Effect of filling ratio and backwash on performance of a continuous-flow SPD reactor packed with PCL as carbon source

In this study, three up-flow fixed-bed bioreactors, named as A, B, and C, packed with polycaprolactone (PCL) under different filling ratios (31%, 62%, and 93%, respectively), were investigated over a long period (96 days). During the stable period, the mean effluent NO3-- N concentrations in reactors A, B, and C were 1.35 +/- 0.50, 1.07 +/- 0.41, and 1.03 +/- 0.27 mg/L, respectively, which showed the removal of NO3-- N was not closely related to filling ratio (p > 0.05, one-way ANOVA). However, it was found that biomass in reactor A was 2.13 and 5.55 times in B and C, respectively. Excessively thick biofilm refrained the enzymatic hydrolysis of PCL and biofilm's specific denitrification rate (SDNR). Backwash stimulated organic matter release and enabled biofilm to restore its denitrification activity. The maximum cycle of backwash was 6 days for the lowest filling ratio reactor. Additionally, the utilization rates for denitrification were 83.3%, 86.4%, and 60.5% in reactors A, B, and C, respectively, which was higher after backwash than before backwash. Practitioner points Excessively thick biofilm refrained the enzymatic hydrolysis of PCL. Backwash stimulated organic matter release and enabled biofilm to restore its denitrification activity. The maximum cycle of backwash was 6 days for the lowest filling ratio reactor. A higher utilization rate of PCL for denitrification was observed after backwash.

Automated summary

The removal of NO3- N was not closely related to filling ratio, but there were significant differences in biomass. Excessively thick biofilm hindered the enzymatic hydrolysis of PCL, while backwash stimulated organic matter release and enabled biofilm restoration of denitrification activity.