Enhanced dark fermentative hydrogen production under the effect of zero-valent iron shavings

Dark fermentative hydrogen production under the effect of zero-valent metal shavings (iron, aluminum and copper) was studied by using a sucrose medium and a mixed bacterial consortium. The iron shavings were found to be unique to promote the hydrogen production, the hydrogen yield obtained from an optimal dose of 8–16 g/L reached 4.2 mol/mol hexose, doubled compared with that obtained from the control without addition of the iron shavings. The effect was more obvious in low pH buffered medium than in higher buffered medium. The aluminum and copper shavings were either inert or toxic to the cultivation. It is evident that the addition of the zero-valent iron helped maintaining the pH to an optimal range for hydrogen production and drove more reducing equivalents to the production of hydrogen. A microbial corrosion system mediated by the hydrogen producing bacteria was proposed to be responsible for the improvement of hydrogen production.     

Phytosynthesized iron oxide nanoparticles and ferrous iron on fermentative hydrogen production using Enterobacter cloacae: Evaluation and comparison of the effects

The effects of FeSO₄ and synthesized iron oxide nanoparticles (0–250 mg/L) on fermentative hydrogen production from glucose and sucrose, using Enterobacter cloacae were investigated, to find out the enhancement of efficiency. The maximum hydrogen yields of 1.7 ± 0.017 mol H₂/mol glucose and 5.19 ± 0.12 mol H₂/mol sucrose were obtained with 25 mg/L of ferrous iron supplementation. In comparison, the maximum hydrogen yields of 2.07 ± 0.07 mol H₂/mol glucose and 5.44 ± 0.27 mol H₂/mol sucrose were achieved with 125 mg/L and 200 mg/L of iron oxide nanoparticles, respectively. These results indicate that the enhancement of hydrogen production on the supplementation of iron oxide nanoparticles was found to be considerably higher than that of ferrous iron supplementation. The activity of E. cloacae in a glucose and sucrose fed systems was increased by the addition of iron oxide nanoparticles, but the metabolic pathway was not changed. The results revealed that the glucose and sucrose fed systems conformed to the acetate/butyrate fermentation type.     

Effect of extrinsic lactic acid on fermentative hydrogen production

In this paper we report the effect of extrinsic lactic acid on hydrogen production from a starch-containing medium by a mixed culture. Study of the effect of addition of four metabolites, namely ethanol, lactic acid, butyric acid and acetic acid illustrated that lactic acid had a positive effect on both the maximum hydrogen production and hydrogen production rate. The addition of 10 mM lactic acid to a batch containing starch increased the hydrogen production rate and hydrogen production yield from 4.31 to 8.23 mL/h and 5.70 to 9.08 mmol H₂/g starch, respectively. This enhancement in hydrogen production rate and yield was associated with a shift from acetic acid and ethanol formation to formation of butyric acid as the predominant metabolite. The increase in hydrogen production yield was attributed to the increase in the available residual NADH for hydrogen production. When lactic acid was used as the sole carbon source, no significant hydrogen production was observed.     

Enhancement effect of gold nanoparticles on biohydrogen production from artificial wastewater

It was the first time to study the enhancement effect of nanometer-sized gold particles on fermentative hydrogen production from artificial wastewater. A biohydrogen production system coupling the polysaccharide degradation by two cultures and hydrogen production using gold nanoparticles as a catalyst was investigated. Data were obtained from tests operating with cultures enriched from natural environment, which included preheat-treated mixed culture and non-heat-treated mixed culture. The percentages and yields of hydrogen produced in the tests using gold nanoparticles were all higher than the corresponding blank test. The tests with 5-nm-gold particles behaved better than others, especially for the preheat-treated one. The maximum cumulative yield of hydrogen obtained at the test with 5-nm-gold particles was 4.48 mol per mol sucrose, which represents the conversion efficiency of sucrose to hydrogen reached 56%. The results indicated that gold nanoparticles could remarkably improve the bioactivity of hydrogen-producing microbes and the enhancement effect strongly depended on the size of gold particles. This work suggests a promising method to enhance the catalytic activity of hydrogenases in the microbes and will be of great importance in biohydrogen production.     

Effect of temperature on fermentative hydrogen production by mixed cultures

Effect of temperatures ranging from 20 °C to 55 °C on fermentative hydrogen production by mixed cultures was investigated in batch tests. The experimental results showed that, at initial pH 7.0, during the fermentative hydrogen production using glucose as substrate, the substrate degradation efficiency and hydrogen production potential increased with increasing temperatures from 20 °C to 40 °C. The maximal substrate degradation efficiency was 98.1%, the maximal hydrogen production potential was 269.9 mL, the maximal hydrogen yield was 275.1 mL/g glucose and the shortest lag time was 7.0 h. The temperature for fermentative hydrogen production by mixed cultures was optimized to be 40 °C. The expanded Ratkowsky models could be used to describe the effect of temperatures on the hydrogen production potential, maximum hydrogen production rate and the lag time during fermentative hydrogen production.     

Extreme-thermophilic biohydrogen production from lignocellulosic bioethanol distillery wastewater with community analysis of hydrogen-producing microflora

Extreme-thermophilic biohydrogen production from distillery wastewater was investigated in batch and continuous-mode operation. Hydrogen-producing mixed culture was enriched by repeated batch cultivations. Effect of temperature and pH on biohydrogen yield was investigated in batch experiments. The highest hydrogen yield of 196. mL/g-volatile solids_addded (VS_added) was obtained at 70 °C and pH 7.0 in batch culture. Continuous biohydrogen production was performed in CSTR reactor with yield of 172.0 mL/g-VS_added at HRT (hydraulic retention time) of 4 days. The main metabolic products were acetate, lactate, and ethanol. Community structure of hydrogen-producing microflora was investigated by 16S rRNA gene sequence analysis. The microorganisms involved in both batch and continuous-mode operation were similar and hydrogen production was carried out by a group of extreme-thermophilic bacterial species related to Thermotoga, Coprothermobacter, Caldanaerobacter, Thermobrachium, and Caldicellulosiruptor.     

Effect of substrate concentration on fermentative hydrogen production from sweet sorghum extract

The aim of the present study was to assess the influence of substrate concentration on the fermentative hydrogen production from sweet sorghum extract, in a continuous stirred tank bioreactor. The reactor was operated at a Hydraulic Retention Time (HRT) of 12 h and carbohydrate concentrations ranging from 9.89 to 20.99 g/L, in glucose equivalents. The maximum hydrogen production rate and yield were obtained at the concentration of 17.50 g carbohydrates/L and were 2.93 ± 0.09 L H₂/L reactor/d and 0.74 ± 0.02 mol H₂/mol glucose consumed, corresponding to 8.81 ± 0.02 L H₂/kg sweet sorghum, respectively. The main metabolic product at all steady states was butyric acid, while ethanol production was high at high substrate concentrations. The experiments showed that hydrogen productivity depends significantly on the initial carbohydrate concentration, which also influences the distribution of the metabolic products.     

Effect of iron and molybdenum addition on photofermentative hydrogen production from olive mill wastewater

Photofermentative hydrogen production from olive mill wastewater (OMW) by Rhodobacter sphaeroides O.U.001 was assessed under iron and molybdenum supplementation. Control cultures were only grown with 2% OMW containing media. The analysis included measurements of biomass accumulation, hydrogen production, pH variations of the medium, and changes in the chemical oxygen demand (COD) of the wastewater. Growth under control and Mo-supplemented experiments yielded about the same amount of biomass (∼0.4 g dry cell weight per L culture). On the other hand, Mo addition slightly enhanced the total volume of H₂ gas production (62 mL H₂), in comparison with the control reactor (40 mL H₂). Fe-supplemented cultures showed a significant increase on H₂ production (125 mL H₂), tough having a longer lag time for the observation of the first H₂ bubbles (24 h), compared to the control (15 h) and Mo-supplemented ones (15 h). Fe-added cultures also yielded better wastewater treatment by achieving 48.1% degradation of the initial chemical oxygen demand (COD) value compared to the control reactor having 30.2% COD removal efficiency. Advances described in this work have the potential to find applications in hydrogen industry while attempting an effective management of cheap feedstock utilization.     

Effect of cell immobilization,hematite nanoparticles and formation of hydrogen-producing granules on biohydrogen production from sucrose wastewater

This study investigated the effect of granules formation, hematite nanoparticles and biofilm carriers on biohydrogen production from sucrose wastewater in continuous stirring tank reactors operated at 12 h HRT, pH of 5.5 and 35 °C. Granular-based bioreactor was subjected to acid incubation period for 24 h by shifting the pH from 5.5 to 3. Before application of the acid incubation, hydrogen-producing granules (HPGs) diameter and hydrogen production rate (HPR) of 0.5 mm and 4.3 L/L.d, respectively were measured at 10 g-sucrose/L. Application of acid incubation enhanced the granulation process, where the particle size increased to 2.8 mm and higher HPR of 7.8 L/L.d was obtained. Higher sucrose concentration (15–30 g?L) enhanced HPGs diameter and increased the HPR. At 10 g-sucrose/L, addition of hematite nanoparticles increased the HPR to 5.9 L/L.d higher than 3.87 L/L.d measured in control reactor. Biofilm-based reactor showed HPR of 2.48 L/L.d lower than the control reactor.     

Ultrafine iron oxide nanoparticles supported on N-doped carbon black as an oxygen reduction reaction catalyst

An oxygen reduction reaction (ORR) catalyst comprising ultrafine iron oxide nanoparticles supported on N-doped Vulcan carbon (FeO_1.4/N-C) was prepared via a two-step method. X-ray photoelectron spectroscopy revealed the iron oxide nanoparticles comprised Fe₂O₃ and FeO phases with a combined average oxidation state of 2.8. The FeO_1.4/N-C catalyst produced an ORR onset potential of −0.056 V and a half-wave potential of −0.190 V in alkaline media, which was comparable to that of commercial Pt/C catalyst. Moreover, FeO_1.4/N-C had higher methanol tolerance than Pt/C catalyst and thus affords a promising non-precious metal ORR catalyst for fuel cells.     

Comparison of magnetite/reduced graphene oxide nanocomposites and magnetite nanoparticles on enhancing hydrogen production in dark fermentation

Magnetite/reduced graphene oxide nanocomposites (Fe₃O₄-rGO NCs) and magnetite nanoparticles (Fe₃O₄ NPs) were added to enhance biohydrogen (bioH₂) production in dark fermentation. Concentration of supplements from 10 to 100 mg/L was appropriate to enhance bioH₂ production, and inhibition appeared once concentration exceeded 100 mg/L. The best bioH₂ yield was 198.30 mL/g glucose at 100 mg/L Fe₃O₄ NPs and 225.60 mL/g glucose at 100 mg/L Fe₃O₄-rGO NCs, which was 42.97% and 62.65% higher than that in the blank group, respectively. Both Fe₃O₄ NPs and Fe₃O₄-rGO NCs could intensify butyrate-type fermentation and change the hydrogen-producing microorganism cells morphology, but the enhancement effect of Fe₃O₄-rGO NCs was superior. Microbial community structure analysis showed that Clostridium-sensu-stricto-1 became more dominant ultimately by Fe₃O₄-rGO NCs.     

pH值调控对发酵产氢的影响

利用厌氧活性污泥作产氢接种物，发酵有机质产生氢气，一般是在酸性条件下进行的。以厌氧活性污泥作接种物，有机酸为基质，在厌氧、恒温25℃、不同的pH值下，启动发酵产氢，以及监测产氢过程中的pH值变化，得出pH值过高时，有大量的甲烷生成，pH值过低时，则对产氢细菌不利，难于产氢。启动发酵产氢时，pH值不宜底于4．3，较为适宜的产氢pH值范围4．5～5．5。     

Green synthesis of magnetite nanoparticle and its regulatory effect on fermentative hydrogen production from lignocellulosic hydrolysate by Klebsiella sp.

This study describes the synthesis and characterization of magnetite nanoparticles (NPs) from water hyacinth (WH) extract and its regulatory effect on fermentative hydrogen production from lignocellulosic hydrolysate by Klebsiella sp. Characterization of WH-magnetite-NP revealed that it was a pure magnetite NP in a spherical shape with an average particle size of 13.5 ± 3.7 nm. The maximum cumulative hydrogen production with an increment of 23.49% and an optimum Y(H₂/S) of 83.20 ± 2.19 mL/g_substrate was obtained with WH-magnetite-NP at 20 mg/L. Monitoring of key node metabolites further established the potential of WH-magnetite-NP to increase the flux distribution of the hydrogen synthesis pathway. The hydrogenase activity was enhanced via WH-magnetite-NP addition, with peak value 2.1 times of the control. The expression of functional genes in key pathways assessed via RT-PCR highlighted the effect of WH-magnetite-NP on the evident promotion of hydrogenase and formate-hydrogen lyase. This is the first attempt to detect the expression of multiple functional genes in key metabolic pathways to explain the regulatory mechanism upon NP addition.     

Evaluation of ultrasonication as a treatment strategy for enhancement of biohydrogen production from complex distillery wastewater and process optimization

Dark fermentation of distillery wastewater (DWW) gives a lower hydrogen yield (HY) and hydrogen production rate (R), owing to the complexity and a recalcitrant nature of effluent. Therefore, an effective pretreatment of DWW becomes imperative for the improvement of biohydrogen production. In the present study, the efficacy of ultrasonic pretreatment for enhancement of biohydrogen production from DWW was evaluated in batch test. Several variables, such as COD input, ultrasonic density (UD), and ultrasonication time (UT) were studied for optimization using response surface methodology integrated with desirability function. The highest HY, 10.95 mmol/g COD, and R, 6.67 mmol/L h, were obtained for batch test of ultrasonically pretreated DWW under optimal conditions for COD, UD and UT at 56 g/L, 0.12 W/mL, and 17 min, respectively. The significant relative enhancement of HY, 101%, and R, 103%, implies that ultrasonically treated DWW is about 1.2–1.4 times more effective for enhanced biohydrogen production from complex DWW compared to unsonicated DWW.     

A bench scale study of fermentative hydrogen and methane production from food waste in integrated two-stage process

A two-stage fermentation process combining hydrogen and methane production for the treatment of food waste was investigated in this paper. In hydrogen fermentation reactor, the indigenous mixed microbial cultures contained in food waste were used for hydrogen production. No foreign inoculum was used in the hydrogen fermentation stage, the traditional heat treatment of inoculum was not applied either in this bench scale experiment. The effects of the stepwise increased organic loading rate (OLR) and solid retention time (SRT) on integrated two-stage process were investigated. At steady state, the optimal OLR and SRT for the integrated two-stage process were found to be 22.65 kg VS/m³ d (160 h) for hydrogen fermentation reactor and 4.61 (26.67 d) for methane fermentation reactor, respectively. Under the optimum conditions, the maximum yields of hydrogen (0.065 m³ H₂/kg VS) and methane (0.546 m³ CH₄/kg VS) were achieved with the hydrogen and methane contents ranging from 29.42 to 30.86%, 64.33 to 71.48%, respectively. Biodegradability analysis showed that 5.78% of the influent COD was converted to the hydrogen in H₂-SCRD and 82.18% of the influent COD was converted to the methane in CH₄-SCSTR under the optimum conditions.     

Effects of potential inhibitors present in dilute acid-pretreated corn stover on fermentative hydrogen production by Escherichia coli

This study reports the inhibitory compounds present in dilute sulfuric acid-pretreated corn stover for fermentative hydrogen production by Escherichia coli. The E. coli W3110-derived strain deficient in lactate and succinate production pathways was used. When dilute acid-treated corn stover liquor containing 175 mM acetate, 21 mM furfural, and 2.6 mM 5-hydroxymethylfurfural was added at fourfold dilution to the xylose-containing culture medium, the microbial growth and hydrogen production were almost completely inhibited. The addition of acetate, furfural, or 5-hydroxymethylfurfural, at up to 200, 80, or 40 mM, respectively, to the xylose- or glucose-containing medium led to dose-dependent inhibition of fermentative hydrogen production. No synergistic inhibition by furfural with acetate or 5-hydroxymethylfurfural at concentrations based on the corn stover hydrolysate was observed. Altogether, these results suggest that the inhibition of the E. coli-based hydrogen production by the corn stover hydrolysate is primarily attributed to acetate under the conditions used.     

Enhancement of biohydrogen production in industrial wastewaters with vinasse pond consortium using lignin-mediated iron nanoparticles

The aim of this work was the enhancement of biohydrogen production by an anaerobic bacterial consortium with incorporation of lignin-mediated iron nanoparticles in the fermentation medium. Lignin magnetic nanoparticles (LMNP), identified as magnetite by XRD, exhibited spherical shape and average particle size of 8.6 nm, while lignin non-magnetic nanoparticles (LNMNP) exhibited high agglomeration and an amorphous nature in TEM and XRD, respectively. The fermentation medium (pH 7) was composed of 88% soft drink wastewater (SDW) and 12% corn steep liquor (CSL) and supplemented with NaHCO₃ (1.0 g/L) and cysteine-HCl (0.5 g/L). Under optimal conditions, BioH₂ production was 17.67 ± 0.54 mL, after 48 h of fermentation at 37 °C. Addition of LMNP and LNMNP increased BioH₂ production in 91.0 and 74.3%, respectively. Additionally, 200 mg/L of LMNP and LNMNP in the fermentation medium improved the BioH₂ yields (mL H₂/g COD_removed) in 2.8- and 2.3-fold, respectively.     

Effects of biomass,COD and bicarbonate concentrations on fermentative hydrogen production from POME by granulated sludge in a batch culture

Effects of three selected variables viz. biomass concentration, initial chemical oxygen demand (COD) concentration and initial bicarbonate alkalinity (BA) on biological hydrogen production from palm oil mill effluent (POME) using the granulated sludge in batch culture were investigated. The experimental results were analyzed and modeled using a central composite design (CCD) of response surface methodology (RSM). In order to carry out a comprehensive analysis of the biohydrogen production process, indicative parameters namely hydrogen yield (Y_H), specific hydrogen production rate (SHPR), and COD removal efficiency were studied as the process responses. Maximum hydrogen yield (124.5 mmol H₂/g COD_removed) and specific hydrogen production rate (55.42 mmol H₂/g VSS.d) were achieved at COD_in 3000 and 6500 mg/l, MLVSS 4000 and 2000 mg/l, and initial BA 1100 mg CaCO₃/l, respectively.     

接种量对易腐垃圾发酵产氢和产甲烷的影响研究

试验研究了不同接种量对易腐垃圾厌氧消化的影响.在垃圾投加量为发酵容积的25%,接种量为发酵容积的12.5%～75%时,垃圾发酵的产氢量与接种量无明显的相关性;当接种量由发酵容积的12.5%提高到37.5%,垃圾的TS降解量、VS降解量、产沼气总量、产甲烷量分别提高了4.2倍、1.6倍、7.9倍、1 972.3倍;当接种量由发酵容积的37.5%提高到75%时,垃圾的TS降解量与VS降解量、产沼气总量及产甲烷量无较大变化,但反应的抑制期从25 d缩短至15 d.试验结果表明,为稳定易腐垃圾厌氧发酵产气,接种量不宜低于发酵容积的37.5%.     

Characteristics of fermentative hydrogen production with Klebsiella pneumoniae ECU-15 isolated from anaerobic sewage sludge

Klebsiella pneumoniae ECU-15 (EU360791), which was isolated from anaerobic sewage sludge, was investigated in this paper for its characteristics of fermentative hydrogen production. It was found that the anaerobic condition favored hydrogen production than that of the micro-aerobic condition. Culture temperature and pH of 37 °C and 6.0 were the most favorable for the hydrogen production. The strain could grow in several kinds of monosaccharide and disaccharide, as well as the complicated corn stalk hydrolysate, with the best results exhibited in glucose. The maximum hydrogen production rate and yield of 482 ml/l/h and 2.07 mol/mol glucose were obtained at initial glucose concentration of 30 g/L and 5 g/L, respectively. Fermentation results in the diluent corn stalk hydrolysate showed that cell growth was not inhibited. However, the hydrogen production of 0.65 V/V was relatively lower than that of the glucose (1.11 V/V), which was mainly due to the interaction between xylose and glucose.