The Use of Constructed Wetlands for Acid Mine Drainage and Stream Restoration - Literature review Example

The Importance of Constructed Wetlands in the Process of Mine Pollution Amelioration Name Institution Tutor Date Table of Contents Table of Contents 2 Introduction 3 Free Water Flow system 7 Rehabilitation of Mined Land 9 Rehabilitation of Ex- Mining ponds 11 Discussion 12 Conclusion 15 References 16 Introduction Mine pollution is one the contentious environment challenges encountered by the mining industry. Amid the pressure to safeguard the environment, the mining industry has experienced intense negative environmental condemnation and tough governmental regulations that require the industry to alleviate pollution. In the previous years, the extraction of minerals and processing has greatly contributed to an increase in amount of contaminants entering the air, water and soil. Furthermore, the mining industry is blamed for a wide range of infertility of land and the development of landscapes that are unproductive. In order to resolve the challenge of pollution and environmental damage, the industry has adopted the construction of wetlands in the process of mine pollution amelioration. Constructed wetlands can be defined as a manmade industrial waste treatment approach that consists of sub-emergent and emergent vegetation, animal life, saturated substrate and water that stimulates the removal of hazardous pollutants from the environment (Hammer, 1990). This paper seeks to describe and assess the significance of constructed wetlands in the process of mine pollution amelioration. Treatment of Acid Mine Drainage Smith (1997) discloses that constructed wetlands have brought about various benefits that assist in mine pollution amelioration. One of the key benefits has been the treatment of acidic mine drainage (AMD). Acidic mine drainage normally takes place when a reaction takes place between sulfide oxidation in the rock with air and water resulting to the creation of hydroxide, hydrogen and sulfate ions. The mineral that influences this reaction for both metal and coal mining is pyrite. Mining activities therefore subject the mineral to weathering water, air and microbial process. Such exposure makes the contaminated water to have elevated levels of heavy metals, increased acidity, sulfate and solids. According to Smith (1997) acid mine drainage (AMD) is perceived as one of the most difficult challenges to solve. This is basically because AMD can take place for a long period of time, which implies that the treatment has to take place until the mining activities have been terminated. The construction of wetlands has therefore been considered as a suitable mediation of this problem. In this respect, various studies have been conducted to demonstrate the potential ability of constructed wetlands in the treatment of acidic mine drainage. A study conducted by Nyquist and Greger (2009), on constructed wetlands for preventing and treating acid mine drainage, evaluated the ability of the wetlands constructed on tailing impoundments to stop the formation of acidic mine drainage that has already formed. The study had a special emphasis on wetland plants that occur in the remediation process. Four different designs of small scale surface wetlands containing sand or mining tailings, an inflow of unpolluted water and emergent plants were constructed in the year 2004 at Kristineberg in northern Sweden. Water samples were gathered each month in the year 2006 at the outflow and inflow in order to analyze the PH, metals, redox potential and sulfate levels. At the end of the year 2006, sediment and plant samples were gathered to facilitate the analysis of metal concentrations. The findings of the analysis disclosed that the concentration of Cd, Zn, sulpate and Cd and the PH did not change after the passage that took place through the treatment of ADM using the wetlands. Nevertheless, the concentration reduced by 36-37% with the decline higher in the presence as opposed to the absence of plants. The study indicated that the concentration of metals in impoundment water seemed to decrease as the water continued to pass through the wetland. Although the study disclosed that the constructed wetlands were not very adequate in the treatment of extensively harsh AMD at the mine, nevertheless, the construction of the wetlands were actually effective in the treatment of acidic mine drainage. Brenner (2001) also conducted a study to examine the use of constructed wetlands for acid mine drainage and stream restoration. The study area was the Pennsylvania Slippery Rock Creek watershed which was adversely affected by acidic mine drainage for over one hundred years with about 74 mine discharges leading to 1,228.8 kg, 282 kg and 69 kg/day of sulfuric acid, iron and aluminum, respectively. After the initiation of the project, the constructed wetlands have assisted in the restoration of the acid mine drainage affected streams. Since the year 1995 the building of seven wetlands have resulted to 192.8 kg of alkalinity and eliminated 39% of the acid loading to a 4.83 km. As more treatment systems have been constructed, it is estimated that there is extra 34.7% decrease in acidic loading taking place in streams (Brenner, 2001). Treatment of Waste Water Wetlands have also been beneficial in remediating acidic metal-rich waste waters (Lens and Hulshoff, 2000). In the recent years, an alternative method to active treatment for remediating acidic metal rich west waters has been the use of natural or constructed wetland ecosystem. The approach also referred to as a passive approach was developed due to observations that outflows that emerge from sphagnum – dominated bogs exhibited better water chemistry in comparison to inflow AMD. The rising PH of the outflow is followed by reduced concentration of iron, sulfate and other metals. In areas where natural wetlands cannot be constructed, artificial wetlands have been constructed in order to reduce acidic metal-rich waste waters. Wetlands consist of a water chemistry that is brought about by various mechanisms which include precipitation (by reduction and oxidation), dilution, uptake of biomass and adsorption. This bioremediating approach has been predominantly popular in the USA where several wetland sites have been constructed to meliorate acidic waste waters that arise from coal mining regions such as Appalachia. Wetlands have also increasingly become popular in Europe and other regions of the world (Lens and Hulshoff, 2000). Constructed wetlands also have the capability of treating wastewater in an environment that is more controlled as opposed to those that take place in the natural wetlands (Patel and Nishitha, 2013). Constructed wetlands for the treatment of wastewater can be categorized as either sub-surface flow (SSF) or the Free Water Flow (FWF) as depicted by Figure (1 and 2 below) Figure I Sub-surface flow treatment system Figure 2 Free Water Flow system In the context of the FWS system, the water flow is usually above the ground and plants are usually fixed in the sediment layer at the water base. In the SSF system, water usually flows through a porous media such as aggregates or gravels in which the plants are rooted. Both systems are usually very appropriate for the treatment of waste waters. The systems are usually suitable for treating primary waste waters due to the fact that there is no direct contact that exists between the atmosphere and the water column. As a result, there is no chance of vermin to breed making the system safe in the perspective of public health. The system has predominantly been useful for the treatment of landfill leachate, septic tank effluent, grey water and water that has high concentration of organic materials (Patel and Nishitha, 2013) Constructed wetlands have also greatly contributed to the long- term stability and efficiency for treating wastewater exposed heavy metals such as Iron and Zinc from mine discharge. Yang et al (2006) highlights that the speedy expansion of industrialization with an enormous raising demand for heavy metals such as Zinc (Zn) and Lead (Pb) has resulted to a high level of anthropogenic emission of such pollutants into water bodies both in the ground water and surface water. As opposed to organic pollutants , metals in wastewater are usually not degraded using biological processes which poses a threat to not only the aquatic ecosystem but also it poses a problem to human health due to contamination of drinking water. Mines that have metal contaminated drainage therefore pose a persistent and serious environmental problem that requires that removal of contamination in the water. Various methods have been used to treat water that is contaminated by heavy metals. Some of the methods include the use of mine affluent which has been found to be expensive and also difficult. Another method is the physio- chemical approach which is expensive and can only treat large volumes of water. The most effective and low cost alternative has been the use of constructed wetlands. Sundaravadivel and Vigneswaran (2001) argue that constructed wetland in an efficient tool in the phytoremediation for the treatment of water that has been polluted by heavy metals from mines. Some of the successful cases of the implementation of the technique indicate that wetlands have been useful in purifying mine drainage water that has been contaminated by metals (Yang et al, 2006). For instance, in China, a wetland was constructed in the year 1983, through the use of Typha latifolia (cattail) as the major plant species. The objective of the wetland was to treat mine drainage that was metal contaminated and was discharged from the matalliferous mine consisting of Zinc and lead. After a monitoring of five years (1986- 1990), it was noted that the quality of the water substantially improved after the wastewater had passed through a stabilized pond and the constructed wetland. The total of suspended solid (TSS) was lowered by 99%, Zinc by 80%, Pb by 95%. The metal accumulation and uptake by Typha latifolia increased in the constructed wetland as the water become clean. From such a success story it can be stated that constructed wetlands have actually been effective in treating wastewater exposed to Iron and Zinc from mine discharge (Yang et al, 2006). Wetlands also improve the quality of water. A wetland is basically a complex assemblage of water, plants (algae and vascular), substrate, litter and invertebrates which consist of worms and insects. What is evident from this composition is that the mechanisms that are required in order to improve the quality of water are often interrelated and numerous. The mechanisms include; settling of particular matter that is suspended, chemical and filtration precipitation through contact of the water with the litter and substrate, transformation of chemicals, ion exchange and absorption on the surfaces, substrate, plants, litter and sediment, transformation and breakdown of pollutants by plants and microorganisms, transformation and uptake of nutrients by plants and microorganism and die- off of pathogens and predation. According to Bastian, (2010) wetlands are the most effective in improving the quality of water due to these mechanisms. Rehabilitation of Mined Land Mining companies are usually necessitated by law to submit plans concerning their commitment in the re habilitation of the mine land once the mine is closed. This requirement has particularly been challenging for small mines. Mining activities usually disfigures landscapes leading to landslides, pollution of soil and water, subsidence and lowering of ground water. Mining explorations have therefore caused much damage on the land. The restoration of mined land is therefore very significant. The process entails revegetation and landscaping. In general the restoration of land has the objective of restoring the productive elements of the land and also its aesthetic features (Aswathanarayana and Divi, 2009). One of the key amelioration methods that have been used in the rehabilitation of mined land is the construction of artificial wetlands. The artificial wetlands are usually developed with the objective of treatment of polluted runoff and acid mine drainage. Studies indicate that approaches such the use of civil engineering techniques such as cementing and terracing, do not work due to the fact that mine wastes may be often toxic and inhabitable. Rehabilitation through vegetation as undertaken in constructed wetlands may have several benefits. One of the benefits is that it is cost effective and environmental friendly. It also requires no imported or costly technology or inputs. Also the beautification of the site can be attained in the process (Aswathanarayana and Divi, 2009). Cobârzan, (2008) conducted a research that used a case study of the coal mining industry in Romania. The study disclosed that there are various consequences that closed mines pose on land. Many Romanian mining companies used various methods in order to rehabilitate the mined lands. The companies even developed budgets that included rehabilitation of mining land as one of the key operational costs (Cobârzan, 2007). However, most of the rehabilitation efforts have not been very beneficial. Nevertheless; the mining companies adopted the use of constructed wetlands which has been beneficial in the rehabilitation of mined land. Rehabilitation of Ex- Mining ponds Several successful projects have been implemented to demonstrate the manner how constructed wetlands can be used in the rehabilitation of ex- mining ponds. A case in point is In Malaysia where the department of Irrigation and Drainage (DID) appointed a task force to undertake the rehabilitation of Ex- Mining ponds. The area of study was situated on a former ex- mining land which was sparsely vegetated and contained sandy soil. The main feature of the site is demonstrated by figure 3 as shown below. Figure 4 demonstrates the constructed wetland and the progress it has made in the rehabilitation of the Ex- Mining pond (Chang, et al, 2008). Figure 3- Ex mining pond Figure 4 – The constructed wetland Discussion The findings and facts presented by the various literatures disclose various significant aspects concerning constructed wetlands. The literatures reveal the fact that the problem of pollution is indeed one of the greatest challenges facing mine industry. Over the years, the mining industry has adopted various strategies in order to deal with this particular challenge. The construction of wetlands has therefore been a significant method that has been used in the process of mine pollution amelioration. The findings of various studies disclose that the construction of wetlands has indeed been beneficial in the process of mine pollution amelioration. Foremost, one of the key benefits is the treatment of acid mine drainage. The challenge of acid mine drainage is considered as one of the biggest problems that the mine industry faces. Many of the studies have indicated that the construction of wetlands is actually resolving this particular problem. Although the studies disclosed that acid mine drainage is a long term problem that requires the adoption of a long term treatment remedy, it can be stated that constructed wetlands have actually been very beneficial in resolving this particular challenge. Wetlands have various attributes that aid to ameliorate acid mine in drainage. The attributes that are needed for a certain process of AMD to take place include ion exchange and adsorption, abiotic and bacterial oxidation, neutralization, dissolution of carbonate mineral, bioaccumulation and reduction (Kleinmann and Perry, 1991). Such attributes were noted in most of the studies as the basic reason why the construction of wetlands is actually effective in handling the challenge of AMD. Treatment of waste water is another crucial benefit that has been noted from the literature. What is evident from the findings of the studies is that constructed wetlands have also greatly contributed to the treatment of waste water. Additionally the literatures identify the fact that constructed wetlands have the ability to facilitate the rehabilitation of ex- mining ponds and also to rehabilitate mining lands. Concerns however exist concerning the use of constructed wetlands in the treatment of acid mine drainage and even in other benefits such as the treatment of water, rehabilitation of ex- mining ponds and the rehabilitation of mining land. One of the concerns arises is the issue of metal accumulation. The use of vegetation in the wetlands implies that there is an entry of heavy metals within the food the food chain. Although studies such as those conducted by Pascoe et al (1994) disclose that no results indicate that there will be an accumulation of heavy metals based on the fact neither animals and plants that live in the wetland receive the metal toxics. Other reports have however disclosed that there are negative implications that exist on the microorganisms that are available in the wetlands (Lacki, et al, 1992). Another key concern is attributed to the fact that suppose the wetlands will last for a long period of time without the anticipation that they could lead to serious effects on the environment, a key concern is whether the wetlands will have the ability to maintain the continuous drainage that is emitted essentially in the context of treatment of AMD. The system of constructed wetlands should therefore entail intense monitoring in order to guarantee that the system does not experience saturation and further lead to the leaking of toxic substances into the environment. It is therefore essential to ensure that the construction of wetlands should consist of monitoring in order to ascertain that the system does not become saturated and further lead to the leaking of toxic substances into the environment. In addition, it is essential to establish precise regulations that pertain to the usage of constructed wetlands in order to treat acid mine drainage, this is a significant step that will particularly be significant in technology that is to be used in the future. In general it can be stated that the construction of wetlands in the process of mine pollution amelioration is a significant technique that should continuously be examined in order to identify possible solution for dealing with the challenge of pollution in the mining industry. Certain key areas that should be evaluated include; design and construction specifics which should be investigated closely before adopting the system in any particular environment. Some of the research areas should include the implications that the wetlands can bring to animals and plants that live within the aquatic system. Such a study will provide an enhanced understanding of the best wetland process and how efficient they can work. Conclusion The above study has examined the significance of constructed wetlands in the process of mine pollution amelioration. From various the various studies and literature, various benefits were identified. Some of the benefits include, treatment of acidic mine drainage, the rehabilitation of ex- mining ponds and land and the treatment of waste water. From the above literature it can be stated that the construction of wetlands to deal with mine pollution amelioration is a workable approach for this particular sector. Many of the studies have disclosed the fact the system is actually working and is beneficial. References Aswathanarayana, U and Divi, R, 2009, Energy Portfolios ,CRC Press. Brenner , J, 2001, Use of constructed wetlands for acid mine drainage abatement and stream restoration, Water Science Technology , 2001;44(11-12):449-54. Bastian, R, 2010, A handbook of constructed wetlands , USDA. Chang, C, Ghani, B, Zakaria , Y and Ayub , S , 2008, Rehabilitation of Ex-Mining Pond and Existing Wetland for Integrated Stormwater Management, 11th International Conference on Urban Drainage, Edinburgh, Scotland. Cobârzan, B, 2007, Brownfield Redevelopment in Romania’, Transylvanian Review of Administrative Sciences, , p 28-46. Cobârzan, B , 2008, Environmental Rehabilitation of closed mines , Transylvanian Review of Administrative Sciences, pp. 34-43. Lens, P and Hulshoff, L, 2000, Environmental Technologies to Treat Sulfur Pollution: Principles and Engineering, IWA publishing . Lacki, J , Webster , J and Hammer, 1992, Mine drainage treating wetland as habitat for herpetofaunal wildlife, Environmental Management , p 16: 513-520. Hammer, D, 1990, Constructed Wetland for Wastewater Treatment, Lewis Publisher, Chelsea. Kleinmann, P and Perry , A , 1991, The use of constructed wetlands in the treatment of acid mine drainage. Natural Resources Forum 15: 178-184. Nyquist, J and Greger, M, 2009, A field study of constructed wetlands for preventing and treating acid mine drainage, Journal of Ecological Engineering, 35(5), Pages 630-642 Patel, P and Nishitha, D, 2013, Manmade wetland for wastewater treatment with Special emphasis on design criteria , Science . Revs. Chem. Communication, 3(3), 150-160. Pascoe, A, Blanchet and G. Linder, 1994, Bioavailability of metals and arsenic to small mammals at a mining waste-water contaminated wetland. Architectural Environmental Contamination Toxicology 27: 44-50. Sundaravadivel, M and Vigneswaran, S, 2001, Constructed wetland for wastewater treatment . Critical reviews in Environmental Science and Technology , 31, 351-409. Yang, B , Lan, C , Liao, W, Chang, H and Shu, W, 2006, Long-term efficiency and stability of wetlands for treating wastewater of Lead/ Zinc mine and the concurrent ecosystem development, Environmental Pollution , 143(2006), p 499-512. Read More