Exploration of flashing light interaction effect on improving biomass, protein, and pigments production in photosynthetic bacteria wastewater treatment

Enhancing bioresource production from purple non-sulfur bacteria (PNSB) in wastewater is important for nutrient recovery. Flashing light is a potential tool for increasing the photosynthetic efficiency of microalgae to enhance biomass production. However, the composition of the photosynthetic apparatus, properties of the linear electron transfer chain, and storage mechanisms of a phototroph are very different between PNSB and microalgae. How flashing light influences the photoheterotrophic organism, PNSB, has never been studied before. In this study, flashing light was first utilised to enhance the bioresource production of PNSB. The results showed that certain flashing lights increased the bioresource production. The highest biomass, protein, carotenoid, and bacteriochlorophyll concentration and protein content were obtained in the flashing light groups, which were 23.2–31.1%, 27.4–56.4%, 55.8–58.3%, 39.4–52.1%, and 23.2%–33.9% higher than those in the corresponding constant light groups, respectively. Luminous light (Ia), duty cycle (φ), and frequency (f) are the most important factors for biomass, protein, and pigment promotion, respectively. For biomass accumulation, high Ia-high f-high φ and low Ia-low f-low φ were beneficial, whereas for protein and pigment production, high Ia-high f-high φ and high f-low φ (whatever Ia) were desirable. Under light stress, flashing light promoted 96.1–118.2% a maximum electron transport rate compared with the constant light group (at the same energy input), which alleviated photoinhibition, increased photosynthetic efficiency, and therefore enhanced biomass accumulation. Flashing light also reduced energy consumption compared to constant light to some extent (8.7–83.3%). Flashing lights may be utilised in PNSB-based industries for bioresource promotion.