Nitrification-related factors involved in the biochemical oxygen demand of leachate from inert-waste landfill site

The 5-day biochemical oxygen demand (BOD₅) is an organic matter indicator used for the maintenance management of inert-waste landfill sites. Previously, we indicated that oxygen consumption derived from the nitrification reaction (N-BOD₅) might have a non-negligible contribution to BOD₅ in leachate. In this study, we investigated changes over time of organic matter indicators in leachate of an inert-waste landfill site, and searched for factors responsible for fluctuations of N-BOD₅. Water quality was measured in two kinds of leachate, before (LBA) and after aeration (LAA), each month from September 2011 to February 2016. The N-BOD₅ component of BOD₅ in LAA was higher than that of LBA. The N-BOD₅ in LAA showed a significant positive correlation with ammonium nitrogen (NH₄-N), and NH₄-N in LAA also had a significant positive correlation with precipitation. As a result of NH₄-N addition test, N-BOD₅ in LAA was increased, but N-BOD₅ in LBA was hardly affected. Furthermore, the composition ratio of nitrifying bacteria in LAA was higher than that in LBA. Therefore, it was suggested that fluctuations of N-BOD₅ are related to the aerobic condition of the environment, NH₄-N levels and the presence of nitrifying bacteria, and are indirectly influenced by precipitation.