# The Influence of Waste Composition on Landfill Gas Generation in a Pilot-Scale Lysimeter
## 3 Results
### Characteristics of Gases and Leachate Generated from the Lysimeter Reactor
It seems that generation of highly concentrated H\({}_{2}\)S at the second landfill site is caused by mixed landfilling, particularly sewage  
Figure 9: Landfill gas and leachate COD\({}_{\text{Cr}}\) and SO\({}_{4}\)\({}^{2-}\) versus time for the mixed waste. sludge having a great influence. It is advisable that when landfilling C&D debris waste, sewage sludge should be separated from C&D debris waste. C&D debris waste + solidified sludge increased, producing 58% of the methane until the 18 th day. After 22 days, the C&D debris waste + solidified sludge gradually decreased and after 47 days it decreased up to 48%. As with the C&D debris waste + sewage sludge, in the C&D debris waste + solidified sludge, H\({}_{2}\)S began to increase. H\({}_{2}\)S generated from C&D debris waste + solidified sludge was 10% less than that from C&D debris waste + sewage sludge. According to [PERSON] et al. (2005), moisture content is one of the key factors for the stabilization of microorganisms [38]. [PERSON] et al. in 2000 reported that in the event that concrete is contained in construction waste, it increases the pH in the leachate creating a less favorable environment for activation of SRB microorganisms [35; 39]. When creating solidified sludge, cement is used as a firming agent. In this study, it was found that the pH in the C&D debris waste + solidified sludge after 100 days was 7.6-8.81, which was higher than that of the other wastes. It appears that SRB microorganisms in the C&D debris waste + solidified sludge were less activated than in the C&D debris waste + sewage sludge given the influence of less moisture and firming agent (Figure 7). C&D debris waste + solidified sludge produced a high H\({}_{2}\)S content of 24%, which implies that it influenced generation of H\({}_{2}\)S at the second landfill site. Sulphur was not found in the domestic waste. For landfill gas, methane was generated from the beginning and on the 72 th day 70% methane was observed. Gas composition and the degradation rate is known to be affected by the types of waste [40]. According to [PERSON] et al. (2019), paper wastes have produced above 50% of CH\({}_{4}\) during 0-50 days of landfill. When paper wastes were mixed with food waste, the waste was degraded altogether, leading to increase in CH\({}_{4}\) up to 60%-70% [41]. Domestic waste is the mixture of paper, plastic, food, and wood, with 50% paper content, leading to a high content of cellulose. Cellulose is degraded slowly compared to glucose and protein. Leading to slow degradation compared to other samples. However, the addition of food waste contributed to CH\({}_{4}\) production above 60%-70%. Hydrogen sulphide was generated at 500 mg/L or less. The COD\({}_{\rm Cr}\) concentration in leachate was high at 600-29,227 mg/L and SO\({}_{4}\)\({}^{2-}\) was 0-88 mg/L (Figure 8). SO\({}_{4}\)\({}^{2-}\) was not produced in the leachate as the sulphur was not involved in the sample. Lack of SO\({}_{4}\)\({}^{2-}\) led to unsuitable condition for the SRB microorganism survival. H\({}_{2}\)S was not generated, but CO\({}_{2}\) and CH\({}_{4}\) were generated in abundance. Accordingly, the generated gas did not have any significant effect on odor problem. Finally, the mixture of C&D debris waste (55%), domestic waste (24%), and sewage (21%) was used for the experiment. Mixed waste containing C&D debris waste, domestic waste, and industrial waste was placed at the second landfill site. The landfill was created in such a manner that it was similar to the second landfill site. When examining generation of landfill gases, it was found that 65% methane was generated until the 13 th day and then it decreased to 50% on the 47 th day. H\({}_{2}\)S increased until the 136 th day and generated up to 17% (Figure 9). SRB depend on other organic material for degradation product supply as SRB does not degrade natural biopolymers such as starch, glycogen, protein, and lipids. Resultingly, microbial competition at the hydrolysis stage of anaerobic digestion does not occur [42].