Enhancing performance of biocarriers facilitated gravity-driven membrane (GDM) reactor for decentralized wastewater treatment: Effect of internal recirculation and membrane packing density.

This study aims to investigate the effect of internal recirculation and membrane packing density on the performance (water quality, membrane performance, and microbial community) of a biocarriers facilitated gravity-driven membrane (GDM) reactor under intermittent aeration condition. The results revealed that the presence of internal recirculation in the GDM reactors could effectively improve water quality (especially increasing nitrogen removal) and membrane performance (especially reducing cake layer resistance) compared to those without internal recirculation. In addition, compared to a high packing density membrane module (1150 m/m), a lower packing density membrane module (290 m/m) benefited to improve 15% of nitrogen removal and 44% of permeate flux due to the effective aeration scouring effect and less-limited eukaryotic activity, as well as reduce 20% of total treatment cost. In addition, the presence and absence of internal recirculation could lead to dissimilar microbial community compositions of the biofilms in the GAC layers and on the membrane surfaces. However, the membrane packing density could play an insignificant effect on the microbial community compositions of the biofilms in the GDM reactors with internal recirculation.