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Lignocellulosic biomass utilization is challenging due to the presence of several carbon sources. Thus, microorganisms with different sugar preferences can be used in co-cultures to overcome this hurdle. This work addressed the simultaneous production of lactic acid (LA) from C5 sugars (i.e., xylose) and bioethanol from C6 (i. e., glucose/fructose) with Bacillus coagulans and Kluyveromyces marxianus, respectively. Sequential inoculation and co-inoculation of microorganisms were also compared. At pH 6, co-inoculation in synthetic media resulted in higher bioethanol (0.51 g/g) and LA (0.98 g/g) yields than sequential inoculation. Furthermore, when using lignocellulosic hydrolysates obtained after enzymatic hydrolysis of 20 % w/w pomegranate peels (PP), 92 % and 98 % of the theoretical maximum bioethanol and LA, respectively, were obtained. This study demonstrated the efficient bioethanol/LA co-generation despite the different optimum fermentation conditions of microorganisms and will pave the way to consider co-cultures for improving process efficiency in lignocellulosic biorefineries.

Abstract A wide range of biofuels and bio-based products can be produced from lignocellulose considering its high compositional diversity. Ethanol production by yeasts from cellulosic glucose is well-known, while hemicellulosic xylose utilization is still challenging. This work proposes the use the xylose for l -lactic acid fermentation. In this context, a sequential cultivation of Saccharomyces cerevisiae and the C5-utilizing Bacillus coagulans is studied. High ethanol yields, around 0.44 g g−1, were obtained from a cellulosic-gardening hydrolysate. The high ethanol concentrations did not affect the evolved B. coagulans A20-EXA obtained by adaptive evolution to ethanol. As a result, 2.6-fold increase in lactic acid yield was achieved when compared with parental B. coagulans strain in presence of 5% (v v−1) ethanol. These results demonstrated the suitability of B. coagulans A20-EXA to be used together with S. cerevisiae for the sequential co-generation of ethanol and lactic acid from lignocellulosic biomass in a biorefinery approach.

Phenols are known as inhibitors for cellulases and fermentative microorganisms in bioethanol production processes. The addition of laccases removes the phenolic compounds and subsequently reduces the lag phase of the fermentative microorganism. However, the application of laccases diminishes glucose release during the enzymatic hydrolysis. In this study a model cellulosic substrate (Sigmacell) together with lignin extract, whole steam-pretreated wheat straw (slurry) and its water insoluble solid fraction (WIS) were subjected to enzymatic hydrolysis to evaluate the effects of laccase treatment in presence of lignin and phenols. The presence of laccase in enzymatic hydrolysis of Sigmacell with lignin extract reduced glucose yield by 37% compared with assays without laccase. Furthermore, this reduction was even more marked in presence of phenols (55% reduction). Interestingly, when hydrolyzing WIS, the addition of phenols coupled with laccase treatment did not show a reduction when compared with only laccase addition. This fact suggests the key role of lignin in the hydrolysis inhibition since in WIS the ratio cellulase per gram of lignin was much lower than in Sigmacell experiments. Finally, the lower cellobiose and xylose recoveries point out that phenolic oligomers formed by laccase oxidation play important roles in the inhibition of endoglucanases, cellobiohydrolases and xylanases. To conclude, the proportion of lignin and the composition of phenols are key players in the inhibition of cellulases when the enzymatic hydrolysis is combined with laccases detoxification.

AbstractAmong biofuel production processes using microalgal biomass, biogas generation seems to be the least complex. This review summarizes information regarding anaerobic digestion of different microalgae species. Various operational parameters and microalgae characteristics (macromolecular distribution and cell wall) are reviewed in the light of their effects on methane production. Additionally, the enhancement of methane production rates achievable by applying biomass pre‐treatments and codigestion of substrates is also reported. The review finally covers the so‐claimed similarities of microalgal biomass and activated sludge as a substrate for anaerobic digestion. © 2011 Society of Chemical Industry and John Wiley & Sons Ltd

AbstractVolatile fatty acids (VFAs) are regarded as building blocks with a wide range of applications, including biofuel production. The traditional anaerobic digestion used for biogas production can be alternatively employed for VFAs production. The present study aimed at maximizing VFAs productions from Chlorella vulgaris through anaerobic digestion by assessing the effect of stepwise organic loading rates (OLR) increases (3, 6, 9, 12 and 15 g COD L−1 d−1). The biological system was proven to be robust as organic matter conversion efficiency into VFAs increased from 0.30 ± 0.02 COD-VFAs/CODin at 3 g COD L−1 d−1 to 0.37 ± 0.02 COD-VFAs/CODin at 12 g COD L−1d−1. Even though, the hydrolytic step was similar for all studied scenario sCOD/tCOD = 0.52–0.58), the highest OLR (15 g COD L−1 d−1) did not show any further increase in VFAs conversion (0.29 ± 0.01 COD-VFAs/CODin). This fact suggested acidogenesis inhibition at 15 g COD L−1d−1. Butyric (23–32%), acetic (19–26%) and propionic acids (11–17%) were the most abundant bioproducts. Population dynamics analysis revealed microbial specialization, with a high presence of Firmicutes followed by Bacteroidetes. In addition, this investigation showed the microbial adaptation of Euryarchaeota species at the highest OLR (15 g COD L−1d−1), evidencing one of the main challenges in VFAs production (out-competition of archaea community to avoid product consumption). Stepwise OLR increase can be regarded as a tool to promote VFAs productions. However, acidogenic inhibition was reported at the highest OLR instead of the traditional hydrolytic barriers. The operational conditions imposed together with the high VFAs and ammonium concentrations might have affected the system yields. The relative abundance of Firmicutes (74%) and Bacteroidetes (20%), as main phyla, together with the reduction of Euryarchaeota phylum (0.5%) were found the best combination to promote organic matter conversion into VFAs.

AbstractThe production of high added‐value products from lignocellulose is proposed as a suitable alternative to petroleum‐based resources in terms of environmental preservation, sustainability, and circular economy. Lactic acid is a versatile building block that can be produced via fermentative routes by several groups of microorganisms, including yeasts and microalgae, which are bacteria recognized to achieve the highest concentrations. Lactic acid, among other substances, can be used as a starting point in the production of poly‐lactic acid, which is a biopolymer with many applications due to its resistance, durability, biodegradability, and biocompatibility. Lactic acid production can be performed from lignocellulosic biomass. However, lactic acid production from lignocellulose faces several hurdles such as carbohydrate hydrolysis to release sugars, the co‐utilization of sugar mixtures by the fermenting microorganism, and the presence of degradation compounds released during pretreatment. In this review, a general overview of lactic‐acid bacterial fermentation from lignocellulose is provided, starting from the potential substrates and their composition, the different metabolic pathways involved, and the purification steps. The main challenges are discussed and the newest approaches to solve the limitations of the process are proposed. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd

Dry anaerobic digestion (D-AD) generates nitrogen-rich effluents that are normally neglected in the circular bioeconomy. The high turbidity and ammonium content hamper nitrogen recovery from these effluents via biological processes, such as microalgae culture. The goal of this study was to demonstrate microalgae growth viability in high-strength D-AD effluents in order to recover nitrogen (N) as microalgae biomass. According to the experimental factorial design conducted in batch reactors, ammonium was identified as the critical inhibitory compound for microalgae growth while turbidity did not exhibit a significantly negative effect. Instead, turbidity resulted advantageous since it promoted high nitrogen uptake rates and biomass production. The presence of organic turbidity resulted in a positive effect that boosted Chlorella growth in a stream with higher ammonium (350 mg NH4+-N L-1) and turbidity (175 NTU) than the inhibition thresholds reported in the literature, reaching 98.7% of N recovery as microalgae biomass. When microalgae culture was scaled up in a photobioreactor operated in continuous mode, microalgae biomass was effectively produced while recovering 100% of N at a hydraulic retention time of 10 days. By imposing long exposure times and high turbidity, Chlorella adaptation to high-strength D-AD effluent resulted in high N uptake and biomass production. This study demonstrated not only the most influencing factor and the optimal NH4+-N and turbidity combination, but also the viability of using D-AD effluents as culture media for microalgae biomass production.

Cellulose valorisation has been successfully addressed for years. However, the use of hemicellulosic hydrolysates is limited due to the presence of C5-sugars and inhibitors formed during pretreatment. Bacillus coagulans is one of the few bacteria able to utilize both C6- and C5-sugars to produce l-lactic acid, but its susceptibility to the lignocellulosic inhibitors needs further investigation. For such a purpose, the tolerance of different B. coagulans strains to increasing concentrations of inhibitors is studied. The isolated A162 strain reached the highest l-lactic acid productivity in all cases (up to 2.4 g L-1 h-1), even in presence of 5 g L-1 of furans and phenols. Remarkably, most of furans and phenolic aldehydes were removed from defined media and hemicellulosic gardening hydrolysate after fermentation with A162. Considering the high productivities and the biodetoxifying effect attained, A162 could be pointed out as a great candidate for valorisation of mixed sugars from hemicellulosic hydrolysates with high inhibitors concentration, promoting the implementation of lignocellulosic biorefineries.