Influence of wavelength photoperiods and N/P ratio on wastewater treatment with microalgae–bacteria

This research investigates the effect of mixing wavelength light photoperiods (12 h blue, 8 h blue: 4 h green, 4 h blue: 8 h green, and 12 h green) and N/P ratios (1.3 to 8.3) on the growth microalgae–bacteria systems, organic matter, and nutrient removals. The highest microalgae–bacteria growth performance (μ = 0.2 d−1, 481.1 ± 15.3 mg DW L−1) was observed when a 8 h blue: 4 h green mixed wavelength and a low N/P ratio were used. For both N/P ratios, biomass productivity was favored when using the blue light dominated at longer time periods. Mechanisms for nitrogen removal by assimilation depend on the N/P ratio, achieving assimilation between 49 and 65% at a low N/P ratio. High nitrogen removal (>50%) showed a strong relation with alkalinity culture conditions (pH > 8.5). The mixing of wavelength photoperiods seems to be a promising strategy to achieve high biomass productivity and nutrient removal. However, for optimal conditions, N/P ratios in the wastewater should be considered. HIGHLIGHTS Mixing wavelength photoperiods and N/P ratio for microalgae–bacteria grown in wastewater was investigated.; The highest biomass productivities were obtained by mixing blue (8 h) and green (4 h) LED wavelengths.; High nitrogen removal and biomass assimilation was observed at a low N/P ratio.; P limitation affects microalgae–bacteria wastewater treatment performance at the high N/P ratio.