Guang-Li Cao

Bioconversion of lignocellulosic biomass to hydrogen: Potential and challenges.

No comprehensive review on the bioconversion of lignocellulosic biomass to hydrogen is presented. This paper provides an up-to-date review on recent research development in biotechnology-based lignocellulosic biomass-to-H(2) conversion. Bioconversion of lignocellulosic prehydrolysate, hydrolysate or cellulose to hydrogen was discussed in terms of the involved microorganisms and the bioaugmentation tactics. To achieve fully the utilization of biomass, the integrated approaches composed of coupled dark-photo fermentation and the dark fermentation and bioelectrohydrogenesis were sketched. Additionally, this review sheds light on the perspectives on the lignocellulosic biomass conversion to hydrogen, and on the scientific and technical challenges faced for the lignocelluloses bioconversion.

Integrated hydrogen production process from cellulose by combining dark fermentation, microbial fuel cells, and a microbial electrolysis cell

Hydrogen gas production from cellulose was investigated using an integrated hydrogen production process consisting of a dark fermentation reactor and microbial fuel cells (MFCs) as power sources for a microbial electrolysis cell (MEC). Two MFCs (each 25 mL) connected in series to an MEC (72 mL) produced a maximum of 0.43 V using fermentation effluent as a feed, achieving a hydrogen production rate from the MEC of 0.48 m(3) H(2)/m(3)/d (based on the MEC volume), and a yield of 33.2 mmol H(2)/g COD removed in the MEC. The overall hydrogen production for the integrated system (fermentation, MFC and MEC) was increased by 41% compared with fermentation alone to 14.3 mmol H(2)/g cellulose, with a total hydrogen production rate of 0.24 m(3) H(2)/m(3)/d and an overall energy recovery efficiency of 23% (based on cellulose removed) without the need for any external electrical energy input.

Biological hydrogen production by dark fermentation: challenges and prospects towards scaled-up production

Among different technologies of hydrogen production, bio-hydrogen production exhibits perhaps the greatest potential to replace fossil fuels. Based on recent research on dark fermentative hydrogen production, this article reviews the following aspects towards scaled-up application of this technology: bioreactor development and parameter optimization, process modeling and simulation, exploitation of cheaper raw materials and combining dark-fermentation with photo-fermentation. Bioreactors are necessary for dark-fermentation hydrogen production, so the design of reactor type and optimization of parameters are essential. Process modeling and simulation can help engineers design and optimize large-scale systems and operations. Use of cheaper raw materials will surely accelerate the pace of scaled-up production of biological hydrogen. And finally, combining dark-fermentation with photo-fermentation holds considerable promise, and has successfully achieved maximum overall hydrogen yield from a single substrate. Future development of bio-hydrogen production will also be discussed.

Simultaneous waste activated sludge disintegration and biological hydrogen production using an ozone/ultrasound pretreatment

This paper offers an effective pretreatment method that can simultaneously achieve excess sludge reduction and bio-hydrogen production from sludge self-fermentation. Batch tests demonstrated that the combinative use of ozone/ultrasound pretreatment had an advantage over the individual ozone and ultrasound pretreatments. The optimal condition (ozone dose of 0.158 g O(3)/g DS and ultrasound energy density of 1.423 W/mL) was recommended by response surface methodology. The maximum hydrogen yield was achieved at 9.28 mL H(2)/g DS under the optimal condition. According to the kinetic analysis, the highest hydrogen production rate (1.84 mL/h) was also obtained using combined pretreatment, which well fitted the predicted equation (the squared regression statistic was 0.9969). The disintegration degrees (DD) were limited to 19.57% and 46.10% in individual ozone and ultrasound pretreatments, while it reached up to 60.88% in combined pretreatment. The combined ozone/ultrasound pretreatment provides an ideal and environmental friendly solution to the problem of sludge disposal.

Fungal pretreatment of cornstalk with Phanerochaete chrysosporium for enhancing enzymatic saccharification and hydrogen production

The feasibility of fungal pretreatment of cornstalk with Phanerochaete chrysosporium for enzymatic saccharification and H(2) production was investigated in this study. Firstly, cornstalk was pretreated with P. chrysosporium at 29 °C under static condition for 15 d, lignin reduction was up to 34.3% with holocellulose loss less than 10%. Microscopic structure observation combined FTIR analysis further demonstrated that the lignin and crystallinity were decreased. Subsequently, the fungal-pretreated cornstalk was subjected to enzymatic hydrolysis by the crude cellulase from Trichoderma viride to produce fermentable sugars which were then fermented to bio-H(2) using Thermoanaerobacterium thermosaccharolyticum W16. The maximum enzymatic saccharification was found to be 47.3% which was 20.3% higher than the control without pretreatment. Upon fermentation of enzymatic hydrolysate, the yield of H(2) was calculated to be 80.3 ml/g-pretreated cornstalk. The present results suggested the potential of using hydrogen-producing bacteria for high-yield conversion of cornstalk into bio-H(2) integrate with biological pretreatment and enzymatic saccharification.

A review on bioconversion of lignocellulosic biomass to H2: Key challenges and new insights.

With the increasing energy crisis and rising concern over climate change, the development of clean alternative energy sources is of great importance. Biohydrogen produced from lignocellulosic biomass is a promising candidate, because of its positives such as readily available, no harmful emissions, environment friendly, efficient, and renewable. However, obstacles still exist to enable the commercialization of biological hydrogen production from lignocellulosic biomass. Thus the objective of this work is to provide update information about the recent progress on lignocellulosic hydrogen conversion via dark fermentation. In this review, the most important technologies associated with lignocellulosic hydrogen fermentation were covered. Firstly, pretreatment methods for better utilization of lignocellulosic biomass are presented, at the same time, hydrolysis methods assisting to achieve efficient hydrogen fermentation were discussed. Afterwards, issues related to bioprocesses for hydrogen production purposes were presented. Additionally, the paper gave challenges and new insights of lignocellulosic biohydrogen production.

Statistical optimization of culture condition for enhanced hydrogen production by Thermoanaerobacterium thermosaccharolyticum W16.

The optimization of culture condition for enhanced hydrogen production by Thermoanaerobacterium thermosaccharolyticum W16 was conducted using statistical experimental design and analysis. Plackett-Burman design was first used to screen the most important variables influencing hydrogen production, and subsequently central composite design was adopted to investigate the optimum value of the selected factors for achieving maximum hydrogen yield. Experimental results showed that xylose, phosphate buffer, and yeast extract had significant influence on hydrogen production and the maximum hydrogen yield of 2.39 mol/mol xylose was predicted when the concentrations of xylose, phosphate buffer, and yeast extract were 12.24 g/L, 0.170 M, and 4.11 g/L, respectively. The results were further verified by repeated experiments under optimal conditions. The excellent correlation between predicted and measured values further confirmed the validity and practicability of this statistical optimum strategy.

Biological abatement of cellulase inhibitors.

Removal of enzyme inhibitors released during lignocellulose pretreatment is essential for economically feasible biofuel production. We tested bio-abatement to mitigate enzyme inhibitor effects observed in corn stover liquors after pretreatment with either dilute acid or liquid hot water at 10% (w/v) solids. Bio-abatement of liquors was followed by enzymatic hydrolysis of cellulose. To distinguish between inhibitor effects on enzymes and recalcitrance of the substrate, pretreated corn stover solids were removed and replaced with 1% (w/v) Solka Floc. Cellulose conversion in the presence of bio-abated liquors from dilute acid pretreatment was 8.6% (0.1x enzyme) and 16% (1x enzyme) higher than control (non-abated) samples. In the presence of bio-abated liquor from liquid hot water pretreated corn stover, 10% (0.1x enzyme) and 13% (1x enzyme) higher cellulose conversion was obtained compared to control. Bio-abatement yielded improved enzyme hydrolysis in the same range as that obtained using a chemical (overliming) method for mitigating inhibitors.

Effects of various pretreatment methods on mixed microflora to enhance biohydrogen production from corn stover hydrolysate

Five individual pretreatment methods, including three widely-used protocols (heat, acid and base) and two novel attempts (ultrasonic and ultraviolet), were conducted in batch tests to compare their effects on mixed microflora to enhance hydrogen (H2) production from corn stover hydrolysate. Experimental results indicated that heat and base pretreatments significantly increased H2 yield with the values of 5.03 and 4.45 mmol H2/g sugar utilized, respectively, followed by acid pretreatment of 3.21 mmol H2/g sugar utilized. However, compared with the control (2.70 mmol H2/g sugar utilized), ultrasonic and ultraviolet pretreatments caused indistinctive effects on H2 production with the values of 2.92 and 2.87 mmol H2/g sugar utilized, respectively. The changes of soluble metabolites composition caused by pretreatment were in accordance with H2-producing behavior. Concretely, more acetate accumulation and less ethanol production were found in pretreated processes, meaning that more reduced nicotinamide adenine dinucleotide (NADH) might be saved and flowed into H2-producing pathways. PCR-DGGE analysis indicated that the pretreatment led to the enrichment of some species, which appeared in large amounts and even dominated the microbial community. Most of the dominated species were affiliated to Enterobacter spp. and Escherichia spp. As another efficient H2 producer, Clostridium bifermentan was only found in a large quantity after heat pretreatment. This strain might be mainly responsible for better performance of H2 production in this case.

Simultaneous saccharification and fermentation of fungal pretreated cornstalk for hydrogen production using Thermoanaerobacterium thermosaccharolyticum W16.

In this research, environmentally friendly fungal pretreatment was first adopted for deconstruction of cornstalk. Then the fungal-pretreated cornstalk was employed to produce hydrogen in simultaneous saccharification and fermentation (SSF) using crude enzyme from Trichoderma viride and Thermoanaerobacterium thermosaccharolyticum W16. The influence of various factors including substrate concentration, initial pH, and enzyme loading on hydrogen production were evaluated. The highest hydrogen yield of 89.3 ml/g-cornstalk was obtained with an initial pH 6.5, 0.75% substrate concentration, and 34 FPU/g cellulose. Compared the result with SSF of physical or chemical pretreated lignocellulosic materials, this research suggested an economic and efficient way for hydrogen production from lignocellulosic biomass.