Biomethane generation in an AnSBBR treating effluent from the biohydrogen production from vinasse: Optimization, metabolic pathways modeling and scale-up estimation

A study was performed regarding the production of methane by an AnSBBR treating wastewater coming from a biohydrogen production process using vinasse (sugar cane stillage). The reactor operated with recirculation of liquid phase in sequencing batch and fed-batch mode. The influence of the applied volumetric organic load (AVOL) was examined by varying influent concentration between 1000 and 4500 mgCOD L−1 (1.5–6.6 kgCOD m−3 d−1). Increasing AVOL resulted in a decrease in organic matter removal efficiency and in an increase in methane productivity. The highest productivity (133.1 molCH4 m−3 d−1) was obtained in fed-batch operation at the highest AVOL. Methane productivity and yield were always higher for fed-batch operation. From the kinetic metabolic model, it was possible to infer that methane is mainly produced via the acetoclastic route in batch mode and via both acetoclastic and hydrogenotrophic routes in fed-batch mode. Energy production of the two-stage system (acidogenic/biohydrogen-methanogenic/methane) was 13.6 kJ per gram of applied COD, which corresponds to a 38.8% increase compared to the traditional one-stage system (methanogenic/methane). The scale-up assessment (based on industrial production and performed with best condition data) proposed an operation of six parallel hydrogen-producing reactors of 6076 m3 each followed by four parallel methane-producing reactors of 1720 m3 each.