Advanced Nitrogen Removal in a Denitrification Bioreactor Using Nonintact Hollow Fiber Membranes As Biofilm Carriers

The selection of biofilm carriers is essential for enriching functional microorganisms. In this study, nonintact hollow fiber membranes were designed as immobilized biofilm carriers in a denitrification bioreactor (DNBR) for treating nitrate in the effluent of wastewater treatment plants. The DNBR performance was studied at varying hydraulic retention times of 18 to 3 h. Results showed that effluent concentrations of total nitrogen (TN) were maintained below 5 mg/L, corresponding to 75.6-84.8% TN removal. The batch tests also showed that the biofilms on nonintact membranes exhibited higher denitrification activities than the sludge flocs (i.e., detached biofilms) in the bioreactor. The 16S rRNA sequencing indicated that the denitrification performance of biofilms was attributed to the enrichment of denitrifying bacteria, particularly Azospira (relative abundance up to ca. 36.5%). Additionally, the colonization of biofilms was dominated by stochastic community assembly processes. The metagenomic analysis revealed that the biofilms harbored abundant functional genes responsible for biofilm formation, glucose metabolism, and nitrogen metabolism. Overall, the reuse of nonintact hollow fiber membranes as biofilm carriers for nitrate removal can be considered a novel approach for "treating waste with waste".