Study on nitrogen transformation and related microbial community changes during the composting process of Chinese medicinal herbal residues

In order to promote the utilization of waste materials from Chinese medicinal herbal residues, the Chinese medicinal herbal residues, reed residue, and soy sauce residue were mixed and composted with different proportions by adding microbial agents. All the mixtures were adjusted to the same C/N ratio. The temperature, microbial quantity (bacteria, actinomycetes and fungi), nitrogen related microbial community (azotobacter, ammonifiers, nitrifying bacteria and denitrifying bacteria), total nitrogen, ammonium nitrogen, nitrate nitrogen and seed germination index were investigated during the composting process, and the nutrient variation of different treatments before and after the composting were also discussed. Results showed that the number of bacteria was at least 10 000 times that of the actinomycetes and fungi, and the change in the number of bacteria and ammoniated bacteria tended to follow the trend of “high-low-high-low”, whereas the number of azotobacter, nitrifying bacteria and denitrifying bacteria tended to be “high-low-high” trend during the composting. When the ratio of Chinese medicinal herbal residues:reed residue:soy sauce residue was 45:30:25, the temperature rised fast and maintained at about 62 ℃, only 4% of nitrogen was lost and germination index was 74.4% after the composting. However, when the ratio of Chinese medicinal herbal residues:soy sauce residue was 75:25, the temperature rised slowly and 53.3% of nitrogen was lost, the germination index was only 34.4% consequently. The antimicrobial substances in traditional Chinese medicine residues influenced the number of microorganisms and the change of nitrogen related microorganisms, which further resulted in the change of compost nutrient during the composting. Our results indicated that when the ratio of Chinese medicinal herbal residues:reed residue:soy sauce residue was 45:30:25, the compost decayed fast and was accompanied by less nitrogen loss. This study could provide reference for the high-temperature aerobic fast composting of Chinese medicinal herbal residues.