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[Display omitted] • GM(1.1) was used to predict the crop straw yield of China. • Using the cellulose degradation model to determine the specific biohydrogen yield. • GHGs emission reduction potential of crop straw was assessed. • Hydrogen yield of 1.31 × 1011 m3 could be produced from crop straw in China. • Reduction of 2.42 × 108 t/a CO 2 -eq from crop straw based biohydrogen in China. In order to achieve the carbon neutrality goal set by Chinese government, the potential contribution of hydrogen production from crop residues by microbial fermentation technology and Greenhouse gas (GHGs) reduction have been studied. Firstly, the annual yield of crop straw was estimated according to crop yield and grass grain ratio, and then the grey model GM (1, 1) was applied to predict the crop residues resources available for hydrogen production in various provinces in China in 2021. The results showed that the maximum resource of straw being available for hydrogen production is about 4.54 × 108 t, corresponding to 1.31 × 1011 m3 of hydrogen, the energy carried by the obtained hydrogen was 73 % and 1.15 times than the energy of national civil natural gas consumption and energy of transportation gasoline consumption, respectively. The potential reduction of greenhouse gas emission was 2.42 × 108 t/a CO 2 -eq, representing 2.4 % of GHGs emissions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrafine grinding pretreatment has significant effect on the hydrolysis of corncob. • The GM(1,N) model has high predictability under the condition of scanty data. • The influence degree of each factor on reducing sugar yield can be identified. • The hydrogen yield from corncob was promoted after Ultrafine grinding pretreatment. 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). [ABSTRACT FROM AUTHOR]

• Hydrogen production from DFEs with different operation modes was investigated. • Longer cell retention resulted in more intracellular substance loss 'during synthesis'. • The semi-continuous fermentation mode was a promising way to promote H 2 from DFEs. • 37.71% substrates electrons were diverted towards hydrogen at semi-continuous mode. In this work, the influence of batch, semi-continuous and continuous mode on biohydrogen production from dark fermentation effluents (DFEs) as substrate and electron distribution was investigated. Results indicated a better H 2 production performance was obtained in semi-continuous mode. 50% decanting volume ratio (DVR) and 24 h feeding interval time (FIT) were found to be the best condition. Maximum average H 2 production rate (HPR) and H 2 yield were obtained of 8.44 mL/h and 1386.22 ± 44.23 mL H 2 /g TOC, respectively. 37.71% substrate electrons partitioning to hydrogen were detected. For continuous mode, more substrate electrons were diverted toward SMPs with the increasing of HRT due to the fact that longer cell retention, more chances were provided for cell lysis. The bad performance in batch mode ascribed to 56.39% substrate electrons were transferred to cell growth and soluble microbial products (SMPs). [ABSTRACT FROM AUTHOR]

[Display omitted] • Lignin removal rate of CS pretreated with NaOH-heat was as high as 77%. • The highest RS yield of 46.1 g/100 g RM was obtained from 2% NaOH-heat pretreated CS. • 4% NaOH-heat pretreated CS had the minimum HY of 44.27 mL/g TS. • 2% NaOH pretreatment increased the HY of CS by 31.9%. • HPLT of CS was shortened by 58.8% after 2% NaOH pretreatment. 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. [ABSTRACT FROM AUTHOR]

Pilot tests of sequential dark and photo fermentation H 2 production were for the first time conducted in a 11 m 3 reactor (3 m 3 for dark and 8 m 3 for photo compartments). A combined solar and light-emitting diode illumination system and a thermal controlling system was installed and tested. With dark fermentation unit maintained at pH 4.5 and 35 °C and photo fermentation unit at pH 7.0 and 30 °C, the overall biogas production rate using hydrolyzed corn stover as substrate reached 87.8 ± 3.8 m 3 /d with 68% H 2 content, contributed by dark unit at 7.5 m 3 -H 2 /m 3 -d and by photo unit at 4.7 m 3 /m 3 -d. Large variation was noted for H 2 production rate in different compartments of the tested units, revealing the adverse effects of poor mixing, washout, and other inhomogeneity associated with large reactor operations. [ABSTRACT FROM AUTHOR]

[Display omitted] • The best dosage of ascorbic acid to mediate 400 mg/L Fe(0) was 150 mg/L. • Ascorbic acid promoted the Fe(Ⅱ) generation through reduction and chelation. • H 2 produced from ascorbic acid-Fe(0) was 2.7–27.5% higher than Fe(0) at pH 6–9. • Initial pH had an important effect on H 2 production and Fe(0) reactivity. Ascorbic acid was introduced to enhance the performance of zero-valent iron (Fe(0)) in hydrogen production by photo fermentation of bean dregs and corn stover. The highest hydrogen production of 664.0 ± 5.3 mL and hydrogen production rate of 34.6 ± 0.1 mL/h was achieved at 150 mg/L ascorbic acid, which was 10.1% and 11.5% higher than that of 400 mg/L Fe(0) alone. The supplement of ascorbic acid to Fe(0) system accelerated the formation of Fe(Ⅱ) in solution due to its reducing and chelating ability. Hydrogen production of Fe(0) and ascorbic acid-Fe(0) (AA-Fe(0)) systems at different initial pH (5, 6, 7, 8 and 9) was studied. Result showed that hydrogen produced from AA-Fe(0) system was improved by 2.7–27.5% compared with Fe(0) system. The maximum hydrogen production of 767.5 ± 2.8 mL was achieved with initial pH 9 in the AA-Fe(0) system. This study provided a strategy for enhancing biohydrogen production. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe0 was first applied to high-load photo fermentation system of corn stover. • Effects of Fe0 sizes (700, 100 and 50 nm) on hydrogen production were compared. • Fe0 buffered pH, stimulated nitrogenase activity and accelerated acid utilization. • Adding 1000 mg/L Fe0-700 obtained the highest hydrogen yield increment of 92.88 %. The aim of this work was to study the effects of Fe0 particle sizes (700 nm, 100 nm and 50 nm) addition on biohydrogen production, liquid culture characteristics and photosynthetic bacterial respond in the high-load photo fermentation system of corn stover within the concentration range of 200–1500 mg/L. Results showed that Fe0 with particle size of 700 nm had a better promotion effect on hydrogen production than 100 nm and 50 nm. The highest hydrogen yield of 74.32 ± 3.48 mL/g TS and hydrogen production rate of 3.31 ± 0.11 mL/g·h TS corn stover were obtained at 1000 and 1500 mg/L Fe0-700 nm, which were significantly increased by 92.88 % and 133.88 % compared with the control group. Further analysis indicated that Fe0 addition effectively alleviated pH drop, enhanced nitrogenase activity, promoted cell growth, and accelerated the consumption of acetic acid and butyric acid. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biochar and nanoscale zero-valent iron added improved the acid tolerance of system. • The increase of bio-H 2 yield was correlated with both additive type and initial pH. • Co-addition provided a negative oxidation–reduction potential for acidic medium. • Nanoscale zero-valent iron enabled maximum bio-H 2 yield of 419.36 mL at pH 6. Anaerobic fermentation system is easy to become acidic due to the generation of small molecular acids, which will affect the metabolism of bacteria. Therefore, it is necessary to improve the acid resistance of system. In this work, the tolerance of photo-fermentative biohydrogen production system amended with biochar, nanoscale zero-valent iron (nZVI) and biochar + nZVI to acidic environment was studied. Results showed that additives improved the stability and performance of the photo fermentation. The best increment of biohydrogen from 0 to 286.83 ± 2.77 mL was obtained by adding biochar and nZVI together at the original pH of 4.5. The additive reduced the oxidation–reduction potential and promoted the consumption of acetate and butyrate. At initial pH of 5, 6 and 7, the highest biohydrogen yield of 361.02 ± 10.11, 419.36 ± 10.70 and 382.67 ± 25.08 mL was obtained by adding nZVI, respectively, representing 42%–44.45% increase compared with the control group under the same conditions. [ABSTRACT FROM AUTHOR]