Ethanol production from residual lignocellulosic fibers generated through the steam treatment of whole sorghum biomass.

Cellulosic ethanol could play a major role in the upcoming circular-economy once the process complexity, low carbohydrate extraction yields and high costs are resolved. To this purpose, different steam-treatment severity factors were employed on whole sweet sorghum biomass, followed by the delignification and hydrolysis of resulted lignocellulose fibers. A modified ASTM International (American Society for Testing and Material) standard cellulose hydrolysis approach as well as a newly developed SACH (Sulfuric Acid Cellulose Hydrolysis) process were used, recovering up to 24.3 wt% of cellulosic carbohydrates. This amounted to a total extractable and constitutive carbohydrate recovery of 51.7 wt% (dry basis) when a mild steam-treatment of whole sorghum biomass and the SACH cellulose hydrolysis were employed. An ethanol potential of 6378 L/ha/year was determined, comparable to values obtained from biomass such as sugarcane in warmer climates, supporting thus the opportunity of implementing this novel approach on a wider scale.

High-efficiency second generation ethanol from the hemicellulosic fraction of softwood chips mixed with construction and demolition residues.

Using lignocellulosic residues for bioethanol production could provide an alternative solution to current approaches at competitive costs once challenges related to substrate recalcitrance, process complexity and limited knowledge are overcome. Thus, the impact of different process variables on the ethanol production by Saccharomyces cerevisiae using the hemicellulosic fraction extracted through the steam-treatment of softwood chips mixed with construction and demolition residues was assessed. A statistical design of experiments approach was developed and implemented in order to identify the influencing factors (various nutrient addition sources as well as yeast inoculum growth conditions and inoculation strategies) relevant for enhancing the ethanol production potential and substrate uptake. Ethanol yields of 74.12% and monomeric sugar uptakes of 82.12 g/L were predicted and experimentally confirmed in bench and bioreactor systems. This innovative approach revealed the factors impacting the ethanol yields and carbohydrate consumption allowing powerful behavioral predictions spanning different process inputs and outputs.

A novel hybrid first and second generation hemicellulosic bioethanol production process through steam treatment of dried sorghum biomass.

Sweet sorghum was subjected to an impregnation step, which recovered most of the 1st generation sugars, prior to a steam-treatment extraction of the 2nd generation sugars, at three different severity factors (SF). A medium severity (3.56 SF) treatment proved to be an optimal compromise between the amount of sugars extracted and the fermentation inhibitors generated following the subsequent depolymerization approaches applied on the broth. Next, a series of detoxification approaches (ozonation, overliming and a combination of both) were investigated following a concentration and depolymerization step. Results show that higher steam-treatment severity required more intense detoxification steps. However, when combining the 1st and 2nd generation streams at a 2:1 ratio, the inhibitors did not affect the fermentation process and ethanol yields above 90% of the theoretical maximum were achieved.

A two-step optimization strategy for 2nd generation ethanol production using softwood hemicellulosic hydrolysate as fermentation substrate.

Ethanol production using waste biomass represents a very attractive approach. However, there are considerable challenges preventing a wide distribution of these novel technologies. Thus, a fractional-factorial screening of process variables and Saccharomyces cerevisiae yeast inoculum conditions was performed using a synthetic fermentation media. Subsequently, a response-surface methodology was developed for maximizing ethanol yields using a hemicellulosic solution generated through the chemical hydrolysis of steam treatment broth obtained from residual softwood biomass. In addition, nutrient supplementation using starch-based ethanol production by-products was investigated. An ethanol yield of 74.27% of the theoretical maximum was observed for an initial concentration of 65.17g/L total monomeric sugars. The two-step experimental strategy used in this work represents the first successful attempt to developed and use a model to make predictions regarding the optimal ethanol production using both softwood feedstock residues as well as 1st generation ethanol production by-products.

Surpassing the current limitations of biohydrogen production systems: The case for a novel hybrid approach.

The steadily increase of global energy requirements has brought about a general agreement on the need for novel renewable and environmentally friendly energy sources and carriers. Among the alternatives to a fossil fuel-based economy, hydrogen gas is considered a game-changer. Certain methods of hydrogen production can utilize various low-priced industrial and agricultural wastes as substrate, thus coupling organic waste treatment with renewable energy generation. Among these approaches, different biological strategies have been investigated and successfully implemented in laboratory-scale systems. Although promising, several key aspects need further investigation in order to push these technologies towards large-scale industrial implementation. Some of the major scientific and technical bottlenecks will be discussed, along with possible solutions, including a thorough exploration of novel research combining microbial dark fermentation and algal photoheterotrophic degradation systems, integrated with wastewater treatment and metabolic by-products usage.

Temperature-dependent transformation of biogas-producing microbial communities points to the increased importance of hydrogenotrophic methanogenesis under thermophilic operation.

Stability of biogas production is highly dependent on the microbial community composition of the bioreactors. This composition is basically determined by the nature of biomass substrate and the physical-chemical parameters of the anaerobic digestion. Operational temperature is a major factor in the determination of the anaerobic degradation process. Next-generation sequencing (NGS)-based metagenomic approach was used to monitor the organization and operation of the microbial community throughout an experiment where mesophilic reactors (37°C) were gradually switched to thermophilic (55°C) operation. Temperature adaptation resulted in a clearly thermophilic community having a generally decreased complexity compared to the mesophilic system. A temporary destabilization of the system was observed, indicating a lag phase in the community development in response to temperature stress. Increased role of hydrogenotrophic methanogens under thermophilic conditions was shown, as well as considerably elevated levels of Fe-hydrogenases and hydrogen producer bacteria were observed in the thermophilic system.

Revealing the factors influencing a fermentative biohydrogen production process using industrial wastewater as fermentation substrate.

BACKGROUND: Biohydrogen production through dark fermentation using organic waste as a substrate has gained increasing attention in recent years, mostly because of the economic advantages of coupling renewable, clean energy production with biological waste treatment. An ideal approach is the use of selected microbial inocula that are able to degrade complex organic substrates with simultaneous biohydrogen generation. Unfortunately, even with a specifically designed starting inoculum, there is still a number of parameters, mostly with regard to the fermentation conditions, that need to be improved in order to achieve a viable, large-scale, and technologically feasible solution. In this study, statistics-based factorial experimental design methods were applied to investigate the impact of various biological, physical, and chemical parameters, as well as the interactions between them on the biohydrogen production rates. RESULTS: By developing and applying a central composite experimental design strategy, the effects of the independent variables on biohydrogen production were determined. The initial pH value was shown to have the largest effect on the biohydrogen production process. High-throughput sequencing-based metagenomic assessments of microbial communities revealed a clear shift towards a Clostridium sp.-dominated environment, as the responses of the variables investigated were maximized towards the highest H2-producing potential. Mass spectrometry analysis suggested that the microbial consortium largely followed hydrogen-generating metabolic pathways, with the simultaneous degradation of complex organic compounds, and thus also performed a biological treatment of the beer brewing industry wastewater used as a fermentation substrate. CONCLUSIONS: Therefore, we have developed a complex optimization strategy for batch-mode biohydrogen production using a defined microbial consortium as the starting inoculum and beer brewery wastewater as the fermentation substrate. These results have the potential to bring us closer to an optimized, industrial-scale system which will serve the dual purpose of wastewater pre-treatment and concomitant biohydrogen production.