Kinetics of nitrous oxide production by denitrification in municipal solid waste

As one of the Nitrous Oxide (N₂O) production pathways, denitrification plays an important role in regulating the emission of N₂O into the atmosphere. In this study, the influences of different substrate concentrations and transient conditions on the denitrification rate and N₂O-reducing activities were investigated. Results revealed that N₂O production rates (i.e. denitrification rates) were stimulated by increased total organic carbon (TOC) concentration, while it was restrained under high oxygen concentrations. Moreover, the impact of nitrate concentrations on N₂O production rates depended on the TOC/NO₃^--N ratios. All the N₂O production rate data fitted well to a multiplicative Monod equation, with terms describing the influence of TOC and nitrate concentrations, and an Arrhenius-type equation. Furthermore, results demonstrated that high temperatures minimized the N₂O-reducing activities in aged municipal solid waste, resulting in an accumulation of N₂O. On the other hand, a transient condition caused by changing O₂ concentrations may strongly influence the N₂O production rates and N₂O-reducing activities in solid waste. Finally, based on the results, we believe that a landfill aeration strategy properly designed to prevent rising temperatures and to cycle air injection is the key to reducing emissions of N₂O during remediation of old landfills by means of in situ aeration.