Dark fermentation of cheese whey - supplement materials control the conversion pathways

The study explores changes in biological conversion pathways of cheese whey due to supplementation of dark fermentation (DF), including additives such as fly ash (FA), biochar (BC), and geopolymer (GP) to improve the biohydrogen (bioH₂) production. Among these, FA (10 g/L) produced the highest bio-H₂ giving 316.68 ml/g yield, showing an increase of 86 % compared to control. The promoting role of FA is attributed to strong buffering due to its high oxide and hydroxide contents, enhancing the system resistance against decrease in pH (drop from 6.5 to 4.79) compared to control that showed a significant drop in pH to 3.91 after 72 h. Detailed characterization of the additives using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), Brunauer, Emmett, Teller (BET) adsorption and analysis of metallic elements, electrical conductivity (EC), pH, volatile fatty acids (VFAs) and volatile solids (VS) removal, confirmed the release of Ca, Na, Mg, K, Fe, Mn, Ni, and Zn, leading to pH regulation and providing nutrients to promote metabolic activities of the microorganisms. Low bio-H₂ production by the addition of GP is due to high EC (6.43 mS/m) achieved, leading to a shift in the conversion pathways from butyric acid production to acetate production.