Selected-Wavelength Illumination for Enhanced Hydrogen and Poly-β-hydroxybutyrate Production from Second Cheese Whey by Rhodopseudomonas palustris

Second cheese whey (SCW), a major by-product of ricotta cheese production, poses significant environmental challenges due to its high organic load. Biohydrogen (bio-H₂) and poly-β-hydroxybutyrate (PHB) production offer a sustainable reuse of SCW, that provides ideal nutrients for microbial growth. This study aimed to convert SCW into Bio-H₂ and PHB using a 5-liter tubular bioreactor in a sequential lactic fermentation and photofermentation system. Two lighting conditions were tested: white LED (WL) and selected LED (SL). Optimal results were achieved with a co-inoculum of <i>Lactococcus lactis</i> MK L84 and <i>Lacticaseibacillus paracasei</i> MK L49 at pH 4.5-5.5, followed by photofermentation with <i>Rhodopseudomonas palustris</i> 42OL under SL condition. The process yielded an average of 0.47 L of H₂ per liter of substrate and 1.66% wPHB/wCDW. This approach successfully transformed dairy waste into high-value products, promoting circular economy principles.