Influencing Mechanism Of Ammonium On Characteristics Of Methane Oxidation In Landfill Cover Soil

Ammonium can not only be nutrient to support the growth of methanotrophs, but also compete with CH4 for active sites of methane monooxygenase (MMO). In this study, Methylosinus sporium and waste bio-cover soil (WBS) were chosed as experimental materials to investigate the effect of ammonium on the activities and community structure of methanotroph. The fate of carbon and nitrogen during CH4 oxidation process and the response of global warming potential (GWP) to ammonium addition were analyzed. Main conclusions were listed as follows.(1)Methylosinus sporium could metabolize ammonium to nitrate or nitrite. pH value of the medium was significantly decreased after ammonium oxidation. The more methanotrophs grew, the more the pH value of the medium decreased.(2)At the same nitrogen concentration (0.14 g 1-1), ammonium was likely more favorable for the growth of Methylosinus sporium. But higher ammonium concentrations (0.5 and 1 g 1-1) could inhibit the growth of Methylosinus sporium and the inhibitory effect became weaker with the transformation of ammonium. Low ammonium concentrations could stimulate the excretion of extracelluar polymeric substances (EPS).(3)Effects of ammonium on CH4 oxidation activity depended on ammonium concentrations.100-300 mg kg-1 of ammonium addition could stimulate the CH4 oxidation activity of WBS, while 600-1200 mg kg-1 of ammonium addition showed inhibitory effects. The CH4 oxidation activities of the experimental WBS increased firstly then decreased and stayed at low levels during the whole course. It might be attributed to the limited nitrogen source or the excretion of EPS.(4)The N2O emission increased with the increasing contents of ammonium addition from 300 to 1200 mg kg-1. But there was no obvious effect in the WBS with low contents of ammonium addition (100 mg kg-1). The GWP calculated based on main greenhouse gases (CH4, CO2 and N2O) showed that the addition of 300-600 mg kg-1 of ammonium could weaken the GWP of greenhouse gases during CH4 oxidation in WBS, while lower (100 mg kg-1) or higher (1200 mg kg-1) contents of ammonium addition could enhance the GWP of greenhouse gases during CH4 oxidation in WBS. It indicated that N2O production from nitrification and denitriftcation should be cautiously considered when ammonium was applied to enhance CH4 oxidation activity. It is necessary to choose proper engineering parameters to weaken the GWP in practical.(5)Type I methanotrophs Methylocaldum, Methylococcaceae and Methylobacter and type II methanotrophs Methylocystis and/or Methylosinus were dominant in WBS. Ammonium addition favored the growth of Methylobacter, while nitrogen-limited condition promoted the growth of type II methanotrophs Methylosinus. Environmental factors including the contents of ammonium, nitrate, total nitrogen, TOC, extracellular polysaccharide (ECPS) and extracellular protein (ECP) and C/N ratio affected the community structure of methanotrophs in WBS with the following order of importance (explicative variable) of the methanotrophic community data:NH4+-N> C/N ratio> NO3-N> TN> ECPS> TOC> ECP. Among the seven factors, ammonium and C/N ratio had a significant influence on the variance by the Monte Carlo permutation test (P= 0.024 and 0.032, respectively).