Effects of the C/N ratio on the microbial community and lignocellulose degradation, during branch waste composting.

Aerobic composting is an efficient and environmentally friendly method of converting organic waste into nontoxic fertilizers or soil quality enhancers. The quality of the resultant compost depends greatly upon the composition of the substrate used. The initial carbon-to-nitrogen (C/N) ratio of the substrate is an important factor affecting the composting process. This study elucidated how initial C/N ratios affect the biodegradation of lignocellulose, due to changes in microbial community structure. Four different C/N ratios (20:1, 25:1, 30:1, and 35:1) were examined during a 35-day composting process. The degradation of cellulose, hemicellulose, and lignin was highest (35.7%, 30.6%, and 19.1% respectively) at a 30:1 C/N ratio; after 30 days, the 25:1 C/N ratio ranked second in terms of lignocellulosic degradation rate. The 30:1 C/N ratio further promoted the growth of functional microorganisms responsible for lignocellulose degradation (Luteimonas, Sphingobium, Trichoderma, Chaetomium, and Rosellinia), while the growth of dominant pathogenic microbes (Erwinia and Ulocladium) decreased significantly. These results confirm that the initial C/N ratio of the substrate has a significant effect on the microbial community and degradation of organic matter, during walnut branch composting. This process could therefore offer an alternative means of efficient recycling and recovery of waste branches.