Anaerobic co-digestion of Pennisetum hybrid and pig manure: A comparative study of performance and microbial community at different mixture ratio and organic loading rate.

To investigate how the changes in performance and the microbial community of the co-digestion system of Pennisetum hybrid and pig manure, two co-digestion systems in a semi-continuous mode were established at different grass:manure mixture ratios (50:50 and 75:25), and at variable organic loading rates (OLRs). The two reactors were in a steady-state at the OLRs of 2.0-5.0 g VS/(L·d), with the specific and volumetric biogas yields of 383.86 ± 65.13 to 574.28 ± 72.04 mL/g VS and 0.87 ± 0.07 to 2.36 ± 0.13 m3/(m3·d), respectively. The co-digestion system with a mixture ratio of 75:25 failed at an OLR of 5.5 g VS/(L⋅d). This failure could be attributed to the accumulation of volatile fatty acids (VFAs) owing to the imbalance between acid-production and -oxidation bacteria. By contrast, the co-digestion system with mixture ratio of 50:50 failed at an OLR of 7.0 g VS/(L⋅d), which was likely due to mechanical issues or improper reactor configuration. The genus Proteiniphilum contributed to the increase in total ammonia nitrogen. These findings provide useful guidance for optimizing co-digestion system, enhancing reactor performance and improving the wastes treatment.

Effect of bioaugmentation on the microbial community and mono-digestion performance of Pennisetum hybrid.

In this study, bioaugmentation with methanogenic propionate-utilizing enrichment was investigated as a method to improve the mono-digestion performance of Pennisetum hybrid in a semi-continuous mode. The effect of bioaugmentation on the microbial community was analyzed as well. The results demonstrate that the steady-state organic loading rate (OLR) of the bioaugmented reactor increased to 4.0 g VS/(L·d) with a volumetric biogas production of 1.95 ±â€¯0.17 m3/(m3·d). In contrast, the non-bioaugmented reactor failed at an OLR of 2.0 g VS/(L·d) accompanied with the accumulation of volatile fatty acids (VFAs). The results of whole genome pyrosequencing analysis suggest that the decrease in relative abundance of syntrophic butyrate and propionate oxidizers, such as Syntrophomonas, Syntrophobacter, and Syntrophorhabdus, reduced the conversion efficiency of butyrate and propionate which leads to the accumulation of butyrate and propionate, influencing the performance of the mono-digestion reactor. Conversely, in the bioaugmented reactor, the higher density of protein- and amino acid-utilizing bacteria, such as Proteiniphilum, Thermovirga, and Lutaonella, as well as the syntrophic association of Syntrophomonas spp. coupled with the methanogens Methanosarcina and Methanocella has a positive effect on system stability and performance.