instrumentation and process control - bioreactor landfill€¦ · · 2013-08-20by the...
TRANSCRIPT
Topics Covered
Critical Monitoring Leachate collection system performanceMoisture measurement In-place specific weight
Critical Monitoring - Waste
Temperature Settlement Specific weight Volatile solids Biochemical Methane PotentialMoisture Content pH
Instrumentation to be Discussed
In situ temperature measurement, Leachate collection system performance
assessment, In situ moisture content measurement, andWaste specific weight measurement.
Temperature Measurement
In anaerobic bioreactors, temperature is controlled by the introduction of moisture.
In aerobic bioreactors temperature is controlled by moisture content and airflow.
High temperatures have been associated with spontaneous combustion and landfill fires.
Temperature does not significantly impact the interface shear strength geomembranes
Technologies
Thermocouples Thermistors Liquid expansion Resistance detectors Infrared radiators Bimetallic thermometers
Thermocouples
Technology most frequently applied to landfills Thermocouples are pairs of dissimilar metal wires
joined at one end. Thermocouples tend to be more rugged and less
expensive than thermistors, however they areslightly less accurate.
Type J thermocouples are most commonly used inlandfills.
Damage to the sensor wiring cable is one of themost common causes of sensor failure.
Thermocouple profile well near anchor trench
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7080.0 85.0 90.0 95.0 100.0 105.0 110.0 115.0 120.0 125.0 130.0
Temperature (degrees F)
Dep
th fr
om T
op o
f Lan
dfill
(ft)
TP3 TP2
TP4 TP1
TP4 TP5
New River Regional LandfillTemperature Profiles
Example of T-Profile Well Results
Thermistors
Measure temperature as a function of the change inelectrical resistance of materials
Composed of inexpensive semiconductor materials. They are accurate over a smaller range than
thermocouples, They are quite stable and accurate over temperature
ranges expected in bioreactor landfills.
Measure Temperature
T < 140 °F
Temperature may be below optimum. Investigate and revise operations as desired. Not a safety hazard.
Process Control –Temperatrue
T < 140 °F
T > 140 °F T < 160 °F
Temperature may be below optimum. Investigate and revise operations as desired. Not a safety hazard.
Optimum conditions. Operate and monitor as scheduled.
T > 160 °F T < 170 °F
T > 170 °F
Possible concern. Check gas concentrations. If anaerobic → Check moisture content monitors. Add leachate or other moisture If aerobic → Reduce air flow rate. Track the rate of temperature increase of this area. If a rate of 1°F per day (weekly average) is exceeded, stop air injection and add leachate/water.
Condition of concern. Stop air injection. Add leachate or other moisture.
Sump Measurements
Head losses must be calculated with little knowledge of the condition of piping and drainage layers. Without an internal means of measuring
hydraulic parameters the actual head on the liner cannot be determined easily.
Piezometers
Limited measurement area,May put the liner at risk,May clog,May interfere with landfill operation, and Vertical wells may be impacted by gas
production
Pressure Transducers
Use a calibrated strain gage mounted on a flexible,silicon diaphragm protected by a membrane.
Transducers used to measure absolute pressurerequire a vent tube be run with the wiring cable.
Landfill applications require either high-gradestainless steel or titanium materials to preventcorrosion
Reference measurements of landfill gas pressuresrequired
Head on the Liner Measurements –New River Regional Landfill
LCS Surface
Pressure Transducer
Geomembrane
Geofabric
Drainage Layer
Easting
624400 624450 624500
1 7 4 6 5 5 0
1 7 4 6 6 0 0
1 7 4 6 6 5 0
1 7 4 6 7 0 0
1 7 4 6 7 5 0
1 7 4 6 8 0 0
Leachate Collection pipe
Slope
Nor
thin
g
Head on Liner Experiment
269410 269415 269425 269430
4 0 4 7 5 0
4 0 4 8 0 0
4 0 4 8 5 0
4 0 4 9 0 0
4 0 4 9 5 0 N
orth
ing
Easting
Central Leachate Collection Point
Slope
Slope Slope
NRRL Cell 3
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1
2
3
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6
03-Jul 03-Aug 03-Sep 04-Oct 04-Nov 05-Dec 06-Jan 06-Feb 12-Mar 16-Apr 17-MayTime (days)
Rai
nfal
l (in
ch)
0
1
2
3
4
5
6
Avg.
Hea
d on
Lin
er (i
nch)
Rainfall vs. Time Avg. Head on Liner vs. TimeHELP Model
o
Failure Causes
Lightning strike at data station Overburden pressure due to waste placed above
sensors Marine grease applied to sensors to prohibit
biological growth from occurring inside of thesensor nose cone
Inability to isolate from influence by atmosphericpressure changes
Process Control – Head on the Liner
Maintain a properly designed leachatecollection system, store or dispose ofleachate outside of the landfill, Remove leachate at sufficient rates Adjust moisture addition rates
Measurement of Moisture
Water balance Collect waste samples and measure
gravimetrically In situ methods
Water Balance
Track moisture into and out of landfill Storage
In
Out
Time
CumVol
LeachateRecirculation
LeachateCollected
In Situ Moisture Measurement
Time domain reflectometry, Time domain transmissometry Neutron density Electrical conductivity
Time Domain Reflectometry
TDR theory states that the time for a transmitted electromagnetic pulse to be reflected is dependent on the dielectric constant of the medium.
Time Domain Reflectometry
ADVANTAGES Provides an in situ
method of moisture determination.
The technology is non-toxic and harmless.
Unaffected by organic carbon content changes.
DISADVANTAGES Is affected by changes
in specific conductivity.
Heterogeneity of landfills may lead to erroneous readings.
Must be calibrated to solid waste matrix
Time Domain Transmissometry
measures the time that a fast pulse takes to travel along a section of transmission line
time measured is a one-way propagation time
Neutron Probe Advantages and Disadvantages
Advantages: Average moisture contents
over depths Readings are related
directly to soil moisture Non-destructive moisture
measurements It has a large radius of
influence between 150 mm in wet soil and 700 mm in dry soil
Disadvantages Cannot measure absolute
moisture content safety hazards The presence of non-water
hydrogen and changes in density may reduce the accuracy
Electrical Resistance
This technology is based on the principle that the moisture of a medium can be determined from the value of the measured electrical resistance.
Electrical Resistance
ADVANTAGES Sensors are
inexpensive. The technology is non-
hazardous permitting in situ monitoring of moisture content.
DISADVANTAGES Gypsum sensors suffer
from hysteresis unless complete wetting is achieved before each drying cycle.
Each sensor may require its own individual calibration.
Moisture Distribution
15 ft
30 ft
50 ft
05/30/03 10/01/03 11/01/03
30
40
50
60
65
70
Lower moisture
Higher moisture
Moisture content obtained from resistance values
Response of MTG
Day 1 = 01/01/03
100 150 200 250 300 3500.001
0.01
0.1
1
10
100
1000
L6E-MiddleL6E-LowerL6E-Upper
Days
Res
ista
nce
(KO
HM
S)
Start of Leachate Recirculation
Moisture content from sensors
Days 150 200 250 300(%
) Gra
vim
etri
c M
oist
ure
Con
tent
20
30
40
50
60
70
80
TDR 11MI5-Middle
Start of leachate recirculation
New Moisture Content Technologies
Gas tracer method Fiber optics Geophysical, noninvasive techniques
electrical sounding, electrical 2-D imaging, electromagnetic mapping, and radar profiling
Process Control – Moisture Content
Evaluate rate of moisture addition Evaluate compaction Evaluate alternative moisture introduction
techniques Identify dry areas of the landfill requiring
longer time to stability
Remaining Questions – In Situ Moisture Content Measurement
How long will they work? Once wetted, do they stay wet? Does installation create preferential flow paths? Can true moisture content be measured, or only
relative moisture content? Are they economical? Can wireless measurement be implemented?
Pressure Measurements Obtained Using the Total Pressure Cell
Average measured specific weights vary between 300-1700 lb/ft3
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1200
7/18/00 10/26/00 2/3/01 5/14/01 8/22/01 11/30/01 3/10/02 6/18/02 9/26/02 1/4/03 4/14/03 7/23/03 10/31/03 2/8/04 5/18/04
time (days)
PSF
0
5
10
15
20
25
30
35
Hei
ght (
ft)
PSFWaste Height