Textile dye removal using diatomite nanocomposites: a metagenomic study in photosynthetic microalgae-assisted microbial fuel cells

Abstract

In this study, Coomassie brilliant blue (CBB), brilliant green (BG), and rhodamine (Rh) dyes were used to simulate dye-rich wastewater. Adsorption and degradation of these dyes (2 μM, 10 μM, and 30 μM) on diatomite (DE) were evaluated under light (L) and dark (D) conditions. The adsorption of dye–DE composites followed pseudo-second-order kinetics at all concentrations and conditions had R² > 0.99, thus showing a good fit. The calculated equilibrium adsorption amount q_e,(cal) was coherent with the value of experimental q_e,(exp). The poorest adsorption and photocatalysis occurred at 30 μM, prompting the functionalization of dyes with TiO₂ and Fe₃O₄ nanoparticles (NP(s)). The highest dye degradation efficiencies (DG_eff) for 30 μM dyes were 86.79% (CBB–DE–Fe₃O₄, 72 h), 96.10% (BG–DE–TiO₂, 52 h), and 81.74% (Rh–DE–TiO₂, 48 h), with Rh–DE–TiO₂ showing the fastest degradation. Functionalized DE–dye (30 μM) nanocomposites were further tested in a photosynthetic microalgae-assisted microbial fuel cell with dye-simulated wastewater at the anode (PMA-MFC-1 with CBB–DE–Fe₃O₄, PMA-MFC-2 with BG–DE–TiO₂ and PMA-MFC-3 with Rh–DE–TiO₂) and Asterarcys sp. GA4 microalgae at the cathode. In dark anode chambers, PMA-MFC-3 achieved the highest DG_eff value of Rh dye as 88.23% and a polarization density of 30.06 mW m⁻², outperforming PMA-MFC-2 with BG dye and PMA-MFC-1 with CBB dye. The molecular identifier analysis of microbes in wastewater at the anode showed the dominance of Sphingobacteria and Proteobacteria in PMA-MFC-3 (Rh–DE–TiO₂) and COD removal of 61.36%, highlighting its potential for efficient dye degradation and bioelectricity generation. Furthermore, PMA-MFC-3 simultaneously demonstrated a superior microalgal lipid yield of 3.42 μg g⁻¹ and an algal growth of 8.19 μg g⁻¹ at the cathode.