Field study of nitrous oxide production with in situ aeration in a closed landfill site

摘要

Nitrous oxide (N_2O) has gained considerable attention as a contributor to global warming and depilation of stratospheric ozone layer. Landfill is one of the high emitters of greenhouse gas such as methane and N_2O during the biodegradation of solid waste. Landfill aeration has been attracted increasing attention worldwide for fast, controlled and sustainable conversion of landfills into a biological stabilized condition, however landfill aeration impel N_2O emission with ammonia removal. N_2O originates from the biodegradation, or the combustion of nitrogen-containing solid waste during the microbial process of nitrification and denitrification. During these two processes, formation of N_2O as a by-product from nitrification, or as an intermediate product of denitrification. In this study, air was injected into a closed landfill site and investigated the major N_2O production factors and correlations established between them. The in-situ aeration experiment was carried out by three sets of gas collection pipes along with temperature probes were installed at three different distances of one, two and three meter away from the aeration point; named points A-C, respectively. Each set of pipes consisted of three different pipes at three different depths of 0.0, 0.75 and 1.5 m from the bottom of the cover soil. Landfill gases composition was monitored weekly and gas samples were collected for analysis of nitrous oxide concentrations. It was evaluated that temperatures within the range of 30-40℃ with high oxygen content led to higher generation of nitrous oxide with high aeration rate. Lower O_2 content can infuse N_2O production during nitrification and high O_2 inhibit denitrification which would affect N_2O production. The findings provide insights concerning the production potentials of N_2O in an aerated landfill that may help to minimize with appropriate control of the operational parameters and biological reactions of N turnover. Implications: Investigation of nitrous oxide production potential during in situ aeration in an old landfill site revealed that increased temperatures and oxygen content inside the landfill site are potential factors for nitrous oxide production. Temperatures within the range of optimum nitrification process (30-40℃) induce nitrous oxide formation with high oxygen concentration as a by-product of nitrogen turnover. Decrease of oxygen content during nitrification leads increase of nitrous oxide production, while temperatures above 40℃ with moderate and/or low oxygen content inhibit nitrous oxide generation.