Transcript WASTE CONTAINMENT TECHNOLOGY

WASTE CONTAINMENT
TECHNOLOGY
Dr. Grace Hsuan
Civil & Architectural Engineering
Outlines
• Waste management methods
• Landfill design and regulations
• Function and usage of geosynthetics in
landfill systems
• Durability of geosynthetics
• Future trend of landfill management
Waste Classification
•
•
•
•
•
Municipal waste
Construction demolition debris
Nonhazardous industrial waste
Incineration ash
Hazardous waste
Amount of Municipal Waste
Million of Tons
200
150
100
50
0
1950
1960
1970
1980
Year
1990
2000
Waste Management Methods
Method
1970
1980
1990
Landfilling
72%
81%
67%
1992
(Goal)
55%
Combustion
21%
9%
16%
20%
Recycling
7%
10%
17%
25%
Source Reduction
Source reduction involves reduction in the
quantity or toxicity of materials during the
manufacturing process via:
• Decrease the amount of unqualified
products by improving quality control
• Decrease the unit weight of the product
by using high quality material.
Weight Reduction (unit of grams)
Container
1980
1992
2-liter PET bottle
65
51
Aluminum can
19
15
Glass soda bottle
255
177
Steel (tin) soup can
48
37
Half-pint milk carton
14
11
Recycling Materials in Percentage of Waste
Materials
Corrugated boxes
Newspapers
Office paper
Glass containers
Steel cans
Aluminum cans
Plastics packaging
Yard waste
Others
Total
1985 1990 Projected 1992
4.4
5.9
6.7
2.1
2.8
3.3
0.7
0.9
1.0
0.7
1.3
1.5
0.1
0.2
0.2
0.4
0.5
0.5
0.1
0.2
0.2
0
2.2
2.7
1.5
3.0
3.8
10
17.1
20.2
Combustion
• Combustion can reduce the volume of the
solid waste up to 90% at the same generate
power.
• There are 140 combustion plants the US.
• Emission must meet the EPA Clean Air Act.
• Residual ash is hazardous material and
should be disposed accordingly.
Landfill
• Landfill implies disposal of waste in the
ground.
• 70% of the waste is disposed in landfill and
the percentage has been gradually
decreasing.
• The amount of waste actually increased
due to population growth.
Landfilling
Approximately 6,500 landfills operate in
the US:
– 57% belong to local governments
– 14% belong to private companies,
– 29% belong to federal agencies or solid
waste authorities.
Landfill Capacity
The size and capacity vary greatly:
• 30% of the landfills receive less
than 30 tons per day
• 5% receive more than 500 tons
The Largest Landfill
•
•
•
•
Fresh Kills,
Staten Island, NY
3,000 acres
2.4 billion cubic
feet of waste
• 25 times of the
great pyramid
Nature of Waste Problem
 Moisture within and flowing on the waste
generates leachate
 Leachate takes the characteristics of the waste
 Thus leachate is very variable and is sitespecific - there is no "typical" leachate
 Flows gravitationally downward into the
leachate collection system
 Enters groundwater unless a suitable barrier
layer or system is provided
Current Legislation
• EPA for both non-hazardous and
hazardous waste
• Superfund via Corps of Engineers
• DOE/NRC for radioactive wastes
• Worldwide approx. 40 countries have
legislation/regulations (survey in GRI Report #23)
Regulations
Solid waste is regulated under the Resource
Conservation and Recovery Act (RCRA).
Classification of non-hazardous and
hazardous waste depends on the chemical
constituents of the leachate.
Hazardous Waste Definition
• Waste is listed in Appendix VIII of Title
40, Code of Federal Regulations, Part 251.
• Waste is mixed with or derived from
hazardous waste.
• Waste is not identified as municipal waste.
• Waste possesses one of the following
characteristics:
– ignitable; corrosive; reactive and toxic.
Minimum Technology Guidance
(MTG)
• Federal regulation on landfill design
requirement is published by the EPA.
• Dependent on the classification of the
waste, MTG is recommended.
• Each state must follows, or exceed, the
MTG.
Non-hazardous Waste
• Non-hazardous waste is regulated under
Subtitle D of RCRA.
• EPA regulations are published in Parts
257 and 258, Title 40, Code of Federal
Regulations (CFR).
Minimum Technology Guidance
(MTG) for a Subtitle D Landfill
“Solid Waste”
Composite
liner
150 mm
Filter (or GT)
300 mm
Drain (or GN/GC)
GT (opt.)
GM*
600 mm
Clay @ 1x10-7 cm/sec
Soil Subgrade
Hazardous Waste
• Hazardous waste is regulated under
Subtitle C of RCRA.
• EPA regulations are published in Part
264.221, Title 40, Code of Federal
Regulations (CFR).
MTG for a Subtitle C Landfill
“Solid Waste”
150 mm
Filter (or GT)
300 mm
Drain (or GN/GC)
P-GM*
300 mm
Drain (or GN)
S-GM*
Composite
liner
900 mm
Clay @ 1x10-7 cm/sec
3.0 m
(to highest groundwater level)
Landfill Closure Activities
• Closure must begin within 30 days of
final receipt of waste; extensions may be
granted by state approval.
• Closure must be completed in accordance
with closure plan within 180 days;
extensions may be granted by state
approval.
• A notation must be placed in the deed.
Landfill Covers
(Non-hazardous landfill without
Geosynthetic on the bottom liner system)
150 mm
450 mm
Erosion Layer
Infiltration Layer
Cover Layers
• Erosion Layer
– Earthen material is capable of sustaining
native plant growth
• Infiltration Layer
– Permeability of this layer of soil should be
less than or equal to the permeability of any
bottom liner system or natural subsoils
present, or permeability less than 1x10-5
cm/sec whichever is less
Landfill Cover System
(Subtitle C & D, and Corp of Eng.)
150 mm
Varies
(frost depth)
Topsoil
Cover Soil
150 mm
Filter (or GT)
300 mm
Drain (or GN)
GM
600 to
900 mm
Clay @ 1x10-7 cm/sec
300 mm
Gas Vent (or GT)
”Solid Waste”
Landfill Site
• Conforms with land use planning of the area
• Easy access to vehicles during the operation
of the landfill
• Adequate quantity of earth cover material
that is easily handled and compacted
• Landfill operation will not detrimentally
impact surrounding environment
• Large enough to hold community waste for
some time
Geosynthetics
 geomembranes (GM)
 geosynthetic clay liners (GCL)
 geonets (GN)
 geotextiles (GT)
 geogrids (GG)
 geopipe (GP)
 geocomposites (GC)
Primary Functions
Type
GM
GCL
GN
GT
GG
GP
GC
S
Y
Y
R
Y
Y
Y
F
Y
Y
D
Y
Y
Y
Y
S = separation, R = reinforcement, F = filtration
D = drainage, B = barrier
B
Y
Y
Y
Natural Soils vs. GSs
Function
Natural Soil
Barrier-Single
CCL
BarrierComposite
GM/CCL
Geosynthetics
GM
GM/GCL
GM/GCL/CCL
Drainage Layer Sand
GT
Gravel or sand GN
Filter Layer
Sand
GT
Liner System
GT
GN
GCL
GM
GG
CCL
Gravel w/
perforated pipe
Final Cover System
Solid Waste
Possible Geosynthetic Layers
in a Waste Containment System
in Final Cover - 7
in Base Liner -
9
16 Layers!
Liquid Barrier Systems
• Single CCL
• Single GM
• Single composite liner
– GM/CCL
• Double composite liner
– GM/CCL-GM/CCL
– GM/GCL-GM/CCL
Composite Barriers
(Intimate Contact Issue)
Leachate
Leachate
CCL
CCL
Clay Liner
Composite Liner
(by itself)
(with intimate contact)
Leachate
GCL
Composite Liner
(GM + GCL)
Does the GT compromise the
composite liner concept?
Ans: Generally no...
Composite Barriers
(Theoretical Leakage)
GM alone (hole area “a”)
Composite liner (GM/CCL)
Leachate
ks
Q = CB a 2 gh
Q = 0.21 a0.1 h0.9 ks0.74
Q=
(for good contact)
1.15 a0.1 h0.9 ks0.74
(for poor contact)
Ref. Bonaparte, Giroud & Gross, GS ‘89)
Generalized Leakage Rates Through Liners
(ref. Giroud and Bonaparte, Jour. G & G, 1989)
Type of
Liner
Geomembrane alone
(between two sand
layers)
Composite liner
(poor field
conditions, i.e.,
waves)
Composite liner
(good field
conditions, i.e., flat)
Leakage
Mechanism
Diffusion
Small holes*
Large holes*
Diffusion
Small holes*
Large holes*
Liquid height on top of the geomembrane
0.03 m
0.3 m
3m
30 m
0.01
1
10
300
300
1,000
3,000
10,000
10,000
30,000
100,000 300,000
0.01
1
100
300
0.8
6
50
400
1
7
60
500
Diffusion
Small holes*
Large holes*
0.01
1
100
300
0.15
1
9
75
0.2
1.5
11
85
Values of leakage rate in lphd (figures to be
divided by approximately 10 to obtain
values expressed in gpad)
*assumes 3 holes/ha (i.e., 1.0 hole/acre)
Response Action Plans (RAP's)
• Only applicable with double liner systems
• Worldwide, 58% HSW (incl. USA) and 14% of
MSW require double liner systems
• Requires measurement of liquid quantity in leak
detection system
• If above the preset action leakage rate (ALR),
different requirements are set in motion, e.g.,
–
–
–
–
continuous monitoring
characterize liquid
stop receiving waste
remove waste to locate leak(s)
Some Comments on RAP's
(a) "de minimum" leakage ~ 10 lphd (~ 1.0 gpad)
 vapor diffusion through perfect geomembrane with no flaws = 0.2
to 20 lphd
(b) typ. action leakage rate (ALR) ~ 50 to 200
 continuous monitoring
 assess liquid characteristics
 compare to primary leachate
(c) typ. intermediate leakage rate (ILR) ~ 200 to 1000
 stop adding waste
 continue monitoring and testing
(d) typ. rapid and large leak (RLL) > 1000 lphd
 remove waste
 repair leak(s)
Note:
all of the above RAP values are for illustration only -- they must be site specifically
determined -- note that EPA only requires the establishment of an ALR value
Average Values of Leakage Quantities
Leakage Rate (lphd)
40
Sand
Leak Detection
30
GM
20
GM/CCL
10
GM/GCL
0
1
2
Life Cycle Stage
3
Average Values of Leakage Quantities
(cont’d)
Leakage Rate (lphad)
20
Geonet
Leak Detection
15
GM/CCL
10
GM
5
GM/GCL
0
1
2
Life Cycle Stage
3
Geomembranes
Widely Used Geomembranes Limited Used Geomembranes
High density polyethylene
(HDPE)
Chlorosulfonated
polyethylene (CSPE)
Linear low density
polyethylene (LLDPE)
Ethylene interpolymer alloy
(EIA)
Flexible polypropylene
Ethylene propylene
trimonomer (EPDM)
(f-PP)
Polyvinyl chloride-plasticized
(PVC-p)
Comments
•
•
•
•
Name is associated with resin type
All have some amount of additives
Additives can vary from 2% to 60%
Some additives are critical to performance
Compositions
(approximate percentage)
Type
Resin
Plasticizer
Antioxidant
Filler
95-97
Carbon
Black
2-3
HDPE
0
1-0.5
0
LLDPE
PVC-p
fPP
95-97
50-70
95-97
2-3
1-2
2-3
0
25-35
0
1-0.5
1-0.5
1-0.5
0
5-10
0
CSPE
40-60
5-40
0
1-0.5
5-15
EPDM
25-30
20-40
0
1-0.5
20-40
Geomembrane Styles
• smooth geomembranes
• Textured geomembranes
• Reinforced geomembranes
Manufacturing Processes
•
•
•
•
Flat extrusion
Blown sheet extrusion
Blown sheet co-extrusion
Calendaring
Material Properties
•
•
•
•
•
•
Mechanical property
Density
Melt flow
Carbon black
Plasticizers
Antioxidant
Tensile Behavior
• Test method varies according to the resin type
and style of the geomembrane.
• Each test method consists of unique shape of
specimen and strain rate.
• Methods:
– HDPE, LLDPE and fPP – ASTM D 638 Type IV
– PVC-p – ASTM D 882
– All reinforced geomembranes – ASTM D 751
Design Concept
Allowable (Test) Property
FS =
Required (Design) Property
Where:
• Test methods are from ASTM, ISO, or others
• Design models from the literatures
• Factor-of-Safety is site specific
Density Methods
• ASTM D 752 (Specific gravity)
• ASTM D 1505 (Density column)
• ASTM D 4883 (Ultrasonic for PE only)
HDPE Geomembranes
• Resin density is around 0.930 g/cc, which is
in the medium density range according to
ASTM D 833.
• The 2.5% carbon black raise the density of
the product to 0.941g/cc, which is the
HDPE range.
product = resin + 0.0044C
Where: C = weight percentage of carbon black
Melt Flow (MI) Method
•
•
•
•
Test Method - ASTM D 1238
Only for thermoplastic materials
Test condition varies with resin type
It is essential for extrusion process, i.e.,
for product manufacturers
• For the same type of polymer, MI can
be correlated to the molecular weight
Function of Carbon Black
• The primary function is as an ultraviolet
light stabilizer to protect polymer being
degraded.
• Carbon black absorption coefficient
increases with loading up to ~ 3%.
• In elastomeric materials, carbon black
also functions as an reinforcement, and
loading can be as high as 30-40%.
Addition of Carbon Black
• The masterbatch technique is utilize to
dispersing carbon black in plastic.
• A masterbatch is a resin containing a high
concentration of carbon black.
• The masterbatch is blended with polymer
resin to achieve the desire percentage.
Carbon Black
• Carbon black content is measured
according to ASTM D1603.
• Carbon black dispersion is evaluated
according to ASTM D 5596.
Plasticizers
• Plasticizers is used in PVC to lower the
glass transition temperature (Tg).
• An addition of 30% plasticizer in PVC can
lower the Tg from 80oC to –20oC.
• The plasticized PVC behaves rubbery at
normal ambient temperature.
• However, plasticizer can slowly leach out
with time.
Analysis Plasticizers
• The amount of plasticizer in the polymer
can be determine by extraction according
to ASTM D 2124.
• The type of plasticizer can be identified
using Infrared (IR) spectroscopic.
Antioxidants
• The function of antioxidants is to protect
polymers from being oxidized during the
extrusion process and service lifetime.
• For polyolefines, antioxidants is vital to
the longevity of the product.
• Antioxidant will be the focus of the
second part of this class.
Degradation of
HDPE Geomembranes
Chemical Related:
– Thermal-oxidation
– Photo-oxidation
Linear PE Structure
• Linear PE is a graft copolymer
• Each co-monomer creates one branch
• Co-monomer can be butene, hexene, or octene
Density of Geomembranes
• Density decreases as the amount of
co-monomer increases
• Density range of PE (ASTM D883)
– > 0.940 g/ml for HDPE
– 0.926 - 0.940 g/ml for MDPE
– 0.910 - 0.925 g/ml for LLDPE
– <0.909 g/ml for VLDPE or ULDPE
II. Oxidation Degradation
• Polyolefins, such as HDPE, PP and PB are
susceptible to oxidation.
• Oxidation takes place via free radical
reactions.
• Free radicals form at the tertiary carbon
atoms (i.e., at branches).
• Oxidation leads to chain scission that
results in decrease of Mw and subsequently
on mechanical properties.
Forming Free Radicals
Different Degradation Stages
Various Stages of Oxidation
Reactions during Induction
Period
RH  R   H 
R  O2  ROO 
ROO   RH  ROOH  R 
Reactions during
Acceleration Period
OH   RH  H2 O  R 
ROOH  RO   OH 
RO   RH  ROH  R 
Functions of Antioxidants
• Primary antioxidants react with free
radical species
• Secondary antioxidants decompose
ROOH to prevent formation of free
radicals
Types of Antioxidants
Category
Primary
Secondary
Chemical Type
Example
Hindered phenol
Irganox 1076 or 1010
Santowhite crystals
Hindered amines
Various of Tinuvin,
Chemassorb 944
Phosphites
Irgafos 168
Sulfur compound
Dilauryl thiodipropionate
Distearyl thiodipropionate
Hindered amines
Various of Tinuvin,
Chemassorb 944
Effective Temperature Range
Phosphites
Hindered Phenols
Thiosynergists
Hindered Amines
0
50
100
150
200
Temperature (oC)
250
300
Depletion of Antioxidants
Two mechanisms:
a. Chemical reactions – by reacting with
free radicals and peroxides
b. Physical loss – by extraction or
volatilization
Arrhenius Model
Rate of reaction = X * Y * Z
Where:
X = collision frequency (concentration or pressure)
Y = energy factor
Z = probability factor of colliding particles
(temperature dependent)
Potential Energy
Potential Energy
transition state
Eact
Separate
Reactants
products of
reaction
DH
Progress of Reaction
Distribution of Energy
dN
dE
Fraction is exp(
Energy
-Eact
RT
)
Arrhenius Equation
Rr = ( X )(e
Eact

RT
Rr = ( A)(e
)( Z )
Eact

RT
)
E act
ln Rr = ln A 
RT
(9)
(10)
(11)
Arrhenius Plot
A
ln Rr
Eact
R
1
high temperature
(lab tests)
low temperature
(site temperature)
Inverse Temperature (1/T)
Experimental Design
• Incubation environment should simulate
the field (i.e., landfill environment)
– Limited Oxygen
– Some degree of liquid extraction
• Utilize elevated temperatures to accelerate
the reactions.
– 55, 65, 75, and 85oC
Incubation Device
1
10
Piezometer
Load
Insulation
Perforated steel loading plate
Sand
Sand
Heat tape
Geomembrane
Tests Performed
• Oxidative inductive time (OIT) for
antioxidant content.
• Melt index for qualitative molecular
weight measurement.
• Tensile test for mechanical property
OIT Tests
• OIT is the time required for the polymer
to be oxidized under a specific test
condition.
• OIT value indicates the total amount (not
the type) of the antioxidant remaining in
the polymer.
OIT Test for Evaluation of
Antioxidant (AO)
• OIT Tests:
– ASTM D3895-Standard OIT (Std-OIT), or
– ASTM D 5885-High Pressure OIT (HP-OIT)
• HP-OIT test is used for AOs which are
sensitive to high temperature testing
Thermal Curve of OIT Test
Test Results
Percent Retained
150
Std-OIT
HP-OIT
Density
Melt Index
Yield Stress
Yield Strain
Break Stress
Break Strain
100
50
0
0
5
10
15
20
25
30
Incubation Time (month)
Changes in Eight Properties with Incubation Time at 85°C
Analysis of OIT Data
a. Determine OIT depletion rate at each
temperature.
b. Utilize Arrhenius Equation to
extrapolate the depletion rate to a
lower temperature.
c. Predict the time to consume all
antioxidant in the polymer.
a) - OIT Depletion Rate
4.5
ln OIT (min.)
4
3.5
3
2.5
55°C
65°C
75°C
85°C
2
1.5
1
0
5
10
15
Incubation Time (month)
20
25
b) –Arrhenius Plot
-1
ln (OIT Depletion Rate)
Standard OIT y = 17.045 - 6798.2x R^2 = 0.953
HP-OIT
y = 16.856 - 6991.3x R^2 = 0.943
-2
-3
-4
-5
0.0027
0.0028
0.0029
1/T (°K)
0.0030
0.0031
c) Lifetime of Antioxidant
• Use the OIT depletion equation to find “t”
ln(OIT) = ln(P) – (S) * (t)
• The OIT value for unstabilized PE is
0.5 min.
• For this particular stabilization package
t = 200 years
Lifetime of Geomembrane
• Induction time and degradation period
(Stages B & C) can be established by using
unstabilized polymer in the experiment.
• It was found by Gedde et al. (1994) that the
duration of Stages B and C is significant
shorter than that of Stage A.
• Antioxidants are critical to the long-term
performance of polyethylene and other
polyolefines.
Future of Waste Containment
• Current waste containment technique is
defined as “dry dome” method by
eliminating leachate from being generated
after closure.
• Waste will not degrade since moisture is a
critical component of the biodegradation
process.
Bioreactor Landfill
“……a sanitary landfill operated for the purpose
of transforming and stabilizing the readily and
moderately decomposable organic waste
constituents within five to ten years following
closure by purposeful control to enhance
microbiological processes. The bioreactor
landfill significantly increases the extent of
waste decomposition, conversion rates and
process effectiveness over what would
otherwise occur within the landfill.”
Why Operate a Landfill as a
Bioreactor?
• to increase potential for waste to energy
conversion,
• to store and/or treat leachate,
• to recover air space, and
• to ensure sustainability
Status
• 1993 - less than 20 landfills recirculating
leachate
• 1997 - ~ 130 landfills recirculating
leachate
• My estimate - ~ 5% of landfills
Aerobic Bioreactor
•
•
•
•
Rapid stabilization of waste
Enhanced settlement
Evaporation of moisture
Degradation of organics which are
recalcitrant under anaerobic conditions
• Reduction of methane emissions
Research Issues - Aerobic
Bioreactor
•
•
•
•
•
How much air is needed?
How can air be delivered?
What is the impact on the water balance?
How are landfill fires prevented?
What are the economic implications?