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

Methane and Landfills ä Aren’t we recycling most of the paper that we throw away? ä Why are Landfills anaerobic? ä Methane Experiment ä Measure the methane production from various landfill components under various conditions ä Compare the energy value of the methane with the energy value of the original waste ä Issues... pH, pressure monitoring, inoculum ä Aren’t we recycling most of the paper that we throw away? ä Why are Landfills anaerobic? ä Methane Experiment ä Measure the methane production from various landfill components under various conditions ä Compare the energy value of the methane with the energy value of the original waste ä Issues... pH, pressure monitoring, inoculum

Solid Waste Composition in 1994 as Generated (US averages) Wood 7% Miscellaneous 9% Paper and paperboard 38% Plastics 10% Food 7% Yard waste 15% Glass 6% Metals 8% 2 kg/cap/day The majority is organic matter!

Landfills... ä Will continue to be the disposal option of choice ä Require long term monitoring ä ________________ ä ____________________________ ä _________________ ä ____________________ ä Why does gas production continue long term? ä Why is much organic matter preserved? ä Will continue to be the disposal option of choice ä Require long term monitoring ä ________________ ä ____________________________ ä _________________ ä ____________________ ä Why does gas production continue long term? ä Why is much organic matter preserved? subsidence leachate collection/treatment cover maintenance gas venting or collection

ä Why are Landfills anaerobic? ä Why are landfills warm? (Average temperature of Fresh Kills Landfill is 29.4 °C) ä Follow carbon flow... ä Why are Landfills anaerobic? ä Why are landfills warm? (Average temperature of Fresh Kills Landfill is 29.4 °C) ä Follow carbon flow... Methane Production Organic Matter Nutrients CH 4 CO 2 NH 3 H2SH2S H2SH2S Refractory organic matter Heat Cells H2OH2O H2OH2O New Cells

keeps runoff and precipitation out of landfill safely vents gases Geomembrane Drainage Layer Cover Soil Compacted Clay WasteWaste Gas Collection Layer Gas Vent Cap System

Experiment Setup Hypodermic needle Crimp cap with septa Pressure sensor Anaerobic solution analog to digital Power Supply (10 V) Connector panel Multiplexer RJ 45 plug Serum bottle 35º C incubator

pH control... ä High partial pressure of CO 2  ____ pH ä Anaerobes require a pH between 6.5 and 7.5 ä Remember ANC... ä Volatile or Non-volatile system? ä High partial pressure of CO 2  ____ pH ä Anaerobes require a pH between 6.5 and 7.5 ä Remember ANC... ä Volatile or Non-volatile system? low

How much ANC do we need? K H has a value of 3.12 x moles/J K 1 has a value of moles/L Simplify alpha terms

ANC Problem ä How much ANC is needed to maintain a neutral pH if the pressure is atmospheric and the CO 2 fraction is 30%?

ANC Problem ä If serum bottles have that much ANC what will the pH be if the CO 2 pressure doubles? CO 2 pressure doubled so H + ________ pH = 6.7 doubles pH was 7 (_____________) so… The system is adequately buffered!

Inoculum ä We need a few good anaerobes... ä Where could we recruit? ä How do we choose inoculum size? ä We need a few good anaerobes... ä Where could we recruit? ä How do we choose inoculum size?

Sample Size ä 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? ä Estimate mass of carbohydrates at 4 grams ä Moles of carbohydrates – 30 g/mole _____ ä moles C ä 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? ä Estimate mass of carbohydrates at 4 grams ä Moles of carbohydrates – 30 g/mole _____ ä moles C Bottle rocket! of C CH 2 O

Samples for Analysis ä Bring 1 sample per person for methane production ä Ideas… ä ________________ ä Bring 1 sample per person for methane production ä Ideas… ä ________________

Pressure Sensors ä Transduce pressure into a voltage! ä Use Strain Gages ä Design of piezoresistive strain gages ä Sensor output ä Signal Conditioning ä Calibration ä Transduce pressure into a voltage! ä Use Strain Gages ä Design of piezoresistive strain gages ä Sensor output ä Signal Conditioning ä Calibration

Strain gage ä What happens to the resistance thru the strain gage if it is stretched ä in the y direction? ________________ ä In the x direction? ________________ ä Strain gage can be made of wire that is then bonded to the objected that is undergoing strain ä Or diffused into a crystalline silicon diaphragm (___________) ä What happens to the resistance thru the strain gage if it is stretched ä in the y direction? ________________ ä In the x direction? ________________ ä Strain gage can be made of wire that is then bonded to the objected that is undergoing strain ä Or diffused into a crystalline silicon diaphragm (___________) x y Little change Great change Piezoresistive

Piezoresistive Diaphragms Excitation + Excitation - Signal + Signal -  R is function of ____________ on crystal and strain. orientation R R R+  R Voltage___

Pressure Sensor Failure ä High pressures – rupture crystal (beware of resulting leak!) ä Water hammer – ä High speed pressure waves (speed of sound) ä Result from flow transients such as rapidly shutting valves ä Install pressure snubber! ä Incompatible materials ä High pressures – rupture crystal (beware of resulting leak!) ä Water hammer – ä High speed pressure waves (speed of sound) ä Result from flow transients such as rapidly shutting valves ä Install pressure snubber! ä Incompatible materials or elastic tubing

Absolute vs. Gage vs. Differential ä Absolute ä Port 2 sealed with vacuum on bottom side of silicon crystal ä Gage ä Port 2 open to atmosphere ä Differential ä Both ports connected to system ä Absolute ä Port 2 sealed with vacuum on bottom side of silicon crystal ä Gage ä Port 2 open to atmosphere ä Differential ä Both ports connected to system Port 1 Port 2 Used in the lab

Pressure Sensor Applications ä Many! ä Level monitoring of municipal water tanks ä Gas tank gage ä Various flow meter devices (orifice, Venturi) ä Stream gage (USGS) ä Instrumentation (Gas and Liquid Chromatographs) ä Many! ä Level monitoring of municipal water tanks ä Gas tank gage ä Various flow meter devices (orifice, Venturi) ä Stream gage (USGS) ä Instrumentation (Gas and Liquid Chromatographs)

Pressure Sensor Signal Conditioning ä Full scale voltage output from the bridge circuit may be in the range of 10 to 100 mV. ä This low voltage may need amplification before being measured by a data acquisition system ä Limit cable length and beware of noise from power cables! ä Time average to reduce noise ä Full scale voltage output from the bridge circuit may be in the range of 10 to 100 mV. ä This low voltage may need amplification before being measured by a data acquisition system ä Limit cable length and beware of noise from power cables! ä Time average to reduce noise

Pressure Sensor Calibration ä Sensor output should be linear ä Calibration involves determining the slope and intercept ä Subtract the voltage obtained under conditions of zero pressure (offset) to get an intercept of zero ä The slope can be determined by applying different pressures to the sensor and measuring the resulting voltages ä Multiply the remaining voltage by the slope ä Sensor output should be linear ä Calibration involves determining the slope and intercept ä Subtract the voltage obtained under conditions of zero pressure (offset) to get an intercept of zero ä The slope can be determined by applying different pressures to the sensor and measuring the resulting voltages ä Multiply the remaining voltage by the slope

Pressure Sensors Summary ä Based on a small change in resistance due to a change in dimension (strain gage) ä Commonly used to monitor industrial and environmental processes ä Easily monitored using data acquisition systems ä Based on a small change in resistance due to a change in dimension (strain gage) ä Commonly used to monitor industrial and environmental processes ä Easily monitored using data acquisition systems

Pressure Complications… ä Pressurized serum bottle ä Placed in incubator and monitored ä Why does pressure increase initially?________________ ä What are the short term fluctuations?_____________ __________________ ä What are the long term fluctuations? ____________ ä Pressurized serum bottle ä Placed in incubator and monitored ä Why does pressure increase initially?________________ ä What are the short term fluctuations?_____________ __________________ ä What are the long term fluctuations? ____________ Temperature! Incubator temperature fluctuations! Atmospheric pressure!