Start-up and performance evaluation of upflow anaerobic sludge blanket reactor treating supernatant of hydrothermally treated municipal sludge: Effect of initial organic loading rate

To investigate methanogenesis performance of upflow anaerobic sludge blanket (UASB) reactor started up using acidified granular sludge, we operated two UASBs with different initial organic loading rates (OLR) for treating supernatant of hydrothermally treated municipal sludge (SHTMS) over a 180-day period. Under a high OLR of 3.7-4.1 g COD/(L d), the Rh reactor obtained a maximum methane conversion efficiency of 61 % along with high volatile fatty acid (VFA) accumulation from day 0 to day 105. By contrast, under a low OLR of 1.9-2.1 g COD/(L d), the Rl reactor achieved a higher methane conversion efficiency of 85 %-88 % along with low WA accumulation. Both reactors successfully completed start-up from day 60 to day 70. When the OLRs of both reactors were adjusted to 3.1-3.3 g COD/(L d) from day 106 to day 180, the same methane conversion efficiency of 71 % and methane yield of 285 mL CH4/g CODinfluent were achieved. Although Methanobacterium, Methanosarcina, Methanosaeta, and Methanomassiliicoccus were predominant in both reactors, they were not significantly correlated with OLR. Firmicutes, Synergistetes, and Bacteroidetes were the most dominant bacterial phyla, and the enriched bacterial microorganisms were deemed likely to survive in the R1 resctor with low OLR start-up. Therefore, the initial OLR has a substantial effect on the degradation performance and the microbial community variations in UASB reactors for SHTMS treatment.

Automated summary

The study investigated the methanogenesis performance of UASB reactors started up using acidified granular sludge for treating SHTMS. The initial organic loading rate (OLR) significantly affected the degradation performance and microbial community variations in the reactors. High OLR led to lower methane conversion efficiency and higher VFA accumulation, while low OLR resulted in higher methane conversion efficiency and lower VFA accumulation. Adjusting OLR after successful start-up helped maintain stable methane conversion efficiency in the reactors.