Biogas production from hydrothermal liquefaction wastewater (HTLWW): Focusing on the microbial communities as revealed by high-throughput sequencing of full-length 16S rRNA genes

Abstract

Hydrothermal liquefaction (HTL) is an emerging and promising technology for the conversion of wet biomass into bio-crude, however, little attention has been paid to the utilization of hydrothermal liquefaction wastewater (HTLWW) with high concentration of organics. The present study investigated biogas production from wastewater obtained from HTL of straw for bio-crude production, with focuses on the analysis of the microbial communities and characterization of the organics. Batch experiments showed the methane yield of HTLWW (R-HTLWW) was 184 mL/g COD, while HTLWW after petroleum ether extraction (PE-HTLWW), to extract additional bio-crude, had higher methane yield (235 mL/g COD) due to the extraction of recalcitrant organic compounds. Sequential batch experiments further demonstrated the higher methane yield of PE-HTLWW. LC-TOF-MS, HPLC and gel filtration chromatography showed organics with molecular weight (MW) < 1000 were well degraded. Results from the high-throughput sequencing of full-length 16S rRNA genes analysis showed similar microbial community compositions were obtained for the reactors fed with either R-HTLWW or PE-HTLWW. The degradation of fatty acids were related with Mesotoga infera, Syntrophomonas wolfei et al. by species level identification. However, the species related to the degradation of other compounds (e.g. phenols) were not found, which could be due to the presence of uncharacterized microorganisms. It was also found previously proposed criteria (97% and 98.65% similarity) for species identification of 16S rRNA genes were not suitable for a fraction of 16S rRNA genes.

Methane potentials of wastewater generated from hydrothermal liquefaction of rice straw: focusing on the wastewater characteristics and microbial community compositions

“…Only our previous study made such analysis and found Firmicutes was dominant in the microbial community during AD of HTLWW [10], which was consistent with the present study. It should be noted that Proteobacteria was also dominant in the samples of the present study.…”

“…However, the HTLWW in the above study was not well characterized. Our recent publication showed that the methane yield of HTLWW obtained from HTL of straw at 27 days can be enhanced by organic solvent extraction, and the HTLWW conversion efficiency was 53% [10]. A biohythane production [11] for high energy recovery and carbon recovery is 79.0 and 67.7%, respectively, from HTL cornstalk, but it was limited by low hydrogen fermentation performance.…”

“…Different technologies have been applied to characterize the organics in wastewater originated from different sources (Landfill leachate, sludge hydrolysate, straw hydrolysate, etc.) [10, 21, 22]. For example, GC–MS was used to identify the main classes of molecules compositions, GC-FID was used to quantify the C 2 –C 6 fatty acids, 3D-EEM fluorescence spectroscopy was used to identify fluorescent organics, and size distribution analysis was used to understand the physical characteristic of organics.…”

Treatment of recalcitrant wastewater and hydrogen production via microbial electrolysis cells

“…Hydrothermal liquefaction (HTL) is a promising and attractive thermo-chemical conversion technology, which can directly transform wet biomass to valuable biocrude oil at high temperatures (200°C-370°C) and pressures (20-23 MPa) [44] , which can be further refined into transportation fuels. However, PHWW is created as one of the main by-products during this process [45] .…”

Molecular microbial ecology of stable versus failing rice straw anaerobic digesters

“…In particular, how RS AD microbial populations respond to different FFs and OLRs is largely unknown, especially for shock loads (Mei et al , ). Some studies have investigated microbial communities in RS AD (Nakakihara et al , ; Yan et al , ; Chen et al , ), but the range of conditions has been limited. Further, no studies have assessed the effect of different FFs on AD microbial community conditions.…”