Reduction of Cu(II) and simultaneous production of acetate from inorganic carbon by Serratia Marcescens biofilms and plankton cells in microbial electrosynthesis systems

Abstract

1Simultaneous Cu(II) reduction (6.42 ± 0.02 mg/L/h), acetate production (1.13 ± 0.02 mg/L/h) from 2 inorganic carbon (i.e., CO 2 sequestration), and hydrogen evolution (0.0315 ± 0.0005 m 3 /m 3 /d) were 3 achieved in a Serratia marcescens Q1 catalyzed microbial electrosynthesis system (MES). The 4 biofilms released increasing amounts of extracellular polymeric substances (EPS) with a higher 5 compositional diversity and stronger Cu(II) complexation, compared to the plankton cells, at higher 6 Cu(II) concentrations (up to 80 mg/L) and circuital currents (cathodic potential of -900 mV vs. 7 standard hydrogen electrode (SHE)). Moreover, the biofilms reduced Cu(II) to Cu(0) more 8 effectively than the plankton cells. At Cu(II) concentrations below 80 mg/L, the dehydrogenase 9 activity in the biofilms was higher than in the plankton cells, and increased with circuital current, 10 which was converse to the lower activities of catalase (CAT), superoxide dismutase (SOD) and 11 antioxidative glutathione (GSH) in the biofilms than the plankton cells, although all these 12 physiological activities were positively correlated with the concentration of Cu(II). This is the first 13 study that evaluates the EPS constituents and the physiological activities of the biofilms and the 14 plankton cells in the MESs, that favors the production of acetate from CO 2 sequestration and the 15 simultaneous reduction of Cu(II) from organics-barren waters contaminated with heavy metals. 16 17 Keywords: microbial electrosynthesis system; Cu-tolerant biofilm and plankton cell; CO 2 fixation; 18 extracellular polymeric substances; physiological activity; variable cathode potential 19 20 21 22 23 24 *Revised manuscript with changes marked Click here to view linked References) in the cathodes and acetate in the anodes (Huang et al., 2015; 2018; Chen et al., 31 2016). Among the variety of heavy metals that can be recovered using microbial 32 electro-metallurgical processes, the recovery of Cu(II) has attracted significant attention due to its 33 frequent occurrence in acid mine drainage wastewaters (Ter Heijne et al., 2010;Zhang et al., 2015; 34 Wu et al., 2016; Kiran et al., 2018). Likewise abiotic cathodes, biocathodes utilizing 35 electrochemically active bacteria (EAB) have been shown to reduce Cu(II) to metallic Cu(0) and thus 36 remove the heavy metal from the catholyte solution (Huang et al., 2015; 2018; Shen et al., 2017; Tao 37 et al., 2017). 38 From another perspective, microbial electrosynthesis systems (MESs) are also emerging as 39 potential systems for the synthesis of valuable products from waste streams. One notable example is 40 the production of acetate from inorganic carbon such as bicarbonate, where the production rate of 41 acetate is modulated artificially by the application of an electrical current that interferes with the 42 microbial metabolism (Bajracharya et al., 2015; Venkata Mohan et al., 2016; Rojas et al., 2018). 43 Therefore, the combination of microbial electro-metallurgical processes of ...

Acetate production from inorganic carbon (HCO3-) in photo-assisted biocathode microbial electrosynthesis systems using WO3/MoO3/g-C3N4 heterojunctions and Serratia marcescens species

“…A non-photosynthetic electrotroph of S. marcescens Q1, capable of metabolizing anaerobically inorganic carbon to acetate [30] was cultured in a sterile medium, and harvested after 24 h incubation. Oxygen was not required during the incubation period, as well as, during the operation of the photo-assisted MES biocathode, thereby preventing the generation of potentially harmful reactive oxygen species [9] and the deleterious effect on the acetate production columbic efficiency.…”

“…This study investigates the production of acetate from inorganic carbon (HCO3 -) using the electrotroph Serratia marcescens Q1 in a photo-assisted MES incorporating a structured electrode consisting of a layer of g-C3N4 coated on graphite felt and decorated with nanoparticles mixtures of WO3 and MoO3. The non-photosynthetic strain S. marcescens Q1 was isolated from biocathodes of other anaerobic bioelectrochemical systems capable of metabolizing inorganic carbon (HCO3 -) to acetate [29][30]. In such photo-assisted MES, it is hypothesized that the irradiation of the Z-scheme of WO3/MoO3/g-C3N4 heterojunction, creates long-lived electrons and holes.…”

Efficient conversion of bicarbonate (HCO3−) to acetate and simultaneous heavy metal Cr(VI) removal in photo-assisted microbial electrosynthesis systems combining WO3/MoO3/g-C3N4 heterojunctions and Serratia marcescens electrotroph

“…The cathode was inoculated with S. marcescens Q1, a nonphotosynthetic electrotroph capable of producing acetate from inorganic carbon under anaerobic conditions, which was originally isolated from other bioelectrochemical systems [12,[17][18]. Prior to the electrotroph inoculation, the catholyte in the cathodic chamber containing NaHCO3 (2.0 g/L), NH4Cl (0.11 g/L), KH2PO4 (0.012 g/L), vitamins 0.6 mL/L, mineral 0.6 mL/L and K2Cr2O7 (170 or 339 mg/L, equal to 60 or 120 mg/L Cr(VI)), was sparged with N2 gas for 15 min to remove the residual oxygen.…”

“…The conductivity in catholyte was regulated to 103 mS/cm with the addition of 0.6 M KCl [12]. The anolyte in the abiotic anode was made by a 50 mM phosphate buffer (pH 5.8) to prevent pH changes due to hydrolysis and the consequent effect on cathode performance during an experimental operational time of 12 h [1][2]12,18]. The anolyte was daily refreshed in experiments lasting more than 24 h to guarantee its pH stability.…”

“…The catholyte pH was also set to 5.8 to avoid unwanted effect due to pH imbalances among the chambers. This pH was selected since it favors the S. marcescens activity in MES [12,18] and hydrogen evolution which is further needed for the microbial reduction of inorganic carbon [1,12]. The cathode potential was kept constant at -1.1 V to favor the production of acetate in the MES [21].…”