Implementing pressurized reactors and volatile fatty acids alleviated technologies for improved anaerobic digestion performance:Process evaluation and microbial community analysis

Anaerobic digestion is a technology that uses organic waste to produce biogas as renewable energy. However, a low methane content (50~70%) and the presence of CO2 (30~50%) are reasons that prevent biogas applications (e.g., natural gas grid injection). In this thesis, high-pressure anaerobic digestion was used to obtain high content biogas (>85%). The process of high-pressure anaerobic digestion was investigated using pressure, substrate types, and hydraulic retention time. In addition, H2 injection can further increase the methane content (94%), which overcomes the carbon acid accumulation problem in a pilot-scale reactor. This result suggests that the combination of high-pressure and H2 addition technologies could be applied in biogas upgrading facilities. Except for a low methane content in the biogas, volatile fatty acids (VFAs) accumulation is another common problem in anaerobic digestion. Organic overload, temperature/pH fluctuation, or high ammonia concentration causes accumulation of VFAs. Furthermore, increasing pressure in AD reactors reduces the VFAs utilization rate, contributing to VFAs accumulation. Therefore, bioaugmentation and activated charcoal were chosen as additives in this study to reduce VFAs inhibition. We found that the combination of bioaugmentation and activated charcoal showed a better performance of the digester. Furthermore, 16S rRNA and proteomics technologies were used to deeply understand the microorganism community and metabolic pathways in this thesis