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

► Glutamic acid was subjected to acidogenic pretreatment to produce metabolites. ► Acidulated solution was treated with zeolite to decrease the NH4+ concentration. ► Pretreated solution was incubated with photosynthetic bacteria to produce H2. ► Residual solution was reused to generate CH4 in sequential methanogenesis. ► H2 and CH4 cogeneration from glutamic acid enhanced energy conversion efficiency. 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 NH4+ 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 NH4+, shows a decrease in NH4+ concentration from 36.7mM to 3.2mM (NH4+ removal efficiency of 91.1%). After NH4+ removal, the treated solution is incubated with photosynthetic bacteria, exhibiting a maximum hydrogen yield of 292.9mL/g(-glutamic acid) during photo-fermentation. The residual solution from photo-fermentation is reused by methanogenic bacteria to produce a maximum methane yield of 102.7mL/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.