Impact of metazoan activity on permeability in granular activated carbon (GAC) and Gravity-Driven membrane (GDM) combined reactors for decentralized wastewater treatment

The low permeability of gravity-driven membrane (GDM) systems poses a significant challenge to their broader application. Thus, this study aimed to enhance the permeability of a submerged granular activated carbon (GAC) and GDM combined reactor by using metazoan organisms present in wastewater. Despite an initially low metazoan activity in the wastewater influent, the metazoan population was effectively increased in a metazoan- facilitated batch reactor. When the metazoan-facilitated biomass obtained from the batch reactor was applied to the submerged GDM reactor equipped with hollow fiber modules, a stabilized permeate flux with a 46 % improvement was achieved without significantly compromising permeate quality. Autopsy results revealed the presence of the introduced metazoans in the biofilm layer on the surface of the hollow fiber membrane. This reduced the deposited mass by 19.2 % and created a heterogeneous and porous structure, which subsequently decreased the fouling resistance. In addition, the movement patterns and motility of key metazoans (nematodes and annelids), which were closely related to biofilm control, were analyzed. Thus, this study demonstrated the high potential of actively utilizing underused metazoans in wastewater to effectively enhance the permeability of GAC + GDM systems for decentralized wastewater treatment.