Characterization of Product and Potential Mechanism of Cr(VI) Reduction by Anaerobic Activated Sludge in a Sequencing Batch Reactor

Abstract

Bioremediation of Cr(VI) and nitrate is considered as a promising and cost-effective alternative to chemical and physical methods. However, organo-Cr(III) complexes in effluent generally causes environmental concerns due to second-pollution. Here, Cr(VI) reduction and immobilization efficiencies of anaerobic activated sludge were investigated. Anaerobic activated sludge showed strong reduction ability of Cr(VI) and possessed a great potential of Cr(III) immobilization. Almost 100.0 mg l−1 Cr(VI) could be completely reduced and immobilized by anaerobic activated sludge in a sequencing batch reactor in 24 h. And most generated Cr(III) was accumulated outside of sludge cells. Extracellular polymeric substances (EPS) could bind to Cr(VI) and form EPS-Cr(VI) interaction to reduce the toxic effect of Cr(VI) and promote the Cr(VI) reduction. Protein-like and humic-like substances were responsible for binding with Cr(VI), meanwhile the process was a thermodynamically favorable binding reaction. Then Cr(VI) was reduced to Cr(III) by membrane-associated chromate reductase of sludge. Eventually, the generated Cr(III) might exist as poly-nuclear Cr(III) complexes adhered to sludge surfaces.

Adsorption mechanism of hexavalent chromium onto layered double hydroxides-based adsorbents: A systematic in-depth review

“…Hexavalent chromium Cr(VI)-a strong oxidizing agent-is a highly toxic chemical that can potentially cause dangerous health outcomes because of its carcinogenic and mutagenic nature and therefore, Cr(VI) removal from water requires urgent attention. As reported in the litearture, Cr(VI) anion in solution entirely/partly reduces to Cr(III) cation when it makes contact with an adsorbent's surface, for instance: natural biomaterial [14], amino-functionalized mesoporous ordered silica adsorbents [15], activated carbon [16], biochar [17], and nanoscale zero-valent iron modified with tetraethyl-ortho-silicate and hexadecyl-trimethoxy-silane [18]. Such an adsorbent can adsorb the reduced Cr(III) through various interactions (i.e., complexation).…”

Effect of Dendritic Cu–In Alloy on Cr(VI) Reduction Synthesized via Pulsed Electrodeposition

“…The figure shows the UV‐Visible spectra of chromium(VI) reduction to chromium(III) by Cu−In alloy catalysts. The absorption spectrum of prepared chromium solution shows two characteristic peaks at 273 nm and 365 nm . On addition of formic acid the peak shifted to 348 nm which is attributed to the electron transfer from formic acid to the heavy metal Cr(VI) ion .…”

Evaluación de los efectos sinérgicos de cromo y plomo durante el proceso de fitorremediación con berro (Nasturtium officinale) en un humedal artificial//Evaluation of the synergistic effects of chromium and lead during the process of phytoremediation with watercress (Nasturtium officinale) in an artificial wetland

“…Mientras en los tallos la mayor cuantificación ocurrió en la concentración más alta de Pb. Se obtuvo el mismo comportamiento observado en el experimento monometálico, la mayor transformándolo en una forma química asimilable para la planta y no tóxica (Jin et al, 2017).…”