Coal ash, also known as coal combustion residuals (CCRs), is the mineral residue that remains from burning coal. Exposure to coal ash and to the toxic substances it contains may pose a health risk to workers in coal-fired power plants and residents living near coal ash disposal sites.
Coal ash is produced at coal-fired power plants. [1] Coal is pulverized and then burned to generate electricity. [2] The particles that remain after burning coal are called coal ash, principally consisting of fly ash and bottom ash. Other coal combustion by-products are boiler slag, flue gas desulfurization gypsum, and other kinds of flue gas desulfurization residues. [1] Depending on the type of coal that was burned, the chemical composition found in coal ash can vary. [3] Coal ash obtained from the combustion of bituminous coal is constituted principally of aluminum oxide (Al2O3), calcium oxide (CaO) and silicon dioxide (SiO2). [3] In the composition of coal, there are many potentially hazardous substances that, if found at elevated concentration in inhaled particles, can cause major health problems in humans. [4] [5] Such constituents that are found at various concentrations in coal ash are arsenic, cadmium, chromium, cobalt, copper, lead, lithium, mercury, molybdenum, selenium, thallium and uranium. [4] [5]
Coal ash in India has been stored in ash ponds and has contaminated surrounding land and water bodies. [6] In the United States approximately 110 million tons of coal ash were generated in 2012. [1] More than half of the coal ash produced in the US was dumped into ash ponds (surface impoundments; wet disposal) or landfills (dry disposal). [5] As of 2020 there are 310 active on-site landfills and 735 active on-site surface impoundments in the US. [7]
Coal ash contains many toxic substances that may affect human health, if people are exposed to them above a certain concentration in the form of particulate matter. So it is necessary to avoid situations in which employees working in coal-fired power plants or public members living close to coal ash landfills will be exposed to high coal ash dust concentrations. [4] Coal ash dust health effects can be considered as a particular case of exposure to particulate matter (particle pollution). Accordingly the health risk of the smallest coal ash particles (respirable particles) has to be evaluated, since they can enter into the lungs. [4] In order to evaluate this risk, levels of exposure of workers or members of the public to particulate matter are compared with "safe threshold levels". Regarding the health of workers, the ACGIH[ clarification needed ] publishes annually a booklet with tables presenting threshold level values (TLV's) - maximal concentrations allowed - for a wide range of substances and materials. Particles of coal ash belong to a category called "PNOS - Particles Not Otherwise Specified". For this category, otherwise known as "nuisance dust", the TLV value is 3 mg/m3 for respirable particles (smaller than 10 micrometers). [8]
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Different constituents can be found in coal ash.
Lead: The direct exposure to lead can cause major damage to the nervous system. [5] Lead exposure can lead to kidney disease, hearing impairment, high blood pressure, delays in development, swelling of the brain, hemoglobin damage, and male reproductive problems. [9] [10] Both low levels and high levels of lead exposure can cause harm to the human body. [9]
Cadmium: The direct exposure to high levels of cadmium is hazardous to the health. [5] More specifically, the lungs directly absorb cadmium into the bloodstream. [9] When humans are exposed to cadmium over a long period of time, kidney disease and lung disease can occur. [5] [9] In addition, cadmium exposure can be associated with hypertension. [5] Lastly, chronic exposure of cadmium can cause bone weakness which increases the risk of bone fractures and osteoporosis. [5]
Chromium: The direct exposure to chromium (VI) is hazardous to health. High levels of chromium (VI) in drinking water can cause ulcers in the small intestine and stomach when ingested. Lastly, skin ulcers can also occur when the exposure to chromium (VI) occurs through the skin.
Arsenic: When high amounts of arsenic is inhaled or ingested through coal ash waste, diseases such as bladder cancer, skin cancer, kidney cancer and lung cancer can develop. [5] [11] Ultimately, exposure of arsenic over a long period of time can cause mortality. [5] Furthermore, low levels of arsenic exposure can cause irregular heartbeats, nausea, diarrhea, vomiting, peripheral neuropathy and vision impairment. [9] [5]
Mercury: Chronic exposure of mercury from coal ash can cause harm to the nervous system. [5] When mercury is inhaled or ingested various health effects can occur such as vision impairment, seizures, numbness, memory loss and sleeplessness. [12] [13]
Boron: When coal ash dust is inhaled, the exposure of boron can cause discomfort in the throat, nose and eye. [5] Moreover, when coal ash waste is ingested, boron exposure can be associated with kidney, liver, brain, and intestine impairment. [5]
Molybdenum: When molybdenum is inhaled from coal ash dust, discomfort of the nose, throat, skin and eye can occur. [14] As a result, short-term molybdenum exposure can cause an increase of wheezing and coughing. [14] Furthermore, chronic exposure of molybdenum can cause loss of appetite, tiredness, headaches and muscle soreness. [5] [14]
Thallium: The exposure of thallium in coal ash dust can cause peripheral neuropathy when inhaled. [5] Furthermore, when coal ash is ingested, thallium exposure can cause diarrhea and vomiting. [5] In addition, thallium exposure is also associated with heart, liver, lung and kidney complications. [5]
Silica: When silica is inhaled from coal ash dust, fetal lung disease or silicosis can develop. [4] Furthermore, chronic exposure of silica can cause lung cancer. [4] In addition, exposure to silica over a period of time can cause loss of appetite, poor oxygen circulation, breathing complications and fever. [4]
Reuse of coal ash may benefit the environment by reducing the production of greenhouse gas and reducing the need to use virgin materials. [15] In addition, when coal ash is recycled, costs related to coal ash disposal sites are avoided. [5] [15]
There are two forms of coal ash recycling: “encapsulated” and “unencapsulated." [5] [15] When coal ash is bound to other materials it is encapsulated. [5] For example, coal ash can be reused in making concrete, bricks and wallboards. [15] On the other hand, unencapsulated use of coal ash is when the ash is not bound to other materials (loose particulate or sludge form). [5] [15] An example of unencapsulated coal ash is distributing the ash on icy roads in the winter. [5]
Even though reusing coal ash minimizes health effects in humans,[ clarification needed ] health problems can still occur when coal ash is recycled. [5] Specifically, workers drilling or cutting encapsulated coal ash increase their risk of inhaling coal ash dust. [5] In addition, when unencapsulated coal ash is scattered on snowy streets in the winter, the loose ash can come in contact with ditches on the side of the road. [5] As a result, the toxins from coal ash can leach into surface water bodies as well as groundwater, which may be drinking water sources. [5] Therefore, both forms of recycled coal ash (encapsulated and unencapsulated) can cause serious health issues in humans.
 | The examples and perspective in this section may not represent a worldwide view of the subject.(June 2020) |
In the United States, when coal ash is disposed into surface impoundments and landfills, the ash is regulated as a "Special Waste" (i.e., non-hazardous) under the Resource Conservation and Recovery Act (RCRA). [16]
EPA published a Coal Combustion Residuals (CCR) regulation in 2015. The agency continued to classify coal ash as non-hazardous (thereby avoiding strict permitting requirements under RCRA Subtitle C), but with new restrictions:
In 2016, the United States Court of Appeals for the District of Columbia Circuit vacated the "early closure" provisions in the regulation at 40 CFR 257.100. EPA then extended the compliance date for inactive ponds that attempted to utilize the early closure provisions. [18] In 2018, at the request of industry, EPA extended the compliance date for unlined ash ponds from 2019 to 2020, and provided more flexibility to state agencies in determining compliance with standards. [19] [20] The 2018 regulation was challenged in litigation and remanded by the court to EPA for further revision. The court ruled that EPA failed to adequately address the problems with unlined ponds, many of which continue to leak into groundwater. [21] In 2019, the court agreed to a voluntary remand while allowing the 2020 compliance deadline for unlined ponds to stay in effect, pending further rulemaking. [22]
EPA published a proposed rule on August 14, 2019 that would use location-based criteria, rather than a numerical threshold (i.e. impoundment or landfill size) that would require an operator to demonstrate minimal environmental impact so that a site could remain in operation. [23]
In response to litigation on the 2015 regulation, EPA published a final RCRA regulation on August 28, 2020 requiring all unlined ash ponds to retrofit with liners or close by April 11, 2021. Some facilities may apply to obtain additional time—up to 2028—to find alternatives for managing ash wastes before closing their surface impoundments. [24] [25]
Hazardous waste is waste that must be handled properly to avoid damaging human health or the environment. Waste can be hazardous because it is toxic, reacts violently with other chemicals, or is corrosive, among other traits. As of 2022, humanity produces 300-500 metric tons of hazardous waste annually. Some common examples are electronics, batteries, and paints. An important aspect of managing hazardous waste is safe disposal. Hazardous waste can be stored in hazardous waste landfills, burned, or recycled into something new. Managing hazardous waste is important to achieve worldwide sustainability. Hazardous waste is regulated on national scale by national governments as well as on an international scale by the United Nations (UN) and international treaties.
Sewage sludge is the residual, semi-solid material that is produced as a by-product during sewage treatment of industrial or municipal wastewater. The term "septage" also refers to sludge from simple wastewater treatment but is connected to simple on-site sanitation systems, such as septic tanks.
Incineration is a waste treatment process that involves the combustion of substances contained in waste materials. Industrial plants for waste incineration are commonly referred to as waste-to-energy facilities. Incineration and other high-temperature waste treatment systems are described as "thermal treatment". Incineration of waste materials converts the waste into ash, flue gas and heat. The ash is mostly formed by the inorganic constituents of the waste and may take the form of solid lumps or particulates carried by the flue gas. The flue gases must be cleaned of gaseous and particulate pollutants before they are dispersed into the atmosphere. In some cases, the heat that is generated by incineration can be used to generate electric power.
Toxic waste is any unwanted material in all forms that can cause harm. Mostly generated by industry, consumer products like televisions, computers, and phones contain toxic chemicals that can pollute the air and contaminate soil and water. Disposing of such waste is a major public health issue.
The Resource Conservation and Recovery Act (RCRA), enacted in 1976, is the principal federal law in the United States governing the disposal of solid waste and hazardous waste.
Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater may be reused or released to a sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants. Most industrial processes, such as petroleum refineries, chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans. This applies to industries that generate wastewater with high concentrations of organic matter, toxic pollutants or nutrients such as ammonia. Some industries install a pre-treatment system to remove some pollutants, and then discharge the partially treated wastewater to the municipal sewer system.
A fossil fuel power station is a thermal power station which burns a fossil fuel, such as coal or natural gas, to produce electricity. Fossil fuel power stations have machinery to convert the heat energy of combustion into mechanical energy, which then operates an electrical generator. The prime mover may be a steam turbine, a gas turbine or, in small plants, a reciprocating gas engine. All plants use the energy extracted from the expansion of a hot gas, either steam or combustion gases. Although different energy conversion methods exist, all thermal power station conversion methods have their efficiency limited by the Carnot efficiency and therefore produce waste heat.
Occupational lung diseases comprise a broad group of diseases, including occupational asthma, industrial bronchitis, chronic obstructive pulmonary disease (COPD), bronchiolitis obliterans, inhalation injury, interstitial lung diseases, infections, lung cancer and mesothelioma. These can be caused directly or due to immunological response to an exposure to a variety of dusts, chemicals, proteins or organisms. Occupational cases of interstitial lung disease may be misdiagnosed as COPD, idiopathic pulmonary fibrosis, or a myriad of other diseases; leading to a delay in identification of the causative agent.
Bottom ash is part of the non-combustible residue of combustion in a power plant, boiler, furnace, or incinerator. In an industrial context, it has traditionally referred to coal combustion and comprises traces of combustibles embedded in forming clinkers and sticking to hot side walls of a coal-burning furnace during its operation. The portion of the ash that escapes up the chimney or stack is referred to as fly ash. The clinkers fall by themselves into the bottom hopper of a coal-burning furnace and are cooled. The above portion of the ash is also referred to as bottom ash.
Construction waste is any kind of debris from the construction process. Different government agencies have clear definitions. For example, the United States Environmental Protection Agency EPA defines construction and demolition materials as “debris generated during the construction, renovation and demolition of buildings, roads, and bridges.” Additionally, the EPA has categorized Construction and Demolition (C&D) waste into three categories: non-dangerous, hazardous, and semi-hazardous.
Coal combustion products (CCPs), also called coal combustion wastes (CCWs) or coal combustion residuals (CCRs), are categorized in four groups, each based on physical and chemical forms derived from coal combustion methods and emission controls:
The health and environmental impact of the coal industry includes issues such as land use, waste management, water and air pollution, caused by the coal mining, processing and the use of its products. In addition to atmospheric pollution, coal burning produces hundreds of millions of tons of solid waste products annually, including fly ash, bottom ash, and flue-gas desulfurization sludge, that contain mercury, uranium, thorium, arsenic, and other heavy metals. Coal is the largest contributor to the human-made increase of carbon dioxide in Earth's atmosphere.
Under United States environmental policy, hazardous waste is a waste that has the potential to:
The Kingston Fossil Plant coal fly ash slurry spill was an environmental and industrial disaster that occurred on December 22, 2008, when a dike ruptured at a coal ash pond at the Tennessee Valley Authority's Kingston Fossil Plant in Roane County, Tennessee, releasing 1.1 billion US gallons of coal fly ash slurry. The coal-fired power plant, located across the Clinch River from the city of Kingston, used a series of ponds to store and dewater the fly ash, a byproduct of coal combustion. The spill released a slurry of fly ash and water which traveled across the Emory River and its Swan Pond embayment onto the opposite shore, covering up to 300 acres (1.2 km2) of the surrounding land. The spill damaged multiple homes and flowed into nearby waterways including the Emory River and Clinch River, both tributaries of the Tennessee River. It was the largest industrial spill in United States history.
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