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Microbially mediated bioreduction of iron oxyhydroxide plays an important role in the biogeochemical cycle of iron. Geobacter sulfurreducens is a representative dissimilatory iron-reducing bacterium that assembles electrically conductive pili and cytochromes. The impact of supplementation with γ-Fe2O3 nanoparticles (NPs) (0.2 and 0.6 g) on the G. sulfurreducens-mediated reduction of ferrihydrite was investigated. In the overall performance of microbial ferrihydrite reduction mediated by γ-Fe2O3 NPs, stronger reduction was observed in the presence of direct contact with γ-Fe2O3 NPs than with indirect contact. Compared to the production of Fe(II) derived from biotic modification with ferrihydrite alone, increases greater than 1.6- and 1.4-fold in the production of Fe(II) were detected in the biotic modifications in which direct contact with 0.2 g and 0.6 g γ-Fe2O3 NPs, respectively, occurred. X-ray diffraction analysis indicated that magnetite was a unique representative iron mineral in ferrihydrite when active G. sulfurreducens cells were in direct contact with γ-Fe2O3 NPs. Because of the sorption of biogenic Fe(II) onto γ-Fe2O3 NPs instead of ferrihydrite, the addition of γ-Fe2O3 NPs could also contribute to increased duration of ferrihydrite reduction by preventing ferrihydrite surface passivation. Additionally, electron microscopy analysis confirmed that the direct addition of γ-Fe2O3 NPs stimulated the electrically conductive pili and cytochromes to stretch, facilitating long-range electron transfer between the cells and ferrihydrite. The obtained findings provide a more comprehensive understanding of the effects of iron oxide NPs on soil biogeochemistry.

BACKGROUND: Microbial reduction of Cr(VI) has been demonstrated as an environmentally friendly remediation protocol in recent years. In this study, the catalytic capability of soluble quinone compounds [i.e. anthraquinone‐2,6‐disulphonate (AQDS), 2‐hydroxy‐1,4‐naphthoquinone (HNQ) and ubiquinone (CoQ)] as well as an immobilized HNQ‐graphene oxide (GO) composite were evaluated for their ability to mediate Cr(VI) bioreduction by Shewanella xiamenensis. Additionally, the mechanism for Cr(VI) bioreduction was rigorously explored. RESULT: At a test concentration of 0.02 mmol L⁻¹, HNQ exhibited the highest efficiency for catalysing Cr(VI) bioreduction compared to AQDS and CoQ. During a 48 h test period, the highest removal efficiency (100%) of Cr(VI) (50 mg L⁻¹) was exhibited in the presence of 0.015 mmol L⁻¹ HNQ compared to biotic supplementations with 0.005, 0.010 and 0.020 mmol L⁻¹ of HNQ. Furthermore, supplementation with 13.0 mg HNQ‐GO composite greatly enhanced Cr(VI) bioreduction compared to the biotic assay without any quinone compounds. Specifically, complete reduction of Cr(VI) was found in the first reaction cycle (following 72 h), compared to

Graphene-based materials have been demonstrated to facilitate electron extracellular transfer (EET) of Shewanella. In this study, compared to group lacking graphene oxide (GO)-based materials, GO films-added group and graphene oxide/polyvinyl alcohol (GO/PVA) film-added group delivered 2.67- and 3.13-fold increases in the Cr(VI) reduction by Shewanella xiamenensis, respectively. The whole reduction process could be divided into three stages, including microbial Cr(VI) reduction and GO reduction stage, microbial GO reduction stage and microbial Cr(VI) reduction mediated by reduced graphene oxide (rGO) stage. Moreover, gene analysis revealed that addition of GO and GO/PVA films stimulated overexpression of several c-type cytochrome (c-Cyts) genes, including mtrA, mtrB, mtrC, mtrD, mtrE, mtrF, omcA, petC and SO-4047. Specifically, appreciable Cr(VI) reduction by the strains that overexpressed mtrA, mtrB, mtrC, mtrD, mtrE, mtrF and omcA further confirmed that overexpression of c-Cyts genes indeed enhanced the efficiency of Cr(VI) reduction. Based on these results, the specific function of every c-Cyt was clearly found in Cr(VI) reduction by the induction of GO-based materials. Our finding has disclosed a synergetic mechanism stimulated by GO-based materials to enhance Cr(VI) bioreduction that was not only mediated through the modification of material but also upregulated the expression of functional genes.

Background With the further development of anaerobic digestion, an increasing output of anaerobically digested wastewater (ADW), which typically contained high concentrations of ammonium, phosphate, and suspended solids, was inevitable. Microalgae cultivation offered a potential waste-to-value strategy to reduce the high nutrient content in ADW and obtain high value-added microalgae. However, ADW generally contained a mass of pollutants (suspended solids, competitors, etc.), which could inhibit microalgae growth and even result in microalgae death by limiting light utilization. Thus, it is highly imperative to solve the problem by a novel modified photobioreactor for further practical applications. Results Four microalgae species, Scenedesmus dimorphus, Scenedesmus quadricauda, Chlorella sorokiniana, and Chlorella vulgaris ESP-6, were cultivated in the membrane photobioreactor (MPBR) fed with ADW to investigate the efficiency of ammonia and phosphorus removal. The results showed that C. sorokiniana had the best performance for the removal of ammonia and phosphorus from ADW. The highest amount of C. sorokiniana biomass was 1.15 g/L, and the removal efficiency of phosphate (66.2%) peaked at an ammonia concentration of 128.5 mg/L after 9 days’ incubation. Moreover, the MPBR with 0.1 μm membrane pore size had the best ammonia and phosphate removal efficiencies (43.9 and 64.9%) at an ammonia concentration of 128.5 mg/L during 9 days’ incubation. Finally, the continuous multi-batch cultivation of C. sorokiniana was performed for 45 days in MPBR, and higher removal ammonia amount (18.1 mg/day) and proteins content (45.6%) were obtained than those (14.5 mg/day and 37.4%) in an normal photobioreactor. Conclusion In this study, a novel MPBR not only eliminated the inhibitory effects of suspended solid and microorganisms, but also maintained a high microalgae concentration to obtain a high amount of ammonia and phosphate removal. The research provided a theoretical foundation for the practical application of MPBRs in various wastewater treatment schemes without pretreatment by algae, which could be used as biofuels or protein feed.