Bioaugmentation as a Strategy to Engineer the Anodic Biofilm Assembly in Microbial Electrolysis Cell Fed with Wastewater

Abstract

Microbial electrolysis cell (MEC) system is a potential technology that could treat wastewater while simultaneously generating H2 (green energy). MEC's electroactive bacteria (EAB) are essential microbes responsible for oxidizing organic pollutants (such as acetate) in wastewater using an electrogenesis process. Since EABs comprise the core of MECs, they are essential for maintaining functional stability (Coulombic efficiency (CE), current density, and pollutant removal) of MECs. The cause of EAB becoming dominant at the anode of MECs fed with wastewater is still unclear. Furthermore, efficient EAB are typically not detected in wastewater, and when they are present their abundance is low, which affects their early colonization on the anode and subsequent growth into a mature biofilm. This study investigated bioaugmentation as a strategy to drive the assembly of functionally redundant anode EAB biofilms to improve MEC performance. Two bioaugmentation strategies (Conditions 2 and 3) with known EABs (G. sulfurreducens and D. acetexigens) were tested during the startup of MECs. Meanwhile, control MEC reactors (Condition 1) were operated with only wastewater as the sole source of inoculum to compare the anodic biofilm assembly and system performance with the bioaugmented reactors. Equal number of G. sulfurreducens and D. acetexigens cells were added to the wastewater-fed MEC (10% inoculum at 2.1E+07 live cells/mL). In Condition 3, anodic-biofilm colonized G. sulfurreducens and D. acetexigens was used as anode in wastewater fed MECs. Using single-chambered MEC reactors, the bioaugmented MECs (Condition 2 and 3) performed more efficiently than the non-bioaugmented (Condition 1) MECs. Current generation, CE and gas production were different between the three conditions tested (Condition 3 > Condition 2 > Condition 1). Analysis of 16S rRNA gene sequencing of anodic biofilm indicates revealed that the bacterial communities was not affected between the tested conditions. However, the relative abundance of EABs, mainly G. sulfurreducens and D. acetexigens, was markedly influenced by bioaugmentation compared to the control reactor. The highest peak current generation (~ 1500 mA/m2), CE (70.3 ± 9%), and gas production (0.04 m3/m3/day) was observed in Condition 3. Collectively, these results provide a framework for engineering the anode microbial communities in MECs for wastewater treatment.