Biological fermentation pilot-scale systems and evaluation for commercial viability towards sustainable biohydrogen production.

Featuring high caloric value, clean-burning, and renewability, hydrogen is a fuel believed to be able to change energy structure worldwide. Biohydrogen production technologies effectively utilize waste biomass resources and produce high-purity hydrogen. Improvements have been made in the biohydrogen production process in recent years. However, there is a lack of operational data and sustainability analysis from pilot plants to provide a reference for commercial operations. In this report, based on spectrum coupling, thermal effect, and multiphase flow properties of hydrogen production, continuous pilot-scale biohydrogen production systems (dark and photo-fermentation) are established as a research subject. Then, pilot-scale hydrogen production systems are assessed in terms of sustainability. The system being evaluated, consumes 171,530 MJ of energy and emits 9.37 t of CO2 eq when producing 1 t H2, and has a payback period of 6.86 years. Our analysis also suggests future pathways towards effective biohydrogen production technology development and real-world implementation.

Enhancement of biohydrogen production by photo-fermentation of corn stover via visible light catalyzed titanium dioxide/activated carbon fiber.

In this study, titanium dioxide/activated carbon fiber (TiO2/ACF) was synthesized by liquid-phase deposition method and the effect of TiO2/ACF on the performance of photo-fermentation biohydrogen production (PFHP) from corn stover under visible light catalysis was discussed. Results show the maximum cumulative hydrogen yield (CHY) obtained under the optimal conditions was 74.0 ± 1.3 mL/g TS with TiO2/ACF addition of 100 mg/L, which was twice that without TiO2/ACF addition (36.9 ± 1.0 mL/g TS). Initial pH value had the most significant effect on CHY. The addition of TiO2/ACF promoted the metabolic pathway of nitrogenase to reduce H+ produced by consuming acetic acid and butyric acid to hydrogen, and also shortened the photo-fermentation period. By scanning electron microscopy and X-ray diffraction analysis, the morphology and phase structure of TiO2/ACF after PFHP did not change significantly. This study laid the foundation for the reuse of TiO2 and its practical application in PFHP.

Effect of deep eutectic solvent pretreatment on biohydrogen production from corncob: pretreatment temperature and duration.

Deep eutectic solvent pretreatment with different temperatures and durations was applied to corncob to increase hydrogen yield via photo-fermentation. The correlation of composition, enzymatic hydrolysis, and hydrogen production in pretreated corncobs, as well as energy conversion was evaluated. Deep eutectic solvent pretreatment effectively dissolved lignin, retained cellulose, and enhanced both enzymatic hydrolysis and hydrogen production. The maximum cumulative hydrogen yield obtained under a pretreatment condition of 50°C and 12 h was 677.45 mL; this was 2.72 times higher than that of untreated corncob, and the corresponding lignin removal and enzymatic reduction of sugar concentration were 79.15% and 49.83 g/L, respectively; the highest energy conversion efficiency was 12.08%. The hydrogen production delay period was shortened, and the maximum shortening time was 18.9 h. Moreover, the cellulose content in pretreated corncob was positively correlated with both reducing sugar concentration and hydrogen yield and had the strongest influence on hydrogen production.

Pretreatment of Arundo donax L. for photo-fermentative biohydrogen production by ultrasonication and ionic liquid.

Combined pretreatment methods were assumed to further enhance photo-fermentative biohydrogen production (PFHP) from lignocellulosic biomass. For this purpose, an ultrasonication assisted ionic liquid pretreatment was applied to Arundo donax L. biomass for PFHP. The optimal condition for the combined pretreatment was 16 g/L of 1-Butyl-3-methylimidazolium Hydrogen Sulfate ([Bmim]HSO4) combined with ultrasonication at a solid to liquid ratio (SLR) of 1:10 for 1.5 h under 60 °C. Under this condition, the maximum delignification of 22.9 % was obtained, in addition, the hydrogen yield (HY) and energy conversion efficiency (ECE) were enhanced by 1.5-fold and 46.4 % (p < 0.05) compared to untreated biomass, respectively. Moreover, heat map analysis was performed to evaluate the correlation between pretreatment conditions and corresponding results, suggesting pretreatment temperature had the strongest (absolute value of Pearson's r was 0.97) linear correlation with HY. Combined multiple energy production approaches might be useful for further improved ECE.

Enhancement of static magnetic field on biological hydrogen production via photo-fermentation of giant reed.

The effect of static magnetic field (SMF) on the system of photo-fermentation biological hydrogen production remains dimness. The goal of this study was to clarify the correlation between external SMF addition and hydrogen production via photo-fermentation from giant reed. SMF with 20 mT improved the cumulative H2 yield by 26.1% and reduced the lag time of hydrogen production by 56.7% compared with that of without external magnetic field. Moreover, 20 mT of SMF not only enhanced the activity of nitrogenase by 94.52%, but also obtained the maximum energy conversion efficiency of 27.27%. The distribution of volatile fatty acids proved that the concentration of acetic acid and butyric acid were 137% and 81% higher than that of without SMF, respectively. The results would help to trigger the positive interaction between SMF and microorganism and to avoid the possible negative interaction.

1-Butyl-3-methylimidazolium acetate pretreatment of giant reed triggering yield improvement of biohydrogen production via photo-fermentation.

Ionic liquids (ILs) have been considered as promising alternatives to traditional reagent for lignocellulosic biomass pretreatment because of their tunable physicochemical and "green" properties. In the study, the influence of 1-Butyl-3-methylimidazolium acetate ([Bmim]acetate) pretreatment of giant reed on H2 yield improvement via photo-fermentation (PF) was evaluated. Under the optimal pretreatment conditions (6 g/L [Bmim]acetate at 70 °C for 4 h), the delignification of giant reed was up to 26.7 %. In addition, the sugar yield (9.5 g/L) and hydrogen yield (72.3 mL/g TS) from giant reed were enhanced by 1.7-fold and 61.7 % over those of untreated giant reed, respectively. Moreover, ternary analysis showed that retention time had the strongest effect on delignification, sugar yield and hydrogen yield of giant reed compared to pretreatment temperature and [Bmim]acetate loading. These experimental results indicated that [Bmim]acetate pretreatment of giant reed is an effective approach to enhance the hydrogen yield via PF.

Biohydrogen production by deep eutectic solvent delignification-driven enzymatic hydrolysis and photo-fermentation: Effect of liquid-solid ratio.

Deep eutectic solvent (DES), a new green solvent, was used to pretreat corncob to enhance biohydrogen production. As a result of the pretreatment, lignin was effectively removed, and the maximum delignification efficiency of 83.12% was achieved. Moreover, the contents of cellulose in the pretreated corncob significantly increased. DES pretreatment effect improved with increasing liquid-solid ratio. The pretreated corncob's enzymatic saccharification activity and hydrogen production were promoted due to the lower content of lignin. The best result was observed at a ratio of 25:1 (DES:corncob, g/g), in which the reducing sugar concentration (53.91 g/L) and the hydrogen yield (151 mL/g) was 6.8 and 3.1 times than that of untreated corncob, respectively. In addition, the lag time of hydrogen production was obviously shortened to 16.53 h due to the utilization of abundant available fermentable sugars, which accelerated hydrogen production.

Forecasting of reducing sugar yield from corncob after ultrafine grinding pretreatment based on GM(1,N) method and evaluation of biohydrogen production potential.

Pretreatment of biomass helps to enhance reducing sugar yield from biomass during enzyme hydrolysis tests. Ultrafine grinding was applied to pretreat corncob. The effect of affecting factors including milling time, initial particle size and ball to power weight on the reducing sugar yield from corncob was investigated firstly. And then, an GM(1,N) model was constructed to model the ultrafine grinding pretreatment system predicting the reducing sugar yield from corncob based on experimental data, the results demonstrate GM(1,N) could predict the reducing sugar yield accurately and effectively without depending on the number of samples. The initial particle size was the most critical influential factor affecting reducing sugar yield according to the driving coefficient. The cumulative hydrogen yield was significantly affected by ultrafine grinding pretreatment, the hydrogen yield of pretreated corncob was 153.60 ± 5.8 mL/g total solids, which was higher than that of untreated corncob (113.20 ± 3.2 mL/g total solids).

Effect of 5-HMF and furfural additives on bio-hydrogen production by photo-fermentation from giant reed.

Substances harmful to photo-fermentative biological hydrogen production (PFHP) were produced during cellulose hydrolysis. This study aimed to evaluate the effect of by-products (5-hydroxymethylfurfural (5-HMF) and furfural) released from lignocellulose during enzymatic hydrolysis process on PFHP. The exist of 5-HMF inhibited the hydrogen production. However, 0.2 g/L furfural improved the hydrogen production by 19 % compared to no addition (511.6 mL) with a maximum concentration of nitrogenase (109.96 IU/L) at 96 h. Furthermore, a 18.7 % enhancement of hydrogen production was also observed when 0.2 g/L 5-HMF and furfural were mixed at a ratio of 1:1, while decrement of hydrogen production at higher addition was observed as well. Through the scatter matrix analysis, it was concluded that 5-HMF and furfural additives had significant effects on PFHP. This study gave an insight into effect of lignocellulosic by-products on biohydrogen production.

Comparison of three ionic liquids pretreatment of Arundo donax L. For enhanced photo-fermentative hydrogen production.

Ionic liquids (ILs) pretreatment has been regarded as a promising green way to treat lignocellulosic biomass. 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), 1-allyl-3-methylimidazolium chloride ([Amim]Cl), and 1-Butyl-3-methylimidazolium Hydrogen Sulfate ([Bmim]HSO4) with different loadings (2, 4, 8, and 16 g/L) were adopted to pretreat the Arundo donax L.. 16 g/L [Bmim]HSO4 pretreated Arundo donax L. obtained the highest sugar yield of 7.9 g/L during the enzymatic hydrolysis and hydrogen yield of 106.1 mL/g TS during the photo-fermentation, which were 68.8 % and 35.3 % higher than those of untreated Arundo donax L., respectively. Moreover, volatile fatty acids (VFAs) distribution revealed that acetic acid was the main by-product during hydrogen production process with ILs pretreated Arundo donax L.. Besides, the relationship between sugar yield and hydrogen yield was the closest based on scatter matrix analysis. This study helps to understand of correlation between ILs pretreatment with the behavior of bioenergy production.

Enhancing photo-fermentative biohydrogen production using different zinc salt additives.

The kinetic properties of the hydrogen yield of photosynthetic bacteria were investigated using Han-Levenspiel and modified Gompertz models to determine the effects of different zinc salts on the growth and hydrogen production of the photosynthetic bacterium HAU-M1. Inorganic zinc salts (zinc standard solution and zinc sulfate) inhibited bacterial growth by 1-4-fold higher than organic zinc salts (zinc lactate and zinc gluconate). Among these four zinc salts, 5 mg/L zinc lactate displayed the weakest inhibition performance. This compound increased cumulative hydrogen production by approximately 57.81% (80.44 mL/g) and maximum hydrogen production rate by 58.27% (3.43 mL/[g·h]). The Han-Levenspiel model with parameters m > n > 0 indicated that the addition of zinc salts influenced the hydrogen production process of the bacterium in a noncompetitive manner. Compared with the inorganic zinc, the organic zinc salts were more suitable as exogenous zinc supplements to promote bacterial growth and its hydrogen production.

Lignin removal, reducing sugar yield and photo-fermentative biohydrogen production capability of corn stover: Effects of different pretreatments.

The effects of different pretreatment methods, including hydrothermal, acid, alkali, acid-heat and alkali-heat on lignin removal, reducing sugar (RS) yield and photo-fermentative biohydrogen production (PFHP) capability of corn stover (CS) were studied. NaOH-heat pretreatment was the most effective for lignin removal from CS, and the lignin removal rate reached 77%. All the studied pretreatment methods improved the total RS yield of CS, and the highest total RS yield (46.1 g/100 g raw material (RM)) was obtained from 2% NaOH-heat pretreated CS. 2% NaOH pretreatment realized the best PFHP of CS, which increased the hydrogen yield (HY), maximal hydrogen production rate (HPR) and highest hydrogen content (HC) by 31.9%, 50.9% and 20.1% respectively, and shortened hydrogen production lag time (HPLT) by 58.8% over that of untreated CS. However, NaOH-heat and 4% NaOH pretreatment weakened the PFHP capability of CS.

Analysis of the characteristics of paulownia lignocellulose and hydrogen production potential via photo fermentation.

Paulownia biomass is rich in carbohydrates, making which a potential feedstock for biohydrogen production. In the study, different parts and varieties of Paulownia were chose as substrates to evaluate hydrogen production potential of paulownia lignocellulose via biohydrogen production by photo fermentation (BHPPF) and energy conversion efficiency (ECE). Results showed the highest cumulative hydrogen yield (CHY) of 67.11 mL/g total solids (TS) and ECE of 4.74% were obtained from leaves of Paulownia, which were 121.06% and 115.45% higher than those of the branches. Moreover, Paulownia jianshiensis leaves were found to be the best variety for BHPPF, with the maximum CHY of 98.83 mL/g TS and ECE of 7.18%. Using Paulownia waste as the substrate to produce hydrogen helps broaden the range of raw materials for BHPPF and improve the economic utilization of forestry waste.

Enhancing photo-fermentation biohydrogen production from corn stalk by iron ion.

This study aimed to investigate the enhancement of iron ion on growth, metabolic pathway, and biohydrogen production performance of biohydrogen producing bacteria HAU-M1. Different concentrations of Fe2+ and Fe3+ were respectively added into fermentation broth of photo-fermentation biohydrogen production (PFHP) from corn stalk. Regular sampling test was used to measure the characteristics of fermentation broth and gas, metabolic pathway, energy conversion efficiency, and kinetic of PFHP. The analysis of experimental data showed that the maximum hydrogen yield of 70.25 mL/g was observed at 2500 µmol/L Fe2+ addition, with an energy conversion efficiency of 5.21%, which was 19.98% higher over no-addition. However, the maximum hydrogen content of 51.41% and the maximum hydrogen production rate of 17.82 mL/h were observed at 2000 µmol/L Fe2+ addition. The experimental results revealed that iron ion played a key role in PFHP, which provided a technical support for improving the performance of PFHP.

Towards high light conversion efficiency from photo-fermentative hydrogen production of Arundo donax L. By light-dark duration alternation strategy.

Suitable illumination project would help in achieving high light conversion efficiency (LCE) for photo-fermentation. This study proposed an improvement strategy for LCE of photo-fermentative hydrogen production (PFHP) with a photosynthetic consortium by adopting light-dark duration alternation. For this purpose, 6 projects (continues light, 24 h light + 24 h dark, 24 h dark + 24 h light, 48 h light + 48 h light, 48 h dark + 48 h light, and continues dark) light disturbances were carried out to estimate the strategy. The fluctuation of cell growth (OD660) was corresponded to the light-dark alternation. 24 h dark + 24 h light alternation achieved the maximum hydrogen yield (HY) of 390.9 mL/g TS cell (6.7 % higher than continuous light) and maximum improvement of LCE of 114.7%. Moreover, heat map analysis revealed that the light period after inoculation had the closest relation (Pearson's r = 1) with the average hydrogen production rate (HPR) of photo-fermentation. Besides, decreased dark period after inoculation would increase the hydrogen yield of photo-fermentation.

Study of the interrelationship between nano-TiO2 addition and photo-fermentative bio-hydrogen production of corn straw.

This study explored the interrelationship between nano-TiO2 addition and photo-fermentative hydrogen production (PFHP) of corn straw. The maximum cumulative hydrogen volume (CHV) was up to 688.8 mL under the optimal photo-fermentative process conditions with nano-TiO2 addition of 300 mg/L. Initial pH and interaction between substrate concentration and light intensity had highly significant effects on PFHP of corn straw with nano-TiO2 addition. With the improvement of CHV, nano-TiO2 addition decreased the optimal initial pH and substrate concentration for PFHP of corn straw. Moreover, nano-TiO2 addition promoted the metabolism of butyric acid and acetic acid by photosynthetic bacteria HAU-M1, and significantly reduced the total concentration of intermediate byproducts during hydrogen production to a low level of 1.6-2.5 g/L, thus making the CHV, maximum hydrogen production rate (HPR) and average hydrogen content (HC) increased by 32.6%, 27.9% and 8.3% respectively over the control without nano-TiO2 addition.

Continuous dark and photo biohydrogen production in a baffled bioreactor and electrons distribution analysis.

This work studied the sequential hydrogen production by dark and photo-fermentation (HPDPF) in continuous baffled bioreactors. Taken enzymatic hydrolysate of corn stover as initial carbon source, the influence of hydraulic retention time (HRT) of dark fermentation (DF) and the dilution ratio (DR) of dark fermentation effluents (DFEs) on the hydrogen production performance of the combined fermentation system and electron distribution were investigated. For DF unit, the highest hydrogen production rate (HPR) of 5.24 L/(L·d) was detected at HRT of 18 h, however, the maximum HPR of 4.60 L/(L·d) was obtained from DFEs with HRT of 12 h and DR of 1:0.5 during photo fermentation unit, meanwhile, the electrons in substrate partitioning to H2 reached the maximum value of 35.69%. In terms of hydrogen yield, the optimum operating conditions of the combined system were HRT of 12 h (DF) and DR of 1:0.5(DFEs), in which the hydrogen yield reached 12.73 L/d.

Recycling of shrub landscaping waste: Exploration of bio-hydrogen production potential and optimization of photo-fermentation bio-hydrogen production process.

Shrub landscaping waste, derived from afforestation of city, has increased annually, making it a promising feedstock for energy production. In this work, the photo-fermentation bio-hydrogen production potential from shrub landscaping waste was evaluated. Eight kinds of shrub landscaping wastes (Photinia fraseri, Buxus megistophylla, Buxus sinica, Pittosporum tobira, Sabina Chinensis, Berberis thunbergii, Ligustrum vicaryi and Ligustrum quihoui) were selected as substrate and the photo-fermentation bio-hydrogen production process of which was optimized. Buxus megistophylla was found to be the most suitable substrate for photo-fermentation bio-hydrogen production. Moreover, the initial pH value, temperature and substrate concentration had significant influence on photo-fermentation bio-hydrogen production. The maximum cumulated hydrogen yield of Buxus megistophylla was 73.82 ± 0.06 mL/g TS under the optimal conditions of light intensity of 3000 Lux, substrate mass concentration of 21.49 g/L, temperature of 29.78 °C, inoculant amount of 25% and initial pH value of 6.78.

A strategy for successive feedstock reuse to maximize photo-fermentative hydrogen production of Arundo donax L.

This study proposed a strategy to maximize the hydrogen yield by reusing feedstock of Arundo donax L. For this purpose, a successive 4-batch photo-fermentative hydrogen production (PFHP) was carried out to test the strategy. About 50% of total hydrogen yield was additionally obtained by reusing the Arundo donax L for successive 4 times in comparison to single 1st batch (161.4 mL/U. cell dry weight). In addition to the highest hydrogen yield, the maximum hydrogen production rate (6.0 mL/U. cell dry weight /h), and the highest volatile fatty acids (VFAs) concentration (32 mM) were also obtained from the 1st batch, while the 2nd batch gave the maximum substrate conversion efficiency (96.5%). Moreover, a positive relationship between the sum of acetic and butyric acids with hydrogen yields was observed. This strategy would help in enhancing hydrogen yield that coupled with cost reduction for biohydrogen production.

Enhancement of the biohydrogen production performance from mixed substrate by photo-fermentation: Effects of initial pH and inoculation volume ratio.

Co-digestion of substrates can improve hydrogen yield (HY) by adjusting carbon nitrogen ratio (C/N) of fermentation substrates. This study evaluated the enhancement of hydrogen production from co-digestion of duckweed and corn straw via photo-fermentation. The maximum HY of 78.0 mL/g Total solid (TS) was obtained from the mixed ratio of 5:1 (C/N of 13.2), which was 25.4% and 29.6% higher than those of single substrate of duckweed and corn straw, respectively. The effects of initial pH and inoculation volume ratio (IVR) on co-digestion photo-fermentative hydrogen production (CD-PFHP) from duckweed and corn straw were further studied. A maximum HY of 85.6 mL/g TS was achieved under the optimal condition (initial pH 8, IVR 20%, mix ratio of duckweed and corn straw of 5:1). Additionally, both mix ratio and initial pH showed statistical difference (p < 0.05). Acetic acid and butyric acid were found to be the main metabolic by-products during CD-PFHP.