Hythane and methane production in a multistage anaerobic hythane reactor (MAHR): Stages separation, functional microbial selection, thermodynamics and kinetics

A multistage anaerobic hythane reactor (MAHR) that integrated two stages of biohythane and biomethane production into a single reactor, which suggested promising potential of efficient hythane and methane production simultaneously. However, separated hythane and methane production in a single reactor still be a challenge, and stages separation in MAHR is not well understood. Moreover, the requirement of heating preselection of inoculum in acidogenesis and hythane production zone is impractical for full-scale application of MAHR due to extra economic and energy input. Therefore, no-preselected and preselected inocula were adopted in this study to reveal the biofuels production and mechanisms of stages separation in MAHRs with different inoculum strategies. Results indicated that the stable hythane and methane production of MAHR without inoculum preselection could be achieved and maintained after a longer start-up period compared to the inoculum preselected one. A comparable hythane and methane production and organics conversion performance were observed in two MAHRs during stable period, in which hythane with a suitable hydrogen concentration (5-25%) and methane content ranged in 57-75%. Further, microbial diversity, thermodynamics and kinetic analysis revealed that the stages separation was highly dependent on microbial dynamics, metabolism characteristics, and reactor configurations. Acetogens (Desulfovibrio, Syntrophobacter) and aceticlastic methanogens (Methanosaeta, Methanosarcina) are more likely wash out form hythane production zone (Mh) and enriched in methane production zone (Mm) comparing to acidogens (Streptococcus, Rikenellaceae_RC9_gut_group, Bacteroides, etc.) and hydrogenotrophic methanogens (Methanobacterium, Methanobrevibacter). These results deepened the understandings of functional microbial community dynamics and stages separation mechanisms, which provided insights for design, start-up and full-scale operation of MAHR.