundwater, to Wilson, Mar. 18,
1997, describing a subterranean system for implementing the Fenton
reaction.
[0009] U.S. Pat. No. 5,789,649, Method for Remediating Contaminated
Soils, to Batchelor, et al., Aug. 4, 1998, describes the use of
zero-valent iron and a catalytic metal to degrade chlorinated
compound contaminated soil. U.S. Pat. Nos. 5,611,936, 5,616,253,
Apr. 1, 1997; and 5,759,389, Jun. 2, 1998, all entitled
Dechlorination of TCE with Palladized Iron, all to Fernando, et
al., describe a method to de-chlorinate TCE with elemental iron
having a palladium coating.
[0010] Zero-valent iron is used for at least part of the
remediation process in establishing subterranean permeable reactive
barriers as described in U.S. Pat. No. 5,733,067, Method and System
for Bioremediation of Contaminated Soil Using Inoculated Support
Spheres, to Hunt, et al., Mar. 31, 1998; U.S. Pat. Nos., 5,833,388,
Nov. 10, 1998, and 5,975,800, Nov. 2,1999, both entitled Method for
Directing Groundwater Flow and Treating Groundwater In Situ, both
to Edwards and Dick; U.S. Pat. No. 5,857,810, In Situ Chemical
Barrier and Method of Making, to Cantrell and Kaplan Jan. 12, 1999;
and U.S. Pat. No. 6,207,114, Reactive Material Placement Technique
for Groundwater Treatment, to Quinn, et al., Mar. 27, 2001.
[0011] Zero-valent iron powder has been used for in-situ
decontamination of halocarbons and metals more noble than iron as
described in U.S. Pat. No. 5,975,798, In Situ Decontamination of
Subsurface Waste Using Distributed Iron Powder, to Liskowitz et
al., Nov. 2, 1999. U.S. Pat. No. 6,132,623, Immobilization of
Inorganic Arsenic Species Using Iron, to Nikolaidis, et al., Oct.
17, 2000, describes the use of zero-valent iron to immobilize
inorganic arsenic species. U.S. Pat. No. 5,783,088, Method of
Removing Oxidized Contaminants from Water, to Amonette, et al.,
Jul. 21, 1998, describes treatment of oxidized contaminants using a
layered aluminosilicate incorporating Fe (II).
[0012] U.S. Pat. No. 5,538,636, Process for Chemically Oxidizing
Highly Concentrated Waste Waters, to Gnann et al., Jul. 23, 1996,
uses the Fenton reaction together with electrolysis and multiple
steps of neutralization to purify wastewater and address problems
associated with the sludge resulting therefrom.
SUMMARY
[0013] The process provided by a preferred embodiment of the
present invention transforms the energetic compounds in waste
associated with munitions production and de-commissioning. It
eliminates the need for subsequent treatment or re-generation with
attendant concerns of possible secondary contamination. The process
involves at least one pre-filtration and two sequential reduction
and oxidation reactions and a post-reaction neutralization process
to break down energetics to innocuous end products such as carbon
dioxide, water, and environmentally benign products precipitated in
a sludge.
[0014] The two-step treatment process combines two known treatment
technologies: zero-valent metal reduction and Fenton oxidation. It
also provides a final "polishing" step in which the acid pH of the
mixture resulting from the Fenton reaction is neutralized and
sediment settled out of the aqueous mixture.
[0015] It capitalizes on the advantages of each of the individual
reduction and oxidation reactions and the resulting synergism of
their serial combination. The neutralization post-treatment step
enables re-use of the water by-product and stabilizes any resulting
precipitated sludge.
[0016] The system uses a pre-filter containing filter media and a
zero-valent metal, a first vessel for conducting the Fenton
oxidation, and a second vessel for pH-neutralizing the treated
waste and allowing it to settle prior to drawing off water for
re-use and pumping any resultant sludge for further disposition.
The system is designed to handle those highly oxidized waste
streams that would not ordinarily lend themselves to Fenton
oxidation, such as those containing energetics, in particular TNT,
RDX, HMX, and combinations thereof.
[0017] The pre-filter system may use natural material as filter
media such as sand or diatomaceous earth or manmade material such
as polystyrene particles. Although elemental iron (Fe.sup.0) is the
most cost-effective and efficient to use, metals such as tin,
aluminum, zinc, magnesium, nickel, palladium, platinum, and
combinations thereof may be used with the filter media. Upon
reaction of the elemental iron with the waste stream, at least part
of it is converted to the ferrous ion (Fe.sup.+2) and combined with
the filtered and now initially treated waste stream. The iron and
sand may be incorporated in a replaceable vented cartridge, the
venting providing for safely dumping accumulating gases, such as
hydrogen.
[0018] The system may also use a mix control module to facilitate
automated control of the mix within the Fenton oxidation reactor
and the settling tank. The mix control module monitors and controls
the pH of each of the reactor and the settling tank as well as the
amount of the oxidizer, typically hydrogen peroxide
(H.sub.2O.sub.2), and metal ion, typically the ferrous ion
Fe.sup.+2, in the Fenton reactor. A preferred reactor would be of
the continuous stirred tank reactor (CSTR) type. Alternatively, the
Fenton reactor could be a tank provided with an impeller mixer.
[0019] For the settlement tank, pH is neutralized to within the
range of 6.0-8.0 by adding a base, such as NaOH, and suspended
solids are permitted to settle, forming sludge. A sludge pump is
provided for emptying the settling tank periodically as needed.
[0020] In a preferred embodiment, the Fenton reactor is positioned
lower than the zero-valent reactor thus enabling gravity feed of
the filtered and reduced waste stream from the zero-valent reactor
to the Fenton reactor. Likewise the settling tank is positioned
lower than the Fenton reactor thus enabling gravity feeding of the
contents of the Fenton reactor to the settling tank. The integrated
use of a preferred embodiment of the present invention in the
processing line of a manufacturing plant is envisioned.
[0021] Also provided is a method for filtering and deoxygenating a
waste stream containing suspended and colloidal highly oxidized
solids. The method comprises:
[0022] physically filtering the waste stream while establishing a
reducing environment via use of zero-valent metal as part of the
filtering;
[0023] subjecting the filtered waste stream to zero-valent metal
reduction in a zero-valent metal column reactor;
[0024] subjecting the product resultant from the zero-valent column
to a Fenton oxidation reaction in a Fenton reactor; and
[0025] pH-neutralizing the output of the Fenton reactor in a
sedimentation tank.
[0026] The process permits reclaiming most of the aqueous portion
of a waste stream's constituents and renders any sludge benign and
suitable for possible re-use or safe disposal. The process further
provides for automated monitoring and control of both the Fenton
reactor and the settling tank.
[0027] Advantages of a preferred embodiment of the present
invention include:
[0028] uses low-cost scrap metal as the zero-valent metal,
typically scrap iron;
[0029] filters and treats both liquids, such as pinkwater and
solids, such as the constituents of TNT, RDX and HMX;
[0030] provides for venting Hydrogen gas at the top of the
zero-valent reactor;
[0031] provides a pH monitoring and control system to optimize the
Fenton reaction;
[0032] treats energetic compounds in a controlled reactor;
[0033] eliminates the need for GAC and concomitant regeneration and
solid waste disposal;
[0034] presents a small footprint when compared to conventional
waste processors;
[0035] suitable for use as a mobile system, to include
trailer-mounting;
[0036] eliminates a complex environmental monitoring system needed
for both the process and resultant products (sludge, CO.sub.2, and
clean water); and
[0037] achieves lower overall system capital and maintenance costs;
and
[0038] achieves lower cost of final by-product disposal.
[0039] monitors the process easier and at less cost; and
[0040] requires a low skill level for system operation.
[0041] Compared to presently used methods, a preferred embodiment
of the present invention replaces traditional GAC filtration while
reducing the need for subsequent processing and regeneration of the
GAC.
BRIEF DESCRIPTION OF DRAWINGS
[0042] FIG. 1 is a schematic of a system embodying a preferred
embodiment of the invention, presenting the sequential zero-valent
metal reduction and Fenton oxidation process.
[0043] FIG. 2 is a graph presenting the results of TNT reduction
with zero-valent iron.
[0044] FIG. 3 is a graph presenting the results of RDX reduction
with zero-valent iron.
[0045] FIG. 4 is a graph presenting the results of HMX reduction
with zero-valent iron.
[0046] FIG. 5 presents the relationship for estimated
concentrations of TNT vs. zero-valent metal column reactor length
at various flow rates using the design equation in which the rate
constant, k, is 0.0285 s.sup.-1, the column inside diameter (ID) is
2.5 cm, and the porosity is 0.66.
[0047] FIG. 6 presents the relationship for estimated
concentrations of RDX vs. zero-valent metal column reactor length
at various flow rates using the design equation in which the rate
constant, k, is 0.0185 s.sup.-1, the column ID is 2.5 cm, and the
porosity is 0.66.
DETAILED DESCRIPTION
[0048] A preferred embodiment of the present invention incorporates
pre-filtration and two reduction/oxidation reaction processes
seriatim. Pre-filtration employs a filter media, such as a fine
sand and a zero-valent metal, to filter solids and de-oxygenate the
waste stream. The first process involves the use of a metal having
an inherent reducing potential, typically elemental iron (Fe.sup.0)
available as scrap iron, while the second process facilitates the
well-known Fenton reaction.
[0049] A schematic diagram of a preferred embodiment of the present
invention is illustrated in FIG. 1. A waste stream is provided via
a pump 101. The first treatment uses a pre-filter 102A and a
zero-valent metal column reactor 102B. A pre-filter 102A containing
sand and zero-valent metal filters solids, such as particles of
TNT, RDX, HMX, nitroglycerin (NG), and "de-oxygenates" the aqueous
portion of the waste stream through a chemical reducing reaction
facilitated by the zero-valent metal in the pre-filter 102A and the
zero-valent column reactor 102B. The ratio of sand to metal is
maintained at a level sufficient to treat the expected waste
stream, with a typical value of 85% sand to 15% elemental iron.
Next, the product from the pre-filter 102A, i.e., filtered water
containing energetic compounds, is reduced in the zero-valent
column reactor 102B. Both the pre-filter 102A and the zero-valent
metal column reactor 102B are vented to prevent accumulation of
hydrogen gas by providing a breather 109 at the top of the
zero-valent column reactor 102B.
[0050] The Fenton reaction reactor 103 uses iron released from a
zero-valent column reactor 102B as Fe.sup.+2, together with
injected hydrogen peroxide 105, H.sub.2O.sub.2, to complete the
remediation of the pinkwater and associated solid wastes. To
optimize the reaction, provision is made for injection of an acid
111, typically sulfuric acid, to maintain a sufficiently low pH of
2.0-3.0. Normally, the amount of Fe.sup.+2 generated in the
zero-valent column reactor 102B will be sufficient to carry the
Fenton reaction. Should this not be the case, the same injection
system used to provide the acid 111 may be used to supplement the
Fenton reaction with additional metal. An impeller mixer 110 is
provided in the Fenton reaction tank 103 to insure complete mixing
and subsequent transformation of the energetic intermediates.
[0051] A settling tank 106 into which a strong base 107, such as
sodium hydroxide (NaOH), is mixed is provided to both neutralize
the resultant product and to separate the aqueous part from the
solids. This tank 106 is also monitored via a controller 104 to
maintain optimum pH. The solids are removed as a benign sludge by a
sludge pump 108 while the aqueous portion 112 is re-cycled as
needed.
[0052] Scrap iron is an industrial waste material that is readily
available and relatively inexpensive. A sand and iron pre-filter
102A, with an inherently long service life, facilitates a passive
process that requires little maintenance or regeneration, requiring
only a pump 101 to draw the waste stream into it. Degradation of
zero-valent iron does not generate toxic by-products. The reduction
products of the energetics may be of concern, however. The
subsequent Fenton oxidation process, fully oxidizing the reduction
products to benign constituents such as CO2, water, and benign
inorganic compounds, breaks down these products.
[0053] It may be difficult for Fenton's reagent alone to oxidize
energetics due to their highly oxidized nature. This is addressed
uniquely in a preferred embodiment of the present invention by
using a combination of a pre-filter 102A and a zero-valent metal
column reactor 102B to reduce the explosives to products that are
much more amenable to processing using the Fenton reaction. Yet
another advantage of a preferred embodiment of the present
invention is the use of the Fe.sup.+2 (a degradation by-product of
the pre-treatment process) in the subsequent Fenton reactor 103,
thereby reducing the need for supplying commercial ferrous
additives.
[0054] This innovative treatment system specifically removes and
"mineralizes" TNT and heterocyclic nitramines (RDX and HMX) from
pinkwater.
[0055] The U.S. Army Engineer Research and Development Center
(ERDC) in cooperation with the University of Delaware conducted
bench scale tests on the processes of the instant invention. Refer
to FIGS. 2-4 for results of TNT, RDX and HMX reduction experiments
conducted on bench scale reactors using these commonly available
materials: sand and scrap iron in a pre-filter 102A, scrap iron in
a zero-valent column reactor 102B, hydrogen peroxide and sulfuric
acid added to a first vessel comprising the Fenton reactor 103, and
sodium hydroxide to base-neutralize the resultant acidic waste
stream in a second vessel. The majority of TNT (FIG. 2) in solution
was removed within 30 minutes. Similarly, RDX (FIG. 3) and HMX
(FIG. 4) in solution were completely removed within 30 minutes.
[0056] Refer to FIGS. 5 and 6. Preliminary experiments using a
glass column of 2.5 cm diameter filled with scrap iron rapidly
reduced TNT (FIG. 5) and RDX (FIG. 6). Results from the column
study show that the concentrations of TNT and RDX in column
effluent can be predicted using the advection-dispersion-reaction
equation: 1 C A t = D L 2 C A x 2 - u C A x - k C A ( 1 )
[0057] where C.sub.a is the concentration of the contaminant in the
aqueous phase; t is time; D.sub.L is the longitudinal dispersion
coefficient, x is the coordinate in the flow direction; .mu. is
mean interstitial water velocity and k is a constant selected for a
class of contaminants.
[0058] To evaluate whether the metal pre-treatment in the
pre-filter and zero-valent metal column reactor 102B will enhance
the subsequent Fenton oxidation process, experiments were carried
out to study mineralization of the reduction products of the
explosive compounds by Fenton's reagent (H.sub.2O.sub.2 and
Fe.sup.+2). A five-fold increase was observed in mineralization of
TNT due to Fe(0) pre-treatment. In another study, H.sub.2O.sub.2
(40 mM) was added to effluent from a zero-valent column reactor
102B, which received a wastewater containing TNT and RDX. No TNT or
RDX was detected in the effluent, indicating that TNT and RDX were
completely reduced to TAT and the ring cleavage products of RDX,
respectively. Subsequent H.sub.2O.sub.2 addition mineralized 50% of
TAT and greater than 95% of RDX reduction products within 100
minutes.
[0059] Refer to FIG. 1. A pump 101 provides the waste to a
preferred embodiment 100 of the present invention. A preferred
embodiment uses a unit 102 that incorporates a pre-filter 102A
containing filter media and zero-valent metal for filtration of
solids and de-oxygenation of the wastewater stream and a
zero-valent metal column reactor 102B to reduce the highly oxidized
state of the energetics in the waste stream; a Fenton reaction
vessel 103 to which a strong oxidizer, typically hydrogen peroxide,
is added to mineralize the metal-treated energetics in the waste
stream; a mix control system 104; a supply 105 of oxidizer; a
neutralization and sedimentation tank 106; and a source 107 of a
strong base. The waste stream may be fed to the Fenton reaction
vessel 103 via gravity feed. Likewise, the clean water from the
neutralization and sedimentation tank 106 may be gravity fed to a
holding tank, or the like. A sludge pump 108 is an option for
removing sediment from the neutralization and sedimentation tank
106 for further disposal.
EXAMPLE
[0060] A pump 101 supplies a waste stream, e.g., pinkwater, to the
bottom of a pre-filter 102A containing a mixture of sand and
zero-valent iron in a ratio of 15:85. The iron de-oxygenates the
pinkwater as the iron transforms from Fe.sup.0 to Fe.sup.+2, and
the sand filters colloidal and suspended particles from the
pinkwater. The pre-filter 102A may be provided in the form of a
disposable cartridge, or be an adapted sand filter available from
swimming pool supply companies.
[0061] As the pinkwater flows upwards through the zero-valent metal
column reactor 102B, the energetics contained therein are reduced
quickly by the zero-valent iron. For example, TNT is reduced to
triaminotoluene (TAT) and RDX and HMX are reduced to ring-cleavage
products. The effluent, which carries the reduction products and
corrosion by-products, such as the ferrous ion (Fe.sup.+2), then
exits from the top of the column 102B and flows to the Fenton
reaction vessel 103 by gravity. A gas vent 109 is located at the
top of the column 102B to release any hydrogen gas generated from
the anaerobic reduction process.
[0062] The Fenton oxidation process takes place in a Fenton
reaction vessel 103 that in one configuration is a completely
stirred tank reactor (CSTR) 103 that uses an externally powered
mixing paddle 110. To the CSTR 103, a hydrogen peroxide solution is
added continually to produce "Fenton's reagent" (i.e., hydrogen
peroxide (H.sub.2O.sub.2) plus Fe.sup.+2). In the presence of
Fe.sup.+2, hydrogen peroxide decomposes to form the hydroxyl
radical (OH.sup.-), a very strong oxidizing agent, with
E.sup.0=+2.33V, that quickly oxidizes the reduction products of the
energetics to stable end products such as carbon dioxide, water,
and a nitrate. For the Fenton reaction to occur optimally, the pH
in the CSTR 103 is maintained within a range of 2.0-3.0 using a mix
control system 104 (e.g., pH meter, recorder, and automated
controller) to add the necessary pH reducer, such as a sulfuric
acid solution (H.sub.2SO.sub.4), from an acid source 111. The
contents of the CSTR 103 are continuously stirred with one or more
mixing paddles 110, such as those used with impeller mixers. Under
normal operation, addition of iron to the CSTR 103 is not required.
However, should the need arise, iron, as a ferrous ion (Fe.sup.+2),
may be injected in the same manner as the acid.
[0063] The treated effluent from the CSTR 103 flows into a
neutralization and sedimentation tank 106 by gravity, where it is
pH-neutralized by adding a base, such as sodium hydroxide (NaOH),
from a supply tank 107 or other source. By bringing the pH to a
neutral value in the range of 6.0-8.0, a sludge containing a ferric
hydroxide is formed from precipitation of the ferric ion. The
sludge is collected and removed at the bottom of the neutralization
and sedimentation tank 106 via a sludge pump 108. The treated water
112 exits the top of the neutralization and sedimentation tank 106
and may be re-used.
[0064] Although a preferred embodiment of the present invention
focuses on pinkwater treatment, any waste containing energetic
compounds (explosives, propellants, and other pyrotechnic
compounds) may be treated efficiently by this system and method.
For example, waste generated from demilitarization activities; air
scrubber fluids or solution containing energetic compounds;
clean-up site lagoon water containing energetic compounds; and
ground water contaminated with energetics that is pumped to the
surface for treatment.
[0065] Although specific functions for this system and method have
been described, other functions using the described apparatus and
method are not excluded from falling within the ambit of the claims
herein.
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