Landfill gas monitoring is the process by which gases that are collected or released from landfills are electronically monitored. Landfill gas may be measured as it escapes the landfill ("Surface Monitoring") or may be measured as it is collected and redirected to a power plant or flare ("Collection System Monitoring").
Surface monitoring is used to check the integrity of caps on waste and check on borehole monitoring. It may give preliminary indications of the migration of gas off-site. The typical regulatory limit of methane is 500 parts per million (ppm) by volume (in California, AB 32 may push this limit down to 200 ppm). In the UK the limit for a final landfill cap is 1×10−3 milligrams per square metre per second, and for a temporary cap it is 1×10−1 mg/m2/s (as measured using the Environment Agency's "Guidance on Monitoring landfill gas surface emissions" LFTGN 07, EA 2004). Surface monitoring can be broken down into Instantaneous and Integrated. Instantaneous monitoring consists of walking over the surface of the landfill, while carrying a flame ionization detector (FID). Integrated consists of walking over the surface of the landfill, while pumping a sample into a bag. The sample is then read with a FID or sent to a lab for full analysis. Integrated regulatory limits tend to be 50 ppm or less.
Gas probes, also known as perimeter or migration probes, are used for subsurface monitoring and detect gas concentrations in the local environment around the probe. Sometimes multiple probes are used at different depths at a single point. Probes typically form a ring around a landfill. The distance between probes varies but rarely exceeds 300 metres. The typical regulatory limit of methane here is 50,000 parts per million (ppm) by volume, or 1% methane and 1.5% carbon dioxide above geological background levels in the UK (see "Guidance on the monitoring of Landfill Gas" LFTGN03, EA 2004).
Ambient air samplers are used to monitor the air around a landfill for excessive amounts of methane and other gases. The principal odoriferous compounds are hydrogen sulfide (which is also toxic) and the majority of a population exposed to more than 5 parts per billion will complain (World Health Organisation : WHO (2000) . Air quality guidelines for Europe, 2nd ed. Copenhagen, World Health Organization Regional Publications, European Series), as well as volatile organic acids.
Monitoring of the landfill gas itself can be used diagnostically. When there is concern regarding the possibility of an ongoing subsurface oxidation event, or landfill fire, the presence in the landfill gas of compounds that are more stable at the high temperatures of such an event (above 500 °C) can be evidence for such a process occurring. The presence of propene, which can be formed from propane at temperatures above several hundred degrees Celsius, supports high temperatures. The presence of elevated concentrations of dihydrogen (H2) in the landfill gas is also consistent with elevated temperatures at remote locations some distance from the gas-extraction well. The presence of H2 is consistent with thermal inactivation of CO2-reducing microbes, which normally combine all H2 produced by fermentation of organic acids with CO2 to form methane (CH4). H2-producing microbes are less temperature-sensitive than CO2-reducing microbes so that elevated temperatures can inactivate them and their recovery can be delayed over the H2-producers. This can result in H2 production without the (usually) corresponding consumption, resulting in elevated concentrations of H2 in the landfill gas (up to >25%[v:v] at some sites). Thermal deactivation of CO2-reducing microbes has been used to produce CO2 (rather than methane) from municipal solid waste (Yu, et al., 2002).
Collection System Monitoring is used to check the characteristics of landfill gas being collected by the gas extraction system. Monitoring may be done either at the individual gas extraction well or at the power plant (or flare). In either case, users are monitoring gas composition (CH4, CO2, O2 & Balance Gas) as well as temperature, pressure and flow rate.
For surface monitoring, a monitor may be either:
For Collection System Monitoring, users are monitoring gas composition (%CH4, %CO2, %O2 & Balance Gas) as well as temperature, pressure and flow rate. There are three distinct ways collected gas can be measured.
Several techniques have been developed for evaluating whether landfill gas (rather than leachate) is the source of volatile organic compounds (VOCs) in groundwater samples. [1] Leachate water frequently has elevated levels of tritium compared to background groundwater and a leachate (water) release would increase tritium levels in affected groundwater samples, while landfill gas has been shown not to do so. Although landfill gas components can react with minerals and alter inorganic constituents present in groundwater samples such as alkalinity, calcium, and magnesium, a frequent major leachate constituent, chloride, can be used to evaluate whether leachate has affected the sample.
Highly soluble VOCs, such as MtBE, diethyl ether, and tetrahydrofuran, are evidence of leachate effects, since they are too water-soluble to migrate in landfill gas. The presence of highly soluble semi-volatile organic compounds, such as phenols, are also consistent with leachate effects on the sample. Elevated concentrations of dissolved CO2 have been shown to be a symptom of landfill gas effects—this is because not all of the CO2 in landfill gas reacts immediately with aquifer minerals, while such reactions are complete in leachate due to the presence of soils as daily cover in the waste. To assess whether VOCs are partitioning into groundwater in a specific location, such as a monitoring well, the headspace gas and dissolved VOC concentrations can be compared. If the Henry's Law constant multiplied by the water concentration is significantly less than the measured gas concentration, the data are consistent with VOCs partitioning from landfill gas into the groundwater.[ citation needed ]
Typical landfill gas composition [2] | %(dry volume basis)a |
---|---|
Methane, CH4 | 45-60 |
Carbon dioxide, CO2 | 40-60 |
Nitrogen, N2 | 2-5 |
Oxygen, O2 | 0.1-1.0 |
Sulfides, disulfides, mercaptans etc. | 0-1.0 |
Ammonia, NH3 | 0.1-1.0 |
hydrogen, H2 | 0-0.2 |
carbon monoxide, CO | 0-0.2 |
Trace constituents | 0.01-0.6 |
aExact percentage distribution will vary with the age of the landfill
Most landfills are highly heterogeneous environments, both physically and biologically, and the gas composition sampled can vary radically within a few metres. [3]
Near-surface monitoring is additionally vulnerable over short time periods to weather effects. As the atmospheric pressure rises, the rate of gas escape from the landfill is reduced and may even become negative, with the possibility of oxygen incursion into the upper layers (an analogous effect occurs in the composition of water at the mouth of an estuary as the sea tide rises and falls). Differential diffusion and gas solubility (varying strongly with temperature and pH) further complicates this behaviour. Tunnelling effects, whereby large items (including monitoring boreholes) create bypass shortcuts into the interior of the landfill, can extend this variability to greater depths in localised zones. Such phenomena can give the impression that bioactivity and gas composition is changing much more radically and rapidly than is actually the case, and any series of isolated time-point measurements is likely to be unreliable due to this variance.
Landfill gas often contains significant corrosives such as hydrogen sulphide and sulphur dioxide, and these will shorten the lifespan of most monitoring equipment as they react with moisture (this is also a problem for landfill gas utilization schemes).
Physical settlement as waste decomposes makes borehole monitoring systems vulnerable to breakage as the weight of the material shifts and fractures equipment.
Carbon dioxide is a chemical compound with the chemical formula CO2. It is made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature, and as the source of available carbon in the carbon cycle, atmospheric CO2 is the primary carbon source for life on Earth. In the air, carbon dioxide is transparent to visible light but absorbs infrared radiation, acting as a greenhouse gas. Carbon dioxide is soluble in water and is found in groundwater, lakes, ice caps, and seawater. When carbon dioxide dissolves in water, it forms carbonate and mainly bicarbonate, which causes ocean acidification as atmospheric CO2 levels increase.
A landfill is a site for the disposal of waste materials. It is the oldest and most common form of waste disposal, although the systematic burial of waste with daily, intermediate and final covers only began in the 1940s. In the past, waste was simply left in piles or thrown into pits.
Tar pits, sometimes referred to as asphalt pits, are large asphalt deposits. They form in the presence of petroleum, which is created when decayed organic matter is subjected to pressure underground. If this crude oil seeps upward via fractures, conduits, or porous sedimentary rock layers, it may pool up at the surface. The lighter components of the crude oil evaporate into the atmosphere, leaving behind a black, sticky asphalt. Tar pits are often excavated because they contain large fossil collections.
Environmental remediation is the cleanup of hazardous substances dealing with the removal, treatment and containment of pollution or contaminants from environmental media such as soil, groundwater, sediment. Remediation may be required by regulations before development of land revitalization projects. Developers who agree to voluntary cleanup may be offered incentives under state or municipal programs like New York State's Brownfield Cleanup Program. If remediation is done by removal the waste materials are simply transported off-site for disposal at another location. The waste material can also be contained by physical barriers like slurry walls. The use of slurry walls is well-established in the construction industry. The application of (low) pressure grouting, used to mitigate soil liquefaction risks in San Francisco and other earthquake zones, has achieved mixed results in field tests to create barriers, and site-specific results depend upon many variable conditions that can greatly impact outcomes.
Methanogenesis or biomethanation is the formation of methane coupled to energy conservation by microbes known as methanogens. Organisms capable of producing methane for energy conservation have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with anaerobic bacteria. The production of methane is an important and widespread form of microbial metabolism. In anoxic environments, it is the final step in the decomposition of biomass. Methanogenesis is responsible for significant amounts of natural gas accumulations, the remainder being thermogenic.
A leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed.
Landfill gas is a mix of different gases created by the action of microorganisms within a landfill as they decompose organic waste, including for example, food waste and paper waste. Landfill gas is approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide. Trace amounts of other volatile organic compounds (VOCs) comprise the remainder (<1%). These trace gases include a large array of species, mainly simple hydrocarbons.
A gas flare, alternatively known as a flare stack, flare boom, ground flare, or flare pit, is a gas combustion device used in places such as petroleum refineries, chemical plants and natural gas processing plants, oil or gas extraction sites having oil wells, gas wells, offshore oil and gas rigs and landfills.
Volcanic gases are gases given off by active volcanoes. These include gases trapped in cavities (vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from lava, from volcanic craters or vents. Volcanic gases can also be emitted through groundwater heated by volcanic action.
Drill cuttings are broken bits of solid material removed from a borehole drilled by rotary, percussion, or auger methods and brought to the surface in the drilling mud. Boreholes drilled in this way include oil or gas wells, water wells, and holes drilled for geotechnical investigations or mineral exploration.
Landfills are the primary method of waste disposal in many parts of the world, including United States and Canada. Bioreactor landfills are expected to reduce the amount of and costs associated with management of leachate, to increase the rate of production of methane for commercial purposes and reduce the amount of land required for land-fills. Bioreactor landfills are monitored and manipulate oxygen and moisture levels to increase the rate of decomposition by microbial activity.
A carbon dioxide sensor or CO2 sensor is an instrument for the measurement of carbon dioxide gas. The most common principles for CO2 sensors are infrared gas sensors (NDIR) and chemical gas sensors. Measuring carbon dioxide is important in monitoring indoor air quality, the function of the lungs in the form of a capnograph device, and many industrial processes.
A thermal oxidizer is a process unit for air pollution control in many chemical plants that decomposes hazardous gases at a high temperature and releases them into the atmosphere.
The Laurel Park, Inc. site, also known as Hunters Mountain Dump, or Murtha's Dump to locals, is a capped landfill that occupies approximately 20 acres (81,000 m2) of a 35-acre (140,000 m2) parcel of land in Naugatuck, Connecticut. The landfill has been in existence since the late 1940s, and several industries disposed of solvents, oils, hydrocarbons, chemical and liquid sludge, chemical solids, tires, and rubber products there. The facility continued to operate as a municipal landfill until 1987. It was owned and operated by Terrence and Howard Murtha.
Municipal solid waste (MSW) – more commonly known as trash or garbage – consists of everyday items people use and then throw away, such as product packaging, grass clippings, furniture, clothing, bottles, food scraps and papers. In 2018, Americans generated about 265.3 million tonnes of waste. In the United States, landfills are regulated by the Environmental Protection Agency (EPA) and the states' environmental agencies. Municipal solid waste landfills (MSWLF) are required to be designed to protect the environment from contaminants that may be present in the solid waste stream.
Landfill gas utilization is a process of gathering, processing, and treating the methane or another gas emitted from decomposing garbage to produce electricity, heat, fuels, and various chemical compounds. After fossil fuel and agriculture, landfill gas is the third largest human generated source of methane. Compared to CO2, methane is 25 times more potent as a greenhouse gas. It is important not only to control its emission but, where conditions allow, use it to generate energy, thus offsetting the contribution of two major sources of greenhouse gases towards climate change.
The former Operating Industries Inc. Landfill is a Superfund site located in Monterey Park, California at 900 N Potrero Grande Drive. From 1948 to 1984, the landfill accepted 30 million tons of solid municipal waste and 300 million US gallons (1,100,000 m3) of liquid chemicals. Accumulating over time, the chemical waste polluted the air, leached into groundwater, and posed a fire hazard, spurring severely critical public health complaints. Recognizing OII Landfill's heavy pollution, EPA placed the financial responsibility of the dump's clean-up on the main waste-contributing companies, winning hundreds of millions of dollars in settlements for the protection of human health and the environment.
The Freeway Sanitary Landfill is a United States Environmental Protection Agency Superfund site that covers 140 acres (57 ha) in Burnsville, Minnesota. In 1971 the Minnesota Pollution Control Agency (MCPA) licensed the landfill to accept 1,920 acre-feet (2,370,000 m3) of household, commercial, demolition, and nonhazardous industrial wastes. The state permit prohibited the disposal of liquids and hazardous wastes; however, heavy metals, acids, and bases were accepted by the landfill from local industries. The landfill also accepted 200 cubic yards (150 m3) of battery casings and 448 short tons (406,000 kg) of aluminum sweat furnace slag. Overall, the landfill contains nearly 5,000,000 cubic yards (3,800,000 m3) of waste. The waste is covered by a low permeability soil cover.
Increasing methane emissions are a major contributor to the rising concentration of greenhouse gases in Earth's atmosphere, and are responsible for up to one-third of near-term global heating. During 2019, about 60% of methane released globally was from human activities, while natural sources contributed about 40%. Reducing methane emissions by capturing and utilizing the gas can produce simultaneous environmental and economic benefits.
Microbial electrochemical technologies (METs) use microorganisms as electrochemical catalyst, merging the microbial metabolism with electrochemical processes for the production of bioelectricity, biofuels, H2 and other valuable chemicals. Microbial fuel cells (MFC) and microbial electrolysis cells (MEC) are prominent examples of METs. While MFC is used to generate electricity from organic matter typically associated with wastewater treatment, MEC use electricity to drive chemical reactions such as the production of H2 or methane. Recently, microbial electrosynthesis cells (MES) have also emerged as a promising MET, where valuable chemicals can be produced in the cathode compartment. Other MET applications include microbial remediation cell, microbial desalination cell, microbial solar cell, microbial chemical cell, etc.,.