Constructed Wetlands and Mine Pollution - Literature review Example

CONSTRUCTED WETLANDS AND MINE POLLUTION By Name Course Instructor Institution City/State Date Table of Contents CONSTRUCTED WETLANDS AND MINE POLLUTION 1 Table of Contents 2 The Importance of Constructed Wetlands in the Process of Mine Pollution Amelioration 3 1.0 Abstract 3 2.0 Introduction 4 3.0 Main Body of the Report 5 3.1 Environmental Technologies 5 3.2 Contemporary Mining and Pollution 6 3.3.0 Constructed Wetlands 8 3.3.1 Aerobic wetlands 9 3.3.2 Anaerobic Wetlands 10 4.0 Discussion 11 Conclusion 13 References 14 The Importance of Constructed Wetlands in the Process of Mine Pollution Amelioration 1.0 Abstract The mining industry has continued receiving negative criticism from environmentalists as well as strong regulations from the government. Evidently, extraction as well as processing of minerals has been a basis of lots of pollutants inflowing to soil, water and air. Mine pollution has also resulted in scores of enormous unproductive landscapes and infertile lands. So as to lessen such contaminants and re-establish ecological productivity to lands that have been mined, the 1977 Surface Mining Control and Reclamation Act (SMCRA) was enacted. This law needed for reclamation standards for mining-related activities, and ever since, the more progress toward the objective of improved environmental sustainability as well as quality has been made in the mining industry. Acid mine drainage (AMD), a type of mine pollution has been termed as the hardest issue to solve, since scores of remediation methods are costly and timely. Considering that AMD can go on for many years, the need for treatment resulted in construction of wetlands. Constructed wetlands as it will be evidenced in the report is an ideal solution to the lasting remediation of mine pollution, especially acid mine drainage. In this case, the report seeks to describe and assess the importance of constructed wetlands in the process of mine pollution amelioration. 2.0 Introduction The mining industry is basically, responsible for the major releases of heavy metals into the ecological system. It as well releases air contaminants such as nitrogen oxides as well as sulphur dioxide; consequently, deserting masses of slag, waste tailings, as well as acid drainage. Environmental and occupational exposure to asbestos, silica, and heavy metals often takes place during milling and mining operations (Occupational Knowledge International, 2013). Besides, the process of smelting is related to the extreme exposures as well as releases into the environment. Studies such as Järup (2003, p.167) have documented the risks to human health brought about by heavy metals exposure, especially mercury, cadmium and lead during mining operations. Such metals are related to various neurological deficits in both grown-ups and children along with numerous systemic effects. For instance, exposure to asbestos and silica may result in pneumoconiosis, lung cancer, as well as other health effects. Whereas mine pollution controls may reduce exposures, such measures are time and again lacking in smelting as well as mining operations. Constructed wetlands can be defined as treatment systems, which utilises natural processes including soils, wetland vegetation, and their elated microbial accumulations with the intention of reducing mine pollution and improving the quality of water (Vymazal & Kröpfelová, 2008, p.XII). Moreover, constructed wetlands may as well be an economical and technically practicable method for wastewater treatment. Importantly, constructed wetlands are economical to construct as compared to conventional options for ameliorating mine pollution, the cost of operating as well as maintaining them, and can handle changing levels of water. Furthermore, constructed wetlands are artistically attractive and are able to reduce odours related to wastewater. The report will focus on mine pollution and constructed wetlands. 3.0 Main Body of the Report 3.1 Environmental Technologies Environmental technologies according to Shrivastava (1995, p.185)can be described as equipment’ for production, procedures and methods, mechanisms for product delivery, and product designs that save natural resources and energy, reduce ecological burden of human activities, as well as defend the natural environment. Environmental technologies consist of hardware, like technologies for cleaner production, equipment for pollution control, and instrumentation meant for environmental measurement (Spiegel & Maystre, 1998, p.15). The technologies as well consists of operating methods, like work arrangements that focuses on conservation, waste management practices (such as waste exchange and materials recycling), and utilised for enhancing and conserving nature. As mentioned by Shrivastava (1995, p.185), environmental technologies are continually changing both as a set of approaches (operating equipment, and technologies procedures) as well as a management orientation. As approaches, Shrivastava (1995, p.185) posits that environment technologies are utilised for waste management, pollution reduction, material, water, and energy conservation, as well as for enhancing technological production efficiency. With regard to management orientation, these technologies ecologically spawned liable techniques towards the management of environment, product design, and also f industrial systems’ design. The l problems within the environment solved by these technologies are extensive; therefore, such technologies have sustained impacts. 3.2 Contemporary Mining and Pollution Contemporary mining can be seen as an industry, which entails the removal of and exploration for minerals, with least environmental damage and in an economical way. Without a doubt, mining is imperative for the reason that minerals are key sources of energy and materials like metals and fertilizers. As stated by McKinley (2011), mining is essential for countries to have reliable and sufficient supplies of materials as well as minerals so as to meet the needs of the economy at suitable economic, energy, and ecological costs. A number of the mined nonfuel minerals, like stone, which is industrial or non-metallic mineral, may be directly used after mining. Conversely, other nonfuel minerals, especially metallic minerals, are normally combined naturally with other materials like ores. In this case, the ores have to be treated first, normally with heat or chemicals so that the metal of interest can be produced (McKinley, 2011). For instance, bauxite ore is changed to aluminium oxide (Al2O3), which is applied for making aluminium metal through additives as well as heat. Coal and uranium, which are fuel minerals are as well processed through chemicals in addition to other methods of treatment so as to create the desired fuel quality. Essentially, there are considerable variances in the techniques of mining as well as the effects to the environment of mining fuel, industrial, and metallic minerals. Evidently, mining is a worldwide industry, and not all countries are blessed with mineral deposits that are large and very profitable. According to World Bank (2006, p.274), there are a lot of factors that have an effect on global mining such as environmental laws and regulations, costs of labour and fuel, lack of access to lands having minerals due to local communities’ resistance, fading ore grades, technological advancements, and closeness to markets. The mining industry present a number of challenges to people within the community, but the main challenge is pollution, especially abandoned mine drainage. Abandoned mine drainage can be defined as a water that is contaminated from connection with mining-related activities, and usually related to coal mining. In most countries, AMD is a prevalent type of mine pollution, especially where massive amounts of mining occurred some time ago (EPA, 2013). Mines that are abandoned normally pollute water through acid, metal and alkaline mine drainage; thus affecting water quality. In this case, acid mine drainage is the movement as well as the creation of acidic water, which is highly rich in heavy metals. As posited by McKinley (2011), all mining techniques have an effect on the air quality. In surface mining, particulate matter is discharged when overloaded and so it is removed from the mining site and stockpiled or taken back to the mine. Upon removing the soil, vegetation is as well eliminated; thus, making the soil to be exposed to the weather conditions; hence, making the particulates to move to the air through road traffic as well as wind erosion. Basically, particulate matter consists of poisonous materials such as lead, cadmium, and arsenic (McKinley, 2011). Generally, particulates released as a result of mining have an adverse effect on the human health; thus, leading to infections associated with the respiratory tract, like emphysema, but as well they can be absorbed or ingested into the body through the skin (McKinley, 2011). Besides that, mining may physically disturb the landscape, consequently, generating carbuncles like open pits as well as waste-rock piles. These disturbances as mentioned by Cuff and Goudie (2009, p.389) can lead to the reduction of plant species and wildlife around the mining area. Moreover, it is likely that lots of the pre-mining features of the surface cannot be substituted after the mining practices stops. Subsidence of the mines can as well result in roads and buildings damage. Almost five hundred features of subsidence collapse between 1980 and 1985 caused by underground metal mines in Galena where lead ores were mined between 1850 and 1970. The whole mining area was as a result, reclaimed in 1995 (McKinley, 2011). Problems of water pollution attributed by mining includes metal contamination, acid mine drainage, as well as increased levels of sediment in watercourses. Pollution sources consists of abandoned or active underground as well as surface mines, tailings ponds, waste-disposal areas, haulage roads, or processing plants. 3.3.0 Constructed Wetlands Metal retention mechanisms in constructed wetlands include: metal hydroxides creation and precipitation; direct uptake by living plants; metal sulphides formations; reactions of organic complexation; as well as exchange on sites that are negatively-charged with other cations. Other feasible mechanisms as highlighted in Ziemkiewicz et al. (2003, p.119) study consists of substrate materials attachment, neutralization, exchange as well as adsorption of metals, in addition to sulphate and iron hydroxides’ microbial dissimilatory reduction. As indicated by Ziemkiewicz et al. (2003, p.119), the manner through which the wetland is constructed eventually impacts how the treatment of waste water takes place. Currently, there are two predominant styles of construction: aerobic wetlands, which involve wetland vegetation such as Typha, planted shallowly about 0.3 meters and also with water-resistant sediments including mine spoil or clay (Ziemkiewicz et al., 2003, p.119). Another construction style is anaerobic wetlands, which akin to aerobic, wetland vegetation are planted, but deeply (more than 0.3 meters), porous sediments consisting of peat moss, soil, sawdust, hay bales, or manure are oft admixed or underlain with limestone. Treatment in aerobic wetlands is controlled by processes within the shallow surface layer while in anaerobic major interactions are involved in the substrate. 3.3.1 Aerobic wetlands As evidenced in Ziemkiewicz et al. (2003, p.119) study, aerobic wetlands are normally utilised for gathering water as well as offering aeration and residence time in order to allow for the precipitation of metals from the mining sites dissolved in the water. Normally, manganese and iron precipitate while they oxidize, and so their precipitates are recollected in the downstream or wetland. Furthermore, these systems are filled with wetland species so as to supplement more organic matter and also for aesthetics purposes. These wetland species allow for more consistent flow, resulting in a wetland area that is more effective. Due to their wide-ranging water surface as well as dawdling flow, Skousen (1997) posits that aerobic wetlands encourage metal hydrolysis as well as oxidation, in so doing allowing for iron, manganese, and aluminium hydroxides precipitation as well as physical retention. The degree of metal removal relies heavily on concentrations of dissolved metal, pH, content of dissolved oxygen in addition to net mine water alkalinity, and water detention time in the constructed wetland (Ziemkiewicz et al., 2003, p.120). The net water alkalinity/acidity and pH are principally imperative for the reason that pH affects the metal hydrolysis as well as oxidation kinetics and the metal hydroxide precipitates’ solubility. According to Skousen (1997), H+ is generated through metal hydrolysis, but the pH is buffered by water alkalinity; thus, allowing precipitation of metal to continue. The rates of inorganic oxidation reaction reduce a hundred times with every decrease in pH unit, but these may be heightened by microbial oxidation. Subsequent to iron oxidation, iron hydroxides are precipitated through abiotic hydrolysis reactions. So, aerobic wetlands are more effective when the water used has a net alkalinity so as to neutralize the acidity of the metal. So in aerobic wetland, manganese and iron residues from mining sites precipitate successively, not concurrently, with Ziemkiewicz et al. (2003, p.120) study results showing that manganese precipitation takes place mostly towards the last stages of wetland flow systems, subsequent to precipitation of iron. 3.3.2 Anaerobic Wetlands Anaerobic wetlands allow water to pass through substrates that are rich in organic, which significantly results in the treatment. According to Ziemkiewicz et al. (2003, p.1190), anaerobic wetlands allow for metal hydrolysis and oxidation in layers of aerobic surface, but as well depend heavily on subsurface microbial reduction as well as chemical reactions so as to neutralize acid and precipitate metals. In this regard, the water penetrates through organic subsurface sediment that is thick and permeable and develops into anaerobic because of high demand of biological oxygen. As compared to aerobic wetlands, a number of treatment techniques have been improved in anaerobic wetlands, which include; metal sulphides creation as well as precipitation; alkalinity that is produced microbially because of reduction reactions; in addition to incessant creation of carbonate alkalinity because of dissolution of limestone under anoxic conditions. Given that anaerobic wetlands generate alkalinity, Skousen (1997) posits that their application may be prolonged to acidic mine drainage with high iron, low pH, as well as high dissolved oxygen. Study results from Ziemkiewicz et al. (2003, p.119) study shows that Microbial techniques of alkalinity creation are considerably crucial for lasting acidic mine drainage treatment. But these claims are refuted by Skousen (1997) study, who point out that efficiency as well as mechanism for AMD treatment differs every season and also affected by the age of wetland (Ziemkiewicz et al., 2003, p.126). Anaerobic wetlands akin to their aerobic counterparts are more effective and efficient when utilized for treating small flows of acidic mine drainage and other pollutions attributed by mining activities. 4.0 Discussion The continuing industrialisation together with the increasing and large demand for heavy metals, like zinc) and lead, have resulted in high anthropogenic release of contaminants into water resources (Yang et al., 2006, p.499). Different from organic contaminants, metals contaminants dissolved in waste water cannot be degraded by means of biological processes; thus, creating threats not just for water bionetworks but as well human wellbeing. So, mine drainages that are contaminated by heavy metals are tenacious and serious ecological setback, creating the need for water decontamination removal. Reuse of treated wastewater as mentioned by Yang et al. (2006, p.499) is a crucial approach for water resources conservation, especially in mining areas experiencing water shortage. A number of techniques have been created with the intention of treating metal-contaminated wastewater, which includes mine waste, and as evidenced by Yang et al. (2006, p.500), it is hard as well as costly process to neutralise enormous volumes of mine pollutions through traditional techniques. So, constructed wetland as an economical substitute for regulating values of pH as well as getting rid of metal elements from metal-contaminated wastewater is a crucial technique in treatment phytoremediation of water contaminated by metals like lead and zinc. Utilisation of constructed wetlands for purification of mine effluent has rapidly advanced in the past three decades and is currently believed to be an established environmental technology, and it has progressively been utilised for treating various mining effluents. Numerous studies have indicated that constructed wetlands successfully decontaminate metal-polluted mine wastewater, and is able to provide a self-maintaining, cost-effective alternative to traditional techniques used for decontamination of wastewater (Heal et al., 2005, p.279; Yang et al., 2006, p.500). Waste water from coal mining activities in China, for example, has brought about a number of serious problems in the environment, but there is little evidence about the utilisation of constructed wetlands so as to treat metal-polluted wastewater released from the mines. In 1983, a cattail (Typha latifolia) was used to construct a wetland, and has since 1985 been the main plant species used for treatment of metal-polluted waste released from metalliferous mine at Shaoguan, China (Yang et al., 2006, p.499). Results from this constructed wetland indicated a considerable improvement in water quality that had been contaminated by heavily metals, with almost 100% reduction of total suspended solids. Yang et al. (2006, p.500) noted a significant difference between wetlands and between metals, based on the extent to which the metal is eradicated from the wetland. A number of studies have pointed out that constructed wetlands had a limited capacity with regard to retention of metals and as a result may ultimately be unsuccessful in removing a number of elements (Cooper & Findlater, 2013, p.587). In addition, factors like temperature and rain were conceivably impacting the long-standing efficiency as well as metals stabilization for removal. Additionally, edaphic and climatic factors, variances in the hydrological system of different environments generate wetlands’ diversity with dissimilar ways of removing metal-polluted wastewater. There are various mechanisms that have an effect on metal removal in constructed wetlands; the first mechanism is adsorption to organic matter as well as fine textured sediments. Another mechanism is precipitation for salts that are not soluble, especially oxyhydroxides and sulphides, and also absorption as well as induced variations in biogeochemical cycles by bacteria and plants (Marchand et al., 2010, p.3448). The last mechanism that affects metal removal is the suspended solids deposition because of low rates of flow. All the above mentioned reactions result in metals accumulation in the constructed wetlands’ substrate. The effectiveness of constructed wetlands relies heavily on hydraulic loading as well as concentrations of inlet metal. Besides that, constructed wetlands may be grouped based on their characteristics; for instance, a constructed wetland system defines four types with regard to the plant species that are dominant: (a) macrophytes that are emerged rooted (such as Typha latifolia and Phragmites australis), (b) floating-leaf macrophytes (such as, Potamogeton gramineus and Nymphea alba), (c) submersed macrophytes (such as Potamogeton crispus and Littorella uniflora), and (d) floating macrophytes (such as Lemna minor and Eichhornia crassipes) (Marchand et al., 2010, p.3448). A different common categorization divides wetlands based on their hydrology such as hybrid systems, vertical and horizontal subsurface flow wetlands, as well as surface flow wetlands. Conclusion In conclusion, it has been argued that wetlands creation for remediating mine pollution is a crucial amelioration technique that must be comprehensively examined and acknowledged as a suitable solution for mine pollution such as acidic mine drainage in both abandoned and active mines. Before constructed wetlands can be considered as an ideal solution for mining pollution, areas such as specifications of construction design must closely be analysed. Certain areas that need more research include the effects of constructed wetlands on animals as well as plants living in such aquatic systems. Constructed wetlands as evidenced in the report have been successful in the removal of metal-contaminated wastewaters in mine drainage. So, constructed wetlands is a possible solution for lasting remediation of acid mine drainage. Reviewed studies have shown positive outcomes concerning application of constructed wetlands in remediating human induced contaminants. To sum up, constructed wetlands for treating mining pollution such as acid mine drainage can offer unceasing, economical as well as effective solution to the increasing pollution problem facing the mining industries these days. References Cooper, P.F. & Findlater, B.C., 2013. Constructed Wetlands in Water Pollution Control. Proceedings of the International Conference on the Use of Constructed Wetlands in Water Pollution Control. Cambridge, UK, 2013. Elsevier. Cuff, D. & Goudie, A., 2009. The Oxford Companion to Global Change. Oxford : Oxford University Press. EPA, 2013. Abandoned Mine Drainage. [Online] Available at: http://water.epa.gov/polwaste/nps/acid_mine.cfm [Accessed 18 February 2015]. Heal, K.V. et al., 2005. Enhancing phosphorus removal in constructed wetlands with ochre from mine drainage treatment. Water Science & Technology, vol. 51, no. 9, pp.275–82. Järup, L., 2003. Hazards of heavy metal contamination. British Medical Bulletin: Oxford Journals, vol. 68, pp.167-82. 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