CE 529 Hazardous Waste Management
Chemical Treatment Methods
1.
STABILIZATION/SOLIDIFICATION (S/S)
•
•
one of the _________ recommended for the treatment of hazardous wastes before disposal at a secured landfill.
commonly used at contaminated sites to _______________ the contaminants - usually as temporary measure
but sometimes as a permanent solution.
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has been widely used for:
(1) the treatment of ________________ from other hazardous waste treatment processes such as ash from
thermal treatment, ___________ from industrial treatment plants - especially waste with inorganic constituents
(2) treatment of ____________________ and hazardous waste sites including in situ applications
Some hazardous waste where S/S has been recommended as BDAT:
________________
Dissolved air flotation float
from petroleum refining
Pb2+
Cr3+
_____________
Metal Finishing Sludge
Cd2+, Ni2+
Pb2+, Cr3+
Distillation tar
Cr3+, Ni2+
___________
•
S/S is designed to accomplish one or more of the following:
(1) improve the _______________ and physical characteristics of the waste, eg., absorption of free liquids
(2) decrease the ________________of the waste mass across which transfer or loss of contaminants can occur
(3) limit the _______________ of any hazardous constituents of the waste, e.g., by pH adjustment, sorption or
precipitation.
Stabilization
- is a process by which ___________________ (additives or reagents) are added to the hazardous waste to convert
the waste and its constituents into their least mobile or toxic form that _______________ the rate of contaminant
migration and the level of toxicity.
• The addition of ________________ to a metal-containing waste to precipitate the metals is an example of
stabilization
• sometimes known as _______________________
Solidification
- is a process by which binders (additives or reagents) are added in sufficient quantities to form a
_______________________ or "_________________" with high structural integrity (generally compressive
strength) and to decrease the permeability of the waste and minimize exposure of the hazardous constituents to
outside conditions.
• Contaminants do not necessarily interact chemically with the reagents. Instead they are
_______________________ or __________________ with the solidified mass.
• Contaminants loss is limited largely by decreasing the ________________ exposed to the environment and
_________________ the contaminants from environmental influences by encapsulating the waste particles.
Mechanism of stabilization/solidification
• _________________ - soluble forms of hazardous constituents are rendered less soluble by forming
precipitates such as hydroxides, sulfides, carbonates and phosphates within the stabilized mass.
Precipitation is generally applicable for metallic constituents. The permanence of the fixation of the metal
precipitates depends on the pH and the redox potential of the environment.
•
__________________ - hazardous waste constituents are entrapped within the crystalline structure of the
solidified matrix at a microscopic level. Even if the matrix deteriorates over time, release of hazardous
constituents may not occur unless the matrix degrades to very fine particles
•
___________________ - hazardous waste constituents are entrapped in a larger structural matrix. This
may be visualized as waste constituents being held in discontinuous pores within the stabilizing materials.
Degradation of the solidified matrix (from compressive stresses, expansion and contraction due to
temperature of presence/absence of moisture) may result in the exposure of the waste constituents to the
surrounding environment, allowing the constituents to freely migrate. Mixing plays an important role in
the stabilization process. Improper mixing may result in some proportion of the waste to be
macroencapsulated rather than microencapsulate.
•
___________________ - contaminants are transferred into the matrix of the sorbent in the same way as a
sponge takes up water. Common absorbents are: fly ash, cement kiln dust, lime kiln dust, clay materials,
sawdust and hay and straw. Absorbents are usually added to remove free liquids in the waste. The liquids
may be squeezed out should the mass be subjected to consolidating stresses.
•
___________________ - contaminants are electrochemically bonded or "fixed" to the surface of the
stabilizing agents within the matrix. Depending on the nature of the bonding, the contaminants are less
likely to be released into the environment than those that are not fixed.
BINDERS
Common binders used are:
• for inorganic wastes, binders used are _____________________________________________, proprietary
chemicals such as _____________________________________
• for organic wastes, binders used are: ______________________________________.
INORGANIC WASTES
________________________________________
• waste materials are mixed with ________________ and water. The hydration of cement forms a crystalline
structure consisting of alumino-silicates. Typically, hydroxides of metals are formed which are much less
soluble than other ionic species of the metals. Small amounts of fly ash, sodium silicate, bentonite, or
proprietary additives are often added to the cement to enhance processing.
• has been applied to ________________________ wastes containing various metals such as cadmium,
chromium, copper, lead, nickel and zinc - predomnantly as precipitates, although microencapsulation may be
also an important mechanism.
• presence of __________________________________ may interfere with the hydration process, reducing final
strength and reducing the crystalline structure resulting in an amorphous material. Additives such as
organically modified clay clays may be used to adsorb the organic contaminants.
• Advantages of cement-based S/S is that cement is easily handled, pumpable and mixed with different types of
hazardous, cost is relatively low as it is widely used in the construction industry, and the alkalinity can
neutralize acidic wastes
• Disadvantage is: _____________________ of cement to the presence of certain contaminants - affecting setting
and hardening of the material
____________________________
• a ________________________ is a material that can react with lime in the presence of water to produce a
cementitious material. The cementitious materials are usually siliceous and aluminosilicate materials
• pozzolanic materials include _______________________________________________________________.
For example, typical ____________ composition is 45% SiO2, 25% Al2O3, 15% Fe2O3, 10% CaO, 1% MgO,
1% K2O, and 1% Na2O
• the final product can vary from a soft fine-grained material to a hard cohesive material similar in appearance to
cement
• pozzolonic reactions tend to be ____________________ than cement reactions
• wastes that have been stabilized/solidified with pozzolans materials include ____________________
containing various metals such as lead, zinc, waste acids and creosote
• unburned carbon in fly ash may adsorb organics from the waste
ORGANIC WASTES
___________________________________
• in this technology, a thermoplastic material such as ______________________________ is used to bind the
waste constituents into a stabilized/solidified mass. The process is usually a microencapsulation process in
which the waste material do not react with the encapsulating material.
• has been applied to __________________________, painting and refinery sludges containing metals and
organics, dry incineration ash and radioactive wastes
________________________________________________
• this process involves the stabilization of organic wastes using an organic monomer such as
__________________________ to form a polymeric material.
• the sponge-like material traps the solid particles within the matrix (microencapsulation).
• the principal advantage of this process is that a low-density material relative to other fixation techniques is
produced and a small quantity of the polymeric material is required
• this technology has been applied to flue gas desulfurization sludge, electroplating sludges, kepone-contaminated
sludge.
Table 5.1 lists the effects of waste components on stabilization/solidification
PROCESS DESIGN
• There is no _________________________ design protocol for S/S process.
• __________________________ are usually conducted to assess the suitability of a binder or a combination of
binders to achieve the desired physical strength and leaching requirements. But in many cases, field-scale
mixing may not be as thorough as bench-scale studies. Usually a pilot-scale demonstration is conducted to
asses further the feasibility of the S/S process.
• The remainder of the design process focuses on the delivery system.
The primary element of a S/S system includes (see figure and flow diagram):
• waste removal
• untreated waste transportation and handling
• reagent storage
• mixing
• S/S waste storage area
Testing
• most S/S waste will be tested for the ______________________________ of the hazardous constituents. For
regulatory purposes the TCLP is used.
• Other protocols to test the S/S waste are basically related to their final use such as compressive strength etc.
Generally, some of tests that are conducted include:
• moisture content - ____________________________ (Paint filter test) to determine the presence of free liquids
• Strength testing - usually ______________________ or __________________________ are used to test
cohesive soil-like or cement-like material behavior under mechanical stress
• Freeze-thaw durability (____________________________) - to assess the resistance of the material to natural
weathering stresses such as freezing and thawing
Advantages of Solidification/Stabilization
• _________________________________are widely available and relatively inexpensive
• the resulting solidified material may require little of no further treatment if proper conditions are maintained
• leaching of contaminants is greatly reduced
Disadvantages
• ________________________ of treated material may increase with the addition of reagents
• delivering reagents to the subsurface and achieving uniform mixing and treatment in situ may be difficult
• _________________________ of volatile organic compounds may occur during mixing procedures
2.
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CHEMICAL OXIDATION
the objective of chemical oxidation is to _____________________ toxic pollutants to ________________ toxic
pollutants by adding an oxidizing agent
chemical oxidation is a well-established technology that is capable of destroying a wide range of organic
compounds such as chlorinated hydrocarbons, mercaptans, phenols and inorganics such as cyanide.
Oxidation is a reaction where there is a __________________(LEO) while reduction is a reaction where there is
_______________________ (GER). [OIL RIG]
¶ The reactant that loses the electrons is called the __________________, i.e., it reduces the
reactant that is receiving the electrons
¶ The reactant that gains the electrons is called the ______________________, i.e., it oxidizes the
reactant that gives up the electrons
Note that when there is oxidation there must be reduction.
eg.,
CH4
+
2O2
====> CO2
+
2H2O
Oxidation state of C changes from -4 in CH4 to +4 in CO2 - loss of electrons -oxidized
but CH4 is the reducing agent
Oxidation state of O changes from 0 in O2 to (-2) in CO2 and H2O - gain in electrons - reduced
but O2 is the oxidizing agent
•
Some of the oxidizing agents used are _________________________________________________.
However, in recent years research in the area of chemical oxidation has advanced to include various
combinations of oxidants and enhancements such as ___________________ (UV), _________________ (US)
and inorganic catalysts to increase the oxidizing power of the oxidants.
Systems engineered to produce hydroxyl radicals are commonly termed as
______________________________________________ (AOPs).
Table 1 lists a host of oxidation agent and their oxidation potential relative to chlorine. The oxidation potential
of an oxidant is related to its oxidation-reduction potential E˚ (V). An oxidant with a high E˚ is a strong
oxidant.
Table 1
Typical Oxidizing Agents and Their Relative Oxidizing Power
Redox reaction
Oxidizing
E˚ (V)
Agent
at 25˚ C
Relative
Oxidative
Power
2.55
F2 + 2e- = 2FF2
3.06
OH + H+ + e- = H2O
OH•
2.80
2.05
Atomic oxygen
O
2.42
1.78
+
O3 + 2H + 2e = H2O
O3
2.07
1.52
+
+
H2O2 + 2H + 2e = H3O2
H2 O2
1.76
1.30
Perhydroxyl radical
HO2•
1.70
1.25
+
MnO4 + 4H + 3e = MnO2 + 2H2O
MnO4
1.68
1.24
HClO2 + 3H+ + 4e- = Cl- + 2H2O
HClO2
1.57
1.15
HOCl + H+ + 2e- = Cl- + H2O
HOCl
1.49
1.10
Cl2 + 2e- = 2ClCl2
1.36
1.00
+
HBrO + H + 2e =
HBrO
1.33
0.97
Br2 + 2e- = 2BrBr2
1.07
0.79
HIO + H+ + 2e- = I- + H2O
HIO
0.99
0.73
I2 + 2e- = 2II2
0.54
0.40
__________________________________________________________________________
Table 2 Oxidation Systems for Hazardous Waste Destruction
Homogeneous system without irradiation
O3/OHH2O2/Fe2+ (Fenton's reagent)
Cl2
O3/ H2O2
Homogeneous system with irradiation
O3/ultraviolet (UV)
H2O2/UV
O3/ H2O2/UV
O3/electron beam
ultrasound (US)
H2O2/US
UV/US
Heterogeneous systems with irradiation
Metal catalyst (TiO2, ZnO)/UV
Metal catalyst/ O3/UV
Metal catalyst/ H2O2/UV
example:
CATAZONE Process - O3/TiO2
CHLORINE
• mostly used as a disinfectant in US (62% of total municipal wastewater is chlorinated (1982 US EPA Survey).
Chlorine form hypochlorous acid (HOCl) and hydrochloric acid (HCl) in water and most of the disinfecting
power of chlorine is from the hypochloride ion (OCl-).
•
A common application of chlorine in hazardous waste treatment is the destruction of cyanide wastes. This
process is called alkaline destruction. The reaction is sensitive to pH and a pH greater than 10 is maintained.
Step 1 - cyanide is oxidized to a less toxic cyanate
__________________________________________________
Step 2 - cyanate is further oxidized to carbon dioxide and nitrogen
________________________________________________________
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other applications include the disinfection of waste especially pathogenic organisms
•
Advantages of chlorine include cost effectiveness, good understanding of chemistry and design of application of
chlorine, high potent against a wide range of pathogens.
•
Disadvantages are that chlorine is toxic to marine organisms, may form chlorinated compounds that may be
more toxic than the original compound, eg., chlorination of phenol forms chlorinated phenolic compounds that
are more toxic than phenol.
OZONE
•
is an allotropic form of oxygen. Ozone is generated from air or pure oxygen when a high voltage is applied
across the gap of a narrowly-spaced electrode. The high energy corona dissociates one oxygen molecule into
two atomic oxygen which then combine with two other oxygen molecules to form two ozone molecules. The
gas stream generated from air by this process will contain about 0.2 to 3 percent ozone by weight and from pure
oxygen is approximately 1 to 6 percent.
___________________________________________________________
127±3Þ
0.126 nm
- 0.224 nm
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ozone is generated as a gas, therefore treatment of aqueous contaminants require the transfer from the gas to
liquid phase (KH = _____________________ atm•m3/mole)
ozone decomposes rapidly in aqueous solutions due to impurities such as organic compounds or particulates
(see figure 5-16). Half lives for Ozone is approximately 18 minutes in ground water, 10 minutes in lake water.
Decomposition of Ozone in distilled water at various pH and temperature of 287.7 K (as presented above) is
given by the following first order equation:
oxidation of compounds in aqueous solution comes from
• ________________ oxidation reaction with molecular ozone
• ________________ pathways in which free radicals, primarily ______________ (OH) radicals or
_____________________ (HO2) radical
Note that most ozone reactions involved a chain reaction involving OH radicals. The reaction rate constant for
the destruction of organics by OH is typically several orders of magnitude greater than for O 3 alone.
molecular ozone oxidation is selective with second order rate constants (with respect to ozone and reduced
species constant) between ____________________________ M-1s-1.
kinetics of OH reaction are several orders of magnitude faster than molecular ozone oxidation
The reactions of ozone in pure is not completely understood, however, Figure 1 and Figure 2 provide probable
reactions
Note: The initial step results in the hydroxyl radicals making alkaline oxidation by ozone several orders of
magnitude higher than ozone oxidation in acidic solution.
(O3- is ozonide ion, O2- superoxide ion)
In a typical aqueous solution, there are:
_________________________ - promotes decomposition of ozone to form radicals, eg., H 2O2, OH-, Fe2+,
UV, formate and humic acid
_________________________ - reacts with OH to form radical species, resulting in propagation of
reactions, eg., organic compounds, humic acid
__________________________ - react with hydroxyl radicals to form secondary radicals which do not
•
promote reaction but rather quench the chain reaction.
Introduction of ultraviolet light results in the photolysis of ozone to produce hydrogen peroxide. The
depronated form of hydroperoxide (HO2-) reacts with ozone to produce ozonide (O3-) and then hydroxyl
radical (OH•).
hv
_________________________________________
__________________________________________
•
Examples of oxidation with ozone
Reaction with alkene results in the oxidation to aldehydes and ketones
Criegee Mechanism
Phenol is readily degraded by ozone to form oxalic acid.
•
Advantages with ozone
¶ lack of persistent toxic residual
¶ increase in effluent dissolved oxygen concentrations
¶ as a disinfectant it is relatively insensitive to pH in the range of 6 to 10 and temperature in
the range of 2˚ C to 30˚ C.
•
Disadvantages are
¶ high capital cost and generation cost (approx. $2,400/kg/day for a plant producing 900 kg/day)
¶ mass transfer of ozone from air phase to aqueous phase is a limiting factor
¶ use of UV to enhance oxidation may be affected by the presence of particles and turbidity of the
wastewater
HYDROGEN PEROXIDE
•
Hydrogen peroxide by itself is slightly more powerful than chlorine. As in ozone, the oxidizing agent is the
hydroxyl (OH•) ion. Hydroxyl ions from hydrogen peroxide may be formed from several methods.
¶
Irradiation of UV
_____________________________________________
¶
Metallic Catalysts - Ferrous ions (Fenton's reagent) or a fixed catalyst eg., titanium oxide
______________________________________________
______________________________________________
or
_______________________________________________
The rate law is
This suggests that the mechanism may be:
with the first reaction the rate limiting reaction.
The above equation implies that Fenton's reagent is strongly dependent on solution pH. In fact in acidic
conditions, OH• is the predominant reactive oxidant. The decomposition of hydrogen peroxide reaches a maximum
at a pH of 3.5.
¶ ______________________ - energy is imparted to hydrogen peroxide in the similar manner as uv to form
hydroxyl radicals.
REACTIONS WITH OH•
• reactions with OH• may proceed in the following pathways:
Hydrogen atom abstraction
OH• + R ===> •R + H2O ===> oxidized products
Hydroxyl addition
OH• + R ===> • ROH ===> oxidized products
Further oxidation occurs with the intermediate radicals (•R and •ROH) as follows:
Fe3+ + • R
===> Fe2+ + products
2 •R
===> R - R (dimerization)
3+
+
Fe
+ •R + H
==> Fe3+ + RH (reduction)
• R + H 2 O2
===> ROH + OH•
•R + OH•
===> ROH
The optimum ratio of Fe2+ to H2O2 needed is at this time unclear.
Examples of reaction with hydrogen peroxide (see Figures)
1. TCE
2. Destruction of chlorophenols with Fenton's Reagent
OZONE/HYDROGEN PEROXIDE/UV SYSTEMS
• A combination of ozone/hydrogen peroxide with UV irradiation has been successfully used to oxidize organic
compounds
• The reaction is speculated to be proceed by H2O2 initiating the decomposition of O3 by single electron transfer
to form hydroperoxide ion (HO2-). The hydroperoxide ion reacts with ozone to produce ozonide ion (O 3-) and
hydroxyl radical (HO•). Reactions as assumed as shown:
Several pilot-scale commercial units for the treatment of contaminated groundwater are available. They are
perox-pure system and the Ultrox International system. Flow diagram of a typical system and some results are
shown.
Typical capital cost for a _______________ gpd Ultrox unit for the treatment of wood treatment
wastewater (chlorophenol, phenol) is $150,000 and operating cost is $1.35 per 1,000 gallons.
ULTRASOUND SYSTEM
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The main mechanism in US systems for the oxidation of toxic pollutants is _______________.
_______________________ is created by the collapse of a gas- or vapor filled bubble in a body of liquid. The
instantaneous temperature and pressure that may be achieved have been estimated to be as high as
_______________ psi and __________________˚ F. This high local pressure and temperature enhance the rate
of chemical reaction.
US is known to decompose water vapor molecules in the bubbles into free radicals such as hydroxyl radicals,
hydrogen radicals and hydroperoxyl radicals.
studies applying US oxidation on chlorobenzene and m-dichlorobenzene achieved more than 90% removal in
60 and 100 minutes respectively.
oxidation may be enhanced by adding some hydrogen peroxide to initiate the reaction.