The Importance of Constructed Wetlands in the Process of Mine Pollution melioration - Term Paper Example

THЕ IMРОRTАNСЕ ОF СОNSTRUСTЕD WЕTLАNDS IN THЕ РRОСЕSS ОF MINЕ РОLLUTIОN АMЕLIОRАTIОN By Name Course Instructor Institution City/State Date Table of Contents Table of Contents 2 1.0 Abstract 2 The Importance of Constructed Wetlands in the Process of Mine Pollution Amelioration 3 2.0 Introduction 3 3.1 Environmental Technologies 4 3.2.0 Mining and Pollution 5 3.2.1 Acid mine drainage 5 3.2.2 Impacts of Mining on Air 6 3.3.0 Constructed Wetlands 7 3.3.1 Aerobic Wetlands 9 3.3.2 Anaerobic Wetlands 9 3.3.3 Metal Uptake 10 4.0 Discussion 11 5.0 Conclusion 14 6.0 References 15 1.0 Abstract Metals’ mining interrupts enormous volumes of rock and soil material and leave them environmentally exposed. As a result of exposure to water as well as air, sulphide minerals usually related to metal deposits, are hydrolysed and oxidised leading to acid mine drainage. Constructed wetlands have since 1980s been utilised in acid mine drainage treatment sourcing from mining sites. Of late, constructed wetlands have been studied and used for metals’ removal in acid mine drainage. However, enduring usefulness of constructed wetlands is still to be known. Given that constructed wetlands are self-sustaining systems, they can remediate mine pollution and can characterise a lasting solution for mine pollution. Wetlands construction on mined lands as it will be evidenced in the report is useful for reclamation given that they are acknowledged as a valuable system in the environment. Moreover, they offer crucial habitat for numerous wildlife species and has the ability to improve the area’s aesthetic appeal. Importantly, constructed wetlands can be utilised as a moderately low-cost tool for treating discharges from the mining sites. For this reason, the report assesses and describes the significance of constructed wetlands in the process of mine pollution amelioration. The Importance of Constructed Wetlands in the Process of Mine Pollution Amelioration 2.0 Introduction Mining is a crucial source of environmental pollution because it discharges metals such as mercury, particularly in ores’ processing. Basically, control measures for mining pollution can reduce metal discharges into the environment (DeGraff, 2007, p.116). For years, coal mining has brought about numerous ecological challenges, which includes dust, soil erosion, water as well as noise pollution, and effects on local biodiversity. Even though measures have been taken in contemporary coal mining operations so as to reduce negative environmental impact, IAEA (2013) posits that much has to be done. Unceasing advances in environmental technology have eliminated or reduced scores of the ecological impacts conventionally related to utilisation of coal for generation of electricity and in steelmaking companies (World Coal Association, 2014). As mentioned by Younos and Grady (2014, p.140), water use in mining operations can have an effect on the quality of nearby groundwater and surface water. In reaction to government regulation as well as environmental concerns, the mining industry across the globe have increased its monitoring on water discharged from the mining sites, and this has been made possible by management strategies for preventing water pollution. In mining, constructed wetlands are shallow pools created purposely for treatment of acidic mine drainage (Canada Mortgage and Housing Corporation, 2014). Importantly, constructed wetlands are designed so as to offer water quality benefits by reducing non-point source and point source pollution before its entrance into the receiving waters such as streams. This report talks about constructed wetlands and mine pollution. 3.1 Environmental Technologies Uneconomical energy policies, shortages of water supply, misuse of resources, global warming, as well as deforestation are few of the challenges that professionals say must be solved in order to achieve sustainability. According to the United Nations, reliance on the environment increases every year, and so almost 3 billion people by 2025 will strain the narrowing water supplies, and the energy needs across the globe will rise by 60% before 2030. These challenges can be solved by environmental technologies, which can improve and maintain quality of air, water, and soil and also reduce the pollution effects on the environment (Goudarzi, 2007). Moreover, Boyce (1996, p.166)believes that environmental technologies can reduce pollutants from sources such abandoned mining sites chemical and oil spills, fertilizer and pesticide runoff, in addition to particulate matter and airborne gaseous from cars. Importantly, environmental technologies model, monitor, as well as protect the natural environment and resources, and limit the destructive effects of human participation. Technological innovation as stated by Goudarzi (2007) does play a crucial role in lowering the costs of decreasing discharges. Environmental technologies can be effectual in mining industry if policymakers can select a higher level of regulation, which can generally be beneficial to the society. 3.2.0 Mining and Pollution 3.2.1 Acid mine drainage When mined materials are exhumed as well as exposed to water and oxygen, IAEA (2013, p.8) posits that acid may generate if iron sulphide minerals (particularly pyrite) are profuse and there is insufficient neutralizing material for counteracting the formation of acid. In turn, the acid will dissolve or leach metals together with other pollutants from the materials that have been mined and create a solution that is metal-rich, high in sulphate and acidic (this includes high concentrations of arsenic, copper, lead, cadmium, and zinc) (IAEA, 2013, p.8). Discharge of contaminated elements, like selenium, arsenic, as well as metals, may take place even when acidic conditions are unavailable. According to IAEA (2013, p.8), high levels of nitrogen and cyanide compounds may as well be present in waters at mining locations, from heap blasting and leaching. Contaminant leaching and acid drainage are the main source of water pollution associated with mining. In scores of mining sites, acid mine drainage has been a concern bearing in mind that metals like molybdenum, silver, copper and gold are usually present in rock with sulphide minerals. So, when the rock’s sulphides are mined and exposed to air and water during mining, they generate sulphuric acid, which has the ability to dissolve other dangerous metals in the nearby rocks. IAEA (2013, p.8) asserts that if not well controlled, the acid mine drainage can leach into groundwater or runoff to surface water. It is worth noting that acid mine drainage can be discharged from all parts of the mine where sulphides are open to water and air, which includes piles of waste rock, open pits, , tailings leach pads, as well as underground tunnels. 3.2.2 Impacts of Mining on Air Emissions into the air take place during all phases of the mine cycle, but particularly during development, exploration, operational, as well as construction activities. As stated by IAEA (2013, p.12), small sized waste piles particles can be dispersed easily by the wind. In mining operations air pollution is attributed by particulate materials conveyed by the wind due to materials’ mining, blasting and shipping, waste dumps, open-pit mining wind erosion, tailings facilities’ fugitive dust, stockpiles, in addition to haul roads (IAEA, 2013, p.12). Mobile sources’ exhaust emissions increase the levels of these particulate, and this is worsened by gaseous emissions from the fuels’ combustion in both mobile and stationary sources, as well as mineral processing. After the contaminants enter the atmosphere, IAEA (2013) point out that they undergo chemical and physical changes prior to getting a receptor. Such contaminants may bring about serious health effects to the communities. Mining in large-scale can considerably lead to air pollution, particularly in the phase of operation (IAEA, 2013, p.12). Every activity during mining rely on processes, generators, equipment, as well as materials, which produce harmful air contaminants like heavy metals, nitrogen oxides, particulate matter, sulphur dioxide, and carbon monoxide. 3.3.0 Constructed Wetlands Constructed Wetlands as per Wastewater Gardens (2004, p.4) is an effective, eco-friendly method of treating both solid and liquid waste. Basically, constructed wetlands are economically beneficial to developed and developing countries through aquaculture and biomass provision. These systems are valuable to local communities, and can be used to reduce pollution effects attributed by mining operations. Constructed wetlands have proven to be successful in reducing biochemical oxygen demand, chemical oxygen demand nitrogen, suspended solids, and phosphorus by almost 98 per cent. Still, in spite of the increasing number of mining sites, the use of constructed wetlands in mining areas has been disappointingly low. According to Wastewater Gardens (2004, p.5), constructed wetlands may be described as systems for treatment that utilises natural processes so as to alleviate, isolate, amass, reduce, mineralise and/or metabolise pollutants. Even though applications of constructed wetlands were primarily limited to treatment of municipal wastewaters as well as storm waters, they are currently being utilised on new pollutants and in new applications. For decades, wetland systems were used as systems for treating natural water, and in the same period people have earnestly utilized and studied wetland systems for meeting objectives such as improved water quality and treatment of waste waters. Wetlands role as a passive method for enhancing the quality of water is a convincing argument for natural wetlands conservation and, recently, construction of wetlands systems have diversified into mining sites for mine pollution amelioration. As stated by Wastewater Gardens (2004), constructed wetland systems make use of saturated, flooded, or shallow soil and rooted wetland plants to offer the needed treatment. Constructed wetlands according to Vymazal and Kröpfelová (2008, p.XII) are designed so as to exploit the natural wetlands’ biological and chemical processes in order to get rid of pollutants from wastewater in mining sites. This technology is currently verified and mature. Progressively, scores of studies such as Laberge Environmental Services (2000) and Smith et al. (2003) have offered proof that constructed wetlands systems can ameliorate acid mine drainage and successfully improve the quality of water while still offering many advantages such as habitat and food for wildlife. Aside from being an effective treatment option for AMD, constructed wetlands can be used to treat harmful mine site wastewaters, wastes from petroleum refinery, landfill leachates, and other industrial wastewaters. Constructed wetlands remove metals from mine wastewaters through various processes such as adsorption and absorption onto organic matter, solids filtration, binding to manganese and iron oxides, hydrolysis as well as oxidation, formation of insoluble sulphides and carbonates, in addition to uptake by bacteria and plants. Rates of metal removal in both surface flow and subsurface flow wetlands may be high, but mostly vary relying upon the concentrations of influent as well as the rate of mass-loading. Rates of metal removal beyond 90 per cent for zinc, lead, and copper have been confirmed in operating subsurface flow and surface flow wetlands (Wastewater Gardens, 2004, p.5). As indicated by Vymazal and Kröpfelová (2008, p.7), constructed wetlands in the sediment have a rich microbial population that cause the contaminants’ biochemical transformation, and are self-sustaining and biologically productive. Moreover, constructed wetlands as well have considerably lesser capital costs and inferior total lifetime costs as compared to traditional treatment systems. 3.3.1 Aerobic Wetlands Aerobic wetlands are style of wetland construction mainly utilised when iron is the key pollutant. As indicated by White (2007, p.4), aerobic wetlands need net alkaline waters which can buffer a rise in hydrogen ions discharged from reactions of metal hydrolysis. Generally, aerobic wetlands are shallow (about 30 centimetres) and consist of plants such as Typha for immobilising heavy metals. The key shortcoming of aerobic wetlands is that the precipitate accumulation over time will severely reduce the abilities of their remediation abilities (White, 2007, p.4). So, it is necessary for precipitates to be removed periodically, either by means of dredging or flushing the area. 3.3.2 Anaerobic Wetlands In anaerobic wetlands, vegetation is planted deeply than in aerobic wetlands (more than 30 centimetres. According to White (2007, p.5), when waters are exceedingly acidic the pH has to be elevated and the waters ideally will achieve the net alkaline conditions. When aluminium and iron are the key pollutants then addition of alkaline together with aerobic settling pond is normally utilised in precipitating metals as well as raising the pH. In anaerobic wetlands, hard rock mines intend to create sulphate-reducing microbes under anaerobic settings and, because of the metabolic needs of the microorganisms, White (2007, p.5) posits that metals are precipitated as sulphides. Generally, anaerobic wetlands go together with a number of chemical or bioreactor addition forms so as to control the alkalinity as well as pH. 3.3.3 Metal Uptake In constructed wetland systems, plants play a crucial role since their roots hold together the substrate; thus, stopping the channels from forming as well as heighten water residence time in the wetland. Plants as well play a crucial role in indirectly removing heavy metals. Plant species I constructed wetlands contrast in their capability to uptake metals (Laberge Environmental Services, 2000, p.24). A number of the plants show high tissue concentrations whereas some display little accumulation. Still, their ability to uptake metals is less significant as compared to other processes of metal removal, which takes place in wetlands. These plants according to Laberge Environmental Services (2000, p.24) generate waste that offer organic matter and habitat needed by bacteria (microorganisms). The bacteriological processes generated by microorganisms play a crucial role in removing heavy metals. Bacteriological processes, which produce net alkalinity, are according to Laberge Environmental Services (2000, p.24) processes that are mostly reductive and consist of sulphate reduction, methanogenesis, denitrification, as well as manganese and iron reduction. Because of the relative shortage of the needed materials (such as nitrate), a number of such processes are inclined to be insignificant in environments affected by acid mine drainage. Still, so long as the sulphate and ferric iron are likely to be exceedingly abundant in acid mine drainage, the genesis of alkali ensuing from these two species’ reduction has a possible consequence in waters impacted by AMD. 4.0 Discussion Out of all methods for treating acid mine drainage, Smith et al. (2003, p.5) posit that passive designs are most favourable for the reason that they do not need constant maintenance. Amongst the passive designs, constructed wetlands have surfaced as the only practically viable alternative for lasting acid mine drainage treatment. So as to solve the issue of AMD coming from abandoned mines, a number of AMD treatment wetlands have been constructed (Smith et al., 2003, p.5). Such wetlands as asserted by , Smith et al. (2003, p.5) signify site-specific applications of the recognised engineering and scientific principles such as that published by the Bureau of Mines in United States. Passive treatment systems for mine drainage are normally sized and chosen based on a multi-step paradigm suggested by the government. The initial stage is AMD’s chemical characterization as well as its flow measurement. The second stage is to categorize the water as a net acidic or net alkaline. Generally, the pH has to be more than 6 or the ferrous iron oxidation may be slow (Smith et al., 2003, p.5). Mine water net alkaline can be treated through aeration so as to improve the processes of metal oxidation. For this reason, aerobic wetland is the most suitable structure of treatment for achieving oxidation as well as settling. Before treatment water characterised as net acidic must be rendered alkaline, and this is attributed by the fact that oxidation steers the metals’ precipitation. Mineral acidity is buffered by alkalinity; thus, enabling the pH to remain in a range where precipitation of metal is likely. In case alkalinity is introduced through a number of solid medium, Davis (1993, p.616) posits that contact with the source of alkalinity must occur before the exposure of AMD to air since metals’ reaction with oxygen bring about rapid precipitation that shields the surfaces of the solid, averting more alkaline material dissolution. To stop this, structures for generating alkalinity are placed earlier in the sequence of treatment. Such may include compost wetlands, anoxic limestone ponds and drains, systems continually producing alkalinity, or concentrated pits for recharging alkaline. The size and structure of constructed wetlands is determined from the water chemistry as well as flow data, and the alkalinity, acidity, dissolved oxygen, aluminium, and iron levels are the most crucial chemical parameters (Smith et al., 2003, p.6). In case acidity is not extremely high and dissolved oxygen in the acid mine drainage is very little, then as stated by Smith et al. (2003, p.6) the compact structure like the anoxic limestone drain will be sufficient to yield the original alkalinity. But if levels of aluminium are high, the anoxic limestone drain must be bypassed, considering that as the pH gets close to neutrality, aluminium will precipitate; hence, plugging the drain. Generally, if the acid mines drainage is excessively acidic or has large amounts of dissolved oxygen, aluminium, or ferric iron, then the state of affairs needs a compost wetland as a way of introducing alkalinity. Immediately after coming up with a way of introducing alkalinity, the final phases of treatment usually sustain aeration as well as the storage and collection of precipitated metals. Eventually the metal removal rates relies heavily on the AMD chemical composition, the existence of active microorganisms, the wetland surface area, as well as water retention time in the wetland. Considering the practical complications involved in obstructing AMD formation at source, normally, the only option is to reduce the effect that this contaminating water has on other water resources, as well as the broader environment; this approach encompasses measures for controlling migration (Johnson & Hallberg, 2005, p.6). Normally, such measures are divided into passive and active processes, the former referring to the utilisation of constructed as well as natural wetland ecosystems, while the latter connoting the incessant use of alkaline materials so as to precipitate metals and neutralise acidic mine waters. As stated by Johnson and Hallberg (2005, p.6), passive systems have the benefit of needing moderately little or no maintenance as compared to active systems, even though they can be costly and/or unfeasible to initiate. Every technology for passive treatment needs some maintenance, but a more beneficial subdivision is between remediation technologies which depend on microbial processes as well as those that do not.. Passive systems for bioremediation which includes both anaerobic and aerobic wetlands have been utilised for AMD full-scale treatment. This can be evidenced by Acid Reduction Using Microbiology system, which has two cells for oxidation wherein, iron is both oxidised as well as precipitated. Further than these, acid mine drainage first passes through a holding cell, and afterwards through two ARUM cells wherein, sulphide and alkali are produced (Johnson & Hallberg, 2005, p.10). As indicated by Johnson and Hallberg (2005, p.10), the organic materials which facilitate reduction of sulphate in the ARUM cells sourced from floating macrophytes. As evidenced in Ciminelli et al. (2001) study, ARUM systems are most effective in treating acid mine drainage in subtropical as well as high latitude locations. 5.0 Conclusion In conclusion, constructed wetlands have demonstrated their effectiveness in treating acid mine drainage in abandoned and active mining sites. Even though constructed wetlands do not handle the pollution source, they contain the spread of pollution to the plant life and soil in the system of treatment. At their current development stage, as evidenced in the report passive systems may consistently be put on practice as the only lasting solution for various types of acid mine drainage and are economical as compared to active treatment. In relation to chemical treatment, passive systems need lasting times of retention as well as bigger space, offer less treatment productivity, and in the long term they are bound to fail. Still, scores of constructed wetlands systems have successfully achieved short-term employment in abandoned and active mine sites and have considerably reduced costs of wastewater treatment. Notably, vegetation is a crucial developmental feature for construction of wetlands because of its vital role in acid mine drainage remediation, and its effect on other characteristics of the wetlands. 6.0 References Boyce, A., 1996. Introduction to Environmental Technology. New York: John Wiley & Sons. Canada Mortgage and Housing Corporation, 2014. Constructed Wetlands. [Online] Available at: http://www.cmhc-schl.gc.ca/en/inpr/su/waho/waho_008.cfm [Accessed 26 February 2015]. Ciminelli, V.S.T. et al., 2001. Biohydrometallurgy: "fundamentals, technology and sustainble development". In proceedings of the International Biohydrometallurgy Symposium, IBS-2001. Ouro Preto, Minas Gerais, 2001. Elsevier. Davis, J.R., 1993. contact with the source of alkalinity must occur before the exposure of AMD. Novelty, OH : ASM International. DeGraff, J.V., 2007. Understanding and Responding to Hazardous Substances at Mine Sites in the Western United States. Boulder, CO : Geological Society of America. Goudarzi, S., 2007. Top 10 Emerging Environmental Technologies. [Online] Available at: http://www.livescience.com/11334-top-10-emerging-environmental-technologies.html [Accessed 26 February 2015]. IAEA, 2013. Overview of Mining and its Impacts. In Guidebook EIA Mining. Vienna: IAEA. pp.1-17. Johnson, D.B. & Hallberg, K.B., 2005. Acid mine drainage remediation options: a review. Science of the Total Environment, vol. 338, pp.3– 14. Laberge Environmental Services, 2000. Investigations Into Passive Wetlands Treatment Of Mine Drainage to Remove Heavy Metals at Various Sites at UKHM. MERG Report. Whitehorse, Yukon: Mining Environment Research Group Laberge Environmental Services. Smith, R.T. et al., 2003. Toxic Metals Removal in Acid Mine Drainage Treatment Wetlands. Survey. Indiana : Indiana Geological Survey Indiana Geological Survey. Vymazal, J. & Kröpfelová, L., 2008. Wastewater Treatment in Constructed Wetlands with Horizontal Sub-Surface Flow. New York: Springer Science & Business Media. Wastewater Gardens, 2004. onstructed Wetlands to treat Wastewater. FRAMEWORK AND SCHEMATIC OVERVIEW. Wastewater Gardens. White, S., 2007. Wetland Use in Acid Mine Drainage Remediation. pp.1-10. World Coal Association, 2014. Coal & the Environment. [Online] Available at: http://www.worldcoal.org/coal-the-environment/ [Accessed 26 February 2015]. Younos, T. & Grady, C.A., 2014. Potable Water: Emerging Global Problems and Solutions. New York: Springer. Read More

When mined materials are exhumed as well as exposed to water and oxygen, IAEA (2013, p.8) posits that acid may generate if iron sulfide minerals (particularly pyrite) are profuse and there is insufficient neutralizing material for counteracting the formation of acid. In turn, the acid will dissolve or leach metals together with other pollutants from the materials that have been mined and create a solution that is metal-rich, high in sulfate, and acidic (this includes high concentrations of arsenic, copper, lead, cadmium, and zinc) (IAEA, 2013, p.8). Discharge of contaminated elements, like selenium, arsenic, as well as metals, may take place even when acidic conditions are unavailable.

According to IAEA (2013, p.8), high levels of nitrogen and cyanide compounds may as well be present in waters at mining locations, from heap blasting and leaching. Contaminant leaching and acid drainage are the main sources of water pollution associated with mining. In scores of mining sites, acid mine drainage has been a concern bearing in mind that metals like molybdenum, silver, copper, and gold are usually present in rock with sulfide minerals. So, when the rock’s sulfides are mined and exposed to air and water during mining, they generate sulphuric acid, which has the ability to dissolve other dangerous metals in the nearby rocks.

IAEA (2013, p.8) asserts that if not well controlled, the acid mine drainage can leach into groundwater or runoff to surface water. It is worth noting that acid mine drainage can be discharged from all parts of the mine where sulfides are open to water and air, which includes piles of waste rock, open pits, tailings leach pads, as well as underground tunnels.Emissions into the air take place during all phases of the mining cycle, but particularly during development, exploration, operational, as well as construction activities.

As stated by IAEA (2013, p.12), small-sized waste piles particles can be dispersed easily by the wind. In mining operations, air pollution is attributed to particulate materials conveyed by the wind due to materials’ mining, blasting, and shipping, waste dumps, open-pit mining wind erosion, tailings facilities’ fugitive dust, stockpiles, besides, to haul roads (IAEA, 2013, p.12). Mobile sources’ exhaust emissions increase the levels of this particulate, and this is worsened by gaseous emissions from the fuels’ combustion in both mobile and stationary sources, as well as mineral processing.

After the contaminants enter the atmosphere, IAEA (2013) points out that they undergo chemical and physical changes before getting a receptor. Such contaminants may bring about serious health effects to the communities. Mining in large-scale can considerably lead to air pollution, particularly in the phase of operation (IAEA, 2013, p.12). Every activity during mining relies on processes, generators, equipment, as well as materials, which produce harmful air contaminants like heavy metals, nitrogen oxides, particulate matter, sulfur dioxide, and carbon monoxide.

Constructed Wetlands as per Wastewater Gardens (2004, p.4) is an effective, eco-friendly method of treating both solid and liquid waste. Basically, constructed wetlands are economically beneficial to develop and developing countries through aquaculture and biomass provision. These systems are valuable to local communities and can be used to reduce pollution effects attributed to mining operations. Constructed wetlands have proven to be successful in reducing biochemical oxygen demand, chemical oxygen demand nitrogen, suspended solids, and phosphorus by almost 98 percent.

Still, despite the increasing number of mining sites, the use of constructed wetlands in mining areas has been disappointingly low. According to Wastewater Gardens (2004, p.5), constructed wetlands may be described as systems for treatment that utilizes natural processes to alleviate, isolate, amass, reduce, mineralize, and/or metabolize pollutants.

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