title: Continuous production of biohythane from hydrothermal liquefied cornstalk biomass via two-stage high-rate anaerobic reactors.
abstract: BACKGROUND
  Biohythane production via two-stage fermentation is a promising direction for sustainable energy recovery from lignocellulosic biomass. However, the utilization of lignocellulosic biomass suffers from specific natural recalcitrance. Hydrothermal liquefaction (HTL) is an emerging technology for the liquefaction of biomass, but there are still several challenges for the coupling of HTL and two-stage fermentation. One particular challenge is the limited efficiency of fermentation reactors at a high solid content of the treated feedstock. Another is the conversion of potential inhibitors during fermentation. Here, we report a novel strategy for the continuous production of biohythane from cornstalk through the integration of HTL and two-stage fermentation. Cornstalk was converted to solid and liquid via HTL, and the resulting liquid could be subsequently fed into the two-stage fermentation systems. The systems consisted of two typical high-rate reactors: an upflow anaerobic sludge blanket (UASB) and a packed bed reactor (PBR). The liquid could be efficiently converted into biohythane via the UASB and PBR with a high density of microbes at a high organic loading rate.
  
  
  RESULTS
  Biohydrogen production decreased from 2.34 L/L/day in UASB (1.01 L/L/day in PBR) to 0 L/L/day as the organic loading rate (OLR) of the HTL liquid products increased to 16 g/L/day. The methane production rate achieved a value of 2.53 (UASB) and 2.54 L/L/day (PBR), respectively. The energy and carbon recovery of the integrated HTL and biohythane fermentation system reached up to 79.0 and 67.7%, respectively. The fermentation inhibitors, i.e., 5-hydroxymethyl furfural (41.4-41.9% of the initial quantity detected) and furfural (74.7-85.0% of the initial quantity detected), were degraded during hydrogen fermentation. Compared with single-stage fermentation, the methane process during two-stage fermentation had a more efficient methane production rate, acetogenesis, and COD removal. The microbial distribution via Illumina MiSeq sequencing clarified that the biohydrogen process in the two-stage systems functioned not only for biohydrogen production, but also for the degradation of potential inhibitors. The higher distribution of the detoxification familyClostridiaceae,Bacillaceae, andPseudomonadaceaewas found in the biohydrogen process. In addition, a higher distribution of acetate-oxidizing bacteria (Spirochaetaceae) was observed in the biomethane process of the two-stage systems, revealing improved acetogenesis accompanied with an efficient conversion of acetate.
  
  
  CONCLUSIONS
  Biohythane production could be a promising process for the recovery of energy and degradation of organic compounds from hydrothermal liquefied biomass. The two-stage process not only contributed to the improved quality of the gas fuels but also strengthened the biotransformation process, which resulted from the function of detoxification during biohydrogen production and enhanced acetogenesis during biomethane production.
authors.affiliation: Laboratory of Environment-Enhancing Energy (E2E), and Key Laboratory of Agricultural Engineering in Structure and Environment, Ministry of Agriculture, College of Water Resources and Civil Engineering, China Agricultural University, Beijing, 100083 China.
authors.forename: Bu-Chun
authors.initials: BC
authors.lastname: Si
authors.affiliation: Laboratory of Environment-Enhancing Energy (E2E), and Key Laboratory of Agricultural Engineering in Structure and Environment, Ministry of Agriculture, College of Water Resources and Civil Engineering, China Agricultural University, Beijing, 100083 China.
authors.forename: Jia-Ming
authors.initials: JM
authors.lastname: Li
authors.affiliation: Laboratory of Environment-Enhancing Energy (E2E), and Key Laboratory of Agricultural Engineering in Structure and Environment, Ministry of Agriculture, College of Water Resources and Civil Engineering, China Agricultural University, Beijing, 100083 China.
authors.forename: Zhang-Bing
authors.initials: ZB
authors.lastname: Zhu
authors.affiliation: Department of Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign, Urbana, 61801 USA.
authors.forename: Yuan-Hui
authors.initials: YH
authors.lastname: Zhang
authors.affiliation: Laboratory of Environment-Enhancing Energy (E2E), and Key Laboratory of Agricultural Engineering in Structure and Environment, Ministry of Agriculture, College of Water Resources and Civil Engineering, China Agricultural University, Beijing, 100083 China.
authors.forename: Jian-Wen
authors.initials: JW
authors.lastname: Lu
authors.affiliation: Laboratory of Environment-Enhancing Energy (E2E), and Key Laboratory of Agricultural Engineering in Structure and Environment, Ministry of Agriculture, College of Water Resources and Civil Engineering, China Agricultural University, Beijing, 100083 China.
authors.forename: Rui-Xia
authors.initials: RX
authors.lastname: Shen
authors.affiliation: Key Laboratory of Industrial Biocatalysis of Ministry of Education of China, Beijing, 100084 China ; Department of Chemical Engineering, Institute of Biochemical Engineering, Tsinghua University, Beijing, 100084 China.
authors.forename: Chong
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Industrial Biocatalysis of Ministry of Education of China, Beijing, 100084 China ; Department of Chemical Engineering, Institute of Biochemical Engineering, Tsinghua University, Beijing, 100084 China.
authors.forename: Xin-Hui
authors.initials: XH
authors.lastname: Xing
authors.affiliation: Laboratory of Environment-Enhancing Energy (E2E), and Key Laboratory of Agricultural Engineering in Structure and Environment, Ministry of Agriculture, College of Water Resources and Civil Engineering, China Agricultural University, Beijing, 100083 China.
authors.forename: Zhidan
authors.initials: Z
authors.lastname: Liu
keywords: Biohythane production; Biomass; Hydrothermal liquefaction; Microbial community; Two-stage fermentation