Monroe L. Weber-Shirk S chool of Civil and Environmental Engineering Biodegradation in Landfills: Methane Production

Monroe L. Weber-Shirk

School of Civil and

Environmental Engineering

Biodegradation in Landfills:Methane Production

Biodegradation in Landfills:Methane Production

Hypodermic needle

Crimp cap with septa

Pressure sensor

Anaerobic solution

analogto

digital Power Supply (10 V)

Connector panel

Multiplexer

RJ 45 plug

Serum bottle

35º C incubator

Hypodermic needle

Crimp cap with septa

Pressure sensor

Anaerobic solution

analogto

digital Power Supply (10 V)

Connector panel

Multiplexer

RJ 45 plug

Serum bottle

35º C incubator

Methane and LandfillsMethane and Landfills

Aren’t we recycling most of the paper that we throw away?

Why are Landfills anaerobic? Methane Experiment

Measure the methane production from various landfill components under various conditions

Compare the energy value of the methane with the energy value of the original waste

Issues... pH, pressure monitoring, inoculum

Aren’t we recycling most of the paper that we throw away?

Why are Landfills anaerobic? Methane Experiment

Measure the methane production from various landfill components under various conditions

Compare the energy value of the methane with the energy value of the original waste

Issues... pH, pressure monitoring, inoculum

Solid Waste Composition in 1994

as Generated (US averages)

Solid Waste Composition in 1994

as Generated (US averages)

Wood7%

Miscellaneous9%

Paper and paperboard

38%

Plastics10%Food

7%

Yard waste15%

Glass6%

Metals8%

2 kg/cap/day

The majority is organic matter!

Landfills...Landfills...

Will continue to be the disposal option of choice

Require long term monitoring ________________ ____________________________ _________________ ____________________

Why does gas production continue long term? Why is much organic matter preserved?

Will continue to be the disposal option of choice

Require long term monitoring ________________ ____________________________ _________________ ____________________

Why does gas production continue long term? Why is much organic matter preserved?

subsidencesubsidence

leachate collection/treatmentleachate collection/treatment

cover maintenancecover maintenance

gas venting or collectiongas venting or collection

Why are Landfills anaerobic? Why are landfills warm? (Average temperature of

Fresh Kills Landfill is 29.4 °C)

Follow carbon flow...

Why are Landfills anaerobic? Why are landfills warm? (Average temperature of

Fresh Kills Landfill is 29.4 °C)

Follow carbon flow...

Methane ProductionMethane Production

Organic MatterOrganic Matter

NutrientsNutrients CH4CH4 CO2CO2NH3NH3 H2SH2S

Refractory organic matterRefractory organic matter

HeatHeat

CellsCellsH2OH2O New CellsNew Cells

keeps runoff and precipitation out of landfillsafely vents gases

GeomembraneGeomembrane

Drainage LayerDrainage Layer

Cover SoilCover Soil

Compacted ClayCompacted Clay

WasteWasteWasteWaste

Gas Collection LayerGas Collection Layer

Gas VentGas VentCap SystemCap System

Experiment SetupExperiment Setup

Hypodermic needle

Crimp cap with septa

Pressure sensor

Anaerobic solution

analogto

digital Power Supply (10 V)

Connector panel

Multiplexer

RJ 45 plug

Serum bottle

35º C incubator

pH control...pH control...

High partial pressure of CO2 ____ pH

Anaerobes require a pH between 6.5 and 7.5 Remember ANC... Volatile or Non-volatile system?

High partial pressure of CO2 ____ pH

Anaerobes require a pH between 6.5 and 7.5 Remember ANC... Volatile or Non-volatile system?

H

H

KKPANC wHCO

21

0

22

H

H

KKPANC wHCO

21

0

22

0

12

HCO KPANC

0

12

HCO KPANC

lowlow

Organic MatterOrganic Matter

NutrientsNutrients CH4CH4 CO2CO2NH3NH3 H2SH2S

Refractory organic matterRefractory organic matter

HeatHeat

CellsCellsH2OH2O New CellsNew Cells

0.00000001

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

pH

con

cen

trat

ion

(m

oles

/L)

H2CO3

HCO3

CO3

H+

OH-

How much ANC do we need?How much ANC do we need?

2

*2 3

HCO

H COK

P

é ùë û=

31 *

2 3

H HCOK

H CO

+ -é ùé ùë ûë û=é ùë û

KH has a value of 3.12 x 10-4 moles/J

K1 has a value of 10-6.3 moles/L

1

0

aa

=

2 1CO HP K KANC

H +=é ùë û

Simplify alpha terms

0

12

HCO KPANC

0

12

HCO KPANC

3

*2 3

HCO

H CO

-é ùë ûé ùë û

= 1K

H +é ùë û

ANC ProblemANC Problem

How much ANC is needed to maintain a neutral pH if the pressure is atmospheric and the CO2 fraction is 30%?

How much ANC is needed to maintain a neutral pH if the pressure is atmospheric and the CO2 fraction is 30%?

ANCx Pa x

molesJ

M

M

FH IK

3 10 312 10 10

10

4 4 6 3

7

c h c h. .

ANCmolesm

46 9 3.

2 1CO HP K KANC

H +=é ùë û

230COP kPa=

ANC ProblemANC Problem

If serum bottles have that much ANC what will the pH be if the CO2 pressure doubles?

If serum bottles have that much ANC what will the pH be if the CO2 pressure doubles?

ANC

KKPH HCO 12 CO2 pressure doubled so H+ ________

72 10H M+ -é ù= ×ë û pH = 6.7

doubles

pH was 7 (_____________) so…71 10H M+ -é ù= ×ë û

The system is adequately buffered!

InoculumInoculum

We need a few good anaerobes... Where could we recruit?

How do we choose inoculum size?

We need a few good anaerobes... Where could we recruit?

How do we choose inoculum size?

Sample SizeSample Size

What happens if you put ¼ of a graham cracker into a 120 mL serum bottle with 60 mL of water and some inoculum and seal it?

Estimate mass of carbohydrates at 4 grams Moles of carbohydrates – 30 g/mole _____ 0.133 moles C

What happens if you put ¼ of a graham cracker into a 120 mL serum bottle with 60 mL of water and some inoculum and seal it?

Estimate mass of carbohydrates at 4 grams Moles of carbohydrates – 30 g/mole _____ 0.133 moles CP

nRTV

P

molPa mmol K

K

m

FHG

IKJ

0133 8 31 308

60 10

3

6 3

. .a f

P MPa 5 7. Bottle rocket!

of CCH2O

Samples for AnalysisSamples for Analysis

Bring 1 sample per person for methane production Ideas…

________________ ________________ ________________ ________________ ________________ ________________ ________________

Bring 1 sample per person for methane production Ideas…

________________ ________________ ________________ ________________ ________________ ________________ ________________

Pressure SensorsPressure Sensors

Transduce pressure into a voltage! Use Strain Gages

Design of piezoresistive strain gages Sensor output Signal Conditioning Calibration

Transduce pressure into a voltage! Use Strain Gages

Design of piezoresistive strain gages Sensor output Signal Conditioning Calibration

Strain gageStrain gage

What happens to the resistance thru the strain gage if it is stretched in the y direction? ________________

In the x direction? ________________

Strain gage can be made of wire that is then bonded to the objected that is undergoing strain

Or diffused into a crystalline silicon diaphragm (___________)

What happens to the resistance thru the strain gage if it is stretched in the y direction? ________________

In the x direction? ________________

Strain gage can be made of wire that is then bonded to the objected that is undergoing strain

Or diffused into a crystalline silicon diaphragm (___________)

x

y

Little change

Great change

Piezoresistive

Piezoresistive DiaphragmsPiezoresistive Diaphragms

Excitation +

Excitation -Signal +

Signal -

R is function of ____________ on crystal and strain.orientation

R R

R+R

R+R

Voltage___

Voltage___

Pressure Sensor FailurePressure Sensor Failure

High pressures – rupture crystal (beware of resulting leak!)

Water hammer – High speed pressure waves (speed of sound) Result from flow transients such as rapidly

shutting valves Install pressure snubber!

Incompatible materials

High pressures – rupture crystal (beware of resulting leak!)

Water hammer – High speed pressure waves (speed of sound) Result from flow transients such as rapidly

shutting valves Install pressure snubber!

Incompatible materials

or elastic tubing

Absolute vs. Gage vs. Differential

Absolute vs. Gage vs. Differential

Absolute Port 2 sealed with vacuum

on bottom side of silicon crystal

Gage Port 2 open to atmosphere

Differential Both ports connected to

system

Absolute Port 2 sealed with vacuum

on bottom side of silicon crystal

Gage Port 2 open to atmosphere

Differential Both ports connected to

system

Port 1

Port 2

Used in the lab

Pressure Sensor ApplicationsPressure Sensor Applications

Many! Level monitoring of municipal water tanks Gas tank gage Various flow meter devices (orifice,

Venturi) Stream gage (USGS) Instrumentation (Gas and Liquid

Chromatographs)

Many! Level monitoring of municipal water tanks Gas tank gage Various flow meter devices (orifice,

Venturi) Stream gage (USGS) Instrumentation (Gas and Liquid

Chromatographs)

Pressure Sensor Signal Conditioning

Pressure Sensor Signal Conditioning

Full scale voltage output from the bridge circuit may be in the range of 10 to 100 mV.

This low voltage may need amplification before being measured by a data acquisition system

Limit cable length and beware of noise from power cables!

Time average to reduce noise

Full scale voltage output from the bridge circuit may be in the range of 10 to 100 mV.

This low voltage may need amplification before being measured by a data acquisition system

Limit cable length and beware of noise from power cables!

Time average to reduce noise

Pressure Sensor CalibrationPressure Sensor Calibration

Sensor output should be linear Calibration involves determining the slope and

intercept Subtract the voltage obtained under conditions of

zero pressure (offset) to get an intercept of zero The slope can be determined by applying different

pressures to the sensor and measuring the resulting voltages

Multiply the remaining voltage by the slope

Sensor output should be linear Calibration involves determining the slope and

intercept Subtract the voltage obtained under conditions of

zero pressure (offset) to get an intercept of zero The slope can be determined by applying different

pressures to the sensor and measuring the resulting voltages

Multiply the remaining voltage by the slope

Pressure Sensors SummaryPressure Sensors Summary

Based on a small change in resistance due to a change in dimension (strain gage)

Commonly used to monitor industrial and environmental processes

Easily monitored using data acquisition systems

Based on a small change in resistance due to a change in dimension (strain gage)

Commonly used to monitor industrial and environmental processes

Easily monitored using data acquisition systems

Pressure Complications…Pressure Complications…

Pressurized serum bottle Placed in incubator and

monitored Why does pressure increase

initially?________________ What are the short term

fluctuations?_______________________________

What are the long term fluctuations? ____________

Pressurized serum bottle Placed in incubator and

monitored Why does pressure increase

initially?________________ What are the short term

fluctuations?_______________________________

What are the long term fluctuations? ____________

Temperature!

Incubator temperature fluctuations!

0

2

4

6

8

10

12

0 5 10 15 20

Time (days)

Pre

ssur

e (k

Pa)

68.8

68.9

69

69.1

69.2

69.3

69.4

69.5

0 1 2 3 4 5

Time (hr)

Pre

ssur

e (k

Pa)

68.8

68.9

69

69.1

69.2

69.3

69.4

69.5

0 1 2 3 4 5

Time (hr)

Pre

ssur

e (k

Pa)

Atmospheric pressure!