Multivariate and multiscale investigation of ammonia production and emission mechanisms during membrane-covered cattle manure/wheat straw aerobic composting

Ammonia (NH3) emissions accompanying aerobic composting cause significant atmospheric pollution and nitrogen losses. Understanding the mechanisms of NH3 production and emission can help optimize composting strategies. Here, environmental parameters, microbial communities, microbial metabolism, and organic component degradation were characterized at the pile and particle scales during atmospheric aerobic composting and in two membrane-covered aerobic composting (MCAC) systems. Pile-scale results showed that NH3 emission was concentrated in the thermophilic phase; MCAC significantly increased the relative abundances of aerobic lignocellulose-degrading bacteria, carbohydrate-degrading enzymes, and deaminases (P < 0.05); MCAC increased microbial ammonification and carbon source use. The degradation and distribution of organic components in compost particles were visualized for the first time by Fourier transform infrared microspectroscopy: MCAC increased the degradation of polysaccharide-like substances and glycoside-like substances in the particles, and accelerated the degradation of proteins to amide-like substances within the outer layer similar to 25 mu m of particles. We speculated that the micro-positive pressure (-500 Pa) created by MCAC enhanced the dissolution-diffusion of oxygen into compost particles, thereby facilitating aerobic degradation of organic components. Taken together, micro-positive pressure in the MCAC systems promoted the co-degradation of carbon and nitrogen substrates, which probably increased NH3 production potential, while the water films attached to the inside and outside of the semi-permeable membrane in MCAC were effective in reducing NH3 release by 7.11 %-12.42 %. These findings provide new insights for MCAC improvement.