# The Influence of Waste Composition on Landfill Gas Generation in a Pilot-Scale Lysimeter
## 1 Introduction  
Waste is generated from various sources including construction, commerce, industrial, domestic, mining, and agriculture. Particularly, construction and demolition waste are on the increase around the world because of urbanisation. Construction and demolition waste accounts for 44% of total waste in Britain [1], 29% in the USA [2], 44% in Australia, and 27% in Canada. Construction and demolition (C&D) debris waste depend on landfills. C&D debris waste is mostly landfilled. About 35% of landfill waste is reported as C&D debris waste [3; 4; 5; 6]. The percentage of C&D debris waste that is brought to a landfill site in the Republic of Korea, the largest in the world, is on the increase because of redevelopment projects such as the new town project. According to the Sudokwon landfill site statistical yearbook, the percentage of C&D debris waste increased up to 26% in 2018. Regarding the composition of the C&D debris waste that is brought to a landfill at the Sudokwon landfill site, brick construction waste including waste concrete accounts for 29%-31%, earth and sand construction waste including silt 23%-26%, and combustible waste 43%-48% [7]. The problem of the landfill site is odor [8]. According to the U.S. Occupational Safety and Health Administration (OSHA), H\({}_{2}\)S is mainly responsible for the odor from C&D debris waste at a landfill site accounting for approximately 1% of landfill gas [9]. H\({}_{2}\)S is generated by the sulphate-reducing bacteria (SRB) sulphate reduction reaction under anaerobic conditions. SRB induces sulphate to betaken into cells and it decomposes and synthesizes ATP via the ATP sulphurylase enzyme in cells. Sulphate (SO4\({}^{2-}\)) is an electron acceptor of H2S and is included in the leachate of C&D debris waste that contains gypsum such as concrete, cement, and drywall [10]. Sulphate (SO4\({}^{2-}\)) oxidizes to decompose ATP converting it into adenosine-5-phosphosil-fate (APS). Sulphate (SO3\({}^{2-}\)) is isolated from APS and sulphite reduces to sulphide (HS\({}^{-}\)) via dissimilatory sulphite reductase (DSR) generating H2S [11]. However, SRB along with methane-producing bacteria (MPB) under anaerobic conditions are known to play an important role in decomposing organic matter [12; 13; 14]. Landfill leachate is produced when the moisture content of the waste exceeds the capacity of the landfill site. Increase of moisture content is the main reason for the leachate production, but it contributes to enhancement of biodegradability of the waste [15; 16]. Accordingly, it has been reported that enhancement of biodegradability leads to rapid stabilization [17]. However, increase of moisture content also causes a decrease in void ratio of the landfilled wastes, leading to the anaerobic condition [18]. When C&D debris wastes is landfilled, it was reported that a large amount of H2S is generated due to the exudation of SO4\({}^{2-}\)[19]. H2S is known to cause acid rain and be harmful to human health because of its severe odor (rotten egg smell). The H2S indoor exposure concentration limit as determined by OSHA is 10 ppm for 10 min. It has been reported that at 100 ppm H2S paralyzes the olfactory nerve within 2-15 min and at 800 ppm lethality reaches 50% (LC50) at an exposure of 5 min. Odor is not accumulated but it causes widespread damage. Specifically, odor from a landfill site stays on the earth's surface as it is not diffused by low pressure making it more severe during the morning and evening. When wetness is high, moisture in the atmosphere easily attaches to the olfactory organ causing stimulation [20]. The Sudokwon landfill is the world's largest landfill and consists of a first landfill site and second landfill site. As the proportion of C&D debris wastes increased, C&D debris wastes were landfilled not only in the first landfill site but also the second landfill site, leading to odor occurrence. It is estimated that earth and sand construction waste that contains gypsum in the form of fine particles is mainly responsible for odor in a landfill site.