Effects of light on municipal wastewater treatment efficiency, byproduct generation, and growth of Scenedesmus quadricauda

The development of green wastewater treatment technologies with low energy consumption and sustainability is a key direction. Emerging microalgae-based technology, harnessing photosynthetic assimilation, demonstrates significant potential for synergistically achieving pollutant removal and resource recovery. To delve deeper into the mechanistic impact of different light conditions on microalgae within real wastewater matrices, this study cultivated Scenedesmus quadricauda ( S. quadricauda ) in non-sterilized municipal wastewater. A coupled regulation of light spectra (white, red, blue) and varying intensities (high, medium, low) was carried out for a multidimensional assessment of growth performance, high-value products synthesis, wastewater purification efficiency, and microbial community evolution. Results demonstrated that red and white light notably boosted the growth and photosynthetic activity of S. quadricauda , resulting in a maximum cell density of 14.5 × 10 5 cells/mL. Under high-intensity illumination, S. quadricauda demonstrated improved pollutant assimilation, with removal efficiencies of 95.4 %, 97.3 %, 98.2 %, and 82.9 % for total nitrogen, total phosphorus, ammonia nitrogen, and permanganate index, respectively. Conversely, blue light stimulated the synthesis of high-value products including polysaccharides, proteins, and lipids, while also substantially enhancing the total yields of unsaturated fatty acids and biodiesel-related pyrolysis products. This compensated for lower biomass production by enhancing total resource recovery. Further, high-cell-density S. quadricauda significantly promoted microbial community succession and shift in diversity indices in municipal wastewater, establishing a stable algal–bacterial symbiotic system. These findings underscore the potential of spectrally and intensity-coordinated S. quadricauda cultures for both wastewater treatment and high-value product synthesis, providing an innovative lighting strategy for algae-based treatment pathways of municipal wastewater. • The first comprehensive study on synergistic effects of light spectra and intensities in microalgal wastewater treatment. • Red- and white-light boosted growth and photosynthetic activity of S. quadricauda . • Blue light favored the synthesis of high-value products in S. quadricauda . • S. quadricauda achieved removal efficiencies of up to 95.4 % for TN, 97.3 % for TP, 98.2 % for NH 3 -N, and 82.9 % for COD Mn . • Establishing a S. quadricauda -dominated algae–bacteria system significantly enhances pollutant removal.