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A constructed wetland-microbial fuel cell system using Leersia hexandra was found to effectively reduce Cr(VI) to Cr(III) with increased dissolved oxygen concentration.

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What they did

System
MFC

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Abstract

Cr (VI) is hazardous to humans and our environment. Leersia hexandra Swartz (L. hexandra) is the first wet chromium hyperaccumulator found in China. This study constructed the L. hexandra constructed wetland-microbial fuel cell (CW-MFC) system to treat Cr (VI) wastewater. It also determined the effects of different dissolved oxygen (DO) concentrations on power generation, pollutant removal, and Cr (VI) reduction. Cathode aeration promoted the voltage output and pollutant removal of the L. hexandra CW-MFC when the DO concentration was 4.5 mg·L⁻¹: the highest voltage was 520 mV, the chemical oxygen demand (COD) removal rate was 93.73%, and the Cr (VI) removal rate was 97.77%. Moreover, the increase in the DO concentration improved the absorption of heavy metal Cr by the substrate and L. hexandra, and promoted the transformation from Cr (VI) to Cr (III). Chromium mostly exists as a residue with low toxicity and low mobility in L. hexandra and the substrate. This proves that the increased DO concentration promotes the redox reaction in the system and plants, reducing Cr (VI) to Cr (III). At the same time, the key micro-organism Geobacter that enhances the performance of the system and Cr (VI) reduction was found. The research results can provide a reference for the subsequent CW-MFC treatment of actual Cr-containing wastewater.

Key findings

  • Cathode aeration with 4.5 mg/L DO concentration increased voltage output to 520 mV.
  • COD removal rate was 93.73% and Cr(VI) removal rate was 97.77% with optimal DO concentration.
  • Increased DO concentration promoted Cr absorption by substrate and L. hexandra, and facilitated Cr(VI) to Cr(III) transformation.

Keywords

Microbial fuel cellChromiumWastewaterEnvironmental chemistryConstructed wetlandAeration

Identifiers

DOI
10.3390/app13053309
Journal
Applied Sciences
Year
2023