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

Abstract

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 NO3‐0.333333em- 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 NO3‐0.333333em- 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.

Effect of pyrite particle size on the denitrification performance of autotrophic or split‐mixotrophic bioreactors supported by pyrite/polycaprolactone

“…The COD eff was primarily associated with the equilibrium relationship between the release rate of organic carbon from PCL and the utilization rate of microorganisms (Yuan et al, 2022). According to previous research, the initial release rate of organic carbon from PCL was high, which might be related to the dissolution of unpolymerized organic small molecules on the PCL surface (Zhang et al, 2016; Zhang, He, et al, 2021). Afterward, the release rate sharply decreased and gradually stabilized after about 10 days (Zhang et al, 2016), which was similar to the case in this study.…”

“…Furthermore, the PCL was mainly biodegraded by enzymatic hydrolysis. When the released COD Cr exceeded the amount available to the bacteria, they would regulate the release rate of organic carbon according to the NO 3 − ‐N load (Lu et al, 2018; Zhang, He, et al, 2021). The PAD process in the FeS 2 layer of R3 PAD + PHD was beneficial to reducing the NO 3 − ‐N load of the PCL layer, thus slowing down the PCL dissolution.…”