Sequential generation of hydrogen and methane from glutamic acid through combined photo-fermentation and methanogenesis

Glutamic acid can hardly produce hydrogen via dark- or photo-fermentation without pretreatment. In this study, a novel process of acidogenic pretreatment with bacteria and zeolite treatment for NH 4 + removal was proposed to use glutamic acid as feedstock in photo-fermentation for efficient hydrogen production. Glutamic acid pretreated with acidogenic bacteria produces soluble metabolite products. After zeolite treatment, the acidulated solution, which mainly contains acetate, butyrate, and NH 4 + , shows a decrease in NH 4 + concentration from 36.7 mM to 3.2 mM ( NH 4 + removal efficiency of 91.1%). After NH 4 + removal, the treated solution is incubated with photosynthetic bacteria, exhibiting a maximum hydrogen yield of 292.9 mL/g(-glutamic acid) during photo-fermentation. The residual solution from photo-fermentation is reused by methanogenic bacteria to produce a maximum methane yield of 102.7 mL/g. The heating value conversion efficiency from glutamic acid to gas fuel significantly increases from 18.9% during photo-fermentation to 40.9% in the combined photo-fermentation and methanogenesis process.