Particle-scale visualization of the evolution of methanogens and methanotrophs and its correlation with CH_4 emissions during manure aerobic composting

摘要

Methane (CH4) emissions are a major environmental concern in composting facilities. Therefore, this study initially visualized the dynamic distribution and quantity of methanogens and methanotrophs in composting particles during manure aerobic composting using fluorescence in situ hybridization-confocal laser scanning microscopy (FISH-CLSM) and quantified their correlation with CH4 emissions. The visualization results showed that methanogens existed inside the particles, while methanotrophs clustered in the outer layer; a facultative anaerobic zone existed in between. The quantification results of integral optical density of methanogens and methanotrophs per unit particle area (U-ger, and U-oxi, respectively) indicated that, in the cooling phase, CH4 generation and oxidation could still be high and could strike a balance if the initial organic matter content of composting materials is high, while both could be extremely low if the content is low. A strong linearity between U-gen obtained by FISH-CLSM and methyl-coenzyme M reductase copy number obtained by quantitative polymerase chain reaction analysis (R-2 = 0.88) was observed, which justified the effectiveness of the FISH-CLSM method and demonstrated that macro-scale CH4 emissions were essentially an accumulation of particle-scale CH4 emissions. CH4 emissions were equal to 3.3297 x 10(7) U-ger, - 3.1814 x 10(6) U-oxi - 3902.9900 (R-2 = 0.98). Overall, the results showed that methanogens exerted more influence on CH4 emissions than methanotrophs. Combining these results with CH4-generation and -oxidation kinetics may help illustrate CH4-emission mechanisms, improve particle-scale CH4-emission models, and thereby provide theoretical guidance for operation optimization and emission reduction in composting processes. (C) 2018 Elsevier Ltd. All rights reserved.