The Importance of Constructed Wetlands in the Processes of Mine Pollution Amelioration - Literature review Example

Title: The importance of constructed wetlands in the processes of mine pollution amelioration Name Institution Table of Contents Title: The importance of constructed wetlands in the processes of mine pollution amelioration 1 Table of Contents 1 Introduction 3 Acid Mine Drainage in mining industries 4 Problems linked with Acid Mine Drainage 4 The structure of wetland 5 How wetland remove Acid Mine Drainage 7 Environmental technology and Acid Mine Drainage 8 Importance of wetlands in mine pollution amelioration 9 The efficacy of wetland in ameliorating AMD 9 Wetland is inexpensive to maintain 9 Wetland nourishes air 10 Handles diverse wastewater loadings 11 Effective utilization of land 11 The wetland performance 12 References 14 Introduction Living in industrial world has become a catastrophe to both organism and community especially when there is no effective management of contaminants from the industries. Mustafa (2013) defined industry as the processes and activities that produce goods from raw materials and in the process, there is creation of by-products which can pollute environment and have adverse effects on the ecosystem. Over the years, the mining industry has experienced a lot of burden of negative ecological criticism and resilient government regulations. Different environmental analysts has the same perception that extraction of minerals and processing is a source of contaminants to water, air and soil especially when effective environmental measures are not observed. Mining industries have also been associated with infertile and unproductive lands. Therefore, in order to reduce the pollutants and recover the environmental particularly in mine lands, different governments passed surface and mining acts. For example, United States passed Surface and Mining Control and reclamation Act 1977 which needed mining operators to achieve the set standards of environmental sustainability and quality. One of the most challenging contaminant to the ecosystem is the acid released by industries. According to Chen, Yan, Lei & Xiao (2014) the techniques which are employed to remedy water pollution is normally timely and have intense cost and in most cases these strategies go for longer years until the mining station is abandon. Acid Mine Drainage (AMD) however has seen a positive solution since the creation of wetlands to remediate pollutants induced by human (Patova & Dorokhova, 2008). Constructed wetlands has a continuous system to treat acid mine drainage at low cost and this has been perceived as an effective solution to the growing pollution from mining industries (Mustafa, 2013). Acid Mine Drainage in mining industries Acid mine drainage (AMD) results when there is a reaction between sulfide oxide in the mines and water and air. This in turn creates sulfate and hydrogen ions. The minerals that are accounted to this reaction are coal and all metal mining solutions (Ohioline.osu.edu, 2015). It is during the process of extraction which exposes these minerals to ‘ride out’ on air, water or microbial processes. This exposure causes contamination to water which increases its acidity. There will be elevation of heavy metals and other dissolved solids which make water become toxic to the uses-both aquatic and terrestrial life. The mining industry has classification of contaminants with particular concern and they include iron, acidity and aluminum. Also, chemosynthetic bacteria are also another source of AMD which are known to catalyze pyrite oxidation process (Zheng, Gu, Zhou & Li, 2013). Problems linked with Acid Mine Drainage Acid Mine drainage has metal components from mines which contaminates water. When the by-product of mining industry is released to the water, they interact with these metals. AMD composition upsets growth and reproduction of aquatic habitats. This may lead to migration or even death of these habitats. Acid has a corroding effect and therefore it affects parts of the infrastructure like bridges and road side guards. This in turn subject public using road transport to the risk of accidents (Sehlke, Hayes & Stevens, 2004). According to Xiao, Xie & Liu, (2009), acid mine drainage is among the three severe water pollution problems in the world. Perhaps acid mine drainage may not be only ecological concern but also it affects the economy of a country as well. In most cases, a region nearing mines which produces AMD has a significant decrease in fish species like trout. These species of fishes are not only for consumption but also offer recreational tourism. Also, the contamination of water means people around the place of mines would lack drinking water supplies. As a result of this, people may contract life-threatening disease like cancers out of metal ions released from mines. Economic production in the country will decline since people will seek for health intervention to manage their health status. This leads to overdependence on the working population (Whitesell, Huddleston & Allred, 1971). The structure of wetland Wetland construction for acid mine drainage treatment vary depending on the site construction. Vymazal (2008) suggested that the most important design of a wetland should incorporate biochemical processes, loading and retention time, substrate, regulations, sediment control, slope and morphometry. Biochemical processes It is important to understand that all the procedures put together in the construction of a wetland are technology driven. Biochemical processes include applying measured conditions that are favorable in reducing chemical and microbial effects. Also, this processes incorporates absorption, offsetting and precipitation which is essential soil conservation, hydrology, flora and construction site development (Vymazal, 2014). In determining the maximum capacity of a wetland, loading rate of the site is considered. The retention time of the load capacity is determined from the volume and the concentration of the AMD. Also, effluent standards, precipitation, infiltration and evapotranspiration are variables to be considered in reducing the contaminants’ volume. Vymazal, (2010) preferred hydrologic holding rate of 400 cubic m/day with seven day holding time. These are thought to be ideal conditions for a wetland in treating wastewater from mining industries. Wetland has a slope of less than 5% which maximizes the contact of vegetation and substrate. This slope stimulates the removal of iron and manganese from the influent. Vegetation and substrate has similar functions in the process of treating AMD. Substrate helps in soil manipulation. Vegetation on the other hand influences wetland’s major characteristics. Two types of vegetation are used which include Typha and Shagnum. Typha is acid tolerant therefore implying that it thrives under various environmental conditions. Its characteristic of versatility and hardness ensures there is absorption of iron and manganese. Sphagnum has excellent ability in acid mine drainage remediation since it is sensitive to stress which is associated with an abrupt change in the chemistry of water. The use of sphagnum is a technological aid introduced from an advanced knowledge. This type of plant influence in reducing sulfate, manganese and iron ions concentration (Vymazal, 2014). The pond is designed and constructed to accommodate high sediment loads and it is done prior to the treatment of a wetland. This normally helps in dredging sediments without disturbing the habitats of the wetland. It is recommended that season harvesting is done to reduce the accumulation of plant biomass. However, this brings in a concern of the level of importance of organic matter that has accumulated in the wetland (Vymazal, 2008). The geometric configuration is extremely influential in constructing a wetland. This technological initiative helps in reducing the effect of AMD on the ecosystem. According to Wallace & Knight (2006) a good geometric configuration offers better habitation of wildlife and in promotes the establishment of macrophyte. Good geometric configuration of the wetland also increases the diversity of habitats since the better nature of it attracts lives. Seasonality of the place where the wetlands is to be constructed should be determined. The places where there is climate fluctuation offers good site for a wetland. This is because the bacteria that is responsible for catalyzing AMD is normally active during cold times and so in the warmer seasons. The catalysis is helped by Typha and Sphagnum during the dormant season which offers the equivalent effects to the remediation of AMD. The last component of wetland is regulations. Standards are provided by governments especially in the management of effluent from the wetland. The regulations offer the standards that should be observed by both the projects and the community. The main objective of regulations is to there is a biological control in the ecosystem during the course of the activities involved in the project. How wetland remove Acid Mine Drainage Acid mine drainage is composed of sulfate, iron and heavy metal ions concentration. Wetland is a technological pollution control that is set to reduce the concentration of these metal ions. The mechanism in the wetlands is the usage of organic substrates that will interchange with dissolved metals in water. The exchange occurs between the metals and the humic acids which are in the substrate. The anaerobic growth in the wetland contains carbon that is responsible for microbial growth. There is creation of anoxic zone which provides favorable conditions for the growth and activation of microbial and chemical processes. This process alters iron and sulfates to hydrogen and sulfites. The anoxic condition of the wetlands also converts the soluble metals to insoluble form. The 5% gradient of the wetland control water velocity. The gentle movement of water provides san effective action of Typha in removal of iron and manganese. Typha and Sphagnum provides microenvironment that aid in reduction and oxidation processes. During this reaction, the bacteria like Desulfovibrio employ anaerobic respiration. This shows the innovative ideas employed in wetlands in controlling the effects of acid mine drainage (Sehlke, Hayes & Stevens, 2004). Environmental technology and Acid Mine Drainage Technology involves innovative treatment and it is described in a wide range of advancement, for example during chemical encapsulation in wetland. The genesis of movement into using technology in remedying AMD was developed from the observation of the wetland which was perceived to be naturally removing metals from contaminated water. However, the treatment of hard metals like zinc and lead are premised behind the use of passive treatment with the objective of inducing metal precipitation which chemically transforms to sulfides. During coal mines, there is application of aerobic processes with or without the use of alkaline. The use of alkaline to reduce the acidity perhaps may not look innovative but in some ways, the exposure of contaminated water (acidic water) to alkaline solutions is innovative (Wong, 2004). Apparently, many if not all technology treatment of AMD applies the same principles: Permeable Reactive Barriers. Constructed wetland uses alkaline agents and sulfates introduction to reduce bacteria in treating mine drainage. Like both Permeable Reactive Barriers and bioreactors, constructed wetland has lined ponds with filled organic matter or alkaline agents and vegetation. The organic matter and vegetation in constructed wetland provides a membrane for metal to be absorbed. The role of anaerobic wetlands is to raise PH and offer sulfate reducing agents. Aerobic wetlands are frequently used especially on alkaline waters as well as during oxygen infiltration. Thus the similarity between constructed wetland and bioreactors, which are both considered innovative methods, is that they provide piping and flow paths of the effluents (Whitesell, Huddleston & Allred, 1971). Importance of wetlands in mine pollution amelioration The efficacy of wetland in ameliorating AMD Wetland provides high level in the treatment of AMD. In a test result conducted by South Africa institute of Mining and Metallurgy, the formation of iron sulphide is due to the organic condition that led to the absorption of iron. This indicated a gradual change of the sediment which showed increase in residual fraction. The implication of this test is that more metal ions were bond by the organic composition of the sediment in the wetland compared to the influent. Therefore, the wetland is considered as immobilizing the pollutants within the AMD (Nedved & Jansz, 2006). Wetland is inexpensive to maintain The materials used in the construction of wetland are minimal. Both energy and equipment needed to run the wetland is nominal thus reducing the operational cost of the project. With the slope of 5% gradient, water, or in this case influent flow by use of gravity all through the system. The gravity will reduce the use of energy though some energy may be needed in pumps. The importance of it is that once the whole system is established and properly designed, the wetland is self-maintaining. Energy that would have been used to pump AMD is conserved and perhaps used somewhere else to boost other sectors of economy (Nedved & Jansz, 2006). Wetland is relatively inexpensive to construct Normally, wetland is site specific considering the variables such as topography, supply of water, type of soil and livestock type. When it comes to selection of sites especially with the following variables specification, then it is cheaper. Focusing on the livestock lot, site near this specific variable have canary grass vegetation that is one of the requirement in creating a wetland. This vegetation is responsible in helping separating solids in the influent to increase the surface area of absorption all through the processes in the wetland thus optimizing the pollution control process of the wetland (Mustafa, 2013). Wetland nourishes air Elimination of odor by the wetland is an indication of growing technology. The by-products from the mine industries have this smell and it normally affects the life of people living around the mining places. Taddeo (1991) calls wetland the ‘earth kidney’ since it purifies the pollutants that flow though into the receiving lakes or rivers. With the help of vegetation around the wetland, it reduces the odor that may be present in the by-products from the mines. For example, the microbes in the wetland converts the organic nitrogen present in the influent into usable inorganic forms which are necessary for plant growth. The release of the inorganic substance into the atmosphere is not harmful. The wetland in this case helps in reducing air contamination through neutralization of harmful gasses present in the AMD released from the mines. It makes sense to build a wetland since it nurtures a healthy habitat that supports life of both animals and plants (Vymazal, 2010). People and plants may be chilling away from the mine areas, but with the present of constructed wetland, it provides a healthy environment of living. For example, useful plant nutrients like nitrogen and phosphorus are normally deposited in the septic during storm water. These nutrients are channeled to the fields around which will act as manures and fertilizers for the farms around the wetlands. In the cases where farming is closely placed to the proximity of the residential places, the wetland gases are detoxified or reduced to low intensity to effect before it is released to the atmosphere (Vymazal, 2014). Handles diverse wastewater loadings Unlike other water treatment plants which handle specific by-products from the industries, wetlands is designed in a diverse way to handle influent not only from mining industries but also from other industries producing pollutants. Though wetland is perceived to focus on reducing heavy metals from the pollutants before being discharged, it serves other functions within its capacity (Wallace & Knight, 2006). Focusing on water loading, the release of AMD from the mines may vary depending on the climatic conditions or the operations within the mines. Wetland is flexible enough to accommodate these changes at a lower cost. This is important because in case of change of water volume or influent volume, the risk of the system to break down is low. The only thing the management is expected to do is managing change and perhaps monitoring, inspecting and maintaining the system where it needs attention (Xiao, Xie & Liu, 2009). Effective utilization of land Constructed wetland only needs a land where the system is installed and it does not necessarily need a space for wastewater application. As the by-products passes through the system, it completely purified and it may not need an extra space for the application of other mechanism of pollution control. Therefore, the economically productive land that would have been used to gather more space for mine byproduct treatment would be used for other purposes such us agriculture and livestock farming which is highly recommendable around the constructed wetlands. According to Zheng, Gu, Zhou & Li (2013), 60% of the people around the coal mines in United States have had their agriculture flourish with the rich of nutrients provided by the constructed wetlands. The wetland performance The bigger the wetland, the effective the performance if gives in the processes of mine pollution reduction improvement. This large surface are provides an effective performance in the removal of biological oxygen demand and chemical oxygen demand that is brought by sedimentation and bacteria oxidation. With the case of heavy metals in the influent, the present of vegetation with a gentle gradient of 5% has increase the effect of reduction of the contaminants in the water and seasonal absorption of is an equal important provided by the wetland. The most appealing fact of the wetland is during effluent disposal. Wetlands effluents can be used directly for irrigation or discharged directly to the ocean, streams or rivers since the effluent is less harmful (Vymazal, 2010). It has been noted that coal and phosphate mines have embraced the creation of wetlands as a system to manage their pollutants. This technology of wetland creation has seen many coal companies reclaim slurry ponds through creation of wetlands. Land reclamation through wetlands provides good environment for habitation for birds, fauna and mammals (Chen, Yan, Lei & Xiao, 2014). The consistency of performance of the wetland is the reason most of the mining companies are embracing its construction. For instance, biological oxygen demand reduction is consistent with a discharge value of 12-19mg/l. Also, neutralization of phosphorus and nitrogen is consistent with low efforts being applied in the process. In conclusion, constructed wetland in the treatment of Acid Mine Drainage is an emerging technology which has not been applied in most parts of the world. Among those who have implemented are the developed countries and the countries will coal ores. The treatment of AMD on the mines by use of wetlands has been effective. A properly constructed wetland works well with topography and has shown many importance in the improvement in AMD treatment including: it provides high standards of treatment where the concentration of heavy metals in the AMD is significantly reduced, the project has low operational cost including low cost of construction. The introduction of wetlands in mines has reduced also the odor problem which has been a problem to residents around the place of mine. People are now living close to the mines in which they can use the sediments from the wetlands to improve their farms. Elements of a good designed wetland for AMC reduction include 5% gradient, pond, substrate, vegetation (Typha and Shagnum), geometric configuration and regulations (Vymazal, 2014). As a result of its low cost of construction and effective treatment of heavy metals, constructed wetlands is currently used mostly in United States which is gaining popularity in the region. However, there is still skepticism in developing countries, it is basically considered as an improvement in the processes of treating mine pollution. Its unique solution in treatment of AMD by improving effluent quality has attracted most industries. References Chen, T., Yan, B., Lei, C., & Xiao, X. (2014). Pollution control and metal resource recovery for acid mine drainage. Hydrometallurgy, 147-148, 112-119. doi:10.1016/j.hydromet.2014.04.024 Mustafa, A. (2013). 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Microbial communities in acid water environments of two mines, China. Environmental Pollution, 157(3), 1045-1050. doi:10.1016/j.envpol.2008.09.035 Zheng, S., Gu, B., Zhou, Q., & Li, Y. (2013). Variations of mercury in the inflow and outflow of a constructed treatment wetland in south Florida, USA. Ecological Engineering, 61, 419-425. doi:10.1016/j.ecoleng.2013.10.015 Read More