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Low biological hydrogen (bioH2) production due to non-optimal metabolic pathways occurs frequently. In this work, magnetic nitrogen-doped activated carbon (MNAC) was prepared and added into the inoculated sludge with glucose as substrate to enhance hydrogen (H2) yield by mesophilic dark fermentation (DF). The highest H2 yield appeared in 400 mg/L AC (252.8 mL/g glucose) and 600 mg/L MNAC group (304.8 mL/g glucose), which were 26.02% and 51.94% higher than that of 0 mg/L MNAC group (200.6 mL/g glucose). The addition of MNAC allowed for efficient enrichment of Firmicutes and Clostridium-sensu-stricto-1, accelerating the metabolic pathway shifted towards butyrate type. The Fe ions released by MNAC facilitated electron transfer and favored the reduction of ferredoxin (Fd), thereby obtaining more bioH2. Finally, the generation of [Fe-Fe] hydrogenase and cellular components of H2-producing microbes (HPM) during homeostasis was discussed to understand on the use of MNAC in DF system. [ABSTRACT FROM AUTHOR]

Manganese doped magnetic carbon (MDMC) was synthesized to enhance bio-hydrogen (H 2) process under the mesophilic and thermophilic conditions. MDMC characterization showed that MnFe 2 O 4 , Fe 2 O 3 and few MnCO 3 were adhered to activated carbon and formed MDMC whose specific surface area and average pore size were 110.92 m2·g−1 and 3.2 nm, respectively. Suitable concentration of MDMC promoted while high dosage suppressed the H 2 production of glucose through anaerobic fermentation by heat-treated sludge. The highest yields of 211 and 148 ml H 2 /g glucose were obtained at 400 mg/L (37 °C) and 600 mg/L MDMC (55 °C), being 55.8% and 19.3% higher than that of the control groups, respectively. Some possible mechanisms were proposed as follows: appropriate concentration of MDMC provided considerable and favorable sites for microbial colonization, released trace elements (e.g. Mn, Fe) into liquid for the microbial growth, and promoted the direct inter-species electron transfer. Moreover, MDMC could be recycled by magnetic separation after bio-H 2 process due to its magnetism. MnFe 2 O 4 , Fe 2 O 3 and few MnCO 3 were adhered to activated carbon, fabricating the manganese doped magnetic carbon (MDMC) that was employed to stimulate bio- hydrogen (H 2) production. Results showed that suitable amount of MDMC increased H 2 yield through providing a composite carrier and trace elements like Fe and Mn for H 2 production bacteria. MDMC could be also recycled via magnetic separation after the bio-process due to its magnetism. Image 1 • MDMC was synthesized, containing MnFe 2 O 4 , Fe 2 O 3 , MnCO 3 and AC. • Suitable addition of MDMC obtained the highest H 2 yield in bio-H 2 process. • The H 2 yields amended with MDMCs increased by 9.6–55.8 %. • MDMC enriched bacteria and promoted their growths and H+ transfer rates. • MDMC could be recycled by magnetic separation after bio-H 2 production. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrothermal carbon was used as an additive to enhance dark fermentation. • 600 mg/L Fe-HCM addition enhanced biohydrogen yield by 59%. • HCM and Fe-HCM enhanced the butyric acid-based fermentation pathway. • HCM and Fe-HCM raised the abundance level of Firmicutes from 35% to 41% and 56%. Dark fermentation (DF) for hydrogen (H 2) evolution is often limited to industrial application due to its low H 2 yield. In this work, hydrothermal carbon microspheres (HCM) and iron modified HCM (Fe-HCM) were prepared by hydrothermal process using waste corn cob. Subsequently, HCM and Fe-HCM were used in DF for more H 2. The highest H 2 yields amended with HCM and Fe-HCM at 600 mg/L were achieved to be 119 and 154 mL/g glucose (0.87 and 1.2 mol H 2 /mol glucose), respectively, being 24% and 59% higher than that of control yield. Soluble metabolites revealed HCM and Fe-HCM promoted butyric acid-based DF. Microbial composition depicted that HCM and Fe-HCM improved the abundance level of Firmicutes from 35% to 41% and 56%, while the abundance level of Clostridium_sensu_stricto_1 rose from 25% to 38% and 51%, respectively. This provides valuable guidance for hydrothermal carbon used in biofuel production. [ABSTRACT FROM AUTHOR]

Hydrogen (H 2 ) gas represents renewable resource candidate to traditional energy resource. Methods to promote the H 2 evolution rate attract increasing attentions. In the present research, ferric oxide/carbon nanoparticles (FOCNPs) were synthesized and evaluated the feasibility to enhance the production rate of H 2 gas from glucose through anaerobic fermentation by mixed bacteria. The results demonstrated that appropriate dose of FOCNPs promoted, while excessive concentration of FOCNPs suppressed the production of H 2 . Addition of 200 mg/L FOCNPs resulted in the highest yield of 218.63 ml H 2 /g glucose, 33.7% higher than 163 ml H 2 /g glucose of the control test without addition of FOCNPs. However, 400 mg/L of FOCNPs inhibited the H 2 evolution to 154 ml/g glucose, 5.5% lower than the control. It was revealed that the H 2 evolution followed the acetic pathways. The FOCNPs had a specific surface area of 27.63 m 2 /g, and thus addition of FOCNPs could provide more attachment sites for the growth of anaerobes. Moreover, FOCNPs could promote the activity of hydrogenase and electron transfer efficiency, beneficial for the bio-H 2 evolution. However, excessive addition of FOCNPs could be toxic to microbes, and further suppressing the H 2 production. The present research provided an effective method to promote the evolution rate of H 2 gas. [ABSTRACT FROM AUTHOR]

This paper investigated the utilization of calcined-red mud (CRM) pretreatment to enhance fermentative hydrogen yields from brewers’ spent grain (BSG). The BSG samples were treated with different concentrations (0.0–20 g/L) of CRM at 55 °C for 48 h, before the biohydrogen process with heat-treated anaerobic sludge inoculum. The highest specific hydrogen production of 198.62 ml/g-VS was obtained from the BSG treated with 10 g/L CRM, with the corresponding lag time of 10.60 h. Hydrogen yield increments increased by 67.74%, compared to the control tests without CRM. The results demonstrated that the CRM could hydrolyze more cellulose and further provided adequate broth and suitable pH value for efficient fermentative hydrogen. The model-based analysis showed that the modified Gompertz model presented a better fit for the experimental data than the first-order model. [ABSTRACT FROM AUTHOR]

This study investigated the use of calcined-lime mud from papermaking process (CLMP) pretreatment to improve fermentative hydrogen yields from corn-bran residue (CBR). CBR samples were pretreated with different concentrations (0–15 g/L) of CLMP at 55 °C for 48 h, prior to the thermophilic fermentation with heat-treated anaerobic sludge inoculum. The maximum hydrogen yield (MHY) of 338.91 ml/g-VS was produced from the CBR pretreated with 10 g/L CLMP, with the corresponding lag-phase time of 8.24 h. Hydrogen yield increments increased from 27.76% to 48.07%, compared to the control. The CLMP hydrolyzed more cellulose, which provided adequate substrates for hydrogen production. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen production via anaerobic fermentation may suffer from instability or inhibition due to volatile fatty acids concentrations and inorganic elements deviations from optimality. A slight addition of white mud from ammonia–soda process (WMA) to the fermentation may show a feasible implement approach to use as buffer and inorganic nutrient. Batch tests were conducted to study the effect of the WMA addition on the hydrogen fermentation of food waste (FW) for the purpose of the maximum hydrogen yield (MHY) while achieving process stability and microbial germination through the endogenous alkalinity and inorganic elements of WMA. This was attributed to the existence of calcium, sodium, magnesium, potassium and alkali-rich materials, like calcium carbonate. 3 g of WMA addition to 200 g FW and fermentation time of 36 h resulted in obtaining the MHY of 145.4 mL H2/g VS, with a corresponding lag-phase time of 3.0 h. Under these operating conditions, the fermentation process demonstrated one of the highest measured stability with final pH 5.3. [Copyright &y& Elsevier]

[Display omitted] • CoAl 0.2 Fe 1.8 O 4 and CoCu 0.2 Fe 1.8 O 4 NPs were synthesized to raise bioH 2 yield. • Humic acids were reduced by addition of CoAl 0.2 Fe 1.8 O 4 or CoCu 0.2 Fe 1.8 O 4 NPs. • CoAl 0.2 Fe 1.8 O 4 acted on cell membrane while CoCu 0.2 Fe 1.8 O 4 acted on EPS. • CoCu 0.2 Fe 1.8 O 4 obtained Clostridium_sensu_stricto_1 more than CoAl 0.2 Fe 1.8 O 4. • CoCu 0.2 Fe 1.8 O 4 NPs improved H 2 yield more than CoAl 0.2 Fe 1.8 O 4 NPs. Two various materials, copper and aluminum doped cobalt ferrite nanoparticles (NPs) were fabricated for investigating their effects of addition amounts on hydrogen (H 2) synthesis and process stability. CoCu 0.2 Fe 1.8 O 4 NPs enhanced H 2 production more than CoAl 0.2 Fe 1.8 O 4 NPs under same condition. The highest H 2 yield of 212.25 ml/g glucose was found at optimal dosage of 300 mg/L CoCu 0.2 Fe 1.8 O 4 NPs, revealing the increases of 43.17% and 6.67% compared with the control without NPs and 300 mg/L CoAl 0.2 Fe 1.8 O 4 NPs groups, respectively. NPs level of more than 400 mg/L inhibited H 2 generation. Further investigations illustrated that CoCu 0.2 Fe 1.8 O 4 NPs were mainly distributed on extracellular polymer substance while CoAl 0.2 Fe 1.8 O 4 NPs were mostly enriched on cell membrane, which facilitated electron transfer behavior. Community structure composition demonstrated that CoCu 0.2 Fe 1.8 O 4 and CoAl 0.2 Fe 1.8 O 4 separately caused a 9.67% and 9.03% increase in Clostridium sensu stricto 1 compared with the control reactor without NPs exposure. [ABSTRACT FROM AUTHOR]

Abstract: The effect of lime mud from paper-making process (LMP) addition on the H2 fermentation of food waste (FW) was investigated. It was found that a slight addition of LMP (1.0–4.0 g in 200 g FW) significantly enhanced the H2 fermentation performance, not only increasing the total amount of H2 produced but also accelerating the whole reaction, shortening the lag period, and increasing the H2 production rate. Fermentation stability and microbial germination were also facilitated by LMP addition. This was attributed to the existence of Ca, Fe, Mn and alkaline substances such as CaCO3 and NaOH. The batch process treating a mixture of FW and LMP was showed that the highest hydrogen production of 137.6 mL H2/g VS was achieved at final pH 5.0, adding 3 g LMP (in 200 g FW) to the fermentation process, which lag-phase time was about 2.5 h. [Copyright &y& Elsevier]

In this work, the cobalt ferrate nanoparticles were prepared by a sol-gel method for investigating their influence on hydrogen production from dark fermentation. A moderate amounts (0.1–0.4 g/L) of these nanoparticles effectively enhanced the fermentation process. The highest hydrogen yield of 205.24 mL/g glucose was achieved at a dosing level of 0.4 g/L, which was a 31.8% enhancement compared to the control, while excess (0.5 g/L) nanoparticles decreased the hydrogen production by 9.7% compared to the control group. The mechanism analysis exhibited that the nanoparticles could either attach to the microbial surface or enter the cell interior without destroying the cell integrity, which promoted the electron transfer to anaerobes and stimulated the activities of hydrogen-producing enzymes such as enzymes and coenzymes. The microbial community revealed that a moderate amount of cobalt ferrate nanoparticles increased the abundance of Clostridium sensu stricto 1 from 14.49% to 18.84%, which was dominant and favored the sustainable conversion of glucose wastewater into clean hydrogen. [Display omitted] • Cobalt ferrate nanoparticles (CoFe 2 O 4 NPs) were synthesized to increase H 2 yield. • BioH 2 production was enhanced by 31.8% with 0.4 g/L CoFe 2 O 4 NPs. • CoFe 2 O 4 NPs changed the type of fermentation to butyric acid fermentation. • CoFe 2 O 4 NPs promoted microbial activity by acting on the microbial interface. • CoFe 2 O 4 NPs improved the abundance of Clostridium_sensu_stricto_1. [ABSTRACT FROM AUTHOR]

To solve the thermodynamic limitations on the hydrogen (H 2) yield by dark fermentation (DF), the conductive carbons are usually used to mediate the H 2 -DF. In this work, the nitrogen (N)-phosphorus (N) doped starch carbon (NPSC) was prepared and characterized to investigate its influence on H 2 -DF. NPSC effectively raise H 2 yield compared with starch-derived carbon (SC). The optimal dosage of SC (400 mg/L) and NPSC (600 mg/L) caused the highest H 2 yield of 219.5 and 261.2 mL/g glucose, respectively, being higher than the control yield (161.4 mL/g glucose). Factually, compared with the control group without any carbon, NPSC optimized the microbial community structure and increased the abundance of C. butyricum from 19.09% to 30.87%. This fact increased the shift of metabolic pathway to butyric acid evolution, thereby promoting the substrate conversion level to H 2. [Display omitted] • Nitrogen and phosphorus doped starch carbon (NPSC) promoted electron transfer. • Optimal dosage of starch-derived carbon (SC) and NPSC were 400 and 600 mg/L. • NPSC enriched Clostridium butyricum more efficient than SC and control groups. • Metabolism analysis revealed NPSC raised the microbial activity in H 2 evolution. • The highest H 2 yields of SC and NPSC groups were 219.5 and 261.2 mL/g glucose. [ABSTRACT FROM AUTHOR]

This work has been performed to investigate the use of lime mud filtrate (LMF) pretreatment to enhance hydrogen (H2) evolution from sewage sludge (SS). The SS samples were pretreated with LMF (pH 8.0-11.0) at 55 °C for 48 h, prior to the H2 fermentation. The maximum H2 yield of 38.30 ml/g-VS (volatile solid) was obtained from the SS pretreated by LMF pH of 10.0, with the corresponding lag time of 3.10 h, which was well described by the modified Gompertz model. Adequate pH of LMF facilitated the solubilization of SS and the release of organic matters, providing adequate substrates for subsequent bio-H2 evolution. The soluble chemical oxygen demand was increased from 25.0 to 91.7%, as compared with the control test without LMF soak. However, further increase in pH of LMF could decrease the concentration of available substrate, thus reducing the H2 yield. This technique revealed sustainable waste management and energy recovery. [ABSTRACT FROM AUTHOR]