The Actual Importance of Constructed Wetlands - Research Proposal Example

Importance of Constructed Wetlands in the Process of Mine Pollution Amelioration Name: Students ID: Unit Code: Date: Time: Instructor: Contents Introduction 2 Constructed Wetlands 3 Discussion 6 Conclusion 14 References 14 Introduction In the recent past, wetlands have attracted much interest especially from conservationists. In fact, some of them have labelled them as nature's kidneys. In particular, constructed wetlands have been lauded as ground-breaking in removing pollutants from water. The wetlands have been recognised due to their natural treatment functions for treatment of point source as well as non-point source pollution. They have become more and more common in treating virtually all forms of water pollution such as cropland runoff, cramped animal wastewater, septic tank runoff, urban storm water, acid mine drainage, municipal wastewater discharge, and manufacturing process waters. Their performance has so far been good (Rankin, 2011). Therefore, constructed wetlands have a wide application in handling pollution. However, in this report, the focus is on the importance of constructed wetlands in the process on mine pollution amelioration. The report is divided into two key parts. In the first part, constructed wetlands are elaborately defined. This is followed by a discussion on the actual importance of constructed wetlands in reducing mine pollution in the second part. The conclusion summarises the whole report based on the scientific scholarly material. Constructed Wetlands Constructed wetlands are a form of passive water treatment and they are the most common. They act as natural purification systems. Constructed wetlands are able to filter and remove lots of contaminates afore transportation into marine or freshwater systems. The constructed wetlands technology originated in Germany in the 1950s at the Max Planck Institute by Kathe Seidel. This followed Seidel’s observation that macrophyte Schoenoplectus lacustris could take out organic as well as inorganic materials from polluted water. Reinhold Kickuth conducted further studies by the 1960s leading to the model of the Root Zone Technique. As a result of these studies, the first active system was installed in Germany in the 1970s and later spread to the UK in the 1980s (Lottermoser, 2012). Constructed Wetlands are created artificially so as to treat wetlands wastewaters, habitat creation or both. In the UK, constructed wetlands are generally called ‘reed beds’ because of the specific species of wetland plant (the Common Reed (Phragmites australis)) used in these systems. They are effective at treating wastewaters owing to three key factors: 1. Plants Aquatic plants are planted on constructed wetlands. They grow in or near water (budding macrophytes). In the UK, the common reed (Phragmites australis) and the broadleaf cattail (Typha latifolia) are the most common species used in treating wetlands. Other aquatic plants can as well be used. It is through these plants roots that water passes through to the matrix. Also, a small amount of oxygen passes into the root zone allowing for aerobic bacterial breakdown of organic contaminants in this area (Younger et al. 2002). 2. Media. This is the matrix (also known as substrate) where the aquatic plants are grown on a constructed wetland. It consists of the sand, gravel, soil, composite or reactive media such as LECA (Light Expanded Clay Aggregates) or blast furnace slag for removing metal substances. Micro-organisms fasten themselves to the surface of the matrix, therefore a bigger the surface area has a higher potential for the removal of microbial pollutants. There is a reasonable equilibrium between retaining microbial quantities and hydraulic conductivity (the amount of water flowing through the matrix) (Hedin, 2003). 3. Microbial activity. These are the micro-organisms responsible for decomposing organic compounds. They are mainly important in removing carbonaceous (measured by means of COD and BOD tests) and nitrogenous (ammonia, nitrite, and nitrate) compounds (Younger et al. 2002). In general, constructed wetlands can be grouped into two main categories based on how water infiltrates through the system. These are: (1) Surface or free water surface, and (2) Sub-surface. These groupings can then further be split up into horizontal flow and vertical flow paths (Blight, 2011). The horizontal flow system is the one that has been the most commonly used. In horizontal flow, effluents that enter on one side of the bed move continuously across the bed where treatment is stimulated by micro-organisms before being collected and discharged on the far side of the bed. These system can work in both the sub-surface flow and the surface flow. Sub-surface flow wetlands have the water flowing underneath the surface of a gravel and sand bed in which the plants’ roots enter to the bottom of the bed (Johnson, 2003). They are often used to reduce the BOD5 (5-day biochemical oxygen) demand that causes lower oxygen levels in the storm water overflow. Sub-surface wetlands offer more attachment surface area for biota and may well treat storm water more rapidly and so encourage smaller constructed wetlands for the same level of treatment. On the other hand, surface flow wetlands have their water level and flow on top of the ground surface. The plants roots emerge on top of the water surface. The shallower surface water level is aerobic whereas the deeper water level and substrate are generally anaerobic (Blight, 2011). Vertical flow is also called the Down Flow reed beds. This type is not common in the UK as the horizontal flow is. The discharge flows across the surface of the bed and gutters down to the base of the bed. Vertical flow systems can work both in a drenched and free draining mode (Younger et al. 2002). Both types can be combined to form composite systems where necessary. Discussion The mining industry has been bedevilled by adverse environmental criticism and tough governmental rules. This troubles stem from the active and abandoned which are a major pollution concern. Mineral extraction and processing has been a big source of lots of pollutants entering our air, water and soil. They have turned many vast lands into unproductive and infertile sceneries. Several Acts have been passes so as to help reduce these contaminants and bring back environmental production to mined lands. Therefore, the mining industry has made numerous innovations to the objective of greater environmental sustainability and quality (Blight, 2011). Their clear goal has been the rebuilding of wetlands where possible to recuperate the antique quality of the residual land. Their intent is naturally to re-establish wetland systems to levels that were before human destruction. Even though this restoration may be legally required, it can as well be prompted by environmental resource management for environmental or improvements to water quality habitat, alongside other functions. In either case, this presents an opportunity that can be very much valuable for watershed-scale conservational planning (Johnson & Hallberg, 2003). Acid mine drainage (AMD) is one tough problem that the mining industry has struggled to solve. AMD comes about the minute sulphide rust in rock reacts with air and water to create sulphate, hydroxide and hydrogen ions. Pyrite the mineral that is guilty for this reaction, for both metal and coal mining. The mining undertakings expose this mineral to weathering by water, air, and microbial processes. This exposure causes the polluted waters to have higher acidity, and raised concentrations of sulphate, heavy metals, along with other entirely dissolved solids. Pollutants that have been of higher concern are metals such as aluminium (Al), iron (Fe) and manganese (Mn) and metalloids, particularly arsenic. Such waters usually bring an additional risk to the surroundings. AMD can as well be caused by chemosynthetic microorganisms including T. thiooxidans, Thiobacillus ferooxidans and Ferrobacillus ferroxidans. These bacteria catalyse the corrosion of pyrite (Neal et al., 2004). AMD may well form in underground workings of deep mines. However, this is by and large of trifling standing once a mine is in active production and water tables are kept artificially low by pumping. As soon as the mines are shut and abandoned, and the pumps turn off, the bounce of the water table may lead to the discharge of polluted groundwater. This can at times be a tragic occurrence such as the one that occurred at the Wheal Jane mine in 1992 after a variety of pollutants got into the surroundings (Younger et al., 2004). The initial drainage water is disposed to be more potentially polluting (in terms of metal content and acidity) than AMD that is discharged afterwards. This is because of the water that fill-ups the mine and dissolves every acidic salts that have built up on the opening spaces of the open walls and ceilings of the underground chambers. Acidic metal-rich waters possibly will also form in mineral tailings and spoil masses (Johnson & Hallberg, 2003). Constructed wetlands have been well thought-out as a conceivable way out to the long standing remediation of AMD. The remediation can be achieved either through aerobic wetlands, anaerobic wetlands, passive bioremediation systems (a combination of aerobic and anaerobic wetlands), or Permeable reactive barriers (PRBs). Aerobic Wetlands Aerobic wetlands consist of wetland vegetation grown in shallow (less than 30 centimetres), somewhat watertight sediments comprised of clay, soil or mine spoil. The vegetation assists in regulating the water flow. Therefore, aerobic wetlands in general accumulate water and offer habitation time and exposure to air so that metals in the water can precipitate. The water in this case typically has net alkalinity, iron and manganese precipitate as they react. The precipitates are retained in the wetland or downstream. Moreover, by allowing oxygen flow from floating parts to their root systems, particular aquatic plants may well speed up the rate of ferrous iron corrosion. Wetland species are grown in these systems to add specific organic substances and for aesthetics (Evangelou, 1995). The plants encourage more even movement and thus improving the effectiveness of the wetland area. Owing to their wide slow flow and water surface, aerobic wetlands encourage metal corrosion and hydrolysis. In that way, they cause precipitation and physical retention of Al, Fe and Mn hydroxides. The degree of metal removal is dependent on dissolved oxygen content, dissolved metal concentrations, there being of active microbial biomass, pH plus the net alkalinity of the mine water, as well as the detention time of the water in the wetland. The net alkalinity/acidity and pH of the water are mainly vital since pH impacts the kinetics of metal corrosion and hydrolysis as well as the solubility of metal hydroxide precipitates (Battaglia-Brunet et al., 2002). The removal of arsenic is another major remediation process that takes place in aerobic wetlands receiving AMD. It primarily originates from the oxidative dissolution of arsenopyrite (FeAsS) found in mine waste matters. According to Coulton et al. (2003), solvable arsenic, mainly existing as anionic in mine waters, may possibly be removed “largely by adsorption onto completely charged ferric iron colloids and, theoretically, by the formation of scorodite (FeAsO4).” Different strains of Thiomonas-like bacteria most likely add to the removal of arsenic in these waters. They probably can be used in fixed bed bioreactor systems for the corrosion and precipitation of iron. Anaerobic Wetlands Anaerobic wetlands consist of wetland vegetation that grow into deep (more than 30 centimetres), penetrable deposits of soil, spent mushroom compost, peat moss, sawdust, hay bales, manure/straw, or various other organic mixtures that are a lot lie beneath or are admixed with limestone. Whereas in aerobic wetlands treatment is controlled by processes in the narrow surface layer, in anaerobic wetlands, treatment involves main dealings in the substrate. Anaerobic wetlands boost the passage of water through organic rich substrates that meaningfully contribute to treatment. The wetland substrate can mix the limestone among the organic matter or contain a layer of limestone beneath the wetland. The plants are transplanted into the organic substrate (Wolkersdorfer, 2008). Anaerobic wetland systems are used once the water has net acidity, therefore alkalinity should be produced in the wetland and introduced to the net acid water prior to the precipitation of dissolved metals. This alkalinity may be spawned in two ways: particular microorganisms, Desulfotomaculum and Desulfovibrio, can use the organic substrate as a carbon source (CH2O), and sulphate as an electron acceptor for growing. The system promotes metal corrosion and hydrolysis in aerobic surface layers, but similarly relies on sub-surface organic as well as bacterial lessening reactions to neutralise acid and precipitate metals. The water penetrates through thick absorptive organic sub-surface remains and turns into anaerobic because of the great organic oxygen demand (Battaglia-Brunet et al., 2002). Passive Bioremediation Systems Passive bioremediation systems are a combination of aerobic and anaerobic wetland systems. They are used for full-blown treatment of AMD. An example is the “Acid Reduction Using Microbiology (ARUM)” system that consists of two oxidation cells in which iron is corroded and precipitated. Past these, AMD passes first all the way through a holding cell, and then through two “ARUM” cells inside which sulphide and alkali are produced. The carbon-based substances that stimulate sulphate lessening in the ARUM cells come from floating macrophytes such as cattails. The ARUM systems have proved their effectiveness in treating AMD in subtropical and high latitude locations. The Wheal Jane mine is an example of a passive treatment plant that is composite (UniPure, 2015). Permeable Reactive Barriers (PRBs) Permeable reactive barriers (PRBs) are more and more being used to treat a wide variety of contaminated groundwater. The ones that have been set up to bio remediate AMD function on the similar basic principles as manure bioreactors. Their construction involves digging a pit or trench in the flow path of polluted groundwater and filling the space with reactive materials, such as a mixture of maybe limestone gravel and organic solids, which are adequately penetrable to permit unconstrained flow of the groundwater, and reforming the distressed surface. Reductive microbiological processes inside the PRB engender alkalinity, which is further boosted by dissolution of limestone and/or other basic minerals, and get rid of metals such as hydroxides, sulphides, and carbonates. According to Younger et al. (2002), the largest PRB thus far built has been set up to remediate very acidic groundwater coming from a big pyritic shale waste dump in Shilbottle, northeast England. This PRB is 180 metres long, 3 metres deep, and 2 metres wide. It is made up of a mixture of composted composted green waste (25%), horse manure and straw (25%), and limestone (50%). In general, constructed wetlands, however simple, can make available all the mechanisms for reducing mine pollution. Constructed wetlands can pull off similar decreases in the concentrations of pollutants removed by more multifaceted machine-driven structures or equipment. Such methods consume a lot of time and are costly, and AMD can linger on over a period of many years, so necessitating treatment of AMD to last up to well after the land has been uninhibited by mining undertakings. Construction of wetlands does not need power and the running expenses are much lower (up to 10-50% less than conventional treatments) (Battaglia-Brunet et al., 2002). The main building costs involved are land purchase, earthwork, pumping water into the wetlands, possible waterproof liner, and planting. Constructed wetlands also have low maintenance requirements. They offer negligible visual effect and afford a justifiable alternative to mechanised wastewater treatments. However, constructed wetlands normally need considerably more land than conventional methods (Brown, 2002). A study conducted by Woulds and Ngwenya (2004), revealed positive results concerning the use of constructed wetlands in remediating human induced contaminants. Their results indicate that the discharge from such wetlands had a higher pH and did not contain, or had very low concentrations of sulphate, iron and trace metals. They also found that constructed wetlands may well provide an uninterrupted, low-cost and effective answer to treating AMD. Furthermore, constructed wetlands offer many water quality improvement functions given that there is control over design, location, and management to make the most out of those water quality functions. They give emphasis to particular attributes to maximise contaminant removal efficiency and to cut down mine pollution before it enters into natural wetlands, streams, or other receiving waters (Coulton et al., 2003). Constructed wetlands are also particularly critical habitats for wildlife. They exceed all other land forms in wildlife productivity. This tailor-made project approach to constructed wetland systems by and large makes them more suitable as wildlife habitats than natural wetlands. They are often planned with ancillary wildlife values in mind that predominantly entails managing wildlife for diversity, underlining non-game and non-waterfowl species. Even as vegetation species diversity and micro fauna and flora are lower in constructed wetlands, bird usage can be higher than that in nearby natural wetlands given the more eutrophic, and therefore more productive, aquatic surroundings in the constructed wetland systems. For that reason, construction of a wetland arranges for a good prospect for managing wetlands for all-encompassing wildlife habitat objectives. However, a major worry with the use of constructed wetlands for wildlife habitat is the potential for directed amassed contaminants up the food chain, with harmful effects to birds along with other consumers. Even though there is no serious problem that has till now been reported, there remains some potential for harm from metals plus other chemical compounds demanding constant evaluation (Brown, 2002). Not only can constructed wetlands offer improved wildlife benefits, but other functions can be enriched simultaneously. Constructed wetlands may well be useful to herpetofauna, mammals and macro invertebrates if water is not acidic and does not have a lot of toxic materials. They may well be stocked with fish apart from being used for leisure activities. Water in constructed wetlands can be used for livestock, crop irrigation, manufacturing purposes, fire protection, and even as a source of water for human use (Johnson, 2003). Conclusion Constructed wetlands have elicited much attraction particularly from conservationists. They have been lauded as ground-breaking in removing pollutants from water. Constructed wetlands have been recognised due to their natural treatment functions for treatment of point source as well as non-point source pollution. Therefore, they have come in handy in dealing with the problem of AMD that has troubled the mining industry for a long time. They act as natural purification systems that are even more preferred than natural wetlands especially in offering habitats for wildlife. They can as well engage other important functions such as crop irrigation, manufacturing purposes, fire protection, and even as a source of water for human use. References Battaglia-Brunet F, Dictor MC, Garrido F, Crouzet C, Morin D, Dekeyser K, et al. 2002. An arsenic (III)-oxidizing bacterial population: selection, characterization, and performance in reactors. Journal of Applied Microbiology, vol. 93, pp. 656–67. Blight, G. 2011. Chapter 5: Mine Waste: A Brief Overview of Origins, Quantities, and Methods of Storage, in Waste: A Handbook for Management, T. Letcher and D. Vallero, Editors. Academic Press: Burlington, M.A. pp. 77-87. Brown, M.P. 2002. Minewater treatment : technology, application and policy\par. (Book, Whole\par). Coulton, R. Bullen, C. and Hallet, C. 2003. The design and optimization of active mine water treatment plants. Land Contaminants Reclamation, vol. 11, pp. 273–279. Evangelou V.P. 1995. Pyrite Oxidation and its Control. New York7 CRC Press, vo. 275 Hedin, R.S. 2003. Recovery of Marketable Iron Oxide From Mine Drainage in the USA. Land Contamination and Reclamation. Vol. 11, no. 2 pp. 93-97. Johnson D.B. 2003. Chemical and microbiological characteristics of mineral spoils and drainage waters at abandoned coal and metal mines. Water Air Soil Pollutant: Focus, vol. 3, pp. 47– 66. Johnson D.B. and Hallberg K.B. 2003. The microbiology of acidic mine waters. Residual Microbiology, vol. 154, pp. 466– 73. Lottermoser, B., 2012. Mine Wastes: Characterization, Treatment and Environmental Impacts, Springer: New York. pp. 400. Neal C, Whitehead P.G, Jeffery H, Neal M. 2004. The water quality of the River Carnon, west Cornwall, November 1992 to March 1994: the impacts of Wheal Jane discharges. Science Total Environment, pp. 3-14. Rankin, W.J. 2011. Minerals, metals and sustainability: meeting future material needs. Collingwood, Vic.: CSIRO Pub. UniPure. 2015. Case Study: Wheal Jane: A Clear Success. [Cited 2015 February 17]; Available from: . Wolkersdorfer, C. 2008. Chapter 11: Mine Water Treatment and Ground Water Protection in Water Management at Abandoned Flooded Underground Mines: Fundamentals, Tracer Tests, Modelling, Water Treatment, A. International Mine Water and I. ebrary, Editors. Springer: Berlin. pp. 235-277. Woulds, C. and Ngwenya, B.T. 2004. Geochemical processes governing the performance of a constructed wetland treating acid mine drainage, Central Scotland. Applied Geochemistry, vol. 19, pp. 1773-1783. Younger, P.L. Banwart, S.A. and Hedin, R.S. 2002. Mine Water: Hydrology, Pollution, Remediation. Dordrecht, The Netherlands: Kluwer Academic Publishers. Read More