Insoluble/immobilized redox mediators for catalyzing anaerobic bio-reduction of contaminants

Chemical-Assisted Microbially Mediated Chromium (Cr) (VI) Reduction Under the Influence of Various Electron Donors, Redox Mediators, and Other Additives: An Outlook on Enhanced Cr(VI) Removal

“…The most suitable range of redox potential for mediators to succeed Cr(VI) reduction lies between −0.320 and 1.28 V, where the previous value belongs to cofactor NADPH, and the latter for chromate ( Kavita and Keharia, 2012 ). Some redox mediators are also reported to overcome thermodynamic barriers of redox conversions and steric hindrance of the reactants ( Sun et al, 2015 ; Dai et al, 2016 ). Appropriate concentrations of electron donors are also a crucial factor for the regeneration of mediators, whereas the absence of suitable electron donors may substantially hamper the activity of mediators ( Chen et al, 2011 ; Xafenias et al, 2013 ; Bai et al, 2018 ).…”

“…Mainly, the carboxyl and phenolic hydroxyl groups present in quinoid compounds of mediators take accountability for the redox conversions between electron donors and the high valence state of the metal ( Xu et al, 2020 ). The position and the presence of chloride ion(s) and other substituents in the aforementioned quinoid compounds also influence electron transfer limitations in Cr(VI) reduction ( Hong et al, 2012 ; Zhang et al, 2014 ; Dai et al, 2016 ; Lian et al, 2016 ). In some investigations, the synergistic associations of Fe(III) minerals and AQDS were involved to deliver an alternative and attractive strategy of enhanced Cr(VI) reduction for co-contaminated sites using microorganisms like Cellulomonas sp., Shewanella oneidensis , and Geobacter sulfurreducens ( Field et al, 2013 ; Meng et al, 2018 ; He et al, 2019 ; Liu et al, 2019b ).…”

“…Even many microorganisms exhibited the ability to utilize multiple electron mediators for the acceleration of Cr(VI) reduction rate ( Field et al, 2013 ; Huang et al, 2019 ; He et al, 2020 ). In different studies, redox mediators were also reported to alter the electron transfer pathway of some microorganisms for Cr(VI) reduction ( Yan et al, 2014 ; Dai et al, 2016 ). The suitable example is the supply of 2-amino-3-chloro-1,4-naphthoquinone-GO (NQ-GO) in Acinetobacter sp.…”

Catalytic reduction of NACs by nano Fe3O4/quinone composites in the presence of a novel marine exoelectrogenic bacterium under hypersaline conditions

“…1,2,5 Nevertheless, there are bottlenecks for further application of these biotreatment programs: rst, the anaerobic reduction of the nitrogen-containing group (e.g., -NO 2 , -N]N-) of NACs is the rate-limiting step in the NAC biodegradation process; second, the industrial effluent contains large amounts of salts, 6,7 which may decrease the activity of microorganisms. Previous studies had demonstrated that immobilized quinone compounds (IQCs) could enhance the bioreduction of various NACs, 8 including azo dyes 8,9 and nitroaromatics, 8,10 even under saline conditions. 11,12 Moreover, compared to soluble quinone compounds (QCs), IQCs need not to be continuously added into reaction systems, which could reduce running cost and avoid secondary contamination.…”

“…11,15,16 Although many IQCs seemed to perform pretty good catalytic activity than the soluble QCs, their performance still need to further improved. 8 Recent interest in nanotechnology has provided a wealth of diverse nanoscaffolds that could potentially support QCs immobilization.…”