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.

将两级产氢甲烷（biohythane）与生物甲烷生产工艺整合于单一反应器内的多级厌氧产氢甲烷反应器（multistage anaerobic hythane reactor, MAHR），展现出同步高效生产产氢甲烷与生物甲烷的良好应用前景。然而，在单一反应器中实现产氢甲烷与生物甲烷的分置生产仍颇具挑战，且MAHR的阶段分离机制尚未得到充分阐释。此外，在产酸阶段与产氢甲烷生产区域对接种物进行加热预筛选的要求，会因额外的经济与能源投入，难以适配MAHR的规模化应用。为此，本研究分别采用未预筛选与预筛选的接种物，探究不同接种策略下MAHR的生物燃料生产性能与阶段分离机制。结果表明，与采用预筛选接种物的反应器相比，未预筛选接种物的MAHR需经过更长的启动周期，方可实现并维持稳定的产氢甲烷与生物甲烷生产。在稳定运行阶段，两组MAHR的产氢甲烷与生物甲烷生产性能、有机物转化效率均相当，其中产氢甲烷的氢气浓度处于5%~25%的适宜区间，甲烷含量则介于57%~75%之间。进一步通过微生物多样性、热力学与动力学分析发现，阶段分离高度依赖微生物群落动态、代谢特征以及反应器构型。与产酸菌（如链球菌属（Streptococcus）、Rikenellaceae_RC9_gut_group、拟杆菌属（Bacteroides）等）和氢营养型产甲烷菌（如甲烷杆菌属（Methanobacterium）、甲烷短杆菌属（Methanobrevibacter））相比，产乙酸菌（如脱硫弧菌属（Desulfovibrio）、互营杆菌属（Syntrophobacter））与乙酸型产甲烷菌（如甲烷鬃菌属（Methanosaeta）、甲烷八叠球菌属（Methanosarcina））更易在产氢甲烷生产区域（Mh）中流失，并在生物甲烷生产区域（Mm）内富集。上述研究结果加深了对功能微生物群落动态与阶段分离机制的理解，可为MAHR的设计、启动以及规模化运行提供理论参考。