chemical sciences - adaptive sensors group
Breda M. Kiernan BSc MPhil PhD
CLARITY: The Centre for Sensor Web Technologies
National Centre for Sensor Research
School of Chemical Sciences
Dublin City University
Phone: +353 1 700 7926
Fax: +353 1 700 7995
PhD. (2006) University of Bradford, U.K.
Title: Solution Speciation of Aqueous Polysulfide Systems
MPhil (2002) University of Bradford, U.K.
Title: FT-Raman Spectroscopy of Sulfonic Acids and Sulfonated Polystyrene Resin Beads
BSc. (2001) University of Bradford, U.K.
Chemistry with Pharmaceutical & Forensic Science
Industrial Placement: One year spent at Freudenberg Nonwovens, Halifax, West Yorkshire, UK
The background to air quality monitoring
The accurate and reliable monitoring of air quality in our environment is of great importance in modern society, as recognised by the evolving national and EU legislation that governs the legally permitted levels of key pollutants. For example, the EU Clean Air for Europe directive (CAFÉ, 2008/50/EC) “establishes the need to reduce pollution to levels which minimise harmful effects on human health ….and the environment as a whole, to improve the monitoring and assessment of air quality…..and to provide information to the public.”
Therefore, the modes of assessing air quality and detecting and monitoring pollutants in the air need to be consistently upgraded and improved upon. The prototype units, developed as part of this project, are doing just that; providing a means to sample, measure and communicate data in near real-time in one unit.
Development of an autonomous gas monitoring platform
There are four key features to be considered when developing platforms for remote monitoring. These are power, robustness, data retrieval and mode of sampling.
The most successful autonomous system will have a low power consumption which is supplemented by a means of energy scavenging from the unit’s immediate environment, e.g., solar panels.
The prototype unit needs to be resistant to the elements, housed in a rugged casing that will ensure the unit is resistant to shattering, water ingress and vandalisation. A way of securing the system at the monitoring site is also necessary, as theft is a recurring problem for environmental monitoring systems.
Data can be collected in real time, but in order to capitalize on this capability, events must also be rapidly defined and detected. Therefore, analytical measurements must be queried at the device level or transmitted to more powerful computation systems for decision making. By using wireless communications, such as Bluetooth, Zigbee and GSM, data can be retrieved in real-time from a remote location and any problems detected by the monitoring unit flagged to necessary parties and rectified before they become serious.
Samples must be representative of the actual component concentrations and the measuring protocol must be accurate and reliable. The sampling procedure, ideally, should not disturb the sample. A high sampling rate inevitably drains the power of the system much quicker, while a low sampling rate means that events of interest can be missed, e.g., gas surges or fluctuations in concentration. Therefore, the sampling rate is usually a compromise between conflicting demands.
The monitoring platform described here can be adapted for a number of target gases. The sampling chamber has been designed with a plug and play option in mind. Depending on the target gas under consideration, the sensor used can be changed and the unit becomes, therefore, application specific without extensive modification. Development of these types of platforms maximises the benefits of the design while minimising the effort needed to produce a prototype for a new application or target gas.
Two specific applications are described here – monitoring of the landfill gas components methane and carbon dioxide and monitoring of carbon monoxide at the exit of a multistorey car park.
What is a landfill?
Landfill is defined as a waste disposal site for the deposit of waste onto or into land. Landfill sites in Ireland are regulated and are given a license by the Environmental Protection Agency to take in waste and dispose of it safely. There are 79 licensed landfill sites in Ireland, but only 29 of these are active. The landfill site is lined with a polyethylene liner before filling takes place and a gas management system is put in place. Pipes are buried in the base of the landfill which extract the generated landfill gas and flare (burn) it off or, in some cases, use it as fuel. As mentioned, the main components of landfill gas are methane and carbon dioxide. Methane is a flammable gas under the correct conditions of temperature and pressure and oxygen concentration. Therefore, monitoring of methane build-up is important for those working on or near landfill sites. Both methane and carbon dioxide are classed as greenhouse gases and, therefore, reducing their emissions to ambient air is also important.
How is landfill gas monitored?
The waste license issued to each landfill site gives threshold limits for the amount of gas which can be present at perimeter borehole wells. These limits are 1.0 % v/v for methane and 1.5 % v/v for carbon dioxide. These borehole well measurements are carried out at least once per month by on-site staff or consultants working for the landfill site management team. A report of these measurements is kept on file and where the borehole measurements exceed the defined threshold limits, an incident report is sent to the EPA.
Landfill Gas Monitoring
Current methods of monitoring use handheld devices based on infrared detection or flame ionisation detection. There are also grab and analysis techniques, where samples of the gases are taken and later analysed in the laboratory. Monitoring a landfill using these techniques is labour intensive and time consuming. Although data are collected in real-time, they are not analysed in real-time. Additionally, they are not collected concurrently across the entire site or uploaded and compared with previous data in real-time. This can cause delays in identifying events on the site.
Why develop new monitoring units?
New monitoring units have been developed because the current sampling regime is labour intensive and measurements are not taken concurrently and uploaded in near real-time. Sampling once per month means that in the 25-30 days that sampling does not take place, “events” on the site can go unnoticed. By sampling more frequently, the management team have more information to use for decision making, meaning the site can be more effectively and efficiently managed and issues on the site such as high gas generation or blocked extraction pipes can be identified and dealt with more quickly. This in turn will decrease the risk of a gas build-up at the perimeter of the landfill site.
How does this system work?
1. Control Circuitry 5. Extraction Pump
2. Blue-tooth communications 6. Extraction Control Valve x2
3. GSM Communications 7. Gas Sample Chamber
4. 12V 7Ah Battery
Figure 1 Landfill Monitoring Unit
Figure 1 shows the design of the prototype for the landfill monitoring unit. The gas is extracted from the borehole well through a valve (6) using an extraction pump (5), and into the sampling chamber (7). Here the sensors measure the gas sample and the data are communicated to the flash memory drive on the electronics board (1). Once, the sampling cycle has been completed, a representative sample of the data are sent to the basestation using the GSM unit (3). When on-site, the data sets can be downloaded using the Bluetooth link (2).
The entire sampling procedure takes 9 minutes. This consists of
· 3 minute baseline with ambient air,
· 3 minute measurement of the extracted landfill gas (and recycling back into the borehole well),
· 3 minute purge of the cell with ambient air.
All data points for each 9 minute sampling cycle are saved on to a flash memory drive onboard the unit. Measurements are taken twice daily at 11 am and 11 pm, representing a 60-fold increase in the sampling rate at the site compared with existing monthly sampling using the handheld units.
The data sent via GSM text message has the following content;
· ADC value for the system battery;
· Baseline sample: average ADC value for the last 10 points for each IR sensor;
· Sample value: Maximum ADC value for each of the four sensors – CO2 IR, CH4 IR, temperature and humidity;
· Purge value: Minimum ADC value for each IR sensor.
From this, the battery power is known and it can be confirmed that all sensors are measuring accurately. Finally, a representative measurement of the maximum concentration of carbon dioxide and methane at the extraction depth in the borehole well can be compared with previous readings from that well.
Field validation trials
Figure 2: Landfill gas monitoring unit on a validation trial
One validation trial was successfully carried out for 4 months at a landfill site, monitoring carbon dioxide and methane. A picture of the unit attached to a borehole well can be seen in Figure 2. Some sample data are shown in Figure 3.
Figure 3 Sample data from field validation trial
On June 12th, Event 1 took place whereby the CO2 concentration exceeded the threshold limit. This event was short lived, with the highest concentration occurring late on a Friday night, when work on the site had stopped and the active cell was covered. Once identified, extraction was increased and the CO2 component fell immediately below its threshold limit. The component concentration did not fall back to negligible levels as had previously been recorded, but did stay below the threshold limit until June 16th.
Event 2, starting June 16th, recorded that the concentration of CO2 migrating to the perimeter of the landfill site increased significantly and exceeded the threshold limit of 1.5 % v/v. The gas build up occurred because the gas management system was not extracting enough gas from the site, leading the excess to migrate to the adjacent borehole well. After 3 days, the remedial measures taken resulted in a decrease in the migration of gas to the perimeter borehole well.
However, Event 3 emerged on June 23rd, when one of the underground pipes used to extract gas from the main site became partially blocked. This decreased the flow rate of gas extracted, resulting in gas migration increasing once more. After the blockage had been identified and removed, the CO2 gas component fell below the threshold limit once again, where it remained for some time.
In this time, it was only the CO2 component which had breached the threshold limit. The CH4 concentration remained below its threshold limit of 1.0 % v/v at all times.
The updating web page showing current field validation trials using these prototype units can be seen at: http://kspace.cdvp.dcu.ie/public/colum/gasMonitor/
Other sensors can be used in this gas mmonitoring platform for the measurement of toxic and odorant gas targets, including hydrogen sulfide, ammonia, carbon monoxide, sulphur dioxide and nitrogen dioxide.
The monitoring platform has already undertaken a field validation trial measuring carbon monoxide concentration in a multi-storey car park.
Figure 4 CO monitoring deployment in multistorey car-park over 7 days
The data shown in Figure 4 clearly shows events taking place at the exit to the multi-storey car park during a typical day. Event 1 occurs between 5 – 6 pm during the working week (Mon-Sat) when most people leave the workplace. On days 1-3 (Wed-Fri), there is also evidence of patrons leaving the carpark after a show in a nearby theatre (Event 2), between 9.30-10.30 pm.
The deployment has proven successful, showing the flexibility of the gas platform for the monitoring of air quality in diverse environments and for a variety of gas targets.
"Monitoring of Gas Emissions at Landfill Sites Using Autonomous Gas Sensors"
Breda M. Kiernan, Stephen Beirne, Cormac Fay, Dermot Diamond
STRIVE Report Series No. 53, Environmental Protection Agency, Ireland, 2010, ISBN: 978-1-84095-353-4
“Determination of carbon dioxide gas concentration using infrared gas sensors and neural networks with Bayesian regularization”
King-Tong Lau, Weimin Guo, Breda Kiernan, Conor Slater, Dermot Diamond
Sensors and Actuators B: Chemical, 2009, 1(2), pp. 242-247
“Measurement of Representative Landfill Gas Migration Samples at Landfill Perimeters: A Case Study”
Breda M. Kiernan, Stephen Beirne, Cormac Fay and Dermot Diamond
Published in conference proceedings Twenty-Fourth International Conference on Solid Waste Technology and Management, pp. 941-952, Philadelphia, PA, USA, March 15 - 18, 2009
"Development of an Autonomous Greenhouse Gas Monitoring System"
Breda M. Kiernan, Cormac Fay, Stephen Beirne and Dermot Diamond
Proceedings of World Academy of Science, Engineering and Technology, Volume 34 October 2008, pp.153-157, Venice, Italy, October 29-31 2008
“Chemical species concentration measurement via wireless sensors”
Jer Hayes, Stephen Beirne, Conor Slater, Breda M. Kiernan, King-Tong Lau and Dermot Diamond
Proceedings of World Academy of Science, Engineering and Technology, Volume 34 October 2008, pp.158-162, Venice, Italy, October 29-31 2008
"Landfill Gas Monitoring at Borehole Wells using an Autonomous Environmental Monitoring System” Breda M. Kiernan, Stephen Beirne, Cormac Fay and Dermot Diamond
Proceedings of World Academy of Science, Engineering and Technology, Vol.33, September 2008, Heidelberg, Germany, Sept. 24-26th 2008, pp.166-171
“A wireless sensor network for methane monitoring”
Jer Hayes, Conor Slater, Breda Kiernan, Claire Dunphy, Weimin Guo, King-Tong Lau, Dermot Diamond
Proc. of SPIE, Vol. 6755, 675504, 2007
“Autonomous monitoring of landfill gas migration at borehole wells on landfill sites using wireless technology”
Breda Kiernan, Weimin Guo, Conor Slater, Jer Hayes, Dermot Diamond
Proceedings of the 10th International Conference on Environmental Science and Technology, Kos Island, Greece, 5-7 September, 2007, Vol. A, pp. 679-685
“Wireless monitoring of landfill gas emissions”
Breda Kiernan, Conor Slater, Jer Hayes, Dermot Diamond
The 22nd International Conference on Solid Waste Technology and Management Philadelphia, PA, USA, 18th-22nd March 2007
“Autonomous Greenhouse Gas Measurement System for Analysis of Gas Migration on Landfill Sites”
Stephen Beirne, Breda M. Kiernan, Cormac Fay, Colum Foley, Brian Corcoran, Alan F. Smeaton and Dermot Diamond
IEEE Sensors Applications Symposium. Limerick, Ireland, 23-25 February, 2010
“Development of Autonomous Gas Monitoring Systems”
Breda M. Kiernan, Stephen Beirne, Cormac Fay and Dermot Diamond
CLARITY Open Day, UCD, November 23rd, 2009
“Gas Monitoring in the Environment using IR Sensing Techniques”