Impact of SRT on the performance of HF and FS MBRs for the treatment of landfill leachate with microbial correlation -

Abstract

This study examines the performance of flat sheet (FS) and hollow fiber (HF) membrane bioreactors (MBRs) for the treatment of landfill leachate (COD = 5010-6900 mg-L, BOD₅ = 406-1228 mg-L; Total Phosphorous (TP) = 14-36 mg-L; Total Nitrogen (TN) = 2300-3400 mg-L) under varying solid retention times (SRT = 5 to 20 days) and a constant hydraulic retention time (HRT = 100 hours). Mixed-liquor bacterial communities were examined over time using 16S rRNA gene sequence analysis in an attempt to define linkages between systems’ performance and microbial community composition. Similarly, biofilm samples were collected at the end of each SRT to characterize the microbial communities that evolved on the surface of the FS and HF membranes. The comparative assessment of the FS-MBR and the HF-MBR showed that both membranes exhibited comparable removal efficiencies for BOD₅ (92percent in FS vs. 90percent in HF), TP (72percent in FS vs. 66percent in HF), PO₄³⁻ (74percent in FS vs. 75percent in HF) and COD (51percent in FS vs. 43percent in HF) at SRT = 20 days. The performance of both systems degraded at shorter SRTs, with the FS system exhibiting better overall nitrogen removal. The statistical analysis showed that the removal efficiencies of TP, PO₄³⁻, COD, and BOD₅ were a function of SRT for both membrane bioreactors (p-value 0.05); yet TN removal was found to be independent of SRT. The biokinetic coefficients governing FS and HF values were estimated with the half-saturation constant (Ks) (mg COD-L) (1123.63 and 1160.30 for the FS-MBR and HF-MBR, respectively) and the maximum specific growth rate (µm) (day⁻¹) (1.42 and 1.72 for the FS and HF, respectively), falling within reported ranges for activated sludge processes (ASP) and MBR applications treating wastewater; yet both the maximum cell yield (Y) (mg VSS-mg COD) (1.04 and 1.87 for the FS-MBR and HF-MBR, respectively) and the endogenous decay coefficient (kd) (day⁻¹) (0.99 and 1.2487 for the FS-MBR and HF-MBR, respectively) wer