Strategies That Aim to Reduce Methane Emissions from Landfills - Essay Example

Strategies that aim to Reduce Methane Emissions from Landfills Introduction Methane production is a by-product from both landfill sites and cattle production. In landfills, the gas is generated by the anaerobic bioreaction of organic matter such as food and yard wastes, organics textiles, paper, leather and wood (Matthews & Themelis, 2007). In the field of cattle production, it is estimated that ruminant livestock produce between 250 and 500 litres of methane per day (Johnson & Johnson, 1995). Factors that influence methane production from cattle include level of feed intake, feed processing, type of carbohydrate that the cattle feed on, incorporation of lipids or ionospheres in the diet, as well as alterations in the ruminal microflora (Johnson & Johnson, 1995). What is clear is that the type of material disposed into a landfill or which is fed to cattle determines the amount of methane released. In landfills, methane and other greenhouse gases are released when the aforementioned materials (waste) come into contact with water (Venkatraman & Ashwath, 2009). Venkatraman and Ashwath (2009) also state that recent studies show that annual global methane releases have considerably risen from 180 Tg yr-1 in the 15th century to around 300 Tg yr-1 ­by the year 2000. Further, these values were expected to increase to between 400 and 600 Tg yr-1 by the year 2010 (Venkatraman & Ashwath, 2009). Methane is one of the gases that contribute to global warming (Huber-Humer, Gebert & Hilger, 2008), hence the need to reduce its production. In view of this background information, this paper focuses on methane production in landfills and evaluates some strategies that are used to suppress emissions of the gas from landfills. How methane is produced in landfills The emission of methane in landfills normally occurs in two stages, namely the methanogenic stage and the non-methanogenic stage (Venkatraman & Ashwath, 2009). The non-methanogenic stage is instigated by hydrolytic processes which reduce complex organic matter to simpler soluble compounds such as simple sugars, fatty acids, amino acids as well as other organic compounds of low molecular weight. This phase facilitates further alteration of the organic material by capturing energy and releasing organic acids, water, ammonia, carbon dioxide and hydrogen. In the methanogenic phase, the methanogenic bacteria release methane under anaerobic conditions. The microorganisms that are active this phase are generally the bacteria of the genus Methanobacterium – which are common inhabitants of sewage and soil (Venkatraman & Ashwath, 2009). According to Luesken et al (2011), ammonium compounds and methane are the major end products of the anaerobic digestion process, whereby the latter is recycled and utilised as a source of energy. Other gases released during the methanogenic phase include hydrogen sulphide and nitrogen (Venkatraman & Ashwath, 2009). Although methane in the gas state can be collected and cleansed easily, dissolved methane is difficult to recover, especially during low temperatures (Luesken et al, 2011). Dissolved methane is slowly released into the atmosphere and it is this effect that contributes to the greenhouse effect, which is undesirable as it can contribute to global climate change (Luesken et al, 2011; Huber-Humer, Gebert & Hilger, 2008). The increasing number of gas collection systems has lowered the danger of escaping methane emissions that enter the atmosphere, but still, the process of capturing gas is not 100 percent efficient. In addition, there are still many scenarios when gas collection systems are not used (Huber-Humer, Gebert & Hilger, 2008), meaning that the gas is left to enter the atmosphere. Therefore, reducing the emission of methane remains the most appropriate strategy to contain the menace. The following section outlines the strategies that are used reduce methane emissions from landfills. Strategies to lower the release of methane from landfills Avoiding the emissions of methane during waste management in landfills is one of the ways suggested by Ngnikam et al (2001) to control the greenhouse gas effect. Ngnikam et al (2001) give an account of reducing emissions through a strategy that involved collection of landfill waste and recuperating biogas to produce electricity in Yaounde, Cameroon. They suggest this as the most preferable approach to reduce methane emissions in moist tropical climates. Other strategies, such as those adopted in Europe through the European Union Landfill Directive, are meant to lower the adverse environmental consequences of land filling (Pan & Voulvoulis, 2007). This is achieved mainly through reducing the amount of organic matter deposited, through measures such as separate gathering and recycling of the organic waste stream or pretreatment of residual wastes before disposing them in the landfill. Apart from incineration and other heating processes, mechanical biological treatment plays an important role (Pan & Voulvoulis, 2007). Pan and Voulvoulis (2007) note that local councils should prioritise the reduction or sorting of certain targeted fractions, such as green waste, paper, card, and other putrescibles from municipal solid waste. There are also mechanical treatment processes that produce organic rich waste referred to as mechanically sorted organic residues. These involve organic content concentration (Pan & Voulvoulis, 2007). According to Venkatraman and Ashwath (2009) however, there are two main ways by which emissions from landfills can be decreased. The first strategy is to use landfill gas recovery implements to extract and utilise methane as mentioned earlier in this paper. The second approach is to boost methane oxidation in soil covers that are placed over the waste. Nevertheless, since the installation of gas recovery system is costly and not convenient for small scale operations, enhancing oxidation is advisable. This method involves phytocapping, which is a new technology promoted for lowering the percolation of water into landfills. Phytocaps are used to mitigate emission by oxidising the methane that is produced into water and carbon dioxide. Further, landfill soil covers have been proven to lower the emission of methane by up to 50 percent (Venkatraman & Ashwath, 2009). The use of soil covers is also explained by Huber-Humer, Gebert and Hilger (2008), who note that the use of bio-engineered systems is one of the most promising and cost-effective options for achieving low-level methane emissions. Oxidation of methane occurs when a group of obligate aerobes referred to as methanotrophs break down the gas to yield energy and incorporate carbon into their biomass (Huber-Humer, Gebert & Hilger, 2008). Venkatraman and Ashwath (2009) posit that oxidation of methane in the soil that covers the waste that may or may not be containing vegetation offers an economical way of reducing methane from landfills. To begin with, the soil covers curtail the entry of water into waste as they store water that may evaporate over time. Secondly, the soil cover offer medium for the growth of organisms such as methanotrophs and plants, which are crucial in the oxidation of methane. See figure 1 for illustration. Figure 1: Illustration of a landfill phytocapping system Source: Venkatraman and Ashwath (2009, p. 3). A study conducted by Kightley et al (1995), cited by Venkatraman and Ashwath (2009) revealed that soil covers can oxidise between 7 percent and 50 percent of the methane released from landfills, with an oxidation capacity of 166 gm-2 d-1. In the same scope, Viswanathan et al. (1999) found the rate of oxidation of methane to be 100 gm-2 d-1 (cited by Venkatraman & Ashwath, 2009). Both values are much higher than the rates reported by Whalen et al (1990) [cited by Venkatraman and Ashwath (2009)]. In Australia, the placement of compacted clay (a conventional cover) over the waste in a landfill has been the most popular method of reducing methane emissions. The primary function of the clay capping is to minimise percolation of water into the waste in order to reduce the landfill’s ability to regenerate leachate. Further studies carried out in the United States have shown that clay caps fail to restrict percolation of water into the waste because of drying and cracking of the clay cover. Moreover, the clay caps do not allow for optimal interaction of the methane gas with oxygen, which is a mandatory requirement for methane oxidation (Venkatraman & Ashwath, 2009). Alternative methods of remediating landfills are therefore necessary, and have been identified to include natural attenuation of the landfill-released methane through aerobic oxidation in the landfill soils and the use of phytocapping systems. The phytocapping method promotes entry of water into unconsolidated soil as opposed to clay capping where water is obstructed from entering the landfills. Consequently, the water that is stored will later be made available for the growth of plants, bio-pumping and promote oxidation of methane. Phytocapping has several advantages such as lower cost of landfill remediation, offering aesthetic values, and acting as a biodiversity corridor. Conclusion This paper has reviewed the strategies that aim to reduce methane emissions in landfills. Gas collections systems have increasingly been used to trap methane but they are not 100 percent efficient. Recuperating biogas to produce electricity has proved to be effective in moist tropical regions such as Cameroon. Other methods of reducing methane emissions include reducing waste, separate gathering and recycling of waste, incineration and mechanical biological treatment. However, the paper has discussed phytocapping as the newest technology adopted to replace landfill gas recovery. Phytocapping involves covering landfill waste with soil to limit percolation of water into the water while providing a medium for the growth of plants and organisms such as methanotrophs that are necessary for oxidising the methane produced. Phytocaps mitigate emissions by oxidising the methane that is produced into water and carbon dioxide. The carbon released is also incorporated into the structure of the methanotrophs as part of their biomass. References Huber-Humer, M., Gebert, G. & Hilger, H. (2008). ‘Biotic systems to mitigate landfill methane emissions’. Waste Management & Research, 2008: 26: 33–46. Johnson, K. A. & Johnson, D. E. (1995). ‘Methane emissions from cattle’. Journal of Animal Science. 73(8):2483-92 (abstract). Retrieved 12 April 2012, from http://www.ncbi.nlm.nih.gov/pubmed/8567486 Luesken, F. A., Sa´nchez, J., van Alen, T. A., Sanabria, J., Op den Camp, H. J.M. Jetten, M. S. M. & Kartal, B. (2011). ‘Simultaneous Nitrite-Dependent Anaerobic Methane and Ammonium Oxidation Processes’. Applied and Environmental Microbiology, 77(19):6802–680. Matthews, E. & Themelis, N.J. (2007). ‘Potential for Reducing Global Methane Emissions From Landfills, 2000-2030’. Proceedings Sardinia 2007, Eleventh International Waste Management and Landfill Symposium S. Margherita di Pula, Cagliari, Italy, 1-5 Oct. 2007 by CISA, Environmental Sanitary Engineering Centre, Italy. Retrieved 12 April 2012, from http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&ved=0CIYBEBYwCQ&url=http%3A%2F%2Fwww.seas.columbia.edu%2Fearth%2Fwtert%2Fsofos%2FMatthews_Themelis_Sardinia2007.pdf&ei=lr6GT4GtGaGm0QX7utjKBw&usg=AFQjCNGLT-mHWyWPqr3V-ZHTrQuk1uIPEA&sig2=adgQlIPavJoVAQvYejP7fw Ngnikam, E., Tanawa, E., Rousseaux, P., Riedacker, A. & Gourdon, R. (2001). ‘Evaluation of the potentialities to reduce greenhouse gases (GHG) emissions resulting from various treatments of municipal solid wastes (MSW) in moist tropical climates: Application to Yaounde’ Waste Management Resources. 2001: 19: 501–513 Pan, J. & Voulvoulis, N. (2007). ‘The role of mechanical and biological treatment in reducing methane emissions from landfill disposal of municipal solid waste in the United Kingdom.’ Journal of Air Waste Management Association. 2007 Feb; 57(2):155-63 (abstract). Retrieved 12 April 2012, from http://www.ncbi.nlm.nih.gov/pubmed/17355076 Venkatraman, K. & Ashwath, N. (2009). ‘Phytocapping: An innovative technique to reduce methane emission from landfills.’ Proceedings of the Environmental Research Event 2009, Noosa, Queensland. Retrieved 12 April 2012, from http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=0CFoQFjAE&url=http%3A%2F%2Fespace.library.uq.edu.au%2Feserv%2FUQ%3A179626%2FVenkatraman_-_ERE2009.pdf&ei=lr6GT4GtGaGm0QX7utjKBw&usg=AFQjCNFsjj2OFz0MKEez9vDo3OuqyhlbMQ&sig2=fpu61Mzd4xuritq2g1fFSQ Read More