Nonconductive anode-associated biocarrier achieved differentiated functional bacteria enrichment and relieved the competitive pressure on anodic biofilm of microbial electrolysis cells

•Biofilm on anode and biocarrier was specialized and functional differentiated in MEC.•The Geobacter reached 43.8% in anode of MEC with biocarrier and pre-fermented sucrose.•The COD removal rate with biocarrier addition rose by 113% in sucrose feeding MECs.•The synergistic effects between functional bacteria improved current density of MEC.