Bioelectromics of a photosynthetic microalgae assisted microbial fuel cell for wastewater treatment and value added production

Abstract

Power generation and recovery of value-added products using microalgae, Haematococcus lacustris is tested in a dual chamber photosynthetic microalgae-assisted microbial fuel cell (PMA-MFCt<inf>1</inf>). The microalgal cells in conical flask act as control. The performance was compared to another, test PMA-MFCt<inf>2</inf>. The control MFC in second test had electrode wires not connected (PMA-MFC<inf>nw</inf>). The PMA-MFCt<inf>1</inf> set had microalgal catholytic media replenished unlike in PMA-MFCt<inf>2</inf>. A comparative PMA<inf>0</inf>-MFC, was used without microalgae and only water as catholyte. The results demonstrated maximum power density (PDmax) of 33.76 mW m⁻² in PMA-MFCt<inf>1</inf>, 15.36 mW m⁻² in PMA-MFCt<inf>2</inf> and 8.05 mW m⁻² in PMA<inf>0</inf>-MFC. The non replenishment of catholytic media in PMA-MFCt<inf>2</inf> set resulted in nutrient limitations, poor photosynthesis, and disrupted redox reactions. Further lowest PDmax in PMA<inf>0</inf>-MFC proves that microalgae are excellent source of free nascent oxygen required for redox reaction. Taxonomic identity of microbes at the anode via 16 S rRNA showed the dominance of catalytic microbes mainly Proteobacteria. The different kinds of carotenoids from microalgae were estimated by UV-Vis and liquid chromatography-mass spectrometry (LC-MS) analysis. The microalgal growth, evaluated in terms of biomass dry weight (DW), was 118 mg L⁻¹, after 40 days of PMA-MFCt<inf>1</inf> operation, which was lesser than in control (conical flask) 123 mg L⁻¹. The pigments including total chlorophyll (a + b), and total carotenoids were 699.7 µg g⁻¹ and 224.6 µg g⁻¹, respectively, on day 16. Microalgal performance in PMA-MFCt<inf>2</inf> and its control (PMA-MFC<inf>nw</inf>) was 10% and 32.52% inferior than in PMA-MFCt<inf>1</inf> and its control. The continuous replenishment of media in PMA-MFCt<inf>1</inf> maintained microalgal cells in continuous state of multiplication and photosynthesis resulting into higher bioelectricity generation and bioproducts than PMA-MFCt<inf>2</inf>, and PMA-MFC<inf>nw</inf>.