Exploring the Influence of Light Wavelength Ranges and Nutrients Reduced Availability’s Impacts on Polyhydroxyalkanoates Accumulation in Purple Phototrophic Bacteria

Purple phototrophic bacteria (PPB) offer a sustainable approach for biological wastewater treatment while simultaneously producing valuable by-products such as polyhydroxyalkanoates (PHAs). This study investigates the effects of continuous light wavelengths over a two-stage nutrient reduction setup on PHA accumulation in a mixed PPB culture grown on fuel synthesis wastewater (FSW). The first stage promoted biomass production under nutrient availability, while the second stage targeted the enhancement of PHA accumulation through nitrogen (N) or phosphorus (P) reduction. Biomass growth remained stable under P reduction but significantly increased under N reduction. The results showed that organics removal efficiency decreased under nutrient reduction, particularly under P reduction, while N reduction conditions enhanced P uptake from the media. Maximum PHA accumulation reached 12.6% CDW under N reduction and 10.0% CDW under P reduction. Light type played a dominant role, with a full-spectrum light that included ultraviolet (UV) and infrared (IR) promoting the highest PHA accumulation, whereas white light with far-red wavelengths (700–770 nm) enhanced biomass growth. These findings highlight the potential of optimizing light conditions and nutrient availability to enhance PHA biosynthesis, paving the way for improved bioplastic production from wastewater streams.