Recycled calcium polypeptides modulate microbial dynamics and enhance bioconversion in kitchen waste-garden waste...

The kitchen waste and garden waste (KW-GW) co-composting system provides an effective method for recycling these two types of municipal solid waste; however, further improvements are needed to enhance bioconversion performance. This study investigates a novel composting additive, calcium polypeptides (CPPs), derived from waste animal and plant proteins, which can enhance the bioconversion capacity of biomass in the KW-GW co-composting system. As a pH regulator and an available nitrogen source, CPPs significantly increase the compost matrix pH, prolong the thermophilic phase, and reduce emissions of exhaust gases such as CH₄, N₂O, NH₃, and H₂S by 52.5%, 37.9%, 17.5%, and 41.3%, respectively. Moreover, the addition of CPPs to the compost product resulted in a 32.6% increase in humic substance content, while the germination index reached 108.5%, significantly promoting the growth of ryegrass. Microbial diversity analysis revealed that CPPs significantly altered microbial richness and diversity in the KW-GW co-composting system. During the heating phase, CPPs positively correlated with the abundance of thermophilic and lignocellulose-degrading species, such as Bacillus, Corynebacterium, and Aspergillus, along with composting temperature, pH, and electrical conductivity. Conversely, CPPs negatively correlated with the abundance of acidogenic and methanogenic species like Lactobacillus, Streptococcus, and Weissella. In the maturation phase, CPPs positively correlated with the abundance of lignocellulose-degrading and humus-forming species, including Pseudoxanthomonas, Sphingobacterium, and Aspergillus, as well as with the germination index. These results indicate that recycled CPPs improve the microenvironment, boosting biomass conversion in the KW-GW co-composting system, providing a viable approach for resourceful waste biomass reuse.