Enhanced carbon sequestration of biological phenol degradation using wastewater-originated microalgae-bacteria coculture system

[Display omitted] •The MBC system achieved a 90.2% PRE at 800 lx of light intensity.•Strong illumination at 3,000 lx resulted in a reduced PRE by bacterial inhibition.•Phenol was degraded in oxygen-free conditions by photosynthetic oxygen supply.•Stoichiometry of the MBC system proves the improved carbon sequestration.•The microalgae and bacteria community shifted by responding to toxic phenol supply. This study explores the phenol removal efficiencies (PREs) of microalgal-bacterial co-culture (MBC) systems under varying light intensities and gas-tight conditions. MBC systems inoculated with microbial seeds cultured from modified anaerobic digestion effluent or Bristol medium showed enhanced PRE, which was attributed to O2 production from photosynthesis. At 800 lx, the MBC systems achieved a PRE of 90.2 %, which decreased to 64.6 % at 3,000 lx owing to the inhibition of bacterial activity. In comparison, pure Pseudomonas putida cultures exhibited only 43.6 % degradation. MBC systems have also demonstrated phenol degradation under O2-free conditions, reducing CODt/COD0 to 16.4 % and showing potential for energy-efficient wastewater treatment. Revised stoichiometric analyses indicated greater carbon sequestration, with an O2 demand of 5.48 mol and CO2 production of 0.08 mol per mol of phenol degraded. The genus Parachlorella exhibited the highest dominance among the microalgae owing to its resistance to phenol toxicity. In contrast, the dominance of Acinetobacter, Methylophilus, and Methylobacterium, and uncultured Moraxellaceae and Xanthomonadaceae families varied significantly depending on the light intensity and characteristics of the inoculated consortia.