Removal characteristics of trace compounds of landfill gas by activated carbon adsorption
Introduction
The most common disposal method for municipal solid wastes (MSW) is landfilling since the usage of intermediate treatments such as incineration, pyrolysis, and recycling are not actively practiced to effectively remove the wastes in Korea (Lee et al., 1996). In 1998, 56% of MSW was landfilled while 35% recycled and 9% incinerated in Korea (Yi et al., 2000). Landfills were thought to have a minimal impact on the environment. However, accumulated evidence in the last few years has indicated that landfilling still poses a threat to human health and the environment by generating landfill gas (LFG) and liquid leachate. Both contain many undesirable potentially toxic chemical compounds, which are produced by the various chemical, physical, and biological waste decomposition processes. Proper procedure to deal with leachate and LFG is the key to the overall successful management of landfills (United States Environmental Protection Agency, 1991, Ham et al., 1993, Allen et al., 1997, El-Fadel et al., 1997, He et al., 1997). LFG is a flammable and potentially harmful mixture of methane, carbon dioxide and a large number of trace constituents, which were generated when MSW decomposed in landfill sites. LFG consists 50–65 vol.% CH4 and 30–40 vol.% CO2 with numerous chemical compounds such as aromatics, chlorinated organic compounds, and sulfur compounds.
The exploitation of LFG for use as an energy resource has become the center of interest since it solves both environmental pollution and energy shortage (Powell et al., 1992, Whalen et al., 1990). Many researches have been devoted to the development of technologies for the treatment of LFG, and a combination of various processes has proved to be the most appropriate solution in terms of removal efficiency of trace compounds and LFG utilization (Rautenbach and Welsch, 1994). One of the most important and effective methods of controlling the emission of trace compounds in LFG is the use of the adsorption process. Amongst the adsorbent materials, activated carbons are used in several industrial processes such as gas separation, purification, and reaction process and also are versatile adsorbent because of their large surface area, micropore structure, various adsorption effect, high adsorption capacity, and high degree of surface reactivity (Pradhan and Sandle, 1999).
There are two main problems in order to use the raw LFG. Firstly, the trace gases have deleterious effects on human health (El-Fadel et al., 1997). Secondly, the corrosion that was caused by its impurities such as hydrocarbon, chlorinated organic compounds, and sulfur compounds reduced the operating life of boilers and combustion engines (Stagmann, 1989, Christensen et al., 1996, Da Costa et al., 1996, Allen et al., 1997, El-Fadel et al., 1997). Some researchers have used an adsorption system to separate the trace toxic compounds from model gases and LFG (He et al., 1997). However, there is not much information for the adsorption characteristics of multi-components and interaction of each gas during adsorption process.
Therefore, in this paper, the adsorption patterns of four kinds of aromatics and four kinds of chlorinated compounds in raw LFG were studied by activated carbon fixed bed in Sudokwon landfill site in Korea. The contents of this study have four major aspects. Firstly, the LFG components were selected and analyzed for the main gas, aromatics, chlorinated compounds and sulfur compounds. Secondly, the moisture removal efficiency of cyclone-type dehydrator and compressor was observed. Thirdly, the adsorption characteristics for granular activated carbon were determined with the change of moisture contents. Fourthly and finally, the adsorption patterns of the target components in raw LFG were discussed by using the breakthrough time and adsorption capacity.
Section snippets
Site description
The Sudokwon landfill, which is located on the west coastal area at Inchon City, is the largest waste treatment site in Korea. The landfill consists of operation Site 1, which is divided into 17 blocks (designed as Cell A through Q) and future landfill Sites 3, 4 and 5. Site 1 began its operation in October 1992. Its capacity is approximately 79 million cubic meters and it covers approximately 4.06 million square meters. The site was designed to have total eight lifts of waste, and total
Concentration of landfill gas
Samples collected from the extraction wells were analyzed and over 100 compounds in LFG were detected, of which about 15 constituents were identified and present in each of the samples taken. In order to ascertain the significance of a single analysis data set, the LFG that was used in these experiments was monitored at monthly intervals from January to December in 1997. The results from this study are summarized in Table 4. The compounds of LFG included the main gases (e.g. CH4, CO2 and
Conclusions
LFG generated from municipal solid wastes consists of moisture and trace compounds such as aromatics, chlorinated compounds, and sulfurs. It is important to reduce and purify the impurities that caused the adverse effect in human health and environment and corrosion for the utilization of LFG. Therefore, the removal characteristics of trace toxic compounds include moisture and the effect of moisture contents for adsorption experiment in LFG were studied. In field, the moisture removal
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