Presentation on theme: "Monitoring Methane Emissions from Landfill Leachate Discharge EV4002 Eimear O’Keeffe Paul O’Mahony."— Presentation transcript:
Monitoring Methane Emissions from Landfill Leachate Discharge EV4002 Eimear O’Keeffe Paul O’Mahony
The Greenhouse Effect Greenhouse effect is defined as the accumulation of energy & the overall warming of the atmosphere. Greenhouse gases are those gases in the atmosphere, both natural & anthropogenic, that absorb & re-emit radiation & hence trap heat in the atmosphere. Fig – Illustration of the greenhouse Effect
Greenhouse Gases Greenhouse gases are made up of H2O, CO2, CH4, N2O & other trace gases. Greenhouse gases absorb more than 90% of the infrared radiation that the Earth emits. Increasing concentrations of these greenhouse gases lead to an enhanced greenhouse effect –i.e. increasing temperatures on Earth. Fig – Total Greenhouse Gases for 2001
Methane Gas & the Greenhouse Effect Methane (CH 4 ) is the 2 nd largest contributor to global warming. Its atmospheric concentration is 1.7ppmv, which is much less than CO 2 concentration of 350ppmv. However, each molecule of CH 4 is 20 times more effective than each molecule of CO 2 at trapping infrared radiation. –Contributes greatly to global warming
Methane Gas & the Greenhouse Effect Approx 60% of CH 4 emitted into the atmosphere is anthropogenic in source. Methane atmospheric concentrations are increasing at a rate of approx 1% per year. Hence the reduction of CH 4 emissions would have a rapid impact on mitigating global warming.
Methane in landfills A large contributor to methane emissions to the atmosphere is the burying of waste in landfills. Methane in landfills exist as a gas & as dissolved CH 4 in landfill leachate. It is produced by decay & decomposition of organic matter in oxygen poor conditions. Reducing CH 4 emissions from landfill will decrease CH 4 emissions into the atmosphere.
Cork City Landfill This is an old landfill site & therefore doesn’t have a bottom liner system in place to separate the rubbish & the leachate. It does have a leachate collection system in place, which collects the leachate & sends it to be treated & then disposes it to the sewer. A gas collection system is also in place, which is a system of pipes which collects the CH4 & transports it to the on-site power generation station. Fig – cross section of a Landfill
Leachate Collection & Treatment Leachate, which has a methane concentration of 5-10mg/l, is collected via a drain network, located on the perimeter of the landfill & pumped into the lagoons. Leachate is then sent to the conditioning plant, via the plant balance tank, where the leachate is aerated in order to drive off excess methane. Methane concentrations are now reduced to 0.2mg/l & sent to sewer via the pipe work. Fig - Leachate Conditioning Plant
Methane in sewers Danger of CH 4 in sewers as a build up of CH 4 from leachate may create pockets of CH 4 gas which may explode in the unventilated sewer Therefore the landfills must monitor CH 4 levels in the sewer
Legislation & Leachate in Europe The following Legislation, which was enacted into the laws of each of the member states is of relevance when considering leachate discharges& the permitting of leachate treatment plants –The EU Landfill Directive –The EU Groundwater Directive –The EU Urban Wastewater Directive-where discharges are pre-treated before discharge to public sewer –The EU Dangerous Substances Directive –The EU Water Framework Directive
IPC Licence Each Landfill facility requires an E.P.A. Waste Licence by law Cork City Councils holds a Waste Licence, which was issued by the E.P.A. This Waste Licence is available to view on the E.P.A. website @ - http://www.epa.ie/licences/waste_lic /12-2lic.pdf http://www.epa.ie/licences/waste_lic /12-2lic.pdf http://www.epa.ie/licences/waste_lic /12-2lic.pdf
Requirements of the Waste Licence Cork City Landfill are required to monitor its emissions to sewer, including its dissolved methane levels going to sewer. The emission limits for dissolved methane in leachate to sewer is 0.2mg/l, daily mean concentration The monitoring of methane emissions to sewer is required on a continuous basis and the analysis technique is by a dissolved methane probe or a headspace monitor
Sampling Techniques As we can see from the above tables, the EPA has placed a limit of 0.2 mg/l on the emission limits of dissolved methane to the sewer. To ensure this level is complied with, the licence specified that the leachate had to be monitored by a dissolved methane probe, and the air above it had to be monitored by a headspace methane monitor. To comply with the licensing regulations Cork city council installed these probes at two locations, at the conditioning plant and at a location before the sewer discharge point. These probes were obtained from ASD Sensortechnik Gmbh.
METS - an underwater methane sensor Developed by Capsum Technologie GmbH for underwater monitoring of CH4 up to a depth of 2000 m The METS sensor is designed for monitoring purposes at platforms, for long term time series measurements, in oceans, rivers and lakes as well as deep-sea and coastal areas The METS sensor is designed for monitoring purposes at platforms, for long term time series measurements, in oceans, rivers and lakes as well as deep-sea and coastal areas. It can be deployed in shallow water areas from a small boat, allowing vertical or horizontal profiles. The adaptation of this sensor to probe systems or loggers is possible because it is quipped with standard analogue outputs. The sensor is based on semi- conductor technology. The semi- conductor is protected from the water by a membrane, through which gases permeate. The sensor is based on semiconductor technology & is protected from water by a special membrane, through which gases permeate. The membrane, semiconductor and electronics are installed in a watertight stainless steel housing. The device is then connected via a cable to the signal processing and storage computer at the surface. The sensor membrane consists of a silicone composite membrane, supported by a spherical layer. The stainless steel head of the METS can be removed from the housing. It is built as a holder for the membrane and for the membrane supporting layer.
METS - an underwater methane sensor METS sensor specification: Measuring range:20 nmol/l to 10 µmol/l other ranges on request between 20 nmol/l and 1 mmol/l Resolution: at 50 nmol/l approx. 4 to 5 nmol/l Response time: 3 to 30 min, conditionned to turbulences Pressure range: 200 bar (other ranges on request) Operational range: +2 to +20°C (other ranges on request) The sensor uses a heated semiconductor that responds to the presence of dissolved methane as well as other hydrocarbons. The hydrocarbon molecules diffuse through a special silicone membrane into the detector room. The adsorption of the hydrocarbons on the active layer leads to electron exchange with oxygen and thus to modification of the resistance, which the electronic transduces into a voltage. The chosen membrane polymer is specialised for methane detection. Silicone has a high permeability for the gas and it is very resistant to fouling. In this sensor the membrane is used as a phase separation between the liquid and the gas detection room. The transition of the gas out of the water / leachate takes place via diffusion through the membrane.
Sensor Performance In previously conducted experiments the sensor gave some indication of enhanced methane concentrations, but was limited by a slow relaxation of the output when the ambient dissolved methane concentration changes. The sensor was deployed on CTD casts during ATLANTIS and SONNE operations during TECFLUX, (Bohrman et al. 2000). The sensor was found to exhibit slow response to changing concentrations, but it does respond at some level. The findings of this journal were that in order for the sensor to be deployed on a wide scale, improved response time is essential The diagram on the right, indicates the results of a 36 day trial in a sewage water treatment plant. The top left sample is the reference membrane. Top right is an antifouling membrane type 1, 10m. Bottom left is antifouling membrane type 2, 10 m. Bottom right is antifouling membrane type 3, 100 m.
Sensor Performance At present there are sensors deployed at the balance tank, the discharge tank and at a point before the sewer is discharged into the water. The sampling process using the sensor technology has been plagued by problems and has proved to be an extremely costly venture, with up to 50,00 Euro already being spent on installation and maintenance. The major problem associated with this form of monitoring is that biofilm growth from the leachate reduces the passage of gas into the probe. This biofilm layer consists of small living organisms along with tiny particles, which slow the diffusion process and can even block it completely. In previous studies the biofilm layer has even been found to produce methane, which leads to excessive readings. Capsum has recognised this as a significant problem and is researching ways of optimising performance. Graph illustrating the effects of the membrane
Cork City Landfill Sampling Procedures Despite the apparent success of the antifouling membrane as seen in the previous slide, Cork City council has had serious problems with the accuracy of their sensor readings. Because of this grab samples are presently being taken once a month, although this is not sufficient to satisfy the EPA licence requirement for a continuous monitoring process. Staff members have found this requirement impossible to meet using the sensor device. Saturated methane in air gives maximum readings of 25 mg/l, however the sensor has recorded values of up to 200 mg/l. Because of these results the staff resorted to the grab sampling technique. The samples taken from the balance tank, discharge tank and sewer samples are placed in a small voc vial which is fully sealed and taken back to lab for analysis A.S.A.P. A syringe is then used to extract the gas from the headspace of the vial and this is then injected into a G.C. A standard is also prepared for comparison. A bottle of methane gas is used to saturate a water sample i.e. 25 mg/l. A known volume is extracted from the headspace in this vial and this is also injected into the G.C. The analysis results in a plot whereby area relates to concentration for both the standard and the site samples.
Sample of results – March 2004 Conclusion: The results for the outlet sewer for dissolved methane are within the licence limit. Note the differing results between the grab samples and the Capsum Probe. Location Dissolved Methane (Alcontrol geochem) mg/l Dissolved Methane (CCC) mg/l pH Conductivit y ms/cm Scada reading Headspace Capsum Probe reading mg/l Inlet2.585.37.984.300------ FHS Tank 0.0030.358.204.2500%(0ppm)0.08 Outlet Sewer 0.0190.208.303.5701.45%(725ppm)1.45 License Discharge Limit 0.20.20 Fig - Capsum Probe
Sampling procedure suggestions Composite Sampling –Time proportional –24hr Flow Proportion Continuous G.C. The use of an Antifouling Membrane
Composite Sampling The grab sampling technique that is presently in operation only occurs once a month, and as previously mentioned, involves simply taking a sample and analysing it as soon as possible. This technique could be improved by taking composite samples. These can be split into two forms, Time proportional and 24 hour flow proportional. Time Proportional: Take samples every hour for a period of 24 hours, no dependence on flow rate. 24 Hour Flow Proportional: Measure the flow rate, e.g. if 10 m3/hr then take 10 ml of sample. If 5 m3/hr take 5 ml of sample. These are also taken over a 24 hour period. The samples would be analysed by G.C. in the same way as the grab samples, however they would result in a more accurate representation of the dissolved methane values.
Continuous G.C. If the composite sampling techniques are still insufficient to satisfy the EPA the final suggestion would be to install an automatic G.C. on site. This would be very expensive, approximately 20,000 Euro, however in lieu of what had already been spent it would be a very wise investment if the EPA would accept this sampling method.
The use of Antifouling Membrane If the EPA will not accept the continuous G.C. method of monitoring, the landfill staff will have to examine the use of Antifouling membranes. Test results from Capsum have shown these to be very successful. Due to the material being analysed this seems to be a very important aspect of the probe which appears to have been overlooked by the staff. If this proves problematic, a weekly cleaning system will have to be implemented, whereby a staff member will go to each location and clean each sensor manually, thus ensuring the sensors can function accurately for continuous monitoring.
Conclusions Due to the well publicised Greenhouse effect of methane, & its highly flammable & explosive nature, it is essential that a continuous monitoring programme of methane in landfill leachate is implemented effectively. In conclusion: Our research suggests that the addition of an Antifouling Membrane would be the most suitable way of achieving the EPA licence demands for the continuous monitoring of dissolved methane in landfill leachate.