Transcript in landfill

Solid Waste Management and
Sustainability Technology (NOTE 6)
Joonhong Park
Yonsei CEE Department
2015. 11. 01
Landfill Technology: Contents
Planning, Siting and Permitting
of Landfills
Landfill Processes
Landfill Design
Background
How residues that have no value can
best be managed and disposed of.
Is Land the best location for waste
disposal? (ocean, space, etc).
Combustion and then Landfill (EU) vs.
Landfill as a bioreactor (US)
One the most difficult facility to plan,
site and permit.
Planning
Design Period: 10 year (short-term plan), 30 year (an
appropriate long-term plan), longer than 50 year
(difficult to predict).
Sufficient landfill capacity for a design period
- MSW (compaction effect has to be considered).
- coverage (20-50% of the volume of the landfill)
- An in-place density of “700 kg/m3”
- facilities for its treatment processes (leachate, gas,
special waste treatments).
Factors affecting the volume requirement after landfill
construction (new regulations, competing facilities,
different cover options, nonresidential waste changes)
Volume Reduction
An important design and operational variable.
Step 1. Set the compaction density (compacted bulk
density) in landfill (1200 lb/yd3 or 700 kg/m3), ρc
Volume basis
Mass basis
Step 2. calculate the overall density, ρo
Step 3. Calculate the fraction remaining of initial volume
as a result of compaction (volume reduction), F
F = ρ o/ ρ c
Calculation of landfill capacity
Year
1
2
.
.
20
Total
population
Per capita
generation
rate
(mass rate)
Diversion
fraction
5.6
5.8
0.25
0.35
6.4
0.35
Waste to
landfill,
(mass)
Waste to
landfill,
(volume)
One year
volume
Accum.
One year’s volume
= [(Population) x (per capita generation rate) x (1-Diversion) x 356 d/yr]
/ (compacted bulk density)
Landfill Capacity (T) = cover soil volume (0.25 * T) + accumulative volume
Siting
The execution is far from easy.
- NOPE (Not on Planet Earth)
- NIMTO (Not In My Term of Office)
Step 1: Determination of geographic boundary.
Step 2: Identification of “unsuitable” locations.
- Fatal flaw analysis (wetlands, flood plain, seismic zone,
endangered species habitat, close to airport, GW
recharge area, unsuitable soil conditions).
Step 3: Ranking potential locations (population, land use,
groundwater quality, visual and noise impact, soil
condition, proximity to the centroid of solid waste
generation.)
Permitting
Subtitle D of RCRA (Resource Conservation and Recovery
Act)
- Examination of requirements (siting,design requirements,
operating conditions, groundwater monitoring, landfill
closure, post closure, and financial assurance).
- Combination of performance standards and design
standards.
Other
- Permitting for land use conformance, air emissions,
groundwater and surface waster discharge, operations,
extraction for cover material and closure
- Cost for Taking Land and Compensation for Relocation
Landfill Processes
- Biological degradation
- Leachate Production
- Gas Production
Biological Degradation
45-60% organic matter among refuse
(proteins, lipids, carbohydrates, and lignins)
67% of the organic matter is biodegradable.
- Readily biodegradable fraction (food and
garden wastes)
- Moderately biodegradable fraction (paper,
textiles, and wood)
33% of the organic matter is recalcitrant (nondegradable or very difficult to degrade).
Predominant decomposition
pathways
Proteins
Carbohydrates
Lipids
Amino acids
Simple sugars
Glycerol
/LCVAs
Hydrogen/CO2
Methane
AcetateFermentationSCVAs
Methane
Methane +
Methanogenesis
CO2
Acetate
Acid formation
Landfill Ecosystem
Soil microbes are responsible for major rate
limiting steps of biodegradation of organic
wastes.
High degree of diversity due to heterogeneous
nature of waste and landfill operating
characteristics.
The greater microbial diversity, the more stable the
system against environmental perturbation.
Electron donor (ED) and Electron acceptor (EA)
- Rich in EDs (organic matters)
- Predominant EAs: CO2 and sulfate.
Seven key microbial groups in
MSW stabilization steps
Microbial group
Substrate
Amylolytic bacteria
Proteolytic bacteria
Celluloytic bacteria
Hemicellulolytic bacteria
Hydrogen-oxidizing methanogenic
bacteria
Acetoclastic methanogenic bacteria
Sulfate-reducing bacteria
Starches
Proteins
Cellulose
Hemicellulose
Hydrogen
Acetic acid
Sulfate
Phases in MSW Stabilization
Phase I – Initial Adjustment
- initial placement of MSW and accumulation of moisture
- acclimation to activate microbial communities
Phase II - Transition Phase
- Aerobic environment => anaerobic environment
- EA use is shifted from O2 to sulfate/nitrate
- hydrolysis
Phase III - Acid Formation Phase
- Conversion into VO acids by acid-formers (decrease in
pH, metal mobilization)
- Rapid consumption of sulfate and nitrate
Phases in MSW Stabilization
Phase IV- Methane Fermentation Phase
- VO acids are consumed by methane-forming
bacteria and converted into methane and CO2.
- Sulfate => Sulfides; nitrate => NH4
- pH increase but self controlled by bicarbontate
buffer system (helpful in methanogenesis)
- Heavy metal transport by complexation and
precipitation.
Phases in MSW Stabilization
Phase V- Maturation Phase
- Limitation of EAs and EAs results in dormancy.
- Gas production drops; leachate pollutant
concentration decreases; reappearance of
oxygen
- Slow degradation of resistant organic fractions
continues with the production of humic-like
substrates
Phases in MSW Stabilization
Transition
Acid
Formation
Methane
Fermentation
Maturation
COD
(mg/l)
Total VOCs
(mg/l)
Ammonia-N
(mg/l)
pH
480-18,000
1,500-71,000 580-9,760
31-900
100-3,000
3,000-18,800 250-4,000
0
120-125
2-1,030
6-430
6-430
6.7
4.7-7.7
6.3-8.8
7.1-8.8
Conductivity
(μS/cm)
2,450-3,310 1,600-17,100 2900-7,700
1,4004,500
Leachate Production
Definition of Leachate: polluted water
generated from MSU landfill.
Quantity
Quality
Leachate Production - Quantity
Precipitation (P)
Infiltration
Interception and
Evaporation by
vegetation
Evapotranspiration (E)
Surface runoff (R)
Percolation (C)
Moisture in MSW (S)
Groundwater
E (evapotranspiration,
mm/yr)
Leachate production
P (precipitation, mm/yr)
R*P here R: runoff coeff. (dimensionless)
(1-R)*P
S, storage within
the soil or waste
(mm/yr)
Leachage Out (Percolation, C)
Leachate Production - Quantity
C = P(1-R) – S - E
HELP (Hydrologic Evaluation of Landfill
Performance, the US Army Corps of
Engineers): good at long-term prediction of
leachate production and at comparision of
various design alternatives.
Study Example 4-3.
 Hydraulic Retention Time (HRT) of
leachate depends on operation history…(not
easy)
Leachate Production - Quality
High concentrations of organic pollutants (BOD=
up to ~100,000 ppm [cf. 200 ppm BOD in raw sewer)
Lead and Cadimum (from batteries, plastics,
packaging, electronic applicances, light bulbs etc.)
Site-to-site specific leachate quality makes landfill
design and operation very difficult (need to more
detailed investigation of quality in leachate).
Need to pretreatment of young leachage to make
it amenable to biodegradation.
Gas Production - Quantity
Gas Production = function (gas yield per
MSW weight, lag time, shape of the lifetime
gas production curve, and the duration of gas
production).
In theory one of MSW produces 442 m3
landfill gas containing 55% methane and a
heat value of 19,730 kJ/m3). => In practice,
only 10% efficiency…..and many other
variables.
Gas Production - Quantity
LandGEM (EPA model; www.epa.gov/ttn/catc.)
n
QT = Σ 2 k Lo Mi e-k * ti
i=1
QT: total gas emission rate from a landfill, volume/time
n = total time periods of waste placement
k = landfill gas emission constant, time-1
Lo = methane generation potential, volume/mass of waste
ti = age of the i th section of waste, time
Mi = mass of wet waste, placed at time i.
Gas Production - Quality
Component
% by volume (dry)
Methane
Carbon dioxide
Nitrogen (N2)
Oxygen
Ammonia
Hydrogen
45-60
40-60
2-5
0.1-1.0
0.1-1.0
0-0.2
Methane is a potent green-house gas
Many of VOCs are odorous and/or toxic.
Landfill Design
- Liners
- Leachate collection, treatment, and
disposal
- Landfill gas collection and use
Design Components
Final Cover
Gas control
Groundwater
Monitoring well
Methane
monitoring
Waste
Liner
(synthetic or
Natural)
Leachate
Collection System
Groundwater
Groundwater
Liner Systems for MSW Landfills
LCS
LCS (Leachate
Collection Sys)
HDPE Liner
GCL (geosynthetic clay liner)
Geomembrane
single-liner system
Low permeability soil
single-liner system
LCS (Leachate
Collection Sys)
LCS
GCL
Low permeability soil
single-liner system
GCL
LDS
(Leachate
Detection
System)
Double liner system
With bottom composite liner
Components of LCS
 protective and drainage layers
Perforated collection lateral and header
pipes
Pump station sump
Leachate pump
Pump controls
Pump station appurtenances
Force main or gravity sewer lines
Leachate-Collection System Design
Q: infiltration rate (L3/T)
A: horizontal area
q 
Q
A
 ( )K
h
x
q: vertical inflow per horizontal
area or design storm (L/T)
(e.g. a 25-yr, 24-h storm)
K: hydraulic conductivity (L/T)
h
x
α
Drainage
Slope = tan
: head gradient (L/L)
Ymax: Max. leachate head
α
P: spacing between collection pipes
Ymax
0.5
2

P  q  K tan 
K tan   2
q 
  
1
 tan    
2  K  
q
q 
K  
Leachate-Collection System
Design Guideline
Parameter
Range
Leachate loading rate (gpd/ac)
600-1000
Max. leachate head (in)
9-12 (30cm)
Pipe spacing, P (ft)
60-400
Collection pipe dia. (in)
6-8
Collection pipe material
PVC or HDPE
Pipe slope (%)
0.5-2
Drainage slope (%) = tan α
0.2-2
PLEASE STUDY EXAMPLE 4-5.
Median
750
11
180
8
HDPE
1
1
Leachate Treatment Options (Table 4-11)
 Biological
-Activated sludge (BOD/COD): good for young leachate
-Aerated lagoons (BOD/COD): good for a small scale
-Anaerobic (BOD/COD): good for high organic conc.
 Physical/chemical
- Coagulation/precipitation (heavy metals): good for Fe, Zn; little
effective for Cd, Pb, and Ni.
- Chemical oxidation (COD): efficient but requiring a great dosage.
- Ion exchange (COD): 10-70% COD removal, slight heavy metal
removal.
- Adsorption (BOD/COD): 30-70% COD removal after biological or
chemical treatment
- Reverse osmosis (total dissolved solids): 90-96% TDS removal. Of
course expensive
Leachate Recirculation
Recirculation of leachate back through the
landfilled waste
 Offers more rapid development of active
anaerobic microbial populations and increases
reaction rates and predictability of these
organisms.
 Moisture may result in reduced efficiency of
Gas collection. Therefore, the location of
leachate recirculaiton should be changed
frequently (an integral part of landfill operations)
Gas Recovery
Gas (CO2 50% and CH4 50%)
-Greenhouse gases
-Modern landfill has facilities to
use methane to generate electricity.
Gas Collection
 Passive collection
-vent collectors
-release the gas to the atmosphere w/o treatment
-typical spacing for a passive vent is one per 7500 m3.
 Active extraction
- extract the gas under vacuum created by a central
blower
- typically vertical gas wells are used.
Typical vertical gas well
Casing: PVC or HDPE pipe (3-8 in)
- Interior Spacing: 200-250 ft.
- Perimeter Spacing: 100-250 ft.
- Min. slope 3%
Wide Slots
(High Permeability)
Crushed Rock
(High Permeability)
Well Bore Seal Zone
Well Depth
(75% of depth or to water table)
Impermeable Zone
Well Bore Seal
(Diameter 24, 30, or 36 in)
Perforations
(min. 25ft)
Cover Soil
(Low Permeability)
Pressure Drop Calculation (p.145-147)
 Gas flow: v = Q/A
-Q: landfill gas flow rate
-A: cross-sectional interior area of the pipe
 Pressure drop ∆P = ρ f L v2/(2gD)
- ρ: gas density = M.W. of the gas * Pressure /(R*T)
- L: length of pipe
- D: diameter of pipe
- f: Darcy-Weisbach friction factor
(function of roughness/D; attainable from a Moody diagram)
- g: gravitational constant
Technical Issues in Gas Use
 Gas Composition has significant impact on
energy recovery, gas cleanup, collection and
operation systems.
 Effects of corrosives on equipment
(organic acids, H2S, water vapor)
Effect of particles on equipment (small soil
particles, combustion of dimethyl siloxane
[gas] into silica deposits)
Effects of H2S and halide compounds on
the efficiency of energy recovery from the
gas.
Applications of Landfill Gas Use
Boilers and other direct combustion applications (e.g.,
vehicle fuel=> reduced NOx): economically feasible.
Conversion of landfill gas to synthetic fuels and chemicals
(e.g.,hydrocarbon production, methanol synthesis):
economically not feasible.
Electrical power generation for internal combustion
engines and gas turbines (the most common landfill gas-toenergy application; for large scale): the most profitable.
 Electrical power generation for fuel cells (well established;
higher energy efficiency; for small scale): also profitable.
Purification to pipeline-quality gas (not that popular):
Tax incentives and favorable purchase price are key nontechnical issues.
Geotechnical Aspects of Landfill Design
Landfill stability: Slope failures during the landfilling and
after its closure. => potential for catastropes.
Critical point of failure: soil/geosynthetic &
geosynthetic/geosynthetic interfacial surfaces as well as
waste slopes
Landfill stability must be investigated under both static and
seismic conditions.
Seepage in a “bioreactor” landfill will result in slope failure.
 side slopes ofcompleted and capped landfills be no
greater than 1:3 with 1:4 being preferable. (risk versus
design volume)
Stormwater Management
Control of the size of the working place: higher
than its surrounding area.
 Placement of interim cover on the waste.
Runon control: prevention of the introduction of
stormwater to the active area of the landfill; a higher
location, ditches, dikes, or culverts to divert flow.
Runoff control: swales, ditches, berms, dikes, or
Channel lining
culverts.
system
Erosion
control
Outlet pipe
Landfill Cap
Purpose: prevent the production of leachate after
closure of a landfill.
Typical side slope:
- 1:3 to 1:4
- the interface friction bet. Adjacent layers must
resist seepage forces
- decrease the contact stresses between layers due
to buildup of water and/or gas pressures.
Landfill Cap
Plant
Revegetated topsoil.
Protective material
Capillary force use
Drainage material
Clay barrier.
Impermeable
Gray (supporter)
* Three
mode of cap failures: Desiccation, Shear
setting, and Rotation setting.
Landfill Operation
Landfill Equipment
Filling Sequences
Daily Cover (disease control, odor and litter
control, air emission, reducing the risk of fire,
minimization of leachate production)
 Monitoring (groundwater, gas)
Post-closure care and use of old landfills
Requirements during post-closure period
-Maintenance of the integrity and effectiveness of
the final cover
-Operation of the leachate collection system
-Groundwater and gas-migration monitoring.
Final use alternatives
-Golf courses
- Natural areas
-Recreation parks
- Ski slopes
-Parking lots
- Building construction
Landfill Mining
If significant biodegradation occurs, it might be
possible to dig up old landfills, separate the
nonbiodegradable fraction, and use the dirt and
organic soil as a cover material for present
landfills.
Problems…..
Only shallow landfills that have few vertical lifts
are candidates for landfill mining since they are
most likely to have fully biodegraded.
May provide an economical alternative to the
siting of new landfill.