Upflow anaerobic sludge blanket reactor operation under high pressure for energy-rich biogas production

Autogenerative high-pressure digestion has an advantage of producing CH4-rich biogas directly from the reactor. However, its continuous operation has rarely been reported, and has never been attempted in an upflow anaerobic sludge blanket reactor (UASB). Here, UASB was continuously operated at 10 g COD/L/d with increasing pressure from 1 to 8 bar. As the pressure increased, the CH4 content in the biogas increased gradually, reaching 96.7 & PLUSMN; 0.8% at 8 bar (309 MJ/m3 biogas). The pH was dropped from 8.2 to 7.2 with pressure increase, but COD removal efficiency was maintained > 90%. The high pressure up to 8 bar did not adversely impact the physicochemical properties of granules, which was due to the increased production of extracellular polymeric substances (EPS), particularly, tightly bound EPS (34% increase). With pressure increase, there was no changes in the microbial community and ATPase gene expression, but 41% increase in carbonic anhydrase gene expression was observed.

Automated summary

Autogenerative high-pressure digestion has the advantage of producing CH4-rich biogas directly. In this study, a continuous operation of upflow anaerobic sludge blanket reactor (UASB) was performed with pressure gradually increasing from 1 to 8 bar. The CH4 content in the biogas gradually increased with increasing pressure, reaching 96.7 ± 0.8% at 8 bar (309 MJ/m3 biogas). The physicochemical properties of granules were not adversely affected by the high pressure, and there was an increase in the production of extracellular polymeric substances (EPS) and carbonic anhydrase gene expression.