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 liter PET bottle6551 Aluminum can1915 Glass soda bottle Steel (tin) soup can4837 Half-pint milk carton1411
Recycling Materials in Percentage of Waste Materials Projected 1992 Corrugated boxes Newspapers Office paper Glass containers Steel cans Aluminum cans Plastics packaging Yard waste Others Total
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 site- specific - 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” 150 mm 300 mm 600 mm Filter (or GT) Drain (or GN/GC) 1x10 -7 cm/sec Soil Subgrade GM* GT (opt.) Composite liner
Hazardous Waste Hazardous waste is regulated under Subtitle C of RCRA. EPA regulations are published in Part , Title 40, Code of Federal Regulations (CFR).
MTG for a Subtitle C Landfill 300 mmDrain (or GN) S-GM* “Solid Waste” 150 mm 300 mm 900 mm Filter (or GT) Drain (or GN/GC) 1x10 -7 cm/sec (to highest groundwater level) P-GM* 3.0 m Composite liner
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) Erosion Layer Infiltration Layer 150 mm 450 mm
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.) 300 mmDrain (or GN) 150 mm 600 to 900 mm Topsoil Filter (or GT) 1x10 -7 cm/sec ”Solid Waste” Varies (frost depth) Cover Soil 300 mmGas Vent (or GT) GM
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
Primary Functions TypeSRFDB GM----Y GCL----Y GN---Y- GTYYYY- GG-Y--- GP---Y- GCYYYYY S = separation, R = reinforcement, F = filtration D = drainage, B = barrier
Natural Soils vs. GSs FunctionNatural SoilGeosynthetics Barrier-SingleCCLGM Barrier- Composite GM/CCLGM/GCL GM/GCL/CCL Drainage LayerSand Gravel or sand GT GN Filter LayerSandGT
Liner System GT GG GN GCL GM CCL Gravel w/ perforated pipe
Final Cover System Geosynthetic ECM GP or GC GT GG Cover Soil GCL GM GC or GN
Possible Geosynthetic Layers in a Waste Containment System in Final Cover -7 in Base Liner 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 CCL Clay Liner (by itself) Leachate CCL Composite Liner (with intimate contact) Does the GT compromise the composite liner concept? Ans: Generally no... Leachate Composite Liner (GM + GCL) GCL
Composite Barriers (Theoretical Leakage) GM alone (hole area “a”) Leachate ksks Composite liner (GM/CCL) QCa gh B 2 Q = 0.21 a 0.1 h 0.9 k s 0.74 (for good contact) Q = 1.15 a 0.1 h 0.9 k s 0.74 (for poor contact) Ref. Bonaparte, Giroud & Gross, GS ‘89)
Generalized Leakage Rates Through Liners (ref. Giroud and Bonaparte, Jour. G & G, 1989) *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 Life Cycle Stage Leakage Rate (lphd) GM GM/CCL GM/GCL Sand Leak Detection
Average Values of Leakage Quantities (cont’d) Life Cycle Stage Leakage Rate (lphad) GM GM/CCL GM/GCL Geonet Leak Detection
Geomembranes Widely Used GeomembranesLimited Used Geomembranes High density polyethylene (HDPE) Chlorosulfonated polyethylene (CSPE) Linear low density polyethylene (LLDPE) Ethylene interpolymer alloy (EIA) Flexible polypropylene (f-PP) Ethylene propylene trimonomer (EPDM) 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
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 FS Allowable (Test) Property Required (Design) Property FS Allowable (Test) Property 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 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 C 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 (T g ). An addition of 30% plasticizer in PVC can lower the T g from 80 o C to –20 o C. 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 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) –> g/ml for HDPE – g/ml for MDPE – 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
Reactions during Acceleration Period
Functions of Antioxidants Primary antioxidants react with free radical species Secondary antioxidants decompose ROOH to prevent formation of free radicals
Types of Antioxidants CategoryChemical TypeExample PrimaryHindered phenol Irganox 1076 or 1010 Santowhite crystals Hindered amines Various of Tinuvin , Chemassorb 944 SecondaryPhosphites Irgafos 168 Sulfur compoundDilauryl thiodipropionate Distearyl thiodipropionate Hindered amines Various of Tinuvin , Chemassorb 944
Effective Temperature Range Phosphites Hindered Phenols Thiosynergists Hindered Amines Temperature ( o C)
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 H E act transition state products of reaction Separate Reactants Potential Energy Progress of Reaction
Distribution of Energy dN dE Energy Fraction is -E-E act RT exp ( )
Arrhenius Equation (9) (10) (11)
Arrhenius Plot A ln R r 1 E act R 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 85 o C
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 Std-OIT HP-OIT Density Melt Index Yield Stress Yield Strain Break Stress Break Strain Incubation Time (month) Percent Retained 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 °C 65°C 75°C 85°C ln OIT (min.) Incubation Time (month)
b) –Arrhenius Plot Standard OIT HP-OIT 1/T (°K) ln (OIT Depletion Rate) y = x R^2 = y = x R^2 = 0.943
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 less than 20 landfills recirculating leachate ~ 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?