Chemical and microbiological characterization of pig manures and digestates

Livestock and poultry breeding modes, feed compositions and manure collection systems have regional characteristics, which can directly affect the composition of livestock and poultry breeding manure, energy production by anaerobic digestion and resource utilization of products. The chemical, heavy metal contents and microbiological characteristics of pig manures and digestates were characterized in five pig farms and biogas plants in Quzhou (Zhejiang Province) in this study. The results showed that hemicellulose and cellulose of pig manures could be partly degraded in anaerobic digestion, but lignin was difficultly degraded and accumulated in digestates. The content of Zn was highest in the pig manure and digestate samples, followed by Cu, Cr, As, Ni, Pb, Cd, T1 and Hg. The As content was 16.09-31.22 mg kg^-1 in the pig manure and digestate samples, which exceeded the standard limitation requirements in fertilizers in China (≤15 mg kg^-1). Bacteroidota, Firmicutes, Proteobacteria and Spirochaetota dominated in the pig manure and digestate samples, with a relative abundance of 73.6%-99.4%. The microbial community structure in the pig manure samples was quite different among the five farms. The pH, contents of lignin, T1 and As had a significant effect on the microbial community structure in the pig manure samples, while the contents of total phosphorus, NO₃^--N, cellulose and Pb could significantly influence the microbial community structure in the digestate samples. These findings can provide a theoretical basis for recycling manure and improving biogas engineering in large-scale pig farms.