Erratum to: Biotechnol Biofuels (2016) 9:254 DOI 10.1186/s13068-016-0666-zAfter this article [1] was published, the authors realised that the funding number for The National Natural Science Foundation of China was incorrect. The correct funding number is as follows: 51561145013, U1562107.

•Fast degradation of human waste and energy recovery via hydrothermal liquefaction.•Biocrude, nutrients and metals in human waste are physically separated via HTL.•Max. liquefied fraction was 87.89%, and highest biocrude yield was 34.44%•HTL is promising for treatment from human wastes, and other wet biowastes.Hydrothermal liquefaction (HTL) is a thermochemical process specifically suitable for treating wet wastes. This study investigated its potential for the production of biocrude oil and the recovery of nutrients and metals from human feces via HTL. Specifically, the effects of temperature (260 °C, 300 °C, 340 °C), retention time (10 min, 30 min, 50 min) and total solid (TS) content (5%, 15%, 25%) were studied. The maximum liquefied fraction was 87.89% and the highest biocrude yield reached 34.44% with a higher heating value of 40.29 MJ/kg. Experimental results showed that 54% of carbon in the human feces was migrated to the biocrude oil while 72% of nitrogen was released to the aqueous phase. In addition, most of heavy and alkaline-earth metal elements in the human feces, including Ca (89%), Mg (81%), Al (88%), Fe (72%) and Zn (94%) were distributed in the solid residue, whereas K (89%) and Na (73%) were mainly dissolved into the aqueous phase. This study demonstrated that the efficient degradation of human waste via HTL without any pretreatment and its potential for the valorization in biocrude oil as well as separated nutrients and metals.Download high-res image (150KB)Download full-size image

Enteromorpha prolifera (Ep), a dominant low-lipid marine macroalgae with about 30% ash content, is seasonally bloomed along the coast of eastern China, whereas crude glycerol is a main byproduct of biodiesel industry. This study focused on the biocrude production from Ep with crude glycerol, in comparison to those from Ep alone, and Ep with glycerol at different reaction temperatures (240 °C −360 °C). The highest biocrude yield of 38.71% was obtained at 320 °C using Ep with crude glycerol (mass ratio: 1:6), which was much higher than those using Ep alone (13.35%) and Ep with glycerol (16.14%) at the same ratios. After the optimization of the mass ratio of Ep to crude glycerol and retention time, the highest biocrude yield further reached 47.28% at a mass ratio (Ep to crude glycerol) of 1:5 and a retention time of 50 min. The addition of crude glycerol significantly improved biocrude production as well as reduced the oil nitrogen content. Elemental analysis indicated the nitrogen contents of biocrude oil from Ep with crude glycerol were nearly less than 1%, much lower than those under other conditions and similar to that of petroleum. This study suggested that the addition of crude glycerol could improve the yield and quality of the biocrude oil from eutrophic low-lipid high-protein algae.

•Study the effect of operational stage on anaerobic fermentation using UASB and PBR.•Higher COD removal and energy recovery were achieved in biohythane system.•Illumina MiSeq sequencing showed notable microbial changes in methane reactors.•Enhanced acetogenesis and acetate-oxidizing in methane reactor in biohythane system.Biohythane consisting of biohydrogen and biomethane via two-stage fermentation is a promising energy carrier for vehicle use. In this study, one-stage biomethane system using upflow anaerobic sludge blanket (UASB) and packed bed reactor (PBR) was shifted to the two-stage biohythane system to study the influence of operational stage. Compared with biomethane system, the biohythane process achieved higher COD removal and energy recovery. Particularly, the total COD removal in the PBR system rose significantly from 74.0 to 97.3%, corresponding to an increased energy recovery from 54.2 to 67.1%. The first-stage hydrogen fermentation had a positive effect on subsequent biomethane production in biohythane system. The analysis of microbial diversity using Illumina MiSeq sequencing showed significant changes of microorganisms in biomethane reactor, which revealed the variation of biochemical pathways. Compared to biomethane system, the relative abundance of acidogenesis bacteria was reduced in biohythane system, such as family Clostridiaceae. By contrast, the amount of acetogens (Syntrophaceae, Syntrophomonadaceae and Desulfovibrionaceae) and acetate-oxidizing bacteria (Spirochaetes) was increased. The archaea community remained stable, and mainly consisted of acetoclastic methanogens from family Methanosaetaceae. These results indicated the biomethane reactors in biohythane system had more efficient acidogenesis and acetate-utilizing microbial community.

•Hydrothermal liquefied wastewater was degraded via microbial electrolysis cell.•Recover hydrogen from hydrothermal liquefied water via microbial electrolysis cell.•High removal of dimethyl phthalate (95.30%) due to dominant genus Xanthobacter.•Proteobacteria and Bacteroidetes were two dominant phyla.Cornstalk, as an abundant renewable biomass resource, could be used for biocrude oil production through hydrothermal liquefaction (HTL), however, recalcitrant wastewater is released as the main byproduct. This study reported the degradation of recalcitrant wastewater and simultaneous hydrogen production via a continuous up-flow fixed-bed microbial electrolysis cell (MEC). Chemical oxygen demand removal rates were over 60% under different applied voltages and the highest reached 80.2% at 1.2 V. Specifically, GC–MS analysis identified recalcitrant organic matter in HTL wastewater like dimethyl phthalate and diethyl phthalate were significantly removed in a ratio of 95.3% and 79.3% via this MEC. A hydrogen production rate of 3.92 mL/L/d was achieved at 1.0 V in the cathode, whereas the maximum power density (305.02 mW/m3) was obtained at 0.6 V. Illumina MiSeq sequencing revealed that the content of phylum Proteobacteria in anodic biofilm (70.19%) was much higher than the inoculum (20.38%). The dominant genus Xanthobacter (58.17%) in anodic biofilm was probably associated with the degradation of dimethyl phthalate. This work suggested that it is feasible to efficiently degrade recalcitrant wastewater from HTL of cornstalk and simultaneously produce hydrogen through MEC.

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.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 family Clostridiaceae, Bacillaceae, and Pseudomonadaceae was 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.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.

•Reaction mode greatly affected hydrogen fermentation and microbial diversity.•UASB showed a higher hydrogen production rate and hydrogen yield than PBR.•Limitation of mass transfer lowered the biohydrogen production in PBR.•PBR had a higher distribution of ethanol and lactic acid producers.•PBR was more favorable for homoacetogenesis and methanogenesis.Biohydrogen production using the high-rate reactor is promising due to its ability of maintaining higher biomass concentrations through forming granules or biofilms. This study investigated the effect of reaction mode on hydrogen fermentation by comparing an upflow anaerobic sludge blanket (UASB) and a packed bed reactor (PBR). UASB and PBR were operated for 120 days at hydraulic retention time (HRT) of 24-12 h and organic loading rates (OLRs) of 0.96–15.36 g COD/L/d. Both UASB and PBR achieved maximal hydrogen production rates as 2.77 ± 0.18 and 1.28 ± 0.12 L/L/d, respectively, at 15.36 g COD/L/d, corresponding to hydrogen yields of 1.44 ± 0.01 and 0.67 ± 0.06 mol/mol glucose. Illumina MiSeq sequencing results revealed Clostridium sp. was the dominant microbial consortium for hydrogen production in UASB (92.1%) and PBR (71.7%). Compared to UASB, PBR showed a greater microbial diversity of ethanol and lactic acid producers, and may be more favorable for methanogenesis and homoacetogenesis. This study demonstrates that reaction mode significantly influenced microbial diversity and biohydrogen production.

•Decrease of HRT suppressed methanogens and homoacetogens in UASB and PBR.•Responses of H2 production and biodiversity to HRT in UASB and PBR were studied.•Low HRT decreased relative abundance of main hydrogen-producers Clostridiaceae.•Low HRT accelerated the proliferation of lactate and ethanol-producers.Methanogenesis and homoacetogenesis are two notorious hydrogen-consuming reactions during dark fermentation for biohydrogen production. The focus of this study was on the role of hydraulic retention time (HRT) to control methanogenesis and homoacetogenesis in an upflow anaerobic sludge blanket (UASB) reactor and a packed bed reactor (PBR). The HRT was changed from 24 to 4 h and 24 to 2 h in the UASB and PBR, respectively. A maximal hydrogen yield of 1.47 mol/mol glucoseadded with a high hydrogen production rate of 4.38 L/L/d was achieved at 8 h HRT in UASB. In comparison, a maximal hydrogen yield of 0.89 mol/mol glucoseadded with a high hydrogen production rate of 10.66 L/L/d was achieved at 2 h in PBR. With the reduction of the HRT, the volumic hydrogen consumption due to methanogenesis in the UASB was decreased from 12.1 to 3.1%. As for PBR, the value was reduced from 66.9 to 31.4%. Homoacetogenesis in the UASB and PBR was dramatically suppressed when the HRT was decreased to 8 and 4 h, respectively. However, these hydrogen-consuming microbes cannot be completely removed. Microbial diversity analysis using Illumina MiSeq sequencing revealed the existence of Clostridium ljungdahlii, a homoacetogen, in UASB and PBR at low HRT. In addition, the low HRT reduced relative abundance of Clostridiaceae and accelerated the proliferation of lactic acid producers and ethanol producers in the UASB and PBR, which were mainly from the families Ruminococcaceae and Leuconostocaceae.

•A novel sensor system was established combining MFC, gas flow meter and pH meter.•Variations of sensor signals were more valuable for diagnosis of anaerobic process.•MFC exhibited compatible signal variations with pH and gas flow meters.•Transient responses of sensor signals were observed subject to disturbances.Process diagnosis is essential to ensure anaerobic fermentation stable and efficient. Here, a novel sensor system combining microbial fuel cell (MFC), gas flow meter and pH meter was developed to evaluate its feasibility for probing the anaerobic process established on a model high-rate bioreactor. Repeated transient responses of electrical signal, proton concentration, and gas flow rate, were observed subject to external disturbances. The transient response lasted from <1 h to 6 h. In addition, MFC obtained compatible signal variations with other sensors, and biofilm MFC (MFCBiofilm) resulted in better agreements than control MFC (MFCControl). These results revealed that 1) the composite sensor system was capable to probe anaerobic process, suggesting a novel approach for process analysis and diagnosis of biogas or biohydrogen production; 2) the variations of sensor signals might provide more valuable information for process diagnosis than sensor signals themselves.